Skip to main content
NCBI home page
RSC Advances logoLink to RSC Advances
. 2026 Aug 24;16(41):49498–49512. doi: 10.1039/d6ra06561a

Novel IIPs integrated with a carbon dot-modified GCE sensor for ultra-sensitive and selective detection of uranyl ions

Mahmoud A Al-Qass a, A B Abdallah a,✉, Fathi S Awad a, Eslam A Ghaith a, Ahmed Fathi Salem Molouk a
PMCID: PMC13501465  PMID: 42639000

Abstract

Efficient monitoring of uranyl ions has gained considerable attention owing to their involvement in various civilian and military applications. Therefore, a new imprinted sensor with high sensitivity and selectivity was fabricated for the monitoring of uranyl ions in various samples. N-allyl-2-(2-cyanoacetyl)hydrazine-1-carbothioamide was used as a specific chelating agent that strongly interacts with uranyl ions and subsequently polymerizes with ethylene glycol dimethacrylate in the presence of potassium persulfate. The uranyl ions were then leached from the polymeric surface using nitric acid, leaving behind imprinted cavities that enabled the selective recognition of the target ions. The synthesized imprinted polymers were fully characterized using several techniques, including FT-IR, SEM, TEM, AFM, EDX, and elemental mapping. The leached ion-imprinted polymer was deposited onto the surface of the glassy carbon electrode to construct the selective imprinted sensor (IIPs/CDs@GCE), following the deposition of carbon dots to enhance sensitivity. The developed sensor exhibited a wide linear range (1.8 × 10−10–8.6 × 10−3 mol L−1), low limit of detection (5.94 × 10−11 mol L−1), excellent selectivity in the presence of competing ions (imprinting factor = 12.4), and high stability (5 weeks). The imprinted sensor was successfully applied for the detection of uranyl ions in tap water, Nile water, industrial water, soil, and sediment samples, achieving excellent recoveries (97.6–99.8%).

A highly sensitive uranyl-imprinted electrochemical sensor was developed using carbon dots, offering excellent selectivity and reliable determination of UO22+ in real samples.graphic file with name d6ra06561a-ga.webp

1. Introduction

Uranium is a naturally occurring heavy metal that exists in several isotopic forms, including uranium-238 (238U, 99.2745%), uranium-235 (235U, 0.7200%), and uranium-234 (234U, 0.0055%). These isotopes are widely utilized across different fields. In the military sector, uranium plays a key role in the production of armor-piercing munitions, the reinforcement of armored combat vehicles, and nuclear weapons manufacturing.1–3 In civilian applications, uranium is used for electricity generation in nuclear power plants, as a colorant in ceramic glazes, and for tinting in early photographic processes. Nuclear energy currently contributes more than 16% of the global electricity supply.2–4 Because of the extensive civil and military applications of uranium, along with inadequate safe disposal of nuclear waste, significant adverse effects on the human body have been reported, leading to serious damage to the bones, liver, and lungs.3–6 Owing to its severe toxicity and hazardous impact on the environment, there is an urgent need to monitor uranium levels using a reliable, sensitive, and selective analytical method.

Several techniques including inductively coupled plasma mass spectrometry (ICP-MS), phosphorescence, inductively coupled plasma, and UV-visible spectroscopy have been applied for the detection of uranyl ion.7–11 However, these techniques cannot be adapted to different fields because of their complex pretreatment requirements, real-time monitoring, and expensive instrumentation. To overcome these drawbacks, electrochemical techniques that depend on imprinting sensors are widely applicable for heavy metals detection, providing ease and high selectivity toward template ions and/or molecules.12,13

Ion-imprinting polymers (IIPs) are considered a lifeline for improving the selectivity of different sensors. Tailored IIPs are designed as polymeric synthetic materials with specific recognition sites for the proposed metal ions, called target template.13–15 The main challenge in the fabrication of IIPs is choosing a chelating ligand that captures the target ions and how to introduce it into the polymeric matrices. Over the last decade, scholars have synthesized various functional ligands bearing chelating groups that bind to the proposed template ions. The synthesized ligand was inserted into the polymer via a trapping process without any covalent and/or non-covalent bonds.14–16 Release of the ligand from the fabricated polymer during the leaching process was observed, thereby reducing the selectivity of the prepared polymer. Therefore, in this study, we aimed to fabricate a new functional monomer containing allyl groups for polymerization and functional groups to facilitate interactions with uranyl ions. Subsequently, polymerization was performed using an initiator in the presence of a crosslinker. The template ions are removed from the polymeric surface, leaving behind imprinted cavities that are complementary in shape, size, and chemical functionality to the target. Owing to their flexibility in monomer–template interactions, IIPs are widely utilized in various fields such as electrochemical sensors (e.g., clinical, pesticides, and heavy metals) and solid-phase extraction.12–18 However, imprinted electrochemical sensors still suffer from low sensitivity, due to the low conductivity of various synthesized polymers. Different superb materials, including carbon dots (CDs), carbon nanotubes (CNT), metal–organic framework (MOF), and graphene oxide (GO), have been extensively used to enhance the electrochemical performance of proposed electrochemical sensors due to their large surface area, good conductivity, and high stability.19–23 Carbon dots are fascinating materials that exhibit high sensitivity toward various target ions due to the presence of functional groups, such as carboxyl, hydroxyl, carbonyl, and amine groups, on their surfaces.

Although considerable progress has been achieved in the development of electrochemical sensors for uranyl determination, several limitations remain. Many reported sensors rely on conventional functional monomers or non-specific interactions, resulting in limited selectivity, particularly in the presence of chemically similar metal ions. In addition, some sensing platforms require complicated fabrication procedures, exhibit relatively narrow linear ranges, or fail to achieve sufficiently low detection limits for trace-level analysis. The development of a simple, highly selective, and ultrasensitive sensing platform based on a rationally designed chelating monomer remains highly desirable. Therefore, in this study, a novel electrochemical sensor was fabricated for the recognition and monitoring of uranyl ions in real samples. The innovation of this work lies in the rational design of a tailor-made chelating monomer, N-allyl-2-(2-cyanoacetyl)hydrazine-1-carbothioamide, specifically engineered to provide multiple coordination sites with high affinity toward UO22+ ions. This enables the formation of well-oriented and highly selective imprinted cavities upon polymerization in the presence of the target ion. After the leaching process, the IIPs were characterized using different techniques, which were then deposited as a second layer at the electrode surface after the CDs layer using Nafion as a binding matrix to ensure stability and uniform film formation. Various electrochemical parameters, including the pH, scan rate, washing time, deposition time, and deposition potential, were optimized.

2. Experimental

2.1. Materials and reagents

All chemicals were of analytical grade and used without further purification. Allyl isocyanate (98%) and 2-cyanoacetohydrazide (98%) were purchased from Sigma-Aldrich (Steinheim, Germany) to synthesize N-allyl-2-(2-cyanoacetyl) hydrazine-1-carbothioamide (94%). Also, carbon dots were used as an electroactive nanomaterial modifier to enhance the electrochemical performance of the glassy carbon electrode (GCE), gained from Sigma-Aldrich (Merck, Germany; catalog No. 900414; characterization inserted in SI (Fig. S1–S3)). All physicochemical characteristics were adopted according to the manufacturer's technical datasheet. Uranium dioxide, ethylene glycol dimethacrylate (EGDMA), potassium persulfate, ethanol (EtOH), methanol (MeOH), and nitric acid were obtained from Merck (Darmstadt, Germany). Phosphoric acid, glacial acetic acid, sodium acetate, and potassium hydroxide were bought from Alfa Aesar (Ward Hill, MA, USA). To remove any contaminants from the glasses and bottles, they were immersed in nitric acid for 8 h, before use.

Ultrapure water with a highly purified system (18.25 MΩ, Bedford, USA) was utilized to prepare all required solutions. Stock solution of uranyl ion (0.005 mol L−1) was prepared by dissolving an appropriate amount of uranium oxide in 100 mL of ultrapure water. 0.745 g potassium chloride was completely dissolved in 100 mL ultrapure water and used as a supporting electrolyte in different electrochemical measurements. For controlling pH measurements during electrochemical detection, a specific concentration of each acid including acetic, boric, and phosphoric was prepared, and then mixed with the others. After that, the resulting solution was titrated with potassium hydroxide to prepare a specific buffer with a stable pH.

2.2. Instrumentation

Fourier transform infrared (FT–IR, Alpha, Bruker, Germany) spectroscopy was used to analyze the functional groups in the polymeric samples over the range of 4000–400 cm−1. The surface morphology and porosity of the synthesized IIPs were characterized using a scanning electron microscope (SEM, JEOL JSM -6510LV, Japan) and atomic force microscopy (AFM, FlexAFM3). Also, the size distribution and morphology of the crystal structure were investigated using transmission electron microscopy (TEM, JEOL JEM-2100, Japan). Density function theory (DFT) methodology was performed by the DMOL3 program in the Material Studio Package with the revised Perdew–Burke–Ernzerhof (RPBE) functional with the DNP as basis set. A high-precision analytical balance (Mettler Toledo, AB204-S, Switzerland) with 0.01 mg readability was used throughout all experimental procedures, including sample preparation, material weighing, and reagent measurements to ensure accuracy and reproducibility. A water bath (WB-10, Memmert, Germany) was used to maintain a stable temperature of 60 °C during the polymerization process. A digital pH mV per meter (Hanna model HI 8519) was utilized for adjusting the pH level of the prepared solution before any electrochemical measurements.

2.3. Synthesis of N-allyl-2-(2-cyanoacetyl) hydrazine-1-carbothioamide

An appropriate amount of 2-cyanohydrazide was completely dissolved in EtOH, then mixed with allyl isocyanate. The solution was refluxed for 4 h and kept at room temperature for one day. Finally, the shiny silver needles precipitate was collected and washed by EtOH to remove any excess reactants yielding 94% without any further purification. The choice of the monomer was guided by its multiple coordination functionalities and strong binding affinity for uranyl ions, which are anticipated to facilitate efficient and selective imprinting via the formation of stable template–monomer complexes during polymerization.

2.4. Synthesis of IIPs

A uranyl-ion-imprinted polymer was prepared via thermal polymerization. The synthesized N-allyl-2-(2-cyanoacetyl) hydrazine-1-carbothioamide was utilized not only as a functional monomer but also as the specific chelating agent that complexed with UO22+ ions. The complex mixture was shaken for 30 min at 50 °C. 0.1 g of potassium persulfate was added to the complexing mixture, followed by addition of EGDMA (20 mmol). Before polymerization, the mixture was purged with nitrogen to remove oxygen. The polymerization reaction was carried out by inserting the polymerization bottle into water bath maintained at 60 °C for 4 h. The polymerization temperature and time were selected based on preliminary experiments to ensure complete polymer formation. After that, the resulting light-yellow solid polymer was filtered through filter paper and then washed with distilled water and ethanol, respectively. The imprinted uranyl ions cavities were formed at the polymeric surface after leaching the template ions using nitric acid (0.01 mol L−1) which leaving behind imprinted cavities that enable selective recognition of target ions (Scheme 1). For controlling the polymerization process, the non-imprinted polymer (NIP) was prepared by the same protocol without uranyl ions.

Scheme 1. Synthesis process of ion-imprinted polymer.

Scheme 1

Open in a new tab

2.5. Preparation of the imprinted sensor

The electrode surface was pretreated by sequential polishing with alumina slurry with different particle sizes (0.3 µm followed by 0.05 µm) until a mirror-like finish was obtained. The polished electrode was thoroughly rinsed with deionized water, ethanol, and deionized water to ensure the complete removal of residual alumina particles. Subsequently, the electrode was dried at room temperature. An appropriate amount of CDs powder was dissolved in DMF in the presence of 1 mL of Nafion solution (0.025%) and then ultrasonicated for 5 min, followed by drop coating of 10 µL of this solution onto the GCE surface (CDs@GCE). After that, the synthesized polymer was dissolved in ethanol, and a small aliquot (5 µL) was transferred using a micropipette and drop-cast onto the electrode surface. The modified electrode was then allowed to dry at room temperature to obtain a thin and homogeneous polymeric layer (IIPs/CDs@GCE) (Fig. 1).

Fig. 1. Scheme of the preparation of IIPs and the electrochemical detection of uranyl ions by electrochemical technique.

Fig. 1

Open in a new tab

2.6. Electrochemical measurements

Electrochemical measurements were performed after the preparation and conditioning of the polymeric-imprinted sensor, which functioned as the working (UO22+–IIPs) electrode in a conventional three-electrode system composed of a reference (Ag/AgCl) electrode and a counter (Pt wire) electrode. The setup was connected to a potentiostat that precisely controlled the applied potential and monitored the resulting current response. The three-electrode system was immersed in a uranyl solution (10.0 mL UO22+, 0.1 mol L−1 KCl, and 0.1 M acetate buffer of pH 5.0), and the instrument was adjusted to a potential window from −1.5 to +1.5 V, with a scan rate of 50 mV s−1. Over a frequency range of 0.1 Hz to 100 kHz, the EIS was recorded in a 0.1 mol L−1 KCl solution containing active probe 5 × 10−3 mol L−1 [Fe(CN)6]3−/4−. Differential pulse anodic stripping voltammetry (DP–ASV) was applied for the sensitive and accurate determination of uranyl ions, with concentrations obtained from a pre-established calibration curve. It is worth mentioning that all measurements were performed in four independent replicates (n = 4), unless otherwise stated.

2.7. Sample preparation

To evaluate the sensor's performance under real environmental conditions, samples were collected from various locations. Water samples, including tap water (Cairo, Egypt), Nile River water (Cairo and Aswan, Egypt), and industrial area water (Helwan and Suez, Egypt), were collected from various sources and stored in clean PET bottles to prevent contamination. The water samples were filtered through filter paper (0.45 µm) to remove all suspended solid contaminants. Buffer was then added to the filtered water samples to adjust the pH to 5.0 before any electrochemical measurements. In addition, rock-solid samples, including soil collected from the Abu Tartur phosphate area, Egypt, and sediment collected from the riverbank in Aswan, Egypt, were selected to evaluate the applicability of the proposed sensor. The Abu Tartur phosphate area was selected because phosphate-rich soils are naturally enriched in uranium owing to the strong geochemical association between uranium and phosphate minerals. The rock samples were ground using a friction machine to form a homogenized sample. Subsequently, it was transferred to a Teflon cup, followed by the addition of 6 mL of a mixture of HF : HNO3 : DDW, and then placed in a microwave for 90 min. After cooling, an appropriate amount of boric acid was added to neutralize the excess HF. After that, a specific amount of buffer was added, and the solution was completed to 50 mL using DDW. Finally, the uranyl concentration was determined using the procedure described above. A standard uranyl solution was added to separate equal-volume aliquots of the real samples to obtain different final concentrations (10.0, 25.0, and 50.0 µg L−1) of uranyl ions. The electrochemical response of the sensor was measured for each spiked aliquot (three replicates for each concentration) to evaluate the accuracy and reproducibility of the measurements.

3. Result and discussion

3.1. SEM, TEM, and AFM

The topography and surface morphology of the synthesized leached and unleached polymers were investigated using different techniques, including SEM, TEM, and AFM. SEM analysis, as shown in Fig. 2A–C, offers detailed insight into the surface morphology of the samples, where a distinct difference is observed between the leached and unleached, and NIP surfaces. The surface of the unleached and non-imprinted polymers appears to be relatively compact and pore-free, in contrast to the leached one which exhibits a more microporous structure and well-distributed spherical nanoparticles. In addition, the TEM micrographs demonstrated significant morphological changes following the removal of the template ions (Fig. 2D and E). The un-leached polymer exhibited a heterogeneous distribution of high-contrast regions, attributed to uranium-rich domains embedded within the polymeric matrix. These results confirmed the successful coordination between the uranium centers and ligand moieties during the polymer fabrication. In contrast, the leached polymer (Fig. 2E) after nitric acid treatment showed a clear decrease in the dark regions previously linked to uranium-rich areas, indicating that uranium was successfully extracted from the polymer. The remaining component was a light, irregular structure corresponding to the material's organic part. The bright background also supports the removal of dense metal content from the system. AFM analysis shows the surface topography of the uranyl imprinted polymer before and after removing the uranyl ion (Fig. 2F and G). In the case of non-leaching, where uranyl remains present, both the images and the calculated parameters—root mean square roughness (Sq = 304.04 nm) and arithmetic mean height (Sa = 240.31 nm)—indicate a relatively smooth surface. Following the leaching process, however, the surface exhibited increased roughness with elevated protrusions, as reflected by the higher Sq (375.65 nm) and Sa (296.54 nm) values. This suggests that the presence of the metal influences the surface topography, whereas its removal leads to a rougher surface with pores that are more evenly distributed, formed during leaching process.

Fig. 2. SEM images of unleached (A), leached (B), and non-imprinted (C) polymers. TEM images of unleached (D) and leached (E) polymers. AFM images of unleached (F) and leached (G) polymers.

Fig. 2

Open in a new tab

3.2. Elemental mapping, EDX, and FT-IR

To ensure that the chemical structure of the polymeric matrices was not affected by the leaching process, elemental mapping and EDX analyses were performed for leached and unleached polymer. As shown in Fig. 3A and B, carbon, nitrogen, oxygen, and sulfur were present without any observable change in color intensity in the leached and unleached polymers. Additionally, the percentage of each atom was calculated using EDX analysis. As depicted in Fig. 3C and D, the elemental composition of the imprinted polymer exhibited noticeable changes after the leaching process, reflected by a slight reduction in the relative contributions of the detected elements compared to the unleached material (Table S1, SI). Importantly, the disappearance of the uranium signal after leaching confirms the effective removal of the template ions, leading to the formation of well-defined and accessible imprinted cavities that are responsible for the selective recognition of uranyl ions during the sensing process.

Fig. 3. Elemental mapping images of unleached (A) and leached (B) polymers. EDX images of unleached (C) and leached (D) IIPs.

Fig. 3

Open in a new tab

Different functional groups of the synthesized chelating agent and different polymeric surfaces were investigated using FT-IR (Fig. S4, SI). The FT-IR spectrum of N-allyl-2-(2-cyanoacetyl) hydrazine-1-carbothioamide shows distinct absorption bands in the regions of 3150–3214, 1686, and 2260 cm−1, which are attributed to the stretching vibrations of the N–H, C Created by potrace 1.16, written by Peter Selinger 2001-2019 O, and –CN (nitrile) groups, respectively. Additionally, new bands in the range of 1180–1250 cm−1 and at 717 cm−1 are observed, which are associated with the C–O stretching vibrations and C–H bending vibration of the allyl group, respectively. After the synthesized ligand chelating the uranyl ions and the unleached polymer was fabricated, notable shifts in the C Created by potrace 1.16, written by Peter Selinger 2001-2019 O and N–H stretching bands, compared with the free ligand, indicated the formation of coordination bonds between the uranyl ion and both the sulfur and nitrogen atoms of the ligand. A distinct band at 1732 cm−1 assigned to the ester C Created by potrace 1.16, written by Peter Selinger 2001-2019 O group, together with a decrease in the intensity of the vinyl C Created by potrace 1.16, written by Peter Selinger 2001-2019 C absorptions, confirmed the formation of the cross-linked polymeric network and the successful polymerization. Moreover, weak bands below 600 cm−1 can be attributed to U–N and U–S vibrations, providing evidence for the coordination of the uranyl ion with the nitrogen and sulfur atoms of the ligand, supporting the formation of coordination bonds within the polymer network. The characteristic bands that appeared in the unleached polymer, around 872–920 cm−1 and below 600 cm−1, became significantly weaker after the leaching process, indicating the successful removal of uranyl from the polymer matrix. It is worth mentioning that the characteristic peaks of the polymer matrix including C Created by potrace 1.16, written by Peter Selinger 2001-2019 O stretching at ∼1723 cm−1 and the phenyl C Created by potrace 1.16, written by Peter Selinger 2001-2019 C stretching at ∼1630 cm−1 were observed, while all uranyl-specific bands were absent, confirming the successful preparation of a polymer completely free of uranyl species.

3.3. Theoretical approaches

The utility of organic monomers in imprinting polymerization is an effective methodology for identifying the elemental ions in real samples. However, these monomers are constrained by their electroactivity and form a stable IIPs matrix within the electropolymerization potential window.24 Computational studies represent a highly effective alternative for selecting the desirable monomer, with fewer chemical trials and lower environmental impacts. Normally, many trials are required to complete a lengthy research period to identify a compatible monomer that exhibits high recognition precision for the uranyl ion, even at ultra trace concentrations. Consequently, a new hybrid chelating ligand, N-allyl-2-(2-cyanoacetyl)hydrazine-1-carbothioamide, was synthesized as a selective functional chelating ligand combining the full characteristics of both monomer and ligand, with a high capability to coordinate the uranyl ion and serving as a simultaneously polymerizable unit within the imprinting polymer matrix, as described in this manuscript. Additionally, the theoretical approaches were performed using density functional theory (DFT) with the DMOL3 program (Material Studio Package) in the presence of DNP as the basis set.25,26Fig. 4 presents the full comparison between the parent chelating ligand and the uranyl complex, depending on various chemical descriptors involving frontier molecular orbitals (HOMO and LUMO), total energy, Egap, global hardness (η), global electronegativity (χ), global electrophilicity index (ω) and softness (S) as essential parameters for understanding the reactivity and stability both complex and ligand which were calculated by the following eqn (1)–(6).27–29

Egap = ELUMO − EHOMO 1
η = ½ (ELUMO − EHOMO) 2
χ = −½ (EHOMO + ELUMO) 3
µ = ½ (EHOMO + ELUMO) 4
ω = µ2/2η 5
S = 1/2η 6

Fig. 4. Frontier molecular orbital levels, MEP, and chemical descriptors for the chelating ligand and electrochemical UO22+ complex.

Fig. 4

Open in a new tab

Notably, the results showed that the uranyl complex is more stable than the chelating ligand. The total energy values indicate that the UO2-complex has lower energy (−59011.682 eV) than the ligand (−965.540 eV), enhancing the stability concept of the uranyl complex over the parent chelating ligand. On the other hand, Fig. 4 presents the greater negative binding energy value for the uranyl complex (−240.707 eV) compared to the binding energy of the cyanoacetamide ligand (−106.420 eV), indicating higher stability and lower susceptibility to dissociation. Molecular electrostatic potential (MEP) maps are utilized for predicting electron-deficient (electropositive) and electron-rich (electron-negative) reactive zones (Fig. 4). The MEP map of the synthesized ligand provides a visual approach to investigate electrostatic regions, with blue indicating a highly positive electrostatic potential and red a negative one. The red region lies between the O Created by potrace 1.16, written by Peter Selinger 2001-2019 C–NH–NH–C Created by potrace 1.16, written by Peter Selinger 2001-2019 S zones, indicating that this region is responsible for electrophilic attack. According to HSAB theory, UO22+ is a hard metal with a low polarization moment; consequently, it prefers to coordinate with the oxygen atom in the carbonyl group (hard basic functionality), rather than coordination with the oxygen atom attributed to the thione group. Whereas the presence of the cyano group as an electron-withdrawing group supports the tautomerism of the carbonyl group. Consequently, all the above-mentioned findings support the proposed mechanism of complex formation through the interaction of nitrogen- and sulfur-bearing atoms. Finally, all obtained data, including bond lengths (Å) (Tables S2 and S3) and bond angles (°) (Tables S4 and S5) for both the ligand and the complex, are reported in the SI. Significantly, the strong binding affinity substantiates the rational design strategy of the proposed monomer and is anticipated to enhance the recognition performance of the fabricated imprinted system. In addition, the obtained electronic descriptors, such as a reduced energy gap and elevated electrophilicity, indicate efficient charge-transfer properties, consistent with the improved electrochemical behavior of the developed sensor. For more details, a lower energy gap and chemical hardness (η) values for the electrochemical uranyl complex compared to the carbothioamide ligand are consistent with the Pearson-HSAB principle. The complexation process leads to hybridization of nonbonding 5f and 6d orbitals of the uranyl ion with molecular orbitals of carbothioamide, decreasing the ΔEgap and chemical hardness for the resulting complex (Fig. 4), consistency of thermodynamic stabilities of the formed complex according to.30 While the increase of electrophilicity of the complex (ω = 5.328) indicates the capability of the formed complex to receive more electrons. In the same context, the higher potentiality (χ = 4.254) of the complex indicates a higher propensity of the electrochemical complex to exchange and accept conductive ligand under the applied electrochemical potential.

3.4. Cyclic voltammetry and electrochemical impedance spectroscopy

To evaluate the electrochemical performance and interfacial properties of the fabricated sensors (GCE, un-leached IIPs/CDs@GCE, leached IIPs/CDs@GCE, and NIP/CDs@GCE), cyclic voltammetry was employed using the redox probe Fe(CN)63−/4− over a potential range of −0.5 to +1.5 V at a scan rate of 50 mV s−1. This technique provides valuable insights into the electron transfer behavior and surface characteristics of the modified electrodes. As illustrated in Fig. 5A, the bare GCE electrode exhibited a very weak and broad peak at a low potential. A pronounced enhancement in the electrochemical signal was observed after modifying the GCE surface with CDs, which can be attributed to their excellent electrical conductivity and accelerated electron transfer kinetics. In addition, CDs offer a high surface area, abundant surface functional groups (e.g., –OH, –COOH), and good dispersibility, which collectively facilitate effective electron transport, increase the number of active sites, and promote stronger interaction with the target analyte, thereby significantly improving the overall sensing performance. In contrast, the unleached imprinted sensor showed a suppressed peak located at nearly the same potential region, reflecting the blocking effect of the template molecules entrapped within the polymeric matrix. After template removal, the leached GCE displayed a sharp and intense peak shifted toward a more positive potential, confirming the presence of accessible imprinted sites capable of specifically binding uranyl ions. Meanwhile, the non-imprinted polymer electrode revealed only a negligible peak change, remaining almost identical to the bare electrode, which indicates the absence of specific recognition sites. Collectively, these peak responses demonstrate that the imprinted electrode provides superior selectivity, sensitivity, and enhanced charge transfer characteristics compared to the control electrodes.

Fig. 5. Cyclic voltammograms of different proposed sensors using an electrochemical probe (A). EIS of different synthesized imprinted sensors using standard probe (B).

Fig. 5

Open in a new tab

On the other hand, electrochemical impedance spectroscopy was employed to evaluate the electrochemical response of the different synthesized sensors toward K3[Fe(CN)6]/K4[Fe(CN)6]. The semicircular and linear parts are the main categories in the impedance spectrum. The semicircular feature observed in the high-frequency domain corresponds to the charge transfer resistance (Rct), which arises from the dielectric characteristics of the electrode–electrolyte interface. In contrast, the linear portion at lower frequencies is attributed to diffusion-controlled resistance. As exhibited in Fig. 5B the bare electrode (GCE) showed a large semicircle with a high Rct, whereas a sharp decrease was noticed after depositing CDs owing to their high surface area and superb conductivity. These results demonstrate that CDs primarily enhance the electron-transfer kinetics and electrical conductivity of the sensing interface. Additionally, Rct increased rapidly after modified the GCE with nonconductive polymeric films, unleached IIPs/CDs and/or NIP/CDs. In contrast, smaller semicircle and lower Rct were observed after the leaching process because the formation of imprinted cavities at the polymeric surface facilitated the movement of the electrochemical probe toward the GCE surface.

3.5. Parameters

3.5.1. Effect of pH

One of the most influential parameters affecting the electrode response or the reaction itself is the pH of the medium. Britton–Robinson buffer solutions with pH values ranging from 2 to 8 were prepared and used to adjust the uranyl solution. As noticed in Fig. S5 (SI), the electrochemical response increased gradually until it reached a maximum value at pH 5 owing to the stable interaction between the uranyl ions and the functionalized monomer at the imprinted cavities on the electrode surface. The low response at low concentrations of hydrogen ions may be due to the formation of less uranyl active species, such as UO2(OH)+ and UO2(OH)2, which have low suitability for 3D imprinted cavities. However, at high hydrogen concentrations, the competition between uranyl and hydrogen ions toward the imprinted polymer is reasonably low response. Thus, pH 5 was selected as the optimum pH for the other experiments.

3.5.2. Effect of scan rate

The route of the accessible pathway of uranyl ions toward the electrode surface and their interaction with the functional monomers were through analyzed by recording the cyclic voltammograms at different scan rates ranging from 50 to 350 mV s−1. Briefly, the imprinted sensor was dipped into an electrochemical cell containing a buffered uranyl solution, which was then connected directly to the reference and auxiliary electrodes, and a potential from −1.5 V to +1.5 V was applied at different scan rates. As exhibited in Fig. S6A (SI), the electrochemical response of the significant peak increased proportionally with the square root of the scan rate (ν1/2), as described by the Randles–Ševčík equation. The linear relationship between Ip and ν1/2 indicates that the electrochemical process is diffusion-controlled, meaning that the rate of electron transfer depends on the diffusion of ions from the bulk solution to the electrode surface. As expected, at higher scan rates, the ions do not have sufficient time to reach the electrode surface, leading to a broader and slightly shifted peak in the cyclic voltammogram, which is characteristic of diffusion-limited processes. In addition, the peak potential varied directly with the logarithm of the scan rate (Fig. S6B, SI), and the number of electrons transferred during the electrochemical process was calculated using the Tafel equation, which was equal to 1.

3.5.3. Leaching solvent

To regenerate the modified electrode, it was necessary to remove the uranyl ions remaining bound to the imprinted polymer after each measurement without affecting the polymer structure. To accomplish this, several washing solutions, including hydrochloric acid, nitric acid, acetic acid, ethylenediaminetetraacetic acid, and sodium hydroxide, were examined to determine the most effective eluent for uranyl ion removal. Nitric acid (0.1 mol L−1) was identified as the most efficient regenerating agent for the complete removal of UO22+ ions from the polymeric surface. This efficiency is attributed to its ability to facilitate the desorption of uranyl ions from the imprinted binding sites via protonation of functional groups and disruption of coordination interactions between the template and the polymer matrix, thereby restoring the accessibility of the imprinted cavities and enabling sensor reuse. This regeneration mechanism was clearly supported by morphological characterization, where TEM images revealed a pronounced disappearance of the dark uranium-rich domains after leaching, confirming the effective extraction of UO22+ ions. Additionally, AFM analysis showed a significant increase in surface roughness (Sq and Sa), indicating the formation of well-defined porous cavities, which further demonstrates the successful role of nitric acid in regenerating the imprinted binding sites. Furthermore, the influence of washing time on regeneration efficiency was investigated from 0.5 to 3.5 min. The peak current increased progressively with increasing washing time, reaching a maximum value at 160 s (Fig. S7, SI). This result indicates that longer washing durations allow the reopening of additional imprinted sites, thereby enhancing the electrochemical response of the sensor owing to the complete elution of uranyl ions from the polymer matrix.

3.5.4. Deposition potential and time

Deposition potential and time are among the most crucial factors affecting on the electrode sensitivity in the DP–ASV technique. Therefore, it is essential to select the potential at which the maximum reduction and deposition of uranyl ions occur on the electrode surface. The applied potential was tested in the range from −0.9 to −1.9 V, and the highest current response was obtained at −1.5 V (Fig. S8A, SI). Beyond this value, hydrogen ion reduction takes place, resulting in the formation of gas bubbles on the electrode surface, which hinders the access of uranyl ions to the IIPs/CDs@GCE surface. To ensure the accumulation of the maximum amount of uranyl ions, the deposition time was also optimized (Fig. S8B, SI). It was observed that increasing the deposition time from 20 to 90 s led to an increase in the current intensity, indicating enhanced uranyl accumulation on the electrode surface. However, the current reached a steady state at 80 s, suggesting that the electrode surface became saturated with the deposited species. Accordingly, −1.5 V and 80 s were selected as the optimal deposition potential and time.

3.5.5. Selectivity

Selectivity, and specificity are key parameters for evaluating the efficacy of IIPs/CDs@GCE to recognize the uranyl ions at its specific recognition sites at the polymeric surface in the presence of different competing ions. For this purpose, the DP–ASV signals of uranyl ions (1.0 × 10−5 mol L−1) were recorded individually and in the presence of various interfering ions, including Cd2+, Fe3+, Cu2+, Al3+, Pb2+, Zn2+, SO42−, CO32−, Cl−, PO43−, and ClO3−, each at a concentration of 5.0 × 10−4 mol L−1 (i.e., 50-fold excess). As exhibited in Fig. 6A, the variation in the uranyl signal remained within ±3%, indicating no significant change and confirming the high selectivity and specificity of the synthesized MIP sensor toward uranyl ions. In addition, carbonate (CO32−) and phosphate (PO43−) ions were intentionally examined because they can strongly coordinate with uranyl ions and therefore represent challenging interferents in uranium determination. Nevertheless, only a negligible variation in the current response (less than 5%) was observed, even at 100- and 200-fold excess concentrations, demonstrating that the ion-imprinted recognition sites retained their high affinity and selectivity toward UO22+ (Fig. S9, SI). Also, the selectivity and activity of the proposed sensor toward uranyl ions were assessed by calculating the imprinting factor (IF) using eqn (7).

IF = ΔIMIP/ΔINIP 7

where ΔIMIP and ΔINIP represent the current signal intensities of uranyl ions obtained using the imprinted and non-imprinted sensors, respectively. The mean differential currents were ΔIMIP = (0.000100 ± 0.000005) mA and ΔINIP = (0.000008 ± 0.000001) mA (n = 4), measured at a fixed uranyl ion concentration of 1 × 10−5 M, leading to a high imprinting factor (IF = 12.4). This is attributable to the presence of well-defined imprinting cavities that are complementary in shape, size, and chemical functionality to uranyl ions in the imprinted sensor, in contrast to the non-imprinted one, thereby confirming the successful formation of selective recognition sites within the polymer matrix. Unlike CDs, which primarily enhance the electrical conductivity and facilitate electron transfer, the ion-imprinted polymer is responsible for the specific recognition of UO22+ through these selective binding cavities, as evidenced by the high imprinting factor.

Fig. 6. (A) Electrochemical response of uranyl ions in the presence of different interfering species. (B) Calibration curve for uranyl ions using leached IIPs/CDs@GCE recorded by DP–ASV technique, with data expressed as mean ± standard deviation (n = 4). Error bars represent standard deviation.

Fig. 6

Open in a new tab

3.5.6. Analytical feature

Under the optimized conditions, the IIPs/CDs@GCE sensor was utilized to quantify uranyl ions via the DP–ASV technique. As shown in Fig. 6B, the differential current (Δi) increased gradually with increasing uranyl ion concentration over the linear range of 1.8 × 10−10–8.6 × 10−3 mol L−1, following the linear regression equation: Δi = −1.639 pC + 1.506 (R2 = 0.998) where C is the uranyl ion concentration (mol L−1) and Δi is the current difference (mA). Moreover, the limit of detection (LOD = 3.3σ/S) and limit of quantification (LOQ = 10σ/S) of the sensor were determined to be 5.94 × 10−11 mol L−1 and 1.8 × 10−10 mol L−1, where σ is the standard deviation of the blank response (n = 4) and S is the slope of the calibration curve (Table S10, SI). The calibration slope for the MIP sensor was −1.639 ± 0.017 (mA pUranyl), whereas the NIP exhibited a negligible response with a markedly lower slope, confirming the superior sensitivity of the imprinted sensor toward uranyl ions. In addition, the reusability and stability of the IIPs/CDs@GCE sensor were evaluated through repeated detection cycles for uranyl ions (5 × 10−5 mol L−1) over a period of 5 weeks. The sensor retained approximately 96.4% of its initial current response, indicating a performance loss of only 3.6%, which confirms good stability and acceptable reusability (Fig. S10, SI). The observed operational stability can be primarily ascribed to the formation of robust coordination complexes between UO22+ ions and the functional moieties embedded within the imprinted cavities, which effectively preserve the structural fidelity and spatial configuration of the recognition sites during successive binding–desorption cycles. Moreover, the integration of CDs contributes significantly to signal stabilization by facilitating accelerated charge transfer kinetics and establishing an interconnected conductive framework, thereby mitigating signal drift and enhancing the overall electrochemical response consistency. Repeatability and reproducibility were assessed by evaluating the response variations over multiple measurements for specific concentration with a single leached IIPs/CDs@GCE and among a set of identical sensors, respectively (Fig. S11, SI). Significantly, the proposed technique exhibited high repeatability (RSD < 2.1%), and good reproducibility (RSD < 1.7%) with low standard errors, which can be ascribed to the homogeneous distribution of imprinted sites and the synergistic effect between the conductive CDs and the well-defined imprinted architecture. Compared to previously reported studies of electrochemical techniques for uranyl detection in 2020–2026, the proposed sensor shows excellent selectivity, enhanced sensitivity and stability, and reliable repeatability and reproducibility (Table 1). Notably, while many of the reported sensors rely on conventional functional materials or non-specific interaction mechanisms, the present work benefits from a rationally designed chelating monomer that enables the formation of well-defined and highly selective binding cavities. The presence of multiple functional groups with strong coordinating ability toward uranyl ions promotes the formation of stable pre-polymerization complexes and enhances the structural and chemical complementarity of the imprinted cavities. Consequently, strong coordination interactions are established between the recognition sites and UO22+ ions, significantly improving the recognition efficiency, selectivity, sensitivity, and detection capability of the proposed sensor, thereby clearly outperforming many previously reported approaches. Also, the incorporation of carbon dots within the imprinted matrix provides a conductive network that facilitates rapid electron transfer, thereby amplifying the electrochemical signal and contributing to the remarkably low limit of detection and a broad linear range.

Table 1. Comparison between different electrochemical techniques for uranyl detection in 2020–2026a.
Analyte Technique Electrode Modified materials Linearity (mol L−1) LOD (mol L−1) LOQ (mol L−1) Selectivity Stability (days) Reproducibility Ref.
UO22+ DPV CPE IIPs, graphene 1.0 × 10−10–1.0 × 10−7 1.81 × 10−9 — Good 30 <2% 31
UO22+ DPV ITO Ag Nd-RGO 1 × 10−6–2 × 10−4 0.85 × 10−6 — Moderate — 3.9% 32
UO22+ DPV GCE PD/RGON 1 × 10−7–50 × 10−6 5 × 10−8 — Moderate 10 2.28% 33
UO22+ DPV GCE AM-GFG 5.5 × 10−8–3.7 × 10−7 9.97 × 10−10 — Moderate 28 4.3% 34
UO22+ DPV GCE Au NP 7.4 × 10−9–3.7 × 10−8 3.8 × 10−10 — Low 7 2.21% 35
UO22+ DPV–ASV GE DNAzyme 1.0 × 10−9–1.0 × 10−6 1.3 × 10−10 — Low 7 2.3% 36
UO22+ DPV GE Au NP, Ag NC 2 × 10−11–5 × 10−9 6.2 × 10−12 — Low 10 5.40% 37
UO22+ DPV GCE ON, BP, MPG 7.4 × 10−8–6.66 × 10−7 2.36 × 10−10 — Low 4 <5% 38
UO22+ DPV–ASV GCE IIPs 4.7 × 10−9–3.5 × 10−7 1.59 × 10−9 — Moderate 28 5.9% 39
UO22+ SW–ASV GE PET, GM, AC 3.7 × 10−9–3.7 × 10−7 2.0 × 10−8 — Low — 5.7% 40
UO22+ PE CPE TPPS, TBPS 1.0 × 10−7–1.0 × 10−1 7.9 × 10−8 — Low — 0.261% 41
UO22+ DPV GCE Au NP 8.8 × 10−9–1.7 × 10−7 1.1 × 10−9 — Low 15 3.3% 42
1.7 × 10−7–1.7 × 10−6
UO22+ EIS PGE FePt core, ZnIn2S4 shell 5 × 10−7–10.0 × 10−6 71.7 × 10−9 — Low — 1.32% 43
UO22+ PE ISE Silica/PN 1 × 10−6–1 × 10−2 1.4 × 10−7 — Low — — 44
UO22+ ACV GDE APS, U-pT-12 5 × 10−8–4.5 × 10−6 50 × 10−9 — Low — — 45
UO22+ PE ISE DOPDH 1.0 × 10−6–1.0 × 10−1 3.90 × 10−7 — Low — — 46
UO22+ DPV–ASV CPE MWCNT 5.0 × 10−3–1.0 × 10−10 2.1 × 10−11 7 × 10−11 Low 42 2.7% 47
UO22+ PE SPE DMAE, BDE 4.7 × 10−7–1.0 × 10−1 1.0 × 10−5 — Low — 0.532 48
1.0 × 10−5–1.0 × 10−1
UO22+ DPV CPE MIIM 1.0 × 10−9–2.0 × 10−7 1.08 × 10−9 3.23 × 10−10 Moderate 30 1.53% 49
UO22+ DPV CPE MGO 1 × 10−8–3.0 × 10−6 1.32 × 10−9 — Good 30 4.60% 50
UO22+ DPV–ASV GCE BCB 7.4 × 10−9–3.3 × 10−7 2.48 × 10−10 — Low 10 5.7% 51
UO22+ DP–ASV GCE IIPs and CDs 1.8 × 10−10–8.6 × 10−3 5.94 × 10−11 1.8 × 10−10 High 35 <1.7% This work
IF = 12.4
Open in a new tab
a

DPV; differential pulse voltammetry, CPE; carbon paste electrode, SW–ASV; square wave -anodic stripping voltammetry; Ag Nd-RGO; silver nanodendrites-reduced graphene oxide, PD/RGON; polydopamine/reduced graphene oxide nanocomposite, AM-GFG; amidoxime-grafted fluorinated graphene, Au NP; gold nanoparticles, Ag NC; silver nanoclusters, ON; oligonucleotides, BP; black phosphorene, MPG; maleimide-polyethylene glycol, PET; poly(ethylene terephthalate), GM; glycidyl methacrylate, AC; acrylonitrile, TPPS; triphenylphosphine sulfide, TBPS; triisobutylphosphine sulfide, PN; polyaniline, APS; 12-AA peptide sequence, DOPDH; 4-(1-((1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1Hpyrazol-4-yl)imino)ethyl)-1-dodecylpyridin-1-ium bromide, MWCNT; multi-walled carbon nanotubes, DMAE; 2-(dimethylamino)ethan-1-ol, BDE; 1-bromododecane ethanolic, MIIM; magnetic ion-imprinted membrane, MGO; modified graphene oxide, BCB; brilliant cresyl blue, PE; potentiometric technique, ACV; alternating current voltammetry, ITO; indium tin oxide electrode, GE; gold electrode, PGE; pencil graphite electrode, ISE; ion selective electrode, GDE; gold disk electrodes, SPE; screen-printed electrodes.

3.5.7. Applications

Following the laboratory performance evaluation, the synthesized imprinted sensor was further validated by monitoring the presence of uranyl ions in real environmental samples including tap water, Nile water, industrial water, soil, and sediment samples, to ensure reliable performance under different matrix conditions. Under optimum conditions, each sample was spiked with different standard uranyl solutions to assess the accuracy of the sensors and then detected for uranyl using DP–ASV. As summarized in Table 2, high recovery values ranging from 97.6% to 99.8% were obtained, demonstrating that the proposed technique is highly suitable for uranyl determination in environmental samples with satisfactory accuracy and precision. These results, together with the interference study, indicate that matrix effects do not significantly affect the performance of the proposed sensor. Additionally, a two-tailed Student's t-test and F-test were performed at a 95% confidence level. As noticed there is no statistically significant difference between the proposed method and ICP-AES results.

Table 2. Detection of uranyl ions in different real samples by the proposed electrochemical technique, using imprinted sensor, and ICP-AESa.
Sample Uranyl added (µg L−1) Uranyl detected (µg L−1) Recovery (%) Uranyl detected by ICP-AES (µg L−1) Recovery (%) F-test t-test
Tap water 0 ND — ND — — —
10 9.92 ± 0.10 99.2 9.90 ± 0.11 99.0 0.82 1.7
25 24.85 ± 0.11 99.4 24.91 ± 0.08 99.6 1.89 1.1
50 49.92 ± 0.11 99.8 49.85 ± 0.12 99.7 0.84 2.1
Nile water 0 ND — ND — — —
10 9.83 ± 0.16 98.3 9.91 ± 0.10 99.1 2.56 1.5
25 24.75 ± 0.21 99.0 24.84 ± 0.18 99.3 1.36 1.3
50 49.81 ± 0.11 99.6 49.90 ± 0.16 99.8 0.47 1.6
Industrial water 0 ND — ND — — —
10 9.93 ± 0.10 99.3 9.96 ± 0.08 99.6 1.56 1.1
25 24.81 ± 0.09 99.2 24.90 ± 0.11 99.6 0.67 1.9
50 48.8 ± 0.21 97.6 49.79 ± 0.16 99.5 1.72 1.7
Soil 0 0.65 ± 0.03 — 0.70 ± 0.02 — 2.25 1.6
10 10.53 ± 0.11 98.8 10.66 ± 0.13 99.6 0.71 1.4
25 25.61 ± 0.07 99.8 25.66 ± 0.04 99.8 3.06 1.6
50 50.59 ± 0.08 99.8 50.62 ± 0.10 99.8 0.64 1.9
Sediment sample 0 ND — ND — — —
10 9.91 ± 0.10 99.1 9.90 ± 0.09 99.0 1.23 1.6
25 24.88 ± 0.09 99.5 24.90 ± 0.11 99.6 0.67 1.9
50 49.90 ± 0.08 99.8 49.91 ± 0.10 99.8 0.64 1.7
Open in a new tab
a

n = 4, tcritical = 2.77, Fcritical = 6.39 at 95.0% confidence limit.

4. Conclusion

A novel sensitive imprinted sensor, IIPs/CDs@GCE, was synthesized for the detection of uranyl ions in various real samples. For this purpose, a promising chelating agent, N-allyl-2-(2-cyanoacetyl) hydrazine-1-carbothioamide, was designed, fabricated, and directly interacted with uranyl ions. Also, the molecular structures of the ligand and its complexation with the uranyl ion were confirmed through density functional theory calculations, accredited by geometry optimization and various quantum descriptors. Subsequently, the complex was polymerized with EGDMA in the presence of potassium persulfate. After that, the uranyl ions were leached from the polymeric surface using nitric acid, leaving behind 3D imprinted cavities that specifically bind with uranyl ions. After dissolving the CDs and leaching IIPs in a specific solvent in separate containers, they were deposited directly onto the GCE surface. The synthesized sensor showed a wide linear range (1.8 × 10−10–8.6 × 10−3 mol L−1) with low limit of detection (5.94 × 10−11 mol L−1), high sensitivity, excellent selectivity in the presence of competing ions (IF = 12.4), and good stability (5 weeks). In addition, our technique exhibited high accuracy (97.6–99.8%) and good precision (RSD < 1.7%), proving the reliability and efficiency of the proposed electrochemical sensor for real-world applications.

Conflicts of interest

There are no conflicts to declare.

Supplementary Material

RA-016-D6RA06561A-s001

Acknowledgments

All authors gratefully acknowledge the Science, Technology & Innovation Funding Authority (STIFA) for providing the equipment's awarded to the Mansoura University Sustainable Energy Research (MSER) laboratory through projects 38313 and 42690, which made it possible to carry out the current work.

Data availability

The data supporting this article have been included as part of the supplementary information (SI). Supplementary information is available. See DOI: https://doi.org/10.1039/d6ra06561a.

References

  1. Ashish A. Bangotra P. Dillu V. Prasad M. Banerjee S. Mehra R. Singh N. L. Human exposure to uranium through drinking water and its detrimental impact on the human body organs. Environ. Geochem. Health. 2026;46:397. doi: 10.1007/s10653-024-02150-9. [DOI] [PubMed] [Google Scholar]
  2. Wang S. Jiang J. He X. Yang S. Wu H. Qin Z. Chu M. Zhang Z. Liao J. Wang X. Research progress of SERS on uranyl ions and uranyl compounds: a review. J. Mater. Chem. C. 2022;10:4006–4018. doi: 10.1039/D1TC05154G. https://dx.doi.org/10.1039/d1tc05154g [DOI] [Google Scholar]
  3. Li J. Zhang Y. Remediation technology for the uranium contaminated environment: a review. Procedia Environ. Sci. 2012;13:1609–1615. doi: 10.1016/j.proenv.2012.01.153. [DOI] [Google Scholar]
  4. Domingo J. L. Reproductive and developmental toxicity of natural and depleted uranium: a review. Reprod. Toxicol. 2001;15:603–609. doi: 10.1016/S0890-6238(01)00181-2. [DOI] [PubMed] [Google Scholar]
  5. Abdallah A. B. Youins A. M. El-Kholany M. R. Selective separation of uranyl ions from some lanthanide elements using a promising benaminoester ligand by cloud point extraction. RSC Adv. 2022;12:8520. doi: 10.1039/D2RA00274D. https://dx.doi.org/10.1039/d2ra00274d [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Yazzie M. Gamble S. L. Civitello E. R. Stearns D. M. Uranyl Acetate Causes DNA Single Strand Breaks In Vitro in the Presence of Ascorbate (Vitamin C) Chem. Res. Toxicol. 2003;16:524–530. doi: 10.1021/tx025685q. [DOI] [PubMed] [Google Scholar]
  7. Feng T. Zhao S. Cao M. Du X. Wang H. Cao X. Feng L. Yuan Y. Wang N. Highly sensitive and specific uranyl ion detection by a fluorescent sensor containing uranyl-specific recognition sites. Sci. Bull. 2025;70:70–77. doi: 10.1016/j.scib.2024.08.013. [DOI] [PubMed] [Google Scholar]
  8. Zhan Y. Lu X. Lan T. Tian Q. Shen J. He W. An AIE fluorescence sensor based on amidoxime for rapid detection of uranyl ions in aqueous solutions. Dyes Pigm. 2023;216:111299. doi: 10.1016/j.dyepig.2023.111299. [DOI] [Google Scholar]
  9. Goyal N. Purohit P. J. Dhobale A. Page A. Sastry M. Electrothermal atomization atomic absorption spectrometric determination of trace metals in uranium-plutonium fuel materials. Z. Anal. Chem. 1988;330:114–115. doi: 10.1007/BF00470718. https://dx.doi.org/10.1007/bf00470718 [DOI] [Google Scholar]
  10. Boomer D. Powell M. Determination of uranium in environmental samples using inductively coupled plasma mass spectrometry. Anal. Chem. 1987;59:2810–2813. doi: 10.1021/ac00150a019. [DOI] [PubMed] [Google Scholar]
  11. Sanyal K. Misra N. Trace element determinations in uranium by energy dispersive X-ray fluorescence spectrometry using thin film specimens. Spectrochim. Acta, Part B. 2019;155:44–49. doi: 10.1016/j.sab.2019.03.004. [DOI] [Google Scholar]
  12. Saher A. Abdallah A. B. Molouk A. F. S. Mortada W. I. Khalifa M. E. MIP/GO/GCE Sensor for the Determination of Aminophylline in Pharmaceutical Ingredients and Urine Samples. Anal. Bioanal. Chem. Res. 2023;10:435–443. doi: 10.22036/abcr.2023.392413.1915. [DOI] [Google Scholar]
  13. Mansour A. H. Mortada W. I. Awad F. S. Molouk A. F. S. Khalifa M. E. Abdallah A. B. Carbon dot-based imprinted electrochemical sensor for ultrasensitive and selective detection of sucralose in real samples. Mater. Chem. Front. 2025;9:3075–3085. doi: 10.1039/D5QM00485C. [DOI] [Google Scholar]
  14. Tarek M. Molouk A. F. S. El-Shinawi H. El-Dafrawy S. M. Abdallah A. B. Rational design of a novel, ultrasensitive molecularly imprinted polymer-based electrochemical sensor for boscalid detection in grape, tomato, and berry samples. Food Chem. 2025;490:145186. doi: 10.1016/j.foodchem.2025.145186. [DOI] [PubMed] [Google Scholar]
  15. Hashem H. M. Ghaith E. A. Eladi A. Abozeid S. M. Abdallah A. B. A novel fluorescent probe based imprinted polymer-coated magnetite for the detection of imatinib leukemia anti-cancer drug traces in human plasma samples. Spectrochim. Acta, Part A. 2024;315:124262. doi: 10.1016/j.saa.2024.124262. [DOI] [PubMed] [Google Scholar]
  16. Shalapy A. E. Molouk A. F. S. Awad F. S. Khalifa M. E. Abdallah A. B. Flexible imprinted electrochemical sensing platform for ultra-trace detection of indigo carmine dye in coloured food additive for candy and ice cream. Inorg. Chem. Commun. 2025;174:113951. doi: 10.1016/j.inoche.2025.113951. [DOI] [Google Scholar]
  17. Cai X. Li J. Zhang Z. Yang F. Dong R. Chen L. Novel Pb2+ Ion Imprinted Polymers Based on Ionic Interaction via Synergy of Dual Functional Monomers for Selective Solid-Phase Extraction of Pb2+ in Water Samples. ACS Appl. Mater. Interfaces. 2014;6:305–313. doi: 10.1021/am4042405. [DOI] [PubMed] [Google Scholar]
  18. Wang L. Li B. Wang J. Qi J. Li J. Ma J. Chen L. A rotary multi-positioned cloth/paper hybrid microfluidic device for simultaneous fluorescence sensing of mercury and lead ions by using ion imprinted technologies. J. Hazard. Mater. 2022;428:128165. doi: 10.1016/j.jhazmat.2021.128165. [DOI] [PubMed] [Google Scholar]
  19. Abdelghany S. Kospa D. A. Abdallah A. B. Ibrahim A. A. Khalifa M. E. Highly porous ligand-embedded carbonized metal–organic framework for the sensitive detection and removal of trace heavy metals in real samples. Inorg. Chem. Commun. 2024;167:112682. doi: 10.1016/j.inoche.2024.112682. [DOI] [Google Scholar]
  20. Bakry A. M. Alamier W. M. Abdallah A. B. Abou El-Reash Y. G. El-Shall M. S. Awad F. S. Enhanced performance of amine and thiol chemically modified graphene oxide for effective removal of Hg(II), Pb(II), and Cr(VI) from aqueous solution. Appl. Water Sci. 2024;14:179. doi: 10.1007/s13201-024-02234-y. [DOI] [Google Scholar]
  21. Al-Qarhami F. Abdallah A. B. Khalifa M. E. Awad F. S. Glutaraldehyde-crosslinked magnetic chitosan nanocomposite for efficient Cr(VI) removal: A sustainable approach to aquatic remediation. Int. J. Biol. Macromol. 2025;310:143459. doi: 10.1016/j.ijbiomac.2025.143459. [DOI] [PubMed] [Google Scholar]
  22. Kuligowska M. Neffe S. Carbon dots as sensors and sorbents in environmental monitoring protection and chemical analysis. TrAC, Trends Anal. Chem. 2024;176:117767. doi: 10.1016/j.trac.2024.117767. [DOI] [Google Scholar]
  23. Liu C. Lin X. Liao J. Yang M. Jiang M. Huang Y. Du Z. Chen L. Fan S. Huang Q. Carbon dots-based dopamine sensors: Recent advances and challenges. Chin. Chem. Lett. 2024;35:109598. doi: 10.1016/j.cclet.2024.109598. [DOI] [Google Scholar]
  24. Zembrzuska D. Kalecki J. Cieplak M. Lisowski W. Borowicz P. Noworyta K. Sharma P. S. Electrochemically initiated co-polymerization of monomers of different oxidation potentials for molecular imprinting of electroactive analyte. Sens. Actuators, B. 2019;298:126884. doi: 10.1016/j.snb.2019.126884. [DOI] [Google Scholar]
  25. Sheliel D. S. Ghaith E. A. El-Ayaan U. Nawar N. Structure elucidation, cyclic voltammetry, fluorescence, DFT, biological potency, and in silico profiling of new bivalent transition metal coordination compounds of 7-amino-4H-pyrazolo [3, 4-b] pyridinone Ligand. J. Mol. Struct. 2025;1348:143427. doi: 10.1016/j.molstruc.2025.143427. [DOI] [Google Scholar]
  26. Hamama W. S. Ibrahim M. E. Ghaith E. A. Zoorob H. H. Peculiar reaction behavior of 1, 3-oxathiolan-5-one toward various reagents: Molecular modeling studies and in vitro antioxidant and cytotoxicity evaluation. Synth. Commun. 2017;47:566–580. doi: 10.1080/00397911.2016.1276190. [DOI] [Google Scholar]
  27. Ali H. A. Ismail M. A. Abd El Salam M. Ghaith E. A. Green synthesis, computational approaches, and bio-efficacy of novel triazines as insect growth regulator (IGR) analogues against Spodoptera littoralis (Boisd.) J. Mol. Struct. 2026;1353:144699. doi: 10.1016/j.molstruc.2025.144699. [DOI] [Google Scholar]
  28. Ghaith E. A. Abd El Salam M. Said G. E. Barbiturate and uracil scaffolds as potential insecticidal agents: Synthesis, DFT studies and in vivo Biochemical Susceptibility of the polyphagous pest, cotton leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae) J. Mol. Struct. 2025;1338:142302. doi: 10.1016/j.molstruc.2025.142302. [DOI] [Google Scholar]
  29. Ghaith E. A. Abdallah A. B. El-Sawi A. A. El-Bana G. G. Ultrasound-Assisted Utility of 1, 2, 4-Triazole as a Multisite-Sequential Scaffold to Construct Different Heterocycles, Accredited by Molecular Modeling and Electrochemical Studies. J. Heterocycl. Chem. 2025;62:505–517. doi: 10.1002/jhet.70003. https://dx.doi.org/10.1002/jhet.70101 [DOI] [Google Scholar]
  30. Xu H. Xu D. C. Wang Y. Natural indices for the chemical hardness/softness of metal cations and ligands. ACS Omega. 2017;2:7185. doi: 10.1021/acsomega.7b01039. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Wang Z. Zhang D. Xiao X. Su C. Li Z. Xue J. Hu N. Peng P. Liao L. Wang H. A highly sensitive and selective sensor for trace uranyl (VI) ion based on a graphene-coated carbon paste electrode modified with ion imprinted polymer. Microchem. J. 2020;155:104767. doi: 10.1016/j.microc.2020.104767. [DOI] [Google Scholar]
  32. Guo W. Xu H. Cao X. Ma J. Liu Y. A novel electrochemical detemination platform of uranyl ion based on silver nanodendrites-reduced graphene oxide. Microchem. J. 2020;158:105134. doi: 10.1016/j.microc.2020.105134. [DOI] [Google Scholar]
  33. Guo W. Xu H. Chen C. Cao X. Ma J. Liu Y. Determination of U(VI) by differential pulse stripping voltammetry using a polydopamine/reduced graphene oxide nanocomposite modified glassy carbon electrode. Microchem. J. 2022;175:107111. doi: 10.1016/j.microc.2021.107111. [DOI] [Google Scholar]
  34. Jiang C. Tang X. He B. Ouyang Y. Xiang R. Li L. Amidoxime-grafted fluorinated graphene nanosheets as a trace electrochemical sensing platform of uranyl ion. Microchem. J. 2024;205:111371. doi: 10.1016/j.microc.2024.111371. [DOI] [Google Scholar]
  35. Han J. Gao J. Chen J. Qi G. Gui Y. Wang Y. Yan Y. Ma F. Chen Q. Xue Y. Electrochemical measurements of uranyl ions in real nuclear wastewater using nanogold-modified electrodes. Microchem. J. 2025;212:113340. doi: 10.1016/j.microc.2025.113340. [DOI] [Google Scholar]
  36. Xiang M. Yin C. Chen Q. Zhu G. Chen Z. Li H. Antwi-Baah R. Tang J. Yang K. Xu S. A label-free electrochemical biosensor for detection of uranyl ions in water based on nucleic acid dye-inducing turn-off of photosensitization. Microchem. J. 2025;213:113811. doi: 10.1016/j.microc.2025.113811. https://dx.doi.org/10.2139/ssrn.4980480 [DOI] [Google Scholar]
  37. Chen L. Liu J. Cao C. Tang S. Lv C. Xiao X. Yang S. Liu L. Sun L. Zhu B. Li L. Dual-signal amplification electrochemical sensing for the sensitive detection of uranyl ion based on gold nanoparticles and hybridization chain reaction-assisted synthesis of silver nanoclusters. Anal. Chim. Acta. 2021;1184:338986. doi: 10.1016/j.aca.2021.338986. [DOI] [PubMed] [Google Scholar]
  38. He J. He B. Ouyang Y. Xie X. Tang X. Oligonucleotide-immobilized PEGylated black phosphorene with enhanced stability and activity for electrochemical detection of trace uranyl. Talanta. 2026;297:128754. doi: 10.1016/j.talanta.2025.128754. [DOI] [PubMed] [Google Scholar]
  39. Hojatpanah M. R. Khanmohammadi A. Khoshsafar H. Hajian A. Bagheri H. Construction and application of a novel electrochemical sensor for trace determination of uranium based on ion-imprinted polymers modified glassy carbon electrode. Chemosphere. 2022;292:133435. doi: 10.1016/j.chemosphere.2021.133435. [DOI] [PubMed] [Google Scholar]
  40. Korolkov I. V. Yeszhanov A. B. Shakayeva A. K. Shlimas D. I. Zhumazhanova A. Zdorovets M. V. Photo-induced graft (co)polymerization of glycidyl methacrylate and acrylonitrile on PET ion-track membranes for electrochemical detection of uranyl ions. Colloids Surf., A. 2022;648:129086. doi: 10.1016/j.colsurfa.2022.129086. [DOI] [Google Scholar]
  41. Ali T. A. Akl Z. F. Mohamed G. G. Novel potentiometric carbon paste electrodes for trace detection of uranyl (II) ions in petroleum water samples, Egypt. J. Pet. 2023;32:1–7. doi: 10.1016/j.ejpe.2023.08.004. [DOI] [Google Scholar]
  42. Shi S. Wu H. Zhang L. Wang S. Xiong P. Qin Z. Chu M. Liao J. Gold nanoparticles based electrochemical sensor for sensitive detection of uranyl in natural water. J. Electroanal. Chem. 2021;880:114884. doi: 10.1016/j.jelechem.2020.114884. [DOI] [Google Scholar]
  43. Zeynali H. Motaghedifard M. Costa B. F. O. Akbari H. Moghadam Z. Babaeianfar M. Rashidi M. J. Design and development a novel uranyl sensor based on FePt/ZnIn2S4 core-shell semiconductor nanostructures. Arabian J. Chem. 2020;13:1429–1439. doi: 10.1016/j.arabjc.2017.11.014. [DOI] [Google Scholar]
  44. Kaur G. Kaur H. Mittal S. K. Electrochemical sensor based on ion-selective membrane of silica/polyaniline nano-composites for selective determination of uranyl ions. Talanta Open. 2022;6:100158. doi: 10.1016/j.talo.2022.100158. [DOI] [Google Scholar]
  45. Thompson C. C. Lai R. Y. Threonine Phosphorylation of an Electrochemical Peptide-Based Sensor to Achieve Improved Uranyl Ion Binding Affinity. Biosensors. 2022;12:961. doi: 10.3390/bios12110961. [DOI] [PMC free article] [PubMed] [Google Scholar]
  46. Akl Z. F. Rapid electrochemical sensor for uranium (VI) assessment in aqueous media. RSC Adv. 2022;12:20147. doi: 10.1039/D2RA02619H. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. Selim A. A. Abdallah A. B. Awad F. S. Khalifa M. E. Molouk A. F. S. Electrochemical sensor based on amine- and thiolmodified multi-walled carbon nanotubes for sensitive and selective determination of uranyl ions in real water samples. RSC Adv. 2023;13:31141. doi: 10.1039/D3RA05374A. [DOI] [PMC free article] [PubMed] [Google Scholar]
  48. Ali T. A. Akl Z. F. Ionic liquid-multi-walled carbon nanotubes modified screen-printed electrodes for sensitive electrochemical sensing of uranium. J. Radioanal. Nucl. Chem. 2021;328:267–276. doi: 10.1007/s10967-020-07573-z. [DOI] [Google Scholar]
  49. He L. Wang Z. Li Y. Yang J. Liao L. Xiao X. Liu Y. A Novel Electrochemical Sensor Modified with a Computer-Simulative Magnetic Ion-Imprinted Membrane for Identification of Uranyl Ion. Sensors. 2022;22:4410. doi: 10.3390/s22124410. [DOI] [PMC free article] [PubMed] [Google Scholar]
  50. Li Y. Wang Z. Liu C. Zhang D. Liao L. Xiao X. Graphene oxide modified H4L-ion imprinting electrochemical sensor for the detection of uranyl ions. Z. Anorg. Allg. Chem. 2021;647:1914–1920. doi: 10.1002/zaac.202100182. [DOI] [Google Scholar]
  51. Zhou Z. Zhou Y. Liang X. Luo J. Liu S. Ma J. Design and fabrication of a sensitive electrochemical sensor for uranyl ion monitoring in natural waters based on poly (brilliant cresyl blue) Microchim. Acta. 2022;189:412. doi: 10.1007/s00604-022-05485-1. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

RA-016-D6RA06561A-s001
RA-016-D6RA06561A-s001.pdf (1.5MB, pdf)

Data Availability Statement

The data supporting this article have been included as part of the supplementary information (SI). Supplementary information is available. See DOI: https://doi.org/10.1039/d6ra06561a.

Articles from RSC Advances are provided here courtesy of Royal Society of Chemistry

RESOURCES