Table 2.

The mechanism and notable advantages or disadvantages of aptamer-based biosensors

Sensor Type/Method	Mechanism of Action	Comments	References
Aptamer-conjugated GNPs and a resonance light-scattering detection system	Aptamers are combined onto GNPs followed by bead-based amplification, one bacterial cell was capable of generating more than 104 GNPs after amplification, and amplified GNPs could be detected by the light-scattering–sensing system	Very short detection time. The detection of a single cell can be reached within 1.5 h without complicated equipment such as thermal cyclers or centrifuges	[44]
CRISPR-Cas12a assisted RCA	The specificity based on the dual functionalized aptamers can initiate bioconjugation to specifically recognize the protein targets and can also convert the protein recognition to nucleic acid signals	Accurate identification and high-sensitive detection of MRSA. Dual amplification of the nucleic acid signal	[32]
Capture platform based on Fe3O4@mTiO2 modified with target aptamer	First, the complex was incubated with blood samples and the aptamer would connect with the target bacteria. After that, the bacteria captured by Apt-Fe3O4@mTiO2 NPs were concentrated with the help of the magnetic field	High bacterial-captured efficiency of about 80%, short detection time within 2 h, and little cross-react with the nontarget components in blood	[45]
Fe3O4-Ce6-Apt nanosystem	Simultaneous blood bacterial species identification and enrichment can be achieved in a single step, and then, enriched bacteria can be detected with fluorescence microscopic determination	Identify and enrich the bacteria in the sepsis blood sample for 1 h. Blood disinfection	[68]
Enzyme-linked aptamer assay	Construct ELAA	High sensitivity to bacterial OMVs as low as 25 ng/mL. A new possibility for the development of cell-free bacterial sensors using bacterial OMVs instead of living bacterial cells	[49]
Vertical capacitance aptasensors	Some bacteria, culture in blood culture media comprising blood (0.2 mL) and culture media (0.8 mL), the biofilm formation and bacterial growth could be detected by measuring capacitance changes at f = 0.5 and 10 kHz, respectively. After treated with antibiotics, the sensitivity of bacteria to antibiotics can be judged by this change	Short AST time within 12 h	[46]
e-AST system	The e-AST system is composed of 60 aptamer-functionalized capacitance sensors, of which 2 sensors were used for the negative control, 3 sensors for positive control, and other 55 sensors for the determination of antibiotic sensitivity to 11 antibiotics at 5 different concentrations	Short AST time within 6 h	[47]
Voltammetric biosensor	After using aptamers immobilized by RGO, and MoS2 is also applied as the matrix of the biosensor with the application of RGO and AuNPs	Simplified operation sequence with fast response and high recovery rate. PEI-rGO-MoS2 nanocomposite with a larger specific surface area, thermal stability and electrical conductivity increases the sensitivity of the sensor	[55]
Acoustic wave biosensor	The SLG film first connects with CS, and then the amino groups in the CS react with the aldehyde in GA to form C = N bonds. After that, the aldehydes groups in GA react with the amine-functionalized aptamer, which is ready for the specific detection of endotoxin	Rapid, simple operations and low costs. Excellent stability from the air phase to the liquid phase	[57]
Microfluidic-based approach	Real-time response of the sensor conductance is monitored with increasing concentration of IL-6, exposure to the sensing surface in buffer solution, and clinically relevant spiked blood samples	Sensitive detection of IL-6 at low concentrations	[62]
Luminex xMAP technology	xMAP assays typically employ a sandwich-type format using antibodies for the capture. For this assay, an RNA aptamer that binds CRP is conjugated to beads to act as the capture agent	The number and type of analytes by using aptamers alone or in conjunction with antibodies expand and the use of sample volumes is low	[66]
Optical sensor	The signal output mode is an optical image, small changes can be converted into optical signals for output	Compatibility to a wide range of surface modifications. The detection limit of the sensor slightly changed with increased use. Some cross-reactivity towards the unspiked human serum	[56, 60, 65, 67]
Fluorescence quenching efficiency	The concentration of LPS can be quantitatively analyzed by observing fluorescence changes	Little consumption of sample. Low recovery of serum sample	[58, 59]
Field-Effect Transistor-Based Approach	The graphene surface immobilized aptamer is unfolded without IL-6 and it would fold after binding with the target. These aptamer structural changes bring the negative charges in IL-6 to the proximity of the graphene-liquid interface	Low-voltage operation (< 1 V), inherent gain amplification, biocompatibility and miniaturization	[63, 64]
Electrochemical	Electrochemical sensors are constructed using various nanomaterials	Gold disk electrodes: Short detection time and little cross-interaction reactivity to plasmid DNA, RNA, proteins, saccharides, and/or lipids which are most likely to coexist with LPS assay Gra AuNPs: Overcome the disadvantage of limited nicking endonuclease recognition and integrate molecular biological technology and nano-biotechnology with electrochemical detection to cascade signal amplification, which can detect target LPS down to the femtogram level Gold atomic cluster: Simple sensor fabrication compared with other electrochemical sensors for LPS RGO/AuNPs: Short LPS detection time within 35 min. Enhanced electrode performance and low LOD down to femtomolar level AuNPs: Label-free detection, simple experimental protocol, high selectivity and low limit of detection	[50–54, 61]