Table 1.
Properties of various photoactive species used in PEC biosensing.
| Photo electrode material | Excitation | Stability (“N” cycles, Rsd (%), period) | Base photo-current (A) | Enhanced absorption | Enhanced charge separation | Ease of functionalization | References |
|---|---|---|---|---|---|---|---|
| 1.1 Inorganic Semiconductors | |||||||
| TiO2 NWs | Simulated sunlight | – | 1.15 × 10−3 | No | No | Yes TiO2 NWs functionalized with HRP via APTES-gluteraldehyde coupling. | Wang et al., 2014b |
| CdTe QD | Xenon lamp; 420 nm cut-off filter | Fairly stable.N = 17, ~Rsd ~9.16%, 360 s | ~2.17 × 10−7 | No | Decreased. Trap sites resulting from Ag2Te formation create new electron–hole recombination centers. | Yes; 3-Mercaptopropionic (MPA) modified CdTe via one pot synthesis; resultant carboxyl terminated surface. | Lin et al., 2016 |
| CdTe QD | 590 nm | Very stable.N = 8, Rsd ~0.9%, 275 s | ~3.80 × 10−7 | No | No | Yes; MPA modified CdTe via one pot synthesis; resultant carboxyl terminated surface. | Li et al., 2018a |
| CdTe QD | 590 nm | Very stable.N = 15, no decrease in photocurrent, 425 s | ~2.10 × 10−7 (anodic) ~1.20 × 10−7 (cathodic) | No | No | Yes; MPA modified CdTe via one pot synthesis; resultant carboxyl terminated surface. | Hao et al., 2017b |
| 1.2 Organic Semiconductors | |||||||
| g-C3N4 | Visible | Very stable.N = 9, no significant decrease in photocurrent, 350 s | ~3.00 × 10−6 | Yes | Yes; MB intercalators following duplex formation at g-C3N4 enhance separation efficiency. | No | Da et al., 2018 |
| FeTMPyP | Chemiluminescence | Very stable.Rsd ~4.3%. Long term stability over 10 days. | ~2.50 × 10−7 | Yes | No | No | Zang et al., 2015 |
| PFBT Pdots (Polymer dots) | 450 nm | Stable.N = 20, 400 s | ~3.00 × 10−8 | No | Yes; photogenerated electrons transferred to the proton in solution at low pH value. | Yes; Carboxylated surface obtained via synthesis procedure allows for easy immobilization of pDNA via amine-carboxyl interaction. | Shi et al., 2018b |
| 1.3 Hybrid Semiconductors | |||||||
| 1.3.1 Inorganic -Inorganic | |||||||
| CdTe-Bi2S3 | Visible | Fairly stable.N = 8, Rsd~7.3%, 350 s | ~4.00 × 10−7 | Yes | Yes; Z-scheme heterojunction formation between CdTe and Bi2S3. | No | Liu et al., 2017b |
| CdS/ZnS | Visible | Good long-term stability; 95.6% of its original value after 5 months | ~3.00 × 10−5 | Yes | Yes; Formation of heterojunction allowed the transfer of photogenerated electrons to ZnS conduction band. | Yes; CdS was modified by carboxyl groups which was used to attach with amine terminated DNA. | Shi et al., 2018a |
| Core–shell NaYF4:Yb,Tm@TiO2 | Infrared | Fairly stable.N = 10, Rsd ~7.9%, 250 s | ~1.25 × 10−7 | Yes | Yes; Enhanced separation due to formation of Z-scheme heterojunction | No | Qiu et al., 2018 |
| 1.3.2 Organic-Inorganic | |||||||
| TiO2-polyethylenimine mesocrystal | Visible | Very stable.N = 10, Rsd ~2.04%, 250 sExcellent long-term stability; 94.8% of initial value after 12 days | ~4.00 × 10−6 | Yes | Yes; Improved charge separation via ligand (OAM/PEI) modification | Yes; Organic ligand (OAM/PEI) modification confers the complex with reactive amine terminations capable of further chemical reaction. | Dai et al., 2017 |
| CdS-MV | Xenon lamp | Poor stability. | ~1.00 × 10−7 | No | Yes; MV coating of CdS facilitates fast charge separation and a slow charge recombination upon irradiation. | Yes; Thioglycolic acid (TGA) capped CdS QDs formed via precipitation-based synthesis; resultant carboxyl terminated surface. | Long et al., 2011 |
| TiO2-EPM | 380-480 nm | Very stable.N = 10, Rsd ~2.04%, 400 s | ~3.00 × 10−6 | Yes | No | Yes; Amine and hydroxyl terminations on TiO2 conferred via EPM (ligand) conjugation. | Ma et al., 2018 |
| 1.3.3 Metal NP -Inorganic/Organic | |||||||
| AuNP-ZnO FRs | Simulated sunlight | Very stable.N = 15, no decrease in photocurrent, 300 s | ~2.50 × 10−5 | Yes | Yes; Au NPs in the Au-ZnO FRs heterostructure enhances charge separation. | No | Han et al., 2017a |
| AuNP on p-CuBi2O4 | >420 nm | Good long-term stability; 99.8% of its original value after 3 weeks | ~4.00 × 10−7 | No | Yes; Au NPs, as a front contact of p-CuBi2O4 enhance the efficiency of charge separation | Yes; Au NPs, as a front contact of p-CuBi2O4 allow conjugation with thiol terminated biomolecules. | Lv et al., 2017 |
| Au NP/Graphene QD/g-C3N4 nanosheet | Xenon lamp | Very stable.N = 15, Rsd ~1.5%, 20 s | ~4.5 × 10−7 | No | Yes; g-C3N4 and GQD reduce the probability of recombination of photogenerated electrons and holes. | Yes; Au NPs allow conjugation with thiol terminated biomolecules | Wang et al., 2018b |
RSD represents relative standard deviation, which signifies the reproducibility of the sensor.