Photoelectrochemical aptasensing for thrombin based on exonuclease III-assisted recycling signal amplification and nanoceria enzymatic strategy.

In the present work, a capture DNA (c-DNA) was immobilized on the TNA/g-C3N4 to develop a sensitive and selective TNA/g-C3N4/c-DNA photoelectrochemical aptasensor for determining thrombin. With the aid of the specific recognition of anti-thrombin aptamer towards thrombin, ingenious design of hairpin DNA, and exonuclease III-assisted recycling signal amplification, more nanoceria could be assembled on the TNA/g-C3N4/c-DNA to form TNA/g-C3N4/nanoceria in the presence of thrombin. Due to the oxidase-mimic catalytic efficiency of nanoceria and the oxygen consumption for glucose oxidation, the photoexcited electrons at the conduction band of g-C3N4 could be well transferred to that of TNA under visible light irradiation, resulting in the increase of the photocurrent of TNA/g-C3N4/nanoceria, and the increase value of photocurrent had a linear relationship with the concentration of thrombin under the optimal conditions. So, the constructed TNA/g-C3N4/c-DNA photoelectrochemical aptasensor exhibited a satisfactory quantitative range from 0.01 pM to 0.5 nM, low detection limit with 3.4 fM for thrombin determination, and was applied for the human serum analysis successfully with RSD of less than 4.8% and the recovery between 95% and 113%.

Self-powered aptasensing for prostate specific antigen based on a membraneless photoelectrochemical fuel cell.

A self-powered aptasensor for prostate specific antigen (PSA) based on a membraneless photoelectrochemical fuel cell (PEFC) with double photoelectrodes was constructed, in which, PSA-binding aptamer was electrostatically immobilized on the KOH-doped g-C3N4 modified TiO2 nanotube arrays (TNA/A-g-C3N4/aptamer), which was used as a photoanode, and Fe3+-doped CuBi2O4 modified indium doped tin oxide (ITO) substrate (ITO/CBFeO) was used as a photocathode. Under visible light irradiation, glucose was photocatalytically oxidized by A-g-C3N4 and generated H2O2 in situ, which was used as the electron acceptor for ITO/CBFeO photocathode, thus producing a high cell output response with a maximum output power of 133.5 µW cm-2 and an open circuit potential of 0.98 V. Due to the specific recognition of PSA by the aptamer and the output power decrease of the PEFC caused by the steric hindrance of the captured PSA on the TNA/A-g-C3N4, the PEFC could be used as a self-powered aptasensor for PSA with a quantitative range of 0.005-50 ng mL-1, a low detection limit of 1.3 pg mL-1 and good selectivity, and has been successfully applied for the analysis of real human serum samples with good precision of the relative standard deviation (RSD) less than 5.6% and good accuracy of the recoveries ranged from 91% to 108%.

Photoelectrochemical determination of alkaline phosphatase activity based on a photo-excited electron transfer strategy.

A sensitive photoelectrochemical (PEC) biosensor for determination of alkaline phosphatase (ALP) activity was constructed based on a photo-excited electron transfer strategy. Immobilization of CdTe quantum dots (QDs) on TiO2 nanotube arrays (TNAs), addition of iron (III) and adenosine triphosphate (ATP) in turn can effectively adjust the photocurrent response of TNAs under visible light irradiation due to a photo-excited electron transfer process, and alkaline phosphatase (ALP) activity can be determined for its catalysis toward dephosphorylation of ATP. The preparation of CdTe QDs, construction of TNA/QD PEC biosensor and the mechanism of photo-excited electron transfer are investigated in the present work. Under the optimal experimental conditions, the TNA/QD PEC biosensor shows a low limits of detection (LODs) (0.05 U L-1) and limits of quantification detection (LOQs) (0.15 U L-1), wide linear range from 0.2 to 15 U L-1, and good selectivity towards ALP determination, which has been successfully applied for human serum analysis with good precision (RSD ≤ 5.4%) and high accuracy (recovery rate, 91-112%).

Photoelectrochemically driven bioconversion and determination of nifedipine based on a double photoelectrode system.

In the present work, a double photoelectrode system has been constructed for photoelectrochemically driven enzymatic bioconversion and determination of nifedipine. In which, the TiO2 nanotube arrays in-situ assembled with g-C3N4 (TNA/g-C3N4) was used as a photoanode, and a cytochrome P450 3A4 (CYP3A4) enzyme was immobilized in the porous ITO/CuO films to fabricate an ITO/CuO/CYP3A4 photocathode. The constructed double photoelectrode system had a significant photocurrent response compared to the single ITO/CuO/CYP3A4 or TNA/g-C3N4 under visible light irradiation. Under optimal conditions, the photocurrent of the double photoelectrode system had a high catalytic activity toward substrate nifedipine with kcat of 5.62 s-1 and catalytic efficiency with kcat/kmapp of 0.94 µM-1 s-1, and the bioconversion yield of nifedipine reached 22.1%. Furthermore, the constructed double photoelectrode system could be used to determine the nifedipine concentration with a high sensitivity of 2.46 µA µM-1 and a low detection limit of 0.015 µM. Therefore, the proposed double photoelectrode system can be used well for study enzyme biocatalysis for target bioconversion, and also has a potential application for toxicity analysis.

Photoelectrochemical TiO2 nanotube arrays biosensor for asulam determination based on in-situ generation of quantum dots.

Inspired by the photoelectrochemical (PEC) properties of TiO2 nanotubes arrays (TNA) and their application as a super vessel for immobilizing biomolecules, we constructed an inhibition-effect PEC biosensor for determination of asulam based on the in-situ generation of CdS quantum dots (QDs) on TNA using an enzymatic reaction. Horseradish peroxidase (HRP) enzyme was covalently assembled on the inner-wall of TNAs, which exhibited good electrochemical and catalytic properties. In the mixture solution containing H2O2, CdY and S2O32-, HRP enzyme in TNAs catalyzed H2O2 reduce S2O32- to S2-. The generated S2- reacted with CdY to form CdS QDs in situ on the TNAs, improving the PEC performance of TNA under visible light irradiation. The photocurrent would decrease after addition of asulam due to its inhibitory effect towards HRP enzyme activity. Under the optimal experimental conditions, the constructed PEC TNA/HRP biosensor exhibited a satisfying linear range (0.02-2.0 ng mL-1), low limit of detection (4.1 pg mL-1) and good selectivity towards asulam determination, and has been successfully applied for the analysis of real environmental water samples with good accuracy of the recoveries ranged from 90% to 114%.