Using G-Quadruplex/Hemin To “Switch-On” the Cathodic Photocurrent of p-Type PbS Quantum Dots: Toward a Versatile Platform for Photoelectrochemical Aptasensing

An ultrasensitive energy-transfer based photoelectrochemical protein biosensor

Using single stranded DNA (ssDNA) as a distance controller and Au nanoparticles (NPs) functionalized with ssDNA as novel energy-transfer nanoprobes, an ultrasensitive energy-transfer based photoelectrochemical protein biosensor was realized.

Graphene-doped Bi2S3 nanorods as visible-light photoelectrochemical aptasensing platform for sulfadimethoxine detection

Bismuth sulphide (Bi2S3) nanorods doped with graphene (G) were synthesized and explored as photoactive materials for constructing a photoelectrochemical (PEC) aptasensor for sulfadimethoxine (SDM) detection. The formation of Bi2S3 nanorods and G nanosheets was observed by scanning electron microscopy (SEM) and further characterized by X-ray diffraction (XRD) spectroscopy. The PEC measurements indicated that the photocurrent response of Bi2S3 was obviously improved by doping suitable amount of G. The G-Bi2S3 composite coated electrode was utilized for fabricating a PEC aptasensor by covalently immobilizing a 5'-amino-terminated SDM aptamer on the electrode surface. Based on the specific interaction between SDM and the aptamer, a PEC sensor responsive to SDM was obtained. Under optimal conditions, the proposed sensor showed a linear photocurrent response to SDM in the concentration range of 1.0-100nM, with a low detection limit (3S/N) of 0.55nM. Moreover, the sensor showed high sensitivity, stability and reproducibility. The potential applicability of the PEC aptasensor was confirmed by detecting SDM in veterinary drug formulation and milk.

Enhanced photoelectrochemical aptasensing platform for TXNDC5 gene based on exciton energy transfer between NCQDs and TiO2 nanorods

The over expression of thioredoxin domain-containing protein 5 (TXNDC5) can promote the growth of castration-resistant prostate cancer (CRPC). A novel highly sensitive photoelectrochemical (PEC) aptsensor was developed for the detection of TXNDC5 by using the nanohybrids (TiO₂ NRs/NCQDs) of nitrogen-doped carbon quantum dots (NCQDs) and TiO₂ nanorods as the photo-to-electron conversion medium. TiO₂ NRs/NCQDs nanohybrids were prepared by controlling the experimental condition. TiO₂ NRs were self-assembled to form the nanopores with good photocurrent conversion efficiency. NCQDs possessed carboxyl groups (−COOH) and amino groups (−NH₂) in the preparation process. −COOH and −NH₂ groups played important roles for anchoring the capture probes (5′ primer and 3′ primer) through covalent binding. The ultrasensitive and stable detection for TXNDC5 was achieved by the specific recognition between the capture probes and the targets. The fabricated aptsensor showed excellent performance with a wide linear range (0.5 fmol/L ∼ 10 nmol/L) and a low detection limit of 0.1 fmol/L. This kind of aptsensor would provide a potential application for TXNDC5.

Construction of Metal-Ion-Free G-quadruplex-Hemin DNAzyme and Its Application in S1 Nuclease Detection

In this work, a new kind of peroxidase-mimicking DNAzyme (G-quadruplex-hemin DNAzyme, G4-hemin) was constructed by using hemin-modified G-rich DNA (hemin-G-DNA). Experimental results demonstrated that the G-rich DNA can form a G-quadruplex structure by the inducement of terminally modified hemin, rendering the assembly of hemin and G-quadruplex structure spontaneously and efficiently. As a result, G-hemin revealed higher peroxidase activity than traditional G-quadruplex/hemin DNAzyme (G4/hemin). Besides, different from G4/hemin, G4-hemin was constructed in one step without the participation of metal ions and adscititious hemin. Accordingly, the construction procedure was significantly simplified and the background signal from dissociative hemin was remarkably reduced. In a proof-of-concept trial, according to the colorimetric signals of G4-hemin, a novel biosensor for the detection of S1 nuclease activity was established, which provides a novel perspective for designing peroxidase-mimicking DNAzyme-based biosensors.

A Cathodic "Signal-off" Photoelectrochemical Aptasensor for Ultrasensitive and Selective Detection of Oxytetracycline

A novel cathodic "signal-off" strategy was proposed for photoelectrochemical (PEC) aptasensing of oxytetracycline (OTC). The PEC sensor was constructed by employing a p-type semiconductor BiOI doped with graphene (G) as photoactive species and OTC-binding aptamer as a recognition element. The morphological structure and crystalline phases of obtained BiOI-G nanocomposites were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The UV-visible absorption spectroscopic analysis indicated that doping of BiOI with graphene improved the absorption of materials in the visible light region. Moreover, graphene could facilitate the electron transfer of BiOI modified electrode. As a result, the cathodic photocurrent response of BiOI under visible light irradiation was significantly promoted when a suitable amount of graphene was doped. When amine-functionalized OTC-binding aptamer was immobilized on the BiOI-G modified electrode, a cathodic PEC aptasensor was fabricated, which exhibited a declined photocurrent response to OTC. Under the optimized conditions, the photocurrent response of aptamer/BiOI-G/FTO was linearly proportional to the concentration of OTC ranging from 4.0 to 150 nM, with a detection limit (3S/N) of 0.9 nM. This novel PEC sensing strategy demonstrated an ultrasensitive method for OTC detection with high selectivity and good stability.