In Situ Enzymatic Ascorbic Acid Production as Electron Donor for CdS Quantum Dots Equipped TiO2 Nanotubes: A General and Efficient Approach for New Photoelectrochemical Immunoassay

Photogenerated Hole-Induced Chemical Redox Cycling on Bi2S3/Bi2Sn2O7 Heterojunction: Toward General Amplified Split-Type Photoelectrochemical Immunoassay

This work reports the elegant bridging of enzymatic generation of electron donor with photogenerated hole-induced chemical redox cycling amplification (RCA) for innovative photoelectrochemical (PEC) immunoassay, by the aid of a heterojunction photoelectrode with split-type strategy. Specifically, the system was exemplified by the alkaline phosphatase (ALP) catalytic generation of ascorbic acid (AA), the redox cycling of AA by tris (2-carboxyethyl) phosphine (TCEP) as reductant, and the use of a novel Bi₂S₃/Bi₂Sn₂O₇ heterojunction and myoglobin (Myo) as the photoelectrode and the target, respectively. After the immunoreaction and ALP-induced production of AA, the subsequent oxidation of AA by the photogenerated holes of the Bi₂S₃/Bi₂Sn₂O₇ heterojunction could be cycled via the regeneration of AA by TCEP from the oxidized product of dehydroascorbic acid, leading to easy signal amplification for the sensitive immunoassay of Myo in real samples. It is believed that this work provided a basis for further design and development of general RCA-based PEC immunoassays.

Cd2+-Doped Amorphous TiO2 Hollow Spheres for Robust and Ultrasensitive Photoelectrochemical Sensing of Hydrogen Sulfide

Hydrogen sulfide is a highly toxic molecule to human health, but high-performance detection of it remains a challenge. Herein, we report an ultrasensitive photoelectrochemical (PEC) sensor for H₂S by modifying indium tin oxide (ITO) electrodes with Cd²⁺-doped amorphous TiO₂ hollow spheres, which are prepared by templating against colloidal silica particles followed by a cadmium-sodium cation exchange reaction. The amorphous TiO₂ hollow spheres act as both the probing cation carrier and the photoelectric beacon. Upon exposure to sulfide ions, the photocurrent of the functionalized photoanode proportionately decreases in response to the formation of CdS nanoparticles. The decreased photocurrent could be attributed to the mismatching bandgap between the amorphous TiO₂ and CdS nanoparticles: the photoexcited electrons and holes from amorphous TiO₂ are transferred to the conduction band and valence band of CdS, respectively, and then recombined. The decrease in photocurrent is linear with the concentration of sulfide ions in the range from 1 to 10 000 pmol L^-1 with a detection limit of 0.36 pmol L^-1. Enabled by a unique sensitization mechanism, this PEC sensor features excellent performance in a wide linear range, high selectivity and sensitivity, high stability, and low fabrication cost.

A review on visible-light induced photoelectrochemical sensors based on CdS nanoparticles

Discovering the distinctive photophysical properties of semiconductor nanoparticles (NPs) has made these a popular subject in recent advances in nanotechnology-related analytical methods.

A new photoelectrochemical biosensor for ultrasensitive determination of nucleic acids based on a three-stage cascade signal amplification strategy

Based on a “signal-on” sensing strategy and a three-stage cascade signal amplification method, an ultrasensitive photoelectrochemical biosensor has been developed for DNA detection.

An ultrasensitive photoelectrochemical bioanalysis strategy for tumor markers based on the significantly enhanced signal of a bismuth oxyiodine microsphere/graphitic carbon nitride composite

An ultrasensitive PEC bioanalysis strategy was designed based on the significantly enhanced signal of BiOI/g-C₃N₄ and amplified signal variation of CuS NPs.

An in situ electron donor consumption strategy for photoelectrochemical biosensing of proteins based on ternary Bi2S3/Ag2S/TiO2 NT arrays

An ascorbic acid oxidase–ascorbic acid bioevent-based electron donor consumption mode is introduced into the PEC bioassay for the first time.

A novel upconversion luminescence derived photoelectrochemical immunoassay: ultrasensitive detection to alpha-fetoprotein

Fabrication of near-infrared light-triggered photoelectrochemical (PEC) sensors based on the upconversion nanophosphors (UCNPs) is a novel approach, which exhibits the advantages of low background signal and non-damage to the biological substance as well as high sensitivity and improved electric detection in PEC sensors. Herein we demonstrate the preparation of novel and high-quality ZnO inverse opal photonic crystals (IOPCs)/Ag/NaYF₄:Yb,Tm hybrid films by different advanced film techniques, including colloidal self-assembling, vapor phase deposition and pulsed laser deposition and its application to sensitive detection of alpha-fetoprotein (AFP). In the complex device, ZnO IOPCs and surface plasmon resonance (SPR) of silver had ability to largely enhance local excitation electromagnetic field of NaYF₄:Yb,Tm, resulting in efficient near-infrared to visible/ultraviolet upconversion luminescence (UCL). The ultraviolet light emitted by NaYF₄:Yb,Tm could b further reabsorbed by ZnO, generating PEC responses. Furthermore, because of the high specific surface area of ZnO IOPCs and the conductivity of Ag films, ZnO IOPCs/Ag/NaYF₄:Yb,Tm hybrid films based near-infrared light-triggered PEC sensors showed ultrasensitive detection of AFP with a linear range from 0.05 ng mL^-1 to 100 ng mL^-1 and a low detection limit of ∼0.04 ng mL^-1 (40 pg mL^-1). Such an advanced device also shows promise in detection of other cancer markers in clinical and biological analysis.

Quantum-dots-based photoelectrochemical bioanalysis highlighted with recent examples

Photoelectrochemical (PEC) bioanalysis is a newly developed methodology that provides an exquisite route for innovative biomolecular detection. Quantum dots (QDs) are semiconductor nanocrystals with unique photophysical properties that have attracted tremendous attentions among the analytical community. QDs-based PEC bioanalysis comprises an important research hotspot in the field of PEC bioanalysis due to its combined advantages and potentials. Currently, it has ignited increasing interests as demonstrated by increased research papers. This review aims to cover the most recent advances in this field. With the discussion of recent examples of QDs-PEC bioanalysis from the literatures, special emphasis will be placed on work reporting on fundamental advances in the signaling strategies of QDs-based PEC bioanalysis from 2013 to now. Future prospects in this field are also discussed.

Gold nanrods plasmon-enhanced photoelectrochemical aptasensing based on hematite/N-doped graphene films for ultrasensitive analysis of 17β-estradiol

It remains a vital task to establish ultrasensitive sensing interfaces for detection of target analytes to meet the demands of modern analysis. Herein, a highly sensitive turn-on photoelectrochemical (PEC) platform for trace 17β-estradiol (E2) assay was developed based on Au nanrods (AuNRs) with surface plasmon resonance (SPR) properties induced signal amplification. Specifically, a ternary hybrid was prepared by integrating hematite (α-Fe₂O₃) nanocrystals and N-doped graphene (NG) with AuNRs, which further served as highly efficient photoactive species. Subsequently, a PEC sensing platform was fabricated based on the specific binding of E2 and its aptamer. On such a sensor, the capture of E2 molecules by aptamers led to increased photocurrent. This was attributed to that the specific recognition reaction between E2 and aptamer resulted in the conformational change of the aptamers and complete dissociation of some aptamers on the PEC sensing interface. It can be confirmed by the electrochemical impedance spectroscopy (EIS) results. This process decreased the steric hindrances between the electrode surface and solution and thus increased the photocurrent response. Under the optimal conditions, the as-prepared PEC aptasensor exhibited superb analytical performances for detection of E2 in the range from 1×10^-15M to 1×10^-9M with a detection limit of 3.3×10^-16M. The aptasensor manifested outstanding selectivity towards E2 when other endocrine disrupting compounds with similar structure coexisted. Furthermore, the aptasensor was successfully applied for the determination of E2 in milk powder. The present strategy provides a potential way to boost the activity of photoactive materials and improve the sensitivity of PEC biosensor.

Hemin/Au nanorods/self-doped TiO2nanowires as a novel photoelectrochemical bioanalysis platform

A sensitive photoelectrochemical platform for GSH was developed by modifying self-doped TiO₂nanowires with mixed Au nanorods at two different aspect ratios as the core sensing unit and hemin for recognition.

Anion-exchange reactions: facile and general access to sensitive photoelectrochemical platforms for biomarker immunosensing

The combination of CdSe NCs with biocatalytic precipitation provides a highly sensitive immunosensing strategy.

A carboxylated graphene nanodisks/glucose oxidase nanotags and Mn:CdS/TiO2 matrix based dual signal amplification strategy for ultrasensitive photoelectrochemical detection of tumor markers

A graphene nanodisk and glucose oxidase based dual signal amplification strategy was developed for a highly sensitive PEC immunoassay of CEA.

DNA sequence functionalized with heterogeneous core-satellite nanoassembly for novel energy-transfer-based photoelectrochemical bioanalysis

This work reports the use of compositionally heterogeneous asymmetric Ag@Au core-satellite nanoassembly functionalized with DNA sequence as unique signaling nanoprobes for the realization of new energy-transfer-based photoelectrochemical (PEC) immunoassay of prostate- specific antigen (PSA). Specifically, the Ag@Au asymmetric core-satellite nanoassemblies (Ag@Au ACS) were fabricated on a two-dimensional glass substrate by a modified controlled assembly technique, and then functionalized with DNA sequences containing PSA aptamers as signaling nanoprobes. Then, the sandwich complexing between the PSA, its antibodies, and the signaling nanoprobes was performed on a CdS QDs modified indium tin oxide (ITO) electrode. The single stranded DNA can server as a facile mediator that place the Ag@Au ACS in proximity of CdS QDs, stimulating the interparticle exciton-plasmon interactions between Ag@Au ACS and CdS QDs and thus quenching the excitonic states in the latter. Since the damping effect is closely related to the target concentration, a novel energy-transfer-based PEC bioanalysis could be achieved for the sensitive and specific PSA assay. The developed biosensor displayed a linear range from 1.0×10^-11gmL^-1 to 1.0×10^-7gmL^-1 and the detection limit was experimentally found to be of 0.3×10^-13gmL^-1. This strategy used the Ag@Au ACS-DNA signaling nanoprobes and overcame the deficiency of short operating distance of the energy transfer process for feasible PEC immunoassay. More significantly, it provided a way to couple the plasmonic properties of the Ag NPs and Au NPs in a single PEC bioanalytical system. We expected this work could inspire more interests and further investigations on the advanced engineering of the core-satellite or other judiciously designed nanostructures for new PEC bioanalytical uses with novel properties.

Recent advances in the use of quantum dots for photoelectrochemical bioanalysis

Photoelectrochemical (PEC) bioanalysis is a newly developed technique for innovative biomolecular detection. Quantum dots (QDs) with unique photophysical properties are key components in realization of various exquisite PEC bioanalyses. Particularly, significant progress has been made in the QD-based PEC bioanalysis. In this work, we briefly summarize the most recent and important developments in the use of traditional and newly emerging QDs for novel PEC bioanalytical applications. The future prospects in this dynamic field are also highlighted.

Photoelectrochemical detection of metal ions

Depending on the situation, metal ions may either play beneficial roles or be harmful to human health and ecosystems. Sensitive and accurate detection of metal ions is thus a critical issue in the field of analytical sciences and great efforts have been devoted to the development of various metal ion sensors. Photoelectrochemical (PEC) detection is an emerging technique for the bio/chemical detection of metal ions, and features a fast response, low cost and high sensitivity. Using representative examples, this review will first introduce the fundamentals and summarize recent progress in the PEC detection of metal ions. In addition, interesting strategies for the design of particular PEC metal ion sensors are discussed. Challenges and opportunities in this field are also presented.