A carbon quantum layer modified BiVO4 photoelectrochemical aptamer biosensor for ultra-sensitive cTnI biomarker detection based on the interface nephelauxetic effect and heterojunction assistance.

The sensitivity and specificity of a semiconductor photoelectrochemical (PEC) aptamer biosensor are determined by the separation and transport of the photoinduced carriers as well as aptamer probe immobilization. In this study, an in situ thermal transformation organic polymer strategy was employed to produce an ∼2.5 nm carbon quantum layer on the surface of the BiVO4(BVO) photoanode. Experimental tests and theoretical calculations have revealed that this carbon quantum layer-coated BVO(C@BVO) heterostructure could generate surface charge depletion regions through an interface nephelauxetic effect. These charge depletion regions facilitated the efficient immobilization of DNA aptamer probes of the acute myocardial infarction biomarker cardiac troponin I (cTnI), while showing almost no immobilization capability on a pure-phase C quantum layer or BVO crystals. Simultaneously, the formation of the C@BVO heterostructure also enhanced the directional transport of photo-generated holes from BVO to the C quantum layer. Due to the above reasons, the C@BVO PEC aptamer biosensor achieved a linear detection range for cTnI from 10-14 g L-1 to 10-10 g L-1, with a record detection limit (LOD) of ∼0.33 × 10-14 g L-1 (N > 3). Meanwhile, the biosensor also demonstrated well the detection reproducibility and specificity for cTnI detection. Therefore, the strategy of using a carbon quantum layer-coated PEC electrode shows good potential to develop PEC biosensors with high sensitivity, specificity, and robustness.

Universal Hydrogen-Treated TiO2 Nanorod Array/Ti2COX MXene PEC Aptamer Sensor Modulated by the Transport Characteristic of Photogenerated Holes.

A semiconductor photoelectrochemical (PEC) aptamer sensor has been widely researched in recent years because of its broad application prospects. However, a universal PEC sensor has not been achieved, and its sensing mechanism based on a photogenerated carrier transfer process has yet to be elucidated. Herein, a novel hydrogen-treated TiO2 nanorod array one-dimensional (1D)/Ti2COX MXene two-dimensional (2D) (H-TiO2/Ti2COX) PEC aptamer sensor is presented, which achieved a record detection range of 10-9-103 µg/L and a limit of detection (LOD) of 1 fg/L for microcystic toxins-LR detection. Besides, the PEC sensor can also test serotonin (5-HT), aflatoxin-B1, and prostate-specific antigen (PSA) with high performance by changing the aptamers, exhibiting favorable application universality. Furthermore, a new phenomenon of a switchable enhanced/suppressed photocurrent detection signal was discovered from H-TiO2/Ti2COX PEC aptamer sensors through the variation of the length of the TiO2 nanorod. Meanwhile, it reveals that the steric hindrance effect determines the photogenerated hole transfer and depolarization processes, which is proposed for the first time as the predominant mechanism of the switchable enhanced/suppressed photocurrent signal for PEC sensors, giving possibilities to develop PEC sensors with higher efficiency.

GaN/AlN Multi-Quantum Wells Infrared Detector with Short-Wave Infrared Response at Room Temperature.

GaN-based quantum well infrared detectors can make up for the weakness of GaAs-based quantum well infrared detectors for short-wave infrared detection. In this work, GaN/AlN (1.8 nm/1.8 nm) multi-quantum wells have been epitaxially grown on sapphire substrate using MBE technology. Meanwhile, based on this device structure, the band positions and carrier distributions of a single quantum well are also calculated. At room temperature, the optical response of the device is 58.6 µA/W with a bias voltage of 0.5 V, and the linearity between the optical response and the laser power is R2 = 0.99931. This excellent detection performance can promote the research progress of GaN-based quantum well infrared detectors in the short-wave infrared field.

Photoelectrochemical Performance Improving Mechanism: Hybridization Appearing at the Energy Band of BiVO4 Photoanode by Doped Quantum Layers Modification.

Surface passivation of the photoelectrode by wide bandgap semiconductor quantum layer is an important strategy to improve work stability and surface state inhibition. However, an inevitable energy barrier is generated during the quantum tunneling process of the photocarriers. To overcome this shortage, a tandem photo-generated hole transfer route is fabricated on BiVO4 photoanode by doped dual-quantum layers modification, Ni-ZnO (5 nm) and Rh-SrTiO3 (≈10 nm). Modulated photoelectrochemical (PEC), Scanning Kelvin Probe (SKP), and DFT calculation method results indicate that a tandem hole ohmic contact route is formed in the photoanode to reduce the quantum tunneling energy barrier, meanwhile, the photon absorption capacity of BiVO4 is improved after doped quantum layers modification. Both a phenomenal attribute to the energy band hybridization between Ni, Rh 3d orbits in quantum layers with BiVO4 photoanode. Then, the modified BiVO4 photoanode achieves the recoded photocurrent density of 6.47 and 5.18 mA cm-2 (Na2 SO3 electrolyte, VRHE  = 1.23 V) under simulated sun light (100 mW cm-2 AM 1.5 G) by xenon lamp illumination without and with UV composition cutting down to ≈5%, respectively. Generally, this work will highlight a potential application in the fields of PEC water splitting and photovoltaic conversion for various semiconductor nanomaterials.

Crystal-reconstructed BiVO4 semiconductor photoelectrochemical sensor for ultra-sensitive tumor biomarker detection.

In this study, we developed a crystal-reconstructed-BiVO4 aptamer photoelectrochemical (PEC) biosensor by a high-energy laser treatment technique. This biosensor achieves a limit of detection (LOD) (0.82 ag mL-1), linear detection range (1 ag mL-1 to 2 ng mL-1), and resolution ratio (∼18 molecules per mL) for prostate-specific antigen (PSA) tumor biomarker detection. Furthermore, reconstructed surface microstructure and oxygen vacancy doping energy formation after crystal reconstruction induce the stereo-hindrance effect and photogenerated hole energy is reduced during PSA target detection. In this case, a photocurrent inhibition phenomenon for PSA detection is noticed. Based on this photocurrent inversion phenomenon, some dysoxidizable nucleonic acid tumor (miRNA-21) and virus biomarkers (RdRp-COVID) can be detected with a LOD level of ∼10-16 M by linking the corresponding base paring probe on the surface of the crystal-reconstructed photoanode. In addition to high sensitivity, this PEC biosensor presents high detection specificity, stability, and accuracy in clinical verification. Thus, this crystal-reconstructed PEC biosensor shows application potential in the fields of multi-tumor or viral biomarker detection.

Enhanced UV Emission from ZnO on Silver Nanoparticle Arrays by the Surface Plasmon Resonance Effect.

Periodical silver nanoparticle (NP) arrays were fabricated by magnetron sputtering method with anodic aluminum oxide templates to enhance the UV light emission from ZnO by the surface plasmon resonance effect. Theoretical simulations indicated that the surface plasmon resonance wavelength depended on the diameter and space of Ag NP arrays. By introducing Ag NP arrays with the diameter of 40 nm and space of 100 nm, the photoluminescence intensity of the near band-edge emission from ZnO was twofold enhanced. Time-resolved photoluminescence measurement and energy band analysis indicated that the UV light emission enhancement was attributed to the coupling between the surface plasmons in Ag NP arrays and the excitons in ZnO with the improved spontaneous emission rate and enhanced local electromagnetic fields.

Fabrication of ultra-sensitive photoelectrochemical aptamer biosensor: Based on semiconductor/DNA interfacial multifunctional reconciliation via 2D-C3N4.

In this work, we fabricate a novel bismuth vanadate/two dimensional-carbon nitride/deoxyribonucleic acid (BiVO4/2D-C3N4/DNA) aptamer photoelectrochemical (PEC) sensor, and this sensor provides a record detection sensitivity area (5 × 10-7 µg/L - 10 µg/L) for Microcystin-LR (MC-LR). Meanwhile, except for MC-LR detection, this sensor presents highly sensitivity for tumor marker, heavy metal ion, antibiotic also by changing the DNA aptamer. Photo charge dynamic and theory calculation results reveal that 2D-C3N4 is a key material for multifunctional interface reconciliation of this PEC aptamer sensor. Firstly, it can serve as photogenerated hole oriented-transfer medium from the BiVO4 photoanode to the detective target; In addition, 2D-C3N4 with large area of π electron cloud can fix the DNA aptamer parallelly by π-π bonding with the nucleic acid in the DNA aptamer to shorten the hole transfer distance from the semiconductor to target. So that, a record MC-LR detection sensitivity has been achieved by the 2D-C3N4 modified BiVO4/DNA aptamer sensor.

Role of polyaniline on the photocatalytic degradation and stability performance of the polyaniline/silver/silver phosphate composite under visible light.

Polyaniline/silver/silver phosphate (PANI/Ag/Ag3PO4) composite was prepared by in situ depositing silver phosphate (Ag3PO4) nanoparticles on the surface of polyaniline (PANI). The best photocatalytic Rhodamine B degradation performance is obtained by the 20 wt % PANI/Ag/Ag3PO4 composite, which is approximately 4 times higher than that of pure Ag3PO4. Meanwhile, the photocatalytic stability of Ag3PO4 is significantly improved by introducing PANI into the PANI/Ag/Ag3PO4 composite. The dramatic promotion of the photocatalytic degradation performance and the photocatalytic stability can be attributed to the formation of a heterojunction electric field between PANI and Ag3PO4, which is approximately 90 mV and points from Ag3PO4 to PANI. The existence of this electric field can dramatically enhance the separation efficiency of the photogenerated electron-hole pairs, accelerate the transfer of photogenerated holes from Ag3PO4 to PANI and therefore inhibit the self-oxidation of Ag3PO4.

Highly efficient photocatalytic performance of graphene-ZnO quasi-shell-core composite material.

In the present paper, the graphene-ZnO composite with quasi-shell-core structure was successfully prepared using a one-step wet chemical method. The photocatalytic Rhodamine B degradation property and the photoelectrochemical performance of the graphene-ZnO quasi-shell-core composite are dependent on the amount of graphene oxide that is added. When the amount of graphene oxide added is 10 mg, the graphene-ZnO quasi-shell-core composite possesses the optimal photocatalytic degradation efficiency and the best photoelectrochemical performance. An efficient interfacial electric field is established on the interface between the graphene and ZnO, which significantly improves the separation efficiency of the photogenerated electron-hole pairs and thus dramatically increases its photoelectrochemical performance. In addition to the excellent photocatalytic and photoelectrochemical properties, the electron migration ability of the grephene-ZnO quasi-shell-core composite is significantly enhanced due to the graphene coating on ZnO surface; therefore, this material has great potential for application as a substrate material to accept electrons in dye solar cell and in narrow bandgap semiconductor quantum dot sensitized solar cells.

A ZnFe2O4-ZnO nanorod array p-n junction composite and its photoelectrochemical performance.

A ZnFe2O4-ZnO nanorod array (NRA) with a three-dimensional network nanometer structure was prepared. The photoelectrochemical performance of the ZnFe2O4-ZnO NRA composite is significantly improved due to the formation of a p-n heterojunction electric field at the interface between ZnFe2O4 and ZnO, the increase of the overall utilization efficiency of incident light energy, and the visible light absorption capability of ZnFe2O4.

High-efficiency photoelectrochemical properties by a highly crystalline CdS-sensitized ZnO nanorod array.

A ZnO nanorod array with comparatively long nanorods was successfully prepared on a Ti substrate by applying a hydrothermal method twice. CdS nanoparticles with high crystallinity were deposited onto the surface of ZnO nanorods through a galvanostatic electrodeposition method. CdS-sensitized ZnO nanorod arrays after being hydrothermally grown twice with the second growth time of 6 h possessed the best photoelectrochemical performance. The photoinduced current densities at a 0 V bias potential are 23.7 and 15.8 mA·cm(-2) under the illumination of simulated sunlight and visible light, respectively. The monochromatic incident photon-to-electron conversion efficiency values at the wavelength of 380-520 nm are in the range of 50-60%, which indicated its high photoelectric conversion efficiency. The contribution from visible light is significantly higher than that from UV light. The prepared photoanodes in the present work exhibit a potential application in photoelectrochemical hydrogen production from water reduction under sunlight.