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.

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.

Parameter study of the high temperature MOCVD numerical model for AlN growth using orthogonal test design.

We investigated the process parameters of the high temperature MOCVD (HT-MOCVD) numerical model for the AlN growth based on CFD simulation using orthogonal test design. It is believed that high temperature growth condition is favorable for improving efficiency and crystallization quality for AlN film, while the flow field in the HT-MOCVD reactor is closely related to the process parameters, which will affect the uniformity of the film. An independently developed conceptual HT-MOCVD reactor was established for the AlN growth to carry out the CFD simulation. To evaluate the role of the parameters systematically and efficiently on the growth uniformity, the process parameters based on CFD simulation were analyzed using orthogonal test design. The advantages of the range, matrix and variance methods were considered and the results were analyzed comprehensively and the optimal process parameters were obtained as follows, susceptor rotational speed 400 rpm, operating pressure 40 Torr, gas flow rate 50 slm, substrate temperature 1550 K.

Ab initio study for molecular-scale adsorption, decomposition and desorption on AlN surfaces during MOCVD growth.

Since AlGaN offers new opportunities for the development of the solid state ultraviolet (UV) luminescence, detectors and high-power electronic devices, the growth of AlN buffer substrate is concerned. However, the growth of AlN buffer substrate during MOCVD is regulated by an intricate interplay of gas-phase and surface reactions that are beyond the resolution of experimental techniques, especially the surface growth process. We used density-functional ab initio calculations to analyze the adsorption, decomposition and desorption of group-III and group-V sources on AlN surfaces during MOCVD growth in molecular-scale. For AlCH3 molecule the group-III source, the results indicate that AlCH3 is more easily adsorbed on AlN (0001) than (000[Formula: see text]) surface on the top site. For the group-V source decomposition we found that NH2 molecule is the most favorable adsorption source and adsorbed on the top site. We investigated the adsorption of group-III source on the reconstructed AlN (0001) surface which demonstrates that NH2-rich condition has a repulsion effect to it. Furthermore, the desorption path of group-III and group-V radicals has been proposed. Our study explained the molecular-scale surface reaction mechanism of AlN during MOCVD and established the surface growth model on AlN (0001) surface.

Gas-Phase Chemical Reaction Mechanism in the Growth of AlN during High-Temperature MOCVD: A Thermodynamic Study.

We presented a comprehensive thermodynamic study of the gas-phase chemical reaction mechanism of the AlN growth by high-temperature metal-organic chemical vapor deposition, investigating the addition reactions, pyrolysis reactions, and polymerization of amide DMANH2 and subsequent CH4 elimination reaction. Based on the quantum chemistry calculations of the density functional theory, the main gas-phase species in different temperature ranges were predicted thermodynamically by comparing the enthalpy difference and free energy change before and after the reactions. When T > 1000 °C, it was found that MMAl, (MMAlNH)2, and (MMAlNH)3 are the three most probable end gas products, which will be the main precursors of surface reactions. Also, in high temperatures, the final product of the parasitic reactions is mainly (DMA1NH2)2 and (DMAlNH2)3, which are easy to decompose into small molecules and likely to be the sources of AlN nanoparticles.

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.

A first-principles study of hydrogen storage capacity based on Li-Na-decorated silicene.

Surface decoration with alkali metal adatoms has been predicted to be promising for silicene to obtain high hydrogen storage capacity. Herein, we performed a detailed study of the hydrogen storage properties of Li and Na co-decorated silicene (Li-Na-decorated silicene) based on first-principles calculations using van der Waals correction. The hydrogen adsorption behaviors, including the adsorption order, the maximum capacity, and the corresponding mechanism were analyzed in detail. Our calculations show that up to three hydrogen molecules can firmly bind to each Li atom and six for each Na atom, respectively. The hydrogen storage capacity is estimated to be as high as 6.65 wt% with a desirable average adsorption energy of 0.29 eV/H2. It is confirmed that both the charge-induced electrostatic interaction and the orbital hybridizations play a great role in hydrogen storage. Our results may enhance our fundamental understanding of the hydrogen storage mechanism, which is of great importance for the practical application of Li-Na-decorated silicene in hydrogen storage.