Enhanced photoelectrochemical aptasensing triggered by nitrogen deficiency and cyano group simultaneously engineered 2D carbon nitride for sensitively monitoring atrazine

Aptamer molecular gate functionalized mesoporous SiO2@MB controlled-release system for pollutant detection using Ti(Ⅲ) self-doped TiO2 NTs as active photoanode coupled with electrostatic modulation

Atrazine (ATZ) is a widely used herbicide that can cause serious harm to organisms and ecosystems. An immobilization-free photoelectrochemical (PEC) aptasensor has been herein developed for ATZ based on aptamer molecular gate functionalized mesoporous SiO2@MB controlled release system. Compared with traditional immobilization-based sensors, immobilization-free sensors (IFSs) avoid the modification of the recognition element on the electrode surface. Mesoporous SiO2 with large surface area and good biocompatibility can be used as nanocontainers to stably encapsulate the signal shuttle molecule methylene blue (MB). The bifunctional aptamer (APT) is used not only as the recognition element for ATZ but also as the signal switch to block or release MB. In the presence of ATZ, the specific recognition between ATZ and APT will cause the detachment of APT from the surface of SiO2, thus the molecular gate will open and release MB. Due to pH modulation, the positively charged MB can reach the surface of the negatively charged Ti(III) self-doped TiO2 NTs (Ti(III)-TiO2 NTs) electrode to act as an electron donor, which increases the photocurrent. The immobilization-free aptasensor has shown ultrasensitive detection of ATZ with a wide linear range from 1.0 pM to 100.0 nM and a low detection limit of 0.1 pM. In addition, the sensor has excellent selectivity, stability and anti-interference ability, and has been used in real water sample analysis successfully. This strategy has provided a new idea for the design of advanced immobilization-free PEC sensors for environmental pollutant detection.

Unveiling Versatile Applications and Toxicity Considerations of Graphitic Carbon Nitride

Metal-free, low-cost, organic photocatalytic graphitic carbon nitride (g-C3N4) has become a promising and impressive material in numerous scientific fields due to its unique physical and chemical properties. As a semiconductor with a suitable band gap of ~2.7 eV, g-C3N4 is an active photocatalytic material even after irradiation with visible light. However, information regarding the toxicity of g-C3N4 is not extensively documented and there is not a comprehensive understanding of its potential adverse effects on human health or the environment. In this context, the term "toxicity" can be perceived in both a positive and a negative light, depending on whether it serves as a benefit or poses a potential risk. This review shows the applications of g-C3N4 in sensorics, electrochemistry, photocatalysis, and biomedical approaches while pointing out the potential risks of its toxicity, especially in human and environmental health. Finally, the future perspective of g-C3N4 research is addressed, highlighting the need for a comprehensive understanding of the toxicity of this material to provide safe and effective applications in various fields.

CdS/Bi2S3/NiS ternary heterostructure-based photoelectrochemical immunosensor for the sensitive detection of carbohydrate antigen 125

The sensitive, accurate and rapid detection of carbohydrate antigen 125 (CA125) is essential for the early diagnosis and clinical management of ovarian cancer, but there is still challenge. Herein, a photoelectrochemical (PEC) immunosensor based on CdS/Bi2S3/NiS ternary sulfide heterostructured photocatalyst was presented for the detection of CA125. The CdS/Bi2S3/NiS was synthesized by a one-step hydrothermal approach. The heterojunction comprising of CdS and Bi2S3 could separate photogenerated carriers, the introduced narrow bandgap NiS could act as electron-conducting bridge to facilitate the transfer of interfacial photogenerated electrons, thereby improving the photoelectric conversion efficiency. Due to their synergistic effect, the photocurrent response produced by the composite was up to 14.6 times of pure CdS. On the basis, a PEC immunosensor was constructed by introducing the CA125 antibody through thioglycolic acid linkage. It was found that the resulting immunosensor showed good performance. Under the optimized conditions, its linear detection range was as wide as 1 pg mL-1-50 ng mL-1, and the detection limit was low to 0.85 pg mL-1. Furthermore, we experimentally tested its anti-interference, stability and reproducibility, and satisfactory results were achieved. The practicable feasibility of the sensor was confirmed by testing serum sample. Thus this work provided a simple, fast and enough sensitive approach for CA125 monitoring.

Self-Powered Immunoassay of Norovirus in Human Stools by π-Electron-Rich Homojunction for Enhanced Charge Transfer

Norovirus (NoV) stands as a significant causative agent of nonbacterial acute gastroenteritis on a global scale, presenting a substantial threat to public health. Hence, the development of simple and rapid analytical techniques for NoV detection holds great importance in preventing and controlling the outbreak of the epidemic. In this work, a self-powered photoelectrochemical (PEC) immunosensor of NoV capsid protein (VP1) was proposed by the π-electron-rich carbon nitride homojunction (ER-CNH) as the photoanode. C4N2 ring derived from π-rich locust bean gum was introduced into the tri-s-triazine structure, creating a large π-delocalized conjugated carbon nitride homojunction. This strategy enhances the C/N atomic ratio, which widens light utilization, narrows the bandgap, and optimizes the electronic band structure of carbon nitride. By introduction of a π-rich conjugated structure, p-type domains were induced within n-type domains to build the internal electric field at the interface, thus forming a p-n homojunction to boost carrier separation and transfer. The ER-CNH photoanode exhibited excellent photoelectric performance and water oxidation capacity. Since VP1 inhibits the water oxidation of the ER-CNH photoanode, the open-circuit potential of the as-prepared PEC immunosensor system was reduced for detecting NoV VP1. The self-powered PEC immunosensor achieved a remarkably low detection limit (∼5 fg mL-1) and displayed high stability and applicability for actual stool samples. This research serves as a foundation concept for constructing immunosensors to detect other viruses and promotes the application of self-powered systems for life safety.

Enhanced biomimetic catalysis via self-cascade photocatalytic hydrogen peroxide production over modified carbon nitride nanozymes for total antioxidant capacity evaluation

The peroxidase mimics usually requires the addition of exogenous hydrogen peroxide (H2O2), which greatly hinder their practical applications. Herein, through rational co-modification of multiple elements (potassium (K), chlorine (Cl) and iodine (I)), the modified carbon nitride nanomaterials (KCl/KI-CN) could serve as efficient bifunctional catalysts. The multiple elements doping and the incorporation of cyano groups (CN) are deemed to enhance their photocatalytic and peroxidase-like activity, respectively. Based on the photocatalytic function, H2O2 can be produced continuously and steadily via two-electron oxygen reduction over modified carbon nitride under visible light irradiation. Subsequently, the KCl/KI-CN could catalyze the chromogenic substrate by the in-situ produced H2O2. Taking advantage of the bifunctional properties of modified carbon nitride, we for the first time demonstrate a self-cascade catalytic process and apply successfully for the ascorbic acid (AA) detection and versatile total antioxidant capacity (TAC) evaluation. This paper not only prepares an efficiently bifunctional catalyst but also provides a new self-cascade photocatalytic H2O2 production strategy for the peroxidase-like application.

Cyano-Rich g-C3 N4 in Photochemistry: Design, Applications, and Prospects

Cyano-rich g-C3 N4 materials are widely used in various fields of photochemistry due to the very powerful electron-absorbing ability and electron storage function of cyano, as well as its advantages in improving light absorption, adjusting the energy band structure, increasing the polarization rate and electron density in the structure, active site concentration, and promoting oxygen activation ability. Notwithstanding, there is yet a huge knowledge break in the design, preparation, detection, application, and prospect of cyano-rich g-C3 N4 . Accordingly, an overall review is arranged to substantially comprehend the research progress and position of cyano-rich g-C3 N4 materials. An overall overview of the current research position in the synthesis, characterization (determination of their location and quantity), application, and reaction mechanism analysis of cyano-rich g-C3 N4 materials to provide a quantity of novel suggestions for cyano-modified carbon nitride materials' construction is provided. In view of the prevailing challenges and outlooks of cyano-rich g-C3 N4 materials, this paper will purify the growth direction of cyano-rich g-C3 N4 , to achieve a more in-depth exploration and broaden the applications of cyano-rich g-C3 N4 .

Magnetic-assisted exciton-plasmon interactions modulated Bi2S3 nanorods@MoS2 nanosheets heterojunction: towards a split-type photoelectrochemical sensing of profenofos

A split-type photoelectrochemical (PEC) sensor was designed for the detection of profenofos (PFF) depending on the magnetic-assisted exciton-plasmon interactions (EPI) between the semiconductor substrate and Au NPs. The core-shell Bi2S3 nanorods@MoS2 nanosheets (Bi2S3 NRs@MoS2 NSs) heterostructure nanomaterial with fascinating performance was synthesized and used as the photovoltaic conversion substrate and signal molecules absorption platform. The PEC sensor is operated by co-incubating with the released Au NPs-cDNA from the surface of magnetic beads, originating from the target-triggered DNA double-stranded structure opening event. Due to the strong EPI effects, the photocurrent of Bi2S3 NRs@MoS2 NSs decreased and varied with the PFF concentrations. The proposed PEC sensor exhibited outstanding analytical performances, including a wide linear range (1.0 pg mL-1~1.0 μg mL-1), low detection limitation (0.23 pg mL-1, at 3 σ/m), excellent specificity, high stability, and applicability. Overall, this work provides a new signal strategy for PEC biosensors and extends its application in environmental analysis.

Treatment of atrazine-containing wastewater by algae-bacteria consortia: Signal transmission and metabolic mechanism

Atrazine is a toxic endocrine disruptor. Biological treatment methods are considered to be effective. In the present study, a modified version of the algae-bacteria consortia (ABC) was established and a control was simultaneously set up to investigate the synergistic relationship between bacteria and algae and the mechanism by which atrazine is metabolized by those microorganisms. The total nitrogen (TN) removal efficiency of the ABC reached 89.24% and the atrazine concentration was reduced to below the level recommended by the Environment Protection Agency (EPA) regulatory standards within 25 days. The protein signal released from the extracellular polymeric substances (EPS) secreted by the microorganisms triggered the resistance mechanism of the algae, and the conversion of humic acid to fulvic acid and electron transfer constituted the synergistic mechanism between the bacteria and algae. The mechanism by which atrazine is metabolized by the ABC mainly consists of hydrogen bonding, H-pi interactions, and cation exchange with atzA for hydrolysis, followed by a reaction with atzC for decomposition to non-toxic cyanuric acid. Proteobacteria was the dominant phylum for bacterial community evolution under atrazine stress, and the analysis revealed that the removal of atrazine within the ABC was mainly dependent on the proportion of Proteobacteria and the expression of degradation genes (p < 0.01). EPS played a major role in the removal of atrazine within the single bacteria group (p < 0.01).

Recent Progress in Interface Engineering of Nanostructures for Photoelectrochemical Energy Harvesting Applications

With rapid and continuous consumption of nonrenewable energy, solar energy can be utilized to meet the energy requirement and mitigate environmental issues in the future. To attain a sustainable society with an energy mix predominately dependent on solar energy, photoelectrochemical (PEC) device, in which semiconductor nanostructure-based photocatalysts play important roles, is considered to be one of the most promising candidates to realize the sufficient utilization of solar energy in a low-cost, green, and environmentally friendly manner. Interface engineering of semiconductor nanostructures has been qualified in the efficient improvement of PEC performances including three basic steps, i.e., light absorption, charge transfer/separation, and surface catalytic reaction. In this review, recently developed interface engineering of semiconductor nanostructures for direct and high-efficiency conversion of sunlight into available forms (e.g., chemical fuels and electric power) are summarized in terms of their atomic constitution and morphology, electronic structure and promising potential for PEC applications. Extensive efforts toward the development of high-performance PEC applications (e.g., PEC water splitting, PEC photodetection, PEC catalysis, PEC degradation and PEC biosensors) are also presented and appraised. Last but not least, a brief summary and personal insights on the challenges and future directions in the community of next-generation PEC devices are also provided.

Engineering surface bromination in carbon nitride for efficient CO2 photoconversion to CH4

The direct conversion of CO₂ into reusable CH₄ fuel by solar energy can effectively solve the problems of energy crisis and carbon emissions. However, the challenge of photocatalytic CO₂ reduction to produce CH₄ is still low conversion efficiency and poor selectivity. Here, surface brominated carbon nitride (named CNBr) is fabricated for stable and efficient photocatalytic CO₂ reduction to produce CH₄ with a rate of 16.68 μmol h^-1 g^-1 (70.27 % selectivity). Br atom in CNBr can substitute the N atom in the tri-s-triazine unites, which promotes local charge separation, narrows band gap and deepens the conduction band of CNBr. Benefiting from Br as active sites, CO₂ can be enriched on the catalyst surface, and localized photogenerated electrons can activate the adsorbed CO₂ to form CH₄ through subsequent hydrogenation. Density functional theory results suggest that Br doping can effectively reduce the energy barrier of the rate-limiting step, accelerate the reaction, and induce the formation of *CHO, thereby improving the selectivity of CH₄. This work reveals that surface modification can simultaneously increase the activation site of CO₂ adsorption activation, enhance light absorption and accelerate charge, laying a solid foundation for the future design of carbon nitride based photocatalyst with high performance.

A fluorescent biosensor for Cd2+ detection in water samples based on Cd2+-fueled wheel DNAzyme walker and its logic gate applications

A fluorescent biosensor was developed for Cd²⁺ detection based on a Cd²⁺-fueled wheel DNAzyme walker. Cd²⁺ can activate the wheel to roll along the DNA walking tracks through DNAzyme cleavage and toehold-mediated strand displacement. The substrate strand was modified with BHQ and Cy5. Through continuous cleavage reactions toward the substrate strands, a high fluorescence signal can be obtained. The biosensor is ultrasensitive, and the detection limit is 0.2 pM (S/N = 3). The fluorescent assay is robust and has been applied to the determination of Cd²⁺ in real water samples with good accuracy and reliability. Using Cd²⁺, Pb²⁺, and Hg²⁺ as the three inputs, we also construct a concatenated AND logic gate. The input combination of (111) can produce an output of 1. Other input combinations produce an output of 0. Our proposed detection platform and logic system hold great promise for the ultrasensitive and intelligent sensing of different heavy metal ions in water samples.

Tailoring enzymatic loading capacity on CdS nanorods@ZnIn2S4 nanosheets 1D/2D heterojunctions: Toward ultrasensitive photoelectrochemical bioassay of tobramycin

Despite advances in the development of photoelectrochemical (PEC) sensor, modulating the PEC response of assembled heterostructure interface is still a great challenge. Here, an ultrasensitive PEC aptasensor for tobramycin (TOB) assay was conducted based on one-dimensional/two-dimensional CdS nanorods@ZnIn₂S₄ nanosheets (1D/2D CdS NRs@ZnIn₂S₄ NSs) heterojunctions by tailoring enzymatic loading capacity. Firstly, alkaline phosphatase modified TOB aptamer (ALP-Apt) was linked via specific base complementary pairing, and insoluble precipitations were then produced through the ALP-triggered catalytic reaction with the aid of Ag⁺, which prevented the charge transfer and resulted in the decrement of photocurrent. In the presence of TOB, partial ALP-Apt detached from the electrode surface due to the strong affinity between TOB and its aptamer, leading to a reduction in the amount of ALP and insoluble precipitate, in turn the PEC response partially recovered. The photocurrents exhibited a wider linear range towards the TOB concentration of 1.0-5.0 × 10⁴ pg mL^-1, with a low detection limit of 0.96 pg mL^-1. The constructed PEC aptasensor gained satisfactory results for TOB assay in milk samples as well, which also offered significant promise for other pollutants in environmental analysis.

Bifunctional photoelectrochemical aptasensor based on heterostructured Ag3PO4/Ag/TiO2 nanorod array for determination of two tumor markers

Constructing of heterostructures can significantly improve the photoelectrical (PEC) response signal by promoting the migration and suppressing the recombination of photogenerated carries. A bifunctional PEC sensing platform was designed for simultaneous high-performance detection of mucin-1 (MUC1) and carcinoembryonic antigen (CEA), which was based on generated Z-scheme heterostructured Ag₃PO₄/Ag/TiO₂ nanorod arrays (NAs) and enzyme-mediated catalytic precipitation by alkaline phosphatase (ALP) and Au/hollow Co₃O₄ polyhedron. The proposed aptasensor displayed linear ranges of 1.0-100 ng mL^-1 and 0.1-50 ng mL^-1 for MUC1 and CEA with limit of detections of 0.430 and 0.058 ng mL^-1, respectively. This strategy offers potential applications for early diagnosis, monitoring progression, and even evaluating the prognosis of breast cancer in practice.

Synergistic Effect in Plasmonic CuAu Alloys as Co-Catalyst on SnIn4S8 for Boosted Solar-Driven CO2 Reduction

The photoreduction of CO2 to chemical fuels represents a promising technology to mitigate the current energy dilemma and global warming problems. Unfortunately, the original photocatalysts suffer from many side reactions and a poor CO2 conversion efficiency. The rational combination of active co-catalyst with pristine photocatalysts for promoting the adsorption and activation of CO2 is of vital importance to tackle this grand challenge. Herein, we rationally designed a SnIn4S8 nanosheet photocatalyst simultaneously equipped with CuAu alloys. The experimental results proved that the CuAu alloy can trap the electrons and enhance the separation and transport efficiency of the photogenerated carrier in the photocatalyst, alleviating the kinetical difficulty of the charge transfer process because of the preferable localized surface plasmon resonance (LSPR). Furthermore, the CuAu alloy works as the synergistic site to increase the CO2 adsorption and activation capacity. The optimized CuAu-SnIn4S8 photocatalyst exhibited a superior performance with CO generation rates of 27.87 μmol g−1 h−1 and CH4 of 7.21 μmol g−1 h−1, which are about 7.6 and 2.5 folds compared with SnIn4S8. This work highlights the critical role of alloy cocatalysts in boosting a CO2 activation and an efficient CO2 reduction, thus contributing to the development of more outstanding photocatalytic systems.

Heat/PMS Degradation of Atrazine: Theory and Kinetic Studies

The degradation effect of heat/peroxymonosulfate (PMS) on atrazine (ATZ) is studied. The results show that the heat/PMS degradation for ATZ is 96.28% at the moment that the phosphate buffer (PB) pH, temperature, PMS dosage, ATZ concentration, and reaction time are 7, 50 °C, 400 μmol/L, 2.5 μmol/L, and 60 min. A more alkaline PB is more likely to promote the breakdown of ATZ through heat/PMS, while the PB alone has a more acidic effect on the PMS than the partially alkaline solution. HO• and SO4−• coexisted within the heat/PMS scheme, and ATZ quantity degraded by HO• and SO4−• in PB with pH = 7, pH = 1.7~1. HCO3− makes it difficult for heat/PMS to degrade ATZ according to inorganic anion studies, while Cl− and NO3− accelerate the degradation and the acceleration effect of NO3− is more obvious. The kinetics of ATZ degradation via heat/PMS is quasi-first-order. Ethanol (ETA) with the identical concentration inhibited ATZ degradation slightly more than HCO3−, and both of them reduced the degradation rates of heat/PMS to 7.06% and 11.56%. The addition of Cl− and NO3− increased the maximum rate of ATZ degradation by heat/PMS by 62.94% and 189.31%.