A photoelectrochemical aptasensor for the determination of bisphenol A based on the Cu (I) modified graphitic carbon nitride

Self-powered molecularly imprinted photoelectrochemical sensor based on Ppy/QD/HOF heterojunction for the detection of bisphenol A

As an emerging porous material, hydrogen-bonded organic framework materials (HOFs) still pose application challenges. In this work, the designed type "I + II" heterojunction extracted hot electrons from HOFs using quantum dots (QDs) and polypyrrole (Ppy), improving the stability and photoelectrochemical performance of materials. In addition to serving as a potential well, electropolymerized Ppy was used as a recognition element for bisphenol A (BPA), and a novel self-powered molecularly imprinted photoelectrochemical (MIP-PEC) sensor was designed. The sensing platform showed a linear relationship from 1 × 10-10 to 1 × 10-7 mol∙L-1 and from 1 × 10-7 to 1 mol∙L-1 with an acceptable detection limit of 4.2 × 10-11 mol∙L-1. This is the first application of HOFs in constructing MIP-PEC sensors and a new attempt to improve the stability of HOFs for the application of porous crystal materials in the sensing field.

Advancements in nanomaterial-based aptasensors for the detection of emerging organic pollutants in environmental and biological samples

The combination of nanomaterials (NMs) and aptamers into aptasensors enables highly specific and sensitive detection of diverse pollutants. The great potential of aptasensors is recognized for the detection of diverse emerging organic pollutants (EOPs) in different environmental and biological matrices. In addition to high sensitivity and selectivity, NM-based aptasensors have many other advantages such as portability, miniaturization, facile use, and affordability. This work showcases the recent advances achieved in the design and fabrication of NM-based aptasensors for monitoring EOPs (e.g., hormones, phenolic contaminants, pesticides, and pharmaceuticals). On the basis of their sensing mechanisms, the covered aptasensing systems are classified as electrochemical, colorimetric, PEC, fluorescence, SERS, and ECL. Special attention has been paid to the fabrication processes, analytical achievements, and sensing mechanisms of NM-based aptasensors. Further, the practical utility of aptasensing approaches has also been assessed based on their basic performance metrics (e.g., detection limits, sensing ranges, and response times).

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.

Atomically dispersed Mn boosting photoelectrochemical SARS-CoV-2 spike protein immunosensing on carbon nitride

The sudden outbreak of coronavirus disease (COVID-19) triggered by SARS-CoV-2 infection has created a terrifying situation around the world. The spike protein of SARS-CoV-2 can act as an early biomarker for COVID-19. Therefore, controlling the spread of COVID-19 requires a low-cost, fast-response, and sensitive monitoring technique of spike protein. Herein, a photoelectrochemical (PEC) immunosensor for the detection of spike protein was constructed using the nanobody and an Mn (Ⅱ) modified graphitic carbon nitride (Mn/g-C₃N₄). The introduction of atomically dispersed Mn (Ⅱ) can accelerate the effective transfer and separation of photogenerated electron-hole pairs, which significantly boosts PEC performance of g-C₃N₄, thereby improving the detection sensitivity. As a recognition site, nanobody can achieve high-affinity binding to the spike protein, leading to a high sensitivity. The linear detection range of the proposed PEC immunosensor was 75 fg mL^-1 to 150 pg mL^-1, and the limit of detection was calculated to be 1.22 fg mL^-1. This stable and feasible PEC immunosensor would be a promising diagnostic tool for sensitively detecting spike protein of SARS-CoV-2.

Highly sensitive and group-targeting detection of steroid estrogens in water environment using a valid oligonucleotide class-specific editing technique

Steroid environmental estrogens (SEEs) are often coexist in water, require complex analytical techniques for separation and monitoring. However, aptamer-based chemical detection often only recognizes one of them, and the detection of SEEs is still a huge challenge. Herein, a group-targeting aptamer with the ability to recognize SEEs was constructed using efficient oligonucleotide class-specific editing technology, and a photoelectrochemical aptasensor capable of detecting the class of SEEs was established. A quantitative analysis of highly toxic SEEs in the environment and carrying similar core carbon skeleton, including 17β-estradiol, esterone, estriol and ethinylestradiol, was performed. The detection limit was as low as 0.1 nM with a response time of only 15 min. Specifically, this method exhibited high anti-interference with different complex media existing. Combining the theoretical calculations with a variety of spectral experiments, the Π-Π stacking and hydrogen bond synergistic interactions between the photoelectric interface and the three ring structures on SEEs and the hydroxyl group of ring 1 were analyzed in depth. Besides, the conformational changes of loose base helix structure and the free rotation limitation of oligonucleotides after the recognition of SEEs at the molecular level were also elucidated, facilitating the transfer of electrons on the surface of the photoelectrode.

C-O band structure modified broad spectral response carbon nitride with enhanced electron density in photocatalytic peroxymonosulfate activation for bisphenol pollutants removal

Here, a simple one-step calcination method uses glycolic acid (GA) and urea to synthesize C-O band structure modified carbon nitride with broad spectral response, which is used to construct a peroxymonosulfate/visible light (PMS/vis) system. The solid-state ¹³C NMR proved that C-O band structure was successfully introduced into the carbon nitride. Density functional theory (DFT) calculation show that the introduction of C-O band structure shortens the band gap of 0.05 g GA modified CN (0.05 GA-CN). Besides, Ultraviolet photoelectron spectroscopy (UPS) further illustrate that the 0.05 GA-CN has a higher charge density and promotes the degradation of pollutants. In PMS/vis system, 0.05 GA-CN can completely degrade bisphenol A (BPA) within 36 min. In addition, 0.05 GA-CN can also degrade bisphenol E (BPE) and bisphenol F (BPF). The cyclic voltammetry (CV) curve show that the introduction of C-O band structure enhances the activation ability of PMS. At the same time, 0.05 GA-CN/PMS has enhanced the activity of degrading BPA under blue light (450-462 nm), green light (510-520 nm) and red light (610-625 nm). This research provides a new method to synthesize carbon nitride with enhanced electron density for degradation of bisphenol pollutants in PMS/vis system.

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.

Phosphorus- and fluorine-co-doped carbon nitride: modulated visible light absorption, charge carrier kinetics and boosted photocatalytic hydrogen evolution

A phosphorus and fluorine co-doped carbon nitride (PF-CN) photocatalyst was synthesized to modulate the band gap structure, visible light response ability and photocatalytic H₂ evolution activity. Experimental results demonstrated that the electronic structure of g-C₃N₄ was regulated by phosphorus replacing the C site and fluorine substituting the N site in the g-C₃N₄ framework to form P-N species and C-F bonds, respectively. P- and F-co-doped carbon nitride gave rise to a more negative conduction band potential, larger surface area, efficient separation of photogenerated charge carriers and a faster charge transfer rate, contributing to an enhancement of photocatalytic H₂ production activity. PF-CN achieved an optimal H₂ evolution activity of 1690.56 μmol g^-1 which was 17.83 times higher with respect to that of pristine g-C₃N₄ (94.81 μmol g^-1). Meanwhile, PF-CN achieved the highest apparent quantum efficiency of 3.76% at 435 nm.

Selective and sensitive photoelectrochemical aptasensor for streptomycin detection based on Bi4VO8Br/Ti3C2 nanohybrids

Sensitive detection of streptomycin (STR) has attracted increasing attention worldwide because of the relationship between food security and human health. In this paper, Bi₄VO₈Br/Ti₃C₂ nanohybrids were obtained by one-pot solvent hydrothermal method. It was modified on ITO electrode, and STR aptamer was acted as the recognition element. With excellent photoelectrochemical (PEC) performance of Bi₄VO₈Br/Ti₃C₂ nanohybrids, an "on-off-on" PEC aptasensor for STR detection was effectively developed. Compared with pure Bi₄VO₈Br, the photocurrent intensity of as-prepared Bi₄VO₈Br/Ti₃C₂ nanohybrids was about 9 times higher, which ascribed to the highly conductive of Ti₃C₂, driving the photogenerated electrons transferred to the ITO electrode rapidly, so that the recombination of photogenerated electron and hole pairs was inhibited viably. Furthermore, the constructed "on-off-on" PEC aptasensor accomplished STR detection with high sensitivity, excellent specificity and distinguished repeatability in honey. The photocurrent increased with the increment of STR concentration with the linear range from1 nM to 1000 nM, and the detection limit of 0.3 nM (S/N = 3). Compared with the national standard method (SN/T 1925-2007), the as-constructed PEC sensor showed the consistent results.

Investigation of the inhibited biotoxicity of heavy metals towards 5- formylcytosine in rice by hydrochar based on photoelectrochemical biosensor

A photoelectrochemical (PEC) biosensor was constructed for 5-formylcytosine (5fC) nucleotide detection based on Ag₂S@WS₂ photoactive material and FeVO₄ catalytic signal quenching. After Ag₂S@WS₂ was modified onto the ITO substrate surface, 5fC recognition reagent of Au@4-amino3hydrazino5mercapto-1,2,4-triazol (Au@AHMT) was further modified through electrostatic adsorption. Afterwards, based on the specific chemical reaction between -NH₂ and -CHO, 5fC can be selectively recognized and captured. Subsequently, the nanoenzyme of FeVO₄ was recognized based on the specific reaction between the phosphate group of 5fC nucleotide and Fe³⁺. Under the catalysis of FeVO₄, the 4-chloro-1-naphthol in the detection solution can be oxidized to generate a precipitate, which will be retained on the electrode surface to inhibit the PEC signal. The developed method presented a widely dynamic range from 0.1 to 400 nM. The detection limit was 0.062 nM (3σ). This method also showed good detection selectivity, reproducibility and stability. The applicability was verified by investigating 5fC content change in genomic DNA of rice tissues after incubated with heavy metals. Moreover, the inhibited influence of hydrochar towards heavy metals was also assessed.

A highly sensitive photoelectrochemical aptasensor based on BiVO4 nanoparticles-TiO2 nanotubes for detection of PCB72

In this work, a simple and highly sensitive photoelectrochemical (PEC) aptasensor has been developed for detecting PCB72 based on TiO₂ nanotubes (NTs) decorated with BiVO₄ nanoparticles (NPs). The BiVO₄ NPs-TiO₂ NTs composites prepared through a simple hydrothermal method exhibit good visible-light adsorption ability, high PEC response and perfect photo-excited stability. The synthesized composites were explored as the photoactive sensing materials for development of a PEC sensing platform for the first time. Here, Au nanoparticles (NPs) were first deposited the composites, and the anti-PCB72 aptamer molecules were immobilized on the Au NPs-deposited BiVO₄ NPs-TiO₂ NTs. The developed PEC aptasensor exhibits high sensitivity and specificity for PCB72 with a wide linear range from 1 ng/L to 500 ng/L and a low detection limit of 0.23 ng/L. The application of the aptasensor was evaluated by determining PCB 72 in the environment water samples. Thus, a simple and efficient PEC sensing platform was established for detecting the content of PCBs in the environment.

A novel aptasensing method for detecting bisphenol A using the catalytic effect of the Fe3O4/Au nanoparticles on the reduction reaction of the silver ions

The gold electrode was functionalized with anti-bisphenol A (BPA) aptamer and captured the BPA as analyte. By dropping the aptamer-modified magnetic Fe₃O₄/Au nanoparticles solution onto the electrode, a BPA molecule attaches to many aptamers that are in contact with a large number of Fe₃O₄/Au nanoparticles. The modified electrode were transferred to a solution containing Ag⁺ ions. Fe₃O₄/Au nanoparticles reduce the Ag⁺ ions to Ag⁰. A potential scan was applied for the oxidation of the Ag⁰-loaded magnetic nanoparticles to the AgCl. The magnitude of the stripping anodic signal of the Ag⁰ was related to the concentration of the BPA. The assay shows a detection limit of 0.6 fmol L^-1 and linear range of 1 fmol L^-1-150 pmol L^-1 and. The applicability of the aptasensor is measured by its successful use in the sensing BPA in water, milk and juice samples and measuring BPA migration from different commercial plastic products.

Recent Advances in Aptamer Sensors

Recently, aptamers have attracted attention in the biosensing field as signal recognition elements because of their high binding affinity toward specific targets such as proteins, cells, small molecules, and even metal ions, antibodies for which are difficult to obtain. Aptamers are single oligonucleotides generated by in vitro selection mechanisms via the systematic evolution of ligand exponential enrichment (SELEX) process. In addition to their high binding affinity, aptamers can be easily functionalized and engineered, providing several signaling modes such as colorimetric, fluorometric, and electrochemical, in what are known as aptasensors. In this review, recent advances in aptasensors as powerful biosensor probes that could be used in different fields, including environmental monitoring, clinical diagnosis, and drug monitoring, are described. Advances in aptamer-based colorimetric, fluorometric, and electrochemical aptasensing with their advantages and disadvantages are summarized and critically discussed. Additionally, future prospects are pointed out to facilitate the development of aptasensor technology for different targets.

Latest Advances in Determination of Bisphenols with Nanomaterials, Molecularly Imprinted Polymers and Aptamer Based Electrochemical Sensors

Contamination of environmental sources such as soils, sediments and rivers and human exposure caused by several endocrine disrupting compounds (EDCs) are considered as the most challenging issues of today's world. EDCs cover a wide variety of compounds ranging from phthalates to parabens and bisphenols (BPs) are the leading group among them. BPs are widely used during the production of different plastic materials such as food and beverage containers, toys, medical equipment and baby bottles that we use in every aspect of our lives. BPs may migrate from those products to different media under certain conditions and this situation causes chronic exposure for humans and other creatures in the environment. Especially bisphenol A (BPA) and its other analogues such as bisphenol F, bisphenol S and tetrabromobisphenol that have similar structures and are preferred as alternatives to BPA cause harmful adverse effects such as endocrine disruption, neurotoxicity, genotoxicity and cytotoxicity. There are legal restrictions and prohibitions by the European Union (EU) in order to prevent possible harmful effects. Therefore, it is important to develop highly sensitive, fast, easy to use and cheap sensors for the determination of BPs in biological, environmental and commercial samples. Electrochemical sensors, which are one of the most widely, used analytical techniques, provide these conditions. Additionally, it is possible to enhance the performance of electrochemical sensors with nanomaterials, molecularly imprinted polymers or aptamer based technologies. This review aims to give comprehensive information about BPs with summarizing most recent applications of electrochemical sensors for their determination in different samples.

A photoelectrochemical aptasensor for sensitively monitoring chloramphenicol using plasmon-driven AgNP/BiOCl composites

A photoelectrochemical (PEC) aptasensor based on silver nanoparticle/BiOCl (AgNP/BiOCl) composites was constructed for detecting chloramphenicol (CAP). The surface-plasmon resonance (SPR) effect of AgNPs can focus the incident light and promote the migration and separation of the photogenerated carriers of AgNP/BiOCl composites. As a result, the AgNP/BiOCl composites showed an enhanced PEC performance compared to that of pure BiOCl. A PEC CAP aptasensor was fabricated using AgNP/BiOCl composites as photoactive materials and a CAP aptamer as a recognition element. The PEC aptasensor exhibited a broad linear response range (0.2 pM-10 nM), a low limit of determination (0.08 pM), satisfactory selectivity, stability, and reproducibility to meet the practical analysis requirements. This work demonstrates that the PEC CAP aptasensor has a promising prospect in environmental assays.