Photoelectrochemical Biosensor for DNA Formylation Detection in Genomic DNA of Maize Seedlings Based on Black Tio2-Enhanced Photoactivity of MoS2/WS2 Heterojunction

Red and near-infrared light-activated photoelectrochemical nanobiosensors for biomedical target detection

Photoelectrochemical (PEC) nanobiosensors integrate molecular (bio)recognition elements with semiconductor/plasmonic photoactive nanomaterials to produce measurable signals after light-induced reactions. Recent advancements in PEC nanobiosensors, using light-matter interactions, have significantly improved sensitivity, specificity, and signal-to-noise ratio in detecting (bio)analytes. Tunable nanomaterials activated by a wide spectral radiation window coupled to electrochemical transduction platforms have further improved detection by stabilizing and amplifying electrical signals. This work reviews PEC biosensors based on nanomaterials like metal oxides, carbon nitrides, quantum dots, and transition metal chalcogenides (TMCs), showing their superior optoelectronic properties and analytical performance for the detection of clinically relevant biomarkers. Furthermore, it highlights the innovative role of red light and NIR-activated PEC nanobiosensors in enhancing charge transfer processes, protecting them from biomolecule photodamage in vitro and in vivo applications. Overall, advances in PEC detection systems have the potential to revolutionize rapid and accurate measurements in clinical diagnostic applications. Their integration into miniaturized devices also supports the development of portable, easy-to-use diagnostic tools, facilitating point-of-care (POC) testing solutions and real-time monitoring.

From Bulk Molybdenum Disulfide (MoS2) to Suspensions of Exfoliated MoS2 in an Aqueous Medium and Their Applications

Two-dimensional (2D) layered materials like graphene, transition-metal dichalcogenides (TMDs), boron nitrides, etc., exhibit unique and fascinating properties, such as high surface-to-volume ratio, inherent mechanical flexibility and robustness, tunable bandgap, and high carrier mobility, which makes them an apt candidate for flexible electronics with low consumption of power. Because of these properties, they are in tremendous demand for advancement in energy, environmental, and biomedical sectors developed through various technologies. The production and scalability of these materials must be sustainable and ecofriendly to utilize these unique properties in the real world. Here, in this current review, we review molybdenum disulfide (MoS2 nanosheets) in detail, focusing on exfoliated MoS2 in water and the applicability of aqueous MoS2 suspensions in various fields. The exfoliation of MoS2 results in the formation of single or few-layered MoS2. Therefore, this Review focuses on the few layers of exfoliated MoS2 that have the additional properties of 2D layered materials and higher excellent compatibility for integration than existing conventional Si tools. Hence, a few layers of exfoliated MoS2 are widely explored in biosensing, gas sensing, catalysis, photodetectors, energy storage devices, a light-emitting diode (LED), adsorption, etc. This review covers the numerous methodologies to exfoliate MoS2, focusing on the various published methodologies to obtain nanosheets of MoS2 from water solutions and their use.

Recent Advances in Black TiO2 Nanomaterials for Solar Energy Conversion

Titanium dioxide (TiO₂) nanomaterials have been widely used in photocatalytic energy conversion and environmental remediation due to their advantages of low cost, chemical stability, and relatively high photo-activity. However, applications of TiO₂ have been restricted in the ultraviolet range because of the wide band gap. Broadening the light absorption of TiO₂ nanomaterials is an efficient way to improve the photocatalytic activity. Thus, black TiO₂ with extended light response range in the visible light and even near infrared light has been extensively exploited as efficient photocatalysts in the last decade. This review represents an attempt to conclude the recent developments in black TiO₂ nanomaterials synthesized by modified treatment, which presented different structure, morphological features, reduced band gap, and enhanced solar energy harvesting efficiency. Special emphasis has been given to the newly developed synthetic methods, porous black TiO₂, and the approaches for further improving the photocatalytic activity of black TiO₂. Various black TiO₂, doped black TiO₂, metal-loaded black TiO₂ and black TiO₂ heterojunction photocatalysts, and their photocatalytic applications and mechanisms in the field of energy and environment are summarized in this review, to provide useful insights and new ideas in the related field.

A "signal-on" photoelectrochemical sensor for human epidermal growth factor receptor 2 detection based on Y6/CdS organic-inorganic heterojunction

A "signal-on" photoelectrochemical (PEC) immunosensor was successfully constructed for determination of human epidermal growth factor receptor 2 (HER2) based on organic-inorganic heterojunction Y6/CdS as photoactive material. Compared with single organic semiconductor, Y6, Y6/CdS exhibited higher photoelectric conversion efficiency due to the formation of heterojunction. In the presence of HER2, sandwich immune structure was formed between HER2 aptamer and anti-HER2 antibody (Ab) by specific recognition. The polydopamine (PDA) nanoparticles were used for signal amplification to enhance photocurrent intensity as PDA can act as electron donor to eliminate holes and promote electron-hole pairs separation. The developed PEC sensor displayed a wide detection range of 5-1000 pg mL^-1 and a low detection limit of 2.2 pg mL^-1 for HER2 (S/N = 3). The sensor was successfully used for the detection of HER2 in serum with recoveries between 94.8 and 104% and relative standard deviations (RSDs) in the range of 1.2-4.3%. Furthermore, the designed immunosensor possessed good stability, selectivity, and reproducibility, which can find potential clinical applications for disease diagnosis. A "signal-on" photoelectrochemical sensor was reported for human epidermal growth factor receptor 2 detection based on Y6/CdS organic-inorganic heterojunction.

Tuning the Surface Molecular Charge of Organic Photoelectrochemical Transistors with Significantly Improved Signal Resolution: A General Strategy toward Sensitive Bioanalysis

Nature makes use of molecular charges to operate specific biological synthesis and reactions. Targeting advanced opto-bioelectronic sensors, organic photoelectrochemical transistors (OPECTs), taking advantage of the light fuel substituting an external gate potential, is now debuting and expected to serve as a universal platform for studying the rich light-biomatter interplay for new bioanalytics. Given the ubiquity of charged biomolecules in nature, molecular charge manipulation should underpin a generic route for innovative OPECT regulation and operation, which nevertheless has remained unachieved. Herein, this work manifests the biological tuning of surface charge toward the OPECT biosensor, which was exemplified by a light-sensitive CdS quantum dot (QD) gate electrode interfaced by a smart DNA superstructure with adenosine triphosphate (ATP) responsiveness. Highly negative-charged supramolecular DNA concatemers were self-assembled via sequential hybridization, and the ATP-triggered disassembly of the DNA concatemers would cause a tandem change of the effective gate voltage and transfer characteristics with significantly improved resolution. The present opto-bioelectronic device translates the events of charged molecules into amplified electrical signals and outlines a generic format for the future exploitation of rich biological tunability and light-biomatter interplay for innovative bioanalytics and beyond.

Photoelectrochemical Sensors with Near-Infrared-Responsive Reduced Graphene Oxide and MoS2 for Quantification of Escherichia Coli O157:H7

The photoelectric response is crucial for photocatalysis, having applications in solar cells and photoelectrochemical (PEC) sensors. In this study, we demonstrate improvements in the near-infrared (NIR)-light-driven PEC response via synergism between reduced graphene oxide (rGO) and MoS₂. Intriguingly, rGO modulates the morphology of MoS₂, facilitating carrier generation and migration, improving the PEC performance of the resultant rGO-MoS₂ sheets (GMS), and yielding an approximately 8-fold increase in the photocurrent compared to that of the pure MoS₂. Based on these findings, a NIR-responsive PEC immunosensing platform for the "turn-on" analysis of Escherichia coli O157:H7 on 980 nm light irradiation is reported. Specifically, the device is a three-dimensional magnetic screen-printed paper-based electrode assembled on a home-made PEC cell, and it enables integrated separation and detection. Using a sandwich-type immunocomplex bridged by E. coli O157:H7 and a GMS PEC probe, the immunosensing platform detected E. coli O157:H7 between 5.0 and 5.0 × 10⁶ CFU mL^-1, having an extremely low detection limit of 2.0 CFU mL^-1. Further, the assay enables the direct analysis of E. coli O157:H7 in milk without the need for pretreatment. Our findings suggest directions for the development of NIR-responsive paper-based PEC materials for portable biomolecule sensing.

Investigation of the effect of antibiotics on 5-formylcytosine content in mazie seedling tissues based on photoelectrochemical biosensor

Given the improved photoactivity of Bi₂S₃ by MXene, an article photoelectrochemical biosensor was designed for 5-formyl-2'-deoxycytidine (5fdCTP) detection, where Bi₂S₃: MXene was selected as photoactive material, polydopamine was used as solid electron donor and 5fdCTP capture reagent, calcined ZIF-8(C-ZIF-8) was chosen as the artificial enzyme. With the catalyzed by C-ZIF-8, 4-chloro-1-naphthol was allegro oxidized by H₂O₂ to form the insoluble benzo-4-chlorohexadienone, and then deposited on the surface of the electrode, Resulting in a decrease of the PEC response. Under the optimum conditions, the sensor has a linear range of 0.001-200 nM and a detection limit of 0.51 pM (3σ). The suitability of the developed method was appraised by investigating the effect of antibiotics on 5fdCTP content in the genomic DNA of the roots of maize seedlings. As a new detection platform, the application of this approach can be expanded to investigative the impact of other pollutants on the content of 5fdCTP in plant or animal tissues, explore the feasibility of 5fdCTP as a new indicator for the ecotoxicological effect of pollutants, and the photoelectrochemical method as a new assessment technique for the ecotoxicological effects of pollutants.

An integrated nanoflower-like MoS2@CuCo2O4 heterostructure for boosting electrochemical glucose sensing in beverage

Excessive glucose in food poses a non-negligible threat to its inherent quality and human health, which makes it imperative to develop a highly sensitive sensor for real-time glucose detection. In this work, an integrated electrochemical glucose sensor based on a nanoflower-like MoS₂@CuCo₂O₄ heterostructure was carefully constructed. Under optimal conditions, the as-fabricated sensor exhibited a high sensitivity of 1,303 μA mM^-1 cm^-2 over a wide range of 0.5-393.0 μmol/L, accompanied by a low determination limit (0.5 μmol/L) and short response time (2.1 s). The favorable sensing performance of the MoS₂@CuCo₂O₄ nanocomposite-modified electrode in electrochemical analyses was attributed to the introduction of unique nanoflower-like heterostructure and the synergistic effects between MoS₂ and CuCo₂O₄. Furthermore, the satisfactory applicability of this sensor in beverages was confirmed. These results demonstrate that the MoS₂@CuCo₂O₄/GCE may be a promising platform for sensitive monitoring of glucose content in food samples.

In situ growth of WO3/BiVO4 nanoflowers onto cellulose fibers to construct photoelectrochemical/colorimetric lab-on-paper devices for the ultrasensitive detection of AFP

In this work, novel dual-mode lab-on-paper devices based on in situ grown WO₃/BiVO₄ heterojunctions onto cellulose fibers, as signal amplification probes, were successfully fabricated by the integration of photoelectrochemical (PEC)/colorimetric analysis technologies into a paper sensing platform for the ultrasensitive detection of alpha-fetoprotein (AFP). Specifically, to achieve an impressive PEC performance of the lab-on-paper device, the WO₃/BiVO₄ heterojunction was in situ grown onto the surface of cellulose fibers assisted with Au nanoparticle (Au NP) functionalization for enhancing the conductivity of the working zone of the device. With the target concentration increased, more immune conjugates could be captured by the proposed paper photoelectrode, which could lead to a quantitative decrease in the photocurrent intensity, eventually realizing the accurate PEC signal readout. To meet the requirement of end-user application, a colorimetric signal readout system was designed for the lab-on-paper device based on the color reaction of 3,3'5,5'-tetramethylbenzidine (TMB) oxidized by WO₃/BiVO₄ nanoflowers in the presence of H₂O₂. Noticeably, it is the first time that the WO₃/BiVO₄ heterojunction is in situ grown onto cellulose fibers, which enhances the sensitivity in view of both their PEC activity and catalytic ability. By controlling the conversion process of hydrophobicity and hydrophilicity on the lab-on-paper device combined with diverse origami methods, the dual-mode PEC/colorimetric signal output for the ultrasensitive AFP detection was realized. Under optimal conditions, the proposed dual-mode lab-on-paper device could enable the sensitive PEC/colorimetric diagnosis of AFP in the linear range of 0.09-100 ng mL^-1 and 5-100 ng mL^-1 with the limit of detection of 0.03 and 1.47 ng mL^-1, respectively.

CRISPR-Cas12a-Derived Photoelectrochemical Biosensor for Point-Of-Care Diagnosis of Nucleic Acid

This work presented a point-of-care (POC) photoelectrochemical (PEC) biosensing for the detection of human papillomavirus-16 (HPV-16) on a portable electrochemical detection system by using CRISPR-Cas12a trans-cleaving the G-quadruplex for the biorecognition/amplification and a hollow In₂O₃-In₂S₃-modified screen-printed electrode (In₂O₃-In₂S₃/SPE) as the photoactive material. G-quadruplexes were capable of biocatalytic precipitation (H₂O₂-mediated 4-chloro-1-naphthol oxidation) on the In₂O₃-In₂S₃/SPE surface, resulting in a weakened photocurrent, but suffered from trans-cleavage when the CRISPR-Cas12a system specifically recognized the analyte. The photocurrent results could be directly observed with the card-sized electrochemical device via a smartphone, which displayed a high-value photocurrent for these positive samples, while a low-value photocurrent for the target-free samples. Such a system exhibited satisfying photocurrent responses toward HPV-16 within a wide working range from 5.0 to 5000 pM and allowed for detection of HPV-16 at a concentration as low as 1.2 pM. The proposed assay provided a smartphone signal readout to enable the rapid screening PEC determination of HPV-16 concentration without sophisticated instruments, thus meeting the requirements of remote areas and resource-limited settings. We envision that combining an efficient biometric PEC sensing platform with a wireless card-sized electrochemical device will enable high-throughput POC diagnostic analysis.

Molecular Imprinted Poly(2,5-benzimidazole)-Modified VO2-CuWO4 Homotype Heterojunction for Photoelectrochemical Dopamine Sensing

A photoactive molecularly imprinted poly(2,5-benzimidazole)-modified vanadium dioxide-cupric tungstate (VO₂-CuWO₄) as an efficient photosensitive n-n type-II heterojunction thin film was electrochemically deposited on Ti substrate for the selective and robust photoelectrochemical (PEC) bioanalysis of dopamine (DA). The optical absorption of n-VO₂/n-CuWO₄ type-II heterojunction was capably broadened toward the visible region, which permitted superior light-harvesting and robust carriers generation, separation, and transfer processes significantly enhancing the anodic photocurrent, as confirmed by a series of PEC analyses. Findings revealed that the as-prepared label-free MIP-PEC sensor can quantitatively monitor DA in a linear range of 1 nM to 200 μM with a detection limit of 0.15 nM. This MIP-PEC sensor showed robust selectivity under conditions with high concentrations of interfering substances, which can be recovered in the real samples of urine, cocoa chocolate, and diluted yogurt, indicating its promising potential applications in biological and food samples. This work not only featured the use of photoelectrically active MIP/VO₂-CuWO₄ for PEC detection of DA, but also provided a new horizon for the design and implementation of functional polymers/metal oxides heterojunction materials in the field of PEC sensors and biosensors.

Liposome-Mediated In Situ Formation of Type-I Heterojunction for Amplified Photoelectrochemical Immunoassay

Exploiting innovative sensing mechanisms and their rational implementation for selective and sensitive detection has recently become one of the mainstream research directions of photoelectrochemical (PEC) bioanalysis. In contrast to existing conventional strategies, this study presents a new liposome-mediated method via in situ combining ZnInS nanosheets (ZIS NSs) with SnS₂ to form a ZIS NSs/SnS₂ type-I heterojunction on fluorine-doped tin oxide (FTO) electrodes for highly sensitive PEC immunoassays. Specifically, alkaline phosphatase (ALP)-encapsulated liposomes were confined within 96-well plates by sandwich immunorecognition and subsequently subjected to lysis treatment. Enzymatically produced H₂S by the released ALP was then directed to react with Sn(IV) to engender the ZIS NSs/SnS₂ type-I heterojunction on the FTO/ZIS NSs-Sn(IV) electrode, resulting in a change in the photogenerated electron-hole transfer path of the photoelectrode and reduction in current signaling. Exemplified by heart-type fatty acid binding protein (h-FABP) as a target, the constructed PEC sensor showed good stability and selectivity in a biosensing system. Under optimal conditions, the as-prepared sensing platform displayed high sensitivity for h-FABP with a dynamic linear response range of 0.1-1000 pg/mL and a lower detection limit of 55 fg/mL. This research presents the liposome-mediated PEC immunoassay based on in situ type-I heterojunction establishment, providing a new protocol for analyzing various targets of interest.

Recent Advances of Nanostructured Materials for Photoelectrochemical Bioanalysis

Nowadays, the emerging photoelectrochemical (PEC) bioanalysis has drawn intensive interest due to its numerous merits. As one of its core elements, functional nanostructured materials play a crucial role during the construction of PEC biosensors, which can not only be employed as transducers but also act as signal probes. Although both chemical composition and morphology control of nanostructured materials contribute to the excellent analytical performance of PEC bioassay, surveys addressing nanostructures with different dimensionality have rarely been reported. In this review, according to classification based on dimensionality, zero-dimensional, one-dimensional, two-dimensional, and three-dimensional nanostructures used in PEC bioanalysis are evaluated, with an emphasis on the effect of morphology on the detection performances. Furthermore, using the illustration of recent works, related novel PEC biosensing patterns with promising applications are also discussed. Finally, the current challenges and some future perspectives in this field are addressed based on our opinions.

AgCu@CuO aerogels with peroxidase-like activities and photoelectric responses for sensitive biosensing

Photoelectrochemical (PEC) enzymatic biosensors integrate the excellent selectivity of enzymes and high sensitivity of PEC bioanalysis, but the drawbacks such as high cost, poor stability, and tedious immobilization of natural enzymes on photoelectrodes severely suppress their applications. AgCu@CuO aerogel-based photoelectrode materials with both remarkable enzyme-like activities and outstanding photoelectric properties were innovatively designed and synthesized to evaluate the activity of xanthine oxidase with a wide linear detection range and a low limit of detection.

CRISPR/Cas12a-mediated liposome-amplified strategy for the photoelectrochemical detection of nucleic acid

This study reports a photoelectrochemical biosensor for dopamine-loaded liposome-encoded magnetic beads cleaved by clustered regularly interspaced short palindromic repeats (CRISPR)/Cas 12a system for the quantification of human papilloma virus (HPV)-related DNA using neodymium-doped BiOBr nanosheets (Nd-BiOBr) as a photoactive matrix. Magnetic beads and dopamine-loaded liposomes are covalently attached to the both ends of ssDNA to construct dumbbell-shaped dopamine-loaded liposome-encoded magnetic bead (DLL-MB) probes. When the guide RNA binds to the target HPV-16, the ssDNA will be cleaved by Cas12a, thereby degrading the double dumbbell probes. After magnetic separation, the dissolved DLLs are treated with Triton X-100 to release the dopamine (as an electron donor), which was then detected by an amplified photocurrent using the Nd-BiOBr-based photoelectrode.

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.

Construction of a Dye-Sensitized and Gold Plasmon-Enhanced Cathodic Photoelectrochemical Biosensor for Methyltransferase Activity Assay

DNA methyltransferases may function as important biomarkers of cancers and genetic diseases. Herein, we develop a dye-sensitized and gold plasmon-enhanced cathodic photoelectrochemical (PEC) biosensor on the basis of p-type covalent organic polymers (COPs) for the signal-on measurement of M.SssI methyltransferase (M.SssI MTase). The cathodic PEC biosensor is constructed by the in situ growth of p-type COP films onto a glass coated with indium tin oxide and the subsequent assembly of biotin- and HS-labeled double-stranded DNA (dsDNA) probes onto the COP film via biotin-streptavidin interaction. The dsDNA probe contains the recognition sequence of M.SssI MTase. The COP thin films possess a porous ultrathin nanosheet structure with abundant active sites, facilitating the generation of a high photocurrent compared with the hydrothermally synthesized ones. The presence of DNA methyltransferases can prevent the digestion of restriction endonuclease HpaII, consequently inducing the introduction of gold nanoparticles (AuNPs) to the dsDNA probes via the S-Au bond and the intercalation of rhodamine B (RhB) into the DNA grooves to produce a high photocurrent due to the dye-photosensitized enhancement and AuNP-mediated surface plasmon resonance. However, in the absence of M.SssI MTase, HpaII digests the dsDNA probes, and neither AuNPs nor RhB can be introduced onto the electrode surface, leading to a low photocurrent. This cathodic PEC biosensor possesses high sensitivity and good selectivity, and it can screen the inhibitors and detect M.SssI MTase in serum as well.

Two-dimensional WS2/MoS2 heterostructures: properties and applications

The successful fabrication of WS₂/MoS₂ heterostructures provides more possibilities for optoelectronic and thermoelectric applications than graphene because of their direct bandgap characteristics; therefore, scientific investigations on WS₂/MoS₂ heterostructures are more significant and thriving. In this paper, we review the latest research progress in WS₂/MoS₂ heterostructures, and look forward to their properties and applications. Firstly, we analyze the crystal structure and electronic structure of WS₂, MoS₂, and their heterostructures. Secondly, we comprehensively present the widely used methods for preparing heterostructures. Finally, based on the unique physical characteristics of WS₂/MoS₂ heterostructures, we focus on their properties and applications in mechanics, electronics, optoelectronics, and thermoelectronics.

Label-free and enzyme-free fluorescence detection of microRNA based on sulfydryl-functionalized carbon dots via target-initiated hemin/G-quadruplex-catalyzed oxidation

Carbon dots (CDs)-based biosensors have attracted considerable interest in reliable and sensitive detection of microRNA (miRNA) because of their merits of ultra-small size, excellent biosafety and tunable emission, whereas complicated labeling procedure and expensive bioenzyme associated with current strategies significantly limit their practical application. Herein, we developed a label-free and enzyme-free fluorescence strategy based on strand displaced amplification (SDA) for highly sensitive detection of miRNA using sulfydryl-functionalized CDs (CDs-SH) as probe. CDs-SH displayed excellent response to G-quadruplex DNA against other DNAs based on based on the catalytic oxidation of -SH into -S-S- by hemin/G-quadruplex. Further, CDs-SH were employed to detect miRNA, using miRNA-21 as target model, which triggered the SDA reaction of P1 and P2 to generate hemin/G-quadruplex, subsequently making CDs-SH transform from dot to aggresome along with the quenched fluorescence. Therefore, label-free, enzyme-free, and highly sensitive analysis of miRNA-21 was readily acquired with a limit of detection at 0.03 pM. This proposed biosensor couples the advantages of CDs and label-free/enzyme-free strategy, and thus has a significant potential to be used in early and accurate diagnosis of cancer.

In Situ Generation of Regularly Ordered 2D Ultrathin Covalent Organic Framework Films for Highly Sensitive Photoelectrochemical Bioanalysis

Developing new photoactive materials and electrode preparation technology with high stability, repeatability, easy fabrication, and a low electron-hole recombination rate is promising for ideal photoelectrochemical (PEC) biosensors, but it remains a great challenge. Here, a porous and crystalline oriented two-dimensional (2D) ultrathin covalent organic framework film (D-TA COF film) was formed in situ on indium-doped tin oxide (ITO) substrates under very mild conditions. The structure and morphology of D-TA COF film were characterized by means of Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and powder X-ray diffraction. Compared with the randomly oriented D-TA COF powder drop-coated on ITO, the photocurrent of the D-TA COF film grown on the ITO surface in situ achieved as high as ∼333-fold increase. This photocurrent can be further amplified by O₂ (acting as electron acceptors). Benefiting from the fabrication in situ, D-TA COF film also exhibited tough adhesion, assuring the film was difficult to separate from the electrode. Accordingly, D-TA COF film was applied as the photoactive material to build a PEC biosensor for H₂O₂ detection based on coupling with large amounts of catalase (CAT) through simple adsorption. The introduced CAT catalyzed the decomposition of H₂O₂ to O₂, leading to an enhancement of the photocurrent response. As a result, a "signal-on" PEC biosensor was fabricated with good sensitivity, rapid response, and high stability, and it can also detect H₂O₂ released from living cells. Taking into account these advantages, the D-TA COF film is expected to be an ideal photoactive material to construct various PEC biosensors, which as far as we know have not been reported.

Fabrication of a Greener TiO2@Gum Arabic-Carbon Paste Electrode for the Electrochemical Detection of Pb2+ Ions in Plastic Toys

A novel greener methodology is reported for the synthesis of titanium dioxide (TiO2) nanoparticles (NPs) using gum Arabic (Acacia senegal) and the characterization of the ensuing TiO2 NPs by various techniques such as X-ray diffraction (XRD), Fourier transform infrared, Raman spectroscopy, scanning electron microscopy-energy dispersive X-ray, transmission electron microscopy (TEM), high resolution-TEM, and UV-visible spectroscopy. The XRD analysis confirmed the formation of TiO2 NPs in the anatase phase with high crystal purity, while TEM confirmed the size to be 8.9 ± 1.5 nm with a spherical morphology. The electrode for the electrochemical detection of Pb2+ ions was modified by a carbon paste fabricated using the synthesized TiO2 NPs. Compared to the bare electrode, the fabricated electrode exhibited improved electro-catalytic activity toward the reduction of Pb2+ ions. The detection limit, quantification limit, and the sensitivity of the developed electrode were observed by using differential pulse voltammetry to be 506 ppb, 1.68 ppm, and 0.52 ± 0.01 μA μM-1, respectively. The constructed electrode was tested for the detection of lead content in plastic toys.