Anodic Response Research Articles

ECL and visual dual-mode detection of miRNA-21 based on HRP/Au NPs composite probe and CRISPR/Cas12a strategy

Signal-amplification sensing strategies for rapid and accurate detection of tumor marker miRNA is of great practical significance for cancer prevention and treatment. Catalytic hairpin assembly (CHA) nucleic acid amplification reaction and CRISPR/Cas12a strategies have exhibited huge prospect due to their flexible design and efficient signal amplification. We constructed an electrochemiluminescence (ECL) biosensor based on horseradish peroxidase/gold nanoparticles (HRP/Au NPs) nanocomposite probe and CRISPR/Cas12a (LbCpf1), and completed a dual-mode detection of miRNA-21. When the target RNA is present in the system, the CHA) cycle was initiated, and the double-stranded DNA containing a specific protospacer adjacent motif (PAM) base sequence was generated to successfully activate the trans-cut activity of CRISPR/Cas12a. After the prepared HRP/Au NPs nanocomposite probe was cleaved by CRISPR/Cas12a, the supernatant containing HRP was collected through magnetic separation and subsequently introduced to the cathode of the bipolar electrode facilitating anodic ECL luminescence response. In addition, the supernatant was added to the TMB chromogenic solution for chromogenic reaction. Thus, ECL detection and visual detection of miRNA-21 were realized. Dual-mode detection improves the accuracy of the sensor, and the utilization of bipolar electrodes on indium tin oxide (ITO) coated glass could also provide some useful references for further development of point-of-care detecting devices for early cancer prevention and diagnosis.

Novel N-doped ZnO and O-doped g-C₃N₄ heterojunction: Enhanced photocatalytic degradation and robust electrochemical biosensing of ascorbic acid

ZnO and g-C₃N₄ are known for their potential in photocatalytic degradation and electrochemical applications, but their limited band gaps and electrical conductivity hinders performance. Doping is a strategy to modify these properties. This study reports the synthesis of nitrogen-doped ZnO (N-ZnO) and oxygen-doped g-C₃N₄ (OCN) nanocomposites using an in-situ hydrothermal process. Structural and compositional analysis confirmed successful synthesis, while FESEM and HRTEM revealed N-ZnO nanorods decorating OCN sheets. Optical analysis indicated a band gap of 2.54 eV, making the material active under visible light. The nanocomposites demonstrated 90 % photodegradation of methylene blue (MB) within 20 min, with a high rate constant (k = 0.1269 min−1), facilitated by a Z-scheme heterojunction. The catalyst remained stable even after 5 cycles. Moreover, electrochemical biosensing of ascorbic acid (AA) showed a regression value of 0.9965 with high anodic current response and small limit of detection (LOD) value, underscoring the potential of nanocomposite material for commercial applications in both photocatalysis and diagnostics.

Modeling Reversible Volume Change in Automotive Battery Cells with Porous Silicon Oxide-Graphite Composite Anodes

Automotive battery manufacturers are working to improve the individual cell and overall pack design by increasing durability, performance, and range, while reducing cost, and active material volume change is a key aspect that needs to be considered during this design process. Recently, silicon oxide-graphite composite anodes are being explored to increase total anode capacity while maintaining a tolerable amount of cell level reversible volume expansion due to the relatively lower reversible volume change of the silicon oxide compared to pure battery grade or metallurgical grade silicon. To predict the blended anode response and contribution to the overall cell volume change, we integrated the mechanical behavior of the individual active materials with the multi-species, multi-reaction model to predict the state-of-lithiation of the active materials in the cell at a given potential. The resulting simulations illustrate the tradeoff in volume change between the silicon oxide and the graphite during cell operation. This type of modeling approach will allow designers to virtually consider the impact of cell level and pack level design changes on overall system mechanical performance for automotive and grid storage applications, namely that relatively small addition of silicon containing materials can drive a significant increase in the volume change at the cell level, as demonstrated by the 5 wt% addition of silicon oxide accounting for half of the overall volume change in the cell.

Unraveling the Corrosion of the Ti–6Al–4V Orthopedic Alloy in Phosphate-Buffered Saline (PBS) Solution: Influence of Frequency and Potential

This paper addresses the interplay between electrical fields in the human body and the corrosion behavior of Ti-6Al-4V alloy, a prevalent orthopedic material. The study investigates the impact of alternative electrical signals at different frequencies on the alloy’s electrochemical behavior in a simulated body environment. The human body always has natural sinusoidal potential due to, e.g., heart palpitations and brain/nervous system activities. Ignoring such natural activities may lead to underestimating the corrosion performance of the Ti-6Al-4V alloy in the body. By analyzing anodic and cathodic responses and the net faradaic current induced by alternating current potential, the research sheds light on the influence of electrical fields on corrosion rates. Understanding these dynamics could lead to improved implant materials, mitigating corrosion-related challenges and enhancing implant performance over the long term. Results of this work indicated that frequent oxidation and reduction at certain frequencies may induce corrosion and hinder biomimetic apatite formation, impacting osseointegration. Natural alternative currents in the body affect the corrosion performance of Ti-based implant alloys, highlighting the need for consideration in biomedical applications.

Density functional theory analysis of Na4Mn4Ti5O18 for sodium ion battery electrode

Density functional theory study has been performed on Na4Mn4Ti5O18 to evaluate its application feasibility as an electrode in Na ion battery. Two types of void in the structure of Na4Mn4Ti5O18, viz., Z shaped tunnel and polyhedral pentagonal void, has been observed that act as guest sites for reversible migration of Na+ ions. It is also noted that electrochemically active sites are placed in Z shaped tunnel that act as host for Na+ during anodic response while it acts as the Na+ donor during cathodic response. The Mn atom, located in the Z-shape tunnel, acts as redox active site for both cathodic and anodic response via formation of redox couple Mn+3/Mn+4 and Mn+3/Mn+2 respectively. On the other hand, Mn atom present at square pyramidal site remains inert during charge–discharge process. The redox action in Na4Mn4Ti5O18, occurring due to intercalation and de-intercalation of 2Na+ ions per formula unit, has been noted to exhibit voltage ∼2.63 V and 3.82 V respectively. The theoretical capacity ∼128 mAhg−1 has been estimated corresponding to migration of 2Na+ in Na4Mn4Ti5O18 structure. The present simulation study indicates the possibility of electrode action in Na4Mn4Ti5O18 for sodium ion battery application.

Utilizing as-synthesized Reduced Graphene Oxide Decorated with Mn1−xZnxFe2−yCuyO4 Doped Magnetic Nanoparticles for Efficient Electrochemical Sensing of Paracetamol

A highly sensitive sensor for paracetamol detection based on the copper and zinc doped manganese ferrite/reduced graphene oxide modified glassy carbon electrode (Mn1−xZnxFe2−yCuyO4/rGO/GCE) is ameliorated. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectrometry (FTIR), zeta-sizer, cyclic voltammetry, and electrochemical impedance spectroscopy are used to examine the structural, morphological, electroanalytical capability of the designed sensor. Results are correlated systematically for the copper/zinc doped manganese ferrite/reduced graphene oxide modified glassy carbon electrode and it is observed that the sensor exhibits two linear ranges as 5–9 μmol l−1 and 9–200 μmol l−1 under the optimized conditions. Doped composite-modified GCE demonstrates an exceptional limit of detection (LOD) (0.04 μmol l−1) and the limit of quantification (LOQ) (0.15 μmol l−1). The possible effect of structurally similar drugs on the anodic current response of paracetamol is evaluated. By analyzing the current generation of the actual pharmaceutical samples, the practical application of the manufactured sensor is assessed. Promising results demonstrated by modified GC electrode affirm its excellent analytical performance for the sensing of paracetamol with trace-level detection and high sensitivity.

Electropolymerization of poly(phenol red) on laser-induced graphene electrode enhanced adsorption of zinc for electrochemical detection

We present a highly sensitive and selective electrode of laser-induced graphene modified with poly(phenol red) (P(PhR)@LIG) for measuring zinc nutrition in rice grains using square wave anodic stripping voltammetry (SWASV). The physicochemical properties of P(PhR)@LIG were investigated with scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), Fourier infrared spectroscopy (FT-IR) and Raman spectroscopy. The modified electrode demonstrated an amplified anodic stripping response of Zn2+ due to the electropolymerization of P(PhR), which enhanced analyte adsorption during the accumulation step of SWASV. Under optimized parameters, the developed sensor provided a linear range from 30 to 3000 μg L−1 with a detection limit of 14.5 μg L−1. The proposed electrode demonstrated good reproducibility and good anti-interference properties. The sensor detected zinc nutrition in rice grain samples with good accuracy and the results were consistent with the standard ICP-OES method.

Evaluation of anti-corrosion potential of Datura Metel plant extract on mild steel upon sulphuric acid exposure

ABSTRACT The present study was aimed to investigate the Datura metel plant extract’s anti-corrosion ability on mild steel against sulphuric acid. A comprehensive set of experiments using conventional methodology were employed for asserting the efficacy and velocity of corrosion inhibitory performance. It was found that the effectiveness of inhibition was 85.73%. The results showed that potentiodynamic polarisation causes inhibition regulated anodic responses. Both factors, linear polarisation resistance and corrosion current were improved by the inhibitors. The protective layer on a vulnerable surface has been induced by the phenomenon known as the ‘blanket effect’. The observed outcome may be attributed to the constraints imposed by the experimental methodology. The protective layer composition of mild steel was analysed using FTIR spectroscopy. Additionally, SEM analysis revealed the protective layer was neither smooth nor rough. In summary, the extract derived from Datura metel could be a potential green inhibitor to act as an anti-corrosion agent.

Bimetallic metal organic framework/Ni doped ZnO nanomaterials modified carbon paste electrode for selective electrochemical determination of ciprofloxacin.

In this work, an efficient and sensitive electrochemical sensor for the determination of ciprofloxacin (CIP) is reported. The sensor was prepared by using a carbon paste electrode (CPE) modified with a combination of bimetallic copper/cerium-based metal organic framework (Cu/Ce-MOF) and nickel doped zinc oxide nanoparticles (NZP). The modifiers were characterized by Brunauer-Emmett-Teller (BET) analysis, Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and elemental mapping analysis (EDS). The electrochemical behavior of the modified electrode was studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The developed electrode was employed for the detection of CIP by differential pulse voltammetry (DPV). Under optimal conditions, the anodic peak current response of the electrode was linearly correlated with CIP concentration in the range of 0.75-100 μmol L-1 with a sensitivity of 1.29 μA μmol-1 L-1. The limit of detection and reproducibility of the method were 0.142 μmol L-1 and 2.7%, respectively. The developed sensor showed good selectivity to CIP against possible interferents. The method was applied to determine CIP in water, milk and urine samples. The results indicated that this method has potential to be applied in the analysis of residue CIP in complex matrices with high selectivity, and good reproducibility.

Thorn apple (Datura stramonium) extract acts as a sustainable corrosion inhibitor for zinc alloy in hydrochloric acid solutions

The inhibition effectiveness of diverse concentrations of Datura Fruit Extract (DFE) on the corrosion of zinc in 0.05–0.1 M HCl solutions was examined by weight loss (WL), Electrochemical Impedance Spectroscopy (EIS), potentiodynamic polarization (PDP), and surface analysis techniques. The mass loss method's results demonstrated that raising the DFE concentration improved the efficiency of the inhibition. The maximum inhibition efficiency was 99.40% at 2.0 g/L of DFE. In the temperature ranging from 303 to 333 K, the effect of temperature on the corrosion behavior while adding DFE was also investigated. A DFE extract had been adsorbed on the surface of the metal by Langmuir adsorption isotherm models. It was established that the DFE's activation parameters and negative Gibb's free energy show that rates of adsorption have been spontaneous. According to polarization analysis, DFE regulates both the cathodic and the anodic response. Images obtained using a SEM (Scanning Electron Microscope) reveal that the DFE reduces surface damage. The adsorption inhibition mechanism is supported by the AFM analysis findings. FT-IR (Fourier transform infrared) spectroscopy has been utilized to ascertain the functional group of the DFE. All of the applicable approaches' experimental findings are in good agreement.

Dual-channel MIRECL portable devices with impedance effect coupled smartphone and machine learning system for tyramine identification and quantification.

We designed a novel, portable, and visual dual-potential molecularly imprinted ratiometric electrochemiluminescence (MIRECL) sensor for tyramine (TYM) detection based on smartphone and deep learning-assisted optical devices. Molecularly imprinted polymer-Ce2Sn2O7 (MIP-Ce2Sn2O7) layers were fabricated by in-situ electropolymerization method as the capture and signal amplification probe. Oxygen vacancies in Ce2Sn2O7 not only enhance the electrochemical redox capability but also accelerate the energy transfer, thereby enhancing the luminescence of cathode ECL. Under optimal conditions, the ECL signals of MIP-Ce2Sn2O7 at the cathode and the anode response of Ru(bpy)32+ was reduced, thus a wide linear range from 0.01μM to 1000μM with the detection limit as low as 0.005μM. Interestingly, combined with an artificial intelligence image recognition algorithm and the principle of optical signal reading by smartphone, the developed MIRECL sensor has been applied to the portable and visual determination of TYM in aquatic samples, and its practicability has been satisfactorily verified.

Bio-inspired benign synthesis of Cr doped ZnO nanoparticles towards electrochemical detection of Bovine Serum Albumin

In this study, we aimed to synthesize monodisperse chromium-doped zinc oxide (Cr-ZnO) nanoparticles (NPs) through green synthesis for the construction of a highly sensitive electrochemical biosensor for BSA detection. Characterization techniques such as X-ray diffraction, FTIR spectroscopy, UV-Vis absorption, and photoluminescence studies confirmed the structural, chemical, and optical properties of the synthesized NPs. FESEM and EDS analysis revealed a spherical nodular morphology with a cauliflower-shaped structure. Nano-bio interaction studies between Cr-ZnO NPs and BSA were conducted using UV-Vis absorption and PL measurements, indicating fluorescence quenching due to complex formation. The synthesized NPs were utilized as electrode material for an electrochemical sensor, demonstrating sensitivity and selectivity in detecting BSA concentrations within the range of 1.5 nM to 48 nM. The sensor's response was linear, showing a decrease in anodic peak current response from 5.08 µA to 3.48 µA for different BSA concentrations. Remarkably, the optical interaction results mirrored the electrochemical findings, emphasizing the consistency between the two methods. The linear response of the electrochemical sensor, coupled with its optical interactions, suggests the versatility and reliability of the synthesized NPs for biosensing applications. With a simple setup requiring minimal samples, the electrochemical sensor offers an inexpensive, rapid, and sensitive screening method for BSA. These findings underscore the potential of the synthesized NPs as a promising electrochemical surface for biosensors, with implications for diagnostic and therapeutic applications, particularly in the context of cattle-related research.

A novel MB-tagged aptasensor for Aflatoxin B1 detection in food using Fe3O4 nanoparticles substantiated with in silico modelling

Aspergillus fungi species found in wheat, maize, rice, and other agricultural products produce the carcinogenic mycotoxin known as Aflatoxin B1 (AFB1), which can cause cancer in animals and humans. Consequently, recent interest has surged regarding the need for inexpensive, selective, and sensitive sensors to detect AFB1 in food. An ultrasensitive electrochemical aptasensor for AFB1 analysis was constructed using carboxylated multiwalled carbon nanotubes (cMWCNTs) and iron oxide (Fe3O4) nanoparticles (NP) on a glassy carbon electrode (GCE). The peptide bond formation by EDC coupling between the aptamer and cMWCNTs-Fe3O4 NP composite exhibited a strong anodic redox response from AFB1 using cyclic voltammetry (CV) in this study. Applying differential pulse voltammetry (DPV), the GCE/cMWCNTs-Fe3O4 NP aptasensor exhibited very low limits of detection (LOD) and quantification (LOQ) of 0.43 fg mL−1 and 1.44 fg mL−1 respectively over a calibration ranging from 0.50 fg mL−1 to 5.00 fg mL−1. For actual sample analysis, excellent spike recoveries from 95 to 105% were obtained for corn and rice flour. Single particle ICP-MS (spICP-MS) confirmed the average mass-based diameter of the synthesized Fe3O4 NPs to be in the nano-range (d ≈ 20 nm), the properties of which are essential for the facilitation of strong electron transfer in DPV sensing. Finally, density functional theory and molecular docking studies predicted the sensing mechanism and supported deductions based on the AFB1 capture by the employed aptamer respectively. As part of South Africa’s quality control and regulatory frameworks, this study aims to contribute toward the prevention of AFB1 exposure in foods.

Decoding Internal Stress‐Induced Micro‐Short Circuit Events in Sulfide‐Based All‐Solid‐State Li‐Metal Batteries via Operando Pressure Measurements

AbstractDespite the relatively low stiffness of sulfide solid‐state electrolytes (SSEs), which makes them capable of better formability and accommodation for volume changes of active materials, the low fracture toughness (KIC) indicates a high susceptibility to fracture caused by electrochemo‐mechanical stresses. This susceptibility to mechanical damages and the subsequent lithium filament penetration, manifesting as micro‐short circuit events, seriously hinders the practical application of lithium metal in high‐energy‐density sulfide‐based all‐solid‐state lithium metal batteries (ASSLMBs). A full understanding of the stress evolution of Li metal anodes during cycling is key to decoding the mechanical damage‐induced micro‐short circuit behavior. Here, an operando and quantitative measurement of the stress evolution of an LTO/SSE/Li configuration all‐solid‐state battery (ASSB) operating with various parameters, including cell capacity and current density, is shown. Two micro‐short circuit modes and their corresponding mechanisms are revealed based on the electrochemo‐mechanical response of the Li metal anode. Furthermore, a finite element model (FEM) is used to explain this mechanical failure and a ′safety zone″ for the Li metal anode related to the ′internal stress″ is given. These findings provide new insight into the micro‐short circuit events induced by electrochemo‐mechanical damage in sulfide‐based ASSLMBs.

Eco-friendly fabrication of V2O5@GO hybrids for direct glucose electrooxidation and sensing: An alternative to noble metals

In the search for efficient electrocatalysts for the electrooxidation of glucose, we present a hybrid nanomaterial V2O5@GO whose GO is obtained from by environmentally friendly electrochemical exfoliation of graphite. In a 0.01 M NaOH environment, the novel hybrid material showed clear electrooxidation peaks. The forward scan was consistent with the hydrogen abstraction reaction mechanism, while the reverse scan followed the chemisorption model. Notably, at 0.25 V, the hybrid showed better glucose electrooxidation performance in the reverse scan compared with previously reported electrodes based on noble metals, thus highlighting the importance of the electrochemical exfoliation process. With a consistent linear anodic current response at glucose concentrations from 0.5 to 7.5 mM, the V2O5@GO material proves to be a promising and cost-effective alternative for glucose sensors and biofuel cell applications.

Mxene quantum dots bipolar electrochemiluminescent platform for hepatitis C virus envelope protein E2 detection

A burgeoning diversified closed bipolar electrochemiluminescent (d-BPE-ECL) based on photothermal amplification biosensor via the thermophysical and photochemical properties of niobium carbide Mxene quantum dots (Nb2C MQDs) has been proposed. The device consists of three components: separated intermediate recognition, cathodic catalytic hydrogen evolution reaction (HER) and anodic ECL response channel. Wherein, the recognition compartment was innovatively designed as a temperature-sensitive conductivity modulated interface, and the introduction of photothermal material PDA@Nb2C MQDs through target mediated rolling circle amplification strategy increases the interface temperature under near-infrared light radiation, thereby enhancing the BPE current and leading to the amplification of the anode ECL signal of Nb2C MQDs. In addition, MoS2@Ni–Cu–P features excellent electrocatalytic activity, which can promote HER and thus accelerate electron transfer, further amplifying the ECL signal. Therefore, a highly sensitive d-BPE-ECL biosensor for hepatitis C virus envelope protein E2 detection with a linear range from 10−4 to 10 ng/mL and detection limit of 3.3 × 10−5 ng/mL was obtained. This work is expected to provide a new direction for exploring BPE multiple signal amplification strategy and broaden the application of BPE-ECL in bioassays.

Anthracene electrochemical sensor at fMWCNTs/ZnO modified glassy carbon electrode

The development of efficient and sensitive methods for polycyclic aromatic hydrocarbon (PAH) determination is necessitated by their potential environmental and health hazards. This study explores the application of glassy carbon electrode (GCE) modified with a nanocomposite of zinc oxide nanoparticles (ZnO NPs) reinforced functionalized multi-walled carbon nanotubes (fMWCNTs) as electrochemical sensor in the determination of anthracene. The functional, structural, and morphological properties of the nanomaterials were examined using techniques such as X-ray powder diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), which validated the authenticity of the synthesis. Fabrication of the glassy carbon electrode was done utilizing the drop-coating method and the electrochemical properties probed in 10 mM [Fe(CN)6]3-/4- redox probe via electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The nanocomposite-modified electrode, GCE/fMWCNTs/ZnO NPs recorded the highest anodic current response in the redox probe towering well above the other electrodes - bare GCE, GCE/ZnO NPs and GCE/fMWCNTs. The synergy between ZnO NPs and the fMWCNTs suggests accelerated transport of electrons between the ferrocyanide - ferricyanide redox probe and the modified electrode. Thereafter, the nanocomposite was explored for anthracene determination using CV and square wave voltammetry. With a similar performance in 0.4 μM anthracene, the GCE/fMWCNTs/ZnO NPs generated a higher cyclic voltammetry anodic current response of (459.05 μA), in contrast to the other electrodes - GCE/fMWCNTs (288.82 μA) GCE/ZnO NPs (19.67 μA), and the bare GCE (16.41 μA) at a scan rate of 25 mV/s, revealing very good electrocatalytic activity. A linear correlation (over a range of 9–75 µM) between the anodic current response and anthracene concentration yielded a micromole limit of detection of 1.27 µM. The proposed electrode was successfully used for the quantitation of anthracene in wastewater.

Engineering 2D heterostructured VS2-rGO-Ni nanointerface to stimulate electrocatalytic water splitting and supercapacitor applications

The electrochemical oxygen evolution reaction (OER) is a key anodic response that turns renewable energy into fuels. Overcoming the obstacles (sluggish kinetics) in OER requires the development of a highly active electrocatalyst with excellent stability. For the first time, this study presents a new kind of nanostructured morphology of VS2-rGO-Ni ternary system for alkaline OER. A systematic investigation was carried out to optimize the excellent electrocatalyst using different arrays in the binary and ternary composites. The homogeneous and well-interconnected network structure is identified between the VS2 nanosheets (∼20 nm thickness) and rGO layered structure, including the dispersion of Ni nanoparticles. The OER performances of VS2-rGO-Ni-3 (rVN-3) in 1 M KOH were excellently stimulated, where the overpotential was lowered to 192 mV at 10 mA cm−2. After 2500 CV cycles and chronopotentiometry tests (10 mA cm−2), the electrocatalyst showed long-term stability without losing much activity. Although, the electrocatalysts were assembled in rVN-3||rVN-3 required cell voltage of 1.70 V which is able to achieve the threshold current density. The interfacial interaction between the VS2, rGO and Ni in the ternary composite leads to synergistic effect that significantly promotes the adsorption of oxygenated intermediates for an excellent OER process. Moreover, rVN-3 provided a reasonable supercapacitor performances, which confirms the multi characteristics properties. The nanostructured morphology with a well-connected network structure provides a large active surface for interacting with charge species and stable performance.

Fabrication of an electrochemical sensor based on eggshell waste recycling for the voltammetric simultaneous detection of the antibiotics ofloxacin and ciprofloxacin

In this work, an accurate, highly sensitive, and economical electrochemical sensor based on a carbon paste electrode modified by Ca2CuO3 nanostructure (Ca2CuO3 NS) was constructed using Eggshell waste recycling as a cheap source of calcium. The Ca2CuO3 NS was analyzed using FTIR, SEM, and XRD measurements. The synthesized nanomaterials utilized for the first time to enhance the electrocatalytic efficiency of carbon paste electrode (CPE) toward fluoroquinolones antibiotics ofloxacin (OFL) and ciprofloxacin (CIP), The drugs used to treat pneumonia caused by COVID-19. The synthesized Ca2CuO3 NS dramatically enhanced the anodic peak response of CPE toward both drugs compared to the unmodified one and other modified electrodes. The simultaneous detection of the two antibiotics was performed in the linear range of 0.09–1.0 μM for OFL and 0.05–0.8 μM for CIP with the LOD of 0.027 μM and 0.012 μM, respectively. The suggested method was applied successfully to determine OFL and CIP in real samples.

Polarity Conversion of the Ag2S/AgInS2 Heterojunction by Radical-Induced Positive Feedback Polydopamine Adhesion for Signal-Switchable Photoelectrochemical Biosensing.

Efficient tuning of the polarity of photoactive nanomaterials is of great importance in improving the performance of photoelectrochemical (PEC) sensing platforms. Herein, polarity of the Ag2S/AgInS2 heterojunction is converted by radical-induced positive feedback polydopamine (PDA) adhesion, which is further employed to develop a signal-switchable PEC biosensor. In the nanocomposites, Ag2S and AgInS2 achieve electron-hole separation, exhibiting a strong anodic PEC response. Under the irradiation of light, the Ag2S/AgInS2 heterojunction is able to produce superoxide radical and hydroxyl radical intermediate species, leading to the polymerization of dopamine (DA) and the subsequent adhesion of PDA onto the Ag2S/AgInS2 heterojunction (Ag2S/AgInS2@PDA). By constructing a new electron-transfer pathway with PDA, the polarity of the Ag2S/AgInS2 heterojunction is converted, and the PEC response changes from anodic to cathodic photocurrents. In addition, since the photoreduction activity of PDA is stronger than that of the Ag2S/AgInS2 heterojunction, more superoxide radical can be produced by Ag2S/AgInS2@PDA once PDA is generated, thereby promoting the generation of PDA. Consequently, a positive feedback mechanism is established to enhance the polarity conversion of the Ag2S/AgInS2 heterojunction and amplify the responding to DA. As a result, the bioanalytical method is capable of sensitively quantifying DA in 10 orders of magnitude with an ultralow limit of detection. Moreover, the applicability of this biosensor in real samples is identified by measuring DA in fetal bovine serum and compared with a commercial ELISA method. Overall, this work offers an alternative perspective for adjusting photogenerated carriers of nanomaterials and designing high-performance PEC biosensors.