Photoelectrochemical bioanalysis: A mini review

Trends in conductive MOFs for sensing: A review

Metal-organic frameworks (MOFs) are porous, ordered arrays formed by coordination bonds between organic ligands and metal ions or clusters. The highly tunable properties of the MOF structure and performance make it possible to meet the needs of many applications. Conductive MOFs are essential in the domain of sensing due to their electrical conductivity, porosity, and catalytic properties, offering an effective platform for detection. Numerous sensing devices that utilize conductive MOFs have been created. This text presents a thorough overview of the diverse applications of conductive MOFs within the sensing field. The results of this work provide insights into the properties and synthesis methods of conductive MOFs and the working mechanisms of sensors based on conductive MOFs, which will help to deepen the study of such materials, provide a new vision for the design and production of novel functional materials, and promote the development and application of sensors based on conductive MOFs.

Target Recognition-Triggered Interfacial Electron Transfer Model: Toward Signal-On Photoelectrochemical Aptasensing for Efficient Detection of Staphylococcus aureus Using Ti3C2Tx-Au NBPs/ZnO NR Composites

Staphylococcus aureus (S. aureus) is one of the most common foodborne pathogens worldwide, which poses a great threat to public health. It is of utmost importance to develop rapid, simple, and sensitive methods for the determination of S. aureus. A signal-on photoelectrochemical (PEC) aptasensor is constructed herein based on titanium carbide (Ti3C2Tx)-Au nanobipyramids (NBPs)/ZnO nanoarrays (NRs). The reliability and capability of the PEC aptasensor make it suitable for the sensitive and selective determination of S. aureus. First, the electrostatically self-assembled Ti3C2Tx-Au NBP nanomaterial was coated on the ZnO NR surface by a spin-coating method. On the one hand, Ti3C2Tx-Au NBPs can broaden the spectral absorption of ZnO NRs, resulting in Ti3C2Tx-Au NBPs/ZnO NR composites that exhibit a wide range of absorption from the ultraviolet to the infrared region. On the other hand, Ti3C2Tx can reduce the agglomeration of nanoparticles, while Au NBPs can effectively fix the aptamer through the Au-S bond. Specifically, the experimental results show that when S. aureus is present, the Au NBPs-aptamer-S. aureus complex is shed from the electrode surface, altering the interfacial electron transfer model and reducing the steric hindrance. Consequently, an amplified photocurrent signal for the quantitative determination of S. aureus is obtained. Under optimal experimental conditions, a linear correlation is observed between the current response of the aptasensor and the logarithm of the S. aureus concentration (ranging from 1.0 to 1.0 × 106 CFU/mL), with an impressive detection limit as low as 0.5 CFU/mL. Furthermore, the aptasensor has been successfully employed for the detection of S. aureus in milk, with the recovery of 93.0%-99.0%. Hence, this research offers a novel approach for the detection of foodborne pathogens and other noxious substances.

Organic photoelectrochemical transistor based on cascaded DNA network structure modulated ZnIn2S4/MXene Schottky junction for sensitive ATP detection

Organic photoelectrochemical transistor (OPECT) biosensor is now appearing in perspective of public, which characterized by amplified the grating electrode potential by ion transport. In this study, the DNA network formed by the hybridization chain reaction (HCR) detects the target adenosine triphosphate (ATP) by adjusting the surface potential of the new heterojunction of ZnIn2S4/MXene. The formation of DNA network amplifies the detection signal of ATP. Significantly, OPECT biosensor could further amplify the signal, which calculated the gain achieved 103, which is consistent with the gain signal of the previously reported OPECT biosensor. Furthermore, the OPECT biosensor achieved a highly sensitivity detection of the target ATP, which the linear detection range is 0.03 pM-30 nM, and the detection limit is 0.03 pM, and illustrated a high selectivity to ATP. The proposed OPECT biosensor achieved signal amplification by adjusting the surface potential of ZnIn2S4/MXene through cascade DNA network, which provides a new direction for the detection of biomolecules.

Photoelectrochemical detection of copper ions based on a covalent organic framework with tunable properties

Copper ions (Cu2+) play an essential role in various cellular functions, including respiration, nerve conduction, tissue maturation, oxidative stress defense, and iron metabolism. Covalent organic frameworks (COFs) are a class of porous crystalline materials with directed structural designability and high stability due to the combination of different monomers through covalent bonds. In this study, we synthesized a porphyrin-tetrathiazole COF (TT-COF(Zn)) with Zn-porphyrin and tetrathiafulvalene (TTF) as monomers and used it as a photoactive material. The strong light absorption of metalloporphyrin and the electron-rich properties of supplied TTF contribute to its photoelectrochemical performance. Additionally, the sulfur (S) in the TTF can coordinate with Cu2+. Based on these properties, we constructed a highly sensitive photoelectrochemical sensor for detecting Cu2+. The sensor exhibited a linear range from 0.5 nM to 500 nM (R2 = 0.9983) and a detection limit of 0.15 nM for Cu2+. Notably, the sensor performed well when detecting Cu2+ in water samples.

Recent Trends in Self-Powered Photoelectrochemical Sensors: From the Perspective of Signal Output

Revolutionary developments in analytical chemistry have led to the rapid development of self-powered photoelectrochemical (PEC) sensors. Different from conventional PEC sensors, self-powered PEC sensors do not require an external power source or complex devices for the sensitive detection of targets. As a result, these sensors have enormous application potential for the development of novel portable sensors. An increasing body of work is making excellent progress toward the implementation of self-powered PEC sensors for detection, but there have been no reviews to date. The present review first introduces the state of the art in the development of self-powered PEC sensors. Then, different types of self-powered PEC sensors are summarized and discussed in detail, including their current, power, and potential. Additionally, single- and dual-photoelectrode systems are classified and systematically compared. Finally, the current developments and major challenges that need to be addressed are also summarized. This review provides valuable insights into the current state of self-powered PEC sensors to promote further progress in this field.

Photoelectrochemical Enzyme Biosensor for Malate Using Quantum Dots on Indium Tin Oxide/Plastics as a Sensing Surface

A photoelectrochemical biosensor for malate was developed using an indium tin oxide (ITO) layer deposited on a poly(ethylene terephthalate) plastic sheet as a transparent electrode material for the immobilization of malate dehydrogenase together with CdTe quantum dots. Different approaches were compared for the construction of the bioactive layer; the highest response was achieved by depositing malate dehydrogenase together with CdTe nanoparticles and covering it with a Nafion/water (1:1) mixture. The amperometric signal of this biosensor was recorded during irradiation with a near-UV LED in the flow-through mode. The limit of detection was 0.28 mmol/L, which is adequate for analyzing malic acid levels in drinks such as white wines and fruit juices. The results confirm that the cheap ITO layer deposited on the plastic sheet after cutting into rectangular electrodes allows for the economic production of photoelectrochemical (bio)sensors. The combination of NAD+-dependent malate dehydrogenase with quantum dots was also compatible with such an ITO surface.

Dual-mode sensing chip for photoelectrochemical and electrochromic visual determination of deoxynivalenol mycotoxin

The successful development of a dual-mode sensing chip for deoxynivalenol (DON) detection using photoelectrochemical (PEC) and electrochromic visualization techniques is reported. By laser etching technology, different functional areas, including the photoanode, the cathode, and the electrochromic area, are fabricated on indium tin oxide (ITO) glass. Then, these three areas are further respectively modified with PEC active materials, platinum nanoparticles, and Prussian blue. Under light illumination, photocurrents generate between the photoanode and the cathode due to the separation of photo-induced electrons and holes in the TiO2/3DNGH material. Meanwhile, the photo-induced electrons are transferred to Prussian blue on the visualization area, which will be reduced to colorless Prussian white. The binding of DON molecules and aptamers can promote electron transfer and reduce the recombination of electrons and holes, allowing for simultaneous quantitative detection of DON using either the photocurrent or color change. The sensor chip has a broad detection range of DON concentrations of 1 fg⋅mL-1 to 100 pg⋅mL-1 in the PEC mode with the limit of detection of 0.37 fg⋅mL-1, and 1 to 250 ng⋅mL-1 in the visualization mode with the limit of detection of 0.51 ng⋅mL-1. This portable dual-mode sensor chip can be used in both laboratory and field settings without the need for specialized instruments, making it a powerful tool for ensuring food safety. At the same time, the analysis of the standard addition method of the actual sample by using the sensor chip shows that, in the PEC mode, the recoveries of the dual-mode aptasensor chip were 91.3 to 99.0% with RSD values of 1.73~2.55%, and in visualization mode, the recoveries of the dual-mode aptasensor chip were 99.2 to 102.0% with RSD values of 1.00~6.21%, which indicate good accuracy and reproducibility.

Molecularly imprinted polymers for per- and polyfluoroalkyl substances enrichment and detection

Per- and polyfluoroalkyl substances (PFAS) are highly toxic pollutants of significant concern as they are being detected in water, air, fish and soil. They are extremely persistent and accumulate in plant and animal tissues. Traditional methods of detection and removal of these substances use specialised instrumentation and require a trained technical resource for operation. Molecularly imprinted polymers (MIPs), polymeric materials with predetermined selectivity for a target molecule, have recently begun to be exploited in technologies for the selective removal and monitoring of PFAS in environmental waters. This review offers a comprehensive overview of recent developments in MIPs, both as adsorbents for PFAS removal and sensors that selectively detect PFAS at environmentally-relevant concentrations. PFAS-MIP adsorbents are classified according to their method of preparation (e.g., bulk or precipitation polymerization, surface imprinting), while PFAS-MIP sensing materials are described and discussed according to the transduction methods used (e.g., electrochemical, optical). This review aims to comprehensively discuss the PFAS-MIP research field. The efficacy and challenges facing the different applications of these materials in environmental water applications are discussed, as well as a perspective on challenges for this field that need to be overcome before exploitation of the technology can be fully realised.

Semiconductor quantum dots in photoelectrochemical sensors from fabrication to biosensing applications

Semiconductor quantum dots (QDs) are a promising class of nanomaterials for developing new photoelectrodes and photoelectrochemistry systems for energy storage, transfer, and biosensing applications. These materials have unique electronic and photophysical properties and can be used as optical nanoprobes in displays, biosensors, imaging, optoelectronics, energy storage and energy harvesting. Researchers have recently been exploring the use of QDs in photoelectrochemical (PEC) sensors, which involve exciting a QD-interfaced photoactive material with a flashlight source and generating a photoelectrical current as an output signal. The simple surface properties of QDs also make them suitable for addressing issues related to sensitivity, miniaturization, and cost-effectiveness. This technology has the potential to replace current laboratory practices and equipment, such as spectrophotometers, used for testing sample absorption and emission. Semiconductor QD-based PEC sensors offer simple, fast, and easily miniaturized sensors for analyzing a variety of analytes. This review summarizes the various strategies for interfacing QD nanoarchitectures for PEC sensing, as well as their signal amplification. PEC sensing devices, particularly those used for the detection of disease biomarkers, biomolecules (glucose, dopamine), drugs, and various pathogens, have the potential to revolutionize the biomedical field. This review discusses the advantages of semiconductor QD-based PEC biosensors and their fabrication methods, with a focus on disease diagnostics and the detection of various biomolecules. Finally, the review provides prospects and considerations for QD-based photoelectrochemical sensor systems in terms of their sensitivity, speed, and portability for biomedical applications.

Band gap and defect engineering of bismuth vanadate using La, Ce, Zr dopants to obtain a photoelectrochemical system for ultra-sensitive detection of glucose in blood serum

Bismuth vanadate (BiVO₄) is a promising photoactive material for the design of photoelectrochemical (PEC) analytical devices for the non-enzymatic detection of glucose. In this work, un-doped and La/Ce/Zr doped BiVO₄ photo anodes were developed by spray pyrolysis coating to generate unique 2D hierarchical architectures using the facile ultrasonic spray coating technique without any complex pre or post-treatment. The influence of different dopants on the morphology and photoelectrochemical activity of BiVO₄ coatings was investigated. X-ray diffraction, scanning electron microscopy, UV-vis optical absorbance, and positron annihilation techniques were used to evaluate the structure, defects, and optical properties of BiVO₄ films. DFT simulation confirmed the Zr doping induced band gap reduction in the BiVO₄ lattice. The Zr doping on the Bi site in BiVO₄ lattice provided significantly low Bi and V-based defect density and a higher bulk diffusion length of charge pairs (4 times that of pristine) as well as charge transfer efficiency and this led to the foremost photocurrent for water splitting. The Zr-doped BiVO₄ photo anode showed remarkable sensitivity in glucose sensing. The sensitivity and limit of detection of the Zr-doped BiVO₄ PEC device towards glucose were 0.14 mA cm^-2 mM^-1 and 1.22 μM, respectively, in the concentration range of 1-7 mM. The system showed sensitive detection of glucose in blood serum. This is the first time that a 2D morphology electrode design consisting of Zr-doped BiVO₄, which leads to exceptionally high sensitivity for glucose sensing, has been reported.

A near-infrared light-driven photoelectrochemical aptasensing platform for adenosine triphosphate detection based on Yb-doped Bi2S3 nanorods

Due to its capability of low spectral interference, high light stability, and minimal photodamage to biological species, near-infrared (NIR) light is advantageous in biosensing and biochemical analysis. This work developed a photoelectrochemical (PEC) aptasensor for adenosine triphosphate (ATP) detection using NIR light as the irradiation source. In order to utilize NIR light, we prepared Yb-doped Bi₂S₃ (Yb-Bi₂S₃) nanorods to act as photoelectric transducing materials. Due to the unfilled 4f orbitals of Yb which introduced the impurity level between the valence band and conduction band of Bi₂S₃, Yb-Bi₂S₃ exhibited admirable photo-to-current conversion efficiency under NIR light irradiation. The Yb-Bi₂S₃ modified electrode was employed to construct a NIR light-driven PEC sensor using an ATP-binding aptamer as the recognition element. When ATP was present, the photocurrent signal of the proposed aptasensor declined, owing to the formation of an ATP-aptamer complex which enhanced the steric hindrance of electron transfer on the electrode. Under optimal conditions, the sensor showed a sensitive response to ATP in the concentration range from 0.5 to 300 nmol L^-1 with a detection limit of 0.1 nmol L^-1. The proposed aptasensor exhibited high selectivity, good repeatability and desirable stability. Moreover, it was successfully applied to ATP detection in human serum samples.

Smartphone-based label-free photoelectrochemical sensing of cysteine with cadmium ion chelation

As an important amino acid, cysteine is related to the development of various diseases. The quantitative detection of cysteine is of great significance for both disease diagnosis and treatment. The current labeling methods mainly rely on fluorescent probes, making it difficult for quantitative cysteine detection in point-of-care testing (POCT). In this study, we proposed a label-free method for cysteine quantification by novel photoelectrochemical (PEC) sensing using a specific ion chelation probe. An indium tin oxide electrode loaded with nanoscale graphitic carbon nitride (g-C₃N₄) was used as the PEC electrode and gold nanoparticle modification was performed to further promote the charge transfer efficiency for enhanced photocurrent detection. Cadmium ions (Cd²⁺) were employed as the specific ion chelation probe for cysteine detection, and the formed Cd²⁺/cysteine chelate complex served as the electron acceptor for sensitive PEC sensing under low-power LED illumination. A portable PEC system was developed for quantitative detection of cysteine by integrating the PEC sensor, a self-designed detection circuit and a smartphone. The detected photocurrents changed linearly with the cysteine concentrations ranging from 0 μM to 40 μM, and the limit of detection is calculated to be 9.2 μM. To demonstrate the capability of this system, cysteine in spiked urine samples was quantified with a recovery rate of 96.1%-100.57%. This system provides high portability, sufficient accuracy and sensitivity, and greatly reduces the complexity and cost of point-of-care cysteine detection.

Multifunctional carbon nanomaterials for diagnostic applications in infectious diseases and tumors

Infectious diseases (such as Corona Virus Disease 2019) and tumors pose a tremendous challenge to global public health. Early diagnosis of infectious diseases and tumors can lead to effective control and early intervention of the patient's condition. Over the past few decades, carbon nanomaterials (CNs) have attracted widespread attention in different scientific disciplines. In the field of biomedicine, carbon nanotubes, graphene, carbon quantum dots and fullerenes have the ability of improving the accuracy of the diagnosis by the improvement of the diagnostic approaches. Therefore, this review highlights their applications in the diagnosis of infectious diseases and tumors over the past five years. Recent advances in the field of biosensing, bioimaging, and nucleic acid amplification by such CNs are introduced and discussed, emphasizing the importance of their unique properties in infectious disease and tumor diagnosis and the challenges and opportunities that exist for future clinical applications. Although the application of CNs in the diagnosis of several diseases is still at a beginning stage, biosensors, bioimaging technologies and nucleic acid amplification technologies built on CNs represent a new generation of promising diagnostic tools that further support their potential application in infectious disease and tumor diagnosis.

Graphene Based Nanohybrid Aptasensors in Environmental Monitoring: Concepts, Design and Future Outlook

In view of ever-increasing environmental pollution, there is an immediate requirement to promote cheap, multiplexed, sensitive and fast biosensing systems to monitor these pollutants or contaminants. Aptamers have shown numerous advantages in being used as molecular recognition elements in various biosensing devices. Graphene and graphene-based materials/nanohybrids combined with several detection methods exhibit great potential owing to their exceptional optical, electronic and physicochemical properties which can be employed extensively to monitor environmental contaminants. For environmental monitoring applications, aptamers have been successfully combined with graphene-based nanohybrids to produce a wide range of innovative methodologies. Aptamers are immobilized at the surface of graphene based nanohybrids via covalent and non-covalent strategies. This review highlights the design, working principle, recent developmental advances and applications of graphene based nanohybrid aptasensors (GNH-Apts) (since January 2014 to September 2021) with a special emphasis on two major signal-transduction methods, i.e., optical and electrochemical for the monitoring of pesticides, heavy metals, bacteria, antibiotics, and organic compounds from different environmental samples (e.g., water, soil and related). Lastly, the challenges confronted by scientists and the possible future outlook have also been addressed. It is expected that high-performance graphene-based nanohybrid aptasensors would find broad applications in the field of environmental monitoring.

MOF@COF Heterostructure Hybrid for Dual-Mode Photoelectrochemical-Electrochemical HIV-1 DNA Sensing

We developed a novel metal-organic framework (MOF)@covalent-organic framework (COF) hybrid with a hierarchical nanostructure and excellent photoactivity, which further acted as the bifunctional platform of a dual-mode photoelectrochemical (PEC) and electrochemical (EC) biosensor for detecting HIV-1 DNA via immobilizing the HIV-1 DNA probe. First, the presynthesized Cu-MOF nanoellipsoids were used as the template for the in situ growth of the COF network, which was synthesized using copper-phthalocyanine tetra-amine (CoPc-TA) and 2,9-bis[p-(formyl)phenyl]-1,10-phenanthroline as building blocks through the Schiff base condensation. In view of the large specific surface area, abundant reserved amino group, excellent electrochemical activity, and high photoactivity, the obtained Cu-MOF@CuPc-TA-COF heterostructure not only can serve as the sensitive platform for anchoring the HIV-1 DNA probe strands but also can be utilized as the signal transducers for PEC and EC biosensors. Thereby, the constructed biosensor shows the sensitive and selective analysis ability toward the HIV-1 target DNA via the complementary hybridization between probe and target DNA strands. The dual-mode PEC and EC measurements revealed that the Cu-MOF@CuPc-TA-COF-based biosensor displayed a wide linear detection range from 1 fM to 1 nM and an extremely low limit of detection (LOD) of 0.07 and 0.18 fM, respectively. In addition, the dual-mode PEC-EC biosensor also demonstrated remarkable selectivity, high stability, good reproducibility, and preferable regeneration ability, as well as acceptable applicability, for which the detected HIV-1 DNA in human serum showed good consistency with real concentrations. Thereby, the present work can open a new dual-mode PEC-EC platform for detecting HIV-1 DNA based on the porous-organic framework heterostructure.

Efficient BiVO4 photoanode decorated with Ti3C2TX MXene for enhanced photoelectrochemical sensing of Hg(II) ion

A highly sensitive photoelectrochemical (PEC) sensing platform was constructed for Hg²⁺ determination based on the Schottky heterojunction between an emerging 2D material Ti₃C₂T_X MXene and a promising semiconductor material BiVO₄. Through simply spin-coating the single-layer Ti₃C₂T_X onto the surface of BiVO₄ film, the modified electrode exhibited significantly enhanced PEC activity. However, the boost in photocurrent could be noticeably suppressed due to the consumption of hole-scavenging agents (reduced glutathione) by the added Hg²⁺. Owing to the selective decrease in the photocurrent with the addition of Hg²⁺, the PEC sensor based on BiVO₄/Ti₃C₂T_X displayed a wide linear range from 1 pM to 2 nM with the limit of detection down to 1 pM. Moreover, the PEC sensor also exhibited satisfactory accuracy and repeatability in practical sample water, the Yangtze River water, demonstrating the great potential for monitoring heavy metal ions in natural water resources.

Synergetic Ag2S and ZnS quantum dots as the sensitizer and recognition probe: A visible light-driven photoelectrochemical sensor for the "signal-on" analysis of mercury (II)

A visible-light-driven photoelectrochemical (PEC) sensor has been developed for the "signal-on" analysis of Hg²⁺ by the synergetic combination of low-bandgap Ag₂S and wide-bandgap ZnS quantum dots (QDs). Ag₂S QDs were synthesized with bead-chain-like structure by the self-assembly route and further covalently bound with ZnS QDs to be coated onto the indium tin oxide (ITO) electrodes. It was discovered that the ZnS@Ag₂S-modified electrodes could display the visible-light-driven PEC behavior, of which Ag₂S and ZnS QDs could act as the PEC sensitizer and Hg²⁺-recognition probe, respectively. More importantly, the photocurrent responses of the developed electrodes could be specifically turned on in the presence of Hg²⁺ under the visible-light irradiation, presumably due to that Hg²⁺ might conduct a Zn-to-Hg exchange on ZnS QDs to trigger the formation of HgS/ZnS@Ag₂S heterojunction towards the enhanced electron-hole separation. The as-prepared PEC sensor could facilitate the detection of Hg²⁺ with concentrations ranging from 0.010-1000 nM, with a detection limit of about 1.0 pM. Besides, the feasibility of practical applications of the developed PEC analysis strategy was verified by probing Hg²⁺ in environmental water samples. Such a visible-light-driven PEC detection platform with the unique "turn-on" signal output may promise for the extensive applications for Hg²⁺ evaluation.

A pro-gastrin-releasing peptide imprinted photoelectrochemical sensor based on the in situ growth of gold nanoparticles on a MoS2 nanosheet surface

Molecularly imprinted PEC platform for Pro-GRP sensing was prepared using lamellar MoS₂ nanosheets assembled with gold nanoparticles as photoactive elements. The molecularly imprinted PEC sensor shows excellent sensing performances towards Pro-GRP.

Recent progress of heterostructure-based photoelectrodes in photoelectrochemical biosensing: a mini review

The heterostructure photoelectrodes have witted the rapid development to improve the performance of PEC biosensors recently.

Sensitive photoelectrochemical immunoassay of Staphylococcus aureus based on one-pot electrodeposited ZnS/CdS heterojunction nanoparticles

We report here a facile synthesis of ZnS/CdS heterojunction nanoparticles on an indium-tin oxide (ITO) electrode and their application in the ultrasensitive photoelectrochemical detection of Staphylococcus aureus (S. aureus). The ZnS/CdS/ITO electrode was prepared using one-pot electrodeposition in an acidic solution containing ZnCl2, CdCl2 and Na2S2O3. The optimal ZnS/CdS heterojunction nanoparticles with a Zn/Cd atomic ratio of 1 : 1 showed a high photoelectrochemical response to l-cysteine. l-Cysteine-encapsulated liposome (cysteine@liposome) immunonanocapsules were prepared and used as the labels for photoelectrochemical detection of S. aureus. By coupling cysteine@liposome immunonanocapsule labeling with immunomagnetic separation/enrichment and photoelectrochemical analysis using the ZnS/CdS/ITO electrode, sensitive photoelectrochemical detection of S. aureus was achieved. Under optimal conditions, the linear range for photoelectrochemical detection of S. aureus was from 1 to 4000 CFU mL-1. The proposed method was successfully used for photoelectrochemical detection of S. aureus in milk and juice samples.

A Sunlight Powered Portable Photoelectrochemical Biosensor Based on a Potentiometric Resolve Ratiometric Principle

As a new analysis tool, photoelectrochemical (PEC) biosensors have been widely studied in recent years. However, common PEC biosensors usually require a highly stable light source to excite the electrical signal and an electrochemical workstation to collect and process the signal data, which limited the development of portable PEC devices. Herein, we propose the design of a sunlight powered portable PEC biosensor that uses sunlight as the light source. The sunlight intensity changes over time and weather and results in varied background PEC currents. To eliminate the interference caused by unstable excitation light, the potentiometric resolve ratiometric principle was introduced. Coupled with a miniature electrochemical workstation and a laptop, a sensitive and portable PEC sensing platform was successfully developed. The detection may be achieved under the irradiation of sunlight and will no longer need an extra light source. In a proof of concept experiment, this platform was successfully applied in aflatoxin B1 analysis, which was promising in the development of portable biosensors.

A sensitive Potentiometric resolved ratiometric Photoelectrochemical aptasensor for Escherichia coli detection fabricated with non-metallic nanomaterials

In this work, a sensitive potentiometric resolved ratiometric photoelectrochemical aptasensor for Escherichia coli (E. coli) detection was successfully fabricated with non-metallic nanomaterials. To avoid the use of precious metals or heavy metals, three-dimensional graphene hydrogel-loaded carbon quantum dots (C-dots/3DGH) and graphene-like carbon nitride (g-C₃N₄) with excellent PEC activity and matched potential were prepared. These two materials were modified onto two adjacent areas on the ITO electrode. By applying different bias voltage, the cathodic current generated by C-dots/3DGH and the anodic current generated by g-C₃N₄ can be clearly distinguished and would not interfere with one another. Then E. coli aptamer was modified onto the surface of C-dots/3DGH. In the presence of targets, the binding of E. coli with aptamer lead to the steric hindrance greatly increased and the cathodic current decreased significantly. Meanwhile, the anodic current generated by g-C₃N₄ was not influenced and it can serve as a stable reference to evaluate the environmental factors. Therefore, the concentration of E. coli can be quantified by the ratio of cathodic current to anodic current, which can effectively eliminate these analyte-independent factors and provide a more precise analysis. In addition, this ratiometric PEC biosensor also showed a good sensitivity and a wide linear range (2.9 cfu/mL to 2.9 × 10⁶ cfu/mL).

A photoelectrochemical immunosensor based on gold nanoparticles/ZnAgInS quaternary quantum dots for the high-performance determination of hepatitis B virus surface antigen

ZnAgInS quaternary quantum dots were prepared using glutathione as the capped reagent. Gold nanoparticles (GNPs) were integrated with ZnAgInS QDs to provide a GNPs/ZnAgInS QDs nanocomposite. The morphological image, component and crystal structure of GNPs/ZnAgInS QDs were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). A glassy carbon electrode surface was coated with GNPs/ZnAgInS QDs nanocomposites to construct an interface for immobilizing the antibody of hepatitis B virus surface antigen (anti-HBsAg). By employing GNPs/ZnAgInS QDs as a photoactive element, a photoelectrochemical immunosensor for hepatitis B virus surface antigen (HBsAg) was developed. The results indicate that gold nanoparticles can dramatically enhance the photocurrent response of ZnAgInS QDs and thus improving the sensing performances of the immunosensor. The experimental conditions including incubation time, incubation temperature, and ascorbic acid concentration were optimized. The relative photocurrent decline [R_i = ΔI/I₀= (I₀ - I)/I₀] shows a linear relationship to the logarithm of HBsAg concentration [lg(c, ng mL^-1)] in the range from 0.005 to 30 ng mL^-1. A detection limit of 0.5 pg mL^-1 was obtained. The immunosensor shows excellent sensitivity, selectivity, stability and reproducibility. The HBsAg concentrations in clinical serum samples were also accurately determined with this new photoelectrochemical immunosensor.

A potentiometric resolved ratiometric photoelectrochemical aptasensor

A novel ratiometric photoelectrochemical aptasensor based on the potentiometric resolved photocurrents generated from different PEC active materials was designed for the first time.