A Novel Photoelectrochemical Sensor for the Organophosphorus Pesticide Dichlofenthion Based on Nanometer-Sized Titania Coupled with a Screen-Printed Electrode

Effects of additives on the performance of a laser-induced graphene sensor modified with ZrO2 nanoparticles for OP detection

In this study, a simple and portable electrochemical sensor based on laser-induced graphene (LIG) has been developed to systematically investigate the feasibility of LIG as an electrode to detect organophosphorus pesticides (OPs). It proves that the LIG-based electrode has a relatively high electrochemically active surface area (ECSA) and heterogeneous electron transfer (HET) of 0.100 cm2 and 0.000825 cm s-1, respectively. In addition, zirconium dioxide nanoparticles (ZrO2 NPs) have been modified on the electrode with three different binders, β-cyclodextrin (β-CD), chitosan (CS) and Nafion, to improve the adsorption capacity of the electrode toward OPs, and the effect of the binders on the performance of the as-fabricated sensor has been investigated in detail. The results show that β-CD increases not only the electrochemically active surface area of the electrode but also the redox peak current of methyl parathion (MP). To evaluate the sensitivity of the sensor, differential pulse voltammetry (DPV) curves have been tested in solutions containing different concentrations of MP using ZrO2-β-CD/LIG as an electrode, which shows a detection range of 5-200 ng ml-1 and a detection limit of 0.89 ng ml-1. In summary, the LIG-based sensor has a low detection limit, high sensitivity and good interference resistance, and thus has tremendous potential for the detection of pesticides in the environment.

Dual mode detection and sunlight-driven photocatalytic degradation of tetracycline with tailor-made N-doped carbon dots

Carbon dots have emerged as one of the most promising materials with various potential applications derived from their unique photophysical and chemical properties. The present work investigates the electrochemical and photochemical properties of one-pot synthesized carbon dots for environmental sustainability. Facile microwave-assisted pyrolysis of urea and glucose yielded nitrogen doped carbon dots (N-doped carbon dots) with blue fluorescence and a quantum yield of 14.9%. As synthesized N- doped carbon dot had intense fluorescence, stability, water solubility, and biocompatibility. In the sensing studies, N-doped carbon dots appeared as a dual sensor for drug tetracycline with excellent sensitivity and selectivity. Beyond sense, the carbon dots have the potential to act as a photocatalyst for the degradation of tetracycline. Further, N-doped carbon dot could bring exhaustive degradation of tetracycline (>95%) within 10 min in the absence of any additives. This is the first time report on the utilization of raw non-metal doped carbon dots as a photocatalyst for the degradation of tetracycline.

Nanozyme-based sensors for detection of food biomarkers: a review

Nanozymes have piqued the curiosity of scientists in recent years because of their ability to demonstrate enzyme-like activity combined with advantages such as high stability, inexpensive availability, robust activity, and tunable properties. These attributes have allowed the successful application of nanozymes in sensing to detect various chemical and biological target analytes, overcoming the shortcomings of conventional detection techniques. In this review, we discuss recent developments of nanozyme-based sensors to detect biomarkers associated with food quality and safety. First, we present a brief introduction to this topic, followed by discussing the different types of sensors used in food biomarker detection. We then highlight recent studies on nanozyme-based sensors to detect food markers such as toxins, pathogens, antibiotics, growth hormones, metal ions, additives, small molecules, and drug residues. In the subsequent section, we discuss the challenges and possible solutions towards the development of nanozyme-based sensors for application in the food industry. Finally, we conclude the review by discussing future perspectives of this field towards successful detection and monitoring of food analytes.

Nanohollow Titanium Oxide Structures on Ti/FTO Glass Formed by Step-Bias Anodic Oxidation for Photoelectrochemical Enhancement

In this study, a new anodic oxidation with a step-bias increment is proposed to evaluate oxidized titanium (Ti) nanostructures on transparent fluorine-doped tin oxide (FTO) on glass. The optimal Ti thickness was determined to be 130 nm. Compared to the use of a conventional constant bias of 25 V, a bias ranging from 5 V to 20 V with a step size of 5 V for 3 min per period can be used to prepare a titanium oxide (TiOx) layer with nanohollows that shows a large increase in current of 142% under UV illumination provided by a 365 nm LED at a power of 83 mW. Based on AFM and SEM, the TiOx grains formed in the step-bias anodic oxidation were found to lead to nanohollow generation. Results obtained from EDS mapping, HR-TEM and XPS all verified the TiOx composition and supported nanohollow formation. The nanohollows formed in a thin TiOx layer can lead to a high surface roughness and photon absorbance for photocurrent generation. With this step-bias anodic oxidation methodology, TiOx with nanohollows can be obtained easily without any extra cost for realizing a high current under photoelectrochemical measurements that shows potential for electrochemical-based sensing applications.

An electrochemical sensor based on the modification of platinum nanoparticles and ZIF-8 membrane for the detection of ascorbic acid

In this manuscript, a layer of 2-methylimidazole zinc salt (ZIF-8) membrane is deposited on the surface of glassy carbon electrode (GCE) modified with platinum nanoparticles (Pt NPs) by reduction electrochemical method to obtain ZIF-8/Pt NPs/GCE, and then used for the detection of ascorbic acid (AA). The deposition of Pt NPs on the surface of GCE can not only guide the nucleation and growth of ZIF-8 membrane, but also exert a synergistic effect with it to enhance conductivity. For ZIF-8 membrane, it can increase the active area of electrode and thus improve the electrochemical response of the sensor for AA. Influence factors such as the deposition current density, deposition time on the surface morphology of the modified electrode, and the detection performance of the modified electrode during the electrochemical deposition of ZIF-8 membrane were explored to get the best performance. In addition, influence of conditions such as sweep speed and pH of the test solution on the electrochemical response signal of AA were also studied. Under the best conditions, the linear range of AA detection by this sensor is from 10 μmol L^-1 to 2500 μmol L^-1, and the detection limit is 5.2 μmol L^-1 based on S/N = 3. What's more, the modified electrode also has good anti-interference ability, reproducibility and stability, and has achieved satisfactory results in the detection for AA in real samples.

Rational design of built-in stannic oxide-copper manganate microrods p-n heterojunction for photoelectrochemical sensing of tetracycline

Tetracycline (TC), a popularly found drug pollutant, can be contaminated in food and aquatic regions and causes a severe impact on human health. In this research, a visible light active p-stannic oxide/n-copper manganate (p-SnO₂/n-CuMnO₂) heterojunction was synthesized and has been applied for a signal on photoelectrochemical sensing of antibiotic TC. Firstly, the n-SnO₂ microrods were synthesized via a simple and efficient homogeneous precipitation method and the p-CuMnO₂ nanoparticles were synthesized by a facile ultrasound-assisted hydrothermal method. The SnO₂/CuMnO₂ microrods p-n heterojunction was prepared through a simple impregnation method and physicochemical properties of the microrods are characterized by using X-ray diffraction (XRD), Raman, Brunauer-Emmett-Teller (BET), Fourier-transform infrared (FTIR), UV-Vis diffuse reflectance spectroscopy (UVDRS), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Mott-Schottky analyses. The photoelectrochemical sensing performance of SnO₂/CuMnO₂ microrods was 2.7 times higher than that of as-synthesized pure SnO₂ microrods is due to the more visible light absorption ability and p-n heterojunction (synergy). The designed SnO₂/CuMnO₂/ITO sensor gives photocurrent signals for the detection of TC in the range of 0.01-1000 μM with the detection limit (LOD) of 5.6 nM. The practical applicability of the sensor was monitored in cow milk and the Taipei River water sample.

Nanostructured β‐tricalcium Phosphate (Ca3(PO4)2 Based Electrochemical Sensor for Detection of Methyl Parathion and Mercury (II) Ions

In this work, we have fabricated a new electrochemical sensor based on β‐tricalcium phosphate (Ca3(PO4)2) nanoparticles (NPs) modified glassy carbon electrode (GCE) for the selective nonenzymatic determination of methyl parathion and mercury (II) ions independently. β‐tricalcium phosphate (β‐TCP) NPs were prepared by chemical precipitation method and structural and morphological properties were investigated by XRD, FTIR, and SEM. The electrochemical behavior of MP and mercury (Hg2+) ions were investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV) techniques using β‐TCP/GCE. The modified electrode exhibited excellent electrocatalytic activity towards both the MP and Hg over a wide linear range from 0.15 to 141 μM and 1–381 µM with the lowest detection limits of 88 and 136.4 nM respectively. The sensor has high selectivity towards MP and Hg in the presence of major interfering compounds such as 3-nitrophenol, 4-nitrophenol, 4-aminophenol, catechol, hydroquinone and heavy metals such as lead, cadmium and arsenic. Applicability of the fabricated sensor for detection of MP and Hg (II) ions has been tested in tap water by standard addition method.

Detection of pollutants in water bodies: electrochemical detection or photo-electrochemical detection?

The massive discharge of pollutants including endocrine-disrupting chemicals (EDCs), heavy metals, pharmaceuticals and personal care products (PPCPs) into water bodies is endangering the ecological environment and human health, and needs to be accurately detected. Both electrochemical and photo-electrochemical detection methods have been widely used for the detection of these pollutants, however, which one is better for the detection of different environmental pollutants? In this feature article, different electrochemical and photo-electrochemical detection methods are summarized, including the principles, classification, common catalysts, and applications. By summarizing the advantages and disadvantages of different detection methods, this review provides a guide for other researchers to detect pollutants in water bodies by using electrochemical and photo-electrochemical analysis.

In situ growth of carbon dots on TiO2 nanotube arrays for PEC enzyme biosensors with visible light response

Carbon dots (CDs) were grown in situ on secondary anodized TiO₂ nanotube arrays (TiO₂ NTAs) via a hydrothermal method. The combination of CDs and TiO₂ NTAs enhanced the photoelectrochemical performance. Morphology, structure, and elemental composition of the CDs were characterized. No simple physical adsorption was found between the CDs and TiO₂, but chemical bonds were formed. UV-vis absorption and fluorescence spectroscopy showed that the CDs could enhance the absorption of TiO₂ in the visible and near-infrared regions. Owing to their up-conversion fluorescence properties, the CDs could convert low-energy photon absorption into high-energy photons, which may be used to excite TiO₂ to produce a stronger photoelectric response. Moreover, the CDs could effectively transport electrons and accept holes, thus contributing to the effective separation of electrons and holes during photoexcitation. Finally, the PEC biosensor was prepared by immobilizing glucose oxidase (GOx) on the surface of the composite. The PEC biosensor exhibited a broad range of 0.1–18 mM with a detection limit of 0.027 mM under visible irradiation because the composite material reflected strong light absorption for visible light, good conductivity, and good biocompatibility.

Carbon dots (CDs) were grown in situ on secondary anodized TiO₂ nanotube arrays (TiO₂ NTAs) via a hydrothermal method.

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 highly conductive thin film composite based on silver nanoparticles and malic acid for selective electrochemical sensing of trichloroacetic acid

A highly conductive thin film composite based on silver nanoparticles (AgNPs) and malic acid (MA) was deposited on glassy carbon electrode (GCE) for the selective and sensitive electrochemical sensing of trichloroacetic acid (TCA). The casting solution containing MA functionalized AgNPs was employed as a precursor for the thermal deposition of the AgNPs integrated MA thin film composite onto the GCE surface. The uniform coverage of AgNPs within the thin film composite at GCE was obtained by field emission scanning electron microscopy (FESEM). A significantly high charge transfer resistance of the modified electrode (85.7 Ω for AgNPs-MA/GCE in 2 mM [Fe(CN)₆]^3-/4- at a bias of +0.235 V as compared to bare GCE (38.01 Ω) verified the optimum coating of AgNPs-MA composite at the surface of the electrode. The AgNPs-MA composite deposited GCE revealed substantial electrocatalytic activity toward TCA reduction with significantly enhanced reduction current. The novel electrode manifested a linear square wave voltammetric (SWV) response over the concentration ranges of 0.1-2 (R² = 0.9953) and 4-100 μM (R² = 0.9969) with a limit of detection (LOD) and limit of quantification (LOQ) of 30 nM and 92.5 nM, respectively. The modified electrode exhibited an excellent long-term stability (30 days) with the retention of >95% of initial current. The selectivity of the proposed electrode for the determination of TCA was examined in the presence of dichloroacetic acid (DCA) and monochloroacetic acid (MCA) with the retention of high recovery percentages.

Electrochemical Biosensors: A Solution to Pollution Detection with Reference to Environmental Contaminants

The increasing environmental pollution with particular reference to emerging contaminants, toxic heavy elements, and other hazardous agents is a serious concern worldwide. Considering this global issue, there is an urgent need to design and develop strategic measuring techniques with higher efficacy and precision to detect a broader spectrum of numerous contaminants. The development of precise instruments can further help in real-time and in-process monitoring of the generation and release of environmental pollutants from different industrial sectors. Moreover, real-time monitoring can also reduce the excessive consumption of several harsh chemicals and reagents with an added advantage of on-site determination of contaminant composition prior to discharge into the environment. With key scientific advances, electrochemical biosensors have gained considerable attention to solve this problem. Electrochemical biosensors can be an excellent fit as an analytical tool for monitoring programs to implement legislation. Herein, we reviewed the current trends in the use of electrochemical biosensors as novel tools to detect various contaminant types including toxic heavy elements. A particular emphasis was given to screen-printed electrodes, nanowire sensors, and paper-based biosensors and their role in the pollution detection processes. Towards the end, the work is wrapped up with concluding remarks and future perspectives. In summary, electrochemical biosensors and related areas such as bioelectronics, and (bio)-nanotechnology seem to be growing areas that will have a marked influence on the development of new bio-sensing strategies in future studies.

A novel and high performance enzyme-less sensing layer for electrochemical detection of methyl parathion based on BSA templated Au–Ag bimetallic nanoclusters

In the present manuscript, a modified glassy carbon electrode with BSA templated Au–Ag bimetallic nanoclusters (Au–Ag@BSA/GCE) was employed for the rapid, selective and sensitive determination of methyl parathion (MP) as an enzyme-less electrochemical biosensor.

The Application of Nano-TiO2 Photo Semiconductors in Agriculture

Nanometer-sized titanium dioxide (TiO₂) is an environmentally friendly optical semiconductor material. It has wide application value in many fields due to its excellent structural, optical, and chemical properties. The photocatalytic process of nano-TiO₂ converts light energy into electrical or chemical energy under mild conditions. In recent years, the study and application of nano-TiO₂ in the agricultural sector has gradually attracted attention. The nano-TiO₂ applications of degrading pesticides, plant germination and growth, crop disease control, water purification, pesticide residue detection, etc. are good prospects. This review describes all of these applications and the research status and development, including the underlying principles, features, comprehensive applications, functional modification, and potential future directions, for TiO₂ in agriculture.

Recent Advances in the Fabrication and Application of Screen-Printed Electrochemical (Bio)Sensors Based on Carbon Materials for Biomedical, Agri-Food and Environmental Analyses

This review describes recent advances in the fabrication of electrochemical (bio)sensors based on screen-printing technology involving carbon materials and their application in biomedical, agri-food and environmental analyses. It will focus on the various strategies employed in the fabrication of screen-printed (bio)sensors, together with their performance characteristics; the application of these devices for the measurement of selected naturally occurring biomolecules, environmental pollutants and toxins will be discussed.

Synthesis and sensing applications of a new fluorescent derivative of cholesterol

The Hg²⁺ quenched emission of a specially designed fluorophore could be fully turned on upon the introduction of organophosphorus pesticides.

A novel sensor for the detection of acetamiprid in vegetables based on its photocatalytic degradation compound

An electrochemical method for the indirect determination of acetamiprid was studied, using titanium dioxide photocatalysts coupled with a carbon paste electrode. The cyclic voltammetric results indicated that the photocatalytic degradation compound of acetamiprid had electroactivity in neutral solutions. The amount of acetamiprid was further indirectly determined by differential pulse anodic stripping voltammetric analysis as a sensitive detection technique. The experimental parameters were optimized with regard to the photocatalytic degradation time, pH of buffer solution, accumulation potential and accumulation time. Under optimal conditions, the proposed electrochemical method could detect acetamiprid concentrations ranging from 0.01 to 2.0μM, with a detection limit (3S/N) of 0.2nM. Moreover, the proposed method displays excellent selectivity, good reproducibility, and acceptable operational stability and can be successfully applied to acetamiprid determination in vegetable samples with satisfying results.

Toward the development of smart and low cost point-of-care biosensors based on screen printed electrodes

Screen printing technology provides a cheap and easy means to fabricate disposable electrochemical devices in bulk quantities which are used for rapid, low-cost, on-site, real-time and recurrent industrial, pharmaceutical or environmental analyses. Recent developments in micro-fabrication and nano-characterization made it possible to screen print reproducible feature on materials including plastics, ceramics and metals. The processed features forms screen-printed disposable biochip (SPDB) upon the application of suitable bio-chemical recognition receptors following appropriate methods. Adequacy of biological and non-biological materials is the key to successful biochip development. We can further improve recognition ability of SPDBs by adopting new screen printed electrode (SPE) configurations. This review covers screen-printing theory with special emphasis on the technical impacts of SPE architectures, surface treatments, operational stability and signal sensitivity. The application of SPE in different areas has also been summarized. The article aims to highlight the state-of-the-art of SPDB at the laboratory scale to enable us in envisaging the deployment of emerging SPDB technology on the commercial scale.

An ON1–OFF–ON2 electrochemiluminescence response: combining the intermolecular specific binding with a radical scavenger

The electrochemiluminescence (ECL) technique was combined with the “ON¹–OFF–ON²” strategy based on the chemical reactions and specific binding among different small chemical compounds for the highly sensitive detection of nonelectroactive organophosphate pesticides.

Photoelectrochemical bioanalysis: the state of the art

This review provides a panoramic snapshot of the state of the art in the dynamically developing field of photoelectrochemical bioanalysis.

A novel electrochemical sensor based on zirconia/ordered macroporous polyaniline for ultrasensitive detection of pesticides

A simple and mild strategy was proposed to develop a novel electrochemical sensor based on zirconia/ordered macroporous polyaniline (ZrO₂/OMP) and further used for the detection of methyl parathion (MP), one of the organophosphate pesticides (OPPs).

Nanostructured photoelectrochemical biosensor for highly sensitive detection of organophosphorous pesticides

A sensitive photoelectrochemical (PEC) biosensor for detection of organophosphorus pesticides (OPs) using the nanocomposite of CdSe@ZnS quantum dots (QDs) and graphene deposited on the ITO coated glass electrode as a photoactive electrode is presented. The integration of CdSe@ZnS/graphene nanocomposite with biomolecules acetylcholinesterase (AChE) as a biorecognition element yields a novel biosensing platform. Under visible light irradiation, the AChE-CdSe@ZnS/graphene nanocomposite can generate a stable photocurrent and the photocurrent is found to be inversely dependent on the concentration of OPs. Under the optimal experimental conditions, the photocurrents were proportional to the logarithm of paraoxon and dichlorvos within the concentration range of 10(-12)-10(-6) M. The detection limits (LOD) of the proposed biosensor for paraoxon and dichlorvos are as low as 10(-14) M and 10(-12) M. The photoelectrochemical biosensor shows good sensitivity, reproducibility, stability, and could be successfully applied to detection of OPs in real fruit samples.

Electrochemical impedance immunosensor for sub-picogram level detection of bovine interferon gamma based on cylinder-shaped TiO₂ nanorods

Bovine interferon gamma (BoIFN-γ) released by T cells plays very important roles in early diagnosis of Mycobacterium tuberculosis (MTB) infections and control of bovine tuberculosis. In this work, a label-free electrochemical impedance immunosensor is for the first time developed for highly sensitive determination of BoIFN-γ. Cylinder-shaped TiO2 nanorods are synthesized by a facile hydrothermal method, and show high surface area and good hydrophicility. The immunosensor is fabricated by the immobilization of BoIFN-γ monoclonal antibody on the TiO2 nanorods modified glassy carbon electrode. The prepared TiO2 and immunosensor are characterized using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, contact angle measurement, cyclic voltammetry, and electrochemical impedance spectra. The BoIFN-γ concentration is measured through the relative increase of impedance values in corresponding specific binding of BoIFN-γ antigen and BoIFN-γ antibody. The relative increased impedance values are proportional to the logarithmic value of BoIFN-γ concentrations in a wide range of 0.0001 to 0.1 ng/mL with a low detection limit of 0.1 pg/mL. The developed BoIFN-γ immunosensor shows a 249-fold decrease in detection limit in comparison with current enzyme-linked immunosorbent assay. This study provides a new, simple, and highly sensitive approach for very potential application in early diagnosis of MTB infections and control of bovine tuberculosis.

Disposable screen printed electrochemical sensors: tools for environmental monitoring

Screen printing technology is a widely used technique for the fabrication of electrochemical sensors. This methodology is likely to underpin the progressive drive towards miniaturized, sensitive and portable devices, and has already established its route from "lab-to-market" for a plethora of sensors. The application of these sensors for analysis of environmental samples has been the major focus of research in this field. As a consequence, this work will focus on recent important advances in the design and fabrication of disposable screen printed sensors for the electrochemical detection of environmental contaminants. Special emphasis is given on sensor fabrication methodology, operating details and performance characteristics for environmental applications.

Ultrathin g-C3N4/TiO2composites as photoelectrochemical elements for the real-time evaluation of global antioxidant capacity

Using utg-C₃N₄/TiO₂, a photoelectrochemical platform was designed for the sensing of global antioxidant capacity, which presented a rapid response, and anti-fouling and colour-interference-proof properties.

A phosphorylation-sensitive tyrosine-tailored magnetic particle for electrochemically probing free organophosphates in blood

Phosphorylation-sensitive tyrosine was coated onto Fe₃O₄ particles, resulting in a “lab-on-a-particle”-based electrochemical detection protocol for probing free organophosphates in blood.

Femtomole level photoelectrochemical aptasensing for mercury ions using quercetin-copper(II) complex as the DNA intercalator

An ultrasensitive and selective photoelectrochemical (PEC) aptasensor for mercury ions was first fabricated based on perylene-3, 4, 9, 10-tetracarboxylic acid/graphene oxide (PTCA/GO) heterojunction using quercetin-copper(II) complex intercalated into the poly(dT)-poly(dA) duplexes. Both the PTCA/GO heterojunction and the quercetin-copper(II) complex are in favor of the sensitivity for the fabricated PEC aptasensor due to band alignment and strong reduction capability, respectively. And they efficiently promote the separation of photoexcited carriers and enhance the photocurrent. The formation of thymine-Hg(2+)-thymine coordination chemistry resulted in the dehybridization of poly(dT)-poly(dA) duplexes and then the intercalator quercetin-copper(II) complex broke away from the surface of the PEC aptasensor. As the concentration of mercury ions increased, the photocurrent gradually decreased. The electrode response for mercury ions detection was in the linear range from 0.01 pmol L(-1) to 1.00 pmol L(-1) with the detection limit of 3.33 fmol L(-1). The label-free PEC aptasensor has excellent performances with ultrasensitivity and good selectivity besides the advantage of economic and facile fabrication. The strategy of quercetin-copper(II) complex as a novel DNA intercalator paves a new way to improve the performances for PEC sensors.