Enzyme-based Sensors Research Articles

Resolution of tonic concentrations of highly similar neurotransmitters using voltammetry and deep learning

With advances in our understanding regarding the neurochemical underpinnings of neurological and psychiatric diseases, there is an increased demand for advanced computational methods for neurochemical analysis. Despite having a variety of techniques for measuring tonic extracellular concentrations of neurotransmitters, including voltammetry, enzyme-based sensors, amperometry, and in vivo microdialysis, there is currently no means to resolve concentrations of structurally similar neurotransmitters from mixtures in the in vivo environment with high spatiotemporal resolution and limited tissue damage. Since a variety of research and clinical investigations involve brain regions containing electrochemically similar monoamines, such as dopamine and norepinephrine, developing a model to resolve the respective contributions of these neurotransmitters is of vital importance. Here we have developed a deep learning network, DiscrimNet, a convolutional autoencoder capable of accurately predicting individual tonic concentrations of dopamine, norepinephrine, and serotonin from both in vitro mixtures and the in vivo environment in anesthetized rats, measured using voltammetry. The architecture of DiscrimNet is described, and its ability to accurately predict in vitro and unseen in vivo concentrations is shown to vastly outperform a variety of shallow learning algorithms previously used for neurotransmitter discrimination. DiscrimNet is shown to generalize well to data captured from electrodes unseen during model training, eliminating the need to retrain the model for each new electrode. DiscrimNet is also shown to accurately predict the expected changes in dopamine and serotonin after cocaine and oxycodone administration in anesthetized rats in vivo. DiscrimNet therefore offers an exciting new method for real-time resolution of in vivo voltammetric signals into component neurotransmitters.

Advancing Diabetes Management: The Future of Enzyme-Less Nanoparticle-Based Glucose Sensors-A Review.

Glucose is vital for biological processes, requiring blood sugar levels to be maintained between 3.88 and 6.1 mmol/L, especially during fasting. Elevated levels signal diabetes, a global concern affecting 537 million people, necessitating effective glucose-monitoring devices. Enzyme-based sensors, though selective, are sensitive to environmental factors. Nonenzymatic sensors, especially those with nanoparticles, offer stability, high surface area, and cost-effectiveness. Existing literature supports their immediate glucose oxidation, showcasing exceptional sensitivity. This review details nonenzymatic sensors, highlighting materials, detection limits, and the promise of nanoparticle-based designs, which exhibit enhanced sensitivity and selectivity in glucose detection. Nanoparticle-based sensors, as reviewed, show potential for glucose monitoring, overcoming enzyme-based limitations. The conclusion suggests future directions for advancing these sensors, emphasizing ongoing innovation in this critical research area.

Synthetization and Characterization of Zinc Oxide Nanoparticles by X- Ray Diffractometry (XRD), Fourier Transforms, Infra-Red Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM) and Antibacterial Activity Test

Purpose: Nanomaterials with their derivable potentials offer wide obtain ability and have recently aroused much attention for biomedical applications. Nowadays, nanomaterials-based colorimetric sensing is a quickly emerging field of sensing applications. Nanomaterials are considered as the main component of colorimetric determination of hydrogen peroxide to replace the natural enzyme-based sensors because of some associated intrinsic drawbacks. Considering the advantageous properties of ionic liquid (IL) for various applications, significant attention has been made to the use of ionic liquid stabilized metal NPs which may serve as a regulator to enhance the catalytic performance of the metal nanoparticles in the different IL reaction medium. 
 Methodology: The peroxidase-like activity of IL coated metal NPs (IL-MNPs) have been considered for the catalytic oxidation reaction of chromogenic substrate 3,3,5,5- tetramethylbenzidine (TMB) in the presence of H2O2 at an estimated wavelength of 652 nm.
 Results: The synthesized metal nanoparticles (Ag) were produced using a chemical reduction method. Various characterization techniques like FTIR, UV-Visible spread Reflectance Spectroscopy [UV-VIS DRS], were employed, which verified the structure, nano-size and successful combination of metal dopant ion into the samples. The molecular structure of ionic liquid with varying cations was produced and confirmed by 1H-NMR spectroscopy. The ionic liquid was coated on metal nanoparticles to enhance their conductivity. 
 Unique Contribution to Theory, Practice and Policy: Optimized reaction conditions like pH, temperature and catalyst dosage affect catalytic activity and color sensing properties. The coating of [Min] Ac on Ag achieved low detection limits and colorimetric detection of [Pyr] based Ag.

Development of non-precious metal oxide-based electrodes for enzyme-free glucose detection: A review

The progress of accurate and economical sensors for glucose determination is vital for the detection and treatment of diabetes. Even though electrochemical enzyme-based sensors have been widely utilized in the medical field for glucose determination, high preparation costs, and poor durability have led to the introduction of a novel type of enzyme-free sensor for glucose recognition. Non-precious metal oxides have been comprehensively explored for the preparation of affordable sensors for non-enzymatic, high-performance glucose detection. This review commences by clarifying the mechanistic aspects of electrochemical sensors for enzyme-free glucose detection, followed by advanced studies on metal oxides with different strategies, including morphology engineering, supported carbon materials, and noble metal doping for efficient glucose detection. Finally, formidable obstacles and future development of non-enzymatic electrochemical glucose sensing are also discussed.

Reversible CeO2–x and CeO2–x:Eu3+ Luminescent Hydrogen Peroxide Sensors with Recovery Rates Controlled by Temperature and UV Irradiation

Hydrogen peroxide (HP) plays an indispensable role in living organisms, being both an intracellular messenger and a substrate or byproduct of a number of enzymes. In this way, HP sensing is important for monitoring the activity of various cell systems and assessing the redox balance of the cell as whole. HP sensors based on luminescent inorganic nanoparticles can be considered as a prospective alternative to traditional dye- and enzyme-based sensors, which usually are unstable and nonreversible. The undoped (CeO2–x) and Eu3+-doped (CeO2–x:Eu3+) colloidal ceria nanoparticles studied in the paper provide HP detection by reversible quenching of Eu3+ (590 nm) and Ce3+ (430 nm) luminescence bands. The dynamics of Eu3+ and Ce3+ luminescence quenching and recovery during HP-nanoceria interaction provides an insight into the microscopic mechanisms of HP sensing by CeO2–x and CeO2–x:Eu3+ nanoparticles. Both CeO2–x and CeO2–x:Eu3+ luminescent sensors are reversible and their recovery rates can be sufficiently increased by temperature and continuous UV irradiation. At the same time, Eu3+ ions deteriorate the catalase-mimetic activity of CeO2–x NPs and worsen their antioxidant properties, which should be kept in mind while using these sensors in biological media.

UiO-66-Derived PBA Composite as Multifunctional Electrochemical Non-Enzymatic Sensor Realizing High-Performance Detection of Hydrogen Peroxide and Glucose.

In this work, a highly efficient multifunctional non-enzymatic electrochemical sensor is successfully fabricated based on a facile two-step synthetic strategy. It resolves two important challenges of poor stability and low reproducibility compared to conventional electrochemical enzyme-based sensors. Herein, a metal-organic framework (UiO-66) is selected as a sacrificial template to construct the corresponding Prussian blue analogue (PBA) target to improve its stability and conductivity, namely, PBA/UiO-66/NF. Target PBA/UiO-66/NF exhibits excellent electrochemical sensing performance as hydrogen peroxide (H2O2) and glucose sensors with ultrahigh sensitivity of up to 1903 μA mM-1 cm-2 for H2O2 and 22,800 μA mM-1 cm-2 for glucose, as well as a very low detection limit of 0.02 μM (S/N = 3) for H2O2 and 0.28 μM for glucose. Especially, extremely high stability can be observed, which will be beneficial for practical application.

Electrochemical Nano-Roughening of Gold Microstructured Electrodes for Enhanced Sensing in Biofluids.

A key challenge for sensor miniaturization is to create electrodes with smaller footprints, while maintaining or increasing sensitivity. In this work, the electroactive surface of gold electrodes was enhanced 30-fold by wrinkling followed by chronoamperometric (CA) pulsing. Electron microscopy showed increased surface roughness in response to an increased number of CA pulses. The nanoroughened electrodes also showed excellent fouling resistance when submerged in solutions containing bovine serum albumin. The nanoroughened electrodes were used for electrochemical detection of Cu2+ in tap water and of glucose in human blood plasma. In the latter case, the nanoroughened electrodes allowed highly sensitive enzyme-free sensing of glucose, with responses comparable to those of two commercial enzyme-based sensors. We anticipate that this methodology to fabricate nanostructured electrodes can accelerate the development of simple, cost-effective, and high sensitivity electrochemical platforms.

Recent Advances of Enzyme-Free Electrochemical Sensors for Flexible Electronics in the Detection of Organophosphorus Compounds: A Review.

Emerging materials integrated into high performance flexible electronics to detect environmental contaminants have received extensive attention worldwide. The accurate detection of widespread organophosphorus (OP) compounds in the environment is crucial due to their high toxicity even at low concentrations, which leads to acute health concerns. Therefore, developing rapid, highly sensitive, reliable, and facile analytical sensing techniques is necessary to monitor environmental, ecological, and food safety risks. Although enzyme-based sensors have better sensitivity, their practical usage is hindered due to their low specificity and stability. Therefore, among various detection methods of OP compounds, this review article focuses on the progress made in the development of enzyme-free electrochemical sensors as an effective nostrum. Further, the novel materials used in these sensors and their properties, synthesis methodologies, sensing strategies, analytical methods, detection limits, and stability are discussed. Finally, this article summarizes potential avenues for future prospective electrochemical sensors and the current challenges of enhancing the performance, stability, and shelf life.

Nanocomposite Based Enzyme-less Electrochemical Sensors for Carbamate and Organophosphorus Pesticides Detection

Background: The excessive application of carbamate and organophosphorus pesticides showed relatively high acute toxicity due to inhibition of acetylcholinesterase enzyme in the neural system of insects and mammals. Objective: This review aimed to assess the current outstanding performance of nanocomposite based enzyme-less electrochemical sensors toward determination of organophosphorus and carbamate pesticides detection. Method: Enzyme based electrochemical sensor (biosensor) and classical (chromatographic) methods have been used widely for detection of organophosphorus and carbamate pesticides. However, instability related to enzymes and complex sample preparation, need for highly trained manpower and other numerous disadvantages associated with chromatographic techniques limit their application for pesticides detection in many conditions. Therefore, currently, nanocomposite based enzyme-less electrochemical sensors are good alternative to enzyme-based sensors for many researchers Results: The reviewed literature revealed that, nanocomposite based enzyme-less sensors with numerous advantages have shown a comparable sensitivity with enzyme-integrated sensor for pesticide detection. Conclusion: Currently nanocomposite materials are widely used for many applications including the fabrication of promising sensors for pesticide detections. The promising sensing potential might be attributed to the special functional groups on the surface of the nanomaterials and their composite form, enabling them to substitute those expensive bio-recognition elements (enzymes) and used as non-bio-recognition element for detection of pesticides.

Development of non-enzymatic screen-printed carbon electrode sensor for glucose using cyclic voltammetry

Enzyme-based sensors frequently produce unsatisfactory results such as poor reproducibility and insufficient long-term stability due to the natural instability of enzymes, stringent experimental conditions, and complicated immobilization procedures. Thus, an electrochemical non enzymatic sensor was fabricated by deposition of the multi-walled carbon nanotube (MWCNT) with zinc oxide nanoparticles (ZnO NP) and also molecular imprinted polymer (MIP) on a screen-printed carbon electrode (SPCE). Then, the modified electrode (SPCE/MWCNT/ZnO/MIP) was formed on the surface area of the SPCE. This study wanted to demonstrate the glucose detection between molecular imprinted polymer (MIP) which contained glucose as template, o-phenylenediamine (oPD) and potassium persulfate as initiators in 0.1 M PBS at pH 7 and non-imprinted polymer (NIP) without addition of the template. The characterization and evaluation of various factor such as sensitivity, selectivity and limit of detection (LOD) were investigated through cyclic voltammetry (CV) and scanning electron microscopy (SEM) was used to look up onto the surface area of the modified electrode. The SPCE/MWCNT/ZnO/MIP electrode sensor showed a linear glucose concentration range from 0, 0.5, 1, 2 to 5 mM (R2 = 0.9709). The sensitivity of the sensor was 0.3386 μA mM-1 cm-2 with low detection limit of 1.81 mM. The sensor showed good stability and reproducibility along with excellent anti-interference properties to ascorbic acid, lactic acid, tartaric acid, and acetic acid. Finally, the applicability of the as-prepared SPCE/MWCNT/ZnO/MIP electrode sensor was successfully studied for detection of glucose. The results obtained for our sensor confirm that it is a promising non-enzymatic glucose sensor to be used for practical purpose.

A photo-sensitive BiVO4@Bi2O3@g-C3N4 sensor for the detection of dopamine

Dopamine (DA) plays an important biological role in cardiovascular, renal, hormone, central nervous systems and human metabolism. Photo-sensitive sensors studies are gained great importance in recent years due to some problems in enzyme-based sensors. In this study, photo-sensitive BiVO4@Bi2O3@g-C3N4 based sensor is fabricated for DA determination. The semiconductors use in this sensor system have important functions; g-C3N4 is a photosensitive material, δ-Bi2O3 is a stable electrode responsible for intermediate contact, and BiVO4 is a good electron conduction material due to its stable structure. DA is analyzed by BiVO4@Bi2O3@g-C3N4 photo-sensitive sensor in 0.1 M PBS medium at solutions with different concentrations. In this study, for the first time, a calibration curve is constructed from Tafel curves of solutions of different concentrations. The DA sensor is worked in a linear range of 25–750 µM. In addition, in this developed sensor, limit of detection (LOD), limit of quantification (LOQ) and sensitivity values are 0.046, 0.154 µM and 0.011 μA µM−1 cm−2, respectively. Our strategy opens a new pathway to determination of some neurotransmitter via photo-sensitive materials.

Facile hydrothermal synthesis CuO microflowers for non‐enzymatic glucose sensors

With diabetes mellitus increasing, developing non-enzymatic glucose sensors to replace enzyme-based sensors has become more urgent, owing to its intrinsic disadvantages of enzymes. Herein, CuO microflowers were successfully synthesized through a green hydrothermal method with no template or surfactant. X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy were used to study the crystalline structure, elemental composition and morphology of the as-obtained sample. Then, the CuO microflowers acted as non-enzymatic glucose sensor electrode material. The electrochemical test results indicate that the glucose oxidation controlled by diffusion at 0.5 V had a short response time(5 s), the linear range was wide(∼11 mM), and the detection limit was low(1.3 µm). Moreover, the CuO microflowers exhibit great selectivity to glucose and have high poison resistance to chloride ions. Thus, all these results imply that the as-fabricated CuO has a great application prospect for non-enzymatic glucose sensor electrode material.

A review on recent advances in hydrogen peroxide electrochemical sensors for applications in cell detection

Hydrogen peroxide (H2O2) is a very simple bioactive small molecule. In living organisms, H2O2 plays an important role in intracellular signaling. It is involved in many physiological processes including cellular physiology, intracellular signaling, oxidative damage and disease progression. The tumor microenvironment enriched with H2O2. Several electrochemical sensors have been developed and some have been put on the market. Such electrochemical sensors provide efficient, cost-effective, rapid and highly selective method of H2O2 detection. So far, much progress has been made in the designing of materials and construction of H2O2 sensors. This review describes the advances in the application of H2O2 electrochemical sensors in cell detection. Enzyme-based sensors have been applied in diverse applications. In addition, recent advancements in nanotechnology have improved the development of nanozymes-based sensors. The application of noble metals, metal oxides, polymers, carbon materials and other two-dimensional materials in the design of H2O2 sensors are discussed in detail. Moreover, the bio-stimulant types of H2O2 sensor are summarized. Finally, the challenges and future perspectives in the application of H2O2 electrochemical sensors in biological detection are discussed.

Engineered Whole-Cell-Based Biosensors: Sensing Environmental Heavy Metal Pollutants in Water-a Review.

The frequent exposure and accumulation of heavy metals in organisms cause serious health issues affecting a range of organs such as the brain, liver, and reproductive organs in adults, infants, and children. Several parts of the world have high levels of heavy metals affecting millions of people, costing millions of dollars for improving the potability of water and medical treatment of the affected. Hence, water quality assessment is required to monitor the degree of heavy metal contamination in potable water. In nature, organisms respond to various environmental pollutants such as heavy metals, allowing their survival in a diverse environmental niche. With the advent of recombinant DNA technology, it is now possible to manipulate these natural bioreporters into controlled systems which either turn on or off gene expression or activity of enzymes in the presence of specific heavy metals (compound-specific biosensors) otherwise termed as whole-cell biosensors (WCBs). WCBs provide an upper hand compared to other immunosensors, enzyme-based sensors, and DNA-based sensors since microbes can be relatively easily manipulated, scaled up with relative ease, and can detect only the bioavailable heavy metals. In this review, we summarize the current knowledge of the various mechanisms of toxicity elicited by various heavy metals, thence emphasizing the need to develop heavy metal sensing platforms. Following this, the biosensor-based platforms including WCBs for detecting heavy metals developed thus far have been briefly elaborated upon, emphasizing the challenges and solutions associated with WCBs.

Facile Fabrication of Stable Enzyme-Based Colorimetric Glucose Biosensor on Cotton Using Polymer Entrapment

Easy and rapid analyte detection can be democratised using fabric-based colorimetric sensor, which can be readily incorporated into everyday clothing or accessories, and digitally imaged by non-expert users using pervasive smartphones. However, fabricating colorimetric arrays, particularly enzyme-based sensors, on fabrics is nontrivial because enzyme activity cannot be guaranteed upon solid-state immobilisation on textiles, and because textiles present a highly-textured surface that could cause interference during digital imaging and reduce the limit of detection of known sensing formulations. Here, an enzyme-based multilayer sensor is fabricated on selected fabrics via physical adsorption and drop-casting, and utilised for proof-of-concept colorimetric detection of glucose on textiles. Substrates like cotton, cotton lycra, and filter paper are compared for colour uniformity and potential interference during digital imaging. Colour development on cotton achieved optimal homogeneity and reproducibility. The entrapment of enzymes with polyvinyl alcohol is demonstrated to enhance linear dynamic range, water fastness, and storage stability under different conditions. An image-processing algorithm is developed in OpenCV to automatically detect the colour spot and aid in quantitative analysis of glucose concentration. The present study suggests a facile strategy to fabricate a robust biosensor on textile that can achieve noninvasive monitoring of glucose in human biological fluid.

3D-Printed, Portable, Fluorescent-Sensing Platform for Smartphone-Capable Detection of Organophosphorus Residue Using Reaction-Based Aggregation Induced Emission Luminogens.

Development of an easy-to-use, low-cost, household device can help the consumer quickly identify an organophosphorus (OP) residue concentration level. In this work, we demonstrate a 3D-printed, portable, fluorescent-sensing platform for smartphone-capable detection of OPs in vegetables. For development of the proposed device, we utilize the smartphone for capturing the strong thiol-activated fluorescence, which was produced by hydrolysis of OPs in the presence of alkali. The thiol-responsive AIEgen (maleimide-functionalized tetraphenylethylene) was non-emissive in both solution and the solid state but could be readily lighted up by the click addition of thiol to its MI pendant. An android application "Detection" has been developed on the basis of the gray value to analyze the different concentration levels of OPs in vegetable samples. The gray value was linearly related with the concentration of five kinds of organophosphorus residue, ranging from 0 to 20 μg/mL. It was also applied for determination of OPs residue in the leaves of cowpea, celery, and Chinese cabbage. Different from acetylcholinesterase enzyme-based sensors for poor stability under high temperature, the proposed method was a direct detection method for OPs and can be used for rapid monitoring of OPs residue concentration levels before LC-MS analysis.

(Invited) Tailoring 2D Materials As Artificial Enzymes for Developing Electrochemical Biosensors

There is a significant need for development of low-cost and portable diagnostics for non-invasive monitoring of biochemical markers. Among various biosensors, electrochemical sensors are at the forefront of point of care diagnostics, due to simple and real-time readout, low cost, high sensitivity, and portability, as evident from the dominance of enzymatic glucose sensors in the healthcare sector.(1) Despite their significant success, one of the main challenges with enzyme-based sensors is the limited (or none) choice of enzymes for analytes beyond glucose and their incompatibility with device engineering processes.(2)Over the past few years, there have been significant advances in flexible sensors, printed electronics, and wireless devices based on graphene and other 2D materials.(2–5) Being atomically thin, with high surface-to-volume ratio, 2D materials are extremely sensitive to surface perturbation, making them suitable for highly sensitive and selective electrochemical sensors. Moreover, their physical, electronic, and electrochemical properties can be modified via doping, defects, and heterostructures to enable new functionalities for biochemical sensing. We have recently made significant progress in developing non-enzymatic electrochemical sensors based on 2D materials and hybrids as ‘artificial enzymes’, with special focus on device scalability and ease of fabrication. In this regard, we have studied the role of substrate in material-analyte interface characteristic,(6) the effect of post-deposition low-temperature annealing of 2D inks on material-analyte interaction, and the importance of defect configuration in tuning the material-analyte band alignment.(7) In this talk, I will present our recent progress and undergoing research in this area.

Finite Element Method Study of Nanostructured Metal Oxide Based on NiO for Nonenzymatic Urea Sensors

Urea electrooxidation has attracted increasing attention because urea is an essential biomarker for diagnosing kidney conditions. Most urea sensors are based on the enzyme; however, enzyme-based sensors have a moderately complicated assembling method [1] due to poor stability. Different from the bulk diffusion of urea in the enzymatic urea oxidation [2], the nonenzymatic urea oxidation has reactions between the reductive and oxidative at the electrode surface [3]. Moreover, in order to use nonenzymatic urea sensors in a biomedical application area, high conductivity and catalytic activities are required. Therefore, a study of nonenzymatic urea sensor on a nanostructured electrode is of substantial interest.For urea detection, various metal oxides, such as ZnO [4], CuO [5], and NiO [6], have been broadly proposed. Practically, NiO catalysts were studied extensively for urea electrooxidation due to successful long-term operation [7]. Typical nonenzymatic catalysts for urea electrooxidation mainly focused on designing new nanostructures and maximizing their catalytic ability. However, quantitative models integrating the physical, chemical, and geometrical design properties still need improvement to develop sensor devices. The urea reaction occurs on the surface of nanostructured metal oxide. Thus, the effect of electrode geometry on the electrochemical reactions is motivated to explore urea sensors application.In the present study, we studied three different NiO structures such as nanorods, nanoflakes, and nanoparticles, for the nonenzymatic electrochemical sensor. Additionally, we developed a new analytical model to understand the nonenzymatic urea sensor using the finite element method. To further adjust the model, the morphology and the composition of the NiO catalysts were investigated using transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The NiO catalysts showed remarkable electrochemical achievement with acceptable linear sensitivity and selectivity to urea electrooxidation. Comprehensive information of the modeling concerning NiO as a catalyst in the nonenzymatic urea sensor will be given.References FATEMA, Kamrun Nahar, et al. “New Design of Active Material Based on YInWO4-G-SiO2 for a Urea Sensor and High Performance for Nonenzymatic Electrical Sensitivity.” ACS Biomaterials Science & Engineering, 2020.Debata, Suryakanti, et al. "Design of CdV2O4-V6O13 micro flowers for non-enzymatic electrochemical detection of urea." In AIP Conference Proceedings, vol. 2115, no. 1, p. 030058. AIP Publishing LLC, 2019.YOON, Jaesik, et al. “Silver-Nanoparticle-Decorated NiOOH Nanorods for Electrocatalytic Urea Sensing.” ACS Applied Nano Materials, 2020, 3.8: 7651-7658.YOON, Jaesik, et al. “Ag/ZnO Catalysts with Different ZnO Nanostructures for Non‐enzymatic Detection of Urea.” Electroanalysis, 2019, 31.1: 17-21.Goda, M. A., et al. “Enhanced Electrocatalytic Oxidation of Urea at CuOx-NiOx Nanoparticle-Based Binary Catalyst Modified Polyaniline/GC Electrodes.” Journal of The Electrochemical Society, 2020 167(6), 064522.Tyagi, Manisha, et al. "NiO nanoparticle-based urea biosensor." Biosensors and Bioelectronics 2013, 41:110-115.BARAKAT, Nasser AM, et al. “Influence of nitrogen doping on the electrocatalytic activity of Ni-incorporated carbon nanofibers toward urea oxidation.” International Journal of Hydrogen Energy, 2017, 42.34: 21741-21750.

An ultra-sensitive electrochemiluminescence probe based on ternary nanocomposite and boron nitride quantum dots for detection of diazinon.

Anew enzyme-free electrochemiluminescence (ECL) pesticide sensor was fabricated based on ternary nanocomposite of ruthenium nanoparticles/silver nanoparticles/graphene oxide on the surface of glassy carbon electrode for ultratrace determination of diazinon. Due to some drawbacks of enzyme-based sensors such as enzyme instability at elevatedtemperature, humidity, changes of pH, and high price of the enzyme, the use ofenzyme was omitted in the construction of the developed sensor. The silver nanoparticles with good electrocatalytic proficiency as a signal improving agent and tris(2,2bipyridine) ruthenium(II) as a popular luminophore were uniformly deposited on the surface of the prepared graphene oxide/GC electrode at nanoscale. Boron nitride quantum dots as an efficient co-reactant created the superior efficiency in amplifying the ECL intensity of the ruthenium-based ECL system. The prepared electrode was utilized for the detection of diazinon via the robust ECL method. For the present sensor, a wide linear dynamic range and low detection limit were achieved (3.0 × 10-15 to 6.5 × 10-9M and 9.5 × 10-16M, respectively). The obtained results confirmed the fabrication of the robust ECL probe, which is characterized by the cooperative effect of silver nanoparticles and the attached luminophore species. The main advantage of the presented sensor was that the samples could be diluted so that the effect of the interference species was negligible. Due to excellent properties toward accurate determination of diazinon, the ECL sensor as a new practical platform was applied for quantitative detection of diazinon in some real samples.

A highly sensitive non-enzymatic ascorbic acid electrochemical sensor based on polyoxometalate/Tris(2,2ˊ-bipyridine)ruthenium (II)/chitosan-palladium inorganic-organic self-assembled film

In this work, a highly sensitive non-enzymatic electrochemical sensor based on an inorganic-organic nanocomposite film consisting of H7P2Mo17V1O62 (P2Mo17V), Ru(bpy)3Cl2·6H2O (Ru(bpy)3) and chitosan-palladium (Cs-Pd) was constructed for the determination of ascorbic acid (AA). The non-enzymatic sensor has advantages such as simple preparation and operation, good reproducibility and superior sensitivity, which overcomes the drawbacks of enzyme-based sensors such as restricted immobilization and easy inactivation due to the combination of three active components in the new film presented here. The sensor displays excellent sensing performance for the detection of ascorbic acid with a fast response time (< 2 s), a wide linear range of 0.125–118 μM and a low detection limit of 0.1 μM (S/N = 3). In addition, the sensor was successfully employed to detect AA in juice.