Polyaniline-modified cholinesterase sensor for pesticide determination

Simple and Fast Pesticide Nanosensors: Example of Surface Plasmon Resonance Coumaphos Nanosensor

Here, a molecular imprinting technique was employed to create an SPR-based nanosensor for the selective and sensitive detection of organophosphate-based coumaphos, a toxic insecticide/veterinary drug often used. To achieve this, UV polymerization was used to create polymeric nanofilms using N-methacryloyl-l-cysteine methyl ester, ethylene glycol dimethacrylate, and 2-hydroxyethyl methacrylate, which are functional monomers, cross-linkers, and hydrophilicity enabling agents, respectively. Several methods, including scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle (CA) analyses, were used to characterize the nanofilms. Using coumaphos-imprinted SPR (CIP-SPR) and non-imprinted SPR (NIP-SPR) nanosensor chips, the kinetic evaluations of coumaphos sensing were investigated. The created CIP-SPR nanosensor demonstrated high selectivity to the coumaphos molecule compared to similar competitor molecules, including diazinon, pirimiphos-methyl, pyridaphenthion, phosalone, N-2,4(dimethylphenyl) formamide, 2,4-dimethylaniline, dimethoate, and phosmet. Additionally, there is a magnificent linear relationship for the concentration range of 0.1-250 ppb, with a low limit of detection (LOD) and limit of quantification (LOQ) of 0.001 and 0.003 ppb, respectively, and a high imprinting factor (I.F.4.4) for coumaphos. The Langmuir adsorption model is the best appropriate thermodynamic approach for the nanosensor. Intraday trials were performed three times with five repetitions to statistically evaluate the CIP-SPR nanosensor's reusability. Reusability investigations for the two weeks of interday analyses also indicated the three-dimensional stability of the CIP-SPR nanosensor. The remarkable reusability and reproducibility of the procedure are indicated by an RSD% result of less than 1.5. Therefore, it has been determined that the generated CIP-SPR nanosensors are highly selective, rapidly responsive, simple to use, reusable, and sensitive for coumaphos detection in an aqueous solution. An amino acid, which was used to detect coumaphos, included a CIP-SPR nanosensor manufactured without complicated coupling methods and labelling processes. Liquid chromatography with tandem mass spectrometry (LC/MS-MS) studies was performed for the validation studies of the SPR.

2D Ti3C2Tx flakes prepared by in-situ HF etchant for simultaneous screening of carbamate pesticides

Present work reports preparation of colloidal single/few layer Ti₃C₂T_x MXene flakes using minimally intensive layer delamination (MILD) method for rapid electroanalytical screening of carbamate pesticides. Lithium fluoride salt and hydrochloric acid (7.5 M LiF/9M HCl) was used to produce in-situ generated HF as etchant to remove Al successfully from Ti₃AlC₂ MAX phase. Unlike the clay method (5 M LiF/6M HCl), this methodology simplified Ti₃C₂T_x synthesis protocol resulting in Li⁺ ions intercalated Ti₃C₂T_x which was delaminated without further sonication. The delaminated Ti₃C₂T_x flakes were found to be single/few layered sheets with mostly -OH and -O terminated surface groups. The characteristic 002 peak observed in X-ray diffraction (XRD) at 2θ = 6.4° with interplaner distance of 1.1137 nm suggested broadening of the peak attributed to the presence of Li⁺ ions between Ti₃C₂T_x flakes. Delaminated Ti₃C₂T_x flakes were utilized as working electrode which demonstrated simultaneous and selective detection of carbamate pesticides methiocarb and diethofencarb by voltammetry. The oxidation peaks of the two pesticides were well separated by a potential difference of 0.35 V in 0.5 M H₂SO₄ and DPV detection limits were calculated as 0.19 μg mL^-1 and 0.46 μg mL^-1 for methiocarb and diethofencarb respectively. Ti₃C₂T_x flakes as electrochemical sensor exhibited long term stability and acceptable recoveries in real sample for environmental applications.

Electro-deposited nano-webbed structures based on polyaniline/multi walled carbon nanotubes for enzymatic detection of organophosphates

We report the development of an ultrasensitive electrochemical sensor using polyaniline (PANi) and carboxyl functionalized multi-walled carbon nanotubes (fMWCNT) for the detection of organophosphates (OPs) in real samples. The sensor was tested in the linear concentration range of 10 ng/L to 120 ng/L. The limit of detection (LoD) was found to be 8.8 ng/L with sensitivity 0.41 mA/ng/L/cm2 for chlorpyrifos (CPF); and 10.2 ng/L with sensitivity 0.58 mA/ng/L/cm2 for methyl parathion (MP). The vegetable samples (cucumber) were also tested. The average % recovery for CPF and MP were found to be 98.05% and 96.63% respectively. The developed sensor showed stability for a period of 30 days. The interference of the sensor was studied with heavy metals (cadmium (Cd), chromium (Cr), lead (Pb), arsenic (As)) which was found to be < 10%. The developed sensor will play a major role in real-time monitoring of food products, leading to food safety.

Conducting Polymers and Their Applications in Diabetes Management

Advances in conducting polymers (CPs) have promoted the development of diabetic monitoring and treatment, which is of great significance in human healthcare and modern medicine. CPs are special polymers with physical and electrochemical features resembling metals, inorganic semiconductors and non-conducting polymers. To improve and extend their properties, the fabrication of CPs and CP composites has attracted intensive attention in recent decades. Some CPs are biocompatible and suitable for biomedical use. Thus, the intriguing properties of CPs make wearable, noninvasive, continuous diabetes managing devices and other potential applications in diabetes possible in the near future. To highlight the recent advances of CPs and their derived materials (especially in conducting polymer hydrogels), here we discuss their fabrication and characterization, review the current state-of-the-art research in diabetes management based on these materials and describe current challenges as well as future potential research directions.

An electrochemical sensor based on single-stranded DNA-poly(sulfosalicylic acid) composite film for simultaneous determination of adenine, guanine, and thymine

Poly(sulfosalicylic acid) and single-stranded DNA composite (PSSA-ssDNA)-modified glassy carbon electrode (GCE) was prepared by electropolymerization and then successfully used to simultaneously determine adenine (A), guanine (G), and thymine (T). The characterization of electrochemically synthesized PSSA-ssDNA film was investigated by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The modified electrode exhibited enhanced electrocatalytic behavior and good stability for the simultaneous determination of A, G, and T in 0.1M phosphate buffer solution (PBS, pH 7.0). Well-separated voltammetric peaks were obtained among A, G, and T presented in the analyte mixture. Under the optimal conditions, the peak currents for A, G, and T increased linearly with the increase of analyte mixture concentration in the ranges of 6.5×10(-8) to 1.1×10(-6), 6.5×10(-8) to 1.1×10(-6), and 4.1×10(-6) to 2.7×10(-5)M, respectively. The detection limits (signal/noise=3) for A, G, and T were 2.2×10(-8), 2.2×10(-8), and 1.4×10(-6)M, respectively.

Review on the use of enzymes for the detection of organochlorine, organophosphate and carbamate pesticides in the environment

Pesticides are released intentionally into the environment and, through various processes, contaminate the environment. Three of the main classes of pesticides that pose a serious problem are organochlorines, organophosphates and carbamates. While pesticides are associated with many health effects, there is a lack of monitoring data on these contaminants. Traditional chromatographic methods are effective for the analysis of pesticides in the environment, but have limitations and prevent adequate monitoring. Enzymatic methods have been promoted for many years as an alternative method of detection of these pesticides. The main enzymes that have been utilised in this regard have been acetylcholinesterase, butyrylcholinesterase, alkaline phosphatase, organophosphorus hydrolase and tyrosinase. The enzymatic methods are based on the activation or inhibition of the enzyme by a pesticide which is proportional to the concentration of the pesticide. Research on enzymatic methods of detection, as well as some of the problems and challenges associated with these methods, is extensively discussed in this review. These methods can serve as a tool for screening large samples which can be followed up with the more traditional chromatographic methods of analysis.

Acetylcholinesterase-polyaniline biosensor investigation of organophosphate pesticides in selected organic solvents

The behavior of an amperometric organic-phase biosensor consisting of a gold electrode modified first with a mercaptobenzothiazole self-assembled monolayer, followed by electropolymerization of polyaniline in which acetylcholinesterase as enzyme was immobilized, has been developed and evaluated for organophosphorous pesticide detection. The voltammetric results have shown that the formal potential shifts anodically as the Au/MBT/PANI/AChE/PVAc thick-film biosensor responded to acetylthiocholine substrate addition under anaerobic conditions in selected organic solvent media containing 2% v/v 0.05 M phosphate buffer, 0.1 M KCl (pH 7.2) solution. Detection limits in the order of 0.147 ppb for diazinon and 0.172 ppb for fenthion in acetone-saline phosphate buffer solution, and 0.180 ppb for diazinon and 0.194 ppb for fenthion in ethanol-saline phosphate buffer solution has been achieved.

Enhancement of a conducting polymer-based biosensor using carbon nanotube-doped polyaniline

A biosensor with improved performance was developed through the immobilization of horseradish peroxidase (HRP) onto electropolymerized polyaniline (PANI) films doped with carbon nanotubes (CNTs). The effects of electropolymerization cycle and CNT concentration on the response of the biosensor toward H2O2 were investigated. It was found that the application of CNTs in the biosensor system could increase the amount and stability of the immobilized enzyme, and greatly enhanced the biosensor response. Compared with the biosensor without CNTs, the proposed biosensor exhibited enhanced stability and approximately eight-fold sensitivity. A linear range from 0.2 to 19 microM for the detection of H2O2 was observed for the proposed biosensor, with a detection limit of 68 nM at a signal-to-noise ratio of 3 and a response time of less than 5s.