This study focused on the development of a sensitive enzymatic biosensor for the determination of pirimicarb pesticide based on the immobilization of laccase on composite carbon paste electrodes. Multi-walled carbon nanotubes (MWCNTs) paste electrode modified by dispersion of laccase (3%, w/w) within the optimum composite matrix (60:40%, w/w, MWCNTs and paraffin binder) showed the best performance, with excellent electron transfer kinetic and catalytic effects related to the redox process of the substrate 4-aminophenol. No metal or anti-interference membrane was added. Based on the inhibition of laccase activity, pirimicarb can be determined in the range 9.90 × 10(-7) to 1.15 × 10(-5) mol L(-1) using 4-aminophenol as substrate at the optimum pH of 5.0, with acceptable repeatability and reproducibility (relative standard deviations lower than 5%). The limit of detection obtained was 1.8 × 10(-7) mol L(-1) (0.04 mg kg(-1) on a fresh weight vegetable basis). The high activity and catalytic properties of the laccase-based biosensor are retained during ca. one month. The optimized electroanalytical protocol coupled to the QuEChERS methodology were applied to tomato and lettuce samples spiked at three levels; recoveries ranging from 91.0 ± 0.1% to 101.0 ± 0.3% were attained. No significant effects in the pirimicarb electroanalysis were observed by the presence of pro-vitamin A, vitamins B1 and C, and glucose in the vegetable extracts. The proposed biosensor-based pesticide residue methodology fulfills all requisites to be used in implementation of food safety programs.

Multi-walled carbon nanotubes (MWCNT) have provided unprecedented advances in the design of electrochemical sensors. They are composed by sp2 carbon units oriented as multiple concentric tubes of rolled-up graphene, and present remarkable active surface area, chemical inertness, high strength, and low charge-transfer resistance in both aqueous and non-aqueous solutions. MWCNT are very versatile and have been boosting the development of a new generation of electrochemical sensors with application in medicine, pharmacology, food industry, forensic chemistry, and environmental fields. This work highlights the most important synthesis methods and relevant electrochemical properties of MWCNT for the construction of electrochemical sensors, and the numerous configurations and successful applications of these devices. Thousands of studies have been attesting to the exceptional electroanalytical performance of these devices, but there are still questions in MWCNT electrochemistry that deserve more investigation, aiming to provide new outlooks and advances in this field. Additionally, MWCNT-based sensors should be further explored for real industrial applications including for on-line quality control.

A bi-enzymatic biosensor (LACC-TYR-AuNPs-CS/GPE) for carbamates was prepared in a single step by electro-deposition of a hybrid film onto a graphene doped carbon paste electrode (GPE). Graphene and the gold nanopar-ticles (AuNPs) were morphologically characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, dynamic light scattering and laser Doppler velocimetry. The electrodeposited hybrid film was composed of laccase (LACC), tyrosinase (TYR) and AuNPs entrapped in a chitosan (CS) polymeric matrix. Exper-imental parameters, namely graphene redox state, AuNPs:CS ratio, enzymes concentration, pH and inhibition time were evaluated. LACC-TYR-AuNPs-CS/GPE exhibited an improved Michaelis-Menten kinetic constant (26.9 ± 0.5 M) when compared with LACC-AuNPs-CS/GPE (37.8 ± 0.2 M) and TYR-AuNPs-CS/GPE (52.3 ± 0.4 M). Using 4-aminophenol as substrate at pH 5.5, the device presented wide linear ranges, low detection limits (1.68 × 10 −9 ± 1.18× 10 −10 -2.15 × 10 −7 ± 3.41 × 10 −9 M), high accuracy, sensitivity (1.13 × 10 6 ± 8.11 × 10 4 -2.19 × 10 8 ± 2.51× 10 7 %inhibition M −1 ), repeatability (1.2-5.8% RSD), reproducibility (3.2-6.5% RSD) and stability (ca. twenty days) to determine carbaryl, formetanate hydrochloride, propoxur and ziram in citrus fruits based on their inhibitory capacity on the polyphenoloxidases activity. Recoveries at two fortified levels ranged from 93.8 ± 0.3% (lemon) to 97.8 ± 0.3% (orange). Glucose, citric acid and ascorbic acid do not interfere signifi-cantly in the electroanalysis. The proposed electroanalytical procedure can be a promising tool for food safety control.

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diamond (BDD) electrodes possess outstanding physical, chemical, and electronic properties and have been successfully, yet in a limited way, explored in the electroanalysis of substances with therapeutic action (analgesics, antipyretics, antibiotics, anti-inflammatories, antihypertensives, antidepressants, vitamins, and others) in diverse milieus (pharmaceutical formulations, urine, serum, whole blood, surface waters, seawaters, groundwater, wastewaters, etc.). Therefore, in this Review, a broad overview of the available scientific information on recent progress and achievements of the application of bare or modified BDD electrodes to the bioanalytical and environmental detection of pharmaceutical compounds is presented. The main parameters, for example boron concentration, applied operational conditions during pretreatment, chemical and physical structure, and other influential factors on the electroanalytical BDD electrodes performance, are discussed.[a] Dr.