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Highlights • A third-generation biosensor based on nitric oxide reductase (NOR) was developed. • A MWCNTs/BMIMBF 4 nanocomposite was optimized to entrap NOR. • PGE/[MWCNTs/BMIMBF 4 /NOR] direct electron transfer behavior was characterized. • High sensitivity was reached towards NO unmediated bioelectrocatalytic reduction. • The biosensor kept 79–116% of its initial response after one month. Abstract Nitric oxide (NO) has a crucial role in signaling and cellular physiology in humans. Herein, a novel third-generation biosensor based on the Marinobacter hydrocarbonoclasticus metalloenzyme (nitric oxide reductase (NOR)), responsible for the NO reduction in the denitrifying processes, was developed through the direct adsorption of a new nanocomposite (multiwalled carbon nanotubes (MWCNTs)/1 -n- butyl-3-methylimidazolium tetrafluoroborate (BMIMBF 4)/NOR) onto a pyrolytic graphite electrode (PGE) surface. The NOR direct electron transfer behavior (formal potential of -0.255 ± 0.003 V vs. Ag/AgCl) and electrocatalysis towards NO reduction (−0.68 ± 0.03 V vs. Ag/AgCl) of the PGE/[MWCNTs/BMIMBF 4 /NOR] biosensor were investigated in phosphate buffer at pH 6.0. Large enzyme loading (2.04 × 10−10 mol/cm2), acceptable electron transfer rate between NOR and the PGE surface (k s = 0.35 s-1), and high affinity for NO (K m = 2.17 μmol L-1) were observed with this biosensor composition. A linear response to NO concentration (0.23–4.76 μmol L-1) was perceived with high sensitivity (0.429 μA/μmolL-1), a detection limit of 0.07 μmol L-1, appropriate repeatability (9.1% relative standard deviations (RSD)), reproducibility (6.0–11% RSD) and 80–102% recoveries. The biosensor was stable during 1 month retaining 79–116% of its initial response. These data confirmed that NOR incorporated in the MWCNTs/BMIMBF 4 nanocomposite can efficiently maintain its bioactivity paving a new and effective way for NO biosensing. [ABSTRACT FROM AUTHOR]

In this work, a norfloxacin selective modified glassy carbon electrode (GCE) based on a molecularly imprinted polymer (MIP) as electrochemical sensor was developed. A suspension of multi-walled carbon nanotubes (MWCNTs) was deposited on the electrode surface. Subsequently, a molecularly imprinted film was prepared by electropolymerization, via cyclic voltammetry of pyrrole (PPy) in the presence of norfloxacin (NFX) as the template molecule. A control electrode (NIP) was also prepared. Scanning electron microscopy (SEM) and cyclic voltammetry in a ferrocyanide solution were performed for morphological and electrochemical characterisation, respectively. Several experimental parameters were studied and optimised. For quantification purposes the MIP/MWCNT/GCE was immersed in NFX solutions for 10 min, and the detection was performed in voltammetric cell by square wave voltammetry. The proposed sensor presented a linear behaviour, between peak current intensity and logarithmic concentration of NFX between 1 × 10 −7 and 8 × 10 −6 M. The obtained results presented good precision, with a repeatability of 4.3% and reproducibility of 9% and the detection limit was 4.6 × 10 −8 M ( S/N = 3). The developed sensor displayed good selectivity and operational lifetime, is simple to fabricate and easy to operate and was successfully applied to the analysis of NFX in urine samples. [ABSTRACT FROM AUTHOR]

A novel electrochemical sensor for ochratoxin A (OTA) detection was fabricated through the modification of a glassy carbon electrode (GCE) with multiwalled carbon nanotubes (MWCNTs) and a molecularly imprinted polymer (MIP). The MWCNTs dramatically promoted the sensitivity of the developed sensor, while polypyrrole (PPy) imprinted with OTA served as the selective recognition element. The imprinted PPy film was prepared by electropolymerization of pyrrole in the presence of OTA as a template molecule via cyclic voltammetry (CV). The electrochemical oxidation of OTA at the developed sensor was investigated by CV and differential pulse voltammetry (DPV). The developed MIP/MWCNT/GCE sensor showed a linear relationship, when using DPV, between peak current intensity and OTA concentration in the range between 0.050 and 1.0 μM, with limits of detection (LOD) and quantification of 0.0041 μM (1.7 μg/L) and 0.014 μM (5.7 μg/L) respectively. With the developed sensor precise results were obtained; relative standard deviations of 4.2% and 7.5% in the evaluation of the repeatability and reproducibility, respectively. The MIP/MWCNT/GCE sensor is simple to fabricate and easy to use and was successfully applied to the determination of OTA in spiked beer and wine samples, with recoveries between 84 and 104%, without the need of a sample pre-treatment step. [ABSTRACT FROM AUTHOR]

• First time a selective MIP electrochemical sensor was developed for Furazolidone (FZD). • QM calculations and MD simulations were used to select the best functional monomer and the optimum polymerisation conditions. • The sensor constructed based on MIP-CPE-MWCNTs showed high selectivity and sensitivity. • The proposed sensor was successfully applied for FZD detection in water samples without any pre-treatment step. Determination of antibiotics in environmental waters is an important global issue. Although furazolidone (FZD) was banned from use in food-producing animals, owing to its mutagenic and carcinogenic effects, this antibiotic has been illegally used across the world and its presence in environment have being noted. In this work, the first selective molecularly imprinted polymer (MIP) was developed for electrochemical detection of FZD. It was constructed based on the modification of the traditional carbon paste electrode (CPE) with MIP microparticles, followed by introduction of multi-walled carbon nanotubes (MWCNTs). Quantum mechanical (QM) calculations and molecular dynamics (MD) simulations were performed to allow rational selection of an appropriate functional monomer and to simulate the best pre-polymerisation conditions, respectively. The MIP were synthetized by polymerization using 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as monomer and FZD as template molecule. The MIP microparticles were then incorporated on CPE-MWCNTs and the electrochemical analysis of FZD were evaluated by differential pulse voltammetry (DPV). After optimisation of experimental conditions, the MIP-CPE-MWCNTs sensor exhibited a good linear response over the concentration range of 0.01 μM to 1 μM with a correlation coefficient of 0.9995. The limit of detection (LOD) was found to be 0.03 μM (S/N = 3). Due to high imprinting efficiency the sensor displayed selectivity to recognise FZD molecules and it was successfully applied in water samples where excellent recovery values (over 90 %) were obtained. The proposed sensor provides an efficient and promising sustainable strategy for monitorisation of FZD in environmental waters. [ABSTRACT FROM AUTHOR]