We have developed a screen-printed electrochemical electrode (SPE) for paraoxon based on its inhibitory effect on the enzyme butyrylcholinesterase (BChE). The electrode was first modified by drop casting with a dispersion of carbon black nanoparticles (CBNPs) in a dimethylformamide-water mixture, and BChE was then immobilized on the surface by cross-linking. The resulting biosensor was exposed to standard solutions of paraoxon, and the enzymatic hydrolysis of butyrylthiocholine over time was determined measuring the enzymatic product thiocholine at a working voltage of +300 mV. The enzyme inhibition is linearly related to the concentration of paraoxon up to 30 μg L-1, and the detection limit is 5 μg L-1. The biosensor is stable for up to 78 days of storage at room temperature under dry conditions. It was applied to determined paraoxon in spiked waste water samples. The results underpin the potential of the use of CBNPs in electrochemical biosensors and also demonstrate that they represent a viable alternative to other carbon nanomaterials such as carbon nanotubes or graphene, and with the advantage of being very affordable
This paper describes a direct competitive immunoenzymatic spectrophotometric assay (ELISA) for tetrodotoxin (TTX) determination and the adaptation of this method for use in an electrochemical assay format. The novelty of this work involves the use of the antigen labelled with alkaline phosphatase (AP); this conjugate was prepared in our laboratory as there is no commercially available conjugate of any kind for TTX. The new conjugate was characterized in terms of its affinity for the specific antibody as well as the residual concentration and the residual activity of the enzyme (AP) incorporated as label. The proposed method based on the new conjugate showed satisfactory results for TTX determination: for the spectrophotometric method the dynamic range was 4-15 ng mL(-1) with a limit of detection (LOD) of 2 ng mL(-1) (R=0.9247), whereas for the electrochemical protocol the dynamic range was 2-50 ng mL(-1) and the LOD was 1 ng mL(-1).
In this work a miniaturized and disposable electrochemical sensor was developed to evaluate the cadmium and lead ion phytoremediation potential by the floating aquatic macrophyte Lemna minor L. The sensor is based on a screen-printed electrode modified "in-situ" with bismuth film, which is more environmentally friendly than the mercury-based sensor usually adopted for lead and cadmium ion detection. The sensor was coupled with a portable potentiostat for the simultaneous measurement of cadmium and lead ions by stripping analysis. The optimized analytical system allows the simultaneous detection of both heavy metals at the ppb level (LOD equal to 0.3 and 2 ppb for lead and cadmium ions, respectively) with the advantage of using a miniaturized and cost-effective system. The sensor was then applied for the evaluation of Pb(2+) or/and Cd(2+) uptake by measuring the amount of the heavy metals both in growth medium and in plant tissues during 1 week experiments. In this way, the use of Lemna minor coupled with a portable electrochemical sensor allows the set up of a model system able both to remove the heavy metals and to measure "in-situ" the magnitude of heavy metal removal.
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