•A Cu2+ ion sensor was developed based on its catalytic oxidation of l-cysteine.•The detection limit of the biosensor can achieve 0.5 nM with high specificity.•This sensor can be simply used in real sample for real-time detection of Cu2+ ion.As an essential element, copper ion (Cu2+) plays important roles in human beings for its participation in diverse metabolic processes as a cofactor and/or a structural component of enzymes. However, excessive uptake of Cu2+ ion gives rise to the risk of certain diseases. So, it is important to develop simple ways to monitor and detect Cu2+ ion. In this study, a simple, facile colorimetric sensor for the ultrasensitive determination of Cu2+ ion was developed based on the following principle: l-cysteine and 1-chloro-2,4-dinitrobenzene (CDNB) could be conjugated to form the yellow product 2,4-dinitrophenylcysteine (DNPC), which was measurable at 355 nm; however, upon addition of Cu2+ ion, the absorbance of DNPC would be decreased owing to the Cu2+ ion catalytic oxidation of l-cysteine to l-cystine in the presence of O2. Thus, the colorimetric detection of Cu2+ ion could be achieved. The optimal pH, buffer, temperature and incubation time for the colorimetric sensor were obtained of pH 6.8 in 0.1 M HEPES solution, 90 °C and 50 min, respectively. A good linearity within the range of 0.8–10 nM (r=0.996) was attained, with a high detectability up to 0.5 nM. Analyses of Cu2+ ion in drinking water, lake water, seawater and biological samples were carried out and the method performances were found to agree well with that obtained by ICP-MS. The developed simple colorimetric sensor proved applicable for Cu2+ ion determination in real samples with high sensitivity and selectivity.

Furazolidone (FZD) has been widely used as an antibacterial and antiprotozoal feed additive for poultry, cattle and farmed fish. Since FZD has been shown to have mutagenic, genotoxic and potentially carcinogenic properties when tested in a variety of systems, there is an increasing need to find a way to remove FZD from contaminated environments. In this report, three bacterial strains Acinetobacter calcoaceticus T32, Pseudomonas putida SP1 and Proteus mirabilis V7 capable of degrading FZD effectively were isolated, identified and characterized. The reduced FZD concentration after degradation was determined by HPLC. After bacterial cells were grown in the media containing 5 mg l−1 FZD for 5 days, almost all FZD was degraded by A. calcoaceticus T32, and more than 50% of FZD was degraded by P. putida SP1 and P. mirabilis V7, respectively. Bacterial GST activity of A. calcoaceticus T32, P. putida SP1 and P. mirabilis V7 was determined to be influenced by different FZD concentrations. Cytotoxicity analysis showed that FZD was degraded to the metabolites with far less cytotoxicity compared to FZD. The inoculation of bacterial strains A. calcoaceticus T32, P. putida SP1 and P. mirabilis V7 into FZD-contained media resulted in a higher degradation efficiency than natural degradation, which indicated the potential application of these strains in treatment of FZD-polluted freshwater or seawater environments.Highlights► Three bacteria capable of degrading furazolidone were isolated and characterized. ► Bacterial GST activity was stimulated by FZD. ► Metabolites of furazolidone generated by bacterial degradation barely possessed cytotoxicity.