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A conductometric tyrosinase biosensor has been developed to determine herbicides, alachlor, diazinon and carbaryl, in aqueous solutions. Tyrosinase from mushroom was immobilized on the sensitive part of interdigitated platinum planar electrodes by cross-linking with bovine serum albumin (BSA) in saturated glutaraldehyde (GA) vapor for 30 min. Herbicides inhibited tyrosinase, and the decrease of enzyme activity was used to determine these herbicides. Parameters influencing the performance of the systems were optimized to be used in the inhibition procedures. Detection limits for diazinon, alachlor and carbaryl were about 5.0×10-8, 1.5×10-7 and 2.0×10-7 M, respectively. A relative standard deviation (RSD) (five times successive measurements) of the conductance responses is 5%. The 90% of the enzyme activity was still maintained after four weeks of storage at 4 oC in 5.0 mM phosphate buffer, pH 7.0.

Finding effective methods for simultaneous removal of antibiotics and heavy metals has attracted increasing concerns. Herein, we investigated the co-adsorption behaviors of chlortetracycline (CTC) and Pb (II) onto struvite loaded diatomite (SD) in aqueous solution, and their interface interactions mechanism was investigated using crystal and microstructure analysis combined with density functional theory (DFT) calculations. The adsorption capacity at equilibrium of CTC increased from 44.28 to 87.58 mmol/kg with the presence of Pb (II), but the adsorption capacity at equilibrium of Pb (II) decreased from 4289.70 to 3559.9 mmol/kg with the presence of CTC. Besides, the effect of environmental factors (solution pH and humic acid) was also evaluated. Microstructure analysis for recovered products demonstrated that the interface interactions brought by the surface Pb(II) of Pb 5 (PO 4 ) 3 OH and carbonyl-O of CTC could facilitate the removal of CTC but inhibit the removal of Pb(II) by suppressing the crystal growth of Pb 5 (PO 4 ) 3 OH, especially the orientation growth of (0 0 1) crystal plane. DFT calculations gave theoretical support for the interface interactions between Pb 5 (PO 4 ) 3 OH and CTC., (Copyright © 2020 Elsevier B.V. All rights reserved.)

A highly sensitive, fast and stable conductometric enzyme biosensor for determination of nitrate in water is reported for the first time. The biosensor electrodes were modified by methyl viologen mediator mixed with nitrate reductase (NR) from Aspergillus niger by cross-linking with glutaraldehyde in the presence of bovine serum albumin and Nafion((R)) cation-exchange polymer. The process parameters for the fabrication of the enzyme electrode and various experimental variables such as pH, the enzyme loading and time of immobilization in glutaralaldehyde vapor were investigated with regard to their influence on sensitivity, limit of detection, dynamic range and operational and storage stability. The biosensor can reach 95% of steady-state conductance value in about 15s. Linear calibration in the range of 0.02 and 0.25 mM with detection limits of 0.005 mM nitrate was obtained with a signal-to-noise ratio of 3. When stored in 5 mM phosphate buffer (pH 7.5) at 4 degrees C, the sensor showed good stability over 2 weeks.