No abstract

Urea Amperometric biosensor was obtained on the base of nanostructured polypyrrole (PPy) and poly orthophenylenediamine (POPDA). The optimal conditions for monomer electropolymerization were determined. The effect of supporting electrolyte and number of deposition cycles on the OPDA and Py electropolymerization were studied. It was proved that POPDA and PPy were affected by pH changes and responded to the ammonium, product of urease catalyzed reaction. SEM images of the modified Pt/PPy electrode were presented. The cycle voltammograms and chrono amperometric curves of Pt/POPDA/urease and Pt/PPy/urease electrodes were studied. A good linear relationship was observed for Pt/POPDA/urease electrode in a concentration range from 6.7 to 54 mM urea. For Pt/PPy/urease electrode the linear relation in the range from 0.02 to 0.16 mM urea was determined. The entrapped carbon nanotubes (CNT) in PPy film and the bipolymer layers were prepared for construction of Pt/PPy/CNT/urease, Pt/POPDA/PPy/urease and Pt/PPy/POPDA/urease biosensors. Obviously, the addition of POPDA to the composition of the two biosensors (Pt/PPy/POPDA/urease and Pt/POPDA/PPy/urease) reduced their sensitivity to urea. Pt/РPy/CNT/urease and Pt/РPy/ urease biosensors were 173 and 138 times more sensitive to urea than biosensor without PPy (Pt/POPDA/urease biosensor). It was found, that the performance of Pt/PPy/CNT/urease electrode was the best from the five obtained biosensors: linear range of urea concentrations-from 0.02 to 0.16 mM; sensitivity-15.22 µA/mM and detection limit-0.005 mM urea.

A fluorescent immunoassay for separate and simultaneous determination of penicillin (PEN) and sulphadimethoxine (SDM) in milk was developed. Monoclonal antibodies immobilised on carboxylic magnetic nanoparticles (MNPs) were used. It was proved that the protein A‐oriented immobilisation method (OI) provided a 1.5‐times more sensitive assay than the random immobilisation one (RI). The activation of MNPs with a mixture of N‐(3‐dimethylaminopropyl)‐N‐ethylcarbodiimide (EDC) and N‐hydroxysuccinimide (NHS) ensured a five‐times higher sensitivity of immunoassay than the activation using EDC. The linearity of standard curves in milk was: 3/10 ng/mL PEN (OI and RI), 50/250 ng/mL SDM (OI), and 50/500 ng/mL SDM (RI).