Sensing elements of optical sensors based on polystyrene with covalently immobilized reagents

A procedure was developed for the preparation of sensing elements for optical sensors based on pressed membranes of optically transparent polystyrene 250 μm in thickness. The procedure for assembling reagents on a matrix surface involved the operating sequence of nitration, reduction, diazotization, and azo coupling with organic reagents from the class of monoazochromotropic acid. This allowed us to prepare sensing elements with reproducible properties. The optical properties of immobilized reagents and their complexes with metal ions are practically analogous to those of compounds formed in solutions. External diffusion is a rate-determining step in the reactions with metal ions. The time constants of various sensing elements at metal concentrations of 4 × 10−7 mol/mL were about 30 s, and the time taken to produce a signal at a 95% level was 50–56 s.