A new thermosensitive fluorescent probe for diol sensing: Poly(N-isopropylacrylamide-co-vinylphenylboronic acid)-alizarin red S complex

The reversible complex formation between newly synthesized temperature sensitive copolymer, N-isopropylacrylamide-co-4-vinylphenylboronic acid and diol carrying molecules was first investigated by fluorescence spectroscopy. This investigation resulted in a development of a temperature sensitive-fluorescent probe used for quantitative determination of diol carrying molecules. In the first stage of competitive assay developed in this study, the receptor (i.e. boronic acid groups of temperature sensitive copolymer) and the reporter (a catechol dye, alizarin red S) associated at the selected pH and temperature to give a fluorescent cyclic boronate ester. The stimuli-responsive character of copolymer allowed to control the formation of fluorescent complex by adjusting the temperature. The maximum intensity was observed at 660 nm in the emission spectrum of the cyclic boronate ester. The fluorescent receptor-reporter complex (i.e. cyclic borate ester formed from boronic acid and ARS) was then partly dissociated in the presence of diol carrying guest due to the formation of another non-fluorescent complex between copolymer and guest. Various agents from different material groups, fructose, ascorbic acid, β-nicotinamide adenine dinucleotide (β-NAD) and horse radish peroxidase (HRP) were used as target diol carrying agents. The decrease in fluorescent intensity due to the dissolution of the receptor-reporter complex is proportional to the concentration of target diol carrying agent.