Resolving the Kinetics of Single-Walled Carbon Nanotube–Polyester Polyurethane Nanoparticle Conjugate Fluorescence Sensors toward Polymer Degrading Enzymes

Single-walled carbon nanotubes (SWCNTs) are fluorescent materials that have been developed as sensors for measuring the activities of enzymes. However, most sensors to date rely on end-point measurement and empirical functions to correlate enzyme concentrations with fluorescence responses. Less emphasis is put on analyzing time-dependent fluorescence responses and their connections with enzymatic kinetics. Here, improved from our previous sensor design, we use trimethylchitosan-wrapped SWCNTs to measure the enzymatic degradation rate of Impranil nanoparticles, a polyester polyurethane model substrate. Through careful analysis of the characteristic time constant and saturation fluorescence, which are resolved from time-dependent brightening responses of the sensors, linear relations are found between fluorescence change rates and both enzyme concentrations and Impranil-to-SWCNT ratios, thus showing that the reaction is first-ordered toward both enzyme and substrate concentrations. The proposed sensor design and data analysis strategy can quantitively determine the relative enzymatic activity and provide insights into the kinetics of sensors and enzymatic reactions.