Thermometric determination of copper(II) using acid urease

Abstract

A thermometric assay for the measurement of copper(II) is reported that makes use of acid urease immobilized on controlled-pore glass (CPG) with coupling to a thermometric continuous-flow sensor system. Enzyme thermistor analysis was performed by a flow injection technique. Urea was injected into the system to give a temperature change corresponding to 100% enzyme activity. After inhibition by copper(II), the enzyme activity and the corresponding temperature change of the reaction were reduced. The percentage inhibition was calculated from the peak heights before and after copper(II) injection. The typical response time was 3–5 min and the dynamic range was from 5 × 10^–6 to 1 × 10^–4 mol l^–1(0.3–6.4 ppm) coper(II). The main advantages of the thermometric biosensor assay are (a) a 20-fold higher sensitivity of acid urease to copper(II) than urease (from jack beans), which is commonly used for metal sensing, (b) the fact that regeneration of the enzyme does not require any metal chelating agent, (c) no decrease in enzyme activity because of irreversible inhibition and (d) the possibility of performing intermittent monitoring of Copper(II) using a thermistor device.