Determination of trace copper ions with ultrahigh sensitivity and selectivity utilizing CdTe quantum dots coupled with enzyme inhibition

Abstract

A fluorescent transducer with the combination of the unique property of CdTe quantum dots (QDs) and enzymatic inhibition assays was successfully constructed for the purpose of ultrasensitive determination of Cu2+ ions. Alcohol oxidase (AO) catalyzed the oxidation of methanol to produce hydrogen peroxide (H2O2), inducing the quenching of QDs fluorescence. In the presence of Cu2+ ions, the activity of AO was inhibited and therefore, the quenching of QDs fluorescence was decreased. Other metal ions showed no intensive inhibition to the AO activity even at 10 or 100 times Cu2+ ions concentration, presenting a high selectivity of this fluorescent sensor. Using this QDs–enzyme hybrid system, the detection limit for Cu2+ ions was found to be as low as 0.176ng/mL (2.75nM) due to the superior fluorescence property of QDs. Practical application of the QDs–enzyme hybrid system has been demonstrated by domestic waste water, agricultural irrigation water and lake water analysis. Results of Cu2+ determinations were in good agreement with those obtained by inductively coupled plasma analytical method. The coupling of efficient quenching of QDs photoluminescence by H2O2 generated from oxidase-catalyzed reaction and the effective enzymatic inhibition make this a simple and sensitive method for heavy metal ions detection.