Water-soluble luminescent CdTe-ZnS quantum dots (QDs) modified by mercaptopropyl-acid was used to determinate H' in aqueous solutions. The fluorescence (FL) of the water-soluble QDs could be irreversibly quenched by H' and the fluorescence intensity of the water-soluble QDs decreased linearly as the pH decreased in the range of 8.0-5.0. Based on this phenomenon, a simple, rapid and specific method to quick determination of enzyme reaction kinetics was proposed. The modified QDs was successfully used as pH probe in monitoring the hydrolysis of glycidyl butyrate catalyzed by porcine pancreatic lipase (PPL). The proposed method demonstrated improved sensitivity, stability and a wider monitoring range for H+ determinations as compared to the already described analytical methods based on PNR (c) 2006 Elsevier Inc. All rights reserved.