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A method is described for the chemiluminescence based determination of the activity of catalase (CAT) using H2O2-sensitive CdTe quantum dots (QDs). It is based on the finding that the chemiluminescence (CL) of the CdTe/H2O2 system is reduced due to the consumption of H2O2 by the catalytic action of CAT. The Michaelis constant is calculated to be 519 ± 27 mM, showing the potential of the method to accurately measure the Km compared to the standard method. The method does not require QDs to be conjugated to biological/organic molecules and therefore is considered to be a rapid and convenient method for determination of CAT in real samples. At an incubation time of 2 s, the LOD was calculated to be 4.5 unit/mL, with a linear range from 6 to 400 unit/mL. The assay is sensitive, simple, and suitable for practical applications.Schematic representation of chemiluminescence-based catalase U(CAT) assay using the CdSe QD/H2O2 system. The reduction of H2O2 is reflected by the chemiluminescence of the QDs. A mechanism is put forward based on the changes in chemiluminescence intensity of the QDs by the consumption of H2O2 due to the catalytic action of CAT. [ABSTRACT FROM AUTHOR]