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Background: Since vascular endothelial growth factor (VEGF) is a significant regulator of cancer angiogenesis, it is essential to develop a technology for its sensitive detection. Herein, we sensitized a chemiluminescence (CL) immunoassay through the combination of H2O2-sensitive TGA-CdTe quantum dot (QD) as signal transduction, dextran as a cross-linker to prepare enzyme-labeled antigen and the ultrahigh bioactivity of catalase (CAT) as reporter enzyme. Results: Under the optimized experimental conditions, the chemiluminescence enzyme-linked immunosorbent assay (CL-ELISA) method can detect VEGF in the excellent linear range of 2–35,000 pg mL−1, with a detection limit (S/N = 3) of 0.5 pg mL−1 which was approximately ten times lower than the commercial colorimetric immunoassay. This proposed method has been successfully applied to the clinical determination of VEGF in the human serum samples, and the results illustrated an excellent correlation with the conventional ELISA method (R2 = 0.997). The suitable recovery rate of the method in the serum ranged from 97 to 107%, with a relative standard deviation of 1.2% to 13.4%. Conclusions: The novel immunoassay proposes a highly sensitive, specific, and stable method for very low levels detection of VEGF that can be used in the primary diagnosis of tumors. With the well-designed sensing platform, this approach has a broad potential to be applied for quantitative analysis of numerous disease-related protein biomarkers for which antibodies are available. [ABSTRACT FROM AUTHOR]

[Display omitted] • QD/H 2 O 2 chemiluminescence system was successfully used in HRP assay and immunoassay. • The calculated Km of HRP was more reliable compared to the colorimetric method. • A broader linear range and improved LOD value was exhibited in T4 detection. • The proposed method showed a significant correlation with the commercial ELISA. • High efficiency of the method can be applied in sensitive detection technologies. Horseradish peroxidase (HRP) is usually used as a label enzyme in immunoassay so the method used for HRP detection in enzyme immunoassay (EIA) plays a key role in sensitivity and precision. The catalytic activity of HRP does not strictly follow classic Michaelis-Menten kinetics, probably due to the inactivation of the enzyme at high concentrations of H 2 O 2. In this paper, a highly sensitive alternative procedure for the HRP assay using H 2 O 2 -sensitive CdTe quantum dots as a chemiluminescence (CL) system is reported. This method can measure a much more accurate and reliable value of K m (187 mM H 2 O 2) in comparison with the standard detection method. This system also was applied to thyroid hormone (T4) detection using HRP-based immunoassay. The QD/H 2 O 2 system exhibits a higher linear range of 0.2–16 μg/dL with the improved LOD value of 0.06 μg/dL and selective response to T4, which was better than the commercial colorimetric immunoassay. Meanwhile, the proposed method has been successfully applied to the clinical determination of T4 in the serum samples, and the results confirmed an excellent correlation with the conventional ELISA method (R2 = 0.9832), indicating the potential applications of the method for clinical diagnosis as well. [ABSTRACT FROM AUTHOR]