Detection of human leptin in serum using chemiluminescence immunosensor: Signal amplification by hemin/G-quadruplex DNAzymes and protein carriers by Fe3O4/polydopamine/Au nanocomposites

A sandwich chemiluminescence (CL) immunosensor for sensitive detection of human leptin was developed with a multiple signal amplification strategy from catalytic hemin/G-quadruplex DNAzymes and functional superparamagnetic nanocomposites. To construct this sensing platform, core–shell structural Fe 3 O 4 /polydopamine (PD)/Au superparamagnetic nanocomposites were synthesized by an in situ method with PD as a substrate adhesive. These nanocomposites were further characterized by scanning electron microscopy, transmission electronic microscopy, energy-dispersive spectroscopy, Fourier transform infrared spectrum and a vibrating sample magnetometer at room temperature. In this immunosensor, the monoclonal anti-human leptin antibody (capture antibody) was bound to the Fe 3 O 4 /PD/Au nanocomposites. Human leptin, biotinylated detection antibodies and streptavidin-DNAzymes were successively combined the above-mentioned nanocomposites to form sandwich-type immunocomplex through specific interactions. The magnetic particles loaded with the immunocomplex were separated by an external magnet, and the DNAzymes in the immunocomplex greatly enhanced the CL emission of the luminol–H 2 O 2 system. The immunosensor exhibited a high sensitivity, a good specificity, and a wide linear range for human leptin detection from 1.0   pg   mL −1 to 8.0   ×   10 2   pg   mL −1 with a low detection limit of 0.3   pg   mL −1 . This sensor is one of the most sensitive methods for leptin detection due to the highly efficient catalysis of the DNAzymes and analyte enrichment on magnetic capture.