Capacitive aptamer-antibody based sandwich assay for the detection of VEGF cancer biomarker in serum

In this paper, we report on in vitro anti-VEGF aptamer selection and the development of a capacitive aptamer-antibody based sandwich assay for sensitive detection of vascular endothelial growth factor-165 (VEGF) in human serum. The assay design involves capturing of VEGF protein through two epitopes, one with anti-VEGF aptamer and the other with the antibody. The capacitive sensor was functionalized with anti-VEGF aptamer which first captures the VEGF protein followed by sandwiching with antibody conjugated magnetic beads (MB-Abs). Changes in capacitance was measured using non-Faradaic electrochemical impedance spectroscopy (nFIS) at different AC electrical frequencies (50-300 MHz). The sandwich assay format exhibited enhanced capacitive signal with respect to concentration with a detection range 5 pg mL−1 to 1 ng mL−1 of VEGF protein in human serum. Use of anti-VEGF aptamers enabled chemical stability on sensors during and after the chemical coupling on sensors. This work demonstrated the successful application of on-chip aptamer-antibody based sandwich assays for detection of target proteins in real serum sample for early cancer diagnosis.