A Gold Nanoparticle Probe-Assisted Antigen-Counting Chip using SEM.

Currently it remains challenging to count protein-biomarker molecules presents in a small droplet of biological samples. Herein, we propose a gold nanoparticle (GNP) probe-assisted sandwich-counting strategy that relies on a GNP probe, an antibody functionalized chip to "count" antigen molecules using Scanning Electron Microscope (SEM). Both standard Carcinoembryonic antigen (CEA) and two real CEA-related tumor samples (tumor tissues and serum) were assayed to demonstrate the proof-of-concept of the counting strategy. Results show that our method is excellently correlative with ELISA assay widely used in clinic for antigen or antibody detection and the limit of detection (LOD) of our enumeration strategy reach down to 0.045 ng/mL, which is ~40 times more sensitive than the conventional ELISA. Therefore, our GNP probe-assisted sandwich-counting strategy has the potential to be used for quantification of protein biomarkers at ultra-low concentration in early tumor specimens and detection of target proteins in much diluted concentration.