Carbon Nanoparticle-Enhanced Immunoelectrochemical Detection for Protein Tumor Marker with Cadmium Sulfide Biotracers

Abstract

We have developed a sensitive electrochemical immu-noassay system for the detection of a protein tumor marker, carcinoembryonic antigen (CEA), that is based on a carbon nanoparticle (CNP)/poly(ethylene imine) (PEI)-modified screen-printed graphite electrode (CNP-PEI/SPGE) covered with anti-CEA antibodies. The signal amplification strategy - using CdS nanocrystals as biotrac-ers and CNPs to enhance electron transfer - improves the sensitivity and detection limit for CEA, suggesting that this system holds promise for development into a point-of-care or disposable home-care self-diagnostic tool. This biosensor is based on a sandwich complex immunoassay, which we assembled from sequential layers of the anti-CEA antibody (αCEA) on CNP-PEI/SPGE, the CEA sample, and the CdS nanocrystal quantum dots (QDs) sensitized with αCEA (αCEA-CdS QD). We used square wave anodic stripping voltammetry (SWASV) to amplify the signal current response obtained from the dissolved rCEA-CdS QDs. The calibration curve for CEA concentration was linear in the range of 0.032-10 ng/mL; the detection limit (estimated as the mean of the blank sample plus three times the standard deviation obtained on the blank sample) was 32 pg/mL (equivalent to 160 fg in a 5 μL sample). This method is suitably precise and sensitive to function as a means of determining urinary CEA, which is a better marker than serum CEA for the early detection of urothelial carcinoma. ? 2009 American Chemical Society.