Realization of practical sheet-type biosensor based on multi wall carbon nanotubes and micro-pore filter paper for early detection of prostate cancer

Abstract

The aim of this study is realization of an inexpensive, simple and sensitive biosensor to detect early stage of prostate cancer using multi wall carbon nanotubes (MWCNTs, diameter 20 nm, length 5 μm) and micro-pore filter paper (pore size 0.45 μm). For the detection of prostate specific antigen (PSA), which is a biomarker of prostate cancer, the carboxylated MWCNTs were activated with PSA antibody (monoclonal antibody of the prostate specific antigen) by using N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide sodium salt (NHSS). The activated MWCNTs were deposited on micro-pore filter paper by using syringe filtering. The biosensor can detect from 0 to 500 ng/mL of PSA level within 90 min with high sensitivity: the signal (electrical resistance) increased up to 150% of the base signal along with the increased concentration of PSA from 0 to 500 ng/mL and the detection limit was 1.18 ng/mL with a bench top digital multimeter (6 1/2 digits). The detection limit of biosensor is enough to diagnose prostate cancer. Because they are suspected to patients of prostate cancer when PSA level in serum is more than 4 ng/mL. Our sensing system is much simple, fast and cheap, but the detection ability of the sensor is comparable to that of commercially available methods. In case of enzyme-linked immunosorbent assay (ELISA) that is conventional method for quantitative analysis of proteins, detection limit was 51 pg/mL. In order to improve performance of the biosensor, MWCNTs were refluxed in concentrated 14 M nitric acid instead of 3 M nitric acid. Then thiolation of the carboxylated MWCNTs was conducted by 2-aminoethanethiol hydrochloride and gold nanoparticles (Au NPs, diameter ~5 nm) were attached by self-assembly (SA) on the surface of thiolated MWCNTs. For the reaction of Au NPs and PSA antibody, citrate that is capping agent of Au NPs was replaced with thioglycolic acid by ligand exchange process. Thiol group in thioglycolic acid was bonded to Au NPs and carboxyl group in thioglycolic acid was used to combine PSA antibody and Au-MWCNTs. Fabrication of biosensor based on Au-MWCNTs and PSA detection were carried out in the same manner as fabrication of carboxylated MWCNTs based biosensor. The Au-MWCNTs based biosensor need additional research and development to improve the performance.