Colloidal Gold Nanoparticles in DNA Diagnostics

Tuan Hoang, Kerrianne Cullen, Tin Christopher Hang and Anthony Guiseppi-Elie*
Department of Chemical Engineering and Center for Bioelectronics Biosensors
and Biochips, Virginia Commonwealth University, Richmond, Virginia 23284.
 

Colloidal gold nanoparticles have emerged with considerable importance in technological applications in molecular immunodiagnostics, in surface plasmon resonance sensors and in Raman spectroscopy. Reported here is the development and use of colloidal gold nanoparticles as impedimetric labels for DNA detection using microfabricated interdigitated electrode arrays (IDAs). Specifically, the molecular recognition via the DNA-cDNA-Au hybridization reaction results in nanoparticle aggregation at the chip surface that produces a measurable change in electrical impedance. The reduction of HAuCl4 by sodium citrate was chosen for the synthesis of colloidal gold nanoparticles that are appropriate for DNA diagnostics. Particles were synthesized over the range 10^-3 -- 5x10^-5 M and characterized by UV-VIS spectrophotometry and by TEM. Colloidal gold nanoparticles were studied for their non-specific interaction with engineered surfaces of different chemical composition. Engineered surfaces were produced by monolayer self-assembly of organosilanes of different w-terminal functional groups, including  -COOH, -NH2, -CN, - Br, -I, and –Cl, on borosilicate glass slides. Surfaces were characterized by contact angles measurements and by the impedimetric response of 10 um line and space IDA chips that were chemically modified and immersed in colloidal gold suspensions. Colloidal gold nanoparticles were treated with acid terminated 3-mercaptopropionic acid. The w-acid functional group was then conjugated to 3' anime functionalized ssDNA probe sequences using carbodiiminde crosslinking chemistry (8). Finally, the interdigit spaces of 10 um line and space IDA chips were chemically modified using 3–iodopropyltrimethoxysilane and the iodo-group converted to –OH via alkaline hydrolysis. 3’-oligos probes were immobilized to the chips. DNA-cDNA hybridization of 20-mers was detected by impedance change as a result of the hybridization at the chip surface. This study addresses diagnostic biosensors for DNA recognition and demonstrates the principle of impedimetric detection using a single 20-mer DNA oligomer and colloidal gold nanoparticle label.