A sensitive DNA biosensor based on a facile sulfamide coupling reaction for capture probe immobilization.

A novel DNA biosensor was fabricated through a facile sulfamide coupling reaction. First, the versatile sulfonic dye molecule of 1-amino-2-naphthol-4-sulfonate (AN-SO3(-)) was electrodeposited on the surface of a glassy carbon electrode (GCE) to form a steady and ordered AN-SO3(-) layer. Then the amino-terminated capture probe was covalently grafted to the surface of SO3(-)-AN deposited GCE through the sulfamide coupling reaction between the amino groups in the probe DNA and the sulfonic groups in the AN-SO3(-). The step-by-step modification process was characterized by electrochemistry and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Using Ru(NH3)6(3+) as probe, the probe density and the hybridization efficiency of the biosensor were determined to be 3.18×10(13) strands cm(-2) and 86.5%, respectively. The hybridization performance of the biosensor was examined by differential pulse voltammetry using Co(phen)3(3+/2+) (phen=1,10-phenanthroline) as the indicator. The selectivity experiments showed that the biosensor presented distinguishable response after hybridization with the three-base mismatched, non-complementary and complementary sequences. Under the optimal conditions, the oxidation peak currents of Co(phen)3(3+/2+) increased linearly with the logarithm values of the concentration of the complementary sequences in the range from 1.0×10(-13)M to 1.0×10(-8)M with a regression coefficient of 0.9961. The detection limit was estimated to be 7.2×10(-14)M based on 3σ.