Electrical sensor array for polymerase chain reaction-free messenger RNA expression profiling

A simple and sensitive electrical sensor array for polymerase chain reaction-free (PCR-free) messenger RNA (mRNA) expression profiling is described in this work. The sensor array, consisting of vertically aligned gold microband electrode/SiO(2)/gold microband electrode sandwich structures (nanogap sensors) in orthogonal configurations, was fabricated on a 1 cm x 1 cm silicon chip. A target mRNA was first hybridized with its specific capture probes (CP) on the bottom side of the nanogap, followed by a second hybridization (annealing) of its poly(A) tail with poly(T) annealing probes (AP) on the top side of the nanogap, holding the hybridized mRNA strands vertically across the nanogap. A subsequent metallization of the hybridized mRNA strands bridged the nanogap and consequently produced a substantial change in conductance, allowing ultrasensitive detection of mRNA without any amplification. Noticeable conductance changes were observed in the presence of as little as 0.10 fM mRNA. A linear relationship between the conductance and mRNA concentration was obtained from 0.50 fM to 1.0 pM with exceptional signal intensity. As little as a 50% difference in mRNA expression was successfully detected. The sensor array also exhibited excellent mismatch discrimination due to its unique vertically aligned nanostructure and the two-step hybridization.