PEMC-based Method of Measuring DNA Hybridization at Femtomolar Concentration Directly in Human Serum and in the Presence of Copious Noncomplementary Strands

Abstract

Piezoelectric-excited, millimeter-sized cantilever (PEMC) sensors having high-mode resonance near 1 MHz are shown to exhibit mass change sensitivity of 1−300 ag/Hz. Gold-coated PEMC sensors immobilized with 15-mer single-stranded DNA (ssDNA) were exposed to 10-mer complementary strands at concentrations of 1 fM, 1 pM, and 1 μM, both separately and sequentially at 0.6 mL/min in a sample flow cell housing the sensor. Decrease in resonance frequency occurred as complementary strands hybridized to the immobilized probe DNA on the sensor surface. Hybridization in three background matrixesbuffer, buffer containing 10 000 times higher noncomplementary strands, and 50% human plasmawere successfully tested. Sensor hybridization responses to 1 fM, 1 pM, and 1 μM complementary strand were nearly the same in magnitude in all three matrixes, but the hybridization rates were different. In each case, the sensor detected the presence of 2 amol of complementary 10-mer strand. The extent of hybridization calculated from resonance frequency change did not decrease in serum. The findings suggest ssDNA can be detected at 2 amol without a sample preparation step and without the use of labeled reagents.