Label-Free Biosensing of DNA in Microfluidics Using Amorphous Silicon Capacitive Micro-Cantilevers

Biosensing uses biorecognition reactions to detect molecules of interest such as biomarkers of disease, food contaminants or environmental agents. Label-free detection techniques, due their simplicity, are promising for point-of-care applications. In this paper, label-free biosensing of DNA is demonstrated with amorphous silicon micromechanical cantilevers operating in the stress-mode. The sensors are fabricated on glass substrates in a bottom electrode configuration, for capacitive readout, and are integrated with microfluidic channels for reproducible fluid handling. The amplitude noise in the capacitance measurement is similar to 20 aF in air and similar to 731 aF in water, corresponding to minimum detectable tip deflections of 42.8 nm in air and 17.2 nm in water. The sensor functionalization is performed using gold-thiol chemistry under optimized conditions, resulting in a DNA probe density of 8.50 x 10(12) molecules cm(-2), corresponding to a coverage of 34 % of the gold surface and an average spacing between molecules of similar to 3.4 nm. With this system, target DNA with the sequence of microRNA-145, a cancer-associated biomarker, is detected with a limit of detection of 63 nM (corresponding to a mass of similar to 613 fg). This type of sensors can be multiplexed to allow the detection of multiple targets and integrated with portable electronics for point-of-use applications.