Development of a DNA-based bioMEMS for the label free detection of specific RNA transcripts

Advances in micro- and nanofabrication technologies are enabling the development of mechanical devices with nanosized moving parts and Complementary MOS (CMOS) technologies allows the co-fabrication on the same silicon chip of MicroElectroMechanical Sensor (MEMS) components and the circuitry, making the design of smart sensors possible without significant increase in cost. Micromechanical biosensors are promising analytical label-free tools, with a strong potential in terms of reliability, ease of use, and low cost. By immobilizing a suitable DNA based biorecognition element on a CMOS-based resonant sensor based on the microbalance principle - a silicon dioxide plate suspended to two springs - a label free biosensor for the detection of a specific human messenger RNA was developed. The resonator is an integrated microbalance where a shift of its resonance frequency can be related to the adsorption, on the preventively functionalised plate, of a specific molecular target. The MEMS/CMOS approach can be followed for biosensors if the specific problems related to the bio-activation of the sensor surface and its compatibility with on-chip MEMS and electronic components are taken into account. By using a drop coating approach the sensor surface was sililated with an aqueous APTES (amino-propyl-triethoxysilane) solution and a ssDNA probe - designed to bind to a 25 nucleotide long sequence of human MGMT (methylguanine-DNA methyltransferase) mRNA - was the immobilized on the resonators surface. The resonators were then characterized in terms of resonance frequency and other parameters and subsequently exposed to a solution containing the target mRNA. After the hybridization the resonators were characterized again and the frequency shift caused by the binding was evaluated by resonators different in thickness and size, showing a good concentration/shift relationship. These results open interesting perspectives for the detection of several molecular species, in a label free approach, by using oligonucleotide-based probes (aptamers, decoys or ssDNA/RNA/LNA).