Nanomechanical Label Free Micro RNA Detection For Cancer And Liver Injury Diagnosis

Abstract

A biosensor is a device in which a biological component is coupled to a transducer which converts a biological recognition event into a detectable signal. Microribonucleic acid (miRNA, microRNA) are non protein coding ribonucleic acid molecules that effect gene expression and have been found at altered levels in diseased tissue. Currently miRNA are detected using quantitative real time polymerase chain reaction (qRT-PCR), which involves purifying, labeling and amplifying the target molecules. However this approach does not function in non purified samples, and does not easily lend itself towards simultaneous miltitarget analysis. Presented in this work is a label free static mode nanomechanical cantilever biosensor platform for direct miRNA detection. A surface biolayer of nucleic acid probes (complimentary sequence to the miRNA target) attached to a silicon interface serves as the biological component in this device. A cantilever array containing eight silicon micro beams acts as the transducer. Upon specific target capture via nucleic acid hybridization (sequence specific binding of two complimentary strands of nucleic acid) a differential surface stress is generated, resulting in the cantilevers deflecting. Cantilever deflections are optically detected by tracking the position of a reflected laser spot off the cantilevers on a position sensitive detector (PSD). The origin of the surface stress can be steric hindrance, hydration or electrostatic repulsion/attraction. In situ reference sensors (cantilevers with nucleic acid probes that do not specifically interact with target molecules) are used to create a specific differential signal. This is achieved by subtracting the reference sensor responses from that of the target specific sensors, allowing negation of environmental and non specific molecular effects. The measurement reveals the effect of specific ligand/receptor interactions. This home-built nanomechanical platform is housed inside a thermally regulated chamber, is controlled via custom made software.