| The purpose of this research is to demonstrate cheap, robust, stand-alone and miniature biosensors. Biomolecules like DNA can be detected by using a cantilever sensor. The immobilization and hybridization of DNA produces surface stress changes on the cantilever. The displacement of the cantilever tip caused by the surface stress changes is given by the Stoney's equation: Dz=31-n L2Et2Ds , where nu is the Poisson's Ratio, E is the Young's Modulus, t is the thickness of the cantilever, L is the length of the cantilever and Deltasigma is the surface stress generated by the absorbed molecules. Since the deflection of the cantilever is inversely proportional to the Young's Modulus of the material, the use of a softer material, e.g. parylene C, will increase the sensitivity of the sensor. Thus, we first developed parylene cantilevers to prove the feasibility of using parylene as the cantilever materials. Optical lever method was used to detect the deflection of the cantilever induced by the surface stress changes. Pervasive experimentation was used to characterize the parylene cantilever biosensors in both air and water. Detection of alkanethioles and DNA immobilization and hybridization was demonstrated using parylene biosensors. Afterward, the cantilever sensors were further improved by adding flatter tips. The sensitivity of the cantilevers was further improved by generating nano-patterns on the surface of the cantilevers by using nano-sphere lithography based on polystyrene nano-particles. Since the optical setup used to detect the bending of the cantilever sensor is bulky and expensive, in the next phase, parylene cantilevers integrated with piezoresistors were developed to achieve portable, low-cost and standalone cantilever-based biosensors. Parylene piezoresistive cantilever sensors were then characterized by series of tests like temperature stability tests, environmental vibrations effect tests, displacement sensitivity test and stability tests in both air and water. Detection of alkanethioles was also demonstrated. Finally, we demonstrated electrostatic actuators based on PDMS (Polydimethylsiloxane), which provides a platform for on-chip electrostatic micropumping. This will result in miniature, easy to operate stand alone, robust and portable Lab-on-Chip with reduced chances of contamination. Thus, this device will be a cost effective solution to issues like biosensing, genetic analyses, environmental observations and forensics. |
