AVS 47th International Symposium
    MEMS Thursday Sessions
       Session MM+BI-ThM

Paper MM+BI-ThM6
High Sensitivity Resonant Biosensor

Thursday, October 5, 2000, 10:00 am, Room 309

Session: Bio-MEMS and Microfluidics
Presenter: B. Ilic, Cornell University
Authors: B. Ilic, Cornell University
D. Czaplewski, Cornell University
H.G. Craighead, Cornell University
P. Neuzil, Institute of Microelectronics, Singapore
C. Campagnolo, Cornell University
C. Batt, Cornell University
Correspondent: Click to Email
There is a growing demand to produce highly selective biological sensors for the detection of small quantities of biological microorganisms using micromachining. In this work, the detection of bacteria using a resonant frequency based mass detection biological sensor has been accomplished. The biological sensor under development consists of an array of resonating cantilever beams fabricated, using bulk silicon micromachining techniques, from both low pressure chemical deposition (LPCVD) and plasma enhanced chemical vapor deposition (PECVD) low stress silicon nitride. For this experiment an array of cantilevers with dimensions of varying length from 15µm to 500µm, varying width of 2µm to 20µm, thickness of 320nm for the LPCVD, and t=600nm for the PECVD nitride, were used. Escherichia coli O157:H7 antibodies were immobilized on the surface of the resonators. Devices were subsequently exposed to varying concentrations of E. Coli cells in solution and any loosely bound cells were removed. In order to determine the mass bound to the cantilever, a frequency spectra was taken before and after the binding of the cells to the cantilever. Signal transduction of the micromechanical oscillators has been accomplished by measuring the out of plane vibrational resonant mode with an optical deflection system. The measured vibrational mode was entirely due to thermal noise and ambient vibrations in air. The measured resonant frequency shift as a function of the binding of additional cells was observed and correlated to the mass of the specifically bound E. Coli O157:H7 cells. Our results indicate good agreement with the predicted theory of linear elasticity. Under ambient conditions where considerable damping occurs, we were able to detect single E. Coli cells. Methods, utilizing vacuum encapsulation and tailoring of the cantilever dimensions, for single molecule detection will be discussed.