[CSBi-events] Thesis Defense - Friday, August 19, 2005

[csbi-events@mit.edu]

          Doctoral Thesis Defense
              -----------------------
                   Thomas Burg

Dept. of Electrical Engineering and Computer Science
Advisor: Prof. S.R. Manalis (Biological Engineering)

Date: Friday, August 19, 2005
Time: 3pm

Location: Bartos Theater (E15, lower level)

Title: Suspended Microchannel Resonators for Biomolecular Detection

Abstract:

Microfabricated transducers enable the label-free detection of 
biological molecules in nanoliter size samples. Integrating 
microfluidic detection and sample-preparation can greatly leverage 
experimental efforts in systems biology and pharmaceutical research 
by increasing analysis throughput while dramatically reducing reagent 
cost.

Microfabricated resonant mass sensors are among the most sensitive 
devices for chemical detection, but degradation of the sensitivity in 
liquid has so far hindered their successful application to 
biochemical assays. This thesis introduces a type of resonant 
transducer that overcomes this limitation by a new device design: 
Adsorption of molecules to the inside walls of a suspended 
microfluidic channel is detected by measuring the change in 
mechanical resonance frequency of the channel. In contrast to 
resonant mass sensors submersed in water, the sensitivity and 
frequency resolution of the suspended microchannel resonator is not 
degraded by the presence of the fluid. The device differs from a 
vibrating tube densitometer in that the channel is very thin, and 
only molecules that bind to the walls can build up enough mass to be 
detected; this provides a path to specificity via molecular 
recognition by immobilized receptors.

Suspended silicon nitride channels have been fabricated through a 
sacrificial polysilicon process and bulk micromachining, and the 
packaging and microfluidic interfacing of the resonant sensor has 
been addressed. Device characterization at 30 mTorr ambient pressure 
reveals a quality factor of more than 10,000 for water filled 
resonators; this is two orders of magnitude higher than previously 
demonstrated Q-values of resonant mass sensors for biological 
measurements.
Theory indicates that detection limits as low as 0.01 ng/cm2 may be 
achieved with the suspended microchannel resonator design, and a 
noise level equivalent to ~0.1 ng/cm2 in a 1 Hz bandwidth has been 
experimentally demonstrated in this work. This resolution constitutes 
a tenfold improvement over commercial quartz crystal microbalance 
based instruments.
The ability to detect adsorbing biomolecules by resonance frequency 
has been validated through binding experiments with avidin and biotin 
conjugated proteins.