Andrea M. Armani

Current single-molecule detection techniques require labeling the target molecule. We report a highly specific and sensitive optical sensor based on an ultrahigh quality (Q) factor (Q > 10(8)) whispering-gallery microcavity. The silica surface is functionalized to bind the target molecule; binding is detected by a resonant wavelength shift. Single-molecule detection is confirmed by observation of single-molecule binding events that shift the resonant frequency, as well as by the statistics for these shifts over many binding events. These shifts result from a thermo-optic mechanism. Additionally, label-free, single-molecule detection of interleukin-2 was demonstrated in serum. These experiments demonstrate a dynamic range of 10(12) in concentration, establishing the microcavity as a sensitive and versatile detector.

We report on a microfabrication technique for realizing re-configurable micro fluidics devices using polymethylsiloxane material (PDMS). The mechanical characteristics of the material, including the Young's modulus and the adhesion energy have been determined experimentally. The magnitude of Young's modulus ranges from 8.7/spl times/10/sup 5/ Pa to 3.6/spl times/10/sup 5/ Pa. The adhesion energy is a function of the PDMS composition as well as chemical treatment. A method for efficiently developing flow interconnects has been demonstrated.

Highly sensitive, label-free biodetection methods have applications in both the fundamental research and healthcare diagnostics arenas. Therefore, the development of new transduction methods and the improvement of the existing methods will significantly impact these areas. A brief overview of the different types of biosensors and the critical parameters governing their performance will be given. Additionally, a more in-depth discussion of optical devices, surface functionalization methods to increase device specificity, and fluidic techniques to improve sample delivery will be reviewed.

Ultra-high-Q optical microcavities (Q>10(7)) provide one method for distinguishing chemically similar species. Resonators immersed in H(2)O have lower quality factors than those immersed in D(2)O due to the difference in optical absorption. This difference can be used to create a D(2)O detector. This effect is most noticeable at 1,300 nm, where the Q(H(2)O) is 106 and the Q(D(2)O) is 107. By monitoring Q, concentrations of 0.0001% [1 part in 106 per volume] of D(2)O in H(2)O have been detected. This sensitivity represents an order of magnitude improvement over previous techniques. Reversible detection was also demonstrated by cyclic introduction and flushing of D(2)O.