SPIE -- Label-free, single-molecule detection is an exciting avenue of study that will someday impact many areas of research, including drug discovery, biosensing, and early stage cancer detection. In order to develop such a technique, a device must first be fabricated that has a high sensitivity and specificity as well as the ability to assay small-volume samples. Optical spectroscopy is a very powerful technique with many properties that make it attractive for application in single-molecule detection, including its high selectivity, remote sensing capabilities, and fast detection time.1 Furthermore, many molecules of interest, including most proteins, have unique absorption features in the mid- to long-wave IR range. Unfortunately, they also have an extremely weak interaction with the light due to their negligible size compared with the broad IR wavelength. The traditional solution to this problem has been to place the molecules in an optical cavity where light will be reflected multiple times, allowing frequent interactions between the light and the target. In fact, recent progress in ultra-high quality (Q)-factor cavities has led to accurate label-free, single-molecule detection.
