Biomedical Engineering Reference
In-Depth Information
both DNA and protein is preferred, particularly for use in medical diagnostics
where variation and cost must be minimized.
A vast number of label-free detection techniques have surfaced over the
last decade or two to address the problems of label-based detection [5-16].
The important figures of merit for these techniques are sensitivity to bound
targets, throughput (number of features evaluated in a single test) and the
ability to scale throughput, and cost per test. Sensitivity is often quantified
by mass per area (pg mm
−
2
) or average height (pm) where 1 pm corresponds
to roughly 1 pg mm
−
2
for protein or DNA [17-25].
6.2 Resonant Cavity Imaging Biosensor
6.2.1 Detection Principle
Two partially reflecting substrates are positioned such that their reflecting
surfaces face each other and form the optical cavity (Fig. 6.1) [26]. The tun-
able wavelength laser light is collimated and incident from the back of one
of the reflectors. The wavelength of the laser is swept in time and at specific
wavelengths the resonant condition of the cavity is met, the light resonates
inside the cavity and couples out. Beyond the cavity, the transmitted light
is imaged on a camera, so that the resonant response at each location of the
cavity is recorded by a corresponding pixel on the camera. The probe biomole-
cules are patterned on one of the reflector surfaces. When target biomolecules
bind to their specific capturing agents, the local resonant response shifts in
Fig. 6.1.
Resonant cavity imaging biosensor (RCIB) setup.
