Resonant cavity imaging: A means toward high-throughput label-free protein detection

The resonant cavity imaging biosensor (RCIB) is an optical technique for detecting molecular binding interactions label free at many locations in parallel that employs an optical resonant cavity for high sensitivity. Near-infrared light centered at 1512.5 nm couples resonantly through a Fabry-Perot cavity constructed from dielectric reflectors (Si/SiO₂ ), one of which serves as the binding surface. As the wavelength is swept using a tunable laser, a near-infrared digital camera monitors cavity transmittance at each pixel. A wavelength shift in the local resonant response of the optical cavity indicates binding. Positioning the sensing surface with respect to the standing wave pattern of the electric field within the cavity controls the sensitivity with which the presence of bound molecules is detected. Transmitted intensity at thousands of pixel locations is recorded simultaneously in a 10 s, 5 nm scan. An initial proof-of-principle setup has been constructed. A test sample was fabricated with 25, 100-μm wide square features, each with a different density of 1-μm square depressions etched 12 nm into the SiO ₂ surface. The average depth of each etched region was found with 0.05 nm rms precision. In a second test, avidin, bound selectively to biotin conjugated bovine serum albumin, was detected.