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Optical interference is a powerful technique for monitoring surface topography or refractive index changes in a thin film layer. Reflectance spectroscopy provides label-free biosensing capability by monitoring small variations in interference signature resulting from optical path length changes from surface-adsorbed biomolecules. Spectral reflectance data can be acquired either by broad wavelength illumination and spectroscopy at a single point, thus necessitating scanning, or by varying the wavelength of illumination and imaging the reflected intensity allowing for acquisition of a spectral image of a large field of view simultaneously. In imaging modalities, intensity fluctuations of the illuminating light source couple into the detected signal, increasing the noise in measured surface profiles. This article introduces a simple technique for eliminating the effects of illumination light power fluctuations by fabricating on-substrate self-reference regions to measure and normalize for the incident intensity, simplifying the overall platform for reflection or transmission-based imaging biosensors. Experimental results demonstrate that the sensitivity performance using self-referencing is equivalent or better than an optimized system with an external reference. [ABSTRACT FROM AUTHOR]

A dual detection system for protein arrays is presented that combines label-free detection by optical interference with chemiluminescence. A planar protein array that targets hepatitis B surface antigen is developed. Surface densities for individual antibody spots are quantitated using optical interference prior to use. Target binding (10 ng/ml) is detected label-free. Target binding (1 ng/ml) is detected by both optical interference and chemiluminescence with the inclusion of secondary antibodies. Binding results using both methods are found to be directly proportion to the capture probe density measured initially. The dual detection system provides the analytical utility of optical interference detection with the established clinical utility of chemiluminescence detection., (Copyright © 2011 Elsevier B.V. All rights reserved.)

We present biological imaging and sensing methods based on optical resonance and interference. In fluorescence microscopy, our nanoscale imaging capability sheds light onto conformational changes of DNA, DNA-protein complexes and polymer coatings on a solid surface. Interference measurements on a layered substrate yield a label-free sensing platform for protein binding in a high-throughput micro-array format.