Evanescent imaging ellipsometry based microarray readers

Microarrays are being widely used in genomic, proteomic, and diagnostic applications. The binding events to the microarrays are measured with fluorescent labels. Fluorescent microarray readers offer high sensitivity and normalization of the reference and test samples. The use of labels increases the number of steps involved in array testing, concerns about storage labels, and cost of additional labeling steps. This paper describes an alternative approach that does not require the use of fluorescent or other labels. The binding events on the microarray introduce changes in polarization of the illuminated light which is measured to determine the concentrations of biomolecules bound to the microarray. Oligonucleotide microarrays were synthesized and tested on the imaging microarray reader. The refractive index changes of 0.006 and changes in thickness of 1 nm are demonstrated at a spatial resolution of 20 μm over a field of view of 1 cm ². This ellipsometric technique offers an attractive alternative to fluorescence-based measurement and could be very valuable in some of the genomic, proteomic, diagnostic, and sensing applications.