High-speed label-free detection by spinning-disk micro-interferometry

Spinning-disk interferometers are a new class of analytic sensors to detect immobilized biomolecules with high speed and high sensitivity. The disks are composed of a large number of surface-normal self-referencing interferometers, analogous to an optical CD, but operating on the principle of microdiffraction quadrature that achieves sensitive linear detection of bound molecules. The surface-normal structures have a small footprint of only 20 mum each, allowing potential integration to over a million interferometric elements per disk. We have fabricated interferometric microstructures on silicon and on dielectric mirror disks to demonstrate the basic principles of the BioCD. We have detected the presence of immobilized anti-mouse IgG and the specific binding of 10 femtomol of mouse IgG at a sampling rate of 100 kilo-samples/s, while also demonstrating negligible non-specific binding. This technique provides a label-free method that could potentially screen hundreds to thousands of proteins per disk. (C) 2004 Elsevier B.V. All rights reserved

Patterned protein microarrays for bacterial detection

Patterned microarrays of antibodies were fabricated and tested for their ability to bind targeted bacteria. These arrays were used in a series of bacterial immunoassays to detect E. coli O157:147 and Renibacterium salmoninarum (RS). Microarrays were fabricated using microcontact printing (muCP) and characterized using scanning probe microscopy (SPM). The high-resolution SPM imaging showed that targeted bacteria had a higher binding selectivity to complementary antibody patterns than to unfunctionalized regions of the substrate. Additional studies indicated a significant reduction in binding of bacteria when the microarrays were exposed to nonspecific bacteria. These studies demonstrate how protein microarrays could be developed into useful platforms for sensing microorganisms

Spinning-disk self-referencing interferometry of antigen-antibody recognition

A gold ridge microstructure fabricated to a height of lambda/8 on a high-reflectivity substrate behaves as a wave-front-splitting self-referencing interferometer in phase quadrature when illuminated by a Gaussian laser beam and observed in the far field along the optic axis. When immuno-gammaglobulin (IgG) antibodies are selectively immobilized on the gold microstructure, they recognize and bind to a specific antigen, which shifts the relative optical phase of the interferometer and modifies the far-field diffracted intensity. We detect bound antigen interferometrically on spinning disks at a sampling rate of 100 kHz and verify the interferometric nature of the signal by using two quadratures of opposite sign to rule out effects of dynamic light scattering. Strong molecular recognition is demonstrated by the absence of binding to nontarget molecules but strong signal change in response to a specific antigen. This BioCD has the potential to be applied as a spinning-disk interferometric immunoassay and biosensor. (C) 2004 Optical Society of America