| Abstract
| - A simple, chip-based implementation of a double-beam interferometer that can separatebiomolecules based on size and that can compensate for changes in matrix composition is introduced.The interferometric biosensor uses a double-layer of porous Si comprised of a top layer with large poresand a bottom layer with smaller pores. The structure is shown to provide an on-chip reference channelanalogous to a double-beam spectrometer, but where the reference and sample compartments are stackedone on top of the other. The reflectivity spectrum of this structure displays a complicated interference patternwhose individual components can be resolved by fitting of the reflectivity data to a simple interferencemodel or by fast Fourier transform (FFT). Shifts of the FFT peaks indicate biomolecule penetration into thedifferent layers. The small molecule, sucrose, penetrates into both porous Si layers, whereas the largeprotein, bovine serum albumin (BSA), only enters the large pores. BSA can be detected even in a large(100-fold by mass) excess of sucrose from the FFT spectrum. Detection can be accomplished either bycomputing the weighted difference in the frequencies of two peaks or by computing the ratio of the intensitiesof two peaks in the FFT spectrum.
|
