We are investigating reactions at Si surfaces and interfaces using infrared spectroscopy in the multiple internal reflection geometry (MIR-IRAS). This technique, in which infrared light beams penetrate a Si crystal wafer internally while reflecting many times, enables us to monitor surface reactions with a quite high surface sensitivity. Since Si surfaces can be observed from inside, we can monitor chemical processes at Si surfaces under various environments. In this review, our MIR-IRAS approaches for the label-free detection of biomolecular interactions are presented. In our MIR-IRAS method, by analyzing IR absorption signals we can detect any structural changes induced by the biomolecular interactions. MIR-IRAS is applicable to in situ real-time monitoring of versatile samples including DNA, proteins, and living cells, regardless of the molecular size and state of the samples.
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