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Immobilization of Proteins in their Physiological Active State at Functionalized Thiol Monolayers on ATR‐Germanium Crystals

Protein immobilization on solid surfaces has become a powerful tool for the investigation of protein function. Physiologically relevant molecular reaction mechanisms and interactions of proteins can be revealed with excellent signal‐to‐noise ratio by vibrational spectroscopy (ATR‐FTIR) on germanium crystals. Protein immobilization by thiol chemistry is well‐established on gold surfaces, for example, for surface plasmon resonance. Here, we combine features of both approaches: a germanium surface functionalized with different thiols to allow specific immobilization of various histidine‐tagged proteins with over 99 % specific binding. In addition to FTIR, the surfaces were characterized by XPS and fluorescence microscopy. Secondary‐structure analysis and stimulus‐induced difference spectroscopy confirmed protein activity at the atomic level, for example, physiological cation channel formation of Channelrhodopsin 2.