Resonance surface plasmon spectroscopy: Low molecular weight substrate binding to cytochrome P450

A new detection mechanism has been developed for low molecular weight substrate binding to heme proteins based on resonance localized surface plasmon spectroscopy. Cytochrome P450 has strong electronic transitions in the visible wavelength region. Upon binding of a substrate molecule (e.g., camphor), the absorption band of cytochrome P450 shifts to shorter wavelength. The event of camphor binding to a nanoparticle surface modified with cytochrome P450 protein receptors is monitored using UV-vis spectroscopy. It is observed for the first time that the binding of the substrate molecules to the protein receptor induces a blue-shift in the localized surface plasmon resonance (LSPR) of the nanosensors. The coupling between the molecular resonance of the substrate-free and substrate-bound cytochrome P450 proteins and the nanoparticles' LSPR leads to a highly wavelength-dependent LSPR response. When the LSPR of the nanoparticles is located at a wavelength distant from the cytochrome P450 resonance, an average of ∼19 nm red-shift is observed upon cytochrome P450 binding to the nanoparticles and a ∼6 nm blue-shift is observed upon camphor binding However, this response is significantly amplified ∼3 to 5 times when the LSPR of the nanoparticles is located at a slightly longer wavelength than the cytochrome P450 resonance, that is, a 66.2 nm red-shift upon cytochrome P450 binding and a 34.7 nm blue-shift upon camphor binding. This is the first example of the detection of small molecules binding to a protein modified nanoparticle surface on the basis of LSPR.