Resonance Localized Surface Plasmon Spectroscopy: Sensing Substrate and Inhibitor Binding to Cytochrome P450

A sensing method based on resonance localized surface plasmon spectroscopy was developed for low molecular weight substrate and inhibitor molecules binding to heme proteins. Cytochrome P450 proteins have Soret and Q absorption bands in the visible wavelength region. The coupling between the molecular resonance of P450 and the localized surface plasmon resonance (LSPR) of functionalized silver nanoparticles leads to a highly wavelength-dependent LSPR response. Binding of substrate (e.g., camphor) or inhibitor (e.g., imidazole) molecules to a cytochrome P450 causes the absorption band of cytochrome P450 shift to shorter or longer wavelengths, respectively. By monitoring the localized surface plasmon resonance (LSPR) of the nanosensors, the binding of camphor/imidazole to a nanoparticle whose surface is modified with cytochrome P450 protein leads to a wavelength-dependent blue/red shift in the LSPR. The magnitude of the LSPR shift induced by camphor or imidazole is consistent with the Soret band wavelength shift observed in P450 in solution.