Localized surface plasmon and molecular resonance: Fundamental study and application

Localized surface plasmon resonance (LSPR) is one of the signature optical properties of noble metal nanoparticles. Since the LSPR wavelength λ _max is extremely sensitive to the local environment, it allows us to develop nanoparticle-based LSPR chemical and biological sensors. In this work, we tuned the LSPR peaks of Ag nanotriangles and explored the wavelength-dependent LSPR shift upon the adsorption of some resonant molecules. The induced LSPR peak shifts (λ _max) vary with wavelength and the line shape of the LSPR shift is closely related to the absorption features of the resonant molecules. When the LSPR of the nanoparticles directly overlaps with the molecular resonance, a very small LSPR shift was observed. An amplified LSPR shift is found when LSPR of the nanoparticles is at a slightly longer wavelength than the molecular resonance of the adsorbates. Furthermore, we apply the "amplified" LSPR shift to detect the substrate binding of camphor to the heme-containing cytochrome P450cam protiens (CYP101). CYP101 absorb light in the visible region. When a small substrate molecule binds to CYP101, the spin state of the molecule is converted to its low spin state. By fabricating nanoparticles with the LSPR close to the molecular resonance of CYP101 proteins, the LSPR response as large as -60 nm caused by the binding of small substrate has been demonstrated.