Localized Surface Plasmon Resonance Spectroscopy for the Detection of Microtubule Nucleation

Abstract

Localized surface plasmon resonance (LSPR) is a collective oscillation of conduction electrons in metal nanoparticles. The excitation of LSPR induces a large electromagnetic field enhancement near the metal surfaces, making it highly sensitive to the local refractive index surrounding the nanoparticles. LSPR spectroscopy uses this localized sensitivity to achieve label-free detection of biological molecules. Previously, LSPR spectroscopy has been employed to study various biomolecular interactions. However, it has not been used to detect biopolymer nucleation. Here, we present a LSPR spectroscopy approach for the detection of microtubule nucleation. Using a combination of an extended Mie theory and computational simulations, we investigate theoretically how the optical responses of spherical and nonspherical gold nanoparticles change when microtubules form around them. Our results indicate that the extinction peak wavelength is sensitive to the formation of short microtubules around the nanoparticles, but is insensitive to their elongation. We also demonstrate that LSPR spectroscopy can detect microtubule nucleation experimentally by inducting spontaneous microtubule formation around spherical gold nanoparticles. Consistent with our theoretical predictions, our experiments show that the peak wavelength changes significantly when short microtubules form around the nanoparticles, but not when they are elongated. We also show that the peak wavelength is sensitive to the formation of microtubule nuclei even when they are too small to be detectable with a turbidity measurement.