Optical biosensors with gold nanoparticles

CATERINA SERAFINELLI; PAULA C. ANGELOMÉ; LUIS M. LIZ-MARZÁN

Granada

Congreso; III Reunión Ibérica de Coloides e Interfases – VIII Reunión del Grupo Especializado de Coloides e Interfases; 2009

In the last years the metallic nanoparticles have attracted a growing interest because of their optical properties. Specifically, these nanoparticles exhibit a strong UV-visible extinction band that is not present in the spectrum of the bulk metal, whichappears when the incident photon’s frequency is resonant with the collective excitation of the conduction electrons,known as localized surface plasmon resonance (LSPR). It is well established that the absorbance’s maximum position, λmax, of the LSPR spectrum depends of the size, shape and interparticle spacing of the nanoparticles as well as the dielectric properties of its local environment (including the substrate, solvent, and adsorbates). According to the Mie theory, the increasing of the refractive index around the particle red-shifts the absorbance maximum in the UV-visible spectra.This interesting property of the LSPR band can be employed in the development of biosensors. In this work we have tested gold nanodecahedra [] supported on glass as optical biosensors. As a first step, we have attached the gold nanodecahedra onto glass slides using two different molecules: APTMS (3-aminopropiltrimethoxisilane) and MPTMS.(3-mercaptopropyltrimethoxisilane).We have found that the best molecule to attach the gold nanodecahedra onto the surface is the APTMS. After that, we have tested the sensitivity of these systems toward the surrounding environment measuring the UV-visible spectra of the glasses immersed in solvents with increasing refractive index. As expected, a red-shift in the LSPR band was observed as the refractive index increases. The sensitivity toward the biological model reaction between biotin and streptavidin was finally tested.. The biotin was attached to the gold surface through a covalent bond and the UV-visible spectrum was taken before and after immersion in streptavidin solution. A red-shift in the LSPR band was observed, demonstrating that our device is sensitive to this biological reaction and that supported gold nanodecahedra could be an interesting platform to develop specific biosensors.