From fluorescence quenching by metal nanoparticles to enhanced spectroscopic detection in microfluidic volumes

The controlled creation of 'hot spots' in metal nanostructures in which the optical spectroscopic response of molecular species is enhanced is a subject of continuing interest, which has gained considerable impetus through recent progress in nanofabrication and self-assembly of metal nanoparticles. One of the effects that is sought after is the enhancement of molecular fluorescence. In simple assemblies of single noble metal nanoparticles with organic chromophores, however, fluorescence quenching frequently dominates. We recently harnessed this quenching to investigate the behaviour of ligand molecules at the surface of metal particles in dilute solution using fluorescence spectroscopic techniques[1,2]. In spite of fluorescence quenching impeding sensitive particle detection through fluorescent labeling, noble metal nanoparticles of sufficient size may be detected with high sensitivity and reasonable selectivity using their resonant plasmonic light scattering[3]. This strong optical response, which also plays a role in the enhancement of molecular spectroscopic signatures, makes noble metal particles interesting materials for highly sensitive detection in the sub-nanoliter volumes of miniaturized 'lab on a chip' devices for biomedical applications[4]. We are developing functionalized gold and silver nanoparticles, and study their optical behaviour using optical spectroscopy. One particular goal is to make the optical response of noble particle assemblies sensitive to chemical and biological analytes and to enhance specific spectroscopic signatures. The particle assemblies are then successfully detected in microfluidic channels using resonant light scattering. The laminar flows inside microfluidic channels allow for a high degree of control over diffusion and mixing, which can be put to good use for controlling the chemistry and assembly of functionalized nanoparticles, and show promise for the development of innovative biosensing schemes. [1] J. R. G. Navarro, M. Plugge, M. Loumaigne, A. Sanchez-Gonzalez, B. Mennucci, A. Debarre, A. M. Brouwer, M. H. V. Werts, Photochem. Photobiol. Sci. 9, 1042-1054 (2010). [2] M. Loumaigne, R. Praho, D. Nutarelli, M. H. V. Werts, A. Debarre, Phys. Chem. Chem. Phys. 12, 11004-11014 (2010). [3] R. A. Zsigmondy, Nobel lecture (1926). [4] M. H. V. Werts, V. Raimbault, R. Texier-Picard, R.Poizat, O. Francais, L. Griscom, J. R. G. Navarro, Lab on a Chip 12, 808-820 (2012).