Single particle spectroscopy and tracking of gold nanospheres in living cells by confocal light scattering microsopy

摘要

Noble metallic nanoparticles exhibit strong absorption and scattering in visible region. This optical response is widely known as localized surface plasmon resonance (LSPR) which originated from the collective oscillations of conduction band electrons. The resonance peak energies and line widths are sensitive to not only the nanoparticle size and shape but also the local dielectric properties of the surrounding medium. Due to this environment sensitivity and potential application towards chemical and biological sensors, investigations of LSPR are topical research subjects. In particular, recent progress in optical microscopes and light detection equipments enable us to investigate optical properties of single nanopartiles by measuring light scattering spectra from an isolated particle using a dark-field illumination setup of an optical microscope.[1-3] Thus, the effects of local environments [4] and adsorption of ions[5], dye molecules [6], and proteins[7] on the LSPR band have been studied in details for single gold nanoaprticles with diameter lager than 40 nm by conventional far-field light scattering microspectroscopy. It is now demonstrated and well recognized that single particle spectroscopy is fruitful and indispensable in studies on optical properties of the LSPR. On the other hand, new labels in bio-analysis that are stable and can be easily functionalized are becoming increasingly important. Among these, plasmon resonant particles followed by light scattering are an interesting alternative to fluorescent labels and quantum dots, as the latter are unfortunately subject to important drawbacks such as optical bleaching and blinking. Silver and gold nanoparticles have been used as contrast agents for decades in the biological field but have more recently found new applications, such as in vitro biosensors. Especially, gold nanoaprticle is interesting because it is chemically stable and less toxic to bio-cells. Thus, gold nanoparticles as in vivo biological sensors or therapeutic agents constitute an even greater challenge and have therefore started to attract scientist's attention during the last few years. In this work, we have developed a new confocal light scattering microspectroscopy and imaging system using a femtosecond supercontinuum white light as a probe light, and have demonstrate LSPR scattering spectra of single gold nanoparticles in/on a living cell (Mouse NIH-3T3 fibroblast).