Gold aggregates- and quantum dots- embedded nanospheres: Switchable dual-mode image probes for living cells

Abstract

A new class of dual-mode image probe has been designed and prepared, which is composed of silica-coated Au aggregates and water-soluble CdTe quantum dots (QDs). In such a probe, the two kinds of optical signals, SERS and fluorescence, can be separately generated and switched by changing the wavelength of the excitation light. Experimentally, the probe exhibited strong fluorescence when excited by light at a wavelength of 458 nm and showed distinct SERS signals while the excitation wavelength changed to 633 nm. The probe was fabricated through two main steps. The first step involves an addition of an SERS reporter, 4-mercaptobenzoic acid (4MBA), to a dispersion of Au nanoparticles to yield 4MBA-tagged Au aggregates for enhanced SERS performance. The aggregates are thereby incorporated as cores into monodisperse silica spheres with a uniform spherical shape using a modified reverse microemulsion procedure. The second step involves adsorption of water-soluble luminescent CdTe QDs onto the surfaces of the amino-functionalized silica nanoparticles, which are finally coated with a layer of poly(allyamine hydrochloride) (PAH) to reduce the toxicity of CdTe QDs. The in vitro experimental results prove that the fluorescence-SERS switchable characteristics of the probe will be maintained after the probe is incorporated into living cells. Such novel composite nanospheres could find wide applications, especially in the fields of biological tracking and verification procedures that simultaneously provide locational and spectroscopic information about biomolecules.