A deposition technique has been developed to create thin metal surfaces composed of functionalized fluorescent silver nanoparticles on top of glass or plastic substrates. Deposition is controlled through excitation of nanoparticles via a confocal microscope, allowing for rapid surface formation, high resolution patterning and convenient imaging. The functionalization of these nanoparticles can be tailored to a desired application. Initial investigations have demonstrated that surfaces can be designed to mimic the glucan and mannan layers of a fungal cell wall, which in turn can be used to stimulate and study responses from human immune cells.
We present experimental results on the multicolor (blue and green) photoluminescence from glycine-coated silver
nanoclusters and small nanoparticles which can be used as novel probes for bio-imaging. Glycine-coated silver
nanoclusters and nanoparticles were synthesized using thermal reduction of silver nitrate in a glycine matrix,
according to a modified procedure described in literature. The size characterization with mass spectrometry,
scanning electron microscopy and dynamic light scattering showed that the diameters of luminescent silver
nanoclusters and small nanoparticles vary from 0.5 nm to 17 nm. Extinction spectroscopy revealed that the
absorption band of the luminescent nanoclusters and nanoparticles was blue-shifted as compared to the nonluminescent
larger silver nanoparticles. This effect indicated the well-known size dependence of the surface
plasmon resonance in silver. The most pronounced photoluminescence peak was observed around 410 nm
(characteristic SPR wavelength for silver) which strongly suggests the enhancement of the photoluminescence from
silver nanoparticles by the SPR. The relative quantum yield of the photoluminescence of silver nanoclusters and
nanoparticles was evaluated to be 0.09.
In terms of their small size, brightness and photostability, noble metal nanoclusters and nanoparticles hold
the most promise as candidates for biological cell imaging, competing with commonly used semiconductor quantum
dots, fluorescent proteins and organic dyes. When applied to the problem of intracellular imaging, metal
nanoclusters and small nanoparticles offer advantages over their much larger sized semiconductor counterparts in
terms of ease of biological delivery. In addition, noble metal nanoparticles and nanoclusters are photostable. The
high quantum yield (QY) of the photoluminescence emission signal enables the isolation of their
photoluminescence from the cellular autofluorescence in cell imaging, improving the image contrast.