Fluorescent Polyelectrolyte Capped Silver Nanoclusters: Optimization and Spectroscopic Evaluation

Abstract

In the present work, we have synthesized water soluble Ag nanoclusters using PMAA as a template with different Ag+: COO-ratios, to optimize it for highest brightness using less UV exposure time. Fluorescence polarization was 0.30 for and was found to vary with excitation and emission wavelength with few hundred picoseconds average fluorescence lifetime. Fluorescence Correlation Spectroscopy data depicts slower diffusion at red excitation compared to blue excitation in confocal volume than conventionally synthesized colloids proving presence of multiple sizes. The optical properties of the particles are dependent upon the excitation wavelength used and the emission wavelength collected.

Keywords: FCS; Fluorescent Ag Nanoclusters; Metal Nanoclusters; Polarization; Polymethylacrylic Acid.

Figure 1

(A) Absorption spectra of different Ag: COO-ratio used in preparation of Ag nanoclusters. (B) Shows the corrected peak emission [black line] and UV exposure time to reach peak emission [blue line] as function of different Ag: COO-ratio (C) Shows the two TEM images of 6:1 Ag+: COO-ratio Ag nanoclusters from different parts of the TEM grid. Red square in the 1st image shows the approximate area from where the second TEM image was captured. (Scale bar 10 nm in 1st image and 2 nm in 2nd image)

Figure 2

(A) Excitation and emission spectrum along with respective excitation and emission anisotropy using 470 nm excitation and 610 nm observation wavelength. (B) Shows the photograph comparing emission intensity of Ag clusters and 5 nm green emission quantum dots when excited with blue laser (470 nm) and observed through parallel (∥) and perpendicular (⊥) polarizer orientation.

Figure 3

Fluorescence intensity decays of Ag nanoclusters in water at room temperature when emission intensity was observed at 610nm (red), 710nm (green), and 810nm (magenta) at 480 nm excitation.

Figure 4

(A) Emission spectra of Ag nanocluster at different excitation (numbers on top of each spectra) (B) Shows the FCS pattern of Ag nanoclusters when excited with blue laser (470 nm) and red laser (633 nm).

Figure 4

(A) Emission spectra of Ag nanocluster at different excitation (numbers on top of each spectra) (B) Shows the FCS pattern of Ag nanoclusters when excited with blue laser (470 nm) and red laser (633 nm).