Rhodamine 6G conjugated to gold nanoparticles as labels for both SERS and fluorescence
studies on live endothelial cells

Abstract

Fluorescence and surface-enhanced Raman scattering (SERS) spectroscopy were employed to investigate the cellular uptake of rhodamine 6G (R6G) alone and of R6G loaded with gold nanoparticles (AuNPs) by endothelial cells. R6G plays the role of a Raman reporter in SERS but also displays strong fluorescence. The presence of bare R6G molecules and R6G-AuNPs in the cytoplasm of the cells is detected via the 2D fluorescence of the dye after a 0.5 h of the incubation with R6G and R6G-AuNPs, and then the concentration of the dye increases within 4 h of exposure. The examination of the cellular uptake of the R6G and R6G-AuNPs species at different temperatures suggests that the internalization of the R6G-AuNPs into endothelial cells occurs mainly via endocytosis. 3D fluorescence imaging of R6G inside cells reveals inhomogeneous distribution of the dye in the cytoplasm. The SERS signal of the Raman reporter inside the cell disappears after 2 h of incubation with R6G-AuNPs and then amino acid residues, purines and pyrimidines become SERS-active via their interactions with the gold. The results highlight the significance of using multiple techniques to cover a spectrum of issues in the application of SERS nanosensors for probing an intracellular environment under comparable and standardized conditions.FigureCellular uptake of bare rhodamine 6G and rhodamine 6G adsorbed onto AuNPs were studied on endothelial cells using fluorescence and surface-enhanced Raman spectroscopy. The internalization of R6G-AuNPs occurs via endocytosis and diffusion resulting in uneven distribution in the cytoplasm.Electronic supplementary materialThe online version of this article (doi:10.1007/s00604-014-1307-5) contains supplementary material, which is available to authorized users.

Label‐Free Molecular Imaging of Biological Cells and Tissues by Linear and Nonlinear Raman Spectroscopic Approaches

“…[177] R6G-AuNPs are taken up by endothelial cells mainly by endocytosis.However, the SERS signal of R6G inside the cells disappears after 2hof incubation, which might be due to detachment from the AuNPs or degradation of R6G.T hus the SERS signals for longer incubation times show the spectral information of amino acid residues,p urines,a nd pyrimidines owing to their interaction with the gold surface.W hen NIR excitation is applied for recording the SERS spectra, the contribution of the dye label to the overall spectrum is decreased as no further resonance Raman enhancement is expected. [177] R6G-AuNPs are taken up by endothelial cells mainly by endocytosis.However, the SERS signal of R6G inside the cells disappears after 2hof incubation, which might be due to detachment from the AuNPs or degradation of R6G.T hus the SERS signals for longer incubation times show the spectral information of amino acid residues,p urines,a nd pyrimidines owing to their interaction with the gold surface.W hen NIR excitation is applied for recording the SERS spectra, the contribution of the dye label to the overall spectrum is decreased as no further resonance Raman enhancement is expected.…”

“…Mainly AuNPs and AgNPs are applied as cores of SERS labels.T oa llow for localization of the nanoparticles inside cells or on tissue samples,the metal nanoparticles are coated with Raman reporter molecules such as dyes or aromatic substances.F or example,r hodamine 6G (R6G) coated AuNPs were used for intracellular investigations of endothelial cells,d ominating the SERS spectra. [177] R6G-AuNPs are taken up by endothelial cells mainly by endocytosis.However, the SERS signal of R6G inside the cells disappears after 2hof incubation, which might be due to detachment from the AuNPs or degradation of R6G.T hus the SERS signals for longer incubation times show the spectral information of amino acid residues,p urines,a nd pyrimidines owing to their interaction with the gold surface.W hen NIR excitation is applied for recording the SERS spectra, the contribution of the dye label to the overall spectrum is decreased as no further resonance Raman enhancement is expected. [178] To improve the stability of SERS labels,m ethylene blue AgNPs were coated with gold.…”

Photocatalytical decoration of thin titania coatings with silver nanostructures provides a robust and reproducible SERS signal

“…Surface‐enhanced Raman spectroscopy (SERS) has become a powerful tool for sensing even at a level of a single molecule as well as for the identification of practically unlimited number of bio/chemical analytes in ex vivo and in vitro experiments . Fabrication of regular and reproducible substrates, which effectively amplify Raman signal on the metal–medium boundaries, still remains a great challenge, and several silver and gold nanostructures have been designed and investigated in terms of their features as plasmonic antennas.…”

“…Surface-enhanced Raman spectroscopy (SERS) has become a powerful tool for sensing even at a level of a single molecule as well as for the identification of practically unlimited number of bio/chemical analytes in ex vivo and in vitro experiments. [1,2] Fabrication of regular and reproducible substrates, which effectively amplify Raman signal on the metal-medium boundaries, still remains a great challenge, and several silver and gold nanostructures have been designed and investigated in terms of their features as plasmonic antennas. Several efficient fabrication methods of SERS periodic nanostructures have been proposed so far, and they rely on nanosphere lithography, [3] reactive ion etching, [4] electrochemical deposition of Ag/Au films on 3D hierarchical templates, [5,6] controlled deposition of metal nanoislands, [7] and so on.…”

Narrow Bandwidth Top-Emitting OLEDs Designed for Rhodamine 6G Excitation in Biological Sensing Applications

“…The OLED in photoluminescence (PL) based sensors operates commonly in pulse mode and enables by excitation the monitoring of any effects on the PL intensity induced by an analyte and also on its PL decay time. Besides PL based sensing in microscopy [3,4], fluorescence studies of cells [5,6] and forensic trace evidence [7] are well established methods in biological and chemical studies and offer extensive possibilities to observe cell growth, metabolism behavior and toxicological effects. However, a remaining challenge is to detect changes in the PL intensity and that the excitation and emission spectrum for bio or chemical markers need to be sufficiently separated.…”