An understanding of the mechanisms of drug diffusion and uptake through cellular membranes is critical for elucidating drug action and in the development of effective drug delivery systems. We study these processes for emodin, a potential anticancer drug, in live cancer cells using surface-enhanced Raman scattering. Micrometer-sized silica beads covered by nanosized silver colloids are passively embedded into the cell and used as sensors of the drug. We demonstrate that the technique offers distinct advantages: the possibility to study the kinetics of drug diffusion through the cellular membrane toward specific cell organelles, the detection of lower drug concentrations compared to fluorescence techniques, and less damage imparted on the cell.
Optical tweezers technique combined with local confocal luminescence spectroscopy is suggested as a tool for
investigation of local optical fields. Utilizing this method plasmon-enhanced optical fields inside a pair of dielectric
2 μm spheres partially covered by 70 nm silver nanoparticles are visualized via field enhanced luminescence of
rhodamine dye solution. Positions of the particles are controlled with submicrometer accuracy by two optical
traps formed by strongly focused laser beams with λ=980nm. A supplementary beam from CW laser with
λ=532nm provided for luminescence excitation is also focused into the sample cavity just to the trapping area.
In order to obtain spatial filtering of the signal and separate luminescence signal from an area near the spheres
pin-hole based confocal system is designed. The focal volume available for luminescence signal collection turns
out to be approximately 3μm x 3 μm x 5 μm. Since optical field is enhanced in the region near plasmon-active 2
μm spheres the enhancement of luminescence intensity is observed. Collective plasmonic effects in two-particle
measurements are also considered.
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