The primary focus of this research is to investigate the potential correlations between the absorption band and surface-enhanced Raman scattering (SERS) activity of solution-based silver nanoparticles and the morphology and size of the silver nanoparticles. Silver nanoparticles were synthesized using sodium borohydride reduction methods. The silver nanoparticles were tested for SERS activity using a highly SERS-active compound, trans-1,2-bis(4-pyridyl)ethylene (BPE). Scanning transmission electron microscopy (STEM) was used to analyze the size and shape of the Ag nanoparticles. The STEM, SERS, and UV−vis data have been investigated in order to make correlations between SERS activity, size, and shape of the nanoparticles and their corresponding λmax or surface plasmon (SP) band. The data suggest that as particle size increases, SERS activity decreases. Thus, using the sodium borohydride reduction and solution-based SERS studies, there appears to be an optimal nanoparticle size that is obtained at a λmax of 390 nm. Highly SERS-active nanoparticles had an average particle size of approximately 15 nm and a λmax at 390 nm. At this wavelength and hence average particle size, SERS activity is the strongest. The correlation between SERS activity, wavelengths associated with the surface plasmon band, and the size of the nanoparticles in solution diverges from most of the work which focuses on nanoparticles on solid-substrate surfaces. Although solid-substrate work has focused primarily on the coupling between nanoparticles and substrates on immobilized surfaces and their profound influence on SERS activity, solution-based studies are needed to understand this coupling and its influence on SERS activity in solution. SERS of solution-based nanoparticles provides a significant opportunity to probe the SERS mechanism in solution while also providing an alternative for using SERS in chemical analyses more suited for solution, such as probes in living cells or as diagnostic tests. Herein we combine UV−vis spectroscopy with high-resolution electron microscopy analysis for the study of the effects of size and λmax of Ag nanoparticles on SERS enhancement.

While the water permeability of the plasma membranes of mammalian cells has been studied extensively, water transport across membranes of subcellular compartments (e.g., lysosomes, macropinosomes) has been difficult to study. Here we demonstrate a new method for measuring water flux in late endosomes and lysosomes of intact living cells using time-lapse fluorescence microscopy. Cells were loaded by fluid-phase uptake with a mixture of the Lucifer Yellow dextran (LY-dex), a D(2)O sensitive dye, and a D(2)O insensitive control dye, Alexa fluor 546 dextran (AF546-dex). LY-dex responded linearly to changes in D(2)O concentration and the LY-dex D(2)O sensitivity was not affected by changes in pH, physiological salt, and protein concentrations. The co-loaded control dye, AF546-dex, showed no signal changes as a function of D(2)O concentration. To measure membrane water flux, the LY-dex fluorescence in labeled organelles was recorded during rapid superfusion of cells with isotonic buffers prepared in D(2)O. The time constant of water exchange across the lysosomal membrane of intact cells was determined by fitting the data to a single exponential function. From these data, together with the measured area of the organelles, observed water permeability for intracellular CHO-K1 lysosomes was calculated to be 5.3 × 10(-3) ± 0.3 × 10(-3) cm/s. This work demonstrates the feasibility of measuring water flux into subcellular organelles in live cells using LY-dex.