Surface-plasmon-initiated interference effects of polyelectrolyte-coated gold nanorods around the two-photon absorption

Surface-plasmon-initiated interference effects of polyelectrolyte-coated gold nanorods around the two-photon absorption of an organic chromophore were investigated. analysis Fenoprofen calcium and showed good agreementdue to constructive and destructive interference effects. overlap the dye’s Fenoprofen calcium TPA maximum. Using the method of Hermann and Ducuing 15 the dye’s TPA cross-section at 800 nm was examined as a function of its spatial separation from AKT1 the platinum nanorod surface. This method has been previously demonstrated to give accurate TPA cross-section enhancement factors that are free of parasitic optical and photophysical effects that would yield an artificially high TPA enhancement factor.14 16 Aspect ratio two(AR 2) platinum nanorodswere synthesized with Fenoprofen calcium an LSPRat approximately 650 nm using a previously reported process.17 The as-synthesized nanorods were stabilized by a positively-charged CTAB bilayer 18 onto which poleyelectrolytes can be wrapped using layer-by-layer deposition.19 Previously we have successfully demonstrated that it is possible to bind at variable distances the TPA chromophore AF348-3A to gold nanorods with polyacrylate (PAA) and polyallyamine hydrochloride (PAH) dielectric polyelectrolyte spacer layers.14 Physique 1 shows the experimental schematic of the platinum nanorods with the attached chromophore molecules for 2 4 6 and 8 polyelectrolyte layer-bearing platinum nanorods; this corresponds to spatial distances of 3 6 9 and 12 nm respectively.19 Fenoprofen calcium Determine 1 Cartoon of a polyelectrolyte-coated gold nanorod with the AF-348-3A chromophore. Platinum bar: platinum nanorod. Dashed collection: A polyelectrolyte spacer layer of thickness that separates the gold surface from your chromophore. Green stars: AF-348-3A chromophore … Electronic absorption spectra of the AF348-3A-bearing 2 4 6 and 8 polyelectrolyte layer-coated platinum nanorods are shown in Physique 2. Slight blue and reddish shifts in the absorption maxima are observed and are associated with the variable refractive index of the space surrounding the platinum nanorods (different degrees of polyelectrolyte hydration). Slight plasmonic broadening at ~800 nm suggests minor aggregation that we cannot eliminate completely. For each sequential polyelectrolyte assembly zeta-potential measurements indicate the expected switch in the effective surface charge (Physique S1) of the platinum nanorods suggesting that electrostatic layer-by-layer self assembly is occurring. The absorption spectrum of AF348-3A is not observed in Physique 2 because the molar absorptivity of the longitudinal plasmon resonance of the gold nanorod is several orders of magnitude higher than that of AF348-3A.14 Physique 2 Normalized electronic absorption spectra of platinum nanorods of aspect ratio two in water bearing two (black) four (red) six (blue) eight (pink) polyelectrolyte spacer layers between the platinum nanorod surface and the AF348-3A chromophores in all cases … Nonlinear measurements were carried outin aqueous solutions (Millipore) with an absorbance of approximately 0.25 at the global absorption maximum. Measurements of the TPA cross-section enhancement factors were obtained using an instrument and technique previously explained.14 Fenoprofen calcium Briefly the 800 nm 150 fs 1000 Hz output of a Ti:Al2O3 regenerative amplifier (Spectra-Physics Hurricane) excited an aqueous answer of the neat dye or dye complexed to platinum nanorods for measurement Fenoprofen calcium of the dye’s two photon fluorescence. The 800 nm output of the laser was also doubled by way of a frequency doubling crystal to a frequency-equivalent wavelength of 400 nm. The sample was excited again and its one photon fluorescence spectrum obtained. The two-photon absorption cross-section of the neat dye or the dye complexed to gold nanorods was obtained the method of Hermann and Ducuing (Eq. 1).15 The ratio of the two-photon absorption cross-section of the gold nanorod-bound dye to that of the neat dye solution is defined as the two-photon absorption cross-section enhancement factor. Only this enhancement factor and not the complete cross-sections will be reported. Our recent related work for the on-resonant case of a two-photon absorber on platinum nanorods featured 200-1000 chromophores per rod.14 The calculation of the AF348-3A two-photon absorption cross-section σ(2) is described by (Eq. 1) where σ(1) represents the linear one photon absorption cross-section φ2ω is the one photon excitation power φω represents the two photon excitation power and I(2PL) and I(1PL) are the two photon- and one photon-fluorescence intensities respectively.15 Using (1) to calculate σ(2) has several advantages. The concentration of the dye around the platinum nanorod.