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. 2006 Mar;81(4):249-55.
doi: 10.1002/bip.20407.

One- And Two-Photon Induced Fluorescence of Pacific Blue-labeled Human Serum Albumin Deposited on Different Core Size Silver Colloids

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One- And Two-Photon Induced Fluorescence of Pacific Blue-labeled Human Serum Albumin Deposited on Different Core Size Silver Colloids

Joanna Lukomska et al. Biopolymers. .
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Abstract

We studied one- and two-photon induced fluorescence of Pacific Blue (PB)-labeled human serum albumin (HSA) in the presence of different size silver colloids. The PB fluorescence emission intensity was observed with small (30-40 nm) and large (about 120 nm) colloids and compared with PB emission in absence of colloids. For the system with a small core size colloids we did not detect any fluorescence enhancement with one-photon excitation and the enhancement observed with two-photon excitation was about 2.5-fold. In contrast, for large silver colloids we observed about a 2-fold increase in PB fluorescence brightness for one-photon excitation, and the enhancement with two-photon excitation excided 13-folds. Much stronger increases in brightness observed with two-photon excitation, compared to one-photon excitation, indicate a dominant role of enhanced local field in fluorescence enhancement on silver colloids in solutions.

Figures

FIGURE 1
FIGURE 1
Extinction spectra of small (—) and large (– –) silver colloids. The large colloids display long-wavelength shoulder in their spectrum.
FIGURE 2
FIGURE 2
AFM images of small (top) and large (bottom) colloids. The left panels show 5 by 5 μm areas and the right panels show randomly selected 1 by 1 μm areas. The large colloids are about 5-fold bigger.
FIGURE 3
FIGURE 3
Emission spectra of Pacific Blue-labeled HSA (L = 1.5) in the presence (—) and absence (– –) of small silver colloids. The measurements were done in front-face format with 360-nm excitation. Also are shown respective backgrounds (no PB) for samples with (- - -) and without (⋯) colloids.
FIGURE 4
FIGURE 4
Emission spectra of Pacific Blue-labeled HSA (L = 1.5) in presence (—) and absence (– – –) of large silver colloids. Also are shown backgrounds for samples with (---) and without (⋯) colloids. The excitation was 360 nm.
FIGURE 5
FIGURE 5
Two-photon induced fluorescence spectra of Pacific Blue-labeled HSA (L = 1.5) in the presence (—) and absence (– –) of small silver colloids. The front-face excitation at 780 nm was from the femtosecond Ti : Sapphire laser. The laser beam was collimated to about 200 μm in diameter. Also are shown respective backgrounds for samples with (- - -) and without (⋯) colloids.
FIGURE 6
FIGURE 6
Two-photon induced fluorescence spectra of Pacific Blue-labeled HSA (L = 1.5) in presence (—) and absence (– –) of large silver colloids. The excitation and observation conditions are the same as for small colloids (Figure 5).
FIGURE 7
FIGURE 7
Emission spectra of Pacific Blue-labeled HSA (L = 7.5) in the presence (—) and absence (– –) of large colloids obtained with one-photon excitation. The conditions are the same as described in Figures 3 and 4. The backgrounds have been subtracted from the spectra.
FIGURE 8
FIGURE 8
Two-photon induced fluorescence spectra of Pacific Blue-labeled HSA (L = 7.5) in the presence (—) and absence (– –) of large silver colloids. The conditions are the same as described in Figures 5 and 6. The backgrounds have been subtracted from the spectra.

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