Identification of chemical species of fluorescein isothiocyanate isomer–I (FITC) monolayers on platinum by doubly resonant sum‐frequency generation spectroscopy

Abstract

Doubly resonant sum-frequency generation (DR-SFG) spectroscopy of fluorescein-4-isothiocyanate isomer-I (FITC) monolayers on platinum was performed. Vibrational spectra of the monolayers for the IRwavenumber of 1750-1450 cm −1 were measured with visible probes ranging from 431 to 582 nm. Two vibrational bands at 1643 and 1610 cm −1 were observed, and their DR-SFG excitation profiles displayed different shapes. By rinsing the monolayers with an alkaline solution, the smaller wavenumber band disappeared and the larger wavenumber band gained intensity. On the basis of the spectral response to the rinsing, we concluded that the FITC molecules existed on platinum as deprotonated and protonated forms; the former corresponds to the 1643 cm −1 band and the latter to the 1610 cm −1 band. The deprotonated form was assigned to an anionic surface species, and the protonated form to a neutral surface species by comparing the DR-SFG excitation profiles with electronic absorption spectra of the protolytic forms of fluorescein in an aqueous solution (Sjöback R et al., Spectrochimica Acta A 1995; 51: L7-L21). The results demonstrate that the measurement of DR-SFG excitation profiles is a useful technique to identify chemical species of monolayers on metal surfaces.

Chemical reactivation of fluorescein isothiocyanate immunofluorescence-labeled resin-embedded samples

“…Since fluorescein isothiocyanate (FITC) had a high fluorescence quantum yield 13,14 and was widely used for monitoring pH values [15][16][17] and immunofluorescence labeling of biological tissues, [18][19][20][21][22] we chose FITC as one representative of pH-sensitive fluorescent probe to realize the idea. First, we investigated whether the fluorescence of FITC would be quenched during resin-embedding process, then further tested whether the quenched immunofluorescence could be reactivated.…”

“…13,14 In brief, the FITC fluorophore has four dominated protolytic forms, cation (FH þ 3 ), neutral species (FH 2 ), anion (FH − ), dianion (F 2− ), 13,14 which make the fluorescence properties remarkably dependent on pH values [ Fig. 3(a)].…”

Editorial

“…These include: a study on polarization-sensitive CARS spectroscopy of free-base porphyrins; [1] a study on the ultrafast bimolecular radical reaction between S 1 p-terphenyl and carbon tetrachloride; [2] a time-resolved resonance Raman and density functional theory study of the deprotonation reaction of the triplet state of para-hydroxybenzophenone in mixed acetonitrile/water solutions; [3] an investigation of femtosecond Raman-induced Kerr effect spectroscopy; [4] a paper on ultrafast vibrational dynamics and solvation complexes of methyl acetate in methanol studied by sub-picosecond infrared spectroscopy; [5] an ultrafast dynamics and photochemistry study of π − π * excited trans-azobenzene; [6] a paper on ultrafast dynamics in Cu(I)bisdiimine complexes from resonance Raman intensities; [7] a three-state model for femtosecond broadband stimulated Raman scattering; [8] a picosecond time-resolved ultraviolet resonance Raman study on photoinduced electron transfer in glucose oxidase; [9] a study on molecular vibrational imaging of a human cell by multiplex coherent anti-Stokes Raman scattering microspectroscopy using a supercontinuum light source; [10] a paper on characteristic wavenumber shifts of the stimulated Raman scattering from interfacial water molecules induced by laser-induced plasma generation at air-water and water-silver interfaces; [11] a study on the identification of chemical species of fluorescein isothiocyanate isomer-I (FITC) monolayers on platinum by doubly resonant sum-frequency generation spectroscopy; [12] a work on coherent acoustic phonons in a thin gold film probed by femtosecond surface plasmon resonance; [13] a review of recent advances in linear and nonlinear Raman spectroscopy; [14] an investigation of the halide-ion-assisted increase of surfaceenhanced hyper-Raman scattering; [15] and finally a study on ultrafast Raman loss spectroscopy [16] . …”

Raman spectroscopy at the beginning of the twenty‐first century II

“…Vibrational spectroscopy can also be used to probe interfaces using sum frequency generation and Maeda et al 27 report the doubly-resonant sum-frequency generation spectroscopy of a fluorescein-4-isothiocyanate isomer-I (FITC) monolayer on platinum. The vibrational spectra of the monolayer for the IR wavenumber range of 1750-1450 cm 1 and its excitation profile were measured using visible probes ranging from 431 to 582 nm.…”