A Total Internal Reflectance Fluorescence Nanoscale Probe of Interfacial Potential and Ion Screening in Polyethylene Oxide Layers Adsorbed onto Silica
✍ Scribed by V.A. Rebar; M.M. Santore
- Book ID
- 102579755
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 245 KB
- Volume
- 178
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
the molecular detail, while in the latter two applications, This work investigated the effect of the ionic environment on the efforts are made to hold the local environment fixed so that fluorescence signal from layers of fluorescein-tagged polyethylene the fluorescence is proportional to the amount of labeled oxide (FITC-PEO) adsorbed onto silica from aqueous solution. molecules in the sample volume. Total internal reflectance The fluorescence intensity from an adsorbed layer in a total interfluorescence (TIRF), an example of the third family of fluonal reflectance fluorescence (TIRF) study was found to be highly rescence methods, is well established for protein adsorption sensitive to the fluid contacting the layer: Deionized water gave (1-13) and has recently been extended to polymer adsorpno signal at all, while the signal was strong for phosphate-buffered tion (14-18) and colloidal deposition (19). Most TIRF apsaline. The bulk solution fluorescence of FITC-PEO, however, was plications attempt to track adsorption kinetics or the surface comparatively less sensitive to the presence of buffer as opposed to deionized water. This suggested that the fluorescent sensitivity excess; however, interfacial conditions often push the underto ionic conditions was an interfacial effect, possibly stemming lying assumptions (the linearity between fluorescence and from the pH sensitivity of fluorescein. Titrations of the fluorescence the surface excess, and the similarity in quantum yield besignal from the adsorbed layer as a function of salt concentration tween fluorophores on free and adsorbed molecules) to the and as a function of phosphate concentration at nearly constant limit. Both the interfacial chemistry and the locally high ionic strength revealed an increase in fluorescence with increasing concentration of adsorbing species can alter fluorescence. concentration of the ionic species, with a sharp sigmoidal transi-Many fluorescence studies of proteins via TIRF (1-7) tion. This transition occurred at 0.0001 M for the phosphate and employed a physiological phosphate-buffered saline (PBS) near 1 M for NaCl, demonstrating the phosphate-buffering species solution. The direct effect of the phosphate and salt ions on to be more effective in producing fluorescence compared with an the fluorescein emissions was not mentioned (1, 3, 5-7), unreactive salt. These experimental observations were best exalthough the influence of the local hydrophilicity on the plained by the weak acid-base reaction of the fluorescein with the quantum yield was discussed in the context of surface relaxbuffer and by the influence of the ionic strength on the debye length near the acidic silica surface. In the presence of buffer, the ations (2, 5).
transition point was shown to be sensitive to the local potential,
In the present TIRF studies of fluorescein-tagged polyethand the extent of the quench at low ionic strengths to the local ylene oxide (FITC-PEO) adsorbed onto silica, a significant pH.