A system of FRET dyes designed to assess the degree of nano-scale contact between surfaces for interfacial adhesion

Functionalizing Surfaces by Physical Vapor Deposition To Measure the Degree of Nanoscale Contact Using FRET

“…There is no FRET signal. (A) Donor and Acceptor bonded thin films prepared by DB, where the dyes were previously dissolved in the films. − Donor and Acceptor molecules can be found through the entire bulk of the film (1.5 μm thickness), and excess fluorescence intensity (not FRET related noise) is detected during the FRET measurements; (B) Donor- and Acceptor nanolayer bonded films prepared by PVD. The dyes can only be found on the material surface, where the NSC and FRET occur.…”

“…For the experiments we used a FRET pair, specially designed by us for the measurement of NSC. , The FRET pair is composed of 7-Amino-4-methyl-cumarin (C120, Figure A) as the Donor dye and 5(6)-Carboxy-2′,7′-dichlor-fluorescein (CDCF, Figure B) as the Acceptor dye. Both molecules present high quantum yields (QY, QY D = 0.91 and QY A = 0.64) and a FRET distance range from 0.6 to 2.2 nm (at 0.1 mM), suitable for the study of NSC and adhesion caused by intermolecular forces that only occur at low nanometric distances (below 1 nm).…”

“…FRET (Förster Resonance Energy Transfer) has recently been introduced as an experimental technique for the measurement of NSC between soft surfaces. − FRET takes advantage of the fluorescence properties of specific compatible molecules to determine their exact nanometric distance (0–20 nm) . Thus, if these molecules, named Donor and Acceptor, are in NSC, a nonradiative Donor → Acceptor energy transfer will occur and a FRET signal can be detected. , The FRET distance range depends on the Förster Radius (R 0 ) of the FRET dyes utilized and can only be properly sensed between 0.5R 0 and 2R 0 .…”

“…Recently it has been demonstrated that the NSC measured with FRET correlates to the adhesion between soft materials. − These studies showed that for bonded thin films pressed under different loads, the FRETeff and adhesion increase with the applied pressure, caused by the correspondent increase of the degree of NSC . Thus, FRET has been introduced as a proper technique to quantify the degree of NSC and establish a relation between FRETeff and adhesion in bonded films.…”

“…In the original proof-of-concept studies, the fluorescent dyes were mixed in soft, thin films, which allow us to produce uniform and well distributed dye films, use exact dye concentrations, and study/develop different FRET systems for the measurement of NSC. This, however, is strongly limiting the applicability of the method to polymer surfaces where the fluorescence molecules must be solubilized in the polymer solution. − Moreover, utilizing these films, the dye molecules were present not only in the interface between the thin films, where FRET can occur within 0.5R 0 –2R 0 , but also through the entire polymeric matrix of the thin films (Figure A). This leads to a strong increase of the pure dyes’ spectral signal which makes it harder to detect the FRET signal, which is the Acceptor intensity increase from I A to I AD (see Figure ), creating a low signal-to-noise ratio in the system.…”