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Theinteraction between a photoacid (8-hydroxy-1,3,6-pyrenetrisulfonate,HPTS) and the surfaces of biomaterials and the diffusion of protonsalong the biomaterial surfaces were examined by following the excited-stateproton transfer (ESPT) from the photoacid, adsorbed on the surfaces,to water molecules next to it. We chose two different types of biomaterialsurfaces, hydrophobic insulin amyloid fibrils and hydrophilic cellulosesurfaces. With the help of steady-state and time-resolved fluorescencetechniques, we found that the rate of ESPT from HPTS on insulin fibrilsto adjacent water molecules is about 1/10thatin bulk water. However, the proton geminate recombination takes placewith an efficiency similar to that in bulk water. ESPT from HPTS inwet cellulose to water depends on the weight percentage of water adsorbedby the cellulose. In a semidry sample (<100% weight percentageof water), the ESPT rate is rather low and thus the quantum efficiencyof the ESPT is also low within the excited-state lifetime. When thewater content is higher, the ESPT rate is almost that of bulk water.We explain these results by the existence of pools of water in celluloseof high water content, in which the triple-negatively charged HPTSmolecules desorb from the cellulose surface to these pools. The useof HPTS has allowed us to examine the biological surface and its interactionwith water molecules, while obtaining important information regardingthe hydration state of the surface that otherwise could not have beenobtained. The model that we propose here for the use of photoacids to followthe hydrated state of a given surface is a promising new method ofexamining the interaction of water molecules with biological surfaces. [ABSTRACT FROM AUTHOR]

There is an indispensable need for a fluorescence markerfor thedetection of amyloid fibrils, where, at present, the most used markeris thioflavin-T (ThT). Here, we present the use of auramine-O (AuO)as a possible alternative to ThT. As with ThT, the increase in theemission of AuO upon binding to amyloid fibrils is the result of inhibitionof the free rotation of the two dimethylamino arms of the molecule.This inhibition prevents the excited-state electronic wave functionfrom moving from the emissive locally excited state to the dark charge-transferstate. We further show that not only AuO is comparable to ThT as afluorescent marker for amyloid fibrils but also it has a unique spectroscopicsignature. AuO has distinct two modes that are characterized by alarge shift in the absorption and emission peak positions betweenits unbound and bound states (before and after the fibrils formation,respectively). In this context, we show that, whereas the emissionband position is red-shifting, the absorption peak shifts to the blueand the spectrum exhibits an isosbestic point. The large shifts inemission and absorption peak positions can be explained by the photoacidactivity of AuO exhibiting an excited-state proton-transfer process. [ABSTRACT FROM AUTHOR]