We report on single-molecule studies of photosensitized interfacial electron transfer (ET) processes in Coumarin 343 (C343)-TiO(2) nanoparticles (NP) and Cresyl Violet (CV(+))-TiO(2) NP systems, using time-correlated single-photon counting coupled with scanning confocal fluorescence microscopy. Fluorescence intensity trajectories of individual dye molecules adsorbed on a semiconductor NP surface showed fluorescence fluctuations and blinking, with time constants distributed from milliseconds to seconds. The fluorescence fluctuation dynamics were found to be inhomogeneous from molecule to molecule and from time to time, showing significant static and dynamic disorders in the interfacial ET reaction dynamics. We attribute fluorescence fluctuations to the interfacial ET reaction rate fluctuations, associating redox reactivity intermittency with the fluctuations of molecule-TiO(2) electronic and Franck-Condon coupling. Intermittent interfacial ET dynamics of individual molecules could be characteristic of a surface chemical reaction strongly involved with and regulated by molecule-surface interactions. The intermittent interfacial reaction dynamics that likely occur among single molecules in other interfacial and surface chemical processes can typically be observed by single-molecule studies but not by conventional ensemble-averaged experiments.

One prevention and therapeutic strategy for diseases associated with peptide or protein fibrillation is to inhibit or delay the fibrillation process. Carbon dots (C–Dots) have recently emerged as benign nanoparticles to replace toxic quantum dots and have attracted great attention because of their unique optical properties and potential applications in biological systems. However, the effect of C-Dots on peptide or protein fibrillation has not been explored. In this in vitro study, human insulin was selected as a model to investigate the effect of C-Dots on insulin fibrillation. Water-soluble fluorescent C-Dots with sizes less than 6 nm were prepared from carbon powder and characterized by UV–vis spectroscopy, fluorescence, Fourier transform infrared spectrophotometry, X-ray photoelectron spectrometry, transmission electron microscopy, and atomic force microscopy. These C-Dots were able to efficiently inhibit insulin fibrillation in a concentration-dependent manner. The inhibiting effect of C-Dots was even observed at 0.2 μg/mL. Importantly, 40 μg/mL of C-Dots prevent 0.2 mg/mL of human insulin from fibrillation for 5 days under 65 °C, whereas insulin denatures in 3 h under the same conditions without C-Dots. The inhibiting effect is likely due to the interaction between C-Dots and insulin species before elongation. Cytotoxicity study shows that these C-Dots have very low cytotoxicity. Therefore, these C-Dots have the potential to inhibit insulin fibrillation in biological systems and in the pharmaceutical industry for the processing and formulation of insulin.

Photo-cross-linking has received a considerable attention for the design of intelligent materials in biochemical and biomedical applications. In this report, we describe the synthesis and properties of a novel photoreversible poly(ethylene glycol)-(PEG-) based hydrogel system. 9-Anthracenecarboxylic acid was used to modify the hydroxyl groups of an eight-armed PEG polymer (molecular weight 20 000) and the degree of substitution was determined to be 87.4%. The PEG-anthracene macromers (PEG-AN) exhibited high photosensitivity at wavelengths close to visible light (absorption maxima at 366 and 380 nm) and underwent rapid and reversible photo-cross-linking upon exposure to alternating wavelengths of irradiation (365/254 nm) in the absence of photoinitiators or catalysts. Changes in light exposure and wavelength of irradiation reversibly altered the physicochemical properties of the PEG-AN hydrogel, including swellability, absorption spectrum, and topography.

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Electric field enhancement distributions encountered in atomic force microscopy (AFM) tip-enhanced surfaceenhanced Raman spectroscopy (SERS) experiments (AFM-SERS) are simulated using a frequency-domain three-dimensional finite element method to solve Maxwell's equations of electric field distributions. We simulated an electromagnetic field enhancement in the vicinity of an AFM tip in close proximity to silver spherical nanoparticles under the illumination of a laser beam of various incident angles under different geometric arrangements. Maximum electric field enhancement is discussed in terms of the relative position of the tip and nanoparticles, as well as the direction of excitation laser propagation. Our results suggest new approaches for using AFM-SERS tip-enhanced near-field technique to image samples on surfaces.