Simultaneous fluorescence and surface charge measurements on organic semiconductor-coated silica microspheres in (non)polar liquids

We present an experimental platform which combines spectroscopic capabilities with time-resolved measurements of effective surface charge at solid-liquid interfaces. Silica microspheres, pristine and coated with various organic semiconductor molecules, were optically trapped either in water or in toluene. Adsorption of organic semiconductor molecules on the microspheres was observed via appearance of fluorescence and dramatic reduction in the effective surface charge, measured concurrently on individual spheres, with elementary charge resolution. The versatile platform accommodates possibilities to study a variety of photoinduced processes simultaneously with measurements of surface charge and can be incorporated in devices such as microreactors and microfluidics. (C) 2017 Optical Society of America under the terms of the OSA Open Access Publishing Agreement