Agarose-Based Fluorescent Waveguide with Embedded Silica Nanoparticle-Carbon Nanodot Hybrids for pH Sensing

The fabrication of a biodegradable and fluorescent cylindrical waveguide with doped hybrid nanoparticles (silica-carbon nanodots) is reported. The fluorescent hybrids were obtained by coupling amino-functionalized fumed silica nanoparticles with the carboxylic acid surface groups of amorphous carbon nanodots obtained from the thermolysis of citric acid. The hybrid nanoparticles present diameters lower than 10 nm, maximum fluorescence at 465 nm, and excitation-wavelength-dependent behavior. They were occluded into an agarose matrix, providing a low-cost and easily scalable sensor capable of detecting pH variations with maximum sensitivity of 5.61 nm/(pH unit) when excited by a 403 nm UV light-emitting diode (LED).