(153f) Development of Sol-Gels and Nanoparticle Enhanced Sol-Gels for pH Sensing Performance

Sol–gel is a wet-chemical process that involves the formation of an inorganic colloidal solution (sol) as the precursor and the gelation of the sol to form a three-dimensional network structure (gel). Sol-gel technology has been applied for the development of optical sensors and biosensors, due to 1) its chemically, photochemically, thermally, and mechanically stable; 2) optically transparent; 3) being formed at low temperature and under mild chemical conditions, allowing the entrapment of molecules with thermal and chemical sensitivity.

The sol–gel process has three major steps: 1) the raw materials (reactants and nanoparticles) were dispersed in the solvent by an ultrasonic treatment, 2) Tetraethyl orthosilicate (TEOS) hydrolyzed to form active monomers, which polymerized to be a sol, and 3) eventually, the sol started to form a gel with a certain spatial structure by aging. Figure 1 shows the intensity spectra for sol-gel pH sensor with cresol red indicator dye.

The incorporation of TiO₂ nanoparticles enhances the hardness and elastic modulus of the gel by 0.18 GPa and 3.7 GPa, respectively, so that it provides a good and solid support for the immobilization of the indicator for a better sensitivity and stability in the sensing film. The TiO₂-sol-gel film can be used to detect pH in a broad range of 1-12 fast and reversibly. It has advantages over the traditional electrochemical analysis with no charge, strong anti-electromagnetic interference, no pollution, and can be employed to develop optic chemical sensor for remote measurement and multi-channel detection. It can be envisaged that the sol-gels and nanoparticle enhanced sol-gels have great potentials to be the solid base for next-gen sensors.