Preliminary study towards the fabrication of the nanoscale optical pH sensor with tailored pKa value by using molecularly imprinting technique

Molecularly imprinting is an advanced technique for producing chemically selective binding sites, which recognize a particular molecule, in a macro porous polymer matrix. The pK_a value of the indicator is significantly changed up to several orders of magnitude by the imprinting synthesis. This fine-tuning of the reactivity of pH indicators by using the imprinting synthesis (molecularly imprinted polymer) may find novel applications in designing pH sensors with tailored pK_a value. Here, we try to describe a technique for the successful imprinting of different structural stages of a pH indicator in a hybrid sol-gel matrix. The proton affinity of the indicator is strongly dependent on this imprinting synthesis. The pH indicator used in this experiment is methyl red. The end result of the proton imprinting technique is the modification of the pK_a value of the indicator in the sol-gel matrix. The fabricated imprinted polymer is likely suitable for the construction of the nanoscale optical pH sensor due to the modified pK_a value, the large surface area and the pore size of the hybrid sol-gel used in this study.