Fabricating a Molecularly Imprinted Polymer for Sensing Creatinine by the Sol-Gel Process

A creatinine (Cre) imprinted polymer was fabricated by the sol-gel method. In this experiment, aluminum chloride (AlCl3) was chosen as the functional monomer, tetraethoxysilane (TEOS) as the cross-linker, hydrochloric acid (HCl) as the catalyst, and deionized water (DIW) as the solvent to prepare a sol. And then, the sol was put at 60 °C for 1 day for gelation to get a gel monolith. After that, Cre was extracted by DIW to get a Cre imprinted polymer. Non-imprinted polymer (NIP) was prepared in the same manner except for adding Cre during preparation. n the performance tests, the imprinting efficiencies of Cre imprinted polymer, fabricated with the molar ratio of Cre:AlCl3:TEOS=1:3:10, were 1.93, 1.93, 1.83, and 2.17 at the concentration of 50, 100, 150, and 200 μM, respectively. In the interferences tests, four compounds, including creatine (Cn), N-hydroxysuccinimide (NHS), L-tyrosine (L-tyr), and acetaminophen (APAP), were chosen as interferences. The selectivities of Cre imprinted polymer were 7.98(Cre/Cn), 39.98(Cre/NHS), 13.87(Cre/L-tyr), and 6.51(Cre/APAP), respectively. NIP was also found selective to Cre, and the selectivities were 4.00(Cre/Cn), 9.20(Cre/NHS), 16.72(Cre/L-tyr), and 6.34(Cre/APAP), respectively. his research also did some investigations on the effects of silanol groups, Lewis acid sites, and AlCl3 toward the adsorption of Cre. In the aspect of silanol groups and AlCl3, it was observed that the imprinted polymer, with adding AlCl3 during fabrication, adsorbed much more Cre than that without adding AlCl3 did. The differences of adsorption amount were 0.84, 1.18, 1.85, 2.49 and 2.98 mg/g at the concentration of 20, 40, 60, 80 and 100 μM, respectively. As for the reasons for making the differences, we first postulated that adding AlCl3 made the particles smaller, more silanol groups being on the surface. This postulation was substantiated by using microcalorimeter to measure the interactions, Fourier transform infrared spectrometer (FTIR) to observe the absorbance of silanol groups, and scanning electron microscope (SEM) to observe the morphology of surface. In addition, the amount of TEOS was doubled to see the effects toward the adsorption amount and the imprinting efficiency. It was shown that the adsorption amounts were lower than that of previous, but the imprinting efficiencies were upgraded a little. (The imprinting efficiencies were 2.52, 2.12, 2.30, and 2.41 at the concentration of 50, 100, 150, and 200 μM, respectively.) Adsorption amounts being lower was considered to be caused by higher cross-linking degree, thus leaving less silanol groups on the surface, while imprinting efficiencies being higher was considered to be caused by higher proportion of silanol groups in the total imprinted sites. uring preparation, AlCl3 was added for the purpose of forming Lewis acid sites in the silica matrix. However, it was shown that only 20% of Al incorporated with silica matrix, and whether the Lewis acid sites was formed was not very clear. In view of this, the silanol groups were capped by reacting with hexamethyldisilazane (HMDS) to give tirmethylsilyl (TMS) terminating groups. The adsorption amounts of capped particles were tested to see the contribution of Lewis acid sites to Cre adsorption singly. However, it was observed that the capped particles didn’t adsorb Cre. Explanations to this phenomenon were given in this research. Lewis acid sites maybe formed in the inner layer of the particles, which became very hydrophobic after capping, so it was not easy for a highly hydrophilic compound, Cre, to diffuse into.