Effect of template removal methods on gold nanoparticles/mesocellular foam silica nanocomposite characteristics for acetylcholinesterase immobilization

Abstract

This research aimed at investigating the effect of template removal methods, calcination and solvent extraction, on characteristics of mesocellular foam silica (MCF) based materials and their applications in acetylcolinesterase (AChE) biosensors. In this study, the experiments were divided into 3 parts. Firstly, efficiency of different template removal methods were tested, and the synthesized MCF-based materials were characterized. Characteristics of calcined mesoporous foam silica (MCF-c) and solvent-extracted mesoporous foam silica (MCF-e) were revealed using nitrogen sorption technique. Both the MCF-c and MCF-e were categorized as a mesoporous materials with the total surface areas of 1075 and 1221 m2/g, and the main pore sizes of 8.1 and 6.7 nm, respectively. The FTIR data showed that these two silicas contained similar surface functional groups, and the template was successfully removed in both cases. However, the SEM and TEM pictures exhibited obvious shrinkage of the MCF-c particles which was most likely due to the damage caused by the high temperature process of calcination. Secondly, effects of template removal methods on 3-aminopropyltriethoxysilane (APTS) and in-situ addition of gold nanoparticles (AuNPs) in the based MCF materials were studied. The synthesized were in the ranges of 2-3 nm depended on the based MCF materials. With long enough Au precursor adsorption time, both AuNPs/MCF-c and AuNPs/MCF-e contained roughly similar density of AuNPs suggesting that the difference in surface silanol concentrations in both materials did not significantly affected incorporation of AuNPs at this level of precursor concentration. Further tests of AuNPs/MCF based sensors revealed higher current responses to acetylthiocholine chloride (ATCl) in the case of MCF-e than MCF-c. Suitable Au precursor concentration was determined at 0.5 mM since the CV response and AChE loading were relatively high. Thirdly, MCF-e and AuNPs/MCF-e of the suitable fabrication method were then applied in AChE biosensors for pesticide detection. The obtained biosensor was denoted as SPCE/MCF-e/AChE/Chitosan and SPCE/MCF-e/AuNPs/AChE/Chitosan. For MCF-e, the inhibition of chlorpyrifos was in the linear ranges of 0.5 to 200 ppb and 200 to 2000 ppb with detection limit of 0.894 ppb. On the other hand, for Au/MCF-e provide the linear ranges of chlorpyrifos responses were from 0.5 to 200 ppb and 200 to 2000 ppb with detection limit of 0.701 ppb. The stability of biosensor stored on MCF-e and Au/MCF-e at 4oC in dry condition was good since it could retain 74.25 and 77.57 % respectively of initial current response after 30 storage days.