Solid phase extraction of neutral analytes through silica gel coated with layers of Au nanoparticles self-assembled with alkanethiols

In this study, we used Au nanoparticle (NP)-coated silica gel as a solid phase extraction sorbent for the preconcentration of neutral analytes (steroid drugs). The sorbent was fabricated using two alkanethiol self-assembly processes: one to deposit the Au NPs onto a 3-aminopropyltrimethoxysilane-modified silica gel and the other to functionalize the surfaces of the Au NPs. A large volume of the steroid solution was passed through the silica gel to facilitate adsorption mediated by hydrophobic interactions between the steroids and the hydrophobic moieties on the silica gel surface. Extraction of the steroids was accomplished by flushing the silica gel with a low-polarity solvent. In this preliminary study, we found that the particle size of the silica gel and the number of layers of Au NPs coated on the silica gel both affected the preconcentration performance for the steroids. When using six layers of Au NPs coated on 5-20-mu m silica gel, the detection limits for steroids were below 80 ng L-1; the preconcentration efficiency was over 170-fold higher than that of the original steroid solution. Our findings provide further evidence that nanotechnology has much to benefit analytical science.