Cholesterol aided etching of tomatine gold nanoparticles: a non-enzymatic blood cholesterol monitor.

Colloidal gold is extensively used for molecular sensing because of the wide flexibilities it offers in terms of modifications of the gold nanoparticles (GNPs) surface with a variety of functional groups. We describe a simple, enzyme free assay for the detection of cholesterol, and demonstrate its applicability by estimating cholesterol in human serum samples. To enable cholesterol detection, we functionalized GNPs with tomatine, a glycoalkaloid found in the leaves and stem of tomato plants. The binding of cholesterol onto tomatine functionalized gold nanoparticles (TGNPs) was characterized by a blue shift in the plasmon absorption spectra (SPR) followed by reduction in the particle size. The TGNPs have been core etched with increasing concentration of cholesterol and with 800 ng/mL of cholesterol particles in the size range of 10-12 nm have been obtained. This behavior was attributed to the enhanced hydrophobicity of the surface acquired by cholesterol binding resulting in the folding or shrinkage of molecule in turn leading to core etching. The method was successfully applied for the detection of cholesterol in real samples and agrees well with values obtained from the conventional method. Because of its significant plasmonic shift and simplicity, this biosensor could be used for cholesterol detection as it does not demand either any hazardous and costly chemicals or any complex synthetic routes.