Detoxification of gold nanorods by conjugation with thiolated poly(ethylene glycol) andtheir assessment as SERS-active carriers of Raman tags

Abstract

We present an effective, low cost protocol to reduce the toxicity of gold nanorods inducedby the presence of cetyltrimethylammonium bromide (CTAB) on their lateral surface as aresult of the synthesis process. Here, we use thiolated methoxy-poly(ethylene)glycol (mPEG–SH) polymer to displace most of the CTAB bilayer cap from theparticle surface. The detoxification process, chemical and structural stability ofas-prepared mPEG–SH-conjugated gold nanorods were characterized using a number oftechniques including localized surface plasmon resonance (LSPR), transmission electronmicroscopy (TEM) and surface-enhanced Raman spectroscopy (SERS). In view of futureapplications as near-infrared (NIR) nanoheaters in localized photothermal therapy ofcancer, we investigated the thermal behaviour of mPEG–SH-conjugated goldnanorods above room temperature. We found a critical temperature at around40 °C at which the adsorbed polymer layer is susceptible to undergo conformational changes.Additionally, we believe that such plasmonic nanoprobes could act as SERS-active carriersof Raman tags for application in cellular imaging. In this sense we successfully tested themas effective SERS substrates at 785 nm laser line with p-aminothiophenol (pATP) as a tagmolecule.