Microwave, Ultrasound-Assisted, and Room Temperature One-Pot Synthesis of Silver and Gold Colloids Using Beta-Cyclodextrin as a Reducing and Capping Agent for SERS Applications

Abstract

Cyclodextrins (CDs) are macrocycles that are well suited for forming inclusion complexes for surface-enhanced Raman scattering (SERS) detection of analytes due to their low Raman activity, which minimizes background SERS signals and enhances the detection of target molecules without interference. In this paper, we systematically investigated the synthesis of both silver (Ag) and gold (Au) nanoparticles (NPs) using CDs as reducing and capping agents in a basic environment using microwave (MW), ultrasound (US), and room temperature (RT) synthesis. We found that replacing NaOH with K2CO3 as an alkaline environment almost doubles the size (from <10 nm to around 20 nm) of AgNPs in the MW-assisted synthesis. Synthesis using the US produces less stable particles due to the sample evolution after US irradiation. Ag (20 nm) and Au (11 nm) were successfully obtained at room temperature in the presence of CDs and K2CO3. All synthesized particles present SERS activity. CD capping allowed us to detect hydrophobic molecules like naphthalene and melamine. In the case of methylene blue, the CD capping prevents the changes induced in the SERS by a basic pH. We also demonstrate that the newly synthesized NPs can discriminate by SERS the propranolol enantiomers. Moreover, propranolol inclusion in CDs leads to a dramatic change in its SERS spectrum.