One-Step Synthesis of PEGylated Gold Nanoparticles with Tunable Surface Charge

The present work reports a rapid, simple and efficient one-step synthesis and detailed characterisation of stable aqueous colloids of gold nanoparticles (AuNPs) coated with unmodified poly(ethylene)glycol (PEG) molecules of different molecular weights and surface charges. By mixing and heating aqueous solutions of PEG with variable molecular chain and gold(III) chloride hydrate (HAuCl4) in the presence of NaOH, we have successfully produced uniform colloidal 5 nm PEG coated AuNPs of spherical shape with tunable surface charge and an average diameter of 30 nm within a few minutes. It has been found out that PEGylated AuNPs provide optical enhancement of the characteristic vibrational bands of PEG molecules attached to the gold surface when they are excited with both visible (532 nm) and NIR (785 nm) laser lines. The surface enhanced Raman scattering (SERS) signal does not depend on the length of the PEG molecular chain enveloping the AuNPs, and the stability of the colloid is not affected by the addition of concentrated salt solution (0.1 M NaCl), thus suggesting their potential use for in vitro and in vivo applications. Moreover, by gradually changing the chain length of the biopolymer, we were able to control nanoparticles’ surface charge from −28 to −2 mV, without any modification of the Raman enhancement properties and of the colloidal stability

PEGylated Gold Nanoparticles with Interesting Plasmonic Properties Synthesized Using an Original, Rapid, and Easy-to-Implement Procedure

In this letter, we report a new, one-step, rapid, and easy-to-implement method for the synthesis of PEGylated gold nanoparticles (PEG-AuNPs) having a narrow size distribution and very interesting plasmonic properties. Unmodified polyethylene glycol molecules with a molecular weight of 1000 g/mole (PEG1000) have been employed as reducing and capping agents for the synthesis of spherical gold nanoparticles having an average diameter of 35 nm, within a few minutes. The novelty of the herein proposed synthesis method consists in the fact that the synthesis takes place inside of a sealed bottle flask containing aqueous solutions of PEG1000, tetrachloroauric(III) acid (HAuCl4), and NaOH, placed in the center of a microwave oven, capable to provide a very uniform temperature environment. It turned out that, during the very short synthesis procedure (2 minutes), PEG 1000 suffers an oxidative transformation in such a manner that its terminal alcohol groups (-CH2-OH) are transformed in carboxylate ones (-COO−). The as-synthesized PEG-AuNPs possess very interesting plasmonic properties allowing the detection of different molecules by means of SER spectroscopy performed either in liquid droplets or on solid spots. As a consequence of their unique plasmonic properties, the SER spectra acquired using this new class of nanoparticles on different molecules of interest (methylene blue, rhodamine 6G, doxorubicin, and 5-fluorouracil) are highly reproducible, making them ideal candidates for further use as SERS substrates