Synthesis and spectroscopic characterization of gold nanoparticles via plasma-liquid interaction technique

N Khatoon,N U Rehman,M Zakaullah,M Younus,H M Yasin,M Zafar Iqbal,W Ahmed

doi:10.1063/1.5004470

Abstract

Fabrication of non-functionalized gold nanoparticles is interesting owing to their potential applications in sensing and biomedicine. We report on the synthesis of surfactant-free gold nanoparticles (AuNPs) by Plasma-Liquid Interaction (PLI) technique, using micro-atmospheric pressure D.C. plasma. The effects of discharge parameters, such as discharge current, precursor concentration and gas flow rates on the structure and morphology of AuNPs have been investigated. Optical Emission Spectroscopy (OES) was employed to estimate the UV radiation intensity and OH radical density. Scanning electron microscopy (SEM) and ultraviolet-visible (UV-Vis) optical spectroscopy were employed to study the morphology and structure of AuNPs. The normalized intensities of UV radiation and OH radical density found to increase with increase in discharge current. We observed that the particle size can be tuned by controlling any of the following parameters: intensity of the UV radiation, OH radical density, and concentration of the Au precursor. Interestingly, we found that addition of 1% Ar in the feedstock gas results in formation of relatively uniform size distribution of nanoparticles. The surfactant-free AuNPs, due to their bare-surface, exhibit excellent surface-enhanced Raman scattering (SERS) properties. The SERS study of Rhodamine 6G using AuNPs as substrates, shows significant Raman enhancement and fluorescence quenching, which makes our technique a potentially powerful route to detection of trace amounts of dangerous explosives and other materials.

Highlights

Gold nanoparticles (AuNPs) have attracted a great deal of attention lately, owing to their tuneable optical and electronic properties.[1]
Micro plasmas operating at atmospheric pressure generate UV radiation, when some fraction of oxygen and/or nitrogen is mixed with helium
Fabrication of uniform sized AuNPs can be achieved by tuning the discharge parameters, such as discharge current, molarity of stock solution and gas flow rates

Summary

Introduction

Gold nanoparticles (AuNPs) have attracted a great deal of attention lately, owing to their tuneable optical and electronic properties.[1] Their wide range of applications include photo-thermal cancer treatment,[2] controlled drug delivery,[3] chemical catalysis,[4] biological sensing,[5,6,7,8,9,10,11] and electrical sensing.[12,13,14,15] The extensive applications of AuNPs follow from their interesting optical properties, which, in turn, result from the surface plasmon resonance characteristics of AuNPs.[16] Surface plasmon resonance is manifestation of the collective oscillations of valence electrons,[2] and is responsible for the strong absorption and scattering of light by AuNPs.[17] the excitation of surface plasmons give rise to very strong local fields close to the AuNPs’ surface, which can markedly enhance the Raman signal of a nearby molecule, making them an excellent candidate for SERS.[18] SERS is a highly sensitive technique for the detection of trace concentrations of molecular targets, such as

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