Abstract
The morphological and optical properties of noble metal nanoparticles prepared by picosecond laser generated plasmas in water were investigated. First, the ablation efficiency was maximized searching the optimal focusing conditions. The nanoparticle size, measured by Scanning Transmission Electron Microscopy, strongly depends on the laser fluence, keeping fixed the other deposition parameters such as the target to scanner objective distance and laser repetition frequency. STEM images indicate narrow gradients of NP sizes. Hence the optimization of ablation parameters favours a fine tuning of nanoparticles. UV-Visible spectroscopy helped to determine the appropriate laser wavelength to resonantly excite the localized surface plasmon to carry out Surface Enhanced Raman Scattering (SERS) measurements. The SERS activity of Ag and Au substrates, obtained spraying the colloids synthesized in water, was tested using crystal violet as a probe molecule. The good SERS performance, observed at excitation wavelength 785 nm, is attributed to aggregation phenomena of nanoparticles sprayed on the support.
Highlights
Over the last decade, noble metal nanoparticles (NPs) attracted strong interest due to their distinctive features that include their optically active plasmonic modes which originate intense absorption and scattering bands in the visible–near infrared interval; the extinction crosssection of NPs can be as high as 106 times that of the best organic chromophores and so is the local field amplification due to plasmon resonances at the basis of Surface Enhanced Raman Scattering (SERS); the easy surface functionalization with a broad range of organic molecules [1]
SERS technique is regarded as a promising analytical tool to analyse biological samples or drugs because it provides detailed spectroscopic information, which can be translated into imaging signal and adapted to an in vivo imaging system
We investigate the morphological and optical properties of ligand-free Ag and Au NPs synthesized by picosecond laser ablation
Summary
Noble metal nanoparticles (NPs) attracted strong interest due to their distinctive features that include their optically active plasmonic modes which originate intense absorption and scattering bands in the visible–near infrared interval; the extinction crosssection of NPs can be as high as 106 times that of the best organic chromophores and so is the local field amplification due to plasmon resonances at the basis of Surface Enhanced Raman Scattering (SERS); the easy surface functionalization with a broad range of organic molecules [1]. Pulsed laser ablation in liquid (PLAL) is a physico-chemical synthesis method that produces ligand-free, high purity NPs with superior conjugation efficiency, grafting density, electroaffinity toward charged biomolecules [4,5,6]. With this synthesis method, it is difficult to achieve the large amounts of NPs required for industrial applications, in a short time, keeping unaltered the morphological properties. Fine tuning of NPs size, that is essential to prepare appropriate SERS active substrates
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