Nanoparticle detection in aqueous solutions using Raman and Laser Induced Breakdown Spectroscopy

We show the chemical identification and quantification of the concentration and size of nanoparticle (NP) dispersions in aqueous solutions by using a combination of Raman Spectroscopy and Laser Induced Breakdown Spectroscopy (LIBS). The two spectroscopic techniques are applied to demonstrate the NP detection for off-line configuration. The implementation of the techniques for further in-line and on-line NP monitoring will allow for the optimization of the synthesis process, reduction of the failure rate and improvement of NP quality. We demonstrate the implementation of the Raman-LIBS technique on two metaloxide nanoparticles: titanium dioxide (TiO2) and a rare earth sesquioxide nanoparticle, holmium oxide (Ho2O3). The determination of the elemental (LIBS) and molecular (Raman) compositions, as well as the determination of the particle size down to 5 nm is demonstrated. The LIBS spectra of NP dispersions reveal the absorption of the continuum emission by the electrons present in the plasma via the inverse Bremsstrahlung effect. This effect manifests as the appearance of dips in the LIBS spectrum, rather than the conventional emission peaks. An interpretation of these spectra that incorporates this absorption effect is presented, enabling new opportunities for understanding the LIBS spectra of liquids. © 2013 Elsevier B.V. All rights reserved.