Current trends in nanoengineering are bringing along new structures of diverse chemical compositions that need to be meticulously defined in order to ensure their correct operation. Few methods can provide the sensitivity required to carry out measurements on individual nano-objects without tedious sample pre-treatment or data analysis. In the present study, we introduce a pathway for the elemental identification of single nanoparticles (NPs) that avoids suspension in liquid media by means of optical trapping and laser-induced plasma spectroscopy. We demonstrate spectroscopic detection and identification of individual 25(±3.7) to 70(±10.5) nm in diameter Cu NPs stably trapped in air featuring masses down to 73±35 attograms. We found an increase in the absolute number of photons produced as size of the particles decreased; pointing towards a more efficient excitation of ensembles of only ca. 7×10 Cu atoms in the onset plasma.

Simultaneous detection of multiple constituents in the characterization of state-of-the-art nanomaterials is an elusive topic to a majority of the analytical techniques covering the field of nanotechnology. Optical catapulting (OC) and optical trapping (OT) have recently been combined with laser-induced breakdown spectroscopy (LIBS) to provide single-nanoparticle resolution and attogram detection power. In the present work, the multielemental capabilities of this approach are demonstrated by subjecting two different types of nanometric ferrite particles to LIBS analysis. Up to three metallic elements in attogram quantities are consistently detected within single laser events. Individual excitation efficiency for each species is quantified from particle spectra showing an exponential correlation between photon production and the energy of the upper level of the monitored atomic line. Moreover, a new sampling strategy based in skimmer-like 3D printed cones that allows for thin dry nanoparticle aerosols to be formed via optical catapulting is introduced. Enhanced sampling resulted in an increase of the sampling throughput by facilitating stable atmospheric-pressure optical trapping of individual particles and spectroscopic chemical characterization within a short timeframe.

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In the present work, the authors introduce a shape-specific methodology for evaluating the full elemental composition of single micro- and nanoparticles fabricated by laser ablation of bulk targets. For this purpose, bronze samples were directly ablated within an ablation cell, originating dry aerosols consisting of multielemental particles. The in situ generated particles were first optically trapped using air at atmospheric pressure as medium and, then, probed by laser-induced breakdown spectroscopy (LIBS). A key aspect of this technology is the circumvention of possible material losses owing to transference into the inspection instrument while providing the high absolute sensitivity of single-particle LIBS analysis. From the results, we deepen the knowledge in laser–particle interaction, emphasizing fundamental aspects such as matrix effects and polydispersity during laser ablation. The dual role of air as the atomization and excitation source during the laser–particle interaction is discussed on the basis of spectral evidences. Fractionation was one of the main hindrances as it led to particle compositions differing from that of the bulk material. To address possible preferential ablation of some species in the laser-induced plasma, two fluence regimes were used for particle production, 23 and 110 J/cm2. LIBS analysis revealed a relationship between chemical composition of the individual particles and their sizes. At 110 J/cm2, 65% of the dislodged particles were distributed in the range of 100–500 nm, leading to a higher variability of the LIBS spectra among the inspected nanoparticles. In contrast, at 23 J/cm2, around 30% of the aerosolized particles were larger than 1 μm. At this regime, the composition better resembled the bulk material. Therefore, we present a pathway to evaluate how adequate the fabrication parameters are toward yielding particles of a specific morphology while preserving compositional resemblance to the parent bulk sample.