Spectral Identification in the Attogram Regime through Laser‐Induced Emission of Single Optically Trapped Nanoparticles in Air

• Published in: Angewandte Chemie International Edition 2017-11, Vol.56 (45), p.14178-14182
• Main Authors: Purohit, Pablo, Fortes, Francisco J., Laserna, J. Javier
• Format: Article
• Language: English
• Subjects: attogram identification; copper; Data analysis; Data processing; laser spectroscopy; Nanoengineering; Nanoparticles; Object recognition; Optical trapping; Photons; Plasma spectra; Pretreatment; single nanoparticle analysis; Spectral emissivity; Spectroscopy
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201708870

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. 7×105 Cu atoms in the onset plasma. Transcending the boundaries of sensitivity: Optical trapping in air and laser‐induced breakdown spectroscopy are combined for sample preparation‐free chemical identification of individual Cu nanoparticles of masses as low as 73±35 attogram. The enhanced excitation efficiency observed in OT‐LIBS as the particle size decreases leads to a limit of detection of 58.9±1.8 ag for Cu, which is unprecedented in optical spectroscopy.