Online Characterization of Single Airborne Carbon Nanotube Particles Using Optical Trapping Raman Spectroscopy

Abstract

Carbon nanotubes (CNTs) have become recognized as a potential environmental and health hazard as their applications are broadening and manufacturing costs are reducing. Fundamental information of CNTs in air is of significant importance to our understanding of their environmental fate as well as to further applications. Extensive efforts have been made over decades on characterizing CNTs; however, a majority of the studies are of bulk or CNTs dispersed on substrates. In the present study, we characterize single CNT particles in air using optical trapping Raman spectroscopy (OT-RS). Different types of CNT particles, as well as glassy carbon spheres, were optically trapped in air. Their physical properties were viewed by microscopic bright field images and scattering images; their chemical properties and structural information can be inferred from characteristic Raman bands. The system can also spatially resolve the morphology and chemical distribution of optically trapped CNT particles in air. The OT-RS technique combines single-particle morphological and chemical information and offers an online method to characterize the physicochemical properties of single CNT particles at their native states in air.

Optical trapping and laser-spectroscopy measurements of single particles in air: a review

“…The Raman spectra in (ii)-(B) was interfered by the background fluorescence of the impurities that were assigned to the clay components by the additional Raman peak at 3087 cm −1 . Well-resolved clear Raman D and G bands of carbon were also reported later in carbon nanotubes trapped in air using different opticaltrapping configurations, such as a standing-wave trap [171], an annular laser beam trap [172], and a UOT [68].…”

“…A recent work introduces a confocal-beam trap that is formed by one forward hollow beam and its reflected backward hollow beam [66]. More recently, Gong et al have demonstrated a universal optical trap (UOT) using two horizontally counter-propagating hollow beams [54,67,68], which can trap single particles of arbitrary properties, ranging from transparent to absorbing, from inorganic/organic to biological, from solids to droplets, from spherical to irregularly shaped particles, or from sub-micron to ∼50 µm in size. In 2019, the UOT design was further advanced by Pan et al using two parabolic reflectors and a hollow laser beam, and higher trapping efficiency and stronger trapping robustness was realized [69].…”

Atomic spectrometry update – a review of advances in environmental analysis

“…Advances in vibrational spectroscopic techniques offer potential for measuring airborne pollutants. An innovative optical-trapping Raman method examined 53 single suspended CNTs, an approach that eliminates measurement artifacts arising from sampling onto filters. A Raman method for the analysis of respirable crystalline silica (RCS) collected on silver filters had 54 a LOD of 0.26 μg, which was an order of magnitude better than that achievable by established XRD and FTIR approaches.…”

Chemical reactions of single optically trapped bioaerosols in a controlled environment

“…Touch-free and charge-free OT techniques have been advanced to trap diverse types of airborne particles in recent years (Gong et al 2018a). With a single particle isolated and trapped in air, Raman spectroscopy was utilized to study single droplets (Kalume et al 2017), mineral dust surrogates (Rkiouak et al 2014), pharmaceutical aerosols (Gallimore et al 2018), and carbonaceous particles (Uraoka, Maegawa, and Ishizaka 2017;Gong et al 2019). Raman spectra from an optically trapped bioaerosol, however, were obtained only very recently (Wang et al 2015;Gong et al 2018b).…”