Photophoretic trapping-Raman spectroscopy for single pollens and fungal spores trapped in air

Abstract

a b s t r a c tPhotophoretic trapping-Raman spectroscopy (PTRS) is a new technique for measuring Raman spectra of particles that are held in air using photophoretic forces. It was initially demonstrated with Raman spectra of strongly-absorbing carbon nanoparticles (Pan et al.[44] (Opt Express 2012)). In the present paper we report the first demonstration of the use of PTRS to measure Raman spectra of absorbing and weakly-absorbing bioaerosol particles (pollens and spores). Raman spectra of three pollens and one smut spore in a size range of 6.2-41.8 mm illuminated at 488 nm are shown. Quality spectra were obtained in the Raman shift range of 1600-3400 cm À 1 in this exploratory study. Distinguishable Raman scattering signals with one or a few clear Raman peaks for all four aerosol particles were observed within the wavenumber region 2940-3030 cm À 1 . Peaks in this region are consistent with previous reports of Raman peaks in the 1600-3400 cm À 1 range for pollens and spores excited at 514 nm measured by a conventional Raman spectrometer. Noise in the spectra, the fluorescence background, and the weak Raman signals in most of the 1600-3400 cm À 1 region make some of the spectral features barely discernable or not discernable for these bioaerosols except the strong signal within 2940-3030 cm À 1 . Up to five bands are identified in the three pollens and only two bands appear in the fungal spore, but this may be because the fungal spore is so much smaller than any of the pollens. The fungal spore signal relative to the air-nitrogen Raman band is approximately 10 times smaller than that ratio for the pollens. The five bands are tentatively assigned to the CH 2 symmetric stretch at 2948 cm À 1 , CH 2 Fermi resonance stretch at 2970 cm À 1 , CH 3 symmetric stretch at 2990 cm À 1 , CH 3 out-of-plane end asymmetric stretch at 3010 cm À 1 , and unsaturated ¼ CH stretch at 3028 cm À 1 . The two dominant bands of the up-to-five Raman bands in the 2940-3030 cm À 1 region have a consistent band spacing of 25 cm À 1 in all four aerosols. Finally we discuss improvements to the PTRS that should provide a system which can trap a higher fraction of particle types and obtain Raman spectra over a larger range (e.g., 200-3600 cm À 1 ) than those achieved here.Published by Elsevier Ltd.

Removal of Cu(II) and tetracycline using an aromatic rings-functionalized chitosan-based flocculant: Enhanced interaction between the flocculant and the antibiotic

“…In curve (i), NAH and CAOAC groups were found at 1602 cm À1 and 1082 cm À1 , respectively [29], which were the characteristic peaks of chitosan. Peaks around 1646 and 1318 cm À1 [30] in curve (ii) were correspond to the stretching vibration of C@N and CAN in aromatic rings of BDAT, which shifted to 1624 and 1393 cm À1 in curve (iii) of the final product. The detected characteristic peaks of BDAT in the synthesized flocculant confirmed directly that the designed targeted functional groups had been introduced onto chitosan backbones.…”

Real-time sensing of bioaerosols: Review and current perspectives

“…The number of particles that can be measured in a given time period using existing RT instruments applying Raman spectroscopy is far smaller than can be measured using fluorescence or mass spectrometry, because the intensity of RS of typical atmospheric particles is weak and so long integration times are necessary (e.g., seconds to minutes for a 1-mm particle). Thus, particles must either be trapped in air electrodynamically (Vehring and Schweiger 1998) or optically (Thurn and Kiefer 1984;Wang et al 2015), or collected onto a substrate and then analyzed (R€ osch et al 2006). Techniques such as surface-enhanced Raman spectroscopy (SERS) that increase Raman signal by orders of magnitude (for molecules within nanometers of SERSactive substrates or nanoparticles) have potential to enable real-time measurement (Craig, Bondy, and Ault 2015;Sivaprakasam, Hart, and Eversole 2017).…”

Conical refraction: fundamentals and applications

“…[172,174]. The photophoretic force has been used as a speckle trap [169], to trap biological samples [175,176], combined with engineered vortex beams as a tractor beam [86,143] and demonstrated to also depend on the polarization of the illuminating source [143,177]. …”