Abstract

While adverse health effects of particulate matter exposure are a generally accepted concern, locating and tracking these nanometer sized particles is not straight forward. Measurements1-3 in polluted air such as absorption photometry and laser induced incandescence (LII) have so far been used to determine particle concentrations, alternatively labeling methods4-6 have been applied in epidemiological and toxicology research such as the technetium-99-m radionuclide marker. In this paper we present a direct, label-free optical contrast mechanism to detect carbon nanoparticles in fluids and cells7. The mechanism is non-incandescence related and demonstrated with dry and suspended carbon black particles (CB), a widely used model compound for soot8, 9, under illumination with femtosecond pulsed near-infrared light (780 nm – 950 nm, 150 fs, 80 MHz). Furthermore, a mechanism based on pump-probe detection, directly interrogating the strong absorption of carbon black particles will be introduced. Picosecond pulsed light with various wavelengths can be applied, as demonstrated here with near-infrared light (780 nm – 1064 nm, 7ps, 80 MHz).

Four different, strongly absorbing CB species with diameters ranging from 13 to 500 nm have been scrutinized, all showing similar detection possibilities. Consequently, the described WL emission and pump probe analysis allow optical detection and unequivocal localization of CB particles in fluids and in cellular environments. The experiments are performed on a typical multiphoton laser-scanning microscopy platform, a system commonly available in research laboratories.