title: Label-Free Fluctuation Spectroscopy Based on Coherent Anti-Stokes Raman Scattering from Bulk Water Molecules.
abstract: Nanoparticles (NPs) and molecules can be analyzed by inverse fluorescence correlation spectroscopy (iFCS) as they pass through an open detection volume, displacing fractions of the fluorescence-emitting solution in which they are dissolved. iFCS does not require the NPs or molecules to be labeled. However, fluorophores in μm-mm concentrations are needed for the solution signal. Here, we instead use coherent anti-Stokes Raman scattering (CARS) from plain water molecules as the signal from the solution. By this fully label-free approach, termed inverse CARS-based correlation spectroscopy (iCARS-CS), NPs that are a few tenths of nm in diameter and at pM concentrations can be analyzed, and their absolute volumes/concentrations can be determined. Likewise, lipid vesicles can be analyzed as they diffuse/flow through the detection volume by using CARS fluctuations from the surrounding water molecules. iCARS-CS could likely offer a broadly applicable, label-free characterization technique of, for example, NPs, small lipid exosomes, or microparticles in biomolecular diagnostics and screening, and can also utilize CARS signals from biologically relevant media other than water.
authors.affiliation: Dept. Exp. Biomolecular Physics/Applied Physics, Royal Institute of Technology-KTH, Albanova University Center, 10691, Stockholm, Sweden.|Institute of Physics, University of Belgrade, Pregrevica 118, 11080, Belgrade-Zemun, Serbia.
authors.forename: M D
authors.initials: MD
authors.lastname: Rabasovic
authors.affiliation: Dept. Exp. Biomolecular Physics/Applied Physics, Royal Institute of Technology-KTH, Albanova University Center, 10691, Stockholm, Sweden.|PicoQuant GmbH, RudowerChaussee 29, 12489, Berlin, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Sisamakis
authors.affiliation: Dept. Exp. Biomolecular Physics/Applied Physics, Royal Institute of Technology-KTH, Science for Life Laboratory, 17165, Solna, Sweden. stewen@kth.se.
authors.forename: S
authors.initials: S
authors.lastname: Wennmalm
authors.affiliation: Dept. Exp. Biomolecular Physics/Applied Physics, Royal Institute of Technology-KTH, Albanova University Center, 10691, Stockholm, Sweden. jwideng@kth.se.
authors.forename: J
authors.identifier: http://orcid.org/0000-0003-3200-0374
authors.initials: J
authors.lastname: Widengren
keywords: CARS (coherent anti-Stokes Raman scattering); FCS (fluorescence correlationspectroscopy); label-free; microparticles; nanoparticles
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