title: Resonance Raman spectroscopy of optically trapped functional erythrocytes.
abstract: We introduce a novel setup combining a micro-Raman spectrometer with external optical tweezers, suitable for resonance Raman studies of single functional trapped cells. The system differs from earlier setups in that two separate laser beams used for trapping and Raman excitation are combined in a double-microscope configuration. This has the advantage that the wavelength and power of the trapping and probe beam can be adjusted individually to optimize the functionality of the setup and to enable the recording of resonance Raman profiles from a single trapped cell. Trapping is achieved by tightly focusing infrared (IR) diode laser radiation (830 nm) through an inverted oil-immersion objective, and resonance Raman scattering is excited by the lines of an argon:krypton ion laser. The functionality of the system is demonstrated by measurements of trapped single functional erythrocytes using different excitation lines (488.0, 514.5, and 568.2 nm) in resonance with the heme moiety and by studying spectral evolution during illumination. We found that great care has to be taken in order to avoid photodamage caused by the visible Raman excitation, whereas the IR trapping irradiation does not seem to harm the cells or alter the hemoglobin Raman spectra. Stronger photodamage is induced by Raman excitation using 488.0- and 514.5-nm irradiation, compared with excitation with the 568.2-nm line.
authors.affiliation: Chalmers University of Technology, Department of Experimental Physics, Goteborg University, S-412 96 Goteborg, Sweden. k.ramser@fy.chalmers.se
authors.forename: Kerstin
authors.initials: K
authors.lastname: Ramser
authors.forename: Katarina
authors.initials: K
authors.lastname: Logg
authors.forename: Mattias
authors.initials: M
authors.lastname: Goksör
authors.forename: Jonas
authors.initials: J
authors.lastname: Enger
authors.forename: Mikael
authors.initials: M
authors.lastname: Käll
authors.forename: Dag
authors.initials: D
authors.lastname: Hanstorp
mesh_terms: D018914:Cells, Immobilized / Q000166:cytology / Q000378:metabolism; D004867:Equipment Design; D019544:Equipment Failure Analysis; D004912:Erythrocytes / Q000166:cytology* / Q000378:metabolism*; D006418:Heme / Q000378:metabolism; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007834:Lasers; D008846:Micromanipulation / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013059:Spectrum Analysis, Raman / Q000295:instrumentation* / Q000379:methods; D020349:Surface Plasmon Resonance / Q000295:instrumentation* / Q000379:methods
chemical_list: D006454:Hemoglobins; D006418:Heme