title: DPSS yellow-green 561-nm lasers for improved fluorochrome detection by flow cytometry.
abstract: BACKGROUND
  Blue-green 488-nm laser sources are widespread in flow cytometry but suffer some drawbacks for cell analysis, including their excitation of endogenous proteins (resulting in high cellular autofluorescence) and their less-than-optimal coincidence with the excitation maxima of commonly used fluorochromes, including the phycoerythrins (PE). Longer wavelength lasers such as green helium-neons and, more recently, diode-pumped solid state (DPSS) 532-nm sources have previously been employed to overcome these difficulties and improve overall sensitivity for PE. In this study, we evaluate an even longer wavelength DPSS 561-nm for its ability to improve PE and DsRed fluorescent protein detection sensitivity.
  
  
  METHODS
  A DPSS 561-nm laser emitting at 10 mW was mounted onto a BD LSR II. Mouse thymoma cells labeled with cell surface marker antibodies conjugated to the R- and B-forms of PE were analyzed and compared with conventional 488-nm excitation using the same bandpass filters and signal travel distances. A similar analysis was carried out with cell lines expressing the red fluorescent protein DsRed, several green-yellow excited low molecular weight fluorochromes, and a rhodamine-based caspase substrate. Additionally, cells labeled with PE and co-labeled with fluorescein or simultaneously expressing green fluorescent protein (GFP) were analyzed to determine if PE excitation at 561 nm with simultaneous fluorescein/GFP detection was feasible.
  
  
  RESULTS
  The DPSS 561-nm laser gave a several-fold improvement in the fluorochrome to autofluorescence ratios between PE-labeled cells and unlabeled controls. Analysis of cells expressing the fluorescent protein DsRed with the DPSS 561-nm source gave a 6-7-fold improvement in sensitivity over 488-nm excitation, and gave excellent excitation of yellow-green excited fluorochromes and rhodamine-based physiological probes. Yellow-green laser light also caused virtually no impingement on the spatially separated fluorescein/GFP detector, a significant problem with green laser sources, and also allowed simultaneous analysis of GFP and PE with virtually no signal overlap or requirement for color compensation.
  
  
  CONCLUSIONS
  DPSS 561-nm laser excitation gave significantly improved sensitivity for both PE-labeled and DsRed expressing cells, with little contamination of a typical fluorescein/GFP detector.
authors.affiliation: Experimental Transplantation and Immunology Branch, Center for Cancer Research, NCI-NIH, Bethesda, Maryland 20892, USA. telfordw@mail.nih.gov
authors.forename: William
authors.initials: W
authors.lastname: Telford
authors.forename: Matilde
authors.initials: M
authors.lastname: Murga
authors.forename: Teresa
authors.initials: T
authors.lastname: Hawley
authors.forename: Robert
authors.initials: R
authors.lastname: Hawley
authors.forename: Beverly
authors.initials: B
authors.lastname: Packard
authors.forename: Akira
authors.initials: A
authors.lastname: Komoriya
authors.forename: Fred
authors.initials: F
authors.lastname: Haas
authors.forename: Charles
authors.initials: C
authors.lastname: Hubert
mesh_terms: D000818:Animals; D002232:Carbocyanines / Q000032:analysis; D002329:Carmine / Q000032:analysis; D045744:Cell Line, Tumor; D005434:Flow Cytometry / Q000295:instrumentation / Q000379:methods*; D019793:Fluorescein / Q000032:analysis; D005456:Fluorescent Dyes / Q000032:analysis*; D049452:Green Fluorescent Proteins / Q000032:analysis; D007834:Lasers; D008164:Luminescent Proteins / Q000032:analysis; D051379:Mice; D008863:Microspheres; D041681:NIH 3T3 Cells; D010799:Phycoerythrin / Q000032:analysis; D012235:Rhodamines / Q000032:analysis
chemical_list: D002232:Carbocyanines; D005456:Fluorescent Dyes; D008164:Luminescent Proteins; D012235:Rhodamines; C089187:cyanine dye 3; C413663:fluorescent protein 583; D010799:Phycoerythrin; D049452:Green Fluorescent Proteins; D002329:Carmine; D019793:Fluorescein