Use of the short-wave near infrared (NIR) region for fluorescence spectroscopy is shown to afford enhanced freedom, relative to the visible spectrum, from background signals and noise resulting from scattering and endogenous fluorescence from the sample matrix itself. The detection of 0.1 attomole (10^-13 mole liter^-1) of two cyanine dyes in methanol solution is demonstrated using diode laser excitation at 780 nm and CCD spectrometric detection. The fluorophores exhibit excellent photostability in this solvent even under prolonged laser illumination. Limitation of sensitivity in this system is imposed by shot noise associated with the solvent Raman signals. When the same dyes are placed in aqueous solutions containing bovine serum albumin (BSA), endogenous fluorescence from the BSA and photobleaching or photolysis of the cyanine raise the practical detection limits to 10^-9 moles liter^-1. Despite these difficulties, the NIR region affords signal to background ratios which are superior to those observed in similar experiments performed in the visible region.

Date Published: 24 June 1993
PDF: 8 pages
Proc. SPIE 1895, Ultrasensitive Laboratory Diagnostics, (24 June 1993); doi: 10.1117/12.146723

Published in SPIE Proceedings Vol. 1895:
Ultrasensitive Laboratory Diagnostics
Gerald E. Cohn, Editor(s)