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Proceedings Paper

Low-cost phase-modulation fluorometer for measuring nanosecond lifetimes using a lock-in amplifier
Author(s): Peter D. Harms; Govind Rao
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Paper Abstract

A Stanford Research Systems SR844 lock-in amplifier was used to build a sub $10,000 phase-modulation fluorometer capable of measuring nanosecond fluorescence lifetimes. The lock-in directly provided both the DC bias and the AC signal used to modulate the intensity of a blue LED excitation source. A photomultiplier tube measured the emission, and the resulting signal was sent back through a DC block to the lock-in with no external signal processing or heterodyning required. A simple computer program was developed to automate the measuring process and correct for the most common sources of error, namely coherent pickup and stray ambient light. Several standard fluorophores were measured, and the results compare favorably with those from a research grade cross-correlation phase fluorometer up to frequencies of 100 MHz. This system can operate in several configurations, each with benefits and limitations. The system is particularly well suited for fluorescence lifetime based sensing applications, demonstrated by measuring dissolved carbon dioxide online in a bacterial fermentation.

Paper Details

Date Published: 3 May 1999
PDF: 8 pages
Proc. SPIE 3602, Advances in Fluorescence Sensing Technology IV, (3 May 1999); doi: 10.1117/12.347543
Show Author Affiliations
Peter D. Harms, Univ. of Maryland/Baltimore County (United States)
Govind Rao, Univ. of Maryland/Baltimore (United States)


Published in SPIE Proceedings Vol. 3602:
Advances in Fluorescence Sensing Technology IV
Joseph R. Lakowicz; Steven A. Soper; Richard B. Thompson, Editor(s)

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