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International Journal of Optics
Volume 2012 (2012), Article ID 260709, 7 pages
Research Article

Effect of Fluorescent Particle Size on the Modulation Efficiency of Ultrasound-Modulated Fluorescence

1Department of Bioengineering, The University of Texas at Arlington, Arlington, TX 76019, USA
2Joint Biomedical Engineering Program, The University of Texas at Arlington, and The University of Texas Southwestern Medical Center at Dallas, TX 75390, USA
3Department of Mechanical Engineering, The Catholic University of America, Washington, DC 20064, USA

Received 15 July 2011; Revised 15 September 2011; Accepted 15 September 2011

Academic Editor: Nanguang Chen

Copyright © 2012 Yuan Liu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


To investigate whether the size of fluorescent particles affects the modulation efficiency of ultrasound-modulated fluorescence (UMF), we measured UMF and DC (direct current) signals of the fluorescence emission from four different-sized fluorescent particles: (1) three carboxylate-modified fluorescent microspheres (FM) with diameters of 20 nm, 200 nm, and 1.0 μm and (2) streptavidin-conjugated Alexa Fluor 647 with a diameter of approximately 5 nm. The UMF and DC signals were simultaneously measured using a broadband lock-in amplifier and a narrowband amplifier, respectively. The ratio of the UMF strength to the DC signal strength is defined as the modulation efficiency. This modulation efficiency was then used to evaluate the effects of fluorophore size and concentration. Results show that the modulation efficiency was improved by approximately a factor of two when the size of the fluorescent particles is increased from 5 nm to 1 μm. In addition, the linear relationship between the UMF strength and ultrasound pressure (observed in our previous study) was maintained regardless of the fluorescent particle sizes.