Imaging Cardiac Dynamics Using Low-cost Ultra-high-power Light Emitting Diodes and Voltage-sensitive Dyes

We describe the characteristics of low-cost ultra-high-power light emitting diodes (LEDs) for use in optical imaging experiments. We use the LEDs in experiments with bullfrog cardiac tissue and find that the signal-to-noise ratio is comparable to other commonly used illumination sources. Contact Information: Duke University, Department of Physics, Box 90305, Durham, NC, 27708 Tel: (919) 660-2512 Fax: (919) 660-2525 email: [email protected] Introduction The development of voltage-sensitive dyes has revolutionized the study of electrical activity in spatially extended biological systems such as the heart [1]. In an optical mapping study, the electrical activity at different spatial locations can be visualized directly using a fluorescent dye in combination with an illumination source to excite the dye and a detector array to record fluoresence. A typical excitation source for use with di-4-ANEPPS (specifications for other dyes are available from Molecular Probes, www.probes.com) needs to provide an intensity of ∼10-100 mW/cm at the tissue surface, a spectral bandwidth less than ∼35 nm, and the variation in the power of the source over time must be much less than the anticipated change in fluorescent power when the cell depolarizes. Some groups have recently investigated the use of light emitting diodes (LEDs) as illumination sources [2,3]. The narrow bandwidth, high efficiency, and the potential for low-noise operation of LEDs satisfy the illumination source requirements for successful optical imaging. However, these early experiments used low-power (0.25-10 mW) LEDs so they could only image small areas of cardiac tissue. In this paper, we report on the use of recently available ultra-high-power LEDs (Lumileds, model Luxeon Star/O and Star/V) as an illumination source in cardiac optical mapping systems. Our study is needed because the LEDs operate at high power where thermal effects can be important and noise in the higher current supplies can be difficult to control. Specifically, it is not obvious that they will operate with sufficiently low noise to be useful in biological imaging experiments. The ultra-high-power LEDs are available in two different models: Star/0, lower power