1. The Field of the Invention
The present invention is directed to a methods and apparatus for exciting fluorescent material and detecting fluorescence in a sample.
2. The Relevant Technology
Various optical detection systems have been developed for use in qualitative and quantitative measurements. One common system involves the use of fluorescent compounds as labels that are associated with targets, such as the reaction products of polymerase chain reaction (PCR) amplification.
Numerous chemical compounds have been identified that exhibit fluorescence when illuminated with light at a suitable excitation frequency. For example, fluorescein is excited by light at a wavelength of about 490 nm, and emits light at a wavelength of about 520 nm. The gap between the excitation and emission wavelengths allows observation and measurement of fluorescence either qualitatively or quantitatively by reference to the emission wavelength.
One conventional fluorescent reading system passes a light through a bandpass filter, which transmits light at the excitation wavelength, through a sample, through a second bandpass filter that transmits light at the emission wavelength, and to a detector. In this classical system, multiple samples are shuttled into place for sequential readings, such as through use of a carousel. In order to speed up the process, alternative stepping systems have been developed (for example, see U.S. Pat. No. 6,015,674) or multiple light emitting diodes have been provided together with a network of optical fibers to perform several tests simultaneously (see, for example, U.S. Pat. No. 6,597,450). Although these types of systems are useful, they produce opto-mechanical noise which reduces sensitivity of the system, and they require a significant amount of time to measure all of the samples due to the time it takes to move the optical system head to the samples, or the samples to the head. Fiber optic systems further suffer from the attenuation of a signal associated with the use of fiber optics, which also reduces sensitivity.