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Blinking Mode Light Emitting Diode for Exciting qPCR Samples Disclosure Number: IPCOM000235493D
Publication Date: 2014-Mar-05
Document File: 8 page(s) / 246K

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I.          Background

This article relates to the excitation of samples utilized in the technique of qualitative polymerase chain reaction (qPCR) by operating a light emitting diode (LED) in a novel blinking mode.

As compared to conventional PCR entailing detection at the end of the reaction, in qPCR the amplified deoxyribonucleic acid (DNA) is detected as the reaction proceeds in real time.  An LED emitting at a specific wavelength is utilized as the excitation source to illuminate a sample containing a fluorescent dye, in conjunction with thermal cycling, and the resulting fluorescence is detected by an optical detector such as a photodiode.

Multiple samples may be analyzed utilizing a scanner containing multiple LEDs for exciting the samples and multiple photodiodes for detecting the resulting fluorescence events.  The samples to be analyzed may be placed in the respective wells of a microplate (or a microtiter plate), which is typically a plastic plate.  The wells are typically arranged in a rectangular matrix such as an 8 x 12 array, although other plate formats may be employed.  Figure 1 shows an example of a 96-well (8 x 12 array) microplate.  Figure 2 shows a microplate loaded in an apparatus containing a scanner.  In operation, the scanner traverses across the microplate from left to right (or right to left) during excitation and detection.  Figure 3 shows an interior portion of the scanner.  The scanner includes six slots for mounting up to six illumination cartridges.  In this example, each cartridge includes a linear array of eight LEDs.  Figure 3 also shows a heat sink, which is located on top of integrated circuits (ICs) utilized to drive the LEDs.

In the conventional technique, referred to in this article as the “continuous on” mode, as the scanner traverses across the microplate the LEDs are on (active) during the entire duration of the scanning procedure.  Thus, in a scanner such as shown in Figures 2 and 3, eight to forty-eight LEDs may be on at the same time.  The conventional mode of leaving the LEDs on throughout the scan may consume an undesirably large amount of current.  Moreover the conventional mode generates excess heat, which is detrimental to the LED driver ICs over time.  The LED drive current is limited by the maximum temperature rating of the LED driver ICs, which will shut down if the maximum temperature limit is exceeded.  The excess heat can also reduce the brightness of the LEDs over time, and may require some elaborate and costly form of cooling system and/or means for venting the heat.  In addition, some of the fluorescent dyes commercially available for use in qPCR require a large amount of illumination relative to other dyes, and hence require more electrical current to drive the LEDs.  The LED drivers of certain qPCR scanners operating in a “continuous on” mode may not be able to reach the level of illuminat...