Handheld Nucleic Acid Amplification Device

A spin off of some of the technology from the Autonomous Genome Sensor(AMG) has led to the development of mobile handheld technology, which uses the heated detection module developed for the AMG, to perform NASBA reactions.

This technology requires sample preparation to be performed by the operator - but represents a field-able instrument to allow point of use genetic analysis.

The instrument core incorporates a simple LED light source, and an integrating photodetector for fluorometry. A MEMS-based infrared radiant heater, and an infrared thermometer module make up the thermal regulation system. All of these components are controlled with custom software communicated through Motorolla’s HC-16 microcontroller. All of the components are commercially available as off-the-shelf items. The LED used for fluorescence excitation in this fluorometer is a high-brightness, 5mm T1, blue LED. Input voltage for the LED can vary, but 2.5 volts is used in these data sets and had a current draw of 31 mA. Fluorescence emission is detected using a blue-enhanced integrating photodiode. At 5 volts power, the photodiode has a response time of 45ns with dark currents of 6.5nA typ. and 26nA max. The active detection area is .200in diameter. Both the LED and the photodiode are optically isolated at 90 o with 9 x 9mm bandpass filters 485nm and 530nm respectively. These wavelengths accommodate the commonly used FAM fluorophores. The 485nm excitation filter has a bandwidth of 22nm and the 530nm emission filter has a bandwidth of 30nm.

In the thermal system, heat is supplied by an Ion Optics, Inc., TO-5 infrared heater with a Germanium Filter. The Germanium filter only transmits the heater-emitted light within a bandwidth of 7 – 12 um to pass into the reaction chamber so as not to interfere with the fluorescence optics. The heater itself is rated for temperatures up to 850 oC, but the maximum recommended operating temperature for this system is 95 oC. Maximum power consumption of the heating element at 850 oC is 2.0 watts, with a maximum current of .77 amps. At an operating temperature of 41 oC, current draws a max current 155 mA when ramping temperature and 75 mA when maintaining temperature. This value does fluctuate downward to lower current draws between PWMs. Output of heat is controlled by pulse-width modulation at a maximum of 2.6 volts. To monitor the temperature of the reaction / optical block, a digital SPI outputting infrared thermometer module by Melexis Microelectronic Integrated Systems is used. This detector has a response time of 500ms and has a temperature range of –20 0C to 120 0C when operated at 5 volts and draws approximately 6 mA. In a typical opto-thermal operation, such as NASBA, total system current draw is less than 300 mA.