Hand-held sensors are field amenable instrumentation packages capable of performing defined tasks while operated by trained personnel. These instruments could be used in monitoring microbial populations in the field or in clinical settings for diagnostic purposes. Our hand-held NASBA amplification platform is designed to incubate reaction assays at 41oC while making fluorescence measurements while the data is being collected by a laptop computer or PDA.
Fig. 1. Schematic of the Hand-held NASBA analyzer. The hand-held analyzer is equipped with a high intensity blue light emitting diode (LED), an optical low pass filter (385nm cut off), and a low noise blue enhanced photo diode. To enhance the sensitivity, the signal was integrated over 1.0 sec, averaged over 60 readings and recorded as one fluorescence reading every minute. To maintain the 41°C necessary for the NASBA reaction, an infrared light source featuring a germanium window for infrared photon emission at 9.5mm was coupled with a digital thermometer. Readings of the fluorescence light intensity were captured using a 12-bit analog to digital converter, processed and routed to the handheld device's RS232 serial output (allows for connection with any computer). The numeric data was then processed using a Lab View 6.0 -based in house developed software to provide a real time fluorescence plotting of the NASBA amplification.
Figure 2. Handheld NASBA analyzer which has been successfully used to detect microbial targets. This system requires external filtration of samples and extraction of nucleic acids prior to initiation of NASBA amplification of target nucleic acid.
Figure 3. Fluorescence data collected with the Hand-Held analyzer (large symbols) or the Nuclisens EasyQ analyzer (Biomerieux) (thin lines) for 10,000 (purple), 1000 (blue) or 100 (yellow) poliovirus particles in NASBA amplification reactions. Green line is reagent control for amplification. Equivalent responses were obtained with the inexpensive Hand-Held analyzer to that obtained with sophisticated bench top instrumentation. Click here to see Figure 3.