Lab-on-a-chip devices are taking shape in miniature microbioanalytical systems to detect hazardous microbes and toxic chemicals at the National Aeronautics and Space Administration's (NASA's) jet propulsion laboratory in Pasadena, Calif. With these systems, analysts could perform tests for microbial species and hazardous chemicals quickly and inexpensively. Each microbioanalytical system would include optoelectronic sensors and sensor-output-processing circuitry that would detect optical change, fluorescence, delayed fluorescence, or phosphorescence signatures from multiple redundant sites-simultaneously. The sensors would look at sites that have interacted with the test biomolecules. Applications include use in hazardous-material laboratories, biological-research laboratories, military operations, and chemical-processing plants.

Included with each system would be an integrated circuit or perhaps several integrated circuits packaged together. Other features would include a source of optical excitation (ambient light, superluminescent, or laser diode); a photodetector-array circuit of the active-pixel-sensor (APS) type-compatible with complementary metal-oxide semiconductor circuitry; and on-chip signal- and data-processing circuits to quickly identify toxic substances and biomolecules, such as antigens, associated with hazardous chemicals, bacteria, and viruses.

Analysts coat each group of pixels in the APS array with an antigen-specific optobiochemical reagent or other substance-changing its optical characteristics. Examples are absorption, fluorescence, and luminescence in response to a biomolecule or hazardous chemical analysts want to identify. In addition, the array could include strips bonded directly to the APS surface to produce APS outputs for on-chip or off-chip calibration.

Using this type of microbioanalytical system-unlike in conventional bioanalytical laboratory practice-analysts detecting biohazards would not be limited by their own vision or even by conventional microscopes. They wouldn't need to repeat tedious procedures under sterile laboratory conditions. Instead, analysts could simultaneously identify quite a few different microbial species or chemical agents within a few seconds-as large as a million in the case of a 1,024-by-1,024-pixel APS array.

In a typical analytical procedure, analysts would dissolve a sample onto the surface of the APS array. Sensing the ambient- or pulsed-light source is next, and gating the APS array (to respond only to the longer-lived fluorescence that would follow the source pulses-and not the light source). Analysts then read the intensity change or delayed fluorescence signal from each pixel. These analyses could include correlation with calibration signals or signals from other pixels. If a pixel's response includes optical or fluorescence signatures from multiple bioanalytical or fluorescent probes associated with different target molecules of interest, analysts could distinguish among them by their position or fluorescence lifetimes.

Source: Robert Stirbl, Philip Moynihan, Gregory Bearman, and Arthur Lane of Caltech for NASA's jet propulsion laboratory (nasatech.com/tsp)