Devices for manipulating fluids on the microscale have been developed to store, hold, and manipulate small amounts of fluids, and have been applied to the detection of analytes in sample fluids. Manipulating fluids and performing capillary electrophoresis in microfluidic devices promises advantages of small size, high throughput, low sample volumes, and low cost.
The performance offered by present microfluidic devices is limited by the interfaces between the microfluidic device and the macroscopic world. Connecting detection units including light sources and other detectors, power sources necessary for any actuators or detectors, and macroscopic amounts of reagent fluid and/or sample fluid to present microfluidic devices is cumbersome, often requiring a lengthy process of trial and error, or limiting the use of the microfluidic device to one reagent source, one detector, or a single configuration.
Although microfluidic devices themselves can have a small form factor, once they are connected to the systems required for their operation — voltage sources, macroscopic fluid sources, and detectors — the entire system can become too large to be portable.
A compact, handheld detection system was developed that places the capability of a fully functional chemistry laboratory at the fingertips of a trained field operator (Figure 1). Sandia's chemical analysis system can rapidly detect and analyze toxic agents such as bacteria, viruses, and protozoa.
The μChemLab™ Bio Detector was designed, demonstrated, and tested over several years. The technology was initially developed for homeland security, defense applications, warfighters, and first responders. A variety of applications and near-term commercialization opportunities now exist in markets such as air and water quality, medical diagnostics, biotechnology, and industrial process control.
The μChemLab determines the presence of a target analyte, and enables fast microfluidic separations of biological samples with high sensitivity. The device miniaturizes bench-scale analyses using fabricated microchannels in a handheld, low-power device (Figure 2). Many different separations can be run simultaneously, and identification of the compound of interest is determined from unique retention-time signatures.
Designed for the rapid detection of proteins, the μChemLab has been used to identify biotoxins such as ricin, staphylococcal enterotoxin B, and botulinum toxin; its capability has been extended in combination with innovative, automated sample preparation technology to enable the identification of viruses and bacteria.
The analyses take place in 10-cm-long sealed microchannels that are chemically etched in 2-cm2 glass chips. The unique chip design allows protein samples tagged with a fluorescent dye to be pressure-injected directly onto the chip with no sample carryover.
Electric fields are used to manipulate nanoliter volumes of fluids in the microchannels. Components of the sample are sorted for identification as they move through the channel under the influence of an electric field. The length of time a compound is retained reveals its identity. Retention times are influenced by conditions in the channel. Separations are complete in less than 10 minutes. A miniature violet laser diode excites dye-labeled proteins, inducing fluorescence. A photomultiplier tube detects the fluorescence emission with nanomolar sensitivity. On-board data processing can identify target proteins in real time.