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Science for Developing Economies
An important problem is to use first-world science to benefit the welfare of people in developing economies. The Whitesides group is using its competencies in materials science, engineering and biology to attack this type of global problem, with a focus on health diagnostics and local energy production. (Other problems include nutrition, sanitation, information technology, education, ecosystem management, and wealth creation.)
Our approach - what we call "simple solutions" - relies on a re-thinking to basic issues of design assumptions, from the ground up, to fit the technology to the socioeconomic constraints present in the developing world. Simple solutions are inexpensive to produce, easy to maintain or replace, simple to use, adaptable to local conditions, scalable for mass consumptions, and easily stored and transported. To the greatest degree possible, they are independent of first-world infrastructure (such as electricity and trained personnel).
Health Diagnostics
A top priority for improving health in developing countries is technology for simple, affordable diagnosis of infectious diseases. We have developed new approaches that provide low-cost, simple, and reliable solutions for (1) signal amplification and detection in microfluidic devices, (2) reagent handling in microfluidics, (3) fabrication of microfluidic systems, and (4) valving. The work demonstrates the potential of simplifying high-performing devices (such as lab-on-a-chip devices) for use as diagnostic tools in developing economies.
POCKET Immunoassay: The POCKET immunoassay "POCKET" is short for portable and cost-effective) is an integrated approach to a miniaturized immunoassay. It is inexpensive and operable with minimal equipment and technical skills, and shows an analytical performance approaching that of enzyme-linked immunosorbent assays (ELISA).
The immunoassay (Figure 1) is performed in an inexpensive, miniaturized platform (made by soft lithography), in which the amplification chemistry is compatible with microfluidics and simple optics. The immunoassay functions with a portable and reusable detector was built from components costing less than $45 US and consists of an InGaAlP red semiconductor laser diode (654 nm) as the light source and an optical integrated circuit as the photodetector (Figure 2). The detector is powered using a single 9V battery and can be used outdoors in daylight without changes in background signal. Instead of enzyme-conjugated secondary antibodies in conventional ELISA, the system uses antibodies conjugated to 10 nm gold colloids; amplification of detection events is accomplished by electroless deposition of a silver film, whose opacity is a function of the concentration of the analyte (Figure 3). In sensitivity, limit of detection, and reproducibility, the POCKET immunoassay performs comparably to conventional ELISA, and within a factor of 10 of the most sensitive ELISA format - chemiluminescence (Figure 4). The POCKET immunoassay can also reliably distinguish the sera of HIV-1-infected patients from those of noninfected patients (Figure 5).
Reagent-Loaded Cartridges: Current techniques for automating fluid delivery in microfluidic devices, which include valves and electroosmosis, require sophisticated microfabrication of the chip, bulky instrumentation, or both. Reagent-loaded cartridges are a simple and reliable technique for storing and delivering a sequence of reagents to a microfluidic device (Figure 6). The technique is low-cost, requires minimal user intervention, and can be performed in resource-poor settings (e.g., outside of a laboratory) in the absence of electricity and computer-controlled equipment. In this method, cartridges made of commercially available tubing are filled by sequentially injecting plugs of reagents separated by air spacers (Figure 7). The air spacers prevent the reagents from mixing with each other during cartridge preparation, storage, and usage. As an example, we used this technology to complete an immunoassay with low-nanomolar sensitivity in a microchannel in 2 min; we demonstrated the diagnosis of HIV in 13 min.
Novel Energy Concepts
Coal is a hugely abundant fuel source. We are exploring approaches to fuel cells in which powdered coal is the fuel. We have developed a prototype coal fuel cell using a solution of sub-bituminous coal (SBC) partially oxidized by Fe-III (Figure 8). The rate of oxidation depended on the concentration of the iron and the surface area of the coal. At 100 deg C, the maximum current density in the cell was 5 A/L and the power density was 0.6 W/L. The cell operated without loss of performance for 1000 hours.
Select Publications
1. Sia, S.K. et al. "An Integrated Approach to Portable and Low-Cost Immunoassay for Resource-Poor Settings." Angew. Chem. Int. Ed. 43, 498-502 (2004).
2. Linder, V., Sia, S.K. and Whitesides, G.M. "Reagent-Loaded Cartridges for Valveless and Automated Fluid Delivery in Microfluidic Devices." Anal. Chem. 77, 64-71 (2005).
3. Weibel, D. B. et al "Modeling the Anodic Half-Cell of a Low-Temperature Coal Fuel Cell" Angew. Chem. 44 (35), 2005, 5682-5686.
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