Microfabricated Surfaces and Particles for Advanced Immunoassay Platforms and High-Efficiency Electrowetting Heat Transfer System
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The ability to screen for diseases that exhibit similar symptoms with very high sensitivity would allow clinicians to more rapidly administer the necessary treatment and improve the quality of life for patients. To address this need, we have developed a prototype point-of-care diagnostic platform, similar in design and ease-of-use to a compact disk player, that integrates microfabricated labels in order to be used for the multiplexed detection of a subset of diseases. For this device, a sample is loaded into a reservoir that is connected to a prefilled, dead-end channel where antibodies to a pathogen panel have been spotted on the channel base. The reservoir is one of many that lies at the perimeter of a disc similar in size to a standard DVD, allowing for the simultaneous screening of many samples. Micron-scale, gold-coated polymer cubes, also functionalized with antibodies, are dispensed into the reservoir, which have been designed to drift through the sample at a pre-defined velocity. During the time they move through the sample, they can capture any pathogen that might be present. Once the cubes are allowed to settle at the base of the reservoir, the disk is rotated, and the centrifugal force acting on the cubes moves them into the channel and across the antibody-coated surface. If the pathogen is present on the surface of the cube, it can be captured at the channel base. Dark-field illumination makes the cubes appear extremely bright, with a unique pattern, and can be counted using a low-cost CMOS sensor attached to a simple microscope lens. The number of cubes present on each antibody-coated spot at the surface at the channel base is correlated to the concentration of antigen in the sample. We have obtained preliminary results in the detection of Human Chorionic Gonadotropin (hCG) on passivated acrylic surface, activated through the exposure to a helium atom beam, which is subsequently functionalized with anti-hCG antibodies. The positive sample microcubes that have been functionalized with anti-hCG and incubated with hCG, showed selective binding on the anti-hCG stripe. On the other hand, the negative sample microcubes that have been functionalized with anti-hCG but have not been exposed to hCG, did not experience capture on the anti-hCG line, which translates to low non-specific binding. These preliminary results validate the working principles of our prototype diagnostic platform. In a separate system, we developed the technology for fabricating retroreflecting substrates at low cost as part of a microfluidic immunoassay platform for the detection of Rickettsia conorii. We simplified the process of micro-retroreflectors fabrication, developing an experimental procedure based on commercial photolithographic techniques. Our collaborators found that the limit of detection of this platform is 4000 R. conorii bacteria per mL in buffer, which is considered as a clinically suitable value for several other pathogenic bacteria detection. Finally, we have developed an electrowetting-modulated nucleate boiling system to enhance heat transfer. We designed and fabricated electrowetting devices on silicon dioxide wafers that contain hydrophilic, continuous hydrophobic or patterned hydrophobic surfaces. Through this collaboration, we found that EW can delay the onset of film boiling and thus, can improve Critical Heat Flux (CHF) of a heat transfer system. Also, the oscillations induced in bubbles when applying an electrowetting signal seemed to promote the departure of the bubbles, and in consequence, enhance heat transfer, as well.