The goal is to develop and demonstrate enabling technology for cell-based sensing. Cell clinics are microenvironments that enable the capture and characterization of cells. Each "clinic" is a micro-electro-mechanical system fabricated on a CMOS chip. Biological systems have high specificity, sensitivity, and adaptability that can be part of a highly integrated sensor. The first goals are sample preparation, cell loading, and system miniaturization using the tools of feedback control, integrated circuits, and microfluidics. Results will leveraged into two ongoing efforts in olfactory sensing and low-false-positive pathogen detection. Three aspects of the system will be demonstrated. (1) Electroosmotic flow control will remove all optically visible (>5 micron) particles from the sample. This will remove dirt, dust, and bacteria and leave behind odorants for presentation to the olfactory cell sensors. This system shall be capable of sufficiently high throughput to be used in real time. (2) Dielectrophoretic actuation for steering cells in three-dimensions will be used to position cells in the plane and to direct them into the cell clinic vials. (3)In order to develop field utility cell-based sensors, a vision system with the same dimensions as cell clinics for cell steering will be developed. The proposed technological advances will allow cell-based sensing to move toward actual implementation and use with real samples.
Cell-based sensing has the potential for selectivity, sensitivity, and speed that far exceed today's chemical and biological sensors. Problems of olfactory sensing and pathogen detection are of immediate relevance to national security. This technology has clear applications in other diverse fields such as health care, pharmaceutical development, and environmental monitoring. The integrated transduction-actuation-control approach is expected to have an impact outside of cell-based sensing to labs-on-a-chip, microfluidics, and nanotechnology by developing basic technology and techniques for sophisticated manipulation of particles at the micro-scale. The PIs are engineers in several disciplines (fluids and controls, micro-fabrication and conjugated polymers, integrated circuits and biosensors) working closely with cell biologists, molecular pathologists, and experts in bio-functionalized surfaces and quantum dots. The PIs are pioneering the development of MEMS education kits that can be used outside of a clean room.
This award funded basic research in enabling technologies for cell-based sensing, the long term goals of which are to combine integrated circuit (IC) technology with living cells to 1) create reliable, highly specific sensors and 2) to create micro-scale laboratories for studying cells, "cell clinics". We made advances in cell and particle manipulation, technology integration, and sensor packaging. Cells must be accurately manipulated at the microscale in order to place them on top of the IC circuit components (transduction elements) that will record signals from them. Using a technique is known as dielectrophoresis (DEP), we developed new methods for steering cells or particles to different locations on the chip using electric fields. DEP forces can discriminate between different types of particles or cells based on their relative degree of attraction or repulsion by the DEP force. We also developed a multiple-frequency DEP technique to push or pull on cells at different locations, and even simultaneously, to guide them with great accuracy. Finally, we developed a simple model for designing systems that can rapidly select one type of particle in a sample containing a mixture of particles. Biological studies to monitor cell responses to stimuli rely heavily on recording fluorescence light from cells, which requires special microscopes that shine excitation light on the sample and detect a much weaker emitted fluorescence. To miniaturize this technology, we developed a mm-scale integrated fluorescence sensor on a chip, and we fabricated a polymer optical filter on its surface. Biocompatibility tests showed that cells survived and proliferated on the chip. This chip was incorporated into hand-held prototypes that included a sample chamber, an excitation source, a filter to block the excitation light, and a photosensor to detect the emitted fluorescence. The sensor was successfully used to measure cell metabolic activity. As another means for weak light detection, we also fabricated a new type of single photon avalanche diode (SPAD) in standard CMOS processes, which are used to fabricate chips such as CPUs and cell phone components. New designs were experimentally characterized and a high density SPAD array was fabricated, which is important because it produces higher resolution images. These types of CMOS detectors can replace the large, expensive optical detectors that are currently used. Also as part of this research, we built a handheld prototype to manipulate cells using microfluidics, a USB web cam, a lens, and a new chip-based vision system with innovative image capture and processing functions. Imaging of cells is challenging because cells are transparent, so additional image processing is necessary to locate them. A laptop performed image processing and sent back control signals to the microfluidic device. We were able to steer as many as five particles simultaneously in complex trajectories. An operator could use a mouse to choose a cell and drag it to a desired position. Successful operation of cell-based sensors requires robust packaging, which is often overlooked in the design of microsystems. Packages for cell-based sensors must allow electrical inputs/outputs while insulating these connections from the aqueous cell culture medium. We have developed packaging methods that embed the 3 mm sized IC chips into a 5 cm epoxy disc to allow handling with tweezers during fabrication of structure on top of the chip, such as electrodes, filters, and microfluidics. This packaging was successful, with a chip that was designed for detecting and amplifying electrical signals remaining functional upon immersion in cell medium at 37 degC for months. The package also survived exposure to solvents and cleaning solutions. From this packaged chip, we recorded electrical signals from human heart cells, demonstrating its functionality.
