Research On The Polymer Microfluidic Chip Technology For Flow Cytometry In Spaceflight

Flow cytometry can be used to monitor the immune function of astronauts by performing a white blood cell count while in orbit,which is very important for monitoring the health of astronauts during spaceflight missions.However,traditional flow cytometers are too bulky and too complicated to be used on a spacecraft.Instruments for spaceflight have to be portable,reliable,microgravity-compatible,easy to operate and maintain.To address the special requirements of spaceflight,the microfluidic technologies of three key procedures in flow cytometry are studied,namely,whole blood sample preparation,cell focusing,and laser-induced fluorescence detection.The challenges associated with the application of flow cytometry in spaceflight are resolved,resulting in a spaceflight-compatible automatic miniature flow cytometer prototype.The main contents are as follows.An automatic microgravity-compatible sample preparation microfluidic chip is proposed to realize the preparation of whole blood samples in spaceflight.The slug flow pattern in the micro channel prevents the liquid from mixing with air.The sampling channel is integrated with automatic delay valves to simplify sample injection in microgravity.A driving accuracy of 0.5 ?L and a mixing efficiency of 95% are achieved in the multi-channel mixing system.Lymphocyte subset tests show this method can prepare whole blood samples equally as well as the traditional manual method.A plug-and-play sheathless focusing microfluidic chip,based on the Poisson process,is proposed along with its fabrication process.The micro channel of 50 ?m×50 ?m focuses cells with a coincidence error of about 0.54%.No sheath fluid is required,which simplifies the fluidic system and improves reliability.The fabrication process,based on hot embossing,ensures the precise profile and position of the focusing channel.These features make the focusing chip very easy to operate for astronauts.In addition,the high surface finish of all six surfaces makes it possible to detect side scatter on the chip.A high-fault-tolerant laser-induced fluorescence detection system is designed for the plugand-play sheathless focusing chip.Side scatter and four colors of fluorescence excited by a 488 nm laser source are measured simultaneously.The distribution of laser intensity with different laser beam parameters and the collection efficiency of fluorescence with different lenses are studied and optimized to achieve even excitation and the detection of fluorescence across the whole detection zone.The difference of laser intensity and collection efficiency across the detection zone is lower than 2%.Based on the study of the three above-mentioned techniques,a spaceflight-compatible automatic miniature flow cytometer prototype is built and evaluated.The fluorescence resolution and sensitivity of the fluorescein isothiocyanate(FITC)channel are 4.0% and 916 MESF,respectively while the sensitivity of side scatter is better than 1 ?m and the maximum cell concentration is higher than 2000/?L with a coincidence error less than 1%.Use of the disposable chip for counting lymphocyte subsets is successfully demonstrated in a foursubject 180-day controlled ecological life support system experiment.Microgravity compatibility is successfully verified in parabolic flight.Until now,318 microfluidic chips have been used by the Astronauts Center of China for training to monitor immune function.