A Compact Microflow Fiber Optic Cytometer for Remote Site and Space Bioanalysis Applications

Flow cytometers are widely used for clinical applications or molecular biology studies on Earth (1). However, classical restrictions of conventional bulkoptics based flow cytometry in medical testing, medical monitoring, and life sciences studies, have been an inherent barrier for translation of the flow cytometry technique to harsh and/or remote site testing environments, such as space. Packaging, miniaturization, operational needs for minimally trained personnel, in situ analysis, are critical requirements that have therefore propelled significant research activities towards development of portable and leading edge technologies intended for remote environment cellular and molecular analysis/diagnostics. In the context of manned space exploration for example, there is a driving need to develop, launch, and install space compatible bioanalysis tools in infrastructures such as the International Space Station (ISS). Compact, robust, light payload, easily operable flow cytometers are highly desirable for the purpose of measuring and monitoring immunological and other biomedical makers (i.e. CD4 T cells, human Th1/Th2 cytokines, hormones or microbial molecules). One can envision the benefits of a standalone, compact, mostly autonomous instrument in space or other remote terrestrial locations for continual testing and access to physiological and granular information on site. In order to translate such a device from benchto-human side (or astronauts’ side), the cytometer must function and perform in a microgravity environment while maintaining its safety to the astronaut operator and within the space craft. To this aim, we have designed and developed a new type of fiber optic based cytometer (Microflow), both compact and portable for on site medical bioanalysis in space intended for the ISS. The technology is based on a custom rectangular fiber optic through which a hole is transversally board through the fiber core, via laser micromachining, and a capillary attached to for sample introduction. The advantage of this fiber optic flow cell platform (FOFC) is that the sample interrogation (fluorescence and scattering) is entirely achieved within the core of a fiber optic. This feature not only enables miniaturization of the fluidics subsystem but renders it a sheathless configuration in which hydrodynamic focusing is not longer needed and thereby minimizing optofluidics management and on-site manipulations. Furthermore, the system is optically “self-aligned” in fabrication and manufacturing of this FOFC, thereby eliminating the need for optical alignment, as is the burden of conventional bulk optics-based flow cytometry, without compromising the instrument’s performance (2). Its robustness is not only attractive for terrestrially deployed applications, but is a particularly critical feature for withstanding, with reliability, unusual vibration and shock conditions associated with launching on a spacecraft. To materialize a compact, portable and space compatible Microflow system, several packaging and miniaturization, and performance optimization goals in the optofluidics, detection optics and optronics have been achieved in its development. The result of this undertaking is a stand alone cytometric system that measures 13′′8′′7′′ (L,W,D), in dimension, is battery powered, based on a simple turnkey style, is plug and play operation to facilitate ease of operation. Such features also reduce the need for operator skill and limits his/her time and interfacing with the system to conduct a full cytometric experiment. Using samples prepared and packaged in a singular cartridge, the sole interface with a human operator is reduced to the sample injection process. An injection module relying on a single cartridge containing multiple pre-integrated samples uses a simple rotary mechanism to initiate a 2-step process; thereafter the system is fully automated in sample release, processing, control electronics, data acquisition, data uploading, and finally, yielding standard .FCS files for remote analysis. As space-applications are particularly sensitive to mass and volume constraints, significant efforts focused on reducing the payload of a 3-channel fiber coupled detection subsystem, and removal of the PC while retaining a 5-6 log scale dynamic range. A 5-fold mass reduction was achieved solely with the detection subsystem circuitry. Integration of a custom PCB board further reduces the digital board by a factor of 2. Some unique additional packaging considerations were also implemented, to enable adapt the Microflow system to function and perform in space. One key development was with respect to optofluidics interfacing quality of the capillary with the interrogation volume of the fiber optic flow cell. Tapering and other modifications to the FOFC not only enabled better laminar flow, but also reduced agglomeration and blocking of the fluidics subsystem, crucial to further enhance the performance of the cytometer. Since multiple samples need to be contained in a singular cartridge, waste management, cleaning and flushing was completely integrated and automated in the body of the device. Lastly, environmental limitations of liquid exposure in space further required a 3-level containment (or leak proofing redundancy) to be integrated in the Microflow system. Miniaturization of the optofluidics system with the aid of a miniature rotary disc pump further reduced the sample volume requirements from 500 uL to 50 uL. These and other packaging, integration and miniaturization elements towards a space compatible, fiber optic Microflow cytometer will be discussed as well as results from experiments conducted in microgravity.