Enceladus is a compelling destination for astrobiological analyses due to the presence of simple and complex organic constituents in cryovolcanic plumes that jet from its subsurface ocean. Enceladus plume capture during a flyby or orbiter mission is an appealing method for obtaining pristine ocean samples for scientific studies of this organic content because of the high science return, reduced planetary protection challenges, and lower risk and expense compared to a landed mission. However, this mission profile requires sufficient amounts of plume material for sensitive analysis. To explore the feasibility and optimization of the required capture systems, light gas gun experiments were carried out to study organic ice particle impacts on indium surfaces. An organic fluorescent tracer dye, Pacific Blue ™ , was dissolved in borate buffer and frozen into saline ice projectiles. During acceleration, the ice projectile breaks up in flight into micron-sized particles that impact the target. Quantitative fluorescence microscopic analysis of the targets demonstrated that under certain impact conditions, 10-50% of the entrained organic molecules were captured in over 25% of the particle impacts. Optimal organic capture was observed for small particles (d~5-15 µm) with velocities ranging from 1 to 2 km s −1. Our results reveal how organic capture efficiency depends on impact velocity and particle size; capture increases as particles get smaller and as velocity is reduced. These results demonstrate the feasibility of collecting unmodified organic molecules from the Enceladus ice plume for sensitive analysis with modern in situ instrumentation such as microfluidic capillary electrophoresis (CE) analysis with ppb organic sensitivity.

Enceladus, an icy moon of Saturn, is a compelling destination for a probe seeking biosignatures of extraterrestrial life because its subsurface ocean exhibits significant organic chemistry that is directly accessible by sampling cryovolcanic plumes. State-of-the-art organic chemical analysis instruments can perform valuable science measurements at Enceladus provided they receive sufficient plume material in a fly-by or orbiter plume transit. To explore the feasibility of plume sampling, we performed light gas gun experiments impacting micrometer-sized ice particles containing a fluorescent dye biosignature simulant into a variety of soft metal capture surfaces at velocities from 800 m ⋅ s−1 up to 3 km ⋅ s−1. Quantitative fluorescence microscopy of the capture surfaces demonstrates organic capture efficiencies of up to 80 to 90% for isolated impact craters and of at least 17% on average on indium and aluminum capture surfaces at velocities up to 2.2 km ⋅ s−1. Our results reveal the relationships between impact velocity, particle size, capture surface, and capture efficiency for a variety of possible plume transit scenarios. Combined with sensitive microfluidic chemical analysis instruments, we predict that our capture system can be used to detect organic molecules in Enceladus plume ice at the 1 nM level—a sensitivity thought to be meaningful and informative for probing habitability and biosignatures.

This study presents the numerical simulation and optimization of a dielectrophoretic (DEP) bio-separation chip for isolating bioparticles such as circulating tumor cells. The chip consists of an array of slanted electrodes placed on the top and bottom walls of the channel with an angle of 5°, 10°, and 15° with respect to the flow direction. The spatially non-uniform electric field produced by the slanted electrodes applies a DEP force on the particles flowing through the channel. The repulsive DEP forces applied by the top and bottom electrode arrays are balanced in the normal direction (y), causing the particles to flow along the centerline of the channel. However, the lateral component (z) of the DEP force deflects particles in the lateral direction, guiding them toward different outlets based on their size. Numerical simulation of the particle-fluid transport was performed using OpenFOAM, an open-source computational fluid dynamics package. The computational model considers the dominant forces such as the DEP, hydrodynamic, and gravitational forces and simulates the deflection and trajectory of the particles within the microfluidic channel based on their size. Additionally, a parametric study was performed to investigate the effects of voltage, flow rate, number of electrode pairs, cell size, channel height, the angle of electrodes, and the width and spacing of electrodes on the separation process and to optimize the utility of the DEP devices for cell separation.

Enceladus is a prime candidate in the solar system for in-depth astrobiological studies searching for habitability and life because it has a liquid water ocean with significant organic content and ongoing cryovolcanic activity. The presence of ice plumes that jet up through fissures in the ice crust covering the sub-surface ocean, enables remote sampling and in-situ analysis via a fly-by mission. However, capture and transport of organic materials to organic analyzers presents distinctive challenges as it is unknown whether, and to what extent, organic molecules imbedded in ice particles can be captured and survive hypervelocity impacts. This manuscript provides a fluorescence microscopic method to parametrically determine the amount of an organic fluorescent tracer dye, Pacific Blue™ (PB) deposited on a metallic surface. This method can be used to measure the capture and survival outcomes of terrestrial hypervelocity impact experiments where an ice projectile labeled with Pacific Blue impacts a soft metal surface. This work is an important step in the advancement of instruments like the Enceladus Organic Analyzer for detecting biosignatures in an Enceladus plume fly-by mission. An apparatus consisting of a substrate humidification shroud coupled with an epifluorescence microscope with CCD detector is developed to measure the intensity of quantitatively deposited Pacific Blue droplets under controlled humidity. Calibration curves are produced that relate the integrated fluorescence intensity of humidified PB droplets on metal foils to the number of PB molecules deposited. To demonstrate the utility of this method, our calibrations are used to analyze and quantitate organic capture and survival (up to 11% capture efficiency) following ice particle impacts at a velocity of 1.7 km/s on an aluminum substrate.

This study presents the numerical simulation and optimization of a dielectrophoretic bio-separation chip for isolating bioparticles such as circulating tumor cells (CTCs). The chip consists of ten pairs of electrodes placed with an angle of 10° with respect to the direction of the flow on the top and bottom walls of the channel. The spatially non-uniform electric field produced by the slanted electrodes applies a repulsive force on the particles that are flowing through the channel. The repulsive force applied by the top and bottom electrodes are balanced and the particles flow along the centerline of the channel. On the other hand, the magnitude of forces resulted from electric field in the x and z-directions deflects particles depending on their size and guides them towards different outlets. Numerical simulation of the particle-fluid transport was performed using an open-source software named OpenFOAM and the deflection of the particles within the microfluidic channel was predicted. The present computational domain considers the dominant forces such as dielectrophoretic and hydrodynamic forces as well as their effects on the design and operating parameters of the chip. The results show that this device is capable of separating various cells based on their size.