Development of a capillary temperature control system for capillary electrophoresis instruments designed for spaceflight applications

Capillary temperature control during capillary electrophoresis (CE) separations is key for achieving accurate and reproducible results with a broad array of potential methods. However, the difficulty of enabling typical fluid temperature control loops on portable instruments has meant that active capillary temperature control of in situ CE systems has frequently been overlooked. This work describes construction and test of a solid-state device for capillary temperature control that is suitable for inclusion with in situ instruments, including those designed for space missions. Two test articles were built, a thermal mass model (TMM) and a functional model (FM). The TMM demonstrated that temperature gradients could be limited using the proposed control scheme, and that our thermal modeling of the system can be relied on for future adaptations of physical geometries of the system. The FM demonstrated CE analytical performance while under active temperature control and that the device was compatible with the harsh thermal-vacuum environments that might be encountered during space flight.

A voltage trade study for the design of capillary electrophoresis instruments for spaceflight

Capillary electrophoresis (CE) systems have undergone extensive development for spaceflight applications. A flight-compatible high voltage power supply and the necessary voltage isolation for other energized components can be large contributors to both the volume and mass of a CE system, especially if typical high voltage levels of 25-30 kV are used. Here, we took advantage of our custom CE hardware to perform a trade study for simultaneous optimization of capillary length, high voltage level, and separation time, without sacrificing method performance. A capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4 D) method recently developed by our group to target inorganic cations and amino acids relevant to astrobiology was used as a test case. The results indicate that a 50 cm long capillary with 15 kV applied voltage (half of that used in the original method) can be used to achieve measurement goals while minimizing instrument size.

Detection of Biosignatures by Capillary Electrophoresis Mass Spectrometry in the Presence of Salts Relevant to Ocean Worlds Missions

Capillary electrophoresis (CE) is a promising liquid-based technique for in situ chemical analysis on ocean worlds that allows the detection of a wide range of organic molecules relevant to the search for life. CE coupled with mass spectrometry (MS) is particularly valuable as it also enables the discovery of unknown compounds. Here we demonstrate that CE coupled to MS via electrospray ionization (ESI) can readily analyze samples containing up to half the saturation levels of salts relevant to ocean worlds when using 5 M acetic acid as the separation media. A mixture containing amino acids, peptides, nucleobases, and nucleosides was analyzed in the presence of two salts, NaCl and MgSO₄, based on their relevance to Europa and Enceladus. We demonstrate here CE-MS limits of detection for these organics ranging from 0.05 to 1 μM (8 to 89 ppb) in the absence of salts. More importantly, we demonstrate here for the first time that organics in the low micromolar range (1-50 μM) are detected by CE-MS in the presence of 3 M NaCl without desalting, preconcentration, or derivatization. This demonstration highlights how CE-MS is uniquely suited for organic analysis on future missions to ocean worlds.

Frequency-specific, valveless flow control in insect-mimetic microfluidic devices

Inexpensive, portable lab-on-a-chip devices would revolutionize fields like environmental monitoring and global health, but current microfluidic chips are tethered to extensive off-chip hardware. Insects, however, are self-contained and expertly manipulate fluids at the microscale using largely unexplored methods. We fabricated a series of microfluidic devices that mimic key features of insect respiratory kinematics observed by synchrotron-radiation imaging, including the collapse of portions of multiple respiratory tracts in response to a single fluctuating pressure signal. In one single-channel device, the flow rate and direction could be controlled by the actuation frequency alone, without the use of internal valves. Additionally, we fabricated multichannel chips whose individual channels responded selectively (on with a variable, frequency-dependent flow rate, or off) to a single, global actuation frequency. Our results demonstrate that insect-mimetic designs have the potential to drastically reduce the actuation overhead for microfluidic chips, and that insect respiratory systems may share features with impedance-mismatch pumps.

Lab-on-a-chip technology for in situ combined observations in oceanography

The oceans sustain the global environment and diverse ecosystems through a variety of biogeochemical processes and their complex interactions. In order to understand the dynamism of the local or global marine environments, multimodal combined observations must be carried out in situ. On the other hand, instrumentation of in situ measurement techniques enabling biological and/or biochemical combined observations is challenging in aquatic environments, including the ocean, because biochemical flow analyses require a more complex configuration than physicochemical electrode sensors. Despite this technical hurdle, in situ analyzers have been developed to measure the concentrations of seawater contents such as nutrients, trace metals, and biological components. These technologies have been used for cutting-edge ocean observations to elucidate the biogeochemical properties of water mass with a high spatiotemporal resolution. In this context, the contribution of lab-on-a-chip (LoC) technology toward the miniaturization and functional integration of in situ analyzers has been gaining momentum. Due to their mountability, in situ LoC technologies provide ideal instrumentation for underwater analyzers, especially for miniaturized underwater observation platforms. Consequently, the appropriate combination of reliable LoC and underwater technologies is essential to realize practical in situ LoC analyzers suitable for underwater environments, including the deep sea. Moreover, the development of fundamental LoC technologies for underwater analyzers, which operate stably in extreme environments, should also contribute to in situ measurements for public or industrial purposes in harsh environments as well as the exploration of the extraterrestrial frontier.

Application of capillary electrophoresis combined with conductometric and UV detection to monitor meteorite simulant bioleaching by Acidithiobacillus ferrooxidans

The importance of microorganisms and biotechnology in space exploration and future planets colonization has been discussed in the literature. Meteorites are interesting samples to study microbe-mineral interaction focused on space exploration. The chemolithotropic bacterium Acidithiobacillus ferrooxidans has been used as model to understand the iron and sulfur oxidation. In this work, capillary electrophoresis with capacitively coupled contactless conductivity detection and UV detection was used to monitor bacterial growth in a meteorite simulant by measuring the conversion of Fe²⁺ into Fe⁺³ . The effect of Co²⁺ and Ni²⁺ (metals also found in meteorites) on the bacterial growth was also evaluated. The presented method allowed the analyses of all metals in a single run (less than 8 min). The background electrolyte was composted of 10 mmol/L α-hydroxyisobutyric acid/Histidine. For comparison purpose, the samples were also analyzed by UV-Vis spectrophotometry. The Fe²⁺ conversion into Fe³⁺ by A. ferrooxidans was observed up to 36 h with the growth rate constant of 0.19/h and 0.21/h in Tuovinen and Kelly (T&K) and in meteorite simulant media, respectively. The developed method presents favorable prospect to monitor the growth of other chemolithotropic microorganisms for biotechnology applications.

Extraction of amino acids from aerogel for analysis by capillary electrophoresis. Implications for a mission concept to Enceladus' Plume

Ocean worlds like Europa and Enceladus in the outer solar system are prime targets in the search for life beyond Earth. Enceladus is particularly interesting due to the presence of a water plume ejecting from the south polar region. The recent discovery of H₂ in the plume, in addition to the presence of previously observed organic compounds, highlights the possibility of life in this moon. The plume provides materials from the underlying ocean that could be collected simply by flying through it. The presence of the plume means that material from the ocean is available for collection during a flyby, without the need for landing or complex sample handling operations such as scooping or drilling. An attractive approach to preserve the organics in particles collected during flyby encounters would be to utilize silica aerogel, the material used to collect particles at hypervelocity during the Stardust mission. Here we demonstrate amino acids can be extracted from aerogel simply by adding water. This simple liquid extraction method could be implemented during a mission prior to analysis with a liquid-based technique like capillary electrophoresis.

Droplet control technologies for microfluidic high throughput screening (μHTS)

The transition from micro well plate and robotics based high throughput screening (HTS) to chip based screening has already started. This transition promises reduced droplet volumes thereby decreasing the amount of fluids used in these studies. Moreover, it significantly boosts throughput allowing screening to keep pace with the overwhelming number of molecular targets being discovered. In this review, we analyse state-of-the-art droplet control technologies that exhibit potential to be used in this new generation of screening devices. Since these systems are enclosed and usually planar, even some of the straightforward methods used in traditional HTS such as pipetting and reading can prove challenging to replicate in microfluidic high throughput screening (μHTS). We critically review the technologies developed for this purpose in depth, describing the underlying physics and discussing the future outlooks.

A fully automated microfluidic micellar electrokinetic chromatography analyzer for organic compound detection

An integrated microfluidic chemical analyzer utilizing micellar electrokinetic chromatography (MEKC) is developed using a pneumatically actuated Lifting-Gate microvalve array and a capillary zone electrophoresis (CZE) chip. Each of the necessary liquid handling processes such as metering, mixing, transferring, and washing steps are performed autonomously by the microvalve array. In addition, a method is presented for automated washing of the high resistance CZE channel for device reuse and periodic automated in situ analyses. To demonstrate the functionality of this MEKC platform, amino acids and thiols are labeled and efficiently separated via a fully automated program. Reproducibility of the automated programs for sample labeling and periodic in situ MEKC analysis was tested and found to be equivalent to conventional sample processing techniques for capillary electrophoresis analysis. This platform enables simple, portable, and automated chemical compound analysis which can be used in challenging environments.

Evaluation of a Portable Microchip Electrophoresis Fluorescence Detection System for the Analysis of Amino Acid Neurotransmitters in Brain Dialysis Samples

A portable fluorescence detection system for use with microchip electrophoresis was developed and compared to a benchtop system. Using this system, six neuroactive amines commonly found in brain dialysate (arginine, citrulline, taurine, histamine, glutamate, and aspartate) were derivatized offline with naphthalene-2,3-dicarboxaldehyde/cyanide, separated electrophoretically, and detected by fluorescence. The limits of detection for the analytes of interest were 50 - 250 nM for the benchtop system and 250 nM - 1.3 μM for the portable system, both of which were adequate for most analyte detection in brain microdialysis samples. The portable system was then demonstrated for the detection of the same six amines in a rat brain microdialysis sample.

Implementation of microchip electrophoresis instrumentation for future spaceflight missions

We present a comprehensive discussion of the role that microchip electrophoresis (ME) instrumentation could play in future NASA missions of exploration, as well as the current barriers that must be overcome to make this type of chemical investigation possible. We describe how ME would be able to fill fundamental gaps in our knowledge of the potential for past, present, or future life beyond Earth. Despite the great promise of ME for ultrasensitive portable chemical analysis, to date, it has never been used on a robotic mission of exploration to another world. We provide a current snapshot of the technology readiness level (TRL) of ME instrumentation, where the TRL is the NASA systems engineering metric used to evaluate the maturity of technology, and its fitness for implementation on missions. We explain how the NASA flight implementation process would apply specifically to ME instrumentation, and outline the scientific and technology development issues that must be addressed for ME analyses to be performed successfully on another world. We also outline research demonstrations that could be accomplished by independent researchers to help advance the TRL of ME instrumentation for future exploration missions. The overall approach described here for system development could be readily applied to a wide range of other instrumentation development efforts having broad societal and commercial impact.

Amine Analysis Using AlexaFluor 488 Succinimidyl Ester and Capillary Electrophoresis with Laser-Induced Fluorescence

Fluorescent probes enable detection of otherwise nonfluorescent species via highly sensitive laser-induced fluorescence. Organic amines are predominantly nonfluorescent and are of analytical interest in agricultural and food science, biomedical applications, and biowarfare detection. Alexa Fluor 488 N-hydroxysuccinimidyl ester (AF488 NHS-ester) is an amine-specific fluorescent probe. Here, we demonstrate low limit of detection of long-chain (C9 to C18) primary amines and optimize AF488 derivatization of long-chain primary amines. The reaction was found to be equally efficient in all solvents studied (dimethylsulfoxide, ethanol, and N,N-dimethylformamide). While an organic base (N,N-diisopropylethylamine) is required to achieve efficient reaction between AF488 NHS-ester and organic amines with longer hydrophobic chains, high concentrations (>5 mM) result in increased levels of ethylamine and propylamine in the blank. Optimal incubation times were found to be >12 hrs at room temperature. We present an initial capillary electrophoresis separation for analysis using a simple micellar electrokinetic chromatography (MEKC) buffer consisting of 12 mM sodium dodecylsulfate (SDS) and 5 mM carbonate, pH 10. Limits of detection using the optimized labeling conditions and these separation conditions were 5-17 nM. The method presented here represents a novel addition to the arsenal of fluorescent probes available for highly sensitive analysis of small organic molecules.

A review of microdialysis coupled to microchip electrophoresis for monitoring biological events

Microdialysis is a powerful sampling technique that enables monitoring of dynamic processes in vitro and in vivo. The combination of microdialysis with chromatographic or electrophoretic methods with selective detection yields a "separation-based sensor" capable of monitoring multiple analytes in near real time. For monitoring biological events, analysis of microdialysis samples often requires techniques that are fast (<1 min), have low volume requirements (nL-pL), and, ideally, can be employed on-line. Microchip electrophoresis fulfills these requirements and also permits the possibility of integrating sample preparation and manipulation with detection strategies directly on-chip. Microdialysis coupled to microchip electrophoresis has been employed for monitoring biological events in vivo and in vitro. This review discusses technical considerations for coupling microdialysis sampling and microchip electrophoresis, including various interface designs, and current applications in the field.

Analysis of thiols by microchip capillary electrophoresis for in situ planetary investigations

Microchip capillary electrophoresis with laser-induced fluorescence detection (μCE-LIF) enables sensitive analyses of a wide range of analytes employing small volumes of sample and reagent (nL to μL) on an instrument platform with minimal mass, volume, and power requirements. This technique has been used previously in the analysis of amino acids and other organic molecules of interest in the fields of astrobiology and planetary science. Here, we present a protocol for the analysis of thiols using μCE-LIF. This protocol utilizes Pacific Blue C5-maleimide for fluorescent derivatization of thiols, enabling limits of detection in the low nM range (1.4-15 nM). Separations are conducted in micellar electrokinetic chromatography mode with 25 mM sodium dodecyl sulfate in 15 mM tetraborate, pH 9.2. This method allows analysis of 12 thiols in less than 2 min following a labeling step of 2 h. A step-by-step protocol, including tips on microchip capillary electrophoresis, is described here.

Capillary and microchip electrophoretic analysis of polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants which can reach the environment and food in different ways. Because of their high toxicity, two international regulatory institutions, the US Environmental Protection Agency and the European Food Safety Authority, have classified PAHs as priority pollutants, generating an important demand for the detection and identification of PAHs. Thus, sensitive, fast, and cheap methods for the analysis of PAHs in environmental and food samples are urgently needed. Within this context, electrophoresis, in capillary or microchip format, displays attractive features. This review presents and critically discusses the published literature on the different approaches to capillary and microchip electrophoresis analysis of PAHs.

Present state of microchip electrophoresis: state of the art and routine applications

Microchip electrophoresis (MCE) was one of the earliest applications of the micro-total analysis system (μ-TAS) concept, whose aim is to reduce analysis time and reagent and sample consumption while increasing throughput and portability by miniaturizing analytical laboratory procedures onto a microfluidic chip. More than two decades on, electrophoresis remains the most common separation technique used in microfluidic applications. MCE-based instruments have had some commercial success and have found application in many disciplines. This review will consider the present state of MCE including recent advances in technology and both novel and routine applications in the laboratory. We will also attempt to assess the impact of MCE in the scientific community and its prospects for the future.

Getting started with open-hardware: development and control of microfluidic devices

Understanding basic concepts of electronics and computer programming allows researchers to get the most out of the equipment found in their laboratories. Although a number of platforms have been specifically designed for the general public and are supported by a vast array of on-line tutorials, this subject is not normally included in university chemistry curricula. Aiming to provide the basic concepts of hardware and software, this article is focused on the design and use of a simple module to control a series of PDMS-based valves. The module is based on a low-cost microprocessor (Teensy) and open-source software (Arduino). The microvalves were fabricated using thin sheets of PDMS and patterned using CO2 laser engraving, providing a simple and efficient way to fabricate devices without the traditional photolithographic process or facilities. Synchronization of valve control enabled the development of two simple devices to perform injection (1.6 ± 0.4 μL/stroke) and mixing of different solutions. Furthermore, a practical demonstration of the utility of this system for microscale chemical sample handling and analysis was achieved performing an on-chip acid-base titration, followed by conductivity detection with an open-source low-cost detection system. Overall, the system provided a very reproducible (98%) platform to perform fluid delivery at the microfluidic scale.

Analysis of thiols by microchip capillary electrophoresis for in situ planetary investigations

The detection of thiols on extraterrestrial bodies could provide evidence for life, as well as a host of potential prebiological or abiological processes. Here, we report a novel protocol to analyze organic thiols by microchip CE with LIF detection. Thiols were labeled with Pacific Blue C5 maleimide and analyzed by MEKC. The separation buffer consisted of 15 mM tetraborate pH 9.2 and 25 mM SDS. The optimized method provided LODs ranging from 1.4 to 15 nM. The method was validated using samples collected from geothermal pools at Hot Creek Gorge, California, which were found to contain 2-propanethiol and 1-butanethiol in the nanomolar concentration range. These samples serve as chemical analogues to material potentially present in the reducing environment of primitive Earth and also at sulfurous regions of Mars. Hence, the protocol developed here enables highly sensitive thiol analysis in samples with complexity comparable to that expected in astrobiologically relevant extraterrestrial settings. This new protocol could be readily added to the existing suite of microfluidic chemical analyses developed for in situ planetary exploration; all that is required is the incorporation of two new reagents to the payload of an existing instrument concept.