Loss of PADI2 and PADI4 ameliorates sepsis-induced acute lung injury by suppressing NLRP3+ macrophages.

Sepsis-induced acute lung injury (ALI) is prevalent in septic patients and has a high mortality rate. Peptidyl arginine deiminase (PADI) 2 and PADI4 play crucial roles in mediating the host's immune response in sepsis, but their specific functions remain unclear. Our study shows that Padi2-/-Padi4-/- double knockout (DKO) improved survival, reduced lung injury, decreased bacterial load in Pseudomonas aeruginosa (PA) pneumonia-induced sepsis mice. Using single-cell RNA sequencing (scRNA-seq), we found that the deletion of Padi2 and Padi4 reduced the Nlrp3+ pro-inflammatory macrophages and fostered Chil3+ myeloid cell differentiation into anti-inflammatory macrophages. Additionally, we observed the regulatory role of NLRP3-Ym1 axis upon DKO, confirmed by Chil3 knockdown and Nlrp3 KO experiments. Thus, eliminating Padi2 and Padi4 enhances the polarization of Ym1+ M2 macrophages by suppressing NLRP3, aiding in inflammation resolution and lung tissue repair. study unveils the PADI2/PADI4-NLRP3-Ym1 pathway as a potential target in treatment of sepsis-induced ALI.

INFLAMMATORY RESPONSES TO POLYMICROBIAL INTRA-ABDOMINAL SEPSIS ARE HIGHLY VARIABLE BUT STRONGLY CORRELATED TO ENTEROBACTERIACEAE OUTGROWTH.

ABSTRACT: Sepsis is a common, heterogeneous, and frequently lethal condition of organ dysfunction and immune dysregulation due to infection. The causes of its heterogeneity, including the contribution of the pathogen, remain unknown. Using cecal slurry, a widely used murine model of intraperitoneal polymicrobial sepsis, as well as 16S ribosomal RNA sequencing and measurement of immune markers, we performed a series of translational analyses to determine whether microbial variation in cecal slurry composition (representing intra-abdominal pathogens) mediated variation in septic response. We found wide variation in cecal slurry community composition that changed markedly over the 24-h course of infection. This variation in cecal slurry bacteria led to large variation in physiologic and inflammatory responses. Severity of inflammatory response was positively correlated with intraperitoneal enrichment with Enterobacteriaceae. Likewise, in a human cohort of patients with intra-abdominal abscesses, Enterobacteriaceae was also associated with increased inflammatory markers. Taken together, these data demonstrate that intra-abdominal Enterobacteriaceae drives inflammation in sepsis both in animal models and human subjects. More broadly, our results demonstrate that pathogen identity is a major driver of the host response in polymicrobial sepsis and should not be overlooked as a major source of phenotypic heterogeneity.

Miniaturized microarray-format digital ELISA enabled by lithographic protein patterning.

The search for reliable protein biomarker candidates is critical for early disease detection and treatment. However, current immunoassay technologies are failing to meet increasing demands for sensitivity and multiplexing. Here, the authors have created a highly sensitive protein microarray using the principle of single-molecule counting for signal amplification, capable of simultaneously detecting a panel of cancer biomarkers at sub-pg/mL levels. To enable this amplification strategy, the authors introduce a novel method of protein patterning using photolithography to subdivide addressable arrays of capture antibody spots into hundreds of thousands of individual microwells. This allows for the total sensor area to be miniaturized, increasing the total possible multiplex capacity. With the immunoassay realized on a standard 75x25 mm form factor glass substrate, sample volume consumption is minimized to <10 µL, making the technology highly efficient and cost-effective. Additionally, the authors demonstrate the power of their technology by measuring six secretory factors related to glioma tumor progression in a cohort of mice. This highly sensitive, sample-sparing multiplex immunoassay paves the way for researchers to track changes in protein profiles over time, leading to earlier disease detection and discovery of more effective treatment using animal models.

A tissue chip with integrated digital immunosensors: In situ brain endothelial barrier cytokine secretion monitoring.

Organ-on-a-chip platforms have potential to offer more cost-effective, ethical, and human-resembling models than animal models for disease study and drug discovery. Particularly, the Blood-Brain-Barrier-on-a-chip (BBB-oC) has emerged as a promising tool to investigate several neurological disorders since it promises to provide a model of the multifunctional tissue working as an important node to control pathogen entry, drug delivery and neuroinflammation. A comprehensive understanding of the multiple physiological functions of the tissue model requires biosensors detecting several tissue-secreted substances in a BBB-oC system. However, current sensor-integrated BBB-oC platforms are only available for tissue membrane integrity characterization based on permeability measurement. Protein secretory pathways are closely associated with the tissue's various diseased conditions. At present, no biosensor-integrated BBB-oC platform exists that permits in situ tissue protein secretion analysis over time, which prohibits researchers from fully understanding the time-evolving pathology of a tissue barrier. Herein, the authors present a platform named "Digital Tissue-BArrier-CytoKine-counting-on-a-chip (DigiTACK)," which integrates digital immunosensors into a tissue chip system and demonstrates on-chip multiplexed, ultrasensitive, longitudinal cytokine secretion profiling of cultured brain endothelial barrier tissues. The integrated digital sensors utilize a novel beadless microwell format to perform an ultrafast "digital fingerprinting" of the analytes while achieving a low limit of detection (LoD) around 100-500 fg/mL for mouse MCP1 (CCL2), IL-6 and KC (CXCL1). The DigiTACK platform is extensively applicable to profile temporal cytokine secretion of other barrier-related organ-on-a-chip systems and can provide new insight into the secretory dynamics of the BBB by sequentially controlled experiments.

Bioinspired Plasmo-virus for Point-of-Care SARS-CoV-2 Detection.

Directly identifying the presence of the virus in infected hosts with an appropriate speed and sensitivity permits early epidemic management even during the presymptomatic incubation period of infection. Here, we synthesize a bioinspired plasmo-virus (BPV) particle for rapid and sensitive point-of-care (POC) detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) via a self-assembled plasmonic nanoprobe array on spike proteins. The BPV enables strong near-infrared (NIR) extinction peaks caused by plasmonic nanogaps. We quantify SARS-CoV-2 in viral transport medium (VTM) at low titers within 10 min with a limit of detection (LOD) of 1.4 × 101 pfu/mL, which is 103 times more sensitive than the current gold-standard method. The high-sensitivity and high-speed POC detection may be widely used for the timely, individualized diagnosis of infectious agents in low-resource settings.

The Modular µSiM: A Mass Produced, Rapidly Assembled, and Reconfigurable Platform for the Study of Barrier Tissue Models In Vitro.

Advanced in vitro tissue chip models can reduce and replace animal experimentation and may eventually support "on-chip" clinical trials. To realize this potential, however, tissue chip platforms must be both mass-produced and reconfigurable to allow for customized design. To address these unmet needs, an extension of the µSiM (microdevice featuring a silicon-nitride membrane) platform is introduced. The modular µSiM (m-µSiM) uses mass-produced components to enable rapid assembly and reconfiguration by laboratories without knowledge of microfabrication. The utility of the m-µSiM is demonstrated by establishing an hiPSC-derived blood-brain barrier (BBB) in bioengineering and nonengineering, brain barriers focused laboratories. In situ and sampling-based assays of small molecule diffusion are developed and validated as a measure of barrier function. BBB properties show excellent interlaboratory agreement and match expectations from literature, validating the m-µSiM as a platform for barrier models and demonstrating successful dissemination of components and protocols. The ability to quickly reconfigure the m-µSiM for coculture and immune cell transmigration studies through addition of accessories and/or quick exchange of components is then demonstrated. Because the development of modified components and accessories is easily achieved, custom designs of the m-µSiM shall be accessible to any laboratory desiring a barrier-style tissue chip platform.

Emerging biotechnologies for evaluating disruption of stress, sleep, and circadian rhythm mechanism using aptamer-based detection of salivary biomarkers.

The internally driven 24-h cycle in humans, called circadian rhythm, controls physiological, metabolic, and hormonal processes, and is tied to the circadian clocks ticking in most of the cells and tissues. The central clock, located in suprachiasmatic nuclei of the hypothalamus, is directly influenced by external cues, particularly light, and entrains the peripheral clocks through neural and hormonal pathways to the external light-dark cycle. However, peripheral clocks also have self-sustained circadian rhythmicity and feeding is the potent synchronizer. The internal clock system regulates the sleep-wake cycle and maintains stress responses through the hypothalamus-pituitary-adrenal axis and autonomic pathways. Any misalignment in this complex network could lead to circadian clock disruption and endocrine and metabolic dysfunction that may induce inflammatory responses. The detrimental consequences of such dysfunction are broad and can lead to serious health problems; however, the extent of the circadian disruption is difficult to assess. New promising techniques based on biosensors and point-of-care devices using aptamers - single-stranded DNA or RNA biorecognition molecules that can measure biomarkers of stress, sleep, and circadian rhythms in bodily fluids such as saliva with high sensitivity and specificity - can provide timely and accurate diagnosis and allow for effective implementation of behavioral and therapeutic interventions. This review provides detailed insight into the complex crosstalk between stress, sleep, and circadian rhythm, their relationship with the body's homeostasis, and the consequences of circadian dysregulation. The review also summarizes the mechanisms of aptamer-based biosensors and/or point-of-care devices developed to date for the detection of salivary biomarkers linked to stress, sleep, and circadian rhythm. Lastly, the review outlines the knowledge gaps in the literature related to the detection of lower concentrations of biomarkers in saliva and discusses the prospects of aptamer-based detection of salivary biomarkers from a high-precision perspective that is crucial for clinical diagnosis, at a time when circadian disruption is evident in unprecedented proportions across the globe.

Machine-Learning-Assisted Microfluidic Nanoplasmonic Digital Immunoassay for Cytokine Storm Profiling in COVID-19 Patients.

Cytokine storm, known as an exaggerated hyperactive immune response characterized by elevated release of cytokines, has been described as a feature associated with life-threatening complications in COVID-19 patients. A critical evaluation of a cytokine storm and its mechanistic linkage to COVID-19 requires innovative immunoassay technology capable of rapid, sensitive, selective detection of multiple cytokines across a wide dynamic range at high-throughput. In this study, we report a machine-learning-assisted microfluidic nanoplasmonic digital immunoassay to meet the rising demand for cytokine storm monitoring in COVID-19 patients. Specifically, the assay was carried out using a facile one-step sandwich immunoassay format with three notable features: (i) a microfluidic microarray patterning technique for high-throughput, multiantibody-arrayed biosensing chip fabrication; (ii) an ultrasensitive nanoplasmonic digital imaging technology utilizing 100 nm silver nanocubes (AgNCs) for signal transduction; (iii) a rapid and accurate machine-learning-based image processing method for digital signal analysis. The developed immunoassay allows simultaneous detection of six cytokines in a single run with wide working ranges of 1-10,000 pg mL-1 and ultralow detection limits down to 0.46-1.36 pg mL-1 using a minimum of 3 µL serum samples. The whole chip can afford a 6-plex assay of 8 different samples with 6 repeats in each sample for a total of 288 sensing spots in less than 100 min. The image processing method enhanced by convolutional neural network (CNN) dramatically shortens the processing time ∼6,000 fold with a much simpler procedure while maintaining high statistical accuracy compared to the conventional manual counting approach. The immunoassay was validated by the gold-standard enzyme-linked immunosorbent assay (ELISA) and utilized for serum cytokine profiling of COVID-19 positive patients. Our results demonstrate the nanoplasmonic digital immunoassay as a promising practical tool for comprehensive characterization of cytokine storm in patients that holds great promise as an intelligent immunoassay for next generation immune monitoring.

Ultrasensitive Multiparameter Phenotyping of Rare Cells Using an Integrated Digital-Molecular-Counting Microfluidic Well Plate.

Integrated microfluidic cellular phenotyping platforms provide a promising means of studying a variety of inflammatory diseases mediated by cell-secreted cytokines. However, immunosensors integrated in previous microfluidic platforms lack the sensitivity to detect small signals in the cellular secretion of proinflammatory cytokines with high precision. This limitation prohibits researchers from studying cells secreting cytokines at low abundance or existing at a small population. Herein, the authors present an integrated platform named the "digital Phenoplate (dPP)," which integrates digital immunosensors into a microfluidic chip with on-chip cell assay chambers, and demonstrates ultrasensitive cellular cytokine secretory profile measurement. The integrated sensors yield a limit of detection as small as 0.25 pg mL-1 for mouse tumor necrosis factor alpha (TNF-α). Each on-chip cell assay chamber confines cells whose population ranges from ≈20 to 600 in arrayed single-cell trapping microwells. Together, these microfluidic features of the dPP simultaneously permit precise counting and image-based cytometry of individual cells while performing parallel measurements of TNF-α released from rare cells under multiple stimulant conditions for multiple samples. The dPP platform is broadly applicable to the characterization of cellular phenotypes demanding high precision and high throughput.

Few-Layer MoS2 Photodetector Arrays for Ultrasensitive On-Chip Enzymatic Colorimetric Analysis.

Enzymatic colorimetric analysis of metabolites provides signatures of energy conversion and biosynthesis associated with disease onsets and progressions. Miniaturized photodetectors based on emerging two-dimensional transition metal dichalcogenides (TMDCs) promise to advance point-of-care diagnosis employing highly sensitive enzymatic colorimetric detection. Reducing diagnosis costs requires a batched multisample assay. The construction of few-layer TMDC photodetector arrays with consistent performance is imperative to realize optical signal detection for a miniature batched multisample enzymatic colorimetric assay. However, few studies have promoted an optical reader with TMDC photodetector arrays for on-chip operation. Here, we constructed 4 × 4 pixel arrays of miniaturized molybdenum disulfide (MoS2) photodetectors and integrated them with microfluidic enzyme reaction chambers to create an optoelectronic biosensor chip device. The fabricated device allowed us to achieve arrayed on-chip enzymatic colorimetric detection of d-lactate, a blood biomarker signifying the bacterial translocation from the intestine, with a limit of detection that is 1000-fold smaller than the clinical baseline, a 10 min assay time, high selectivity, and reasonably small variability across the entire arrays. The enzyme (Ez)/MoS2 optoelectronic biosensor unit consistently detected d-lactate in clinically important biofluids, such as saliva, urine, plasma, and serum of swine and humans with a wide detection range (10-3-103 µg/mL). Furthermore, the biosensor enabled us to show that high serum d-lactate levels are associated with the symptoms of systemic infection and inflammation. The lensless, optical waveguide-free device architecture should readily facilitate development of a monolithically integrated hand-held module for timely, cost-effective diagnosis of metabolic disorders in near-patient settings.

Machine learning-based cytokine microarray digital immunoassay analysis.

Serial measurement of a large panel of protein biomarkers near the bedside could provide a promising pathway to transform the critical care of acutely ill patients. However, attaining the combination of high sensitivity and multiplexity with a short assay turnaround poses a formidable technological challenge. Here, the authors develop a rapid, accurate, and highly multiplexed microfluidic digital immunoassay by incorporating machine learning-based autonomous image analysis. The assay has achieved 12-plexed biomarker detection in sample volume <15 µL at concentrations < 5 pg/mL while only requiring a 5-min assay incubation, allowing for all processes from sampling to result to be completed within 40 min. The assay procedure applies both a spatial-spectral microfluidic encoding scheme and an image data analysis algorithm based on machine learning with a convolutional neural network (CNN) for pre-equilibrated single-molecule protein digital counting. This unique approach remarkably reduces errors facing the high-capacity multiplexing of digital immunoassay at low protein concentrations. Longitudinal data obtained for a panel of 12 serum cytokines in human patients receiving chimeric antigen receptor-T (CAR-T) cell therapy reveals the powerful biomarker profiling capability. The assay could also be deployed for near-real-time immune status monitoring of critically ill COVID-19 patients developing cytokine storm syndrome.

Optimized gene expression from bacterial chromosome by high-throughput integration and screening.

Chromosomal integration of recombinant genes is desirable compared with expression from plasmids due to increased stability, reduced cell-to-cell variability, and elimination of the need for antibiotics for plasmid maintenance. Here, we present a new approach for tuning pathway gene expression levels via random integration and high-throughput screening. We demonstrate multiplexed gene integration and expression-level optimization for isobutanol production in Escherichia coli The integrated strains could, with far lower expression levels than plasmid-based expression, produce high titers (10.0 ± 0.9 g/liter isobutanol in 48 hours) and yields (69% of the theoretical maximum). Close examination of pathway expression in the top-performing, as well as other isolates, reveals the complexity of cellular metabolism and regulation, underscoring the need for precise optimization while integrating pathway genes into the chromosome. We expect this method for pathway integration and optimization can be readily extended to a wide range of pathways and chassis to create robust and efficient production strains.

An ultrahigh-throughput screening platform based on flow cytometric droplet sorting for mining novel enzymes from metagenomic libraries.

Uncultivable microbial communities provide enormous reservoirs of enzymes, but their experimental identification by functional metagenomics is challenging, mainly due to the difficulty of screening enormous metagenomic libraries. Here, we propose a reliable and convenient ultrahigh-throughput screening platform based on flow cytometric droplet sorting (FCDS). The FCDS platform employs water-in-oil-in-water double emulsion droplets serving as single-cell enzymatic micro-reactors and a commercially available flow cytometer, and it can efficiently isolate novel biocatalysts from metagenomic libraries by processing single cells as many as 108 per day. We demonstrated the power of this platform by screening a metagenomic library constructed from domestic running water samples. The FCDS assay screened 30 million micro-reactors in only 1 h, yielding a collection of esterase genes. Among these positive hits, Est WY was identified as a novel esterase with high catalytic efficiency and distinct evolutionary origin from other lipolytic enzymes. Our study manifests that the FCDS platform is a robust tool for functional metagenomics, with the potential to significantly improve the efficiency of exploring novel enzymes from nature.

Rapid single-molecule digital detection of protein biomarkers for continuous monitoring of systemic immune disorders.

Digital protein assays have great potential to advance immunodiagnostics because of their single-molecule sensitivity, high precision, and robust measurements. However, translating digital protein assays to acute clinical care has been challenging because it requires deployment of these assays with a rapid turnaround. Herein, we present a technology platform for ultrafast digital protein biomarker detection by using single-molecule counting of immune-complex formation events at an early, pre-equilibrium state. This method, which we term "pre-equilibrium digital enzyme-linked immunosorbent assay" (PEdELISA), can quantify a multiplexed panel of protein biomarkers in 10 µL of serum within an unprecedented assay incubation time of 15 to 300 seconds over a 104 dynamic range. PEdELISA allowed us to perform rapid monitoring of protein biomarkers in patients manifesting post-chimeric antigen receptor T-cell therapy cytokine release syndrome, with ∼30-minute sample-to-answer time and a sub-picograms per mL limit of detection. The rapid, sensitive, and low-input volume biomarker quantification enabled by PEdELISA is broadly applicable to timely monitoring of acute disease, potentially enabling more personalized treatment.

A digital protein microarray for COVID-19 cytokine storm monitoring.

Despite widespread concern regarding cytokine storms leading to severe morbidity in COVID-19, rapid cytokine assays are not routinely available for monitoring critically ill patients. We report the clinical application of a digital protein microarray platform for rapid multiplex quantification of cytokines from critically ill COVID-19 patients admitted to the intensive care unit (ICU) at the University of Michigan Hospital. The platform comprises two low-cost modules: (i) a semi-automated fluidic dispensing/mixing module that can be operated inside a biosafety cabinet to minimize the exposure of the technician to the virus infection and (ii) a 12-12-15 inch compact fluorescence optical scanner for the potential near-bedside readout. The platform enabled daily cytokine analysis in clinical practice with high sensitivity (<0.4 pg mL-1), inter-assay repeatability (∼10% CV), and rapid operation providing feedback on the progress of therapy within 4 hours. This test allowed us to perform serial monitoring of two critically ill patients with respiratory failure and to support immunomodulatory therapy using the selective cytopheretic device (SCD). We also observed clear interleukin-6 (IL-6) elevations after receiving tocilizumab (IL-6 inhibitor) while significant cytokine profile variability exists across all critically ill COVID-19 patients and to discover a weak correlation between IL-6 to clinical biomarkers, such as ferritin and C-reactive protein (CRP). Our data revealed large subject-to-subject variability in patients' response to COVID-19, reaffirming the need for a personalized strategy guided by rapid cytokine assays.

Treatment of Cytokine Storm in COVID-19 Patients With Immunomodulatory Therapy.

Observational evidence suggests that excessive inflammation with cytokine storm may play a critical role in development of acute respiratory distress syndrome (ARDS) in COVID-19. We report the emergency use of immunomodulatory therapy utilizing an extracorporeal selective cytopheretic device (SCD) in two patients with elevated serum interleukin (IL)-6 levels and refractory COVID-19 ARDS requiring extracorporeal membrane oxygenation (ECMO). The two patients were selected based on clinical criteria and elevated levels of IL-6 (>100 pg/ml) as a biomarker of inflammation. Once identified, emergency/expanded use permission for SCD treatment was obtained and patient consented. Six COVID-19 patients (four on ECMO) with severe ARDS were also screened with IL-6 levels less than 100 pg/ml and were not treated with SCD. The two enrolled patients' PaO2/FiO2 ratios increased from 55 and 58 to 200 and 192 at 52 and 50 hours, respectively. Inflammatory indices also declined with IL-6 falling from 231 and 598 pg/ml to 3.32 and 116 pg/ml, respectively. IL-6/IL-10 ratios also decreased from 11.8 and 18 to 0.7 and 0.62, respectively. The two patients were successfully weaned off ECMO after 17 and 16 days of SCD therapy, respectively. The results observed with SCD therapy on these two critically ill COVID-19 patients with severe ARDS and elevated IL-6 is encouraging. A multicenter clinical trial is underway with an FDA-approved investigational device exemption to evaluate the potential of SCD therapy to effectively treat COVID-19 intensive care unit patients.

Integrated on-site collection and detection of airborne microparticles for smartphone-based micro-climate quality control.

The rapid emergence of air-mediated diseases in a micro-climate demands on-site monitoring of airborne microparticles. The on-site detection of airborne microparticles becomes more challenging as the particles are highly localized and change dynamically over time. However, most existing monitoring systems rely on time-consuming sample collection and centralized off-site analysis. Here, we report a smartphone-based integrated microsystem for on-site collection and detection that enables real-time detection of indoor airborne microparticles with high sensitivity. The collection device, inspired by the Venturi effect, was designed to collect airborne microparticles without requiring an additional power supply. Our systematic analysis showed that the collection device was able to collect microparticles with consistent negative pressure, regardless of the particle concentration in the air sample. By incorporating a microfluidic-biochip based on inertial force to trap particles and an optoelectronic photodetector into a miniaturized device with a smartphone, we demonstrate real-time and sensitive detection of the collected airborne microparticles, such as Escherichia coli, Bacillus subtilis, Micrococcus luteus, and Staphylococcus with a particle-density dynamic range of 103-108 CFU mL-1. Because of its capabilities of minimal-power sample collection, high sensitivity, and rapid detection of airborne microparticles, this integrated platform can be readily adopted by the government and industrial sectors to monitor indoor air contamination and improve human healthcare.

A Digital Protein Microarray for COVID-19 Cytokine Storm Monitoring.

Despite widespread concern for cytokine storms leading to severe morbidity in COVID-19, rapid cytokine assays are not routinely available for monitoring critically ill patients. We report the clinical application of a machine learning-based digital protein microarray platform for rapid multiplex quantification of cytokines from critically ill COVID-19 patients admitted to the intensive care unit (ICU) at the University of Michigan Hospital. The platform comprises two low-cost modules: (i) a semi-automated fluidic dispensing/mixing module that can be operated inside a biosafety cabinet to minimize the exposure of technician to the virus infection and (ii) a 12-12-15 inch compact fluorescence optical scanner for the potential near-bedside readout. The platform enabled daily cytokine analysis in clinical practice with high sensitivity (<0.4pg/mL), inter-assay repeatability (~10% CV), and near-real-time operation with a 10 min assay incubation. A cytokine profiling test with the platform allowed us to observe clear interleukin-6 (IL-6) elevations after receiving tocilizumab (IL-6 inhibitor) while significant cytokine profile variability exists across all critically ill COVID-19 patients and to discover a weak correlation between IL-6 to clinical biomarkers, such as Ferritin and CRP. Our data revealed large subject-to-subject variability in a patient's response to anti-inflammatory treatment for COVID-19, reaffirming the need for a personalized strategy guided by rapid cytokine assays.

Microfabricated ionic liquid column for separations in dry air.

Micro gas chromatography (µGC) is a technique developed for rapid, in situ analysis of volatile organic compounds (VOCs) for environmental protection, industrial monitoring, and toxicology. While reduced µGC size and power requirements allow for increased portability, the low moisture and oxygen resilience of current microcolumn technology result in increased peak broadening and tailing for humid samples, which necessitates the use of bulky helium or nitrogen carrier gas cartridges. Developing a microcolumn to address these deficiencies is desirable to improve µGC field performance and further reduce µGC system size. This paper reports the development and characterization of a microfabricated phosphonium ionic liquid (µIL) column and demonstrates separation of both polar and nonpolar compounds using this column via analyses of alcohols, chloroalkanes, aromatics, aldehydes, fatty acid methyl esters, and alkanes. The µIL column achieved operation at temperatures up to 345 °C for fatty acid methyl ester and alkane separation. Notably, all separations in this study used dry air as the carrier gas, showing that analysis of a diverse range of compounds was possible in the presence of oxygen. After exposure to dry air for 48 h at temperatures up to 220 °C, the µIL column's peak capacity was only degraded by 8.92%, which validated its long-term robustness against oxygen. The column's separation performance was not degraded by high moisture concentrations or long-term moisture exposure, also manifesting its robustness to moisture. The high temperature, moisture, and oxygen resilience of the µIL column enable more rapid separations in varying field environments without requiring additional µGC accessories (e.g., humidity filters and carrier gas cartridges). The µIL column is therefore expected to be useful for integration into future µGC devices.

Peak focusing based on stationary phase thickness gradient.

This paper reports the development of a stationary phase thickness gradient gas chromatography (GC) column that enables analyte peak focusing and improves separation resolution. Theoretical analysis and simulation demonstrate focusing via a positive thickness gradient, i.e., the stationary phase thickness increases along the column. This effect was experimentally verified by coating a 5 m long capillary column with a film thickness varying from 34 nm at the column inlet to 241 nm at the column outlet. The column was analyzed in forward (thin to thick) and backward (thick to thin) modes and compared to a uniform thickness column with a thickness of 131 nm, using alkanes ranging from C5 to C16 and aromatics. Comparison of resolutions between forward mode and the uniform thickness column demonstrated an overall focusing rate (i.e., improvement in peak capacity) of 11.7% on alkanes and 28.2% on aromatics. The focusing effect was also demonstrated for isothermal room temperature separation of highly volatile compounds and temperature programmed separation with different ramping rates. In all cases, peak capacities from forward mode separations are higher than those from other modes, indicating the ability of a positive thickness gradient to focus analyte peaks. This thickness gradient technique can therefore be broadly applied to various stationary phases and column types as a general method for improving GC separation performance.