Energetics of high temperature degradation of fentanyl into primary and secondary products.

Fentanyl is a synthetic opioid used for managing chronic pain. Due to its higher potency (50-100×) than morphine, fentanyl is also an abused drug. A sensor that could detect illicit fentanyl by identifying its thermally degraded fragments would be helpful to law enforcement. While experimental studies have probed the thermal degradation of fentanyl, little theoretical work has been done to understand the mechanism. Here, we studied the thermal degradation pathways of fentanyl using extensive ab initio molecular dynamics simulations combined with enhanced sampling via multiple-walker metadynamics. We calculated the free energy profile for each bond suggested earlier as a potential degradation point to map the thermodynamic driving forces. We also estimated the forward attempt rate of each bond degradation reaction to gain information about degradation kinetics.

Chemical Profiling of Volatile Organic Compounds in the Headspace of Algal Cultures as Early Biomarkers of Algal Pond Crashes.

Algae ponds used in industrial biomass production are susceptible to pathogen or grazer infestation, resulting in pond crashes with high economic costs. Current methods to monitor and mitigate unhealthy ponds are hindered by a lack of early indicators that precede culture crash. We used solid-phase microextraction (SPME) coupled with gas chromatography-mass spectrometry (GC-MS) to identify volatiles emitted from healthy and rotifer infested cultures of Microchloropsis salina. After 48 hours of algal growth, marine rotifers, Brachionus plicatilis, were added to the algae cultures and volatile organic compounds (VOC) were sampled from the headspace using SPME fibers. A GC-MS approach was used in an untargeted analysis of VOCs, followed by preliminary identification. The addition of B. plicatilis to healthy cultures of M. salina resulted in decreased algal cell numbers, relative to uninfected controls, and generated trans-ß-ionone and ß-cyclocitral, which were attributed to carotenoid degradation. The abundances of the carotenoid-derived VOCs increased with rotifer consumption of algae. Our results indicate that specific VOCs released by infected algae cultures may be early indicators for impending pond crashes, providing a useful tool to monitor algal biomass production and pond crash prevention.

Thermodynamic Studies on a Hydrogen Bonded Acidic 3,5-Bis(trifluoromethyl)phenol-functionalized Polymer as a Gas Chromatography Stationary Phase for Selectively Speciating Chemical Warfare Agents.

We describe for the first time hydrogen bonded acid (HBA) polymer, poly{methyl[3-(2-hydroxyl, 4,6-bistrifluoromethyl)phenyl]propylsiloxane}, (DKAP), as stationary phase for gas chromatography (µGC) of organophosphate (OP), chemical warfare agent (CWA) surrogates, dimethylmethylphosphonate (DMMP), diisopropylmethylphosphonate (DIMP), diethylmethylphosphonate (DEMP), and trimethylphosphate (TMP), with high selectivity. Absorption of OPs to DKAP was one-to-several orders of magnitude higher relative to commercial polar, mid-polar, and nonpolar stationary phases. We also present for the first-time thermodynamic studies on the absorption of OP vapors and quantitative binding energy data for interactions with various stationary phases. These data help to identify the best pair of hetero-polar columns for a two-dimensional GC system, employing a nonpolar stationary phase as GC1 and DKAP as the GC2 stationary phase, for selective and rapid field detection of CWAs.

Volatile Metabolites Emission by In Vivo Microalgae-An Overlooked Opportunity?

Fragrances and malodors are ubiquitous in the environment, arising from natural and artificial processes, by the generation of volatile organic compounds (VOCs). Although VOCs constitute only a fraction of the metabolites produced by an organism, the detection of VOCs has a broad range of civilian, industrial, military, medical, and national security applications. The VOC metabolic profile of an organism has been referred to as its 'volatilome' (or 'volatome') and the study of volatilome/volatome is characterized as 'volatilomics', a relatively new category in the 'omics' arena. There is considerable literature on VOCs extracted destructively from microalgae for applications such as food, natural products chemistry, and biofuels. VOC emissions from living (in vivo) microalgae too are being increasingly appreciated as potential real-time indicators of the organism's state of health (SoH) along with their contributions to the environment and ecology. This review summarizes VOC emissions from in vivo microalgae; tools and techniques for the collection, storage, transport, detection, and pattern analysis of VOC emissions; linking certain VOCs to biosynthetic/metabolic pathways; and the role of VOCs in microalgae growth, infochemical activities, predator-prey interactions, and general SoH.

Pulsed Discharge Helium Ionization Detector for Highly Sensitive Aquametry.

Trace moisture quantitation is crucial in medical, civilian and military applications. Current aquametry technologies are limited by the sample volume, reactivity, or interferences, and/or instrument size, weight, power, cost, and complexity. We report for the first time on the use of a pulsed discharge helium ionization detector (PDHID-D2) (∼196 cm(3)) for the sensitive (limit of detection, 0.047 ng; 26 ppm), linear (r(2) >0.99), and rapid (< 2 min) quantitation of water using a small (0.2 - 5.0 µL) volume of liquid or gas. The relative humidity sensitivity was 0.22% (61.4 ppmv) with a limit of detection of less than 1 ng moisture with gaseous samples. The sensitivity was 10 to 100 to fold superior to competing technologies without the disadvantages inherent to these technologies. The PDHID-D2, due to its small footprint and low power requirement, has good size, weight, and power-portability (SWAPP) factors. The relatively low cost (∼$5000) and commercial availability of the PDHID-D2 makes our technique applicable to highly sensitive aquametry.

Development of a Mesoscale Pulsed Discharge Helium Ionization Detector for Portable Gas Chromatography.

Miniaturization of gas chromatography (GC) instrumentation enables field detection of volatile organic compounds (VOCs) for chembio-applications such as clandestine human transport and disease diagnostics. We fabricated a mesoscale pulsed discharge helium ionization detector (micro-PDHID) for integrating with our previously described mini-GC hardware. Stainless steel electrodes fabricated by photochemical etching and electroforming facilitated rapid prototyping and enabled nesting of inter-electrode insulators for self-alignment of the detector core during assembly. The prototype was ∼10 cm(3) relative to >400 cm(3) of a commercial PDHID, but with a comparable time to sweep a VOC peak from the detector cell (170 ms and 127 ms, respectively). Electron trajectory modeling, gas flow rate, voltage bias, and GC outlet location were optimized for improving sensitivity. Despite 40-fold miniaturization, the micro-PDHID detected 18 ng of the human emanation, 3-methyl-2-hexenoic acid with <3-fold decrease in sensitivity relative to the commercial detector. The micro-PDHID was rugged and operated for 9 months without failure.

Three-dimensional modeling and simulation of DNA hybridization kinetics and mass transport as functions of temperature in a microfluidic channel.

A 3D finite element model was developed to optimize the kinetics and mass transfer characteristics of low concentration, 18 bp ssDNA targets in bulk media solution, to 18 bp complimentary oligonucleotide probes immobilized on electrochemical detection electrodes positioned along the length of a microfluidic channel. Conditions considered in the model were fluid flow rate, diffusion time, DNA melting temperature, number of matching base pairs, and temperature of the fluid in the channel. System optimization was based on maximizing the uniformity and surface concentration of the specifically bound hybridized DNA, minimizing waste volume generation and the hybridization time. With the coupled simulation method used, the total experiment time was reduced from 150 to 60 min and the simulated results were consistent with experimental results found in the literature. A stopped flow procedure was investigated as a means to improve hybridization. This procedure can not only improve uniformity and capture efficiency, and reduce waste, but can also decrease overall signal intensity relative to continuous flow operation. Finally, the use of temperature in reducing mismatched hybridization and improving duplex stability was also successfully modeled and simulated.

Diagnostic potential of the pulsed discharged helium ionization detector (PDHID) for pathogenic Mycobacterial volatile biomarkers.

Pathogenic Mycobacteria cause diseases in animals and humans with significant economic and societal consequences. Current methods for Mycobacterial detection relies upon time- and labor-intensive techniques such as culturing or DNA analysis. Using gas chromatography and mass spectrometry, four volatile compounds (methyl phenylacetate, methyl p-anisate, methyl nicotinate and o-phenyl anisole) were recently proposed as potential biomarkers for Mycobacteria. We demonstrate for the first time the capabilities of a field-deployable, pulsed discharge helium ionization detector (PDHID) for sensing these volatiles. We determined the analytical performance of the PDHID toward these Mycobacterial volatiles. Detector performance was moderately affected over the temperature range of 150 to 350 °C. The linear dynamic range for all four analytes exceeded three orders of magnitude. The limits of detection (LOD) and quantitation (LOQ) were calculated as 150 and 450 pg respectively, for all compounds, except methyl phenylacetate (LOD and LOQ, 90 and 270 pg, respectively). Control charts revealed that the PDHID detection system was generally stable, and deviations could be traced to common causes and excluded special causes. Grob tests and ionization potential data suggest that the PDHID is capable of detecting Mycobacterial volatiles in a complex milieu such as culture headspace or breath samples from tuberculosis patients. The diagnostic potential of the PDHID is critical to our goal of a handheld, field-deployable 'sniffer' system for biological pathogens and chemical warfare agents.

In situ dissolution or deposition of Ytterbium (Yb) metal in microhotplate wells for a miniaturized atomic clock.

Current atomic clocks are burdened by size, weight, power and portability limitations to satisfy a broad range of potential applications. One critical need in the fabrication of a miniaturized atomic clock is small, low-power metallic sources. Exploiting the relatively high vapor pressure of ytterbium (Yb) and its dissolution in anhydrous ammonia, we report two independent techniques for depositing Yb inside a well micromachined into a microhotplate. Subsequent in situ evaporation of Yb from the microhotplate well serves as a low-power metallic source suitable for atomic clocks. The deposition and evaporation of Yb were confirmed using a variety of physicochemical techniques including quartz crystal microbalance, scanning electron microscopy, energy dispersive X-ray spectroscopy, and laser fluorescence. We also describe the fabrication of the microhotplate device, an integral component of our Yb-based miniature atomic clock. The Yb deposition/evaporation on a microhotplate well is thus useful as a low power Yb source during the fabrication of a miniaturized atomic clock, and this technique could be used for other applications requiring a vapor of a metal that has a moderate vapor pressure.

Thermally-activated pentanol delivery from precursor poly(p-phenylenevinylene)s for MEMS lubrication.

The synthesis of two new polyphenylene vinylene (PPV) precursor polymers which can be thermally induced to eliminate pentanol is presented. Pentanol has recently been discovered to be a very useful lubricant in MicroElectroMechanical Systems. The utilization of the elimination reaction of precursor polymers to PPV as a small molecule delivery platform has, to the best of our knowledge, not been previously reported. The elimination reactions were examined using thermal gravimetric analysis, gas chromatography, and UV-Vis spectroscopy. Using PPV precursors allows for (1) a high loading of lubricant (one molecule per monomeric unit), (2) a platform that requires relatively high temperatures (>145 °C) to eliminate the lubricant, and (3) a non-volatile, mechanically and chemically stable by-product of the elimination reaction (PPV).

Invited article: A materials investigation of a phase-change micro-valve for greenhouse gas collection and other potential applications.

The deleterious consequences of climate change are well documented. Future climate treaties might mandate greenhouse gas (GHG) emissions measurement from signatories in order to verify compliance. The acquisition of atmospheric chemistry would benefit from low cost, small size/weight/power of microsystems. In this paper, we investigated several key materials science aspects of a phase-change microvalve (PCµV) technology with low power/size/weight/cost for ubiquitous GHG sampling. The novel design, based on phase-change material low-melting-point eutectic metal alloys (indium-bismuth, InBi and tin-lead, SnPb), could be actuated at temperatures as low as 72 °C. Valve manufacturing was based on standard thick and thin-film processes and solder technologies that are commonly used in industry, enabling low-cost, high-volume fabrication. Aging studies showed that it was feasible to batch fabricate the PCµVs and store them for future use, especially in the case of SnPb alloys. Hermetic sealing of the valve prototypes was demonstrated through helium leak testing, and Mil spec leak rates less than 1 × 10(-9) atm cm(3)/s were achieved. This confirms that the sample capture and analysis interval can be greatly expanded, easing the logistical burdens of ubiquitous GHG monitoring. Highly conservative and hypothetical CO(2) bias due to valve actuation at altitude in 1 cm(3) microsamplers would be significantly below 1.0 and 2.2 ppmv for heat-treated InBi and SnPb solders, respectively. The CO(2) bias from the PCµV scales well, as a doubling of sampler volume halved the bias. We estimated the shelf life of the SnPb PCµVs to be at least 2.8 years. These efforts will enable the development of low cost, low dead volume, small size/weight microsystems for monitoring GHGs and volatile organic compounds.

A monolithically-integrated µGC chemical sensor system.

Gas chromatography (GC) is used for organic and inorganic gas detection with a range of applications including screening for chemical warfare agents (CWA), breath analysis for diagnostics or law enforcement purposes, and air pollutants/indoor air quality monitoring of homes and commercial buildings. A field-portable, light weight, low power, rapid response, micro-gas chromatography (µGC) system is essential for such applications. We describe the design, fabrication and packaging of µGC on monolithically-integrated Si dies, comprised of a preconcentrator (PC), µGC column, detector and coatings for each of these components. An important feature of our system is that the same mechanical micro resonator design is used for the PC and detector. We demonstrate system performance by detecting four different CWA simulants within 2 min. We present theoretical analyses for cost/power comparisons of monolithic versus hybrid µGC systems. We discuss thermal isolation in monolithic systems to improve overall performance. Our monolithically-integrated µGC, relative to its hybrid cousin, will afford equal or slightly lower cost, a footprint that is 1/2 to 1/3 the size and an improved resolution of 4 to 25%.

Nuclear translocation kinetics of NF-kappaB in macrophages challenged with pathogens in a microfluidic platform.

We have developed a microfluidic platform for real-time imaging of host-pathogen interactions and cellular signaling events. Host cells are immobilized in a controlled environment for optical interrogation of the kinetics and stochasticity of immune response to pathogenic challenges. Here, we have quantitatively measured activation of the toll-like receptor 4 (TLR4) pathway in RAW264.7 murine macrophage-like cells. This was achieved by measuring the cytoplasm-to-nucleus translocation kinetics of a green fluorescent protein fusion construct to the NF-kappaB transcription factor subunit RelA (GFP-RelA). Translocation kinetics in response to live bacteria and purified lipopolysaccharide (LPS) challenges were measured, and this work presents the first demonstration of live imaging of host cell infection on a microfluidic platform with quantitative analysis of an early (<0.5 h from infection) immune signaling event. Our data show that a 1,000x increase in the LPS dose led to a ~10x increase in a host cell activation metric we developed in order to describe NF-kappaB translocation kinetics. Using this metric, live bacteria challenges were assigned an equivalent LPS dose as a first step towards comparing NF-kappaB translocation kinetics between TLR4-only pathway signaling (activated by LPS) and multiple pathway signaling (activated by whole bacteria). The device also contains a unique architecture for capturing and fluidically isolating single host cells for the purpose of differentiating between primary and secondary immune signaling.