Dual electro-optic frequency comb photonic thermometry.

We report a precision realization of photonic thermometry using dual-comb spectroscopy to interrogate a π-phase-shifted fiber Bragg grating. We achieve readout stability of 7.5 mK at 1 s and resolve temperature changes of similar magnitude-sufficient for most industrial applications. Our dual-comb approach enables rapid sensing of dynamic temperature, and our scalable and reconfigurable electro-optic generation scheme enables a broad sensing range without laser tuning. Reproducibility on the International Temperature Scale of 1990 is tested, and ultimately limited by the frequency reference and check-thermometer stability. Our demonstration opens the door for a universal interrogator deployable to multiple photonic devices in parallel to potentially unravel complex multi-physical quantity measurements.

Modified Sawhorse Waveform for the Voltammetric Detection of Oxytocin.

Carbon fiber microelectrodes (CFMEs) have been used to detect neurotransmitters and other biomolecules using fast-scan cyclic voltammetry (FSCV) for the past few decades. This technique measures neurotransmitters such as dopamine and, more recently, physiologically relevant neuropeptides. Oxytocin, a pleiotropic peptide hormone, is physiologically important for adaptation, development, reproduction, and social behavior. This neuropeptide functions as a stress-coping molecule, an anti-inflammatory agent, and serves as an antioxidant with protective effects especially during adversity or trauma. Here, we measure tyrosine using the Modified Sawhorse Waveform (MSW), enabling enhanced electrode sensitivity for the amino acid and oxytocin peptide. Applying the MSW, decreased surface fouling and enabled codetection with other monoamines. As oxytocin contains tyrosine, the MSW was also used to detect oxytocin. The sensitivity of oxytocin detection was found to be 3.99 ± 0.49 nA/µM, (n=5). Additionally, we demonstrate that applying the MSW on CFMEs allows for real time measurements of exogenously applied oxytocin on rat brain slices. These studies may serve as novel assays for oxytocin detection in a fast, sub-second timescale with possible implications for in vivo measurements and further understanding of the physiological role of oxytocin.

Unrealized potential from smaller institutions: Four strategies for advancing STEM diversity.

Diversity within science, technology, engineering, and mathematics (STEM) remains disturbingly low. Relative to larger, highly funded universities, smaller schools harbor more diverse student demographics and more limited resources. Here, we propose four strategies leveraging the unique advantages of smaller institutions to advance underrepresented scholars along STEM pathways.

Polyvinyl alcohol-montmorillonite composites for water purification: Analysis of clay mineral cation exchange and composite particle synthesis.

Municipal and residential water purification rely heavily on activated carbon (AC), but regeneration of AC is costly and cannot be performed at the point-of-use. Clay minerals (CMs) comprise a class of naturally abundant materials with known capacities for analyte adsorbance. However, the gel-forming properties of CMs in aqueous suspension pose problems for these materials being used in water-purification. In this study, we have taken three main steps to optimize the use of CMs in these applications. First, we produced several variants of montmorillonite CMs to evaluate the effect of interstitial cation hydrophobicity on the ability of the CM to uptake chargecarrying organic pollutants. These variants include CMs with the following cations: sodium, hexyl(triphenyl) phosphonium, hexyadecyl(triphenyl)phosphonium, and hexyl(tributyl)phosphonium. Second, we synthesized polymer-clay mineral composite films composed of polyvinyl alcohol (PVA), crosslinked in the presence of a CM variant. These films were evaluated for their ability to uptake malachite green (MG). Finally, we developed a one-pot synthetic method for the generation of polymer-clay particles for use in a continuous column process. We synthesized polymer-clay mineral particles using the highest performing CM (based on the film experiments) and evaluated the equilibrium capacity and kinetics of MG uptake from solution.

Gold Nanoparticle Modified Carbon Fiber Microelectrodes for Enhanced Neurochemical Detection.

For over 30 years, carbon-fiber microelectrodes (CFMEs) have been the standard for neurotransmitter detection. Generally, carbon fibers are aspirated into glass capillaries, pulled to a fine taper, and then sealed using an epoxy to create electrode materials that are used for fast scan cyclic voltammetry testing. The use of bare CFMEs has several limitations, though. First and foremost, the carbon fiber contains mostly basal plane carbon, which has a relatively low surface area and yields lower sensitivities than other nanomaterials. Furthermore, the graphitic carbon is limited by its temporal resolution, and its relatively low conductivity. Lastly, neurochemicals and macromolecules have been known to foul at the surface of carbon electrodes where they form non-conductive polymers that block further neurotransmitter adsorption. For this study, we modify CFMEs with gold nanoparticles to enhance neurochemical testing with fast scan cyclic voltammetry. Au3+ was electrodeposited or dipcoated from a colloidal solution onto the surface of CFMEs. Since gold is a stable and relatively inert metal, it is an ideal electrode material for analytical measurements of neurochemicals. Gold nanoparticle modified (AuNP-CFMEs) had a stability to dopamine response for over 4 h. Moreover, AuNP-CFMEs exhibit an increased sensitivity (higher peak oxidative current of the cyclic voltammograms) and faster electron transfer kinetics (lower ΔEP or peak separation) than bare unmodified CFMEs. The development of AuNP-CFMEs provides the creation of novel electrochemical sensors for detecting fast changes in dopamine concentration and other neurochemicals at lower limits of detection. This work has vast applications for the enhancement of neurochemical measurements. The generation of gold nanoparticle modified CFMEs will be vitally important for the development of novel electrode sensors to detect neurotransmitters in vivo in rodent and other models to study neurochemical effects of drug abuse, depression, stroke, ischemia, and other behavioral and disease states.

A photonic pH sensor based on photothermal spectroscopy.

Although the determination of pH is a standard laboratory measurement, new techniques capable of measuring pH are being developed to facilitate modern technological advances. Bio-industrial processing, tissue engineering, and intracellular environments impose unique measurement requirements on probes of pH. We describe a fiber optic-based platform, which measures the heat released by chromophores upon absorption of light. The optical fibers feature fiber Bragg gratings (FBG) whose Bragg peak redshifts with increasing temperature. Using anthocyanins (pH-sensitive chromophores found in many plants), we are able to correlate visible light absorption by a solution of anthocyanins to heat released and changes in FBG signal over a pH range of 2.5 to 10. We tested the ability of this platform to act as a sensor coating the fiber within a layer of crosslinked polyethylene glycol diacrylate (PEG-DA). Incorporating the anthocyanins into the PEG, we find that the signal magnitude increases over the observed signal at the same pH in solution. Our results indicate that this platform is viable for assessing pH in biological samples and point at ways to optimize performance.

Toward 3D Printed Hydrogen Storage Materials Made with ABS-MOF Composites.

The push to advance efficient, renewable, and clean energy sources has brought with it an effort to generate materials that are capable of storing hydrogen. Metal-organic framework materials (MOFs) have been the focus of many such studies as they are categorized for their large internal surface areas. We have addressed one of the major shortcomings of MOFs (their processibility) by creating and 3D printing a composite of acrylonitrile butadiene styrene (ABS) and MOF-5, a prototypical MOF, which is often used to benchmark H2 uptake capacity of other MOFs. The ABS-MOF-5 composites can be printed at MOF-5 compositions of 10% and below. Other physical and mechanical properties of the polymer (glass transition temperature, stress and strain at the breaking point, and Young's modulus) either remain unchanged or show some degree of hardening due to the interaction between the polymer and the MOF. We do observe some MOF-5 degradation through the blending process, likely due to the ambient humidity through the purification and solvent casting steps. Even with this degradation, the MOF still retains some of its ability to uptake H2, seen in the ability of the composite to uptake more H2 than the pure polymer. The experiments and results described here represent a significant first step toward 3D printing MOF-5-based materials for H2 storage.

Perception of the importance of chemistry research papers and comparison to citation rates.

Chemistry researchers are frequently evaluated on the perceived significance of their work with the citation count as the most commonly-used metric for gauging this property. Recent studies have called for a broader evaluation of significance that includes more nuanced bibliometrics as well as altmetrics to more completely evaluate scientific research. To better understand the relationship between metrics and peer judgements of significance in chemistry, we have conducted a survey of chemists to investigate their perceptions of previously published research. Focusing on a specific issue of the Journal of the American Chemical Society published in 2003, respondents were asked to select which articles they thought best matched importance and significance given several contexts: highest number of citations, most significant (subjectively defined), most likely to share among chemists, and most likely to share with a broader audience. The answers to the survey can be summed up in several observations. The ability of respondents to predict the citation counts of established research is markedly lower than the ability of those counts to be predicted by the h-index of the corresponding author of each article. This observation is conserved even when only considering responses from chemists whose expertise falls within the subdiscipline that best describes the work performed in an article. Respondents view both cited papers and significant papers differently than papers that should be shared with chemists. We conclude from our results that peer judgements of importance and significance differ from metrics-based measurements, and that chemists should work with bibliometricians to develop metrics that better capture the nuance of opinions on the importance of a given piece of research.

Protein-templated gold nanoparticle synthesis: protein organization, controlled gold sequestration, and unexpected reaction products.

Emerging applications that exploit the properties of nanoparticles for biotechnology require that the nanoparticles be biocompatible or support biological recognition. These types of particles can be produced through syntheses that involve biologically relevant molecules (proteins or natural extracts, for example). Many of the protocols that rely on these molecules are performed without a clear understanding of the mechanism by which the materials are produced. We have investigated a previously described reaction in which gold nanoparticles are produced from the reaction of chloroauric acid and proteins in solution. We find that modifications to the starting conditions can alter the product from the expected solution-suspended colloids to a product where colloids are formed within a solid, fibrous protein structure. We have interrogated this synthesis, exploiting the change in products to better understand this reaction. We have evaluated the kinetics and products for 7 different proteins over a range of concentrations and temperatures. The key factor that controls the synthetic outcome (colloid or fiber) is the concentration of the protein relative to the gold concentration. We find that the observed fibrous structures are more likely to form at low protein concentrations and when hydrophilic proteins are used. An analysis of the reaction kinetics shows that AuNP formation occurs faster at lower protein (fiber-forming) concentrations than at higher protein (colloid-forming) concentrations. These results contradict traditional expectations for reaction kinetics and protein-fiber formation and are instructive of the manner in which proteins template gold nanoparticle production.

The chemical, mechanical, and physical properties of 3D printed materials composed of TiO2-ABS nanocomposites.

To expand the chemical capabilities of 3D printed structures generated from commercial thermoplastic printers, we have produced and printed polymer filaments that contain inorganic nanoparticles. TiO2 was dispersed into acrylonitrile butadiene styrene (ABS) and extruded into filaments with 1.75 mm diameters. We produced filaments with TiO2 compositions of 1%, 5%, and 10% (kg/kg) and printed structures using a commercial 3D printer. Our experiments suggest that ABS undergoes minor degradation in the presence of TiO2 during the different processing steps. The measured mechanical properties (strain and Young's modulus) for all of the composites are similar to those of structures printed from the pure polymer. TiO2 incorporation at 1% negatively affects the stress at breaking point and the flexural stress. Structures produced from the 5 and 10% nanocomposites display a higher breaking point stress than those printed from the pure polymer. TiO2 within the printed matrix was able to quench the intrinsic fluorescence of the polymer. TiO2 was also able to photocatalyze the degradation of a rhodamine 6G in solution. These experiments display chemical reactivity in nanocomposites that are printed using commercial 3D printers, and we expect that our methodology will help to inform others who seek to incorporate catalytic nanoparticles in 3D printed structures.

Protein-based ferrogels.

We present a novel synthesis in which hemoglobin and Fe(2+) react, in the presence of KNO3 and KOH, to produce protein microgels that contain magnetic iron oxide nanoparticles. The synthesis results in microgels with polymer properties (denaturing and glass transition temperatures) that are consistent with the dried protein. The iron oxide nanoparticles that exhibit an average diameter of 22nm, are ferrimagnetic, and display properties consistent with Fe3O4. The multiple functional capabilities displayed by these materials: biocompatibility, magnetism, dye uptake and controlled release, and other properties archetypal of hydrogels, will make the magnetic hydrogels attractive for a number of biomedical applications.

Concurrent zero-dimensional and one-dimensional biomineralization of gold from a solution of Au3+ and bovine serum albumin.

A technique was developed for preparing a novel material that consists of gold nanoparticles trapped within a fiber of unfolded proteins. These fibers are made in an aqueous solution that contains HAuCl4 and the protein, bovine serum albumin (BSA). By changing the ratio of gold to BSA in solution, two different types of outcomes are observed. At lower gold to BSA ratios (30-120), a purple solution results after heating the mixture at 80 °C for 4 h. At higher gold to BSA ratios (130-170), a clear solution containing purple fibers results after heating the mixture at 80 °C for 4 h. UV-Vis spectroscopy and light scattering techniques show growth in nanocolloid size as gold to BSA ratio rises above 100. Data indicate that, for the higher gold to BSA ratios, the gold is sequestered within the solid material. The material mass, visible by eye, appears to be an aggregation of smaller individual fibers. Scanning electron microscopy and transmission electron microscopy indicate that these fibers are primarily one-dimensional aggregates, which can display some branching, and can be as narrow as 400 nm in size. The likely mechanism for the synthesis of the novel material is discussed.

Communicating chemistry for public engagement.

The communication of chemistry to wider society is difficult because of 'chemophobia', its inherent complexity and its lack of unifying grand themes. To engage with citizens about the benefits and related dangers of the field, chemists must improve their dialogue with broader sections of the public ­ but how?

Electron tunneling through sensitizer wires bound to proteins.

We report a quantitative theoretical analysis of long-range electron transfer through sensitizer wires bound in the active-site channel of cytochrome P450cam. Each sensitizer wire consists of a substrate group with high binding affinity for the enzyme active site connected to a ruthenium-diimine through a bridging aliphatic or aromatic chain. Experiments have revealed a dramatic dependence of electron transfer rates on the chemical composition of both the bridging group and the substrate. Using combined molecular dynamics simulations and electronic coupling calculations, we show that electron tunneling through perfluorinated aromatic bridges is promoted by enhanced superexchange coupling through virtual reduced states. In contrast, electron flow through aliphatic bridges occurs by hole-mediated superexchange. We have found that a small number of wire conformations with strong donor-acceptor couplings can account for the observed electron tunneling rates for sensitizer wires terminated with either ethylbenzene or adamantane. In these instances, the rate is dependent not only on electronic coupling of the donor and acceptor but also on the nuclear motion of the sensitizer wire, necessitating the calculation of average rates over the course of a molecular dynamics simulation. These calculations along with related recent findings have made it possible to analyze the results of many other sensitizer-wire experiments that in turn point to new directions in our attempts to observe reactive intermediates in the catalytic cycles of P450 and other heme enzymes.

Protein binding and the electronic properties of iron(II) complexes: an electrochemical and optical investigation of outer sphere effects.

Metalloenzymes and electron transfer proteins influence the electrochemical properties of metal cofactors by controlling the second-sphere environment of the protein active site. Properties that tune this environment include the dielectric constant, templated charge structure, van der Waals interactions, and hydrogen bonds. By systematically varying the binding of a redox-active ligand with a protein, we can evaluate how these noncovalent interactions alter the electronic structure of the bound metal complex. For this study, we employ the well-characterized avidin-biotin conjugate as the protein-ligand system, and have synthesized solvatochromic biotinylated and desthiobiotinylated iron(II) bipyridine tetracyano complexes ([Fe(BMB)(CN)(4)](2-) (1) and [Fe(DMB)(CN)(4)](2-) (2)). The binding affinities of 1 and 2 with avidin are 3.5 × 10(7) M(-1) and 1.5 × 10(6) M(-1), respectively. The redox potentials of 1 and 2 (333 mV and 330 mV) shift to 193 mV and 203 mV vs Ag/AgCl when the complex is bound to avidin and adsorbed to a monolayer-coated gold electrode. Upon binding to avidin, the MLCT1 band red-shifts 20 nm for 1 and 10 nm for 2. Similarly, the MLCT2 band for 1 red-shifts 7 nm and the band for 2 red-shifts 6 nm. For comparison, the electronic properties of 1 and 2 were investigated in organic solvents, and similar shifts in the MLCT bands and redox potentials were observed. An X-ray crystal structure of 1 bound to avidin was obtained, and molecular dynamics simulations were performed to analyze the protein environment of the protein-bound transition metal complexes. Our studies demonstrate that changes in the binding affinity of a ligand-receptor pair influence the outer-sphere coordination of the ligand, which in turn affects the electronic properties of the bound complex.

Probing melittin helix-coil equilibria in solutions and vesicles.

Melittin is a toxic, amphipathic peptide that rearranges from a random coil in solution to a helical structure upon binding to cell membranes or lipid vesicles. We have found that mutation of the valine at position five of the peptide to a phenylalanine or 3-nitrotyrosine induces aggregation and helix formation at low concentrations (20-80 microM). Donor-acceptor distances obtained from analyses of fluorescence energy transfer kinetics experiments with the 3-nitrotyrosine mutant indicate that both coil and helix structures are present in 2 and 20 microM aqueous solutions. The helical peptide population increases upon addition of phospholipid vesicles or in high ionic strength solutions.

Synthesis and electrochemical characterization of a transition-metal-modified ligand-receptor pair.

The energetics of weak interactions (van der Waals forces, hydrogen bonding) are difficult to quantify in biological ligand-receptor pairs. Insight into the biochemical role these forces play is critical to an understanding of signal transduction events and the drug discovery process. Ruthenium pentaammine and iron tetracyano complexes modified with either biotin or desthiobiotin have been synthesized and characterized. These modified biological ligands bind to the protein avidin in a manner similar to that of native biotin. Experiments using redox mediators show that the avidin-bound complexes are electrochemically accessible.