Μm Dia Research Articles

Mass transfer and hydrodynamic studies in a 100 μm diameter microfluidic channel in a rotated helical configuration

A simple 3D rotated microfluidic mixer design is reported with evaluation of hydrodynamic and mass transfer performance. Proposed device had a minimalistic configuration of 3 turns, rotated in x, y, and z planes. The helical mixer volume was only 3.14 μL due to usage of 100 μm dia micro bore tubing. The proposed device was different from conventional CFI and its variants. The analysis for hydrodynamic performance indicated a massive specific interfacial area, much more than for the 50 mm centrifugal extractor with the same PUREX aqueous-organic pair. Higher volumetric amass transfer coefficients were reported for the proposed device as compared to conventional mixers (impellers and Taylor-Couette mixers). Energy dissipation values were also reported to be much higher than that of a contemporary annular centrifugal extractor. Mixing-time values (tm) were estimated at least two-order lower than residence time values (τ). Proposed design complied all the four directives of the concurrent PI paradigm.

Cultural, Morphological and Pathogenic Variability in the Colletotrichum capsici Isolates, Inciting Anthracnose and Fruit rot of Chilli (Capsicum annuum L.) in different Agro-Climatic Zones of Kerala, India

Aims: To study the cultural, morphological and pathogenic variability existing among the pathogen isolates of Colletotrichum capsici, inciting anthracnose and fruit rot of chilli in Kerala. Study Design: Completely randomized design (CRD). Place and Duration of Study: Department of Plant Pathology, College of Agriculture (Kerala Agricultural University), Vellayani, Thiruvananthapuram during 2018-2019. Methodology: A survey was conducted in the five agro-climatic zones (ACZs) of Kerala viz., Northern zone, Central zone, Special problem zone, High range zone and Southern zone to assess the incidence and severity of anthracnose disease. The various symptoms in the surveyed locations were also noted. Pathogen isolates were grown in PDA medium in the laboratory and colony characters (colour and mycelial growth rate of pathogen colonies) were observed. Also, the morphological characters viz., mycelial width, shape and size of conidia, acervular diameter, number and size of setae, appressorial size were recorded. Results: Maximum anthracnose incidence of 90 per cent and severity of 52.60 per cent were noticed at Regional Agricultural Research Station (RARS), Pilicode (Northern zone). Characteristic leaf spot, fruit rot and die-back symptoms were observed in the survey locations. Pathogen colonies showed different shades of white, off-white to grey turning brown or black with regular or irregular margins and concentric rings of black acervuli in the potato dextrose agar (PDA) medium. The diameter of growth of C. capsici isolates ranged from 7.20 to 8.60 cm at 7 days after incubation. All the C. capsici isolates initiated hyaline mycelium having a width of 1.73 - 2.36 µm and produced numerous sickle shaped conidia with a size range of 19.42 - 20.46 µm × 2.16 - 3.09 µm. Black coloured, circular or ellipsoidal acervuli (122.14 - 189.08 µm dia.) had 20 – 46 setae of length 74.13 to 107.30 µm. Also, brown or black appressoria of size 8.64 - 12.64 µm × 5.54 - 7.84 µm were formed in slide culture. Cc3 from College of Agriculture, Vellanikkara was obtained as the most virulent isolate producing a lesion size of 1.13 cm and PDI of 45.33 in the artificially inoculated chilli fruits (var. Vellayani Athulya) at 5 days after inoculation. Conclusion: All the nine C. capsici isolates exhibited variability in their cultural, morphological and pathogenic characteristics. Variability in phytopathogenic fungi helps in identifying novel and sustainable control methods to tackle the diseases incited by them. Understanding pathogen variability provides new insights for developing effective disease management methods. This will help in promoting sustainable agriculture and preventing severe crop losses.

Effective Optical Image Assessment of Cellulose Paper Immunostrips for Blood Typing.

Novel high-performance biosensing devices, based on a microporous cellulose matrix, have been of great interest due to their high sensitivity, low cost, and simple operation. Herein, we report on the design and testing of portable paper-based immunostrips (IMS) for in-field blood typing in emergencies requiring blood transfusion. Cellulose fibrils of a paper membrane were functionalized with antibodies via supramolecular interactions. The formation of hydrogen bonds between IgM pentamer and cellulose fibers was corroborated using quantum mechanical calculations with a model cellulose chain and a representative amino acid sequence. In the proposed immunostrips, paper with a pore size of 3 µm dia. was used to enable functionalization of its channels with antibody molecules while blocking the red blood cells (RBC) from channel entering. Under the optimized test conditions, all blood types of AB0 and Rh system could be determined by naked eye examination, requiring only a small blood sample (3.5 µL). The durability of IgM immunostrips against storing has been tested. A new method of statistical evaluation of digitized blood agglutination images, compatible with a clinical five-level system, has been proposed. Critical parameters of the agglutination process have been established to enable future development of automatic blood typing with machine vision and digital data processing.

Carbon allotropes form a hybrid material: Synthesis, characterization, and molecular dynamics simulation of novel graphene-glassy carbon hybrid material

Using graphene (Gr) and glassy carbon (GC) as building blocks, we introduce a hybrid material with superior electrical and electrochemical properties. The formation of the hybrid material is demonstrated and validated through (a) synthesis process, (b) comprehensive morphological and surface characterizations, and (b) molecular dynamics simulation. Chemical bonds and surface morphology were characterized through FTIR and SEM, respectively, while its nanostructure was imaged through scanning transmission electron microscopy (STEM) and qualitatively compared with classical molecular dynamics simulations outcomes. In addition, electron energy loss spectroscopy (EELS) provided insights to chemical composition of the nanostructure where a combination of sp2 and sp3 characteristics were dominant at the interface of Gr and GC. Taken together, the characterization and simulation outcomes confirm that 5- 6-, and 7- membered carbon rings formed a predominantly sp2 hybridized bond at the Gr and GC interface, contributing to the formation of a unique and novel hybrid material. The hybrid material's capability to form 3D and complex components with active functional groups together with its high charge storage capacity (56.5 ± 0.7 mC/cm2) and low impedance (∼8.95 kΩ @ 1 KHz for 300 μm dia. microelectrode) will offer new possibilities in advanced semi-conductor devices and ultra-sensitive biochemical sensors.

Characterization and bio-efficacy of entomopathogenic Beauveria associated with cuticle-degrading enzymes to restrain sucking pest Bemisia tabaci.

The entomopathogenic Beauveria spp. were acquired from insect cadavers and soil rhizosphere of cotton, groundnut, and castor. Among Beauveria, five spp. derived from infected insects, eight Beauveria found from soil, and one strain of Beauveria bassiana collected from MTCC 9544. Beauveria were characterized for morphology and cuticle-degrading enzyme activity associated with virulence against Bemisia tabaci. The colony morphology, conidial arrangement, size, and shape confirmed all isolates as Beauveria. The chitinase (EC 3.2.1.14) and lipase (EC 3.1.1.3) activities were observed the highest in Beauveria JAU2, while higher protease (EC 3.4.21.4) activity found in JAU4 followed by JAU2 at 240h. The bio-efficacy of Beauveria (1 × 107 conidia.ml-1) illustrated that potent JAU2 was examined with the highest % mortality and corrected mortality of B. tabaci at 144h followed by JAU1. The LC90 and LC50were determined from potent (JAU1 and JAU2) and weak (JAU6), and it was found the lowest in JAU2. The most potent Beauveria JAU2, isolated from insect cadaver (Harmivora armigera), was illustrated higher virulence than other isolates. The Beauveria JAU2 were recognized as Beauveria bassiana based on the shape of conidia and size (2.00 to 2.09µm dia) as examined in SEM. Study insight into recognition of potent Beauveria bassiana JAU2 was linked with cuticle-degrading enzyme activity for insecticidal action. The JAU2 isolate established the most positive correlation (P0.01: 0.864) between chitinase activity and corrected mortality of insect.

Ballistic delivery of compounds to inner layers of the cornea is limited by tough mechanical properties of stromal tissue

The barrier characteristics of the cornea are interrogated using the impact of micro-particles into ex vivo porcine cornea. Using a commercial gene gun (BioRad; PDS1000), microparticles were accelerated and made to embed in target materials: either ballistic gelatin as a reference or corneal tissue. Statistical analysis of penetration of polydisperse spherical microparticles (5–22 μm dia.) with density of 2.5 g/cc, 4.2 g/cc, and 7.8 g/cc (soda-lime glass, barium-titanate glass and stainless steel; more limited examination of 1.1 g/cc polyethylene and 19.2 g/cc tungsten) spanned almost two decades in kinetic energy. Penetration profiles in ballistic gelatin show that the particle embedding depth is sensitive to particle size and density. In the cornea, penetration is a weak function of size and density, and the corneal stroma is an effective stopping medium for high velocity microparticles. Despite the high water content of corneal tissue (76% w/w) compared to the stratum corneum of skin (40% w/w), the resistance to penetration of the cornea is comparable to what is seen in previous research of penetration in skin tissue. Using low density polymer particles with a therapeutic agent payload, it is demonstrated that bulk material can be ballistically delivered to the central 1 cm2 of the corneal epithelium in an even layer with high bioavailability of therapeutic compound.

Electrochemical PEDOT Sensor for Antioxidantsin Beverages and Milks

Introduction The conducting polymer PEDOT (poly(3,4-ethylenedioxythiophene)) as an electrochemical sensor element possesses redox-mediating properties that allow excellent separation of signals due to antioxidants present in beverages such as teas and coffee [1]. This includes the phenolic acids present in white wines, with specific features noted for nanostructured microelectrodes [2]. Excellent separation of signals due to ascorbic acid and sulfites, alongside the response due to the oxidation of polyphenols in beverages, has been achieved using the redox-mediating properties of PEDOT [3]. Method PEDOT films were grown by cycling to +1.2 V (Ag/AgCl) on 3 mm dia. glassy carbon electrodes and 10 µm dia. gold microelectrodes in 0.1 M EDOT/ 0.1 M LiClO4 in propylene carbonate at 100 mV s-1. The electrodes were then transferred to undiluted milks (c. pH 6.5), or to an aqueous 0.1 M sodium phosphate buffer (PBS) at pH 6.6 containing uric acid and ascorbic acid standards, prior to testing by cyclic voltammetry (CV). A background PEDOT curve was taken in the PBS solution and subtracted from the voltammograms obtained for the milk samples. Results and Conclusions The PEDOT sensor showed an excellent response for the oxidation of uric acid, with an anodic peak seen at 350 mV (Ag/AgCl), taken at pH 6.6, with both uric acid standards and undiluted milks [4]. A small peak due to ascorbic acid was at times located close to 0 mV, enabling the simultaneous detection of the two antioxidants. Very good linear relationships were obtained between peak current intensities and concentrations in the range of 6-100 μM for uric acid and 30-500 μM for ascorbic acid. The newly developed sensor was then successfully applied to 36 commercial milk samples for a fast voltammetric determination of uric acid and ascorbic acid concentration. An independent HPLC analysis was also performed immediately after running the same milk samples, with a pre-treatment step to remove fats and proteins from the milk. The average difference between the results for uric acid from the two methods was 7%, demonstrating an acceptable degree of agreement between the two measurement methods. At the same time the results were obtained much more rapidly with the electrochemical method than in the lengthy HPLC procedure.The polyphenols present in teas, chocolate and flavoured milks present additional analytical challenges, due to strong adsorption effects. PEDOT-modified electrodes have been successfully developed to quantify flavonoids present in chocolate-flavoured milks, and hydroxycinnamic acids present in coffee-flavoured milks. Strong adsorption effects were seen with regular and flavoured milks at PEDOT microelectrodes. Rather than a diffusion-controlled plateau current, peaks with current densities up to 1000 times greater than observed at the corresponding macroelectrodes were observed, consistent with an extremely high surface area and fractal-type growth of PEDOT at microelectrodes [2].

Changes of the acute and chronic toxicity of three antimicrobial agents to Daphnia magna in the presence/absence of micro-polystyrene

The effects of microplastics on aquatic organisms are drawing growing attention, but little has been focused on their effects on the toxicity of other chemicals. In this study, we examined the acute and chronic toxicity of micro-polystyrene (5.8 μm dia.), and its effects on the toxicity of three antimicrobial agents (triclosan, triclocarban and methyl-triclosan) to Daphnia magna. Results indicated that polystyrene had a low acute toxicity with an EC50 of 36.5 mg/L. The presence of polystyrene (1 mg/L) did not produce significant effect on the acute toxicity of three chemicals, because the 95% confidence intervals of their EC50 values had a large overlap of 11.3%–48.3%. For the 21 day chronic toxicity, polystyrene alone had significant toxicity with concentrations of at least 2 mg/L, which prolonged the time of the first brood, limited the number of broods, and reduced the total number of neonates. Compared with the chemicals alone, the addition of polystyrene enhanced their reproduction toxicity. Based on the various reproduction indicators, an intrinsic rate of natural increase (rm) was calculated to assess the rate of population growth. Results suggested that the rm values of three chemicals decreased in the presence of PS, and further decreased with increasing PS concentrations. Among the three chemicals, methyl-triclosan was the most affected. These results suggested that the presence of microplastics would exacerbate the detrimental influence of pollutants on Daphnia magna.

Nanoaperture fabrication via colloidal lithography for single molecule fluorescence analysis.

In single molecule fluorescence studies, background emission from labeled substrates often restricts their concentrations to non-physiological nanomolar values. One approach to address this challenge is the use of zero-mode waveguides (ZMWs), nanoscale holes in a thin metal film that physically and optically confine the observation volume allowing much higher concentrations of fluorescent substrates. Standard fabrication of ZMWs utilizes slow and costly E-beam nano-lithography. Herein, ZMWs are made using a self-assembled mask of polystyrene microspheres, enabling fabrication of thousands of ZMWs in parallel without sophisticated equipment. Polystyrene 1 μm dia. microbeads self-assemble on a glass slide into a hexagonal array, forming a mask for the deposition of metallic posts in the inter-bead interstices. The width of those interstices (and subsequent posts) is adjusted within 100–300 nm by partially fusing the beads at the polystyrene glass transition temperature. The beads are dissolved in toluene, aluminum or gold cladding is deposited around the posts, and those are dissolved, leaving behind an array ZMWs. Parameter optimization and the performance of the ZMWs are presented. By using colloidal self-assembly, typical laboratories can make use of sub-wavelength ZMW technology avoiding the availability and expense of sophisticated clean-room environments and equipment.

A novel polymer electrolyte fuel cell flow-field: The through-plane array

Flow-field plates are essential components for polymer electrolyte fuel cells (PEFCs), the most common types incorporating parallel or serpentine channels. A novel flow-field, the ‘through-plane array’ (TPA), is presented which provides significantly improved performance at higher current density with the advantage of lower backpressure. The concept modifies a conventional flow-field operating in dead-ended mode and incorporates an array of holes (<10 μm dia.) in the land areas that allows gas exit. In this case, the cathode is the focus, as this electrode suffers from the greatest reactant access and water flooding challenges. By forcing gas to enter the gas diffusion layer (GDL) in order to exit, the reactant is exposed to areas under the land and removal of product water is enhanced.

Deposition of Multiscale Thickness Graphene Coating by Harnessing Extreme Heat and Rapid Quenching: Toward Commercialization

Deposition of graphene as a coating material over large-scale areas is an intense topic of research because of complexities involved in the existing deposition techniques. Higher defects and compromised properties restricted in realizing the full potential of graphene coating. This work aims to deposit graphene coatings by adopting a traditional technique, that is, plasma spraying, which has inherent merits of extremely high cooling rate (∼106 K/s) and low plasma exposure time (∼0.1-10 μs). Graphene nanoplatelets (GNPs) were spray-dried into spherical agglomerates (∼60 μm dia.) and coatings were deposited over a wide range of surfaces. Continuous monitoring of temperature and velocity of in-flight GNPs was done using a diagnostic sensor. Deposition of GNP coatings was the result of striking of quasi-2D melted GNPs with higher velocity (∼197 m/s) toward the substrate. Postcharacterizations confirmed that GNPs did not collapse even after being exposed to harsh environments in plasma. Instead, high temperatures proved to be beneficial in purifying the commercial GNPs. The coatings were transparent even in the short-wavelength infrared region and remained electrically conductive. A proof-of-concept was established by carrying out preliminary corrosion and antifriction tests. Outstanding reduction of ∼3.5 times in corrosion rate and 3 times in coefficient of friction was observed in GNP-deposited coating. It is envisaged that graphene coating by plasma spraying can bring a revolution in commercial sectors.

Influence of wire feed rate on microslit width fabricated by wire ECM process

Miniaturisation of metallic structures has become a prime issue and to meet high demand, modern fabricators extensively use different micro machining techniques. Wire electrochemical machining (wire ECM) is such a process of removing excess material electrochemically. However, the process is still new and further research is needed. Hence, the present work aims in developing suitable wire ECM setup to find out the influence of wire feed rate at varying voltage settings on corresponding width of the generated microslits. For this, experimentations have been carried out with 50 μm dia tungsten wire and machined micro features have been carefully observed under optical microscope. Additionally, the experimental results have been represented graphically where the minimum average width of the microslit is found to be 83.117 μm with an aspect ratio of 1.2. Moreover, complex microfeature with varying width has been fabricated by changing corresponding feed values in a single run.

Two Phase Flow Modeling and Characterization of Oxygen Bubbles in PEM Water Electrolysis Cells

The formation, growth, and stability of oxygen bubbles inside the porous transport layer (PTL) pores of a polymer electrolyte membrane water electrolysis (PEMWE) cell have been modeled. In a PEMWE cell, O2 bubbles form and grow inside the anode catalyst layer (ACL) and PTL pores. The most critical impact of the O2 bubbles on the overall performance is the screening of the ACL surface. Semi-empirical relations for the current density-surface coverage for gas evolving electrodes have previously been developed [1] and were used for our PEMWE modeling [2]. This screening effect has been evaluated as an overpotential term, and the results were used to predict the effects of the catalyst and PTL properties on the electrolysis cell performance. The fluctuations in the cell current density were used to identify different types of bubbles and their detachment frequency from the anode electrode. In this work, the anode catalyst surface has been described as a smooth, planar and horizontal plane. The PTL pores are described as identical straight hydrophilic cylinders with 1-mm height. Such a structure resembles tunable PTL structures such as those synthesized by Kang et al. [3]. Stable O2 bubble nuclei form mainly at the intersection of the anode catalyst layer and the PTL pore wall [3,4]. Our modeling results show the effects of three different types of bubbles in a PEMWE cell: i) nucleation-driven, ii) drag-driven, and iii) buoyancy-driven bubbles. Figure 1 shows the relative lifetime and overpotential effects of the O2 bubbles in a PEMWE with a PTL consisting of 11 μm dia. pores operated at a fixed temperature of 80°C and a balanced pressure of 1 bar [5]. Comparing the current density fluctuations in chronoamperometry experiments with the bubble detachment frequencies obtained through modeling provides a distribution of different types of bubbles in the electrolysis cell. These frequencies vary according to the PTL structure and the PEMWE cell operating conditions. Understanding of bubble growth and detachment mechanisms are of significant importance for reduction of mass transport-related losses and enhancement of PEMWE performance.

Two Phase Flow Modeling and Characterization of Oxygen Bubbles in PEM Water Electrolysis Cells

The formation, growth, and stability of oxygen bubbles inside the porous transport layer (PTL) pores of a polymer electrolyte membrane water electrolysis (PEMWE) cell have been modeled. In a PEMWE cell, O2 bubbles form and grow inside the anode catalyst layer (ACL) and PTL pores. The most critical impact of the O2 bubbles on the overall performance is the screening of the ACL surface. Semi-empirical relations for the current density-surface coverage for gas evolving electrodes have previously been developed [1] and were used for our PEMWE modeling [2]. This screening effect has been evaluated as an overpotential term, and the results were used to predict the effects of the catalyst and PTL properties on the electrolysis cell performance. The fluctuations in the cell current density were used to identify different types of bubbles and their detachment frequency from the anode electrode. In this work, the anode catalyst surface has been described as a smooth, planar and horizontal plane. The PTL pores are described as identical straight hydrophilic cylinders with 1-mm height. Such a structure resembles tunable PTL structures such as those synthesized by Kang et al. [3]. Stable O2 bubble nuclei form mainly at the intersection of the anode catalyst layer and the PTL pore wall [3,4]. Our modeling results show the effects of three different types of bubbles in a PEMWE cell: i) nucleation-driven, ii) drag-driven, and iii) buoyancy-driven bubbles. Figure 1 shows the relative lifetime and overpotential effects of the O2 bubbles in a PEMWE with a PTL consisting of 11 μm dia. pores operated at a fixed temperature of 80°C and a balanced pressure of 1 bar [5]. Comparing the current density fluctuations in chronoamperometry experiments with the bubble detachment frequencies obtained through modeling provides a distribution of different types of bubbles in the electrolysis cell. These frequencies vary according to the PTL structure and the PEMWE cell operating conditions. Understanding of bubble growth and detachment mechanisms are of significant importance for reduction of mass transport-related losses and enhancement of PEMWE performance.

Influence of spinning parameters on synthesis of alumina fibres by centrifugal spinning

The present study investigates the synthesis of alumina fibres of 5–15 µm dia. by sol-gel process through centrifugal spinning. Among various spinning parameters such as rpm, viscosity, humidity, chamber temperature etc., effect of rpm and viscosity on quality of spun fibres was examined in order to spin less defective (less shots) fibres. From the rpm vs viscosity experiments, it was concluded that viscosity between 13 and 42 Pa.s with 3000 rpm was favourable for obtaining fibres containing less shots. It was shown that besides viscosity, refractive index and percent weight loss of the aged sol can be used as indicator for determining spinnability of alumina precursor sols. Influence of only preheating and continuous heating of the chamber during spinning were also investigated and it was found that only preheating did not help in producing fibres. Besides this, influence of hot air blower (HAB) aligned in different directions with respect to the spinnerette, on fibre quality was tested. It was observed that the quality of fibres did not change due to change in HAB direction.

Hydrodynamic blood cell separation using fishbone shaped microchannel for circulating tumor cells enrichment

Cancer patients have a range of from 1 to 1000 circulating tumor cells (CTCs) with 5 × 109 erythrocytes in 1 ml volume of their peripheral blood. Due to this rarity of CTCs, a pre-process for the enrichment of CTCs in blood sample is required. For a fast and passive CTCs enrichment process, we developed a fishbone shape microchannel, which has geometry of 50 repeated 45° angled expansion and contraction channels. The enrichment process can be achieved from the differences between the dominant forces with respect to the diameter of each type of cell. For the feasibility test, we used three different sizes of microparticles of 2 μm, 6 μm, and 13 μm dia. to mimic platelet, erythrocytes, and leukocyte or human breast cancer cells, respectively. The results show that the smaller particles (2 μm or 6 μm dia.) laterally move to both side wall directions by dominant inertial lift force, whereas the larger particle (13 μm dia.) focused on the centerline of the channel by dominant momentum change-induced inertial force under appropriate fluid flow velocity. We also performed a cell separation experiment using MCF-7 and a human erythrocyte mixture. The recovery efficiency of MCF-7 is over 98% at the detection window with a high throughput (250 μl/min).

Surface Morphology and Optical Properties of Aluminosilicate Glass Manufactured by Physical and Chemical Etching Process

Surface morphology and optical properties such as transmittance and haze effect of glass etched by physical and chemical etching processes were investigated. The physical etching process was carried out by pen type sandblasting process with 15~20 μm dia. of Al2O3 media; the chemical etching process was conducted using HF-based mixed etchant. Sandblasting was performed in terms of variables such as the distance of 8 cm between the gun nozzle and the glass substrate, the fixed air pressure of 0.5bar, and the constant speed control of the specimen stage. The chemical etching process was conducted with mixed etching solution prepared by combination of BHF (Buffered Hydrofluoric Acid), HCl, and distilled water. The morphology of the glass surface after sandblasting process displayed sharp collision vestiges with nonuniform shapes that could initiate fractures. The haze values of the sandblasted glass were quantitatively acceptable. However, based on visual observation, the desirable Anti-Glare effect was not achieved. On the other hand, irregularly shaped and sharp vestiges transformed into enlarged and smooth micro-spherical craters with the subsequent chemical etching process. The curvature of the spherical crater increased distinctly by 60 minutes and decreased gradually with increasing etching time. Further, the spherical craters with reduced curvature were uniformly distributed over the etched glass surface. The haze value increased sharply up to 55 % and the transmittance decreased by 90 % at 60 minutes of etching time. The ideal haze value range of 3~7 % and transmittance value range of above 90 % were achieved in the period of 240 to 720 minutes of etching time for the selected concentration of the chemical etchant.

Custom designed metal anchored SnO2 sensor for H2 detection

Herein, we report sputter deposited SnO2 thin film based sensor structures anchored with different metal clusters (Pt, Au, Cu, In, W and Cr) for efficient detection of H2 gas. Controlled decoration of ∼9 nm thin Pt clusters having 200 μm dia on the top surface of SnO2 thin film exhibited dramatically outperformed results. The Pt/SnO2 sensor shows an improvement upto two orders in sensing response S∼1.68 × 102 towards 500 ppm of H2 gas at a relatively low operating temperature of 110 °C. The sensor exhibited excellent gas sensing characteristics in the concentration range 2–5000 ppm H2 at operating temperatures of 70–230 °C. The sensor revealed negligible cross sensing signals against other interfering gases like acetone, IPA, TCE, NO2, methane, LPG, petrol and NH3. The structural and surface morphological studies of SnO2 thin films were carried out. Reliability analysis and selectivity demonstration by Pt/SnO2 sensor was found to be consistent over long term. The work envisions towards realization of targeted H2 detection system at low temperature.

Electrode modifications to lower electrode impedance and improve neural signal recording sensitivity

Objective. Although electrode size should be miniaturized to provide higher selectivity for neural signal recording and to avoid tissue damage, small sized electrodes induce high impedance, which decreases recording quality. In this work, the electrode surface was modified to increase the effective surface area to lower the electrode impedance and to improve the neural signal detection quality by optimizing plasma conditions. Approach. A tetrafluoromethane (CF4) plasma was used to increase the effective surface area of gold electrode sites of polyimide-based neural probes. In vitro electrode impedance and in vivo neural signal recording and stimulation were characterized. Main results. For 15 μm diameter (dia.) electrode size, the average surface roughness could be increased from 1.7 to 22 nm after plasma treatment, and the electrode impedance was decreased by 98%. Averaged background noise power in the range of 1 to 1000 Hz was decreased to −106 dB after the 30 μm dia. electrodes were plasma modified—lower than the noise level of −86 dB without plasma treatment. Neural probes with plasma-modified electrode sites of 15 and 30 μm dia. were implanted to the anterior cingulate cortex (ACC) region for acute recording of spontaneous and electrical evoked local field potential (LFP) of neural signals. Spontaneous LFP recorded in vivo by the plasma-modified electrodes of 30 μm dia. was two times higher compared to electrodes without treatment. For a stimulation current of 400 μA, electrically evoked LFP recorded by the plasma-modified electrodes was seven times higher than those without plasma exposure. Significance. A controllable technology was developed to increase the effective surface area of electrodes using a CF4 plasma. Plasma-modified electrodes improved the quality of the neural probe recording and more sensitive to record spontaneous and evoked LFP in the ACC region.

The 2015 Colin G. Fink Summer Research Fellowship -- Summary Report: Crystal Orientation Effects on the Oxygen Evolution Reaction on Iridium Oxide

1The electrochemical behavior of metal catalysts is strongly dependent on the structure of the electrode material. 2,3 Therefore a deeper understanding of the relation between the electrode surface structure, in terms of crystal orientation, and its corresponding OER activity, is required in order to find the optimum form of iridium oxide catalysts with enhanced catalytic activity and stability. In this project, a polycrystalline iridium (p-Ir) wire (250 μm dia) was subjected to annealing and electrochemical etching to increase grain size and make the grain