Polymer microcantilever biochemical sensors with integrated polymer composites for electrical detection

Micro fabricated sensors based on nanomechanical motion with piezoresistive electrical readout have become a promising biochemical sensing tool. The conventional microcantilever materials are mostly silicon-based. The sensitivity of the sensor depends on Young's modulus of the structural material, thickness of the cantilever as well as on the gauge factor of the piezoresistor. UV patternable polymers such as SU-8 have a very low Young's modulus compared to the silicon-based materials. Polymer cantilevers with a piezoresistive material having a large gauge factor and a lower Young's modulus are therefore highly suited for sensing applications. In this work, a spin coatable and photopatternable mixture of carbon black (CB) and SU-8, with proper dispersion characteristics, has been demonstrated as a piezoresistive thin film for polymer microcantilevers. Results on percolation experiments of SU-8/CB composite and fabrication of piezoresistive SU-8 microcantilevers using this composite are presented. With our controlled dispersion experiments, we could get a uniform piezoresistive thin film of thickness less than 1.2 μm and resistivity of 2.7 Ω cm using 10 wt% of CB in SU-8. The overall thickness of the SU-8/composite/SU-8 is approximately 3 μm. We further present results on the electromechanical characterization and biofunctionalization of the cantilever structures for biochemical sensing applications. These cantilevers show a deflection sensitivity of 0.55 ppm/nm. Since the surface stress sensitivity is 4.1 × 10⁻³ [N/m]⁻¹, these cantilevers can well be used for detection of protein markers for pathological applications.     

Crystallization of aqueous ammonium sulfate particles internally mixed with soot and kaolinite: crystallization relative humidities and nucleation rates

Using optical microscopy, we investigated the crystallization of aqueous ammonium sulfate droplets containing soot and kaolinite, as well as the crystallization of aqueous ammonium sulfate droplets free of solid material. Our results show that soot did not influence the crystallization RH of aqueous ammonium sulfate particles under our experimental conditions. In contrast, kaolinite increased the crystallization RH of the aqueous ammonium sulfate droplets by approximately 10%. In addition, our results show that the crystallization RH of aqueous ammonium sulfate droplets free of solid material does not depend strongly on particle size. This is consistent with conclusions made previously in the literature, based on comparisons of results from different laboratories. From the crystallization results we determined the homogeneous nucleation rates of crystalline ammonium sulfate in aqueous ammonium sulfate droplets and the heterogeneous nucleation rates of crystalline ammonium sulfate in aqueous ammonium sulfate particles containing kaolinite. Using classical nucleation theory and our experimental data, we determined that the interfacial tension between an ammonium sulfate critical nucleus and an aqueous ammonium sulfate solution is 0.064 +/- 0.003 J m(-2) (in agreement with our previous measurements), and the contact angle between an ammonium sulfate critical nucleus and a kaolinite surface is 59 +/- 2 degrees. On the basis of our results, we argue that soot will not influence the crystallization RH of aqueous ammonium sulfate droplets in the atmosphere, but kaolinite can significantly modify the crystallization RH of atmospheric ammonium sulfate droplets. As an example, the CRH50 (the relative humidity at which 50% of the droplets crystallize) ranges from about 41 to 51% RH when the diameter of the kaolinite inclusion ranges from 0.1 to 5 microm. For comparison, the CRH50 of aqueous ammonium sulfate droplets (0.5 microm diameter) free of solid material is approximately 34.3% RH under atmospheric conditions.     

Experimental Determination of NH3 Solubility in Toluene at Pressures up to 340 kPa at 398 K

Journal of Solution Chemistry - The solubility of ammonia in toluene has been measured at 398 K and at pressures up to 340 kPa using a static, synthetic and isochoric technique....     

Measurement of mixing time and holdup of solids in gas–solid fluidized bed using radiotracer technique

Mixing times and holdup of solids were measured in a gas–solid fluidized bed using radiotracer technique. Sand and air were used as solid and gas phase, respectively in the fluidized bed. Gold-198 labeled sand particles were used as radiotracer for mixing time measurement at different operating conditions and ¹³⁷Cs sealed source was used for holdup measurement at different axial and radial positions. The experiments were conducted at different operating conditions. The measured mixing times ranged from 1.4 to 21 s at different conditions. It was observed that at a particular bed height, the mixing time initially decreases with increasing gas velocity and tend to become constant at higher gas velocities. However, mixing time increases with increasing bed height. The holdup fraction of solid was found to be more towards the wall compared to the centre of the column. The study provided inputs to improve the existing design, design of a new system and scale-up of the process.     

Residence time distribution study in a pilot-scale gas–solid fluidized bed reactor using radiotracer technique

This paper describes a radiotracer study carried out to measure residence time distribution (RTD) of coal particles in a pilot-scale gas–solid fluidized bed reactor (FBR). Gold-198 labelled on coal particles was used as radiotracer. RTD measurements were conducted for selected operating conditions and mean residence times (MRTs) of the coal particles were determined. Gamma function model was used to simulate the measured RTD data and mixing of coal particles in the reactor was investigated. Based on the results, the performance of the air distributor used in the reactor was evaluated.     

A simple sample pretreatment device with supported liquid membrane for direct injection of untreated body fluids and in‐line coupling to a commercial CE instrument

A simple sample pretreatment device was developed employing extractions across supported liquid membranes (SLMs) and in‐line coupling to a commercial CE instrument. The device consisted of two polypropylene conical units interspaced with a polypropylene planar SLM, which were impregnated with 1‐ethyl‐2‐nitrobenzene. The two units and the SLM were pressed against each other, donor unit was filled with 40 μL of an untreated body fluid and acceptor unit with 40 μL of DI water. The device was then placed into conventional CE vial fitted with a soft spring, which was depressed during injection into CE capillary and ensured that the SLM was not ruptured. Position of separation capillary injection end and high‐voltage electrode in the CE instrument was optimized in order to ensure efficient injection of pretreated body fluids. The device can be easily assembled/disassembled and SLMs can be replaced after each extraction thus minimizing sample carry‐over, avoiding tedious SLM regeneration, and reducing total pretreatment time and costs. The pretreatment device was examined by direct injection of human urine and serum spiked with nortriptyline, haloperidol, and loperamide. The basic drugs were diffusionaly transported across the SLM within 10 min and were injected into the separation capillary directly from the SLM surface in the acceptor unit, whereas matrix components were retained by the SLM. The in‐line SLM‐CE method showed good repeatability of peak areas (3.8–11.0%) and migration times (below 1.4%), linear relationship (r² = 0.990–0.999), and low LODs (12–100 μg/L).     

Direct conversion of natural gas to higher hydrocarbons: A review

Direct conversion of methane to higher hydrocarbons is an effective process to solve the problem of natural gas utilization. Although remarkable progress has been achieved on the dehydro-aromatization of methane (DAM), low conversion caused by severe thermodynamic limitations, coke formation, and catalysis deactivation remain important drawbacks to the direct conversion process. Molybdenum catalysts supported on HZSM-5 type zeolite support are among the most promising catalysts. This review focuses on the aspects of direct methane conversion, in terms of catalysts containing metal and support, reaction conditions, and conversion in different types of reactors. The reaction mechanism for this catalytic process is also discussed.     

Efficacy of zinc and tourmaline in mitigating corrosion of carbon steel in non-flow mode

Laboratory corrosion immersion tests were carried out to investigate the effectiveness of a physical water treatment (PWT) using zinc and ceramic tourmaline-based catalytic materials for the control of carbon steel corrosion in acidic still water (i.e., pH 4.5–5). The tests were carried out at different water temperatures over 168 h. Our results showed a maximum of 22 % reduction in the corrosion rate using PWT in comparison with the control case. Furthermore, the corrosion products depicted more agglomerated particles after the PWT treatment. In both cases, differences were observed in the crystal structures, showing in general lower corrosion activity when PWT was used. The present results could find potential applications in water distribution systems and where metallic materials are exposed to stagnant acidic water.     

Synthesis, characterization and fluorescence studies of 3,5-diaryl substituted 2-pyrazolines

A series of 2-pyrazolines have been synthesized from α, β unsaturated ketones and hydrazine hydrate with acetic/formic acid in ethanol/DMSO. The structures of 2-pyrazolines have been established by spectroscopic techniques i.e. UV, IR, (1)H NMR, (13)C NMR and micro element analysis. Fluorescence spectra were recorded in the solution at fixed concentration and same excitation wavelength at 290 nm. The absorption band positions of all the compounds broadly lie between 280 and 336 nm and fluorescence band positions in the range between 300 and 370 nm, the near ultraviolet region.     

Chemical diversity in Mentha spicata: antioxidant and potato sprout inhibition activity of its essential oils

The essential oils from fresh aerial parts of Mentha spicata L. collected from ten different natural habitats of Uttarakhand, India were analyzed by a combination of GC, GC/MS and NMR spectroscopy. The analysis revealed that monoterpenoids (46.1%-91.6%), mainly carvone (15.3%-68.5%), piperetenone oxide (24.0%-79.2%) and alpha-humulene (0.1%-29.9%), were the major constituents of the essential oils, but with significant qualitative and quantitative differences among the other constituents. Cluster analysis of the oil composition was carried out in order to discern the differences and similarities within different accessions collected from different natural habitats. The essential oils were also screened for their antioxidant activities by chelating properties of Fe2+, DPPH radical-scavenging activity, and their reducing power. The essential oils of two chemo variants (viz. carvone and piperetenone oxide types) were also tested for potato (Solanum tuberosum L.) sprout suppressant activity. The results showed that these oils exhibit good sprout inhibition activity in comparison to CIPC and iodine, the standard sprout suppressant.