Sensitivity-Enhanced CMOS Phase Luminometry System Using Xerogel-Based Sensors

We present the design and implementation of a phase luminometry sensor system with improved and tunable detection sensitivity achieved using a complementary metal-oxide semiconductor (CMOS) integrated circuit. We use sol-gel derived xerogel thin films as an immobilization media to house oxygen (O₂) responsive luminescent molecules. The sensor operates on the principal of phase luminometry wherein a sinusoidal modulation signal is used to excite the luminophores encapsulated in the porous xerogel films and the corresponding phase shift of the emission signals is monitored. The phase shift is directly related to excited state lifetimes of the luminophores which in turn are related to the concentration of the target analyte species present in the vicinity of the luminophores. The CMOS IC, which consists of a 16 times 16 high-gain phototransistor array, current-to-voltage converter, amplifier and tunable phase shift detector, consumes an average power of 14 mW with 5-V power supply operating at a 38-kHz modulation frequency. The output of the IC is a dc voltage that corresponds to the detected luminescence phase shift with respect to the excitation signal. As a prototype, we demonstrate an oxygen sensor system by encapsulating the luminophore tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) within the xerogel matrices. The sensor system showed a fast response on the order of few seconds and we obtained a detection sensitivity of 118 mV per 1% change in O₂ concentration. The system demonstrates a novel concept to tune and improve the detection sensitivity for specific concentrations of the target analyte in many biomedical monitoring applications.     

Synthesis and characterization of zirconia-based catalyst for the isomerization of n-hexane

Sulfated zirconia is a very strong solid acid catalyst which can be utilized for various reactions. The present study focuses on synthesis of zirconia-based catalyst with high acidity and high surface area, particularly for isomerization reaction. Sulfated zirconia has been obtained by sulfation of zirconia prepared by hydrothermal route. The catalyst was developed by impregnating tungstophosphoric acid on sulfated zirconia by wet incipient method. The catalyst was characterized through Brunauer–Emmett–Teller (BET) surface area, temperature-programmed desorption of ammonia, temperature program reduction of hydrogen, Fourier transmission infrared spectroscopy, and thermogravimetric analysis. The results revealed that the catalyst is crystalline in nature with surface area 190–225?m² g^?1 and acidity 0.135–0.558?mmol?g^?1. Twenty-five percent conversion was obtained (as confirmed by gas chromatography) at 225°C using n-hexane as model hydrocarbon in fixed-bed microreactor.     

Selenium levels in biological matrices in adult population of Mumbai, India

Selenium (Se) levels in whole blood, serum, urine, muscle and saliva of Mumbai adults have been estimated by differential pulse cathodic stripping voltammetry (DPCSV); the detection limit of Se is 0.05 ng ml(-1). The reliability of estimation is further assessed through the analysis of Standard Reference Materials. The Se levels in whole blood (n = 35) and blood serum (n = 201) of the Mumbai adult population is 99.6 and 100 ng ml(-1); approximately 34.8% of the population have serum Se levels between 80 and 100 ng ml(-1). The blood serum levels of Se for Mumbai adults are comparable to those of whole blood. The mean concentration of Se in urine on a 24-h basis is 5.2 ng ml(-1). Muscle and saliva of the Mumbai adult population contain 195.4 ng g(-1) and 2 ng ml(-1) of Se, respectively. A good correlation between serum Se and dietary Se is observed with a correlation coefficient of 0.89.     

Dielectric and mechanical properties of PZN-PFN-BZN ternary system

The Ferroelectric relaxor ternary system 0.5PZN-(0.5 – x)PFN-xBZN was prepared using the columbite precursor method. The stability of the perovskite phase was studied as a function of BZN content in the system. It was observed that BZN is a good stabilizer of perovskite phase because of the high value of electronegativity difference between its cation and anion. It has also been observed that addition of BZN increases the dielectric maxima peak value and decrease the Curie temperature of the ceramics. The ternary composition 0.5PZN-0.425PFN-0.075BZN has been identified for MLCs applications. It has a T _c of around room temperature with a peak dielectric constant 6400 and tan 0.05. The mechanical properties of relaxor materials have also been studied and reported.     

Daily intake of manganese by the adult population of Mumbai

The daily intake of manganese (Mn) estimated through air, water and duplicate dietary analysis is found to range from 0.67 to 4.99 mg with a mean value of 2.21 mg. Ingestion through food contributed to the predominant fraction of the intake. The turnover rate of Mn through blood is approximately 2 h, based on the mean concentration of Mn in blood of 1.54 microg l(-1). The average concentrations of Mn in water and air were approximately 1.42 microg l(-1) and 37 ng m(-3), respectively. The daily intake of Mn by the adult population of Mumbai is closer to the lower bound of the recommended limit of 2-5 mg. Electro Thermal Atomic Absorption Spectrophotometry (ET-AAS), has been used for the determination of Mn in a variety of environmental and human biological fluids. The detection limit of Mn for a volume injection of 20 microl is 2 pg absolute. The precision of the method is established by analyzing a synthetic mixture containing various elements in different quantities (0.5-10 ppm) and is found to be within +/- 8%. The reliability of estimation is further assessed through the analysis of Standard Reference Materials (SRMs) of soil, hay, milk powder and fish tissue obtained from IAEA.     

Medium modified nucleon-nucleon cross sections in a nucleus

A simple reliable formalism is presented for obtaining nucleon-nucleon cross sections within a nucleus in nuclear collisions for a given projectile and target nucleus combination at a given energy for use in transport, Monte Carlo and other calculations. The method relies on extraction of these values from experiments and has been tested for absorption experiments to give excellent results.     

Effect of interlayer interaction in high-T c cuprate superconductors

We have studied the role of interlayer attractive interaction in a high-T _c system having two layers per unit cell. The single band two-layer tight binding model Hamiltonian is considered and the double time Green's function technique is applied within the mean field approximation. The expressions for the hole density, transition temperature, and intra- and interlayer order parameters are obtained which are found to be dependent on the interlayer interaction and other parameters appearing in the Hamiltonian. The numerical analysis shows that the coupling of the charge carriers (holes) between the layers provides better conditions for the stabilization of long-range order and high superconducting transition temperature in layered superconductors. It is also observed that superconductivity is confined to a narrow region of hole concentration and the single particle tunneling suppresses the transition temperature.     

Effect of Interlayer Interaction on the Specific Heat of High-Tc Superconductors

The effect of interlayer interactions on the electronic specific heat of high-T _c layered superconductors has been studied within the framework of the Hirsch model. In the present paper we extend our previous work in order to evaluate the expression for specific heat. It is shown that the inclusion of interlayer interactions suppresses the height of the jump in the specific heat at T _c.