Kajal Jindal

CuO thin film based uric acid biosensor with enhanced response characteristics

An efficient reagentless uric acid biosensor has been realized using a copper oxide (CuO) thin film matrix grown onto platinum (Pt) coated corning glass substrates by pulsed laser deposition (PLD) technique. The p-type CuO matrix successfully introduces redox property in the electrode and provides enhanced electron communication features. Sensing response obtained by the bioelectrocatalytic oxidation of uric acid by uricase/CuO/Pt/glass electrode was studied without any external mediator using cyclic voltammetry (CV) and photometric assay. The studies reveal that the uricase/CuO/Pt/glass bio-electrode exhibits good linearity over a wide range of 0.05 mM to 1.0mM uric acid concentration with enhanced response of 2.7 mA/mM and high shelf life (>14 weeks). A low Michaelis-Menten constant (K(m)) of 0.12 mM, indicate that the immobilized enzyme (uricase) has enhanced affinity towards its analyte (uric acid). The results confirm promising application of the p-type CuO thin film matrix for the realization of a reagentless integrated implantable biosensor.

Inducing electrocatalytic functionality in ZnO thin film by N doping to realize a third generation uric acid biosensor.

A third generation uric acid biosensor has been developed by exploiting the electrocatalytic functionality of nitrogen (N) doped zinc oxide (ZnO:N) thin film matrix deposited using pulsed laser deposition technique. The electrochemistry of ZnO:N thin film based electrode is investigated by using electrochemical impedance spectroscopy and cyclic voltammetry. The obtained results demonstrate that nitrogen doping in ZnO matrix offers a striking electrocatalytic activity to the immobilized uricase towards the oxidation of analyte (uric acid) and promotes the direct transfer of electrons from active sites of enzyme onto the electrode without any mediator. In contrast to pure ZnO, ZnO:N (8% N) thin film based uric acid biosensor gives a high sensitivity of about 1.38 mA/mM in the absence of mediator. Moreover, ZnO:N derived bio-electrode exhibits excellent selectivity and outstanding analytical stability and reproducibility, which enables a reliable and sensitive determination of uric acid in the serum. The ZnO:N thin film based biosensor exhibits a linear sensing response in the range from 0 to 1.0mM of uric acid concentration and the apparent Michaelis-Menten kinetic parameter (Km) is estimated to be about 0.13 mM which indicates the high affinity of the prepared bio-electrode towards uric acid. The obtained results are encouraging and indicate that the ZnO:N thin film matrix offers a new and promising platform for the development of novel third generation biosensors without using any mediator.

Structural and magnetic properties of N doped ZnO thin films

Experimental investigations and first-principle calculations based on density functional theory are effectively combined to shed light on origin of room temperature ferromagnetism in nitrogen doped ZnO (ZnO:N) based intrinsic dilute magnetic semiconductors. ZnO:N thin films grown by pulsed laser deposition show a well defined M-H hysteresis loop at room temperature, reflecting ferromagnetic behavior in contrast to undoped ZnO thin films grown under the same processing condition. Isotropic behavior of magnetism in ZnO:N reveals the dominant contribution of N incorporation on the magnetism and is attributed to p-p interaction between nitrogen and neighboring oxygen atoms having potential for room temperature spintronic applications.

Transition from diamagnetic to ferromagnetic state in laser ablated nitrogen doped ZnO thin films

Transition from room temperature diamagnetic to ferromagnetic state in N doped ZnO (ZnO:N) films grown by pulsed laser deposition with tunable energy density has been identified. ZnO:N films deposited with moderate laser energy density of 2.5 J/cm2 are single phase and nearly defect free having N dopant substitution at O sites in ZnO lattice, exhibiting intrinsic ferromagnetism. When energy density reduces (<2.5 J/cm2), defects in ZnO:N film degrades ferromagnetism and exhibit diamagnetic phase when grown at energy density of 1.0 J/cm2. Growth kinetics, which in turn depends on laser energy density is playing important role in making transition from ferromagnetic to diamagnetic in ZnO:N films.

Raman scattering and photoluminescence investigations of N doped ZnO thin films: Local vibrational modes and induced ferromagnetism

N doped ZnO (ZnO:N) thin films are prepared by pulsed laser deposition in an oxygen environment using ZnO:N targets with varying nitrogen doping concentrations (1%–10%). The impact of nitrogen incorporation on the microstructural properties of prepared ZnO:N thin films has been studied using Raman scattering. The Raman shift of E2(high) mode towards lower frequencies indicate the substitution of N at O lattice sites (NO). A local vibrational mode corresponding to Zn–N was observed at 480.3 cm−1 in N doped ZnO thin films and highlights the increased strength of the Zn–N bond in the ZnO lattice. Photoluminescence studies reveal the dominant near band edge emission peak in the ultraviolet region and the absence of deep level emission due to defects. The ZnO:N thin films are found to possess room temperature ferromagnetism. N is found to play a significant role in arising ferromagnetism in ZnO and possess a solubility limit of 8% for uniform and homogeneous atomic substitution in ZnO. The present study confir...

Study of half-metallicity in BiMnxFe1-xO3

Spin polarized calculations are performed to study the structural and electronic properties of Mn doped BiFeO3 (BMFO) using simplified local spin density approximation (LSDA) functional under density functional theory (DFT). The B-site doping concentration of Mn in BMFO considered to be 16.7 % (BiMn0.167Fe0.833O3). Density of states calculations are carried out for both ferromagnetic (FM) and anti-ferromagnetic (AFM) order in BMFO. The results predict that BMFO is a half metal for both FM and AFM BMFO with magnetization of 29.0000 µB/cell and 1.0000 µB/cell respectively. The ground state of BMFO is found to be antiferromagnetic and demonstrates BMFO to be a potential candidate for spintronic applications.

Stabilization of Ferromagnetism in Co Codoped ZnO:N

First principle calculations were performed to study room temperature ferromagnetism in N doped ZnO (ZnO:N) using spin density functional theory. Substitution of O by N in ZnO results in spin polarized state exhibiting half metallic ferromagnetic characteristics. Each N dopant introduces magnetic moment of 1.0 μB/supercell, which is from 2p electrons of N but the magnetization energy (ΔE = 14.42 meV) is too small to stabilize ferromagnetism at room temperature. Cobalt (Co) co-doping in ZnO:N is found to enhance ferromagnetism (magnetic moment = 4.24 μB/supercell) with enhanced stability (ΔE = 635 meV) and is driven by hybridization between N 2p and Co 3d states.

Realization of Surface Acoustic Wave (SAW) and Semiconductor Gas Sensors for Room Temperature Detection of NO2 Gas

SnO2 thin films deposited using RF sputtering technique have been exploited to detect NO2 gas using two different gas sensing techniques namely: (i) conductometeric sensing and (ii) surface acoustic wave (SAW) sensing. The surface morphology and structural property of the sensing SnO2 thin film were studied using, Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) techniques respectively. The SnO2 thin film based conductometric sensor is found to exhibit higher sensing response (1.6 × 104) as compared to the one obtained using SAW gas sensor (-25 MHz). However, the conductometric sensor demands a high operating temperature of 100 oC and exhibits relatively poor response time and recovery time of about 2 min and 22 min respectively. Whereas, the SAW sensor shows the possible room temperature sensing of NO2 gas with faster response and recovery speeds of 8 s and 40 s respectively.

A theoretical and experimental formalism of electronic structure of BFO:Cr thin films and modulation of their electrical properties upon visible light illumination

BiFeO3 (BFO) and BiFe1-xCrxO3 (BFCO) (x = 0, 0.01, 0.02, 0.03) thin films have been fabricated using chemical solution deposition technique. The bandgap of BFO and BFCO thin films is found to be lying in the visible region making these films suitable candidates for potential solar energy harvesting applications. Density functional theory based calculations have also been performed to study the effect of B-site (Cr) doping on the electronic properties of BFO and BFCO. The BiFe1-xCrxO3 (x = 0.02) thin films exhibited well saturated PE hysteresis loops with a maximum remanent and saturation polarization of about 43 μC/cm2 and 64 μC/cm2, respectively. In contrast to pure BFO, a high value of short circuit current density (Jsc) of magnitude 766.60 μA/cm2 along with the open circuit voltage (Voc) of 106 mV was obtained for BiFe0.98Cr0.02O3 thin film structure under illumination with a laser of wavelength 470 nm and intensity 20 mW/cm2. The Au/BiFe0.98Cr0.02O3/ITO/glass heterostructure displays a remarkably enhanced value of Ion/Ioff ratio (8.4 × 104). The observed results clearly highlight the potential of Cr doped BFO thin film structure for the development of cost effective light-driven devices.

Room Temperature Ferromagnetism in PLD Grown Zn1-xLixO1-yNy Thin Films

Zn1-xLixO1-yNy (ZnO:(N,Li)) thin films grown by Pulsed Laser Deposition (PLD) technique are found to exhibit intrinsic ferromagnetic behavior at room temperature (RT). XRD reveals that the grown Zn1-xLixO1-yNy thin films (x = 0.05, y = 0.08) are single phase and preferred oriented along c-axis. In contrast to pure ZnO thin films, ZnO thin films doped with non-magnetic nitrogen (ZnO:N) result in good M-H hysteresis loop at RT. Co-doping of ZnO:N with Li is found to enhance the saturation magnetization (Ms) appreciably. The room temperature ferromagnetic behavior and semiconducting property of Zn1-xLixO1-yNy thin film could be promising for spin injection based functional devices.