Showing papers by "Biswajit Das published in 2014"

Fabrication of tunable Au SERS nanostructures by a versatile technique and application in detecting sodium cyclamate

Abstract: In this work, three typical morphologies of SERS substrates with the compositions of Au nanoparticles, short Au nanowires (NWs) with small Au nanoparticles filled in the nanogaps and long Au NWs intertwined into a self-supporting film, were fabricated by a versatile nanocluster fabrication technique. This physical fabrication technique is easy to implement and cost-effective, and the fabricated SERS substrates have a large-area, good homogeneity and long-term stability. More importantly, the SERS substrates prepared by this physical method will not incorporate reductants and surfactant chemicals, and thus can yield clean surfaces, which are suitable for analytes with a weak affinity to the substrate surface. In this study, the fabricated substrate with the highest enhancement factor (EF) successfully acquired the SERS spectrum of sodium cyclamate, a restricted food additive, with a good signal–noise-ratio. Finally, a set of piece-wise linear equations were produced according to the correlation between SERS intensity and sodium cyclamate concentration with a detection limit of 1.6 × 10−9 M.

Electrical conduction of nanoparticle monolayer for accurate tracking of mechanical stimulus in finger touch sensing.

Abstract: A flexible strain gauge is an essential component in advanced human-machine interfacing, especially when it comes to many important mobile and biomedical appliances that require the detection of finger touches. In this paper, we report one such strain gauge made from a strip of nanoparticle monolayer onto a flexible substrate. This proposed gauge operates on the observation that there is a linear relationship between electrical conduction and mechanical displacement in a compressive state. Due to its prompt temporal response, the gauge can accurately track various mechanical stimuli running at the frequencies of interest. Experiments have confirmed that the proposed strain gauge has a strain detection limit as low as 9.4 × 10−5, and its gauge factor can be as large as 70, making this device particularly suitable for sensitive finger touch sensing. Furthermore, negligible degradation in the gauge's output electrical signal is observed even after 9000 loading/unloading cycles.

Direct Writing of Metallic Nanoparticle Concentric Multi‐Ring Structures by Template‐Directed Convective Self‐Assembly Processes

Abstract: We report a simple and inexpensive method to directly write complex ring-typed monolayer arrays of metallic nanoparticles by a combination of template-directed and convective selfassembly processes. Our method rotates the nano-stepping piezo stage and uses an attached stationary pipette to create circular tracks with a diameter of hundred micrometers on a thin gold film. These tracks serve as templates to create ring-typed structures by simultaneously depositing gold colloid as an ink from the pipette, similar to a pen. The diameter of the ring can be independently controlled by positioning the pipette on the rotation stage via a linear nanostepping motor. By driving the attached pipette to different locations, one can create concentricring structures. We demonstrate that the fabricated ring-typed nanostructures combined with the gold film can induce collective surface plasmon resonance and significantly enhance the fluorescence and Raman intensities. The written ordered metallic nanostructures can find many important technological applications.

Assessment of Serum Magnesium and Uric Acid Levels in Women with Normal Pregnancy and Pre-Eclampsia in Rohilkhand Region in Uttar Pradesh, India. -

Abstract: The present study have been undertaken to evaluate and compare the maternal serum concentrations of magnesium and uric acid among non-pregnant healthy women, women with uncomplicated pregnancy and pregnant women with pre-eclampsia and also to find if there is any importance of serum magnesium and uric acid levels in management of pre-eclampsia. The present study included 120 women divided into three groups (group-A, group-B and group-C). Estimation of maternal serum magnesium and uric acid were analyzed by using Calmagite method and Modified Trinder Peroxidase method. The mean ± SD systolic, diastolic and mean arterial blood pressure (MAP) of group-B women were significantly higher than group-A women (128.0 ± 6.8 vs 119.0 ± 10.3 mm of Hg, 75.1 ± 7.5 vs. 70.3 ± 8.7 mm of Hg and 92.7 ± 5.48 vs. 86.5 ± 6.68 mm of Hg) and group-C women were significantly higher than group- B women ( 172.2 ± 13.1 vs. 128.0 ± 6.8 mm of Hg, 107.4 ± 7.3 vs. 75.1 ± 7.5 mm of Hg and 129.03 ± 6.5 vs. 92.7 ± 5.48 mm of Hg ). The mean serum magnesium levels were significantly decreased in women with uncomplicated pregnancy when compared with non-pregnant healthy women, p< 0.05. The mean serum concentrations of uric acid in normotensive pregnant was significantly higher when compared to healthy non-pregnant women , p< 0.05. There was highly significant decrease in the mean value of serum magnesium in pre-eclamptic pregnant women when compared to normotensive pregnant women. The mean value of serum uric acid in pre-eclamptic pregnant women was significantly elevated when compared to normotensive pregnant women, p< 0.05. We conclude that magnesium and uric acid homeostases are altered during pregnancy and these alterations appear to be more pronounced in women with pre-eclampsia.