Naga Siva Kumar Gunda

Mobile Water Kit (MWK): a smartphone compatible low-cost water monitoring system for rapid detection of total coliform and E. coli

In this work, we have developed and demonstrated a rapid and low-cost water monitoring sensor that can simultaneously detect total coliform and Escherichia coli (E. coli) bacteria in contaminated drinking water samples. The test method, called Mobile Water Kit (MWK), comprises a set of custom chemical reagents that would serve as colorimetric or fluorometric chemosensors, syringe filter units and a smartphone platform that would serve as the detection/analysis system. The MWK provides information about the presence/absence of total coliform and E. coli in water samples. The MWK has preliminarily been tested for its selectivity, sensitivity and accuracy, with samples of known concentrations of bacteria. The MWK has also been tested with contaminated water samples collected during the two field trials conducted in Canada and India, and the obtained results were confirmed with conventional laboratory methods. With this MWK, we were able to detect the total coliform and E. coli bacteria in water samples within 30 min or less, depending on the concentration of the bacteria. For one of the field samples, the MWK was able to detect the total coliform within 35 s, which is faster than any rapid test methods available in the market. This new technology can dramatically improve the response times for the outbreak of water-borne diseases and will help water managers and individuals to assess the quality of water sources.

Modeling of dielectrophoretic transport of myoglobin molecules in microchannels

Myoglobin is one of the premature identifying cardiac markers, whose concentration increases from 90 pgml or less to over 250 ngml in the blood serum of human beings after minor heart attack. Separation, detection, and quantification of myoglobin play a vital role in revealing the cardiac arrest in advance, which is the challenging part of ongoing research. In the present work, one of the electrokinetic approaches, i.e., dielectrophoresis (DEP), is chosen to separate the myoglobin. A mathematical model is developed for simulating dielectrophoretic behavior of a myoglobin molecule in a microchannel to provide a theoretical basis for the above application. This model is based on the introduction of a dielectrophoretic force and a dielectric myoglobin model. A dielectric myoglobin model is developed by approximating the shape of the myoglobin molecule as sphere, oblate, and prolate spheroids. A generalized theoretical expression for the dielectrophoretic force acting on respective shapes of the molecule is derived. The microchannel considered for analysis has an array of parallel rectangular electrodes at the bottom surface. The potential and electric field distributions are calculated using Greens theorem method and finite element method. These results also compared to the Fourier series method, closed form solutions by Morgan et al. [J. Phys. D: Appl. Phys. 34, 1553 (2001)] and Chang et al. [J. Phys. D: Appl. Phys. 36, 3073 (2003)]. It is observed that both Greens theorem based analytical solution and finite element based numerical solution for proposed model are closely matched for electric field and square electric field gradients. The crossover frequency is obtained as 40 MHz for given properties of myoglobin and for all approximated shapes of myoglobin molecule. The effect of conductivity of medium and myoglobin on the crossover frequency is also demonstrated. Further, the effect of hydration layer on the crossover frequency of myoglobin molecules is also presented. Both positive and negative DEP effects on myoglobin molecules are obtained by switching the frequency of applied electric field. The effect of different shapes of myoglobin on DEP force is studied and no significant effect on DEP force is observed. Finally, repulsion of myoglobin molecules from the electrode plane at 1 KHz frequency and 10 V applied voltage is observed. These results provide the ability of applying DEP force for manipulating nanosized biomolecules such as myoglobin.

Under-water superoleophobicity of fish scales

Recent surge in the development of superhydrophobic/superoleophobic surfaces has been motivated by surfaces like fish scales that have hierarchical structures, which are believed to promote water or oil repellency. In this work, we show that the under-water oil repellency of fish scales is entirely due to the mucus layer formation as part of its defense mechanism, which produces unprecedented contact angle close to 180°. We have identified the distinct chemical signatures that are responsible for such large contact angle, thereby making fish scale behave highly superoleophobic inside the water medium. In absence of the mucus layer, it is found that the contact angle decreases quite dramatically to around 150°, making it less oleophobic, the degree of such oleophobicity can then be contributed to its inherent hierarchical structures. Hence, through this systematic study, for the first time we have conclusively shown the role of the fishs mucus layer to generate superoleophobicity and negate the common notion that hierarchical structure is the only reason for such intrinsic behavior of the fish scales.

Detection of Escherichia coli in potable water using personal glucose meters

This communication describes the applicability of personal glucose meters for regularly monitoring the quality of potable water. We have demonstrated a simple method that can accurately detect very low levels of E. coli contamination in water and has the potential to be developed into a comprehensive test kit, which can provide both qualitative and quantitative results.

Characterization of nanometer-scale porosity in reservoir carbonate rock by focused ion beam-scanning electron microscopy.

Sedimentary carbonate rocks are one of the principal porous structures in natural reservoirs of hydrocarbons such as crude oil and natural gas. Efficient hydrocarbon recovery requires an understanding of the carbonate pore structure, but the nature of sedimentary carbonate rock formation and the toughness of the material make proper analysis difficult. In this study, a novel preparation method was used on a dolomitic carbonate sample, and selected regions were then serially sectioned and imaged by focused ion beam-scanning electron microscopy. The resulting series of images were used to construct detailed three-dimensional representations of the microscopic pore spaces and analyze them quantitatively. We show for the first time the presence of nanometer-scale pores (50-300 nm) inside the solid dolomite matrix. We also show the degree of connectivity of these pores with micron-scale pores (2-5 μm) that were observed to further link with bulk pores outside the matrix.

Study on the use of dielectrophoresis and electrothermal forces to produce on-chip micromixers and microconcentrators

The present study uses the dielectrophoresis (DEP) and electrothermal (ET) forces to develop on-chip micromixers and microconcentrators. A microchannel with rectangular array of microelectrodes, patterned either on its bottom surface only or on both the top and the bottom surfaces, is considered for the analysis. A mathematical model to compute electrical field, temperature field, the fluid velocity, and the concentration distributions is developed. Both analytical and numerical solutions of standing wave DEP (SWDEP), traveling wave DEP (TWDEP), standing wave ET (SWET), and traveling wave ET (TWET) forces along the length and the height of the channel are compared. The effects of electrode size and their placement in the microsystem on micromixing and microconcentrating performance are studied and compared to velocity and concentration profiles. SWDEP forces can be used to collect the particles at different locations in the microchannel. Under positive and negative DEP effect, the particles are collected at electrode edges and away from the electrodes, respectively, irrespective of the position, size, and number of electrodes. The location of the concentration region can be shifted by changing the electrode position. SWET and TWET forces are used for mixing and producing concentration regions by circulating the fluid at a given location. The effect of forces can be changed with the applied voltage. The TWDEP method is the better method for mixing along the length of the channels among the four options explored in the present work. If two layers of particle suspension are placed side by side in the channel, triangular electrode configuration can be used to mix the suspensions. Triangular and rectangular electrode configurations can efficiently mix two layers of particle suspension placed side-by-side and one-atop-the-other, respectively. Hence, SWDEP forces can be successfully used to create microconcentrators, whereas TWDEP, SWET, and TWET can be used to produce efficient micromixers in a microfluidic chip.

Optical biosensors with an integrated Mach-Zehnder Interferometer for detection of Listeria monocytogenes.

In this work, we have demonstrated an efficient optical immunoassay technique for the detection of a food-borne pathogen, Listeria monocytogenes, using a Mach-Zehnder Interferometer (MZI) configuration. We have investigated ten different MZI configurations with angular and Sbend Y-junction geometries. An efficient Hydrofluoric acid (HF) based technique was used for rapid and specific binding of L. monocytogenes to the sensor arm of the MZI biosensor. The MZI biosensor was able to detect L. monocytogenes at concentrations of the order of 105 CFU/ml, which is lower than the infection dose for healthy human beings. SEM analysis and light intensity measurements showed the biosensor is highly selective to L. monocytogenes over other microbial species (such as Escherichia coli). Finally, a novel calibration scheme of the MZI biosensor was developed from experimental data that can be used for determining unknown concentrations of L. monocytogenes.

Dynamics of liquid droplets in an evaporating drop: liquid droplet “coffee stain” effect

In this paper, we demonstrate the dynamics of bidispersed oil droplets in an evaporating water sessile drop. This phenomenon is therefore equivalent to a unique liquid droplet based “coffee stain” effect, with the depositing colloidal particles (of a classical “coffee stain” problem) being replaced by the oil droplets partially wetting the substrate. The important difference with respect to the classical “coffee stain” problem, as revealed by our experiments, is that the oil droplets, unlike the colloidal particles, cannot reach the contact line; rather the aversion of the oil droplets to the air ensures that the oil droplets always remain at a finite distance from the contact line. We call this effect an “enclosure” effect, characterized by this distance. We provide a theoretical model to explain this phenomenon, and our theoretical results match well with the experimental observations. The “enclosure” effect depends on the droplet size, thereby allowing an automatic size-based separation of the oil droplets. Additionally, this effect depends on the wettability of the oil droplets and the sessile drop, as well as the relative velocity of the oil droplets with respect to the rate of decrease of the sessile drop contact angle. Our identification of this new phenomenon in a liquid-droplet based “coffee stain” problem will have a huge impact on microscale control and manipulation of liquid droplets in a two phase system.

Micro-spot with integrated pillars (MSIP) for detection of dengue virus NS1

In this paper, we demonstrate an extremely efficient technique of diagnosing dengue virus non-structural protein (NS1) using Micro-Spot with Integrated Pillars (MSIP). Detection using MSIP is performed by employing fluorescence immunoassay specific to dengue virus NS1. MSIPs are chemically modified to ensure efficient covalent binding of antibodies on the micropillars, whereas the enormous increase in the surface area (available for the reaction) induced by the micropillars amplifies the apparent rate, which enhances the signal intensity. Therefore, the detection response of a MSIP, quantified by the intensity of the fluorescence signal, is found to be almost five times magnified than the response of a similar size micro-spot without micropillars. The response of the micropillars also depend on the pillar arrangement, since for identical concentration of dengue NS1 antigen, a stronger intensity signal is obtained for a hexagonal close packed array (staggered) pillar arrangement as compared to a square array arrangement.

Evaluation of the antimicrobial activity of Moringa oleifera seed extract as a sustainable solution for potable water

Pathogen contamination in drinking water sources is of great concern, particularly for communities with limited resources across the globe. At the same time, there is a pressing need to develop water treatment solutions which are sustainable and are ‘green’. To address this issue, we have provided a detailed antimicrobial study of the seed extract of Moringa oleifera, which is a common medicinal plant found all over southeast Asia and Africa. In this study we report the efficacy of the extract in inhibiting bacterial growth on agar and in nutrient medium (lauryl tryptose broth) and the role of different parameters of bacteria concentration and extract concentration on its antimicrobial activity. This study further involves the determination of the decay rates of a Gram-negative (Escherichia coli) and a Gram-positive (Bacillus subtilis) bacteria in 100 mL of non-turbid water in the presence of 2, 3, 5 and 10 mL of the seed extract. The seed extract volume of 10 mL led to a maximum bacterial decay of 93.2% for E. coli and 96.2% for B. subtilis. The bacterial decay data were fitted to exponential curves and three different regimes of decay were observed over a period of 6 h. B. subtilis showed 35% re-growth during the third regime compared to the initial test concentration, which can be attributed to the resistance created by the modification of the peptidoglycan backbone of the cell wall.