DipTest: A litmus test for E. coli detection in water.

We have developed a new litmus paper test (DipTest) for detecting Escherichia coli (E. coli) in water samples by performing enzymatic reactions directly on the porous paper substrate. The paper strip consists of a long narrow piece of cellulose blotting paper coated with chemoattractant (at bottom edge), wax hydrophobic barrier (at the top edge), and custom formulated chemical reagents (at reaction zone immediately below the wax hydrophobic barrier). When the paper strip is dipped in water, E. coli in the water sample is attracted toward the paper strip due to a chemotaxic mechanism followed by the ascent along the paper strip toward the reaction zone due to a capillary wicking mechanism, and finally the capillary motion is arrested at the top edge of the paper strip by the hydrophobic barrier. The E. coli concentrated at the reaction zone of the paper strip will react with custom formulated chemical reagents to produce a pinkish-red color. Such a color change on the paper strip when dipped into water samples indicates the presence of E. coli contamination in potable water. The performance of the DipTest device has been checked with different known concentrations of E. coli contaminated water samples using different dip and wait times. The DipTest device has also been tested with different interfering bacteria and chemical contaminants. It has been observed that the different interfering contaminants do not have any impact on the DipTest, and it can become a potential solution for screening water samples for E. coli contamination at the point of source

Rapid detection of fluoride in potable water using a novel fluorogenic compound 7-O-tert-butyldiphenylsilyl-4-methylcoumarin

In the present work, we have synthesized a new water soluble colorless chemical compound 7-O-tert-butyldiphenylsilyl-4-methylcoumarin (TBDPSC) that releases fluorescent molecules imparting blue fluorescence to the solution, upon interaction with fluoride ions in water. The blue fluorescence can be visualized using simple hand held ultraviolet (UV) lamps. TBDPSC has excellent sensitivity and selectivity towards fluoride and our results indicate that fluoride concentrations as low as 0.2 mg/L can be accurately detected within a few seconds. Fluoride testing with TBDPSC is simple and rapid compared to the conventional methodologies without the requirement of trained personnel. Hence, the present fluoride detection method can be easily field deployable and particularly useful for monitoring water quality in limited resource communities

Characterization of nanometer-scale porosity in reservoir carbonate rock by focused ion beam\u2013scanning 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\u2013scanning 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\u2013300 nm) inside the solid dolomite matrix. We also show the degree of connectivity of these pores with micron-scale pores (2\u20135 \u3bcm) that were observed to further link with bulk pores outside the matrix.Peer reviewed: YesNRC publication: Ye

Comparison of DipTest wait (response) times for the appearance of the pinkish red color with respect to various dip times.

<p>The plot is shown for various known concentrations of <i>E</i>. <i>coli</i> spiked water samples.</p

Development of pinkish red color on the DipTest device after 2 hrs based on the concentrations of <i>E</i>. <i>coli</i> (CFU/mL).

<p>The control strip is with DI water, which shows no color.</p

Representation of the use of DipTest device to test the water sample for the presence of <i>E</i>. <i>coli</i> bacteria.

<p>Representation of the use of DipTest device to test the water sample for the presence of <i>E</i>. <i>coli</i> bacteria.</p

Existing paper based test strips for the detection of <i>E</i>. <i>coli</i>.

<p>The commercial product is denoted by “*”.</p

DipTest results for 40 different water samples used in this work.

<p>DipTest results for 40 different water samples used in this work.</p