Detection of Cyanobacteria in Eutrophic Water Using a Portable Electrocoagulator and NanoGene Assay

We have demonstrated the detection of cyanobacteria in eutrophic water samples using a portable electrocoagulator and NanoGene assay. The electrocoagulator is designed to preconcentrate cyanobacteria from water samples prior to analysis via NanoGene assay. Using <i>Microcystis aeruginosa</i> laboratory culture and environmental samples (cell densities ranging from 1.7 × 10⁵ to 4.1 × 10⁶ and 6.5 × 10³ to 6.6 × 10⁷ cells·mL^–1, respectively), the electrocoagulator was evaluated and compared with a conventional centrifuge. Varying the operation duration from 0 to 300 s with different cell densities was first investigated. Preconcentration efficiencies (obtained via absorbance measurement) and dry cell weight of preconcentrated cyanobacteria were then obtained and compared. For laboratory samples at cell densities from 3.2 × 10⁵ to 4.1 × 10⁶ cells·mL^–1, the preconcentration efficiencies of electrocoagulator appeared to be stable at ∼60%. At lower cell densities (1.7 and 2.2 × 10⁵ cells·mL^–1), the preconcentration efficiencies decreased to 33.9 ± 0.2 and 40.4 ± 5.4%, respectively. For environmental samples at cell densities of 2.7 × 10⁵ and 6.6 × 10⁷ cells·mL^–1, the electrocoagulator maintained its preconcentration efficiency at ∼60%. On the other hand, the centrifuge’s preconcentration efficiencies decreased to nondetectable and below 40%, respectively. This shows that the electrocoagulator outperformed the centrifuge when using eutrophic water samples. Finally, the compatibility of the electrocoagulator with the NanoGene assay was verified via the successful detection of the microcystin synthetase D (<i>mcyD</i>) gene in environmental samples. The viability of the electrocoagulator as an in situ compatible alternative to the centrifuge is also discussed

Quantitative Detection of Single Walled Carbon Nanotube in Water Using DNA and Magnetic Fluorescent Spheres

Carbon nanotubes (CNTs) possess unique properties that have led to an increase in their research and usage for a wide variety of fields. This growing demand of CNTs poses a major public health risk given its unregulated release into the environment. Unfortunately there is a significant information gap on the actual quantity of CNTs in the environment due to limitation of existing detection methods. This is mainly owing to the ubiquitous carbon chemistry of CNT. In response we developed a method (<i>CNT-capture method</i>) that is able to structurally differentiate CNT from other interference carbon materials in an aqueous medium. The affinity between single walled nanotubes (SWNTs) and specific single stranded DNA (ssDNA) was employed to capture SWNTs in water. SWNT-specific separation was obtained via magnetic separation. Dual fluorescent labels attached to sandwich ssDNA probes were used for quantification. The specific affinity between DNA and SWNTs was verified and no significant side-interactions were observed. With optimized incubation duration (30 min) and buffer composition (10^–7 % sodium dodecyl sulfate and pH 7.9), a calibration curve of quantification (<i>R</i>² = 0.90) was obtained with a range of SWNT concentration (0.05–10 μg/mL) against graphene as a planar analog. Comparison to other spectroscopy based methods was carried out to highlight the specificity and sensitivity of the presented method for CNT detection in aquatic sample

Highly Sensitive Detection of Bisphenol A by NanoAptamer Assay with Truncated Aptamer

For the sensitive quantification of bisphenol A (BPA), we have developed NanoAptamer assay, which employs aptamer and complementary signaling DNA, a set of quantum dots (QD), and magnetic beads (MBs). Signaling DNA–QD₆₅₅ was tethered to MB–QD₅₆₅ via the aptamer. The affinity of the aptamer to BPA resulted in the release of the signaling DNA–QD₆₅₅ from the complex and hence the corresponding decrease in the QD₆₅₅ fluorescence measurement signal. Three new aptamers (23, 58, and 24-mer) were designed via truncation of the reference aptamer (73-mer). The sensitivity and selectivity of each aptamer for BPA detection via NanoAptamer assay were investigated. One of the truncated aptamers (24-mer) has shown a significantly better performance (limit of detection, LOD, 0.17 pg/mL) than the reference 73-mer aptamer (LOD, 570 pg/mL). It has also shown the best selectivity for BPA detection over BPA analogues (i.e., bisphenol B, bisphenol C, and diethylstilbestrol). It corresponded to a normalized fluorescence change of 33.7% at the environmentally relevant concentration of 1 ng/mL (1 ppb) BPA; however, the analogues remained unchanged (2.3–3.9%)

Adsorption of selected micropollutants on powdered activated carbon and biochar in the presence of kaolinite

<p>Commercially available powdered activated carbon (PAC) and activated biochar (produced in the laboratory), combined with kaolinite, were used to determine the adsorption of a beta-blocker (atenolol, ATN) and sunscreen compounds (benzophenone, BZP; and benzotriazole, BZT); a hypothesis was made that the presence of kaolinite would increase the adsorption of those target compounds. Various synthetic solutions were prepared by altering the pH, background ions, ionic strength, and glucose/humic acid content to mimic various natural water conditions. The removal efficiency of biochar–kaolinite was higher than that of PAC–kaolinite, presumably because the relatively high surface area and pore volume of biochar resulted in a higher adsorption capacity for the target compounds. Removal of the compounds in the absence of kaolinite followed the order BZP > ATN > BZT (<i>a</i> (mg/g); Langmuir maximum adsorption capacities were as follows: 85.0, 20.6, and 15.6 for PAC, and 125, 37.5, and 25.9 for biochar, respectively). An increase in the pH from 3.5 to 10.5 decreased the adsorption of ATN, BZP, and BZT by 14.5, 2.1, and 14.4%, respectively, by biochar–kaolinite. Additionally, an increase in background ions and their ionic strength, using NaCl, Na₂SO₄, and CaCl₂, increased the adsorption of the target compounds slightly, by 2.0–6.6%, depending on the target compound. Overall, biochar had a higher adsorption capacity for all chemicals tested compared with PAC, suggesting that biochar derived from loblolly pine chip may be a promising sorbent for water/wastewater treatment and environmental applications.</p