Adsorption of Triclosan on Nylon 66 Membrane: Preconcentration and Ultrasensitive Colorimetric Detection.

In this work, adsorption of triclosan (TCS) on nylon 66 membrane is explored to develop a preconcentration and sensing platform. Nylon 66 membrane exhibits superior sorption ability even for trace amounts of TCS (10 µg/L). Investigating the surface adsorption chemistry by XPS analysis revealed the formation of a hydrogen bond between the hydroxyl group of TCS and the amide group of nylon 66. In the absence of TCS, the amphiprotic water molecule forms a multilayer OH group on the membrane surface. However, TCS showed preferential adsorption on the membrane-replacing water molecule due to its higher hydrophobic partition coefficient. We validated the effective preconcentration of TCS on the membrane using LC-MS analysis. Performing colorimetry directly on the TCS-enriched membrane surface showed a visible color change for concentrations as low as 10 µg/L. The relative blue intensity was found to vary linearly over a concentration range of 10-100 µg/L, and we achieved a detection limit of 7 µg/L for a 5 mL sample. This method utilizes easy-to-use resources which drastically reduce the cost and complexity of analysis.

Adsorptive preconcentration integrated with colorimetry for ultra-sensitive detection of lead and copper.

This work proposes a novel detection method for the ultra-sensitive colorimetric determination of lead and copper in complex water matrix. The method integrates signal amplification with analytical sensing, achieved by adsorptive preconcentration and a colorimetric assay. We report for the first time a strategic application of batch adsorption as a preconcentration method and colorimetry performed directly on the adsorbent surface enriched with metal. Commercially available kaolin was used as the adsorbent to preconcentrate the metals. The colorimetric detection of Pb and Cu was achieved using sodium rhodizonate and bathocuproine salt as chromogenic indicators, respectively. This method eliminates the involvement of complex instrumentation and the need for new sensing material preparation. The proposed method possesses high sensitivity for both Pb and Cu under optimized conditions. A linear calibration curve is obtained in two concentration ranges, spanning 1 to 100 µg L-1 with a low detection limit of 0.6 and 1.2 µg L-1 for Pb and Cu, respectively. Further, the method enables visual detection of Pb at concentrations as low as 2.5 µg L-1 by the naked eye. We demonstrate the practical applicability of the method by simultaneous detection of Pb and Cu in six different real-water samples with good apparent recovery % [90-120%]. Detection using hand-held devices indicates the feasibility for on-site analysis. Overall, this platform method offers a high scope for de-centralized monitoring of pollutants at concentrations which are prevailing in the environment. Integrating adsorptive preconcentration with colorimetric assay enables quantitative metal detection in environmental water sample matrix.

Semi-batch and continuous production of Pickering emulsion via direct contact steam condensation.

We propose a versatile strategy for the production of highly stable water in oil Pickering emulsion by direct contact condensation of steam. In contrast to conventional methods that use mechanical energy for creating drops, the condensation of steam brought in contact with a non-aqueous colloidal dispersion is exploited to produce Pickering emulsions in two modes of operation, namely, semi-batch and continuous. As steam that comes in contact with oil condenses into water drops, the particles adsorb to the interface and thus arrest drop-drop coalescence. The adsorption of particles on the drop's surface imparts kinetic stability to the emulsions. The dependence of size of the emulsions as a function of parameters such as steam temperature, flow rate, particle type and particle concentration is investigated. We show that the tailoring of these parameters allows a precise control over droplet size distribution. The flexibility of continuous mode of operation makes it a potential technique for large scale production of emulsions suited for many applications.

Pleural fluid residue as a diagnostic tool for cytology-negative malignant pleural effusion: A proof-of-concept study.

Background: Pleural fluid residue, or macroscopic tissue, circulating freely in the pleural fluid obtained through direct filtration, may carry diagnostic histopathological information. We aimed to determine the histopathological concordance of pleural fluid residue in diagnosing TPE and MPE, compared with conventional pleural biopsy. This was a prospective cohort study of consecutive inpatients with cytology-negative exudative effusion who underwent pleuroscopy and had their initial suctioned pleural fluid filtered for residue samples. Pleural fluid residue demonstrated malignant cells in four out of seven cases of pleural biopsy-confirmed malignancy. Pleural fluid residue has comparable cytomorphology but reduced cellularity compared with pleural biopsy. No tuberculous histological features were present in the pleural fluid residue samples. In this preliminary study pleural fluid residue provided histopathological information for malignant pleural effusion, but no incremental diagnostic information for tuberculous effusion. However larger and more definitive studies are required to clarify these findings, and to explore the utility and suitability of pleural fluid residue for mutational analysis. What the study adds: This study demonstrates the potential of pleural fluid residue as a non-invasive diagnostic method for confirming malignancy in cytology-negative exudative effusion. What are the implications of the findings: In resource-limited settings or patients contraindicated for pleural biopsy, pleural fluid residue may provide a viable diagnostic alternative; however, this observation needs further validation.

Adsorptive colorimetric determination of chromium(VI) ions at ultratrace levels using amine functionalized mesoporous silica.

There is an urgent need for a rapid, affordable and sensitive analytical method for periodic monitoring of heavy metals in water bodies. Herein, we report for the first time a versatile method for ultratrace level metal detection based on colorimetric sensing. The method integrates preconcentration using a nanomaterial with a colorimetric assay performed directly on the metal-enriched nanomaterial surface. This method circumvents the need for tedious sample pre-processing steps and the complex development of colorimetric probes, thereby reducing the complexity of the analytical procedure. The efficacy of the proposed method was demonstrated for chromium(VI) ions detection in water samples. Amine functionalized mesoporous silica (AMS) obtained from a one-pot synthesis was utilized as a pre-concentration material. The structural and chemical analysis of AMS was conducted to confirm its physico-chemical properties. The pre-concentration conditions were optimized to maximise the colorimetric signal. AMS exhibited a discernible colour change from white to purple (visible to the naked eye) for trace Cr(VI) ions concentration as low as 0.5 µg L-1. This method shows high selectivity for Cr(VI) ions with no colorimetric signal from other metal ions. We believe our method of analysis has a high scope for de-centralized monitoring of organic/inorganic pollutants in resource-constrained settings.

Sensitive and selective determination of triclosan using visual spectroscopy.

Triclosan is a commonly used biocide effective against bacterial and fungal infections. However, its overuse in pharmaceutical and personal care products has resulted in its abundance in the natural environment. The detection of triclosan by visual spectroscopy can be carried out using the azo-coupling reaction of diazonium complexes. However, the reaction is also common to other phenolic compounds and aromatic amines, posing significant challenge. In this work, we investigate the azo-coupling reaction of triclosan and several commonly occurring analogous compounds to develop an improved spectroscopic method for the selective determination of triclosan without interference. We find that the azo-coupling reaction between the diazotized derivative and the phenolic compounds is highly dependent on the pH of the reaction media. At pH 7.2, the absorbance of the azo dye product of triclosan shows a peak at 452 nm which has minimal interference from other phenolic azo-dye products with the exception of naphthol. Naphthol shows an interference corresponding to 58% of the analytical signal of equimolar triclosan concentration. To overcome this, we develop an analytical model for the simultaneous determination of triclosan and naphthol from mixed solutions of the compounds. A linear calibration plot from 1.7 to 34 µM was obtained for both triclosan and naphthol with limit-of-detection (LOD) of 0.62 µM and 1.03 µM respectively. The developed protocol was tested for the analysis of water samples collected from various environmental sources spiked with different concentrations of triclosan and naphthol. The samples were enriched by solid-phase-extraction which allowed a 50-fold enhancement in detection of triclosan. The average relative recovery of triclosan in real samples was found to be 98.6% .

Numerical study of enhanced mixing in pressure-driven flows in microchannels using a spatially periodic electric field.

We propose an innovative mechanism for enhancing mixing in steady pressure driven flow of an electrolytic solution in a straight rectangular microchannel. A transverse electric field is used to generate an electroosmotic flow across the cross-section. The resulting flow field consists of a pair of helical vortices that transport fluid elements along the channel. We show, through numerical simulations, that chaotic advection may be induced by periodically varying the direction of the applied electric field along the channel length. This periodic electric field generates a longitudinally varying, three-dimensional steady flow, such that the streamlines in the first half of the repeating unit cell intersect those in the second half, when projected onto the cross-section. Mixing is qualitatively characterized by tracking passive particles and obtaining Poincaré maps. For quantification of the extent of mixing, Shannon entropy is calculated using particle advection of a binary mixture. The convection diffusion equation is also used to track the evolution of a scalar species and quantify the mixing efficiency as a function of the Péclet number.