Comparative Degradation Kinetics Study of Polyamide Thin Films in Aqueous Solutions of Chlorine and Peracetic Acid Using Quartz Crystal Microbalance

Monocationic versus dicationic-based monomethine cyanine dyes for ultrasensitive colorimetric detection of hypochlorite ion in water

Detecting residual chlorine as a hypochlorite ion (ClO-) in drinking water is crucial for ensuring disinfection effectiveness and safety. In the present study, we report two novel Quinolium Benzothiazole-Based Cyanine (3ethylbenzothiazol-2(3 H)-ylidene)methyl)-1-(4-iodobutyl)quinolin-1-ium tetrafluoroborate (IBTQ) and 1-(3-(4-(dimethylamino)pyridin-1-ium-1-yl)propyl)-4-((3-methylbenzothiazol-2(3 H)-ylidene)methyl)quinolin-1-ium diiodide (DMP-BTQ) hypochlorite (ClO-) sensors using UV- visible, colorimetric, and quartz crystal microbalance (QCM) techniques. The two sensors generate distinct absorption spectra, frequency shifts, and color changes that are visible to the naked eye. They exhibit high sensitivity and selectivity towards ClO-. The sensors have limits of detection (LOD) values in the range of 13.92 ppm and 0.127 ppm for IBTQ and DMP-BTQ, respectively, based on absorption performance with no interference of potential ions in drinking water. The method yields good recovery results, ranging from 97.4 to 103.0%, for ClO- detection in the studied water samples. In addition, the LOD for the QCM technique is 0.06 ppm for IBTQ and 0.045 ppm for DMP-BTQ with low quantification. The sensors can be loaded on paper strips for naked-eye detection of ClO- in domestic tap water and water treatment facilities. The sensors also provide low-cost, low cytotoxicity, high sensitivity, selectivity, and reusability of ClO- in water. The sensing mechanism was rationalized in terms of radical cation generation upon ClO- oxidizing action. The ease of cyanine oxidation was substantiated by quantum chemical studies including density functional theory (DFT) calculations, natural bond orbital (NBO) analysis, molecular electrostatic potential (MESP), and time-dependent density functional theory to support the experimental results.

Novel ultra-sensitive and highly selective cyanine sensors based on solvent-free microwave synthesis for the detection of trace hypochlorite ions in drinking water

The adoption of chlorine in drinking water disinfection with the determination of residual chlorine in the form of hypochlorite ion (ClO-) is in widespread demand. Several sensors including colorimetric, fluorometric, and electrochemical methods are currently in use, but detection limits and ease of application remain a challenge. In this work, two new cyanine derivatives-based ClO- sensors, that were prepared by solvent-free microwave synthesis, are reported. The two sensors are highly sensitive and selective to ClO-, exhibiting a noticeable color change visible to the naked eye. Additionally, the sensors can detect ClO- without interference from other potential water pollutants, with low detection limits of 7.43 ppb and 0.917 ppb based on absorption performance. When using fluorometric methods, the sensors' detection limits are pushed down to 0.025 ppb and 0.598 ppb for sensors I and II, respectively. The sensors can be loaded with paper strips for field and domestic detection of ClO- in tap water treatment installations. Using the quartz crystal microbalance (QCM) technique, these sensors showed strong detection sensitivity to ClO-, with detection limits of 0.256 ppm and 0.09 ppm for sensors I and II, respectively. Quantum chemical studies using density functional theory (DFT) calculations, natural bond orbital (NBO) analysis, molecular electrostatic potential (MESP), and time-dependent density functional theory (TD-DFT) supported the findings. The sensing mechanism is rationalized in terms of radical cation formation upon ClO- oxidation of cyanine sensors I and II.

Enhanced Removal of Photoresist Films through Swelling and Dewetting Using Pluronic Surfactants

Organic photoresist coatings, primarily composed of resins, are commonly used in the electronics industry to protect inorganic underlayers. Conventional photoresist strippers, such as amine-type agents, have shown high removal performance but led to environmental impact and substrate corrosiveness. Therefore, this trade-off must be addressed. In this study, we characterized the removal mechanism of a photoresist film using a nonionic triblock Pluronic surfactant [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)] in a ternary mixture of ethylene carbonate (EC), propylene carbonate (PC), and water. In particular, the removal dynamics determined by using a quartz crystal microbalance with dissipation monitoring was compared with those determined by performing confocal laser scanning microscopy and visual observation to analyze the morphology, adsorption mass, and viscoelasticity of the photoresist film. In the absence of the Pluronic surfactant, the photoresist film in the ternary solvent exhibited a three-step process: (i) film swelling caused by the penetration of a good solvent (EC and PC), (ii) formation of photoresist particles through dewetting, and (iii) particle aggregation on the substrate. This result was correlated to the Hansen solubility parameters. The addition of the Pluronic surfactant not only prevented photoresist aggregation in the third step but also promoted desorption from the substrate. This effect was dependent on the concentration of the Pluronic surfactant, which influenced diffusion to the interface between the photoresist and the bulk solution. Finally, we proposed a novel photoresist stripping mechanism based on the synergy between dewetting driven by an EC/PC-to-water mixture and adsorption by the Pluronic surfactant.

Degradable optical resonators as in situ microprobes for microscopy-based observation of enzymatic hydrolysis

Optical resonators work as precise physical and chemical sensors. Here, we assemble a whispering gallery mode resonator from a natural polymer, fibroin protein, and successfully observe its catalytic degradation reaction as a spectral shift. This methodology will contribute to the precise in situ observation of biological reactions by optical microscopy.