Sensitive and fast optical HCl gas sensor using a nanoporous fiber membrane consisting of poly(lactic acid) doped with tetraphenylporphyrin

Curcuma longa-Based Optical Sensor for Hydrochloric Acid and Ammonia Vapor Detection

In this research, we present a prototype optical system that offers significant advances in detecting hydrochloric acid (HCl) and ammonia (NH3) vapors. The system utilizes a natural pigment sensor based on Curcuma longa that is securely attached to a glass surface support. Through extensive development and testing with HCl (37% aqueous solution) and NH3 (29% aqueous solution) solutions, we have successfully demonstrated the effectiveness of our sensor. To facilitate the detection process, we have developed an injection system that exposes C. longa pigment films to the targeted vapors. The interaction between the vapors and the pigment films triggers a distinct color change, which is then analyzed by the detection system. By capturing the transmission spectra of the pigment film, our system allows a precise comparison of these spectra at different concentrations of the vapors. Our proposed sensor exhibits remarkable sensitivity, allowing the detection of HCl at a concentration of 0.009 ppm using only 100 µL (2.3 mg) of pigment film. In addition, it can detect NH3 at a concentration of 0.03 ppm with a 400 µL (9.2 mg) pigment film. Integrating C. longa as a natural pigment sensor in an optical system opens up new possibilities for detecting hazardous gases. The simplicity and efficiency of our system, combined with its sensitivity, make it an attractive tool in environmental monitoring and industrial safety applications.

BODIPY-based fluorescent chemosensor for phosgene detection: confocal imaging of nasal mucosa and lung samples from mouse exposed to phosgene

The improper use of phosgene, either as a chemical warfare agent or a leak during chemical production, causes significant risks to human life and property. Therefore, it is particularly important to develop a rapid and highly selective method for the detection of phosgene. In this article, a highly selective fluorescent sensor ONB with a BODIPY unit as a fluorophore and o-aminophenol as a reactive site was constructed for the selective and rapid detection of phosgene in solution. The ONB-containing nanofibers were sprayed onto a non-woven fabric by electrostatic spinning and cut into test films, which can be used well for the detection of gaseous phosgene. While, there were no reported bio-imaging applications for phosgene detection. In this work, nasal mucosa and lung samples from the mice exposed to gaseous phosgene after dropping the ONB solution through the nasal cavity achieved bio-imaging applications successfully.

QCM-Based HCl Gas Detection on Dimethylamine-Functionalized Crosslinked Copolymer Films

In this work, sensing behaviors and mechanisms of two crosslinked copolymers with dimethylamine and dimethylamide functional groups were compared and investigated for their ability to detect hydrogen chloride (HCl) gas. The crosslinked copolymer films were photopolymerized on quartz crystal electrodes using a micro-contact printing technique. The gas sensing behaviors were analyzed by measuring resonant frequency (Δf) of quartz crystal microbalance (QCM). The HCl binding capacity of photopolymerized films, with a mass between 4.6 and 5.9 μg, was optimized. Under optimized film mass conditions, the poly(2-dimethylaminoethyl methacrylate-co-ethylene glycol dimethacrylate) (DMAEMA-co-EGDMA), poly(DMAEMA-co-EGDMA), film, C2-DMA, showed a 13.9-fold higher binding capacity than the poly(N,N-dimethylacrylamide-co-ethylene glycol dimethacrylate, poly(DMAA-co-EGDMA), film, C0-DMA, during HCl gas adsorption. HCl gas was effectively adsorbed on the C2-DMA film because of the formation of tertiary amine salts through protonation and strong ionic bonding. Furthermore, the C2-DMA film exhibited excellent sensitivity, of 2.51 (ng/μg) (1/ppm), and selectivity coefficient (k* = 12.6 for formaldehyde and 13.5 for hydrogen fluoride) compared to the C0-DMA film. According to the experimental results, and due to its high functionality and stability, the C2-DMA film-coated QC electrode could be used as an HCl gas sensor, with low-cost and simple preparation, in future endeavors.

Covalent organic frameworks as multifunctional materials for chemical detection

Sensitive and selective detection of chemical and biological analytes is critical in various scientific and technological fields. As an emerging class of multifunctional materials, covalent organic frameworks (COFs) with their unique properties of chemical modularity, large surface area, high stability, low density, and tunable pore sizes and functionalities, which together define their programmable properties, show promise in advancing chemical detection. This review demonstrates the recent progress in chemical detection where COFs constitute an integral component of the achieved function. This review highlights how the unique properties of COFs can be harnessed to develop different types of chemical detection systems based on the principles of chromism, luminescence, electrical transduction, chromatography, spectrometry, and others to achieve highly sensitive and selective detection of various analytes, ranging from gases, volatiles, ions, to biomolecules. The key parameters of detection performance for target analytes are summarized, compared, and analyzed from the perspective of the detection mechanism and structure-property-performance correlations of COFs. Conclusions summarize the current accomplishments and analyze the challenges and limitations that exist for chemical detection under different mechanisms. Perspectives on how future directions of research can advance the COF-based chemical detection through innovation in novel COF design and synthesis, progress in device fabrication, and exploration of novel modes of detection are also discussed.

Ultrafine Tungsten Oxide Nanowires: Synthesis and Highly Selective Acetone Sensing and Mechanism Analysis

By using WCl₆ as a precursor and absolute ethanol as a solvent, ultrafine W₁₈O₄₉ nanowires (UFNWs) were synthesized by a one-pot solution-phase method and used as gas sensing materials. Their crystal structure, morphology, and specific surface area can be regulated by controlling precisely the content of the WCl₆ precursor in the solution. It has been found that, when the content of the precursor is 4 mg/mL, the formed products are UFNWs with a diameter of about 0.8 nm, only one crystal plane [010] is exposed, and the specific surface area is 194.72 m²/g. After the gas sensing test, we found that they have excellent selectivity to acetone. The response of 50 ppm acetone reaches 48.6, the response and recovery times are 11 and 13 s, respectively. In order to evaluate the interaction between W₁₈O₄₉ surfaces and different volatile organic compound (VOC) molecules, we simulated and calculated the adsorption energy (E_Ads) among different W₁₈O₄₉ surfaces and different VOCs by DFT. The calculated results are in agreement with the experimental results, further confirming the ultrahigh selectivity of W₁₈O₄₉ UFNWs to acetone. The above results demonstrate that the high selectivity of W₁₈O₄₉ UFNWs to acetone is due to the exposure of its single crystal plane [010]. This work has practical significance for better detection of acetone.

Fluorescent Chemosensor for Dual-Channel Discrimination between Phosgene and Triphosgene

As highly toxic and accessible chemical reagents, phosgene and triphosgene have become a serious threat to public safety. So, it is highly desirable to develop facile methods to detect and recognize them. In this article, a novel fluorescent chemosensor, Phos-4, has been constructed with 1,8-naphthalimide as the fluorophore and 2-(2-aminophenyl)imidazol as the recognition sites for discrimination between phosgene and triphosgene in a dual-channel mode for the first time. Owing to the difference in electrophilicity between chlorocarbonyl and trichloromethoxycarbonyl, the sensing reaction of Phos-4 with phosgene undergoes two carbamylations to afford a cyclic product with green fluorescence, and only one carbamylation occurs for triphosgene to form a noncyclic product with blue fluorescence. The sensor Phos-4 exhibits high sensitivity (the limit of detection, 3.2 nM, for phosgene, and 1.9 nM, for triphosgene) and high selectivity in solutions. Furthermore, facile test papers containing Phos-4-embedded nanofibrous membrane have been fabricated by the electrospinning technology. The test papers can provide visual and selective detection of phosgene with a lower limit of detection (42 ppb) and a faster response (≤10 s) in the gas phase over those in solutions. The test paper with Phos-4 is promising to be a practical detection tool of gaseous phosgene.

A gaseous hydrogen chloride chemosensor based on a 2D covalent organic framework

A tetraphenylethene-based 2D covalent organic framework (COF) has been synthesized. It exhibits a very fast response and high sensitivity to the presence of gaseous HCl by way of distinct changes in fluorescence emission and color, which makes the COF a good chemosensor for spectroscopic and naked-eye detection of gaseous HCl.

HCl Gas Sensor Coating Based on Poly(N-isopropylacrylamide) Nanoparticles Prepared from Water-Methanol Binary Solvent

Poly(N-isopropylacrylamide) (PNIPAM) nanoparticles formed in water-methanol binary solvent were successfully deposited on a resonator surface at room temperature by exploiting the cononsolvency effect on the phase transition of PNIPAM aqueous solutions. Scanning electron microscopic observation revealed that the nanoparticles were secondary and made up of agglomerated primary spherical particles of about 10-nm diameter, buried in the film. The magnitude of the sensor response toward HCl gas was larger than that of the nanoparticle sensor prepared from pure water solvent, and the sensitivity to 1 ppm of HCl of sensor-coated nanoparticles based on the present method was 3.3 Hz/ppm. The recovery of the sensors was less than 90% at first cycle measurement, but had improved to almost 100% at the third cycle.

Humidity-insensitive temperature sensor based on a quartz capillary anti-resonant reflection optical waveguide

A compact, humidity-insensitive, fiber optic temperature sensor based on a quartz capillary, antiresonant reflecting optical waveguide was proposed and experimentally demonstrated. The transmission spectral responses of the proposed sensor were experimentally investigated regarding temperature variation and environmental humidity. Resonant dips exhibited temperature sensitivity as large as 201 pm/°C from -30 to 45 °C in a humid environment. By coating a sufficiently thick gold film onto the sensor surface, the humidity cross-sensitivity issue was effectively resolved. This proposed sensor was anticipated to find potential applications in humid environments, and moreover, immunity to humidity-sensitivity ensures its applicability in marine environments.

A fluorescent and colorimetric sensor based on a porphyrin doped polystyrene nanoporous fiber membrane for HCl gas detection

A fluorescent and colorimetric HCl gas sensor based on the use of the optical probe 5,10,15,20-tetraphenylporphyrin (TPPH₂) contained in a polystyrene nanoporous fiber membrane was facilely fabricated by electrospinning method.