Observed Color Changes Research Articles

Solution plasma synthesis of nitrogen-doped carbon dots from glucosamines: Comparative fluorescence modulation for dopamine detection

The intriguing fluorescence characteristics of carbon dots (CDs) have led to many sensor applications, particularly for dopamine (DA), a molecule linked to various diseases. This study prepares CDs from glucose and glucosamine (nitrogen-free and nitrogen-containing precursors) using a simple solution plasma process (SPP). We explore how nitrogen elements and counterions in glucosamine (hydrochloride and sulfate) affect CD properties and their ability to modulate fluorescence for DA detection. Glucosamine offers three advantages over glucose: (i) single-step CD synthesis via SPP, (ii) enhanced fluorescence of CDs, and (iii) improved fluorescence response to DA. We investigate the DA detection capabilities of N,S-CDs (from glucosamine sulfate) and N,Cl-CDs (from glucosamine hydrochloride). Both can sense DA with distinct photoluminescence responses. N,S-CDs show selectivity and fluorescence brightening upon DA interaction, with a detection limit of 33.05 μM. N,Cl-CDs demonstrate higher sensitivity with a lower detection limit of 0.1212 μM through fluorescence quenching. Silver ions (Ag+) may also contribute to N,Cl-CDs quenching; however, the observed color change to gray due to silver nanoparticle (AgNP) formation helps pinpoint the quenching substance. The varied photoluminescence responses arise from different surface functional groups: N,S-CDs have amino-rich surfaces, while N,Cl-CDs have conjugated carbonyl-rich surfaces. This study illustrates the mechanisms of DA detection and AgNP formation, suggesting the potential of CDs in medical diagnostics as selective tools for disease diagnosis. Additionally, we compare the DA sensing methodology of our CDs with existing literature, highlighting the advantages of our sensor.

An Optical Au3+ Sensor Based on layer-by-layer PEI/PAA-Rho thin Films on ITO.

This study presents the development of a sensitive and selective gold ion (Au3+) sensor utilizing layer-by-layer (LbL) assembled thin films composed of polyethylenimine (PEI) and poly (acrylic acid) (PAA) conjugated with rhodamine (Rho). The first study revealed that the polymeric sensors (PAA-Rho) demonstrated significant selectivity and sensitivity in their colorimetric and fluorescence responses to Au3+ compared to other metal ions. In their spirolactam form, the polymeric sensors were non-fluorescent but could selectively transform into the fluorescent ring-opened amide form upon interaction with Au3+ ions, resulting in fluorescence enhancement and observable color changes. Common co-existing metal ions showed negligible interference in the detection of Au3+. The LbL sensor exhibited a linear increase in absorbance with the addition of bilayers, confirming successful film deposition. Surface morphology analysis using SEM, along with structural confirmation via ATR-FTIR and XRD, further validated the sensor's capability to detect cation. Results demonstrated that the LbL sensor exhibited selectivity for Au3+ ions within the range 1 × 10-6 to 1 × 10-3 M. This approach offers an easily understandable and intrinsically sensitive means for detecting Au3+ ions in both environmental and biological applications.

Fluorescence and Colorimetric Dual-Readout Detection of Tetracycline Using Leucine-Conjugated Iron Oxide Quantum Dots

This study developed a dual-readout system utilizing fluorescence and colorimetry based on iron oxide quantum dots (IO-QDs) for detecting tetracycline (TCy). IO-QDs were synthesized within 6 h using L-leucine as a surface modifier, achieving a more efficient route. Upon interaction with TCy, IO-QDs exhibited a significant decrease in fluorescence response and observable color changes, while fluorescence lifetime remained consistent regardless of TCy presence. Moreover, IO-QDs’ fluorescence response remained stable across various temperatures. The Förster resonance energy transfer distance of less than 2 nm and a quenching constant of 2.90 × 1012 M–1s–1 indicated static quenching in the presence of TCy. Additionally, significant changes in observed and corrected fluorescence efficiency suggested the involvement of the inner filter effect in the fluorescence quenching of IO-QDs. The synthesized IO-QDs were then utilized for selective and rapid fluorescence-based TCy detection, showing a linear range of 0.5 to 80 μM. Simultaneously, a colorimetric method for TCy detection was established, demonstrating a good linear relationship within the range of 0.5 to 20 μM. The detection limits for TCy were determined as 0.539 and 0.329 μM using fluorescence and colorimetric approaches, respectively. Furthermore, IO-QDs were applied to detect real samples, and the dual-readout probe exhibited satisfactory recoveries, confirming the practical reliability of the developed method for analyzing milk and drinking water samples.

Enhancing thermal stability and corrosion resistance of carbon-carbon composites with iridium coatings deposited by electron beam physical vapor deposition

Abstract Carbon–carbon (C−C) composites are extensively used in high-temperature environments such as Combustor Liners and Turbine Blades in jet engines and Throat Inserts, Nozzle Extensions and Exit Cones in rocket engines due to their excellent thermal stability and mechanical properties. However, at temperatures exceeding 800 °C, these composites require additional protection to prevent degradation. This study aims to investigate the behavior of C−C composites when coated with high-purity metallic iridium using Electron Beam Physical Vapor Deposition (EBPVD). The research problem focuses on enhancing the high-temperature performance and corrosion resistance of C−C composites for aerospace applications. The methodology involves depositing a uniform 5.6 microns thick iridium coating on C−C substrates and characterizing the coating’s microstructure, hardness, and corrosion resistance. FESEM micrographs reveal that the iridium coating adheres uniformly to the substrate without any seepage, and XRD analysis confirms an FCC crystal structure with a densely packed grainy surface. Corrosion tests were conducted using a BIOLOGIC electrochemical workstation in a sodium chloride environment indicate a corrosion rate of 0.00307 mm year−1. The Nyquist, Bodo plots, and Taffel plots were constructed for the better understanding of the corrosion mechanism. While the OCP was constructed to understand the stability and the corrosion resistance of the C−C samples. Microhardness of the coating, measured under a normal applied load of 0.20 N, is 702 HV. The coated samples also could withstand thermal shocks between −40 °C and 1500 °C for 40 h without observable damage or color change. These findings demonstrate the potential of iridium-coated C−C composites to maintain structural integrity and performance in extreme aerospace environments, significantly impacting the field by providing a reliable protective solution for high-temperature applications.

Dual-mode iodine sensing: Colorimetric and electrochemical detection methods using functionalized gold nanoparticles

Iodine in natural and treated waters exists mainly as iodide, iodate, and molecular iodine (I2). I2 is a highly volatile and reactive species impacting biological and chemical systems. Iodine, a vital micronutrient, is essential for human and animal growth and metabolism. It also plays a crucial role in synthesising artificial adrenaline within the metabolic processes of humans and animals. It is also widely used as an antiseptic, disinfectant, and for emergency water disinfection. Moreover, iodine deficiency can result in various diseases, especially hypothyroidism and goitre. Given its critical functions, it is imperative to have a straightforward, dependable, and efficient method for monitoring iodine levels. This study introduces a simple and innovative I2 detection system based on its reactivity, toxicity, and role as an indicator of oxidative conditions in water. It operates in terms of based on optical and electrochemical signal changes, utilising the anti-aggregation mechanism of gold nanoparticles (AuNPs) and 6-mercaptohexanol (MHA) for sensitive and selective detection under mild conditions. I2 determination is achieved by observing the colour change in AuNPs, which is influenced by competitive interactions between MHA, I2, and AuNPs. The optical detection system, with its low detection limit (LOD=260 nM), is based on the straightforward observation of colour changes. On the other hand, the electrochemical detection method utilises changing redox peaks observed in anodic region, providing selective and sensitive I2 detection (LOD=100 nM). The probe effectively detects the presence of I2 in real water samples as a practical application. Moreover, the proposed method revolutionises I2 detection by incorporating a smartphone for signal reading, eliminating the need for specialised equipment and significantly reducing the detection cost. This cost-effective approach carries the potential to expedite on-site and naked-eye I2 detection, opening up new possibilities for research and application.

Thermochromic Properties of 3C-, 6H- and 4H-SiC Polytypes up to 500°C

The thermochromic properties (color change with temperature) of n type doped SiC wafers of different polytypes (3C, 4H and 6H) have been investigated up to 500°C under air. It was found that 3C-SiC color passes from bright yellow at room temperature to deep orangeat 500°C leading to a color contrast (ΔE) as high as 64. The hexagonal polytypes undergo also a color change upon heating but far less pronounced, with ΔE values <20. All these semiconductors undergo band gap shrinkage upon heating which effect largely participated to the observed color change. This effect is very sensitive for 3C polytypesince its bandgap is already in the visible energy range at room temperature. The thermochromicity of 3C-SiC was found to be reversible thanks to its thermal stability and its resistance towards oxidation.

Investigating Ion-Coupled Electron Transfer of Conducting Polymers

After years of basic and applied studies of electron transfer in redox active films, the fundamentals of ion transfer during the exchange remain to be understood. Empirically, the processes are ion-transport limited. Using a conducting polymer as a model system, we aim to study the relationship between electron and ion transfer during redox switching.We work on electrochromic conducting polymers because of their observable and detectable color changes in addition to the current during the redox switching. Tracing optical signals can enhance the understanding of electrical signals from redox reactions. When a potential is applied to the electroactive polymer, its color will change from lighter to darker or vice versa. Keeping in mind that absorbances are additive, the ratio of the contents that make up the overall color of the polymer changes. This ratio change is directly proportional to the amount of matter under inter-conversion during the redox reaction.This study aims to explore the ion-electron mechanism in conductive polymers using the simultaneous Spectro-CV method. To achieve this, we conducted cyclic voltammetry at exceptionally high scanning rates, leveraging the conductive polymer's color-changing property. At these high rates, ion movement was restricted due to limited time for forward and backward motion, potentially reaching a point of stagnation. The investigation focused on whether the polymer would continue changing color, providing insights into ion-electron transfer. In addition, we are conducting EIS measurements alongside simultaneous Spectro-CV measurements and attempting to fit the impedance response of the polymer with an appropriate model. We aim to track the time constants provided by the polymer at different voltage values and understand the corresponding physical processes associated with these time constants. Additionally, we aim to use our EIS model to validate the desired redox current information obtained from optical data. We mathematically reach the faradaic portion of the total current with EIS and compare the results obtained from optical data.

Azo Based Chromogenic Sensor: An Approach for Naked Eye Detection of Biologically Relevant Anions and Metal Cations

Abstract: It was previously reported that azo compounds are vigorous and chemically stable compounds and well-known chromophores. Having different chromophores, the azo dyes act as probing units for capturing the charged particles either by electron transfer or deprotonation mechanisms. The probing efficiency usually exhibits in the magnitude of variations in UV absorbance, NMR peaks and visually observed color changes. The sensing application is a prerequisite for numerous analytical techniques involved in pharmaceutical as well as pathological discipline. In the last two decades, numerous azo based sensors have been developed, which render low cost and effective sensing approaches towards ionic diagnosis through instantaneous eye beaming chromogenic change. This sensing approach is simple, cost-effective, and precise and provides reliable quantitative and qualitative statistics of an analyte present in a complex environment. Our present study culminates the recent progress on the synthesis of azo compounds and their chromogenic sensing application towards various reactive analytes through reviewing spectral variations and colorimetric observations. This review article assesses the potential of azo dyes in chromogenic sensing for different analytes. We believe this review will be of interest and important for researchers working on designing azo-based chromogenic sensors.

Control of the size distribution of AuNPs for colorimetric sensing by pulsed laser ablation in liquids

Gold nanoparticles (AuNPs) are extensively employed in colorimetric sensing, taking advantage of their optical properties to detect variables via observable color changes. These properties are primarily driven by localized surface plasmon resonance (LSPR), particularly pronounced in AuNPs within the visible spectrum. In this study, AuNPs were synthesized via pulsed laser ablation in liquids (PLAL) with a laser pulse energy (Ep) ranging from 25 mJ to 75 mJ. Size distributions, hydrodynamic diameters, polydispersity indices (PDI), absorbance intensity, and LSPR were characterized. Spherical AuNPs with FCC structure were synthesized, exhibiting a maximum absorption peak centered at approximately 529 nm wavelength and a size range between 50 nm and 178 nm, easily adjustable depending on the laser pulse energy used in the synthesis process. An anomalous behavior was noted at Ep=50 mJ, exhibiting three peaks in size distribution, high PDI, low absorbance intensity, and indistinct LSPR. By extending the ablation time from 10 min to 30 min, particle size decreased alongside lower PDI. Size distributions transitioned from three to two peaks, absorbance increased, and LSPR became readily identifiable. These findings underscore the size control over AuNP characteristics achievable through PLAL synthesis parameters, promising significant implications for the optimization of colorimetric sensor design and development.

A novel fluorescence sensor film for hydroquinone based on a graphene quantum dots-nano activated carbon composite

A novel film sensor, composed of graphene quantum dots-nano activated carbon, chitosan, and PVA, offers a simple and effective hydroquinone (HQ) detection. This film exhibits impressive HQ adsorption under ambient conditions (room temperature, pH 7, 3 h) and utilizes a readily observable fluorescence color change for quantification. Upon HQ binding, the film's fluorescence color shifts from yellow-green to blue, enabling a linear detection range of 1.0–150 mg⋅L−1 based on intensity analysis of the blue component (B value). Calibration curves generated on the same day (n = 3) exhibit high precision, with standard deviations of the linear equation parameters below 0.014 and a low detection limit of 0.5 mg⋅L−1. The film exhibits exceptional stability, retaining its color and performance for up to 20 days. This stability is further corroborated by recovery experiments utilizing HQ-spiked water samples at concentrations of 2.5 mg⋅L−1 and 40 mg⋅L−1, where recoveries of 106 % and 95 % were achieved, respectively. These results demonstrated the sensor's reliable quantification capabilities. Notably, the sensor exhibited insignificant interference from commonly co-existing substances such as ethanol, ascorbyl glucoside, arbutin, kojic acid, and methylene blue. However, Cu²⁺, Fe³⁺, and catechol did cause some interference. This versatility, coupled with its straightforward operation, makes the film sensor a promising candidate for on-site HQ detection in diverse environmental monitoring applications.

A Cobalt(II) based coordination architecture for efficient colorimetric sensing of ammonia and amine vapors

This work presents the design, synthesis, and characterization of a new cobalt (II) based coordination architecture, {[Co(toua)(4,4′-bpy)].2H2O}n (1); where toua is 3,6,9-trioxaundecanaote and 4,4′-bpy is 4,4′-bipyridine tailored for efficient sensing of ammonia and amines. The formation and identity of 1 was confirmed by elemental analysis, spectroscopic study (FTIR and UV–visible spectroscopy), PXRD, XPS, FESEM, and BET analysis. The colorimetric sensing capability of 1 towards ammonia and various smaller-sized amines in the vapor phase through observable color changes is explored in this study. Their interaction with 1 is elucidated through FTIR, UV–Visible and Fluorescence spectroscopy, FESEM, and TCSPC analysis. The fluorescence sensing experiments demonstrate a remarkable quenching/enhancement effect with the addition of ammonia and various amines, showcasing the compound’s sensitivity and selectivity. The quenching/enhancement efficiency follows the order: NH3>Ethylenediamine (EDA)>1,3-diaminopropane (DAP)>n-propylethylenediamine (n-PEDA), following the molecular dimensions and steric hindrance surrounding nitrogen atoms. Hydrogen bonds and host-guest interactions, including (C–H)pyridinium⋅⋅⋅N interactions, are identified as the driving forces for the sensing process. Additionally, the paper reveals a rare occurrence of both “turn-off” and “turn-on” sensing behavior for the same compound, showcasing its versatility. The calculated RSD for the fluorometric sensor was found to be 1.03 % calculated from its triplicate readings at 240 nm. Limits of detection (LODs) and Limit of Quantification (LOQs) for NH3 (0.52 μM, and 1.74 μM) EDA (1.2 μM, and 4.2 μM), DAP (3.1 μM, and 10.5 μM), and n-PEDA (3.3 μM, and 11.2 μM) respectively) underscore the effective sensing capabilities of 1. The robustness of 1 upon exposure to amines was confirmed by PXRD. These findings justify that 1 is a promising vaporchromic probe for the fast and selective detection of ammonia and amines.

An enhanced multifunctional chitosan-based active packaging film reinforced with cinnamon essential oil encapsulating onion peel anthocyanins

The fabrication of bio-hybrid composites utilizing polymers, nanomaterials, essential oils, and other substances is gaining popularity due to its multi-functionality and application across various fields. Many industries today effectively employ innovative composite and multilayer materials by considering their benefits in several areas. In particular, the food industry uses innovative, multi-functional packaging materials based on biodegradability to accomplish multiple tasks. Many researchers have recently shown interest in an innovative and intelligent food packaging film with indicators for real-time food safety and protection. It is preferable to use anthocyanins, as an indicator in the active packaging film to track the freshness of food by observing color changes in the packaged film upon a shift in pH. In the current investigation, ethanol was used as a solvent to obtain anthocyanin-rich onion peel extracts (AROPE), using conventional and ultrasound-assisted extraction techniques, which were then used as an indicator in the packaging films. To develop antioxidant and pH-sensing films, anthocyanin-rich onion peel extract was blended into the chitosan and cinnamon essential oil matrix. Films displayed significant color variations in acidic and alkaline environments over short periods making them easy to perceive with the naked eye. For real-world applications, the fabricated films mechanical, structural, and physical characteristics were further explored. Because of their sensory qualities, colors, and antimicrobial benefits, these novel chitosan-based films could be ideal for food packaging to enhance food security.

Portable Sensing Platform for the Visual Detection of Iodide Ions in Food and Clinical Samples

The detection of iodide ions (I−), despite challenges due to low concentrations and potential masking, is crucial for studying physiological processes and diagnosing diseases. A colorimetric sensor was developed to improve I− ion monitoring and facilitate on-site detection based on filter paper, which is a cost-effective platform. The sensor observed color changes in response to the exposure of hydrogen peroxide (H2O2), 3,3′,5,5′-tetramethylbenzidine (TMB), from colorless to yellowish brown. The sensor demonstrated a detection limit of 0.125 × 10−6 M for I− ions in a relatively wide range of 0.01 to 15 × 10−6 M under optimized conditions including gel concentration, temperature, incubation time, TMB and H2O2 concentration, and pH. Furthermore, the proposed sensor was successfully employed in a variety of applications, such as biological (urine and blood serum), food (egg yolk and snacks), and environmental samples (tap water). The study established effective recoveries in complex media for visual on-site I− ion monitoring, indicating the developed assay as a potent, affordable, and practical platform.

Effect of silver nanoparticles synthesized by Lecanicillium lecanii and their combinations with insecticides (Sivanto and Deltamethrin) on larvae and adults of Tribolium confusum Duv. (Tenebrionidae : Coleoptera)

This research focused on developing a nanopesticide derived from silver nanoparticles (AgNPs) synthesized through the metabolic activities of the fungus Lecanicillium lecanii Gams & Zare 2001). The study aimed to assess its efficacy against the flour beetle Tribolium confusum and explore its synergistic effects with two chemical pesticides, Sivanto 20% and deltamethrin 2.5%. Biotinylated AgNPs were successfully produced using the biomass of the fungus L. lecanii. Characterization of silver nanoparticles was achieved through the observable color change of silver nitrate solution (AgNO₃) from a clear or watery state to red, brown, or dark red, confirmed by UVV is spectroscopy, with the highest absorption peak at 420 nm, indicative of silver element absorption. Transmission electron microscope images illustrated that the biologically prepared AgNPs with L. lecanii exhibited spherical shapes with sizes ranging from 12 to 40 nanometers. Various concentrations of nanopesticide, Sivanto, and deltamethrin were tested for the treatment of grains. A concentration of 1 ml/L of deltamethrin showed superior performance, with the mortality ratio increasing with prolonged exposure. Both Sivanto and deltamethrin (0.5 ml/L and 0.4 ml/L) caused 100% mortality, followed by the nanopesticide (30% concentration), reaching a corrected mortality rate of 39.3% against adults of T. confusum. In the larval experiment, the mortality rate was high when applying AgNPs at a concentration of 100%, comparable to Sivanto 0.5 ml/L under similar conditions. Deltamethrin exhibited complete mortality at a 1 ml/L concentration. [ Keywords: Silver Nanoparticles, Lecanicillium lecanii, Tribolium confusum

Design and Fabrication of Biosensor for a Specific Microbe by Silicon-Based Interference Color System.

In this paper, one of the great challenges faced by silicon-based biosensors is resolved using a biomaterial multilayer. Tiny biomolecules are deposited on silicon substrates, producing devices that have the ability to act as iridescent color sensors. The color is formed by a coating of uniform microstructures through the interference of light. The system exploits a flat, RNA-aptamer-coated silicon-based surface to which captured microbes are covalently attached. Silicon surfaces are encompassed with the layer-by-layer deposition of biomolecules, as characterized by atomic force microscopy and X-ray photoelectron spectroscopy. Furthermore, the results demonstrate an application of an RNA aptamer chip for sensing a specific bacterium. Interestingly, the detection limit for the microbe was observed to be 2 × 106 CFUmL-1 by visually observed color changes, which were confirmed further using UV-Vis reflectance spectrophotometry. In this report, a flexible method has been developed for the detection of the pathogen Sphingobium yanoikuyae, which is found in non-beverage alcohols. The optimized system is capable of detecting the specific target microbe. The simple concept of these iridescent color changes is mainly derived from the increase in thickness of the nano-ordered layers.

Green production of functionalized few-layer borophene decorated with cerium-doped iron oxide nanoparticles for repeatable hydrogen peroxide detection

Functionalized few-layer borophene (FFB) was prepared using gallnut extract and coffee waste extract as natural exfoliating and stabilizing agents in an environmentally friendly ultrasonic and high shear exfoliation. Here, a facile precipitation method was employed to grow iron oxide nanoparticles doped with cerium (Ce-FeONPs) onto the surface of FFB. This intriguing combination of materials yielded Ce-FeONPs nanoparticles that exhibited exceptional peroxidase-like activity, efficiently catalyzing the conversion of 3,3′,5,5′-tetramethylbenzidine (TMB) to a blue oxidized TMB (oxTMB) in the presence of hydrogen peroxide (H2O2). Additionally, the introduction of FFB contributes a reducibility effect to the catalytic oxidation of TMB, facilitating the restoration of the oxTMB to TMB. Thus, FFB-Ce-FeONPs showcase intriguing properties encompassing both oxidative and reductive characteristics, suggesting their potential as a reagent for repeated detection of H2O2. Moreover, a colorimetric sensing system enabled the liner detection of H2O2 spanning a concentration range from 0.08 to 1 mM, with a detection limit of 0.03 mM. Noteworthily, FFB-Ce-FeONPs demonstrated sustained efficacy over ten successive recycling cycles, as indicated by consistent slopes and observable color changes. In summary, this work reports the first application of nanoenzymes in repetitive H2O2 detection. Even after ten multiple cycles, the detection limit remains virtually unaltered, underscoring the robustness and enduring effectiveness of the engineered nanomaterial. The proposed simultaneous oxidation and reduction strategies for detecting H2O2 showed a commendable capability in ten cycles of H2O2 detection, thus providing a promising approach in the field of H2O2 detection.

Structural Colored Based Humidity Sensor Consisting of High Resolution 3D Printed Photonic Crystal Coated with Ultrathin Responsive Hydrogels.

Today, humidity sensors have become an integral part of the daily lives. In particular, humidity sensors using an electronic measuring principle have become the standard. Although these sensors have proven to be a stable measurement method, they have some disadvantages, such as their long response time or the danger of using them in explosiveenvironments. This work introduces photonic crystals as an alternative optical measurement approach. The novel technology of ultra-fast two-photon polymerisation printing is combined with a thin-film deposition process, namely iCVD. This allows to print large area high-precision 3D templates, which are subsequently coated with a humidity responsive hydrogel thin film (p(HEMA) of 20nm.The limits of 2PP technology are being pushed allowing the production ofs table and periodic large-area 3D structures. The flexible customization of hydrogels for ambient conditions make them exceptionally promising for a wide range of sensing applications. Additionally, optical methods for measuring humidity seem to be an excellent alternative to overcome the limitations for current state of the art humidity sensors. The optical detection of changes in ambient air humidity is achieved by observing color changes of the printed structure within the visible wavelength range.

Dual-responsive solvatochromic sensor for simultaneous detection and mechanism of Cr(III) and Co(II) cations by a new N2O4-donor tetrabenzodiaza-crown ether Macrocyclic ligand anchored to dipyridine moieties

The present study describes the chemosensing capability of an N2O4-donor tetrabenzodiaza-crown ether macrocyclic ligand derivatized by two pyridine side arms to afford the flexible macrocyclic ligand, 5,20-bis(pyridin-4-ylmethyl)-5,6,12,13,19,20,26,27octahydrotetrabenzo [e,i,o,s][1,4,11,14]tetraoxa[7,18]diazacycloicosine (PMHBOA). A selective colorimetric behavior of PMHBOA for the prompt detection of Cr(ΙΙΙ) and Co(ΙΙ) can be observed with naked eyes. The 1H, 13C{H} NMR, and infrared spectroscopy disclosed the ligand binding capability for selective metal ions, ascribed to a 1:1 complex formation with Cr(III) and Co(II) cations in isopropanol. The limit of detection (LOD) values were calculated as 580 and 850 nM for Cr(ΙΙΙ) and Co(ΙΙ), respectively, accompanied with suitable LOQs as 1.95 µM for Cr(III) and 2.85 µM for Co(II), respectively. The reusability was confirmed in the presence of ethylenediaminetetraacetic acid (EDTA). Moreover, a TLC-based fabricated paper strip successfully applied PMHBOA as a chemosensor for synchronous visible detection of Cr(III) and Co(II) in their alcoholic solution. Meanwhile, the observed color change along with the turn-off fluorescent of PMHBOA guaranteed a felicitous choice of candidate for Cr(III) in the presence of other library metal ions in isopropanol:H2O (9/1 v/v) solution. A fast separation test on the filter paper, impregnated with PMHBOA, was also employed to separate Cr(III) and Co(II) cations from aqueous solutions by recording UV–vis spectra. The 1H NMR spectroscopy supported the macrocycle ring and side arms as the parallel coordination site of PMHBOA with Cr(III) and Co(II).

Sprayable Diacetylene-Containing Amphiphile Coatings for Visual Detection of Gas-Phase Hydrogen Peroxide

Colorimetric chemical sensing of target gases, such as hydrogen peroxide vapors, is an evolving area of research that implements responsive materials that undergo molecule-specific interaction, resulting in a visible color change. Due to the intuitive nature of an observable color change, such sensing systems are particularly desirable as they can be widely deployed at low cost and without the need for complex analytical instrumentation. In this work, we describe our development of a new spray-on sensing material that can provide a colorimetric response to the presence of a gas-phase target, specifically hydrogen peroxide vapor. By providing a cumulative response over time, we identified that part per million concentrations of hydrogen peroxide vapor can be detected. Specifically, we make use of iron chloride-containing formulations to enable the catalysis of hydrogen peroxide to hydroxyl radicals that serve to initiate polymerization of the diacetylene-containing amphiphile, resulting in a white to blue color transition. Due to the irreversible nature of the color change mechanism, the cumulative exposure to hydrogen peroxide over time is demonstrated, enabling longitudinal assessment of target exposure with the same coatings. The versatility of this approach in generating a colorimetric response to hydrogen peroxide vapor may find practical applications for environmental monitoring, diagnostics, or even industrial safety.

Novel Star-Shaped Viologens Containing Phenyl and Triphenylamine Moieties for Electrochromic Applications.

The two star-shaped viologens containing 1,3,5-substituted phenyl (1) and triphenylamine (2) central cores and n-hexyl chains were synthesized and characterized. Both compounds exhibited promising optoelectronic properties and underwent multiple oxidation/reduction processes resulting in various colors. Four possible redox states of tripyridium salt containing a phenyl or triphenylamine core can occur depending on the applied potentials. The wide color range, from colorless through blue, azure to green-gray, was observed during the electrochemical reduction of compound 1. In the case of compound 2, the color change observed during spectroelectrochemical measurements was from yellow to colorless during the cathodic process and from yellow to green during the anodic process. The observed color change for both viologens was reversible. The triphenylamine-cored viologen (2) also exhibited emission in visible range and solvatochromism. It also exhibited luminescence in the solid state when excited with a UV lamp. These studies provide insights into the design of advanced materials for applications in displays.