Clear Color Change Research Articles

Selection of novel ssDNA aptamer for ultra-sensitive colorimetric detection of acetamiprid using ultra-small dot assay

An innovative ssDNA aptamer-mediated colorimetric biosensor utilizing an ultra-small dot assay has been developed for the ultra-sensitive detection of acetamiprid, a hazardous insecticide widely used in agriculture. This “Dot assay” leverages ultra-low volumes of less than 20 µL, allowing for rapid visual detection within seconds and addressing the urgent need for accessible and efficient detection methods. Through a non-immobilized graphene oxide-based systematic evolution of ligands by exponential enrichment (SELEX) approach, a specific 79-mer aptamer (Apt-SS5) was identified after 15 enrichment cycles. The Apt-SS5 aptamer demonstrated a remarkable binding affinity for acetamiprid, with a melting temperature (Tm) of 53 °C and a Gibbs free energy (ΔG) of −7.24 kcal/mol at 37 °C. Notably, the binding pocket is formed by nucleotides C-16 to T-32, with critical interactions occurring at C-10, C-16, G-25, A-26, G-27, G-28, and A-29. The optimized colorimetric assay achieved an impressive limit of detection (LOD) of 0.039 ppb and resulted in a significant reduction in assay costs. The target specificity and cross-reactivity of Apt-SS5 were tested against other pesticides, including imidacloprid, thiachloprid, thiamethoxam, chlorpyrifos, pyriproxyfen, and chlorantraniliprole, with no significant color change observed for these non-targets. In contrast, a clear visual color change was noted in the presence of acetamiprid, confirming the aptamer’s high specificity. Additionally, the aptasensor proved effective for testing river and water samples, yielding recovery rates of 84.40 % to 101.66 %. This innovative approach enhances sensitivity and simplifies the detection process, paving the way for rapid screening of pesticide residues in various samples.

Rational design of carbon dot nanozymes for ratiometric dual-signal and smartphone-assisted visual detection of nitrite in food matrices

Developing reliable nitrite (NO2−) sensors is essential for food safety and reducing health risks from NO2− exposure. In this study, we strategically designed nitrogen-doped carbon dot (N-CD) nanozymes to establish an accessible dual-signal ratiometric sensing system for detecting NO2− in food matrices. This system utilizes the photoluminescence and enzyme-like properties of N-CD nanozymes combined with NO2−-triggered diazotization reactions of substrates such as o-phenylenediamine (OPD) or 3,3′,5,5′-tetramethylbenzidine (TMB). The resulting N-CD/OPD and N-CD/TMB composites provide dual-mode detection—fluorescence and colorimetric—with high selectivity for NO2− and excellent resistance to interference. These sensors exhibit clear color changes under both ultraviolet and visible light, and can be combined with smartphones for visual, on-site detection of NO2−. By incorporating a ratiometric strategy, dual-signal output, and smartphone compatibility, our system achieved a low detection limit (≤ 1.92 μM) and satisfactory recovery rates (85.6–115 %) in environmental water and food samples. This highlights the potential of smartphone-assisted sensors for environmental monitoring and food safety applications. Our carbon dot-based platform offers a practical and effective solution for on-site NO2− detection, contributing valuable insights to the field.

A turn-on anthraquinone-derived colorimetric and fluorometric dual-mode probe for highly selective Hg2+ determination and bioimaging in living organisms

Mercury ion (Hg2+) is considered a harmful neurotoxin, and real-time monitoring of Hg2+ concentrations in environmental and biological samples is critical. Fluorescent probes are a rapidly emerging visualization tool owing to their simple design and good selectivity. Herein, a novel fluorescence (FL) probe 2-(4-((6-((quinolin-8-yloxy)methyl)pyridin-2-yl)methyl)piperazin-1-yl)anthracene-9,10-dione (QPPA) is designed using piperazine as a linker between the anthraquinone group, which serves as a fluorophore, and N4O as the Hg2+ ligand. The probe exhibits FL “turn-on” sensing of Hg2+ because the complex inhibits the photo-induced electron transfer (PET) process. Moreover, QPPA can overcome the invasion by other possible cations, resulting in a clear color change from orange to colorless with the addition Hg2+. The chelation of QPPA with Hg2+ in a 1:1 ratio. Subsequently, the theoretically determined binding sites of the ligand to Hg2+ are validated through 1H NMR titration. The in situQPPA–Hg2+ complex can be subjected to Hg2+ extraction following the introduction of S2− owing to its robust binding capacity. The exceptional limit of detection values for Hg2+ and S2− are obtained as 63.0 and 79.1 nM (S/N = 3), respectively. Moreover, QPPA can display bright red FL in the presence of Hg2+ in different biological specimens such as HeLa cells, zebrafish, onion root tip tissues, and water flea Daphnia carinata, further providing an effective strategy for environmental monitoring and bioimaging of Hg2+ in living organisms.

Colorimetric detection of clotrimazole environmental pollutant using a newly developed chemosensor; an experimental and theoretical study

ABSTRACT Clotrimazole (CTZ), as an antifungal medication, is used to treat dermatological infections in humans, and to remove fungal infections from plants in agriculture, but its widespread usage has led to pharmaceutical pollution and environmental concerns. In this study, a new bromopyrogallol red (BPR) and N i 2 + based colorimetric sensor was developed for the selective and sensitive detection of CTZ. The BPR-Ni complex showed a clear colour change from purple to violet in the presence of CTZ, and a significant change was observed in the UV-Vis spectrum. The stoichiometric ratio of 1:1 between BPR and N i 2 + was determined using the Benesi-Hildebrand method. DFT and time-dependent DFT (TD-DFT) were applied to identify the molecular and electronic structures of the BPR, BPR-Ni, and BPR-Ni-CTZ in ground and excited states. The nature of electronic excitations and charge transfers was evaluated using the natural transition orbitals (NTO). The NTO analysis reveals that the Ni atom facilitates the charge transfer process between BPR and CTZ and improves the sensitivity of the chemosensor. The quantum theory of atoms in molecules (QTAIM) was employed to determine the nature of interactions between BPR, N i 2 + , and CTZ. This study paves the way for the detection of environmentally harmful pharmaceutical pollution using simple but effective colorimetric sensors.

Facile and cost-effective fabrication of wearable alpha-naphtholphthalein-based halochromic sensor for wound pH monitoring

The sensor, designed to be worn directly on the skin, is suitable for real-time monitoring of the recovery level of not only general wounds, but also difficult-to-heal wounds, such as those with chronic inflammation. Notably, healthy skin has a pH range of 4–6. When a wound occurs, the pH is known to be approximately 7.4. In this study, alpha-naphtholphthalein (Naph) was immersed in a cotton-blended textile to produce a wearable halochromic sensor that clearly changed color depending on the pH of the skin in the range 6–9, including pH 7.4, which is the skin infection state. The coating was performed without using an organic solvent by dissolving it in micelle form using cetyltrimethylammonium bromide, a surfactant, in water. Naph-based halochromic sensor shows light yellow, which is the dye’s own color, at pH 6, which is a healthy skin condition, and gradually showed a clear color change to light green-green-blue as pH increased. Even after washing and drying by rubbing with regular tap water, the color change due to pH was maintained more than 10 times. Naph-based halochromic sensors use a simple solution production and coating method and are not only reusable sensors that can be washed with water but also use environmentally friendly water, making them very suitable for developing commercial products for wound pH monitoring. In addition, it can be easily applied to medical supplies, such as medical gauze, patient clothes, and compression bandages, as well as everyday wear, such as clothing, gloves, and socks. Therefore, it is expected to be widely used as a wound pH sensor, allowing real-time monitoring of the skin condition of individuals with chronic skin inflammation, including patients requiring wound recovery.

Novel composite based on cellulose nanomaterial for detection and selective removal of cadmium (II) ions from wastewater

In this study, we made a sustainable composite material from wheat straw agriculture waste. This material is environmentally friendly and has unique surface properties. We used it as a substrate because of its network and ability for surface modifications. To make this material, we embedded 2-(2-(di(thiophen-2-yl)methylene)hydrazineyl)-4-methylphenol (TMHM) chromophoric ligand on its surface. This enabled preconcentration, spectrophotometric determination, and removing of Cd2+ ions from real wastewater effluent samples. The resulting CNF-TMHM composite material displays exceptional sensitivity towards Cd2+ ions in aqueous solutions, accomplishing a remarkable detection limit as low as 4.17 ppb. Thus, sensitivity permits efficient naked-eye detection. Significantly, the CNF-TMHM composite material has a rapid and clear color change, shifting from pale yellow to wine red color, within less than two minutes when exposed to variable concentrations of Cd2+ ions. Furthermore, this developed CNF-TMHM composite material reveals remarkable effectiveness for Cd2+ ions detection and removal from wastewater samples. These dual potential addresses the serious environmental interests related to the pollution of water and achieving the sustainability development goals related to clean water.

A soluble electron conjugated polymer for fast electrochromism and exceptional metal ion detection

The design of soluble electrochromic materials with fast responsivity for use in flexible displays and electronic papers remains a challenge. Most of the materials explored properties such as excellent contrast and rich color variation, while fast responsivity is also one of the key properties, which together push electrochromic materials into everyday life. Here we report a soluble electron conjugated polymer PDT-BTz, i.e., poly[3,3-dimethyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine-alt-(2-(heptan-3-yl)benzo[d]thiazole], which was designed to be highly redox active polymeric backbone for electrochromism and constructed to engineer with chelating sites for metal ion detection, via direct (hetero)arylation polymerization of 3, 4-propenyldioxythiophene with benzothiazole derivative. The resultant PDT-BTz exhibited a pair of distinct redox peaks in the range of 0.41–––1.20 V, corresponding to a clear color change in the visible region between yellow and light green as revealed by cyclic voltammetry. PDT-BTz is easily casted into thin film and is highly responsive to visible light to achieve a very short response time of only 0.21 s, which is much far superior to other polymers reported so far. Remarkably, this electrochromic PDT-BTz is highly luminescent and enables to selectively detect iron Fe (III) and Ru (III) ions, via built-in C–S and C = N chelating units, with exceptional rate constants and detection limits. Together with the high thermal stability, the electron polymer opens a way to a novel class of soluble conjugated polymer that can merge dual functions of electrochromism with ion detection capability into one material.

Hydrogen Video Imaging System for Visualizing Microstructure-Dependent Hydrogen Diffusion Behaviors in Polycrystalline Metals

Hydrogen diffusion in polycrystalline metals is known to depend on microstructure. The hydrogen-microstructure interactions have been extensively studied last decades, but the microstructure-dependent hydrogen diffusion behavior is still unclear. To clarify the hydrogen diffusion behavior, it is necessary to visualize the time variations of the microscopic hydrogen distribution in polycrystalline metals. Thus, we developed a hydrogen video imaging system (HVIS) in this study to analyze the hydrogen distribution in polycrystalline metals with sub-micrometer spatial and video-rate time resolutions. The inexpensive and atmospheric-control-free system is expected to be widely used as a versatile approach for analyzing the hydrogen-microstructure interaction in detail.Pure polycrystalline Ni (thickness: 125 µm) was used as a specimen. The specimen was electrochemically polished at a constant voltage of 50 V in a mixed solution of perchloric acid and acetic acid. The thickness was approximately 110 µm after polishing. Subsequently, a polyaniline layer (PANI) was polymerized on one side of pure Ni. The specimen was set to the acrylic cell, which is used to preserve a 0.1 M NaOH aqueous solution. So, only the bare Ni side of the specimen was exposed to the 0.1 M NaOH solution. Electrochemical hydrogen charging was conducted at the bare Ni side of the specimen at a constant current density of -10 A / m2. An inverted optical microscope was used to observe the color distribution of the PANI side. In our previous studies,1-3) it has been clarified that PANI changes its color due to the reaction with hydrogen in metals. Thus, the distribution of hydrogen permeated through pure polycrystalline Ni can be observed as a color distribution of PANI during hydrogen charging.The color of PANI was purple before the hydrogen charging. After 20 h of hydrogen charging, the color of PANI partially turned white. If PANI reacts with hydrogen, the color changes from purple or dark blue to yellow or transparent.1,2) Therefore, the local whitening of PANI is thought to be caused by the reaction with atomic state hydrogen permeated through pure polycrystalline Ni. The number of color changed areas increased with time during hydrogen charging. After 120 h of hydrogen charging, the specimen was immersed in a 1 M NaOH aqueous solution to remove PANI. Subsequently, the microstructure of pure polycrystalline Ni was analyzed using FE-SEM and EBSD. It was found that the color changed area of PANI corresponded to the grain boundaries (GBs) of pure Ni. This suggests that the GBs in pure Ni are preferential hydrogen diffusion paths. Furthermore, the clear color change of PANI was observed at the random GBs, while the whitening scarcely occurred at the Σ3 GBs, indicating that the preferential hydrogen diffusion mainly occurred at the random GBs. The results showed that HVIS can clarify the microstructure-dependent hydrogen diffusion in polycrystalline metals.

High-Sensitivity Mechanochromic Sensor Using Core-Shell Colloidal Crystals

The Colloidal Crystals-based mechanochromic sensor changes color as the arrangement of colloidal particles changes in response to mechanical deformation, which can be detected through optical measurement. This type of sensor can be used in various applications, such as automobile collision detection, structural deformation detection, and medical equipment, among others. In this study, we prepared a stretchable film by dispersing surface-functionalized colloidal particles in an elastic polymer matrix. Surface of silica colloidal particle was modified with an initiator for Atom Transfer Radical Polymerization (ATRP), followed by surface-initiated ATRP of poly(t-butyl methacrylate) (PtBMA). The core-shell colloidal particles were composited with various acrylic monomers, to fabricate crystalline colloidal array which transforms to elastic film by photopolymerization exhibiting structural color. The prepared film showed a clear color change for deformation within 10%, and the peak reflectance showed more than 30%.

Smart Indicator Film Based on Sodium Alginate/Polyvinyl Alcohol/TiO2 Containing Purple Garlic Peel Extract for Visual Monitoring of Beef Freshness.

The aim of this study was to prepare a novel pH-sensitive smart film based on the addition of purple garlic peel extract (PGE) and TiO2 nanoparticles in a sodium alginate (SA)/polyvinyl alcohol (PVA) matrix to monitor the freshness of beef. FT-IR spectroscopy revealed the formation of stronger interaction forces between PVA/SA, PGE, and TiO2 nanoparticles, which showed good compatibility. In addition, the addition of PGE improved the tensile strength and elongation at break of the composite film, especially in different pH environments, and the color response was obvious. The addition of 1% TiO2 nanoparticles significantly improved the mechanical properties of the film, as well as the light barrier properties of the film. PGE could effectively be uniformly dispersed into the composite film, but it also had a certain slow-release effect on the release of PGE. PGE had high sensitivity under different pH conditions with rich color changes, and the color showed a clear color change from red to yellow-green when the pH increased from 1 to 14. The same change was observed when it was added to the film. In particular, by applying this film to the process of beef preservation, we judged the freshness of beef by monitoring the changes in the TVB-N value and pH value during the storage process of beef and found that the film showed obvious color changes during the storage process of beef, from blue (indicating freshness) to red (indicating non-freshness), and finally to yellow-green (indicating deterioration), which indicated that the color change of the film and the freshness of the beef maintained a highly consistent.

Development of a Colorimetric Paper Sensor for Hg2+ Detection in Water Using Cyanuric Acid-Conjugated Gold Nanoparticles.

Hg2+ is one of the most dangerous pollutants that can cause damage to organs and the immune system. The common detection methods of Hg2+ require sophisticated instrumentation and a long time for analysis. The purpose of this study was to develop a sensor for the detection of Hg2+ using filter paper immobilized by gold nanoparticles (AuNPs) conjugated with cyanuric acid (CA). The clear color change from pink to bluish purple is the response of the CA-AuNPs filter paper sensor to exposure to Hg2+. Detection can be observed visually with the naked eye and/or with imageJ software; the detection limit is 0.05 µM. The colorimetric response of the sensor was also selective towards Hg2+ after testing with different metal ions. In addition, the response from the sensor was also consistent for lake water samples spiked with Hg2+. The results of this research provide a promising basic technology for the development of sensors that are affordable, fast, portable, and easy to use for the detection and monitoring of Hg2+ levels in water.

Smart pH indicating functional fabric based on reversible acidichromic self-colored microparticles

Our study focuses on developing a novel wearable fabric with reversible acidichromic properties by dyeing it with self-colored hollow microparticles as polymeric dyes. To synthesize the pH-responsive chromophore, we introduced a self-synthesized 3-methyl-3-2,2′-dihydroxydiethylamine azobenzene (MDPD) to polyurethane microparticle shells. This prevented any dye leakage compared to conventional dye microcapsules. The self-colored microparticles exhibited an approximately spherical shape, with the particle size distribution ranging from 400 nm to 900 nm, peaking around 600 nm. By covalently bonding MDPD to the molecular chain of the polyurethane shell, we increased thermal stability and avoided dye leakage. We calculated the actual content of MDPD in the shell to be 3.84 %. To investigate the pH-responsive chromic mechanism of self-colored hollow microparticles, we characterized their color properties at various pH values. The polyester fabric dyed with pH-responsive self-colored microparticles showed a K/S value of up to 4.8. The dyed fabric exhibited a clear color change from yellow to rose red after decreasing the pH value, with a highly reversible mode, excellent color fastness, and aging resistance. Furthermore, we analyzed the combination mechanism of microparticles and polyester fabrics, highlighting the reversibility and large-area flexibility of pH-responsive microparticle dyed fabrics. The ability to accurately monitor pH levels in real-time using these fabrics opens new avenues for creating intelligent and responsive textile-based devices. As we continue our research and development, we aim to explore and maximize the potential of these fabrics, making them a valuable and innovative addition to the realm of wearable technologies.

Aniline‐Doped MOF‐199 in MOF‐Sensitized Solar Cells

AbstractMetal‐organic framework (MOF)‐sensitized solar cells (MSSC) were fabricated using aniline‐doped MOF‐199. The light harvesting and semiconductor properties of MOF‐199 were fine‐tuned by introducing aniline as guest molecules. After doping with aniline structural changes were not depicted in the powder X‐ray diffraction pattern confirming the undisturbed 3D framework of MOF‐199. A clear color change was observed after doping due to which enhanced absorbance peaks were observed in the UV‐visible spectra. The modified MOF‐199 was then utilized in MOF‐sensitized solar cells as the light‐absorbing material that demonstrated a 73 % enhancement in the overall device efficiency when compared to MSSC fabricated with unmodified/neat MOF‐199.

Colorimetric Determination of Glucose based on BiVO4 Coupled with Gold Nanoparticles as a Photoactivated Mimic Enzyme of Oxidase

Background: The spectrophotometric detection of glucose usually requires the use of glucose oxidase (GOD) and horseradish peroxidase (HRP). These natural enzymes have specificity and can react with substrates efficiently and quickly, but their performance is easily influenced by external factors, such as humidity, temperature, and solution pH. In this study, no enzyme method was developed for the detection of glucose. Objective: In this work, gold nanoparticles (AuNPs) and BiVO4 were calcined onto the glass surface, offering excellent glucose oxidase-like activity under light irradiation. Coupled with silver nanoparticles (AgNPs), it can be applied to the colorimetric detection of glucose without the use of any natural enzyme. Methods: The heterostructure of AuNPs and BiVO4 onto glass substrate (G/AuNPs/BiVO4) was synthesized by deposition and calcination at 500°C. It exhibited oxidase-like activity towards glucose oxidation in the presence of oxygen (O2) under light irradiation and then generated gluconic acid and hydrogen peroxide (H2O2). The production of H2O2 could etch AgNPs, resulting in a clear color change of the solution. Results: A decrease in the absorbance showed a good linear relationship with glucose concentration in the range of 20-400 μM, with a detection limit of 5 μM. Conclusion: An enzyme-free method is proposed for the colorimetric detection of glucose. The photoactivated enzyme mimic of G/AuNPs/BiVO4 exhibited good recyclability with water rinsing. This is promising for wide applications in various fields.

Synthesis, Spectral, Redox and Theoretical Studies of Stable Nonaromatic Dicarba Dithia Hexaphyrin(2.0.1.1.1.0)s with Two Inverted Thiophenes.

A series of dicarba dithia hexaphyrin(2.0.1.1.1.0)s containing two p-phenylene rings, two thiophene rings, and two pyrrole rings connected via five meso carbons were synthesized by condensing the key precursor, hexapyrrane, which was prepared over a sequence of steps, with the appropriate aromatic aldehyde under acid catalytic conditions followed by alumina chromatographic purification. Detailed one-dimensional (1D) and two-dimensional (2D) NMR studies revealed that the two thiophene rings were inverted and facing outward from the macrocyclic core. Interestingly, one of the inverted thiophene rings adopts a normal orientation in the protonated derivatives of macrocycles generated by addition of trifluoroacetic acid to the appropriate macrocyclic solution. The spectroscopic studies support the non-aromatic nature of macrocycles, and the macrocycles exhibit a distinct sharp band at ∼425 nm along with a broad band in the range of 550-1000 nm, which experienced a red shift with a clear color change in the protonated derivatives. The redox studies showed lower oxidation potentials, indicating their electron-rich nature. The density functional theoretical (DFT) studies showed that the hexaphyrins adopt oval-shaped structures, and time-dependent-DFT (TD-DFT) studies parallelly matched the experimental observations of macrocycles.

Spray-On Colorimetric Sensors for Distinguishing the Presence of Lead Ions.

Sprayable stimuli-responsive material coatings represent a new class of detection system which can be quickly implemented to transform a surface into a color-responsive sensor. In this work, we describe a dipicolylamine-terminated diacetylene-containing amphiphile formulation for spray coating on to a simple paper substrate to yield disposable test strips that can be used to detect the presence of lead ions in solution. We find the response to be very selective to only lead ions and that the sensitivity can be modulated by altering the UV curing time after spraying. Sensitive detection to at least 0.1 mM revealed a clear color change from a blue to red phase. This represents the first demonstration of a spray-on sensor system capable of detection of lead ions in solution.

Visual perceptual load and processing of somatosensory stimuli in primary and secondary somatosensory cortices

Load theory assumes that neural activation to distractors in early sensory cortices is modulated by the perceptual load of a main task, regardless of whether task and distractor share the same sensory modality or not. While several studies have investigated the question of load effects on distractor processing in early sensory areas, there is no functional magnetic resonance imaging (fMRI) study regarding load effects on somatosensory stimuli. Here, we used fMRI to investigate effects of visual perceptual load on neural responses to somatosensory stimuli applied to the wrist in a study with 44 participants. Perceptual load was manipulated by an established sustained visual detection task, which avoided simultaneous target and distractor presentations. Load was operationalized by detection difficulty of subtle or clear color changes of one of 12 rotating dots. While all somatosensory stimuli led to activation in somatosensory areas SI and SII, we found no statistically significant difference in brain activation to these stimuli under high compared to low sustained visual load. Moreover, exploratory Bayesian analyses supported the absence of differences. Thus, our findings suggest a resistance of somatosensory processing to at least some forms of visual perceptual load, possibly due to behavioural relevance of discrete somatosensory stimuli and separable attentional resources for the somatosensory and visual modality.

Development of a flexible high-friction pressure sensor with structural colors for soft gripper fingers

For energy-efficient and lightweight sensor applications, structural colors were utilized to sense the pressure applied to the surface. However, conventional structural color sensors have been usually fabricated with nanoscale features focusing on high pressure sensitivity with small load limits. In this study, a flexible surface with high frictional force and wide pressure-sensing capability was fabricated by ultra-precision machining for soft gripper applications. Friction and grip detection are very important for gripping performance and sensors for soft grippers are required to cope with loads of over 1 kg. Here, microscale three-dimensional trapezoidal patterns were fabricated and transferred to a polymer to increase the contact area for higher friction and improve structural color expression. The effects of pattern geometry on structural color changes due to the varying loads were analyzed using the hue, saturation, and brightness (HSB) model. The hues of the patterned surfaces decreased with loads. Clear color changes were apparent as the pattern width and depth varied; patterns with blue colors (hue of ~240) at no-load status sensed pressure most effectively. Based on the experimental results, a sensor was designed to have a clear color change in terms of pressure and then was applied to soft gripper fingers. Significant color changes were evident as the pressure changed during gripping even under large loads of up to 1200 g; the high friction (compared to that of a plain surface) also improved gripping performances. The sensor provides intuitive information detectable by the naked eye, and there is no need for any power source, wire, or data acquisition system. This research can contribute to the development of multi-functional, lightweight energy-efficient systems.

Coumarin Xanthene Combined Probe for the Multi-Color Detection of Metal Ions and Electrospun Fibers Developed for Real-Time Monitoring.

A coumarin-rhodamine (RhBC)-fused colorimetric/fluorescent probe was designed and synthesized. The probe is effective in Cu2+/Hg2+ ion sensing. With the added Cu2+ to RhBC in water: N, N-dimethyl formamide (8:2, v/v), the cyclic form of RhBC, is converted into the open ring form and shows a clear color change from yellow to red. In the presence of additional participating cations, this moiety shows effectiveness for Cu2+ and Hg2+ ions. The RhBC's detection limit by the UV-visible spectral method was 8.81 × 10-6M for Cu2+ ions and 2.26 × 10-5M for Hg2+ ions. The detection limit in the fluorescence titration spectra was 2.02 × 10-7M for Cu2+ ions and 6.11 × 10-8M for Hg2+ ions. A 1:1 stoichiometric ratio was validated between the probe and copper/mercury ions by the method of the job plot. Moreover, RhBC-combined polyurethane electrospun nanofibers were synthesized. These nanofibers could detect Cu2+ in real samples with no complications, with an instinctive color difference from yellow to red and a weak orange color for mercury ions.

Colorimetric sensing of fluoride ion by a Chlorophosphonazo III-based Al3+ complex in aqueous media via indicator displacement approach

We have developed a colorimetric chemosensor for fluoride ion in pure aqueous solution using an Al3+ complex of Chlorophosphonazo III (CPA) via indicator displacement approach. CPA can form a complex with Al3+ in a 1:1 M ratio (CPA-Al3+), resulting in the change of the solution color from red to purple. The CPA-Al3+ complex showed a selective response to fluoride ion with a hypsochromic shift in absorption spectra with the clear color change from purple to red through the regeneration of CPA by the binding of fluoride ion to Al3+ in a 3:1 M ratio. Moreover, the recognition of fluoride ion was not hampered by the presence of other anions. Hence, CPA-Al3+ is efficient in the highly selective and sensitive colorimetric detection of fluoride ion in 100 % aqueous media.