Development of an Inexpensive RGB Color Sensor for the Detection of Hydrogen Cyanide Gas

An α-benzithiazolyl 3-pyrrolyl BODIPY probe for ratiometric selective sensing of cyanide ions and bioimaging studies

A simple chromo-fluorogenic chemodosimeter probe, α-benzithiazolyl 3-pyrrolyl BODIPY, was synthesized by reacting α-formyl 3-pyrrolyl BODIPY with 2-aminothiophenol in DMF at reflux under basic conditions. The probe was structurally characterized by X-ray, HR-MS, and 1D & 2D NMR techniques. The X-ray structure revealed that the appended pyrrole was almost in the plane with a small deviation of 12.15° from the 12-atom mean plane of the BF2-dipyrrin core and the benzithiazolyl moiety was also deviated by 18.74° from the BF2-dipyrrin core. The α-benzithiazolyl 3-pyrrolyl BODIPY exhibits one intense absorption band at 608 nm and a less intense band at 412 nm corresponding to the 3-pyrrolyl BODIPY and benzithiazolyl moiety, respectively. The strongly fluorescent probe shows one intense emission band at 637 nm with a quantum yield of 0.48. The probe acted as an exclusive colorimetric and chemodosimetric sensor for CN- ions over other anions with high sensitivity (LOD = 13 nM) and quick response time (10 s) in an aqueous CH3CN medium. The CN- ion attacks the imine group of the benzithiazolyl moiety of 3via a nucleophilic addition reaction and converts the sp2 to sp3 carbon which disrupts the conjugation between the 3-pyrrolyl BODIPY and benzithiazolyl moieties, which is reflected in the clear colour change from red fluorescence to blue fluorescence as well as significant changes in the spectral and electrochemical properties. The detection of cyanide with the probe for biological applications was also performed with plant tissue. DFT/TD-DFT studies were in agreement with the experimental observations.

Development of a colorimetric sensor based on nanofiber cellulose film modified with ninhydrin to measure the formalin index of fruit juice

In this research, a color sensor based on nanofiber cellulose film modified with ninhydrin was designed to measure amino acids and formalin index in fruit juice. For this purpose, three types of cellulose films with porosity of 5, 30 and 125 μm were used. These films were treated with standard solution of ninhydrin. The characteristics of modified films were investigated using Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and X-ray Diffraction (XRD) tests. The color factors of the sensors (a and b) changed in the presence of amino acids and juice with different levels of formalin index. Therefore, the modified films with ninhydrin as a colorimetric sensor were calibrated using 7 types of amino acids and based on the formalin index of 4 types of juice. Then the sensors were used to measure the formalin index in 4 types of juice. The results showed that the sensors have relative selectivity towards methionine amino acid. The formalin index values calculated in the juices by the sensor were compared with the titration method as a reference method. All three types of sensors were able to detect formalin index. The results of the sensor performance verification showed that the sensors can measure formalin index in different juices with 95-98 % accuracy. These sensors showed fast sensitivity and selectivity to the amino acids in juice, also these sensors are safe and the measurement method is fast and simple.

High Reactivity of Supermolecular Nanoentities of a Vitamin B12 Derivative in Langmuir-Schaefer Films Toward Gaseous Toxins

Recently, we have described the first supermolecular nanoentities (SMEs) of a vitamin B12 derivative, viz., a monocyano form of heptabutyl cobyrinate ((CN-)BuCby), unique nanoparticles with strong noncovalent intermolecular interactions, and emerging optical and redox properties. In this work, the fast response of thin films based on the SMEs of the B12 derivative to gaseous toxins (viz., hydrogen cyanide, ammonia, sulfur dioxide, and hydrogen sulfide) particularly dangerous for humans was demonstrated. The reaction between SMEs of (CN-)BuCby in Langmuir-Schaefer (LS) films and HCN generates dicyano species and proceeds ca. 5-fold more rapidly than the process involving drop-coated films that contain (CN-)BuCby in molecular form. The highest sensitivity toward HCN was achieved by using thicker LS films. The reaction proceeds reversibly: upon exposure to air, the dicyano complex undergoes partial decyanation. The decyanated complex retains reactivity toward HCN for at least four subsequent cycles. The processes involving SMEs of (CN-)BuCby and NH3, SO2, and H2S are irreversible, and the sensitivity of the films toward these gases is lower in comparison with HCN. Presented data provides mechanistic information on the reactions involving solid vitamin B12 derivatives and gaseous toxins. In the case of NH3, deprotonation of the coordinated Co(III)-ion water molecule occurs, and the generated hydroxocyano species exhibit high air stability. After binding of SO2, a mixture of sulfito and dicyano species is produced, and the regenerated film contains aquacyano and diaqua or aquahydroxo species, which possess high reactivity toward gaseous toxins. Reaction with H2S produces a mixture of the Co(III)-dicyano form and Co(II)-species containing sulfide oxidation products, which are resistant to aerobic oxidation. Our findings can be used for the development of naked-eye, electronic optic, and chemiresistive sensors toward gaseous toxins with improved reactivity for prompt cyanide detection in air, blood, and plant samples and for analysis of exhaled gases for the diagnosis of diseases.

Recent advances in fluorescent and colorimetric chemosensors for the detection of chemical warfare agents: a legacy of the 21st century

Chemical warfare agents (CWAs) are among the most prominent threats to the human population, our peace, and social stability. Therefore, their detection and quantification are of utmost importance to ensure the security and protection of mankind. In recent years, significant developments have been made in supramolecular chemistry, analytical chemistry, and molecular sensors, which have improved our capability to detect CWAs. Fluorescent and colorimetric chemosensors are attractive tools that allow the selective, sensitive, cheap, portable, and real-time analysis of the potential presence of CWAs, where suitable combinations of selective recognition and transduction can be integrated. In this review, we provide a detailed discussion on recently reported molecular sensors with a specific focus on the sensing of each class of CWAs such as nerve agents, blister agents, blood agents, and other toxicants. We will also discuss the current technology used by military forces, and these discussions will include the type of instrumentation and established protocols. Finally, we will conclude this review with our outlook on the limitations and challenges in the area and summarize the potential of promising avenues for this field.

RGB color analysis of formaldehyde in vegetables based on DNA functionalized gold nanoparticles and triplex DNA

A highly sensitive and selective RGB color analysis for the detection of formaldehyde (FA) was developed by using a DNA functionalized gold nanoparticle (AuNPs-DNA) probe. When complementary oligonucleotides (oligo 2 and oligo 3) and a silver ion (Ag⁺) were added to the AuNPs-DNA solution, triplex DNA was formed, resulting in the aggregation of AuNPs, and accompanied by a solution color change from red to purple. With the addition of formaldehyde, it reacted with Ag⁺, decreased the stability of triplex DNA between AuNPs-DNA, induced the dispersion of AuNPs, and the color of AuNPs recovered to red. Therefore, the formaldehyde concentration could be estimated with the RGB (red, green, blue) values of the AuNP solution by using a smartphone application (APP). The R value of the system was proportional to the concentration of formaldehyde within the range of 0.23-4.50 mg L^-1, with a detection limit of 0.14 mg L^-1. The method has been successfully applied to detect the residues of formaldehyde in vegetable samples and has the potential of the on-site determination of formaldehyde.

Unveiling of a smartphone-mediated ratiometric chemosensor towards the nanomolar level detection of lethal CN-: combined experimental and theoretical validation with the proposition of a molecular logic circuitry

A promising naphthalene-functionalized ratiometric chemosensor (E)-1-((naphthalen-5-yl) methylene)-2-(2,4-dinitrophenyl) hydrazine (DNMH) is unveiled in the present work. DNMH demonstrates brisk discernible colorimetric response from yellow to red in the presence of CN⁻, a lethal environmental contaminant, in a near-perfect aqueous medium with a LOD of 278 nM. The “key role marker” controlling the electrochemical and non-covalent H-bonding interaction between DNMH and CN⁻ is through the commendable role of acidic –NH functionalities. Kinetic studies reveal a pseudo second order reaction rate and the formation of an unprecedented photostable adduct. The negative value of ΔG as evaluated from ITC substantiates the spontaneity of the DNMH⋯CN⁻ interaction. The sensing mechanism was further reinforced with state-of-the-art theoretical investigations, namely DFT, TDDFT and Fukui indices (FIs). Moreover, the proposition of a reversible multi-component logic circuitry implementing Boolean functions in molecular electronics has also been triggered by the turn-over spectrophotometric response of the ditopic ions CN⁻ and Cd²⁺. The cytotoxicity of DNMH towards Bacillus thuringiensis and Escherichia coli is successfully investigated via the MTT assay. Impressively, “dip stick” and “easy to prepare” test paper device and silica gel-based solid-phase CN⁻ recognition validate the on-site analytical application of DNMH. Furthermore, the involvement of a synergistic approach between ‘chemistry beyond the molecule’ and ‘engineering’ via an exquisitely implemented smartphone-assisted colorimetric sensory prototype makes this work unprecedented among its congeners and introduces a new frontier in multitudinous material-based functional product development.

A ratiometric chemosensor (DNMH) is unveiled herein, demonstrating selective chromogenic response towards CN⁻, with a LOD of 278 nM. Consequently, molecular logic circuitry and a smartphone-based colorimetric sensory prototype has been explored.

Remote Detection of HCN, HF, and Nerve Agent Vapors Based on Self-Referencing, Dye-Impregnated Porous Silicon Photonic Crystals

A one-dimensional photonic crystal is prepared from porous silicon (pSi) and impregnated with a chemically specific colorimetric indicator dye to provide a self-referenced vapor sensor for the selective detection of hydrogen fluoride (HF), hydrogen cyanide (HCN), and the chemical nerve agent diisopropyl fluorophosphate (DFP). The photonic crystal is prepared with two stop bands: one that coincides with the optical absorbance of the relevant activated indicator dye and the other in a spectrally "clear" region, to provide a reference. The inner pore walls of the pSi sample are then modified with octadecylsilane to provide a hydrophobic interior, and the indicator dye of interest is then loaded into the mesoporous matrix. Remote analyte detection is achieved by measurement of the intensity ratio of the two stop bands in the white light reflectance spectrum, which provides a means to reliably detect colorimetric changes in the indicator dye. Indicator dyes were chosen for their specificity for the relevant agents: rhodamine-imidazole (RDI) for HF and DFP, and monocyanocobinamide (MCbi) for HCN. The ratiometric readout allows detection of HF and HCN at concentrations (14 and 5 ppm, respectively) that are below their respective IDLH (immediately dangerous to life and health) concentrations (30 ppm for HF; 50 ppm for HCN); detection of DFP at a concentration of 114 ppb is also demonstrated. The approach is insensitive to potential interferents such as ammonia, hydrogen chloride, octane, and the 43-component mixture of VOCs known as EPA TO-14A, and to variations in relative humidity (20-80% RH). Detection of HF and HCN spiked into the complex mixture EPA TO-14A is demonstrated. The approach provides a general means to construct robust remote detection systems for chemical agents.

Integrating Target-Triggered Aptamer-Capped HRP@Metal-Organic Frameworks with a Colorimeter Readout for On-Site Sensitive Detection of Antibiotics

Colorimetric analytical strategies exhibit great promise in developing on-site detection methods for antibiotics, while substantial recent research efforts remain problematic due to dissatisfactory sensitivity. Taking this into account, we develop a novel colorimetric sensor for in-field detection of antibiotics by using aptamer (Apt)-capped and horseradish peroxidise (HRP)-embedded zeolitic metal azolate framework-7 (MAF-7) (Apt/HRP@MAF-7) as target recognition and signal transduction, respectively. With the substrate 3,3',5,5'-tetramethylbenzidine (TMB)-impregnated chip attached on the lid, the assay can be conveniently operated in a tube and reliably quantified by a handheld colorimeter. Hydrophilic MAF-7 can not only prevent HRP aggregation but also enhance HRP activity, which would benefit its detection sensitivity. Besides, the catalytic activity of HRP@MAF-7 can be sealed through assembling with Apt and controllably released based on the bioresponsivity via forming target-Apt complexes. Consequently, a significant color signal can be observed owing to the oxidation of colorless TMB to its blue-green oxidized form oxTMB. As a proof-of-concept, portable detection of streptomycin was favorably achieved with excellent sensitivity, which is superior to most reported methods and commercial kits. The developed strategy affords a new design pattern for developing on-site antibiotics assays and immensely extends the application of enzyme embedded metal-organic framework composites.

Elevating Chemistry Research with a Modern Electronics Toolkit

With the rapid development of high technology, chemical science is not as it used to be a century ago. Many chemists acquire and utilize skills that are well beyond the traditional definition of chemistry. The digital age has transformed chemistry laboratories. One aspect of this transformation is the progressing implementation of electronics and computer science in chemistry research. In the past decade, numerous chemistry-oriented studies have benefited from the implementation of electronic modules, including microcontroller boards (MCBs), single-board computers (SBCs), professional grade control and data acquisition systems, as well as field-programmable gate arrays (FPGAs). In particular, MCBs and SBCs provide good value for money. The application areas for electronic modules in chemistry research include construction of simple detection systems based on spectrophotometry and spectrofluorometry principles, customizing laboratory devices for automation of common laboratory practices, control of reaction systems (batch- and flow-based), extraction systems, chromatographic and electrophoretic systems, microfluidic systems (classical and nonclassical), custom-built polymerase chain reaction devices, gas-phase analyte detection systems, chemical robots and drones, construction of FPGA-based imaging systems, and the Internet-of-Chemical-Things. The technology is easy to handle, and many chemists have managed to train themselves in its implementation. The only major obstacle in its implementation is probably one's imagination.

A New Portable Colorimetric Sensor Based on RGB Chromaticity for Quantitative Determination of Sarin in Water

Background:

Sarin is a nerve agent which is lethal to people due to its high toxicity. According to its extreme toxicity, sarin, relatively lack of color, highly toxic, miscible in water, poses viable threats to potable water sources. Therefore, there is an urgent need for portable, rapid and yet reliable methods to monitor for adulteration of potable water sources by sarin on spot.

Methods:

A stock solution of 30 mg/L sarin was prepared daily by dissolving 300 μg of sarin in 10 mL isopropanol. A certain amount of sarin was added to the glass tube, and then o-dianisidine and hydrogen peroxide were added. The pH value of the solution was adjusted to 9.8. The solution was transferred to the test tube after 10 minutes. A test tube of 2 mL was placed between the light source and the RGB color sensor. The LED light source illuminates directly over the test tube while the RGB sensor obtained the generated spectral response. This RGB voltage output is connected to the ADC and microcontroller to convert these analog voltages to three digital data. This RGB digital data is linked to the microcomputer through the serial port that is interfaced with the user interface. The data thus obtained in the sensor can be processed to display the sarin concentration.

Results:

Under the optimum conditions as described above, the calibration curve of chromaticity value versus sarin concentration was linear in the range of 0.15 mg/L to 7.8 mg/L. According to the IUPAC definition, theoretical detection limits of this method were 0.147 mg/L and 0.140 mg/L for R and B values, respectively. The practical detection limit was 0.15 mg/L. The sensor was successfully applied to the determination of sarin in artificial water samples and the recoveries were between 86.0% to 95.9%.

Conclusion:

The results in the present work have demonstrated the feasibility to design a new portable colorimetric sensor based on the RGB chromaticity method for quantitative determination of sarin in water. The influences of chromogenic reagent, oxidant, reaction time, o-dianisidine concentration, hydrogen peroxide concentration, reaction temperature, pH on the chromaticity values were investigated. The results showed that the sensor possessed high selectivity, sensitivity and good repeatability. The method would be potentially applied to the analysis of other toxic compounds in environment, such as other chemical warfare agents.

Tandem Detection of Sub-Nano Molar Level CN- and Hg2+ in Aqueous Medium by a Suitable Molecular Sensor: A Viable Solution for Detection of CN- and Development of the RGB-Based Sensory Device

An inimitable urea-based multichannel chemosensor, DTPH [1,5-bis-(2,6-dichloro-4-(trifluoromethyl)phenyl)carbonohydrazide], was examined to be highly proficient to recognize CN- based on the H-bonding interaction between sensor -NH moiety and CN- in aqueous medium with explicit selectivity. In the absorption spectral titration of DTPH, a new peak at higher wavelength was emerged in titrimetric analytical studies of CN- with the zero-order reaction kinetics affirming the substantial sensor-analyte interaction. The isothermal titration calorimetry (ITC) experiment further affirmed that the sensing process was highly spontaneous with the Gibbs free energy of -26 × 104 cal/mol. The binding approach between DTPH and CN- was also validated by more than a few experimental studies by means of several spectroscopic tools along with the theoretical calculations. A very low detection limit of the chemosensor toward CN- (0.15 ppm) further instigated to design an RGB-based sensory device based on the colorimetric upshots of the chemosensor in order to develop a distinct perception regarding the presence of innocuous or precarious level of the CN- in a contaminated solution. Moreover, the reversibility of the sensor in the presence of CN- and Hg2+ originated a logic gate mimic ensemble. Additionally, the real-field along with the in vitro CN- detection efficiency of the photostable DTPH was also accomplished by using various biological specimens.

Sonochemical versus reverse-precipitation synthesis of CuxO/Fe2O3/MoC nano-hybrid: removal of reactive dyes and evaluation of smartphone for colorimetric detection of organic dyes in water media

In the present work, an ultrasound-assisted reverse-precipitation method was applied as a new approach for the synthesis of Cu_xO/Fe₂O₃/MoC. In the sonication method, a bath type sonicator as a simple, cost-effective, and low intensity sonicator was used. To determine the influence of ultrasonic waves on the morphology and application of nano-hybrid as nano-sorbent, it was also synthesized using the reverse precipitation method. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR), transmission electron microscopy (TEM), Zeta-potential measurement, and vibrating sample magnetometer (VSM) techniques. The XRD analysis confirmed that the sono-synthesized sample has higher crystallinity than the conventional one and CuO/Cu₂O/MoC/Fe₂O₃ phase was obtained under ultrasound. According to the TEM and FESEM, sono-synthesized nanoparticles were rod-like with a width and length of 3 nm and 40 nm, respectively. Also, a well-dispersed shape and uniform morphology of nanoparticles were obtained using sonication. In comparison with the conventional nano-hybrid, this structure results in more void and accessible sites for adsorption of pollutants. The efficiency of resulting nanoparticles in adsorption of reactive dyes as a model of the pollutant was evaluated by sorption and sono-sorption processes. The sono-synthesized sample removed the pollutants more efficient than the conventional sample. The removal efficiencies were about 99% for the removal of reactive dyes using the sono-synthesized sample and sono-sorption method. Besides, determining factors including pH, pollutant concentration, temperature, and contact time were optimized in the sono-sorption and sorption processes. A colorimetric method based on RGB value was used to determine dye concentration in aqueous media. The images were taken by a smartphone and analyzed by ImageJ software. The accuracy of RGB results was confirmed by a UV-Vis spectrophotometer. Graphical abstract The figures on the left side show the FESEM images of nano-sorbent synthesized in the presence of ultrasonic irradiation (US method) and the absence of it (MS method). A well-dispersed shape and uniform morphology of nanoparticles were obtained using sonication. The scheme on the right side illustrates the process of sono-sorption for the removal of dyes and determination of their concentration using the colorimetric method. A colorimetric method based on RGB value was used to determine dye concentration in aqueous media. The graph shows the removal efficiencies of RY84 onto nanosorbent. The removal efficiencies were about 99% for the removal of reactive dye using the sono-synthesized sample and sono-sorption method.

A novel supramolecular polymer gel-based long-alkyl-chain-functionalized coumarin acylhydrazone for the sequential detection and separation of toxic ions

A novel approach for the detection and separation of toxic ions was successfully developed via the introduction of competitive reactions into a long-alkyl-chained acylhydrazone-based coumarin supramolecular polymer, chemosensor OGC (3%, n-BuOH/H₂O), which showed sequential detection and separation of CN^-, Fe³⁺ and S^2-, Ag⁺ in the gel state with high selectivity and sensitivity. Moreover, the ion-responsive films were prepared for the convenient and continuous detection of CN^-, Fe³⁺ and S^2-, Ag⁺ in water solution.