Selective Optical Detection Research Articles

A label-free 5CB-based aptasensor for highly selective optical detection of amoxicillin residue in freshwater samples

ABSTRACT A novel application of thermotropic liquid crystal (LC) 5CB in an optical aptasensor for the sensitive detection of amoxycillin (AMOX) antibiotic has been reported. In the studied system, the glass substrates were treated with dimethyloctadecyl [3–(trimethoxysilyl) propyl] ammonium chloride (DMOAP) and an aqueous solution of cationic surfactant cetyltrimethylammonium bromide (CTAB) was used to obtain a homeotropically aligned 5CB monolayer at the LC-aqueous interface resulting in a uniformly dark appearance. A highly specific amoxycillin aptamer (AMXA) was immobilised on the glass substrate as a target recognition probe for AMOX molecules. The specific binding of AMXA and AMOX molecules induces orientational changes in LC ordering resulting in a change in LC optical textures observed under a Polarized Optical Microscope (POM). A low limit of detection (LOD) of 10 nM for AMOX was obtained using this sensing system. Additionally, a high specificity for AMOX was also observed during comparative analysis. Finally, the developed biosensor was used to successfully detect AMOX in environments of potential application like tap water and lake water samples. Thus, the developed LC-based aptasensor can be a simple, sensitive and label‐free platform for monitoring real‐time levels of AMOX in freshwater environments.

Bioinspired CuZn-N/C Single-Atom Nanozyme with High Substrate Specificity for Selective Online Monitoring of Epinephrine in Living Brain.

Though many elegant laccase mimics have emerged, these mimics generally have no substrate selectivity as well as low activity, making it difficult to fulfill the demand for monitoring in physiological conditions. Herein, inspired by the Cu-N ligand structure in the active site of natural laccase, we revealed that a carbon nanomaterial with atomically dispersed Cu and Zn atoms (CuZn-N/C) and a well-defined ligand structure could function as an effective laccase mimic for selectively catalyzing epinephrine (EP) oxidation. Catalytic activity of the CuZn-N/C nanozyme was superior to those of Cu-N/C and Zn-N/C and featured a Km value nearly 3-fold lower than that of natural laccase, which indicated that CuZn-N/C has a better affinity for EP. Density functional theory (DFT) revealed the mechanism of the superior catalytic ability of dual-metal CuZn-N/C as follows: (1) the exact distance of the two metal atoms in the CuZn-N/C catalyst makes it suitable for adsorption of the EP molecule, and the CuZn-N/C catalyst can offer the second hydrogen bond that stabilizes the adsorption; (2) molecular orbitals and density of states indicate that the strong interaction between the EP molecule and CuZn-N/C is important for EP catalytic oxidization. Furthermore, a sensitive and selective online optical detection platform (OODP) is constructed for determining EP with a low limit of detection (LOD) of 0.235 μM and a linear range of 0.2-20 μM. The system allows real-time measurement of EP release in the rat brain in vivo following ischemia with dexmedetomidine administration. This work not only provides an idea of designing efficient laccase mimics but also builds a promising chemical platform for better understanding EP-related drug action for ischemic cerebrovascular illnesses and opens up possibilities to explore brain function.

Selective and Rapid Optical Detection of Citalopram Using a Fluorescent Probe Based on Carbon Quantum Dots Embedded in Silica Molecularly Imprinted Polymer.

In this study, a citalopram optical nano-sensor was developed. Citalopram is a well-known antidepressant drug that reduces the reuptake of serotonin in neurons as a result, serotonin neurotransmission, the primary response to antidepressant treatments, increases in many parts of the brain. This study introduces a carbon quantum dots (CQDs)-based optical nanosensor for rapid detection of citalopram. This fluorescent nanosensor was made through the polymerization of tetraethyl orthosilicate in the presence of CQDs as the fluorescent materials and citalopram as the template molecule. Following the polymerization, the templated molecules were washed and removed from the structure, and the matrix of the polymer was left with some cavities that resembled citalopram in terms of size and shape. The final structure which is used as a chemical nanosensor, is named carbon quantum dots embedded silica molecularly imprinted polymer (CQDs-SMIP). The materials used in designing nano-sensors were characterized using FTIR, UV/Vis, and fluorescence spectroscopy, as well as high-resolution transmission electron microscopy (HR-TEM), and field emission scanning electron microscopy (FESEM). CQDs-SMIP showed a strong fluorescence emission at 420nm in the absence of the template molecule. The fluorescence intensity of the nanosensor decreased in the presence of citalopram. The correlation between the extent of the fluorescence quenching and the concentration of citalopram provided the nano-sensor signal. The nano-sensor was used to measure citalopram in complex matrices such as human plasma and urine samples with remarkable selectivity and sensitivity. The detection limit of 10.3µg.L-1 over a linear range of 100 to 700µg.L-1, and RSD of 3.15% was obtained. This nano-sensor was applied to analyze of citalopram in plasma and human urine samples with remarkable results.

Alkali-Etched Imprinted Mn-Based Prussian Blue Analogues with Superior Oxidase-Mimetic Activity and Precise Recognition for Tetracycline Colorimetric Sensing.

As a typical antibiotic pollutant, tetracycline (TC) is producing increasing threats to the ecosystem and human health, and exploring convenient means for monitoring of TC is needed. Here, we proposed alkali-etched imprinted Mn-based Prussian blue analogues featuring superior oxidase-mimetic activity and precise recognition for the colorimetric sensing of TC. Simply etching Mn-based Prussian blue analogues (Mn-PBAs) with NaOH could expose the sites and surfaces to significantly improve their catalytic activity. Density functional theory calculations were employed to screen the molecularly imprinted polymer (MIP) layer for target identification. Consequently, the designed Mn-PBANaOH@MIP possessed the rich channels for substrates to get in touch with the active Mn-PBANaOH core, showing an excellent catalytic capacity to trigger the chromogenic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) without the use of H2O2. If TC was introduced, it would be recognized selectively by the MIP shell and masked the channels for TMB access, resulting in the obstruction of the chromogenic reaction. According to this mechanism, selective optical detection of TC was achieved, and performance stability, reusability, and reliability as well as practicability were also verified, promising potential for TC monitoring in complex matrices. Our work not only presents an effective way to enhance the enzyme-like activity of Prussian blue analogues but also provides a facile approach for TC sensing. Additionally, the work will inspire the exploration of molecularly imprinted nanozymes for various applications.

Ln-MOF Based Ratiometric Luminescent Sensor for the Detection of Potential COVID-19 Drugs.

Countless people have been affected by the COVID-19 pandemic on a global scale. Favipiravir, has shown potential as an effective drug for SARS-CoV-2, attracting scientists' attention. However, overuse of Favipiravir easily leads to serious side effects, requiring real-time monitoring in body fluids. Given this, a new lanthanide metal-organic framework (MOF) was prepared under solvothermal conditions from either Eu (Eu-MOF or (1)) or Tb (Tb-MOF or (2)) using the highly delocalized imidazoledicarboxylic acid linker H2 L (H2 L=5-(4-(imidazol-1-yl) phenyl) isophthalic acid) and could be successfully applied to selective optical detection of Favipiravir. In this MOF framework, the organic linker H2 L provides a high excitation energy transfer efficiency that can sensitize luminescence in lanthanides. In addition, through deliberate tuning of Eu/Tb molar ratio and reaction concentration in the lanthanide framework, ratiometric recyclable luminescent Eux Tb1-x -MOF nanoparticles with open metal sites have been constructed, which present a high detection sensitivity (Ksv =1×107 [M-1 ], detection limit is 4.63 nM) for Favipiravir. The detection mechanism is discussed with the help of Density Functional Theory (DFT) calculations that sheds light over the selective sensing of Favipiravir over other related COVID-19 drug candidates. Finally, to explore the practical application of Favipiravir sensing, MOF based thin films have been used for visual detection of Favipiravir and recycled 5 times.

Optical and quantitative detection of cobalt ion using graphitic carbon nitride-based chemosensor for hydrometallurgy of waste lithium-ion batteries

A hydrometallurgy is one of the most important techniques for recycling waste LIBs, where identifying the exact composition of the metal-leached solution is critical in controlling the metal extraction efficiency and the stoichiometry of the regenerated product. In this study, we report a simple and selective optical detection of high-concentrated Co2+ using a graphitic carbon nitride (g-CN)-based fluorescent chemosensor. g-CN is prepared by molten salt synthesis using dicyandiamide (DCDA) and LiI/KI. The mass ratio of LiI/KI to DCDA modifies the resulting g-CN (CNI) in terms of in-plane molecular distances of base sites including cyano functional groups (─CN) and fluorescent emission wavelength via nucleophilic substitution. The fluorescent sensing performance of CNIs is evaluated through photoluminescence (PL) emission spectroscopy in a broad Co2+ concentration range (10-4-100M). The correlation between the surface exposure of hidden nitrogen pots (base sites) and PL intensity change is achieved where the linear relationship between the PL quenching and the logarithm of Co2+ concentration in the analyte solution is well established with the regression of 0.9959. This study will provide the design principle of the chemosensor suitable for the fast and accurate optical detection of Co2+ present in a broad concentration range for hydrometallurgy for the recycling of waste LIBs.

A unique covalently linked pyridine-tetrathiafulvalene as a stimuli-sensitive sensor for the specific, selective optical and electrochemical detection of Pb2+

A Py-TTF dyad designed for specific detection and release of Pb2+ ions.

Cation-Exchange in Metal-Organic Framework as a Strategy to Obtain New Material for Ascorbic Acid Detection.

Ascorbic acid (AA) is an important biomolecule, the deficiency or maladjustment of which is associated with the symptoms of many diseases (e.g., cardiovascular disease or cancer). Therefore, there is a need to develop a fluorescent probe capable of detecting AA in aqueous media. Here, we report the synthesis, structural, and spectroscopic characterization (by means of, e.g., XRD, XPS, IR and Raman spectroscopy, TG, SEM, and EDS analyses), as well as the photoluminescent properties of a metal-organic framework (MOF) based on Cu2+ and Eu3+ ions. The ion-exchange process of the extraframework cation in anionic Cu-based MOF is proposed as an appropriate strategy to obtain a new material with a nondisturbed structure and a sensitivity to interaction with AA. Accordingly, a novel Eu[Cu3(μ3-OH)(μ3-4-carboxypyrazolato)3] compound for the selective optical detection of AA with a short detection time of 5 min is described.

A Label-Free Gold Nanoparticles-Based Optical Aptasensor for the Detection of Retinol Binding Protein 4.

Retinol-binding protein 4 (RBP4) has been implicated in insulin resistance in rodents and humans with obesity and T2DM, making it a potential biomarker for the early diagnosis of T2DM. However, diagnostic tools for low-level detection of RBP4 are still lagging behind. Therefore, there is an urgent need for the development of T2DM diagnostics that are rapid, cost-effective and that can be used at the point-of-care (POC). Recently, nano-enabled biosensors integrating highly selective optical detection techniques and specificity of aptamers have been widely developed for the rapid detection of various targets. This study reports on the development of a rapid gold nanoparticles (AuNPs)-based aptasensor for the detection of RBP4. The retinol-binding protein aptamer (RBP-A) is adsorbed on the surface of the AuNPs through van der Waals and hydrophobic interactions, stabilizing the AuNPs against sodium chloride (NaCl)-induced aggregation. Upon the addition of RBP4, the RBP-A binds to RBP4 and detaches from the surface of the AuNPs, leaving the AuNPs unprotected. Addition of NaCl causes aggregation of AuNPs, leading to a visible colour change of the AuNPs solution from ruby red to purple/blue. The test result was available within 5 min and the assay had a limit of detection of 90.76 ± 2.81 nM. This study demonstrates the successful development of a simple yet effective, specific, and colorimetric rapid assay for RBP4 detection.

Decorating Zirconium on Graphene Oxide to Design a Multifunctional Nanozyme for Eco-Friendly Detection of Hydrogen Peroxide

Peroxidase enzymes are crucial in analytical chemistry owing to significant peroxide analytes and their key role in hydrogen peroxide (H2O2) detection. Therefore, exploiting appropriate catalysts for the peroxidase like reactions has become crucial for achieving desired analytical performance. Zirconium (Zr) has attracted growing interest, as a safe and stable potential eco-friendly catalyst for various organic transformations that address increasing environmental challenges. Hence, aiming at fast, sensitive and selective optical detection of H2O2, a colorimetric platform is presented here, based on the excellent peroxidase enzyme-like activity of Zr decorated on graphene oxide (GO). The synergistic effect achieved due to intimate contact between an enzyme like Zr and the high surface area 0f GO ensures efficient electron transfer that increases the chemical and catalytic activity of the composite and advances the decomposition of H2O2 into hydroxyl radicals. The designed probe, thus, efficiently catalyzes the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB), via hydroxyl radicals, thereby transforming the colorless TMB into blue oxidized TMB within 2 min. The catalytic mechanism of the Zr-GO enzyme mimic is proposed herein and verified using a fluorescent probe terephthalic acid (TA) and other scavenger experiments. The multifunctional optical probe allows sensitive and highly selective recognition of H2O2 in a linear range from 100 to 1000 µM with a low detection limit of 0.57 µM. Essentially, the direct accessibility of Zr prevents having to use the complicated preparation and purification procedures mostly practiced for conventional biozymes and nanozymes. The devised method offers several gains, including being green and an inexpensive catalyst, having lower LOD, being fast, cost-effective and sensitive, and having selective work-up procedures.

One A3B Porphyrin Structure-Three Successful Applications.

Porphyrins are versatile structures capable of acting in multiple ways. A mixed substituted A3B porphyrin, 5-(3-hydroxy-phenyl)-10,15,20-tris-(3-methoxy-phenyl)-porphyrin and its Pt(II) complex, were synthesised and fully characterised by 1H- and 13C-NMR, TLC, UV-Vis, FT-IR, fluorescence, AFM, TEM and SEM with EDX microscopy, both in organic solvents and in acidic mediums. The pure compounds were used, firstly, as sensitive materials for sensitive and selective optical and fluorescence detection of hydroquinone with the best results in the range 0.039–6.71 µM and a detection limit of 0.013 µM and, secondly, as corrosion inhibitors for carbon–steel (OL) in an acid medium giving a best performance of 88% in the case of coverings with Pt-porphyrin. Finally, the electrocatalytic activity for the hydrogen and oxygen evolution reactions (HER and OER) of the free-base and Pt-metalated A3B porphyrins was evaluated in strong alkaline and acidic electrolyte solutions. The best results were obtained for the electrode modified with the metalated porphyrin, drop-casted on a graphite substrate from an N,N-dimethylformamide solution. In the strong acidic medium, the electrode displayed an HER overpotential of 108 mV, at i = −10 mA/cm2 and a Tafel slope value of 205 mV/dec.

A highly efficient and selective optical detection method for Heparin that works in 100% human serum

Sensing Heparin in 100% serum matrix is a challenging task and is rarely reported in literature. Herein, we present a tetracationic porphyrin based probe that detects Heparin in 100% serum matrix, both, colorimetrically and fluorometrically, with a clinically relevant LOD. The probe also shows high selectivity towards Heparin when compared with its structurally related analogs, chondroitin sulfate and hyaluronic acid along with other relevant analytes. The porphyrin probe-Heparin complex could also be used for the detection of Protamine, which is the only clinically approved antitoxin for Heparin overdose. The easy commercial availability of the probe coupled with its other desirable attributes is expected to significantly improve its prospect in Heparin sensor applications and Heparin related bio-chemical research.

Luminescent β-diketonate coordinated europium(III) sensor for rapid and sensitive detection of Bacillus Anthracis biomarker

The hazardous B. Anthracis are harmful pathogens causes anthrax could be potentially used as biothreat agents or bioweapons and have severe consequences to public health. These bacterial endospores contain dipicolinic acid (DPA) as calcium dipicolinate (CaDPA) as a primary cell wall constituent (1 M, 10 15 molecules/spore). The anthrax attacks in USA by shipping spores in postal mails have triggered the hunt for a simple, rapid, sensitive, and selective detection of Bacillus Anthracis spores. Therefore, a fast and sensitive sensing platform for anthrax spores is critical to contain such biothreats and outbreaks of infection. Herein, we intend to develop a sensitive and selective optical detection strategy for anthrax spore biomarker based on DPA-sensitized lanthanide luminescence. The anionic hard DPA 2− strongly binds with hard Ln 3+ forming thermodynamically stable complex and sensitizing unique Ln III time-resolved luminescence originated from f - f transitions with a high S/N ratio. Here, we employed and repurposed a simple luminescent Eu III complex: [Eu(TTA) 3 (H 2 O) 2 ] ( 1 ) (TTA: 3-thenoyltrifluoroacetonate) for the detection of the DPA 2− biomarker. Complex 1, when titrated with DPA, displayed instant Switch-ON optical response by 10-fold enhancement in the time-resolved luminescence (TRL) intensity of the 5 D 0 → 7 F 2 transition, which is sensitive to the changes in the symmetry of the Eu III primary coordination sphere. Upon binding with DPA, we also observed shifting of the excitation wavelength ( λ ex ) from ∼345 nm to 275 nm in the presence of ∼3.0 mol equivalent of dipicolinic acid. After stoichiometric reaction with DPA, the resulting complex has a long-lived, highly stable excited state of the Eu III ion with a lifetime of 2100 μs in solution compared to only 260 μs for the original probe. We proposed possible displacement of the TTA − and H 2 O from the primary coordination sphere of the Eu III ion by potent chelating antenna ligand DPA 2− . This reaction results in the formation of nine-coordinated [Eu(DPA) 3 ] 3- complex in solution confirmed by ESI-MS analysis. The luminescence response of the complex 1 is found highly selective for DPA in the presence of various interfering carboxylic acids and quantitatively able to detect up to 1.20 μ M. A Eu(III) β-diketonate complex was used as a luminescent “Turn-On” sensor for the detection of Bacillus Anthracis biomarker dipicolinic acid based on the competitive binding of the anionic ligands via an excitation switch. • An Eu(III) β -diketonate complex was used as a luminescent “Turn On” sensor for the detection of Anthrax biomarker dipicolinic acid. • Displacement of TTA by stronger binding dipicolinic acid from inner-coordination sphere of Eu III ions results in switching of excitation. • Selective detection of dipicolinic acid is achieved in the presence of various competing interferents.

Selective and Rapid Optical Detection of Citalopram Using a Fluorescent Probe Based on Carbon Quantum Dots Embedded in Silica Molecularly Imprinted Polymer

Selective and Rapid Optical Detection of Citalopram Using a Fluorescent Probe Based on Carbon Quantum Dots Embedded in Silica Molecularly Imprinted Polymer

Passivated Porous Silicon Membranes and Their Application to Optical Biosensing.

A robust fabrication method for stable mesoporous silicon membranes using standard microfabrication techniques is presented. The porous silicon membranes were passivated through the atomic layer deposition of different metal oxides, namely aluminium oxide Al2O3, hafnium oxide HfO2 and titanium oxide TiO2. The fabricated membranes were characterized in terms of morphology, optical properties and chemical properties. Stability tests and optical probing noise level determination were also performed. Preliminary results using an Al2O3 passivated membranes for a biosensing application are also presented for selective optical detection of Bacillus cereus bacterial lysate. The biosensor was able to detect the bacterial lysate, with an initial bacteria concentration of 106 colony forming units per mL (CFU/mL), in less than 10 min.

Rapid selective optical detection of sulfur containing agrochemicals and amino acid by functionalized cyclodextrin polymer derived gold nanoprobes

Rapid and accurate evaluation of sulfur-based pollutant contamination in an aqueous solution is one of the major tasks in environmental monitoring. A novel cyclodextrin phthalate ester polymer was used to synthesize gold and silver nanoparticles (NPs) with less than 15 nm size. The potential of the NPs solutions as chemosensor was assessed for the colourimetric detection of sulfur-based compounds. An agglomeration of only gold nanoparticles was induced selectively upon interaction with cysteine and sodium diethyldithiocarbamate (SDDC) leading to visual readout. The sensing, as well as quantification of cysteine (hydrophilic) and sodium diethyldithiocarbamate (SDDC) compounds (hydrophobic), occurred within seconds due to the dual binding ability of cyclodextrin. The limit of detection was determined using the linearity of absorbance plots. The proof of concept experiments demonstrates the rapid colourimetric determination in the range of 0.01–0.25 µM with a satisfactory limit of detection as 0.05 and 0.07 µM for SDDC and Cysteine respectively. The effect of pH and NaCl concentration on sensing was also investigated and optimized. 6 and 10 are the optimum pH values for the determination of cysteine and SDDC respectively. The optimum salt concentration was found to be 0.02 M for both the analytes. AuNPs nanosensor was much superior to AgNPs nanosensor as Au has an affinity for sulfur groups thus assisting a selective detection of cysteine and sulfur-containing pesticides in aqueous medium as well as allicin from onion and garlic extract.

Unmodified Green Silver Nanoparticles as Multisensor for Zn2+ and Catalyst for Environmental Remediation

AbstractThis paper details the selective optical, fluorescent and electrochemical detection of Zn2+ among various divalent metal ions in aqueous solution by the green synthesized silver nanoparticles (AgNP) using the fresh extract of Myristica fragrans (MF) with the aid of microwave energy. The synthesized silver nanoparticles stabilized with MF were analysed using UV‐vis., Fourier‐transform infrared (FT‐IR), X‐ray diffraction (XRD), and transmission electron microscopy (TEM) techniques. Due to the effective complexation between silver nanoparticles and metal ions, absorbance of AgNP‐MF diminished with increasing concentration of Zn2+. This is visually identified through the color changes. Fluorescent sensing studies involved the changes in fluorescent intensity of AgNP‐MF in the presence of Zn2+. Electrochemical sensing of Zn2+ was carried through cyclic and differential pulse voltammetric techniques using AgNP‐MF modified platinum electrode (AgNP‐MF−Pt). The developed electrochemical sensor showed a limit of detection (LOD) of 0.6148 μM and its good sensing ability was checked for the detection of Zn2+ in environmental water samples. Recoveries of Zn2+ in the various real water samples were obtained in the range from 100.2 % to 100.6 %. The multi‐functional utility of the AgNP‐MF as a catalyst towards the reduction of two environmentally toxic contaminants such as o/p‐nitroanilines through NaBH4 was also evaluated. The complete degradations were achieved within few minutes and the reactions followed pseudo first order kinetics. The effect of catalytic dosage on the rate of reduction reactions was also studied.

Ultra-thin film sensors based on porphyrin-5-ylphosphonate diesters for selective and sensitive dual-channel optical detection of mercury(II) ions

Reusable dual-channel optical sensors for Hg 2+ ions were prepared by Langmuir-Schaefer (LS) method from amphiphilic ( trans -A 2 )BC-type porphyrins functionalized at meso- positions of the tetrapyrrolic macrocycle by sterically demanding diethoxyphosphoryl and mesityl groups as well as electron donating RO, RS or RNH substituents (R = n -C 8 H 17 ). These three novel amphiphilic porphyrin derivatives were synthesized in good yields and their floating films at the air⎯water interface were investigated. In these monolayers, porphyrin molecules display a slipped stack-of-card orientation, but their strong π stacking is prohibited by bulky diethoxyphosphoryl and mesityl groups. The heteroatom substituent plays a key role in the molecular organization of the monolayers because it can participate in intermolecular hydrogen bonding, which influences the monolayer structure. Sensing properties of the porphyrins organized in Langmuir monolayers differ from those in the solution environment. Selective spectrophotometric detection of Hg 2+ ions by these floating films is observed because interfering Cu 2+ , Zn 2+ , Cd 2+ , and Pb 2+ ions are coordinated to donor centers located at the periphery of the macrocycle. Transfer of these floating films onto a polyvinyl chloride surface by LS technique affords perforated multilayer films with a tight molecular coverage of the solid support. The effect of the heteroatoms on the organization of these films was demonstrated by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Both absorption and emission studies provide a strong evidence that chromophore-chromophore interactions are rather weak in these LS films. Binding of mercury(II) ions by the films and the regeneration of the sensors were explored visually and using reflection absorbance and fluorescence spectroscopies and then confirmed by X-ray fluorescence analysis. Detection limit of these selective and reusable dual-channel (absorbance and fluorescence) thin-film sensors is about 10 −8 M (2 ppb), that corresponds to the action level for Hg 2+ ions in drinking water recommended by the U.S. Environmental Protection Agency (EPA). • Porphyrin-based reusable dual-channel (absorbance/emission) sensors for Hg 2+ were prepared by Langmuir-Schaefer technique. • The structure of synthesized porphyrins was tuned to form stable non-aggregated films. • Detection limit of Hg 2+ ions in aqueous media by thin-film sensors was 2 ppb. • Sensing properties of LS films remarkably differ from those of their molecular precursors and cast films.

Highly exfoliated g-C3N4 as turn OFF-ON (Ag+/CN−) optical sensor and the intermediate (g-C3N4@Ag) for catalytic hydrogenation

Abstract Highly exfoliated mono/few-layered graphitic carbon nitride (g-C3N4) was prepared through the thermal oxidation method. The obtained exfoliated g-C3N4 (Ex_g-C3N4) shows multiple emission (λem ≈ 433, 458, and 484 nm) peaks with an excitation independent fluorescence property. The luminescent Ex_g-C3N4 was tested for the selective optical detection of silver (Ag+) and cyanide (CN−) ions using PL spectroscopy. The quenching in the PL signal was noticed by the addition of Ag+ ions (Turn OFF) to the Ex_g-C3N4. Regeneration of the PL signal occurred upon the addition of CN− ions to Ag+ treated Ex_g-C3N4 (Turn OFF-ON). The minimum detection limit of Ag+ and CN− was calculated to be 2.15 and 380 nM respectively. The achieved nanomolar level sensitivity is advantageous since detection limits are far less than the WHO recommended limits. This method is beneficial over other traditional detection methods like spectroscopic and colorimetric methods in terms of cost, sensitivity, selectivity, and limits of detection. Additionally, we demonstrated the enhanced catalytic hydrogenation of the microgram quantity of p-nitrophenol to p-aminophenol using the nanogram quantity of recovered Ag+ treated Ex_g-C3N4 (g-C3N4@Ag).

Hybrid Copper Iodide Cluster-Based Pellet Sensor for Highly Selective Optical Detection of o-Nitrophenol and Tetracycline Hydrochloride in Aqueous Solution

o-Nitrophenol (o-NP) and tetracycline hydrochloride (TCH) residues in various aquatic environments are two environmental contaminants, which are seriously dangerous to both social safety and the en...