Picric Acid Research Articles

Direct immersion single-drop microextraction combined with fluorescence detection using an optical probe. Application for highly sensitive determination of rhodamine 6G

The use of an optical probe for fluorescence detection combined with direct immersion single-drop microextraction has been demonstrated as an innovative approach. The optical probe served both as a drop holder for extractant and as a measuring device which made it possible to eliminate the use of cuvettes. A laser and a light emitting diode (LED) were tested as possible light sources. Both of them showed comparable results. However, given the much smaller half-band width of the laser radiation, its use has proven to be preferable since background correction can be eliminated. Direct immersion single-drop microextraction of an ionic association complex of rhodamine 6G with picric acid with subsequent fluorescent detection (λex was 532 nm and 525 nm for laser and LED, respectively; λem was 560 nm for both laser and LED) was used a model system to evaluate the new approach. The extractant phase was a 55 μL amyl acetate microdrop fixed in the optical part of the probe. LOD, LOQ and linear calibration range were found as 0.14, 0.48 and 0.5–10 nmol L−1, and 0.15, 0.50 and 0.5–5 nmol L−1 for laser and LED light sources, respectively. The accuracy of the method was assessed by analyzing real water samples.

Dual functional porous organic polymer: Reversible iodine capture and selective sensing of picric acid

The development of porous organic materials for removing radiotoxic iodine from nuclear plant waste is significantly relevant to environmental remediation as well as the detection of trace amounts of nitroexplosive picric acid for environmental safety is challenging. To achieve reversible iodine adsorption by the porous material, we have synthesized a highly stable porous organic polymer POF-1 by Schiff base condensation of tris(4-aminophenyl)methane and 2,2′-bithiophene-5,5′-dicarbaxaldehyde under microwave irradiation. POF-1 showed high affinity towards iodine adsorption due to electron-rich sulfur and nitrogen atoms in the porous structure which interact with iodine and form polyiodide ions by electrostatic interactions. POF-1 showed a remarkable iodine uptake capacity of 4.25 g g−1 in the vapor phase and could efficiently remove iodine from an iodine-cyclohexane solution with an adsorption efficiency of 141.0 mg/L. The iodine adsorption follows Langmuir's isothermal model i.e. monolayer adsorption and Pseudo second-order kinetics. POF-1 exhibited good recyclability towards reversible iodine capture even after five cycles. Furthermore, the luminescence characteristic of POF-1 has been employed for the selective detection of picric acid with high sensitivity with a detection limit of 8 μM among a range of nitroaromatic. The Fluorescence quenching mechanism is mainly attributed to photo-induced electron transfer and the inner filter effect.

A Straight Green Fluorescent N,N‐Dimethylbenzamine ‐ Carbazole Probe for Recognition of Explosive Picric Acid

AbstractThe sensor 4‐(9H‐carbazol‐9‐yl)‐N,N‐dimethylbenzenamine, CNDMA a green fluorescent ligand developed for selective sensing of picric acid in DMSO/H2O (1 : 9) over different other nitroaromatic compounds. The sensing mechanism involves emission quenching significantly in the presence of picric acid with a color change from green to non‐fluorescent yellow. The sensing process drives through electrostatic and Hydrogen bonding interaction with formation of an Electron Donor‐Acceptor complex. In addition, inner filter effect also play role on the fluorescence quenching. The fluorescence quenching is a mixed‐type of both static and dynamic quenching process. The binding nature was figured out using the 1H NMR and FTIR titration studies. In addition the sensor showed good quenching efficiency and quenching constant with a lowest detection limit (LOD) of 5.09×10−8 M (R=0.99964) at 358 nm. Test strip experiment is demonstrated to understand the practical feasibility of the sensor.

MoS2 Nanosheets@Metal organic framework nanocomposite for enhanced visible light degradation and reduction of hazardous organic contaminants

Present research focuses on the environmental cleanup of hazardous organic pollutants that are discharged into the natural aquatic bodies which upshots an undesirable shift in the ecological balance. Recently, aromatic nitro compounds and hazardous organic dyes have been recognized as a threat to fauna, flora and human life forms. Therefore, effective and selective eradication of these hazardous pollutants from wastewater systems is a pressing global issue for the academic community. This study aims to design a MoS2 Nanosheets (NS)@Cu-MOF (MS−HK) catalyst via a convenient hydrothermal approach for the elimination of organic and aromatic nitro contaminants from wastewater effluent. Under visible light irradiation, this photocatalyst presented 96.4% removal efficiency for Rose Bengal (RB) dye within a short duration of 30 min, with a first order degradation rate constant of 0.12223 min−1and a catalyst loading of 240 mg/L. Again, the rate constant of the room temperature reduction of 2,4,6−trinitrophenol (TNP) using NaBH4 as a reducing agent, in presence of the prepared nanocatalyst was calculated to be 2.7 × 10−3 s−1. This excellent degradation efficiency could be due to the loading of HKUST-1 with a narrow band gap semiconductor MoS2 leading to enhanced visible light absorption, effective separation and transport of photoinduced h+−e− pairs that limit their recombination. The plausible photodegradation mechanism was supported by photoluminescence and radical trapping experiments. In addition, the impact of various inorganic ions, water matrices, environmental conditions, different dye molecules and mixed dye system was explored on the RB degradation of the synthesized catalyst. Meanwhile, the as-prepared MS−HK nanocomposite displayed significant stability during the photocatalytic experiments, as evident from XRD results, until four successive cycles maintaining an outstanding degradation efficiency of >89%.

Exploring the dual sensing properties of an anthraldehyde based Schiff base for the successive determination of picric acid using AIEEF and copper using colorimetric methods

A novel and lucid Schiff base, designated as AHN, exhibiting multiple analytical responses comprising AIEE (Aggregation Induced Emission Enhancement) and colorimetric activity towards distinct analytes has been designed and synthesized. The probe, AHN, effectively leverages AIEE activity to selectively detect picric acid (PA) on behalf of fluorescence switch-off response amidst other nitro chemicals. Additionally, it offers remarkable colorimetric selectivity to bivalent copper ions (Cu2+) via a distinct colour change from colourless to yellow. The multi-response characteristics of AHN propel its practicality for naked-eye detection of these analytes. The addition of PA to the aggregate of AHN in DMSO with a 90% water fraction induces a quenching in the fluorescence intensity of the AHN aggregate and the limit of detection of PA was found to be 24.5 × 10−7 M with a quenching constant value of 6.21 × 107 M−1. Stern Volmer plots and lifetime measurements, clearly indicate that both static and dynamic processes were involved in the quenching mechanism. It is also evident that ground-state complexation between electron-rich fluorescent aggregates of AHN and electron-deficient PA takes place through π-π interactions and intramolecular hydrogen bonding interactions. Further, AHN in DMSO exhibits a selective colorimetric response to bivalent copper among various metal ions with a detection limit of 3.16 µM which is substantially below the permitted limit recommended by WHO in drinking water. The mechanism of colorimetric response is the complexation of AHN with Cu2+ in the 2:1 stoichiometry, as confirmed by Job’s plot method. Consequently, the versatility of probe AHN in detecting PA and Cu2+ through distinct mechanisms fosters its significance in the field of sensing and opens promising avenues for practical sensing applications.

A Review on the Non-Linear Optical Performance of Picric Acid based Crystals

This review delves into the nonlinear optical characteristics of crystals derived from picric acid, providing a comprehensive analysis of their unique properties and potential applications in the realm of nonlinear optics. Picric acid, with its distinctive molecular structure, has been widely explored for its nonlinear optical behaviour, making it a fascinating subject for research and development. The review begins by elucidating the fundamental need and significance of crystal growth. The summary of preparation, spectral analysis and nonlinear optical characteristics and the significance of picric acid as a promising material in this domain is also discussed. The interpretation of nonlinear behaviour in optical properties of various compounds of picric acid is reviewed and discussed. The structural data of aminoacidic picrate crystals in the field of non-linear applications are reviewed. The conceptual background of nonlinear optical properties is well deliberated and used in order to have a better knowledge of the optical behaviour of the picrate crystals. UV-VIS spectroscopy and Second harmonic efficiency of picric acid compounds are also briefly discussed. In conclusion, this review provides a comprehensive overview of the nonlinear optical performance of picric acid-based crystals, offering valuable insights for researchers, scientists, and engineers working in the field of nonlinear optics.

Bis-pyrene-containing fluorescent receptor for explosive picric acid and Au(III) via dynamic excimer quenching process in aqueous medium: Practical application

In this paper, we developed a bis-triazole-pyrene sugar derivative 1 to recognize PA and Au(III) in an 80 % aqueous ethanol system. The recognition ability of 1 toward PA and Au(III) was evaluated from spectroscopic studies and DFT calculations. The dynamic excimer emission of 1 was reduced efficiently with PA and Au(III) ions compared to other NACs, metal species and anions. The sugar backbone provides the actual stereochemistry for forming dynamic excimer in aqueous ethanol medium after excitation at 345 nm. The bis-pyrene system 1 generated intramolecular pyrene dynamic excimer emission in the aqueous system. After interacting with PA, the excimer quenching was attributed to the charge and energy shifting from electron-dense pyrene units to electron-lacking PA in the ground state. Receptor 1 demonstrated a 1:1 stoichiometric ratio for PA and Au(III) ion with low micromolar detection limits (0.05 µM for PA and 0.75 µM for Au3+). The quenching and interaction mechanisms were demonstrated from DFT calculations. The recognition property of 1 for PA was also executed in the solid-supported system. Finally, the practical usefulness of the proposed method was described by the PA and Au(III) recovery abilities in various environmental water systems.

Carbon dots-embedded ZIF-8 nanocomposite for fluorescence sensing of Cr(VI) anion and picric acid

An ingenious fluorescence sensor was constructed by in-situ encapsulating carbon dots (CDs) into zeolitic imidazolate framework-8 (ZIF-8) to resist aggregation-caused quenching of CDs. The obtained CDs@ZIF nanocomposite showed excellent sensing abilities towards Cr2O72- anion and picric acid with quenching constant values of 7.08 × 104 M−1 and 1.50 × 105 M−1, respectively. The fluorescent responsiveness of CDs@ZIF nanocomposite for Cr2O72- anion and picric acid can be ascribed to the inner filter effect.

Development of a low-cost, at-home device for early detection of chronic kidney disease

Abstract Chronic kidney disease (CKD) is classified according to patient's kidney state and functionality. Stage 1 represents the initial renal damage, maintaining normal function, while Stage 5 indicates end-stage of CKD, marked by renal insufficiency and the need for dialysis or transplant. Patients in the early stages of CKD may be asymptomatic, but may experience symptoms as fatigue, weakness, and a general feeling of unwellness as the disease progresses, making diagnosis accessibility an essential aim of the health system. A low-cost and home-based device accompanied by a mobile app were developed as an early indicator of CKD, using colorimetry to determine the creatinine levels and chromogens in urine deposited in the device, designed using a solution of picric acid, sodium lauryl sulphate, borate solution, and sodium hydroxide. A range of chromogens was assigned to creatinine concentrations, calibrated by analysing diluted creatinine samples in triplicate, taking 1.2 ml of the sample and adding defined amounts of alkaline picrate according to the calibration curve. The absorbances were recorded at 45, 60, and 180 seconds for each of the creatinine samples combined with alkaline picrate in the creatinine analysis. Finally, the curves corresponding to each time were compared, providing a final absorbance to each creatinine level by subtracting the blank curves’ values. The chromogen is obtained according to the patient's health status, and compared in a database in the application, displaying the possible health status of the kidneys, without providing a diagnosis, but rather an early alert of the kidneys state and approximate glomerular filtration rate. The device has the potential to offer an early diagnosis accessible to all population with a history or risk of CKD. Early detection of CKD may improve patient health through frequent medical appointments, medication, dietary restrictions, and lifestyle changes. Key messages • Early stages of CKD can go unnoticed by patients and physicians, making early diagnosis a valuable tool. • At-home health devices can be designed for the early detection of CKD.

Trinitroaromatic explosives: Modern application, toxicological characterization, and methods of determination

Explosives such as tetryl and picric acid, which were common in the past, now have lost their combat relevance. However, they are often used for peaceful purposes individually and in combination with other trinitroaromatic compounds (e.g., trinitrotoluene). As a result of their use, environmental pollution occurs, followed by intoxication of plants, animals, and people. Cases of explosive poisoning during their production are also described.
 The symptoms of poisoning include both of general disorders and specific phenomena such as skin staining, impaired physiological efficiency of NADPh-dependent enzymes, genotoxicity, and immunotoxicity.
 Previous scientific studies established a trend toward the development of chemical-analytical probes. Various options for the sensor surface of the device and methods for detecting compounds are considered. To determine the explosives, ion mobility spectrometry is widely used, which is very rare for the chemicaltoxicological analysis of other groups of compounds.
 Simultaneously, methods commonly used in the analysis of narcotic and psychotropic substances (gas chromatography/ combination of high-performance liquid chromatography and mass spectrometry methods) are also applicable to determine trinitroaromatic explosives. However, the presence of nitro groups in their structure complicates such an analysis. This problem can be resolved by injecting cold samples directly to the column.
 Despite the availability of various developed techniques and methods, the possibility of their application to study biological matrices remains insufficient.
 Therefore, further studies of the chemicaltoxicological nature should be conducted to establish the optimal conditions for extracting the substances in question, the parameters of instrumental analysis, and the possibility of storing samples and for solving other problems of forensic medical examination.

Synthesis of p-Azaquinodimethane-based Quinoidal Fluorophores.

Quinoidal π-conjugated systems are sought-after materials for semiconducting applications because of their rich optical and electronic characteristics. However, the analogous fluorescent compounds are extremely rare, with just two reports in the literature. Here, we present the design and development of a third series of quinoidal fluorophores [(2,5-diarylidene)-3,6-bis(hexyloxy)-2,5-dihydropyrazine (Q1-Q5)] that incorporates p-azaquinodimethane. The fluorophores are synthesized in a two-step synthetic approach employing Knoevenagel condensation of N,N-diacetyl-piperazine-2,5-dione with different aromatic aldehydes followed by O-alkylation in high yields. Q1-Q5 are strongly emissive, and by altering the aryl-substituents, the emission colors can be modulated from blue to orange. The compounds possess emission maxima (λem) at 475-555 nm in the solution state and 510-610 nm in the solid state, with fluorescence quantum yields of up to 60%. To the best of our knowledge, the reported systems are the first quinoidal dual-state emissive (solution- and solid-state) compounds. In trifluoroacetic acid, Q5 exhibits halochromic behavior, with a dramatic color change from yellow to blue. Furthermore, the preliminary fluorescent sensing studies demonstrated that Q5 could act as a selective turn-off fluorescence probe for electron-deficient picric acid (PA), with an emission quenching of >90% in the solution state. The thin-layer chromatography (TLC) strip sensor of Q5 was also designed to detect PA in water.

Radiolytically prepared blue photoluminescent Silicon Oxide nanocomposites for highly selective sensing of picric acid: Mechanism and development of paper strip-based detection

Herein, we wish to report highly selective sensing of picric acid (PA), one of the primary explosive ingredients as well as a well-known environmental hazard in 100 % water medium. For the said purpose, radiolytically synthesized blue photoluminescent PEGylated silicon oxide nanocomposites (PEG@SiONCs) with ∼49 % quantum efficiency (QE) were used as fluorescence probe. The limit of detection (LOD) of PA was determined to be ∼0.16 μM in the 2–85 μM range. Substantial reduction in blue photoluminescence of PEG@SiONCs, and shift in the emission colour from blue towards green in presence of specific concentrations of PA, are the interesting highlights of the present work. This colour change can be utilized to confirm the presence of PA in the sample. Mechanistic investigations involving temperature-dependent steady-state photoluminescence, and PA concentration-dependent lifetime studies revealed inner filter effect (IFE) based photoluminescence quenching mechanism. In addition, the interference studies carried out in the presence of 21 other organic/inorganic compounds demonstrated the highly selective sensing of PA by PEG@SiONCs. The PA sensing ability of the nanocomposites was also tested in the pH window ranging from 2 to 12. Meanwhile, paper strips were prepared using PEGylated SiONCs, and samples containing various metal ions and organic compounds were tested to examine their suitability for real-time detection of PA.

An AIE active imidazole conjugated α-cyanostilbene based sensor for the selective and sensitive detection of picric acid in an aqueous medium

Due to increasing pollution threats, terrorism-sensitive rapid sensing of aromatic nitro explosives (picric acid) has gained predominant significance in environmental safety. Herein, imidazole-derived monofunctional fluorescent sensor 2-(4-aminophenyl)-3-(3-(4,5-diphenyl-1H-imidazol-2-yl)-2-hydroxyphenyl) acrylonitrile (ADHA) was successfully developed for the selective recognition of explosive picric acid. The D-π-A configuration of ADHA facilitates extraordinary photophysical properties with remarkable aggregation-induced emission (AIE). The detection process is induced by the photon-induced electron transfer (PET) and resonance energy transfer (RET) and results in the generation of ADHA+PA complex. The structural relationship and the photophysical properties of ADHA were extensively studied by DFT (Density Functional Theory) methods and spectroscopic analysis. It has been calculated that the detection limit of the formed complex is 6.26 nM. In addition, 1H NMR titrations DFT calculations, and HRMS analysis were performed to understand the detection mechanism better. Test strip-aided detection and invisible ink applications confirmed that ADHA is a versatile sensor for sensitively detecting picric acid without sophisticated instruments. In addition, ADHA was implemented to detect PA in real water samples with remarkable recovery.

Comparative assessment of urea, creatinine, and blood urea nitrogen in male and female patients with different age groups of chronic kidney disease in Shaheed Benazir Abad, Sindh

Chronic kidney disease (CKD) is a heterogeneous disorder that affects the structure and function of the kidney. The primary biochemical markers for diagnosis and evaluating stages of CKD include urea (Ur), blood nitrogen urea (BUN), and creatinine (Cr). In this study, we investigate three biochemical parameters such as Ur, BUN, and Cr levels in CKD patients’ gender-vice with different age groups. Blood samples (n = 300) of males and females were collected from the Biochemistry Lab, Peoples University of Medical and Health Science, Shaheed Benazirabad during the 2023 year. Blood samples (5ml) were collected from the individuals through venipuncture and centrifuged for further analysis. Reagent 1 (2-Oxoglutarate ADP Urease GLDH and NADH) and Reagent 2 (tris), Reagent 1 (Picric acid) and Reagent 2 (Sodium hydroxide) were used for Ur and Cr analysis. Reagent A1 (Sodium salicylate, sodium nitroprusside, phosphate buffer) Reagent A2 (Urease) reagent B (Sodium hypochlorite, sodium hydroxide) reagent S (Glucose/Urea/Creatinine standard) used for BUN. Four age groups were studied in our research for both genders. The highest positive coefficient correlation was shown by Ur and BUN with ‘r’=0.99 in this study. The statistical analysis showed a significantly higher average value of Ur, Cr, and BUN in males comparatively than in females with the age group of 61-80 years old. Whereas in the young age group (1-20 years old), female showed a significantly higher value than in the male sex group. Our study revealed a significant variation of Ur, Cr and BUN in male and female with different age groups, as male possessed higher muscle mass with increased dietary protein intakes than females. These biochemical markers aid in the proper assessment and are used for several routine analyses of CKD with different age groups of genders

Selective recognition of Zn(II) by a novel Schiff base chemosensor with the formation of an AIE active Zn(II) complex having picric acid detection ability: Application in live cell imaging study

The present work highlights the development and spectroscopic identification of a Schiff base chemosensor, (Z)-4-bromo-2-(((1-methoxybutan-2-yl)imino)methyl)phenol, (HL), for selective detection Zn(II) via turn-on fluorescence among a number of competing cations in a 9:1 DMSO-water media. The high binding constant value, measured during titration of HL and Zn(II), boosts to conduct a straightforward condensation reaction between HL and Zn(II) which results in solid crystals of Zn(II) complex (complex 1). In 7:3 DMSO-water media, complex 1 display Aggregation Induced Emission (AIE) behavior, as a result of which, with increasing the water percentage, under UV light optically the cyan color complex 1 solution converts to green color with the enhancement of fluorescence intensity. The UV, fluorescence, DLS, and SEM studies, fully approve the probe's AIE active behavior. The AIE active property of complex 1 is implemented to detect picric via turn-off fluorescence. The chelation-induced enhanced fluorescence (CHEF) on and Excited state internal proton transfer (ESIPT) off are the key factors in showing the luminescence property of complex 1 and the distortion of aggregation behavior of complex 1 in the presence of picric acid leads to the turn-off fluorescence of the complex 1 solution. The mass spectral and IR spectral analysis supports the 1:1 stoichiometric addition of the probe and analyte and the structure of the probe-analyte complexes is optimized using density Functional Theory (DFT) study. Finally, the live cell imaging study enables us to independently verify the biosensing behavior of complex 1 and HL towards Zn(II) and picric acid respectively.

Dual mode detection of picric acid with fluorescence and smartphone colorimetry via AIE active tetraphenylethylene derivatives

In this study, six tetraphenylethene (TPE) derivatives had been designed and synthesized, named as TPEH, TPEOMe, TPEtBu, TPEOH, TPECN and TPEPy, which exhibited intramolecular charge transfer (ICT) character and aggregation-induced emission (AIE) performance. Based on the electron-donating ability originated from the highly localized π electrons, electrons could be transferred from these TPE derivatives to electron-deficient nitroaromatic explosive picric acid (PA) resulting in quenched fluorescence emission. Thus, they had excellent sensitivity and selectivity for PA detection in aggregate states. The limits of detection (LOD) were 1.64, 0.50, 0.93, 1.48, 0.49 and 0.35 μM for them, respectively, captured from fluorescence signal. Moreover, a semi-quantitative detection method based on smartphone digital image was developed to detect PA with LOD of 490, 26.6, 69.1, 74.1, 3.57 and 100 μM, respectively. The dual-mode sensors had excellent detection character improving the accuracy of the detection result. The fluorescence quenching mechanism was explored as photoinduced electron transfer (PET) and energy transfer. This study provided a new strategy for the design of AIE active materials, expanded the application of smartphones in explosive detection which had practical potential in effective sensing.

Synthesis and structural characterization and DFT calculations of the organic salt crystal obtaining 9-aminoacridine and picric acid: 9-Aminoacridinium picrate

Organic salt, 9-aminoacridinium picrate (9-AAcPc), containing equimolar quantities of 9-aminoacridine and picric acid was obtained and a single crystal was grown by the slow evaporation method in the mixture of methanol: tetrahydrofuran solvent (1: 1, v: v). The molecular structure of the prepared compound was confirmed by FT-IR, 1H NMR, and 13C NMR spectroscopic methods, as well as single crystal X-ray diffraction analysis. The X-ray diffraction analysis of the crystal structure of the title compound showed the presence of the triclinic space group P-1 with no. 2, a = 8.2811(7) Å, b = 10.1003(9) Å, c = 13.4484(13) Å, α = 83.521(3)°, β = 83.330(3)°, γ = 66.595(3)°, V = 1022.56(16) Å3, Z = 2, μ(MoKα) = 0.108 mm-1, Dcalc = 1.375 g/cm3, 56338 reflections measured (5.89° ≤ 2Θ ≤ 56.704°), 5097 unique (Rint = 0.0400, Rsigma = 0.0210) which were used in all calculations. The final R1 was 0.0552 (I > 2σ(I)) and wR2 was 0.1757 (all data). The molecular geometry was also optimized using density functional theory. The frontier molecular orbitals were calculated, and we discussed the probability that the proton transfers from the phenolic OH group of picric acid to different nitrogen units. The calculated electronic structure properties of the title molecule, such as the HOMO and LUMO analysis, and different molecular electrostatic potential maps, were obtained by using the density functional theory method, and the calculated structure was compared with the experimental structure. The thermal stability of the crystal was also analyzed using the TGA/DTG technique.

Highly sensitive and stable SERS sensing on superhydrophobic ladder-like nanostructures

A new type of plasmonically active Laser-Induced Periodic Surface Structures (LIPSS) is fabricated on the stainless-steel surface. In particular, these LIPSS appear as ladder-like periodic patterns whose periodicity can also be controllable at a nanoscale. Here we demonstrated the ability to use these structured surfaces for sensitive SERS (Surface Enhance Raman Spectroscopy) signal measurements. Also, these nanostructured substrates exhibit hydrophobic nature with a contact angle of ∼147 ± 2. The hydrophobic nature of the surface confines the test samples to a small area without spreading, which increases the sensitivity of SERS signals by several folds. These SERS measurements are demonstrated using standard methylene blue (MB) dye with a 532 nm Raman excitation wavelength. Structural uniformity over a large area allows it to qualify as a reliable SERS platform. The random signal measurement across a large sample showed only a 7 % relative standard deviation. The lowest detectable concentration between 10 fM to 100 fM, with an enhancement factor of 2 × 109 for 10 fM, is demonstrated by drop casting the silver nano particles on the substrate. The substrate provides excellent thermal stability to the analyte due to better heat conduction, which reduces laser exposure-induced photodegradation of samples. Also, the lowest detectable concentration of picric acid is 10 µM. The demonstrated SERS active substrates can be used ubiquitously for all sensing applications with great sensitivity, greater repeatability, and increased photodegradation threshold energy. They get better with aging after fabrication and can be scaled to industrial productions.

Sensing of picric acid using an AIEE active “Turn Off” fluorescent probe derived from hydroxy naphthaldehyde and benzyloxy benzaldehyde

A novel Schiff base with AIEE characteristics has been developed and used as a chemosensor for picric acid in aqueous media. The Schiff base 1-((E)-((E)-(4-(benzyloxy) benzylidene) hydrazono) methyl) naphthalen-2-ol [BBHN] with strong fluorescence emission was obtained by the simple condensation of 1-(hydrazonomethyl)naphthan-2-ol and 4-benzoxy benzaldehyde. The characterization of BBHN was done using Fourier Transfer Infra-Red, UV–visible, Magnetic Resonance (1H and 13C) spectroscopy, and HRMS. The sensing behaviour of BBHN aggregates towards nitro explosive was then investigated. The aggregates of BBHN showed a quick, highly selective, and sensitive fluorescence ‘Turn Off’ response towards picric acid (PA) in an aqueous medium among various other nitroaromatics. The limit of detection was 4.04 µM with 2.03 × 106 M−1 as the quenching constant. The fluorescence “Turn Off” response in the presence of PA is mainly due to π-π interactions, and non-covalent hydrogen bonding interactions. Moreover, steady-state fluorescence lifetime measurement and Stern − Volmer plots reveal that the fluorescence quenching followed mixed quenching strategies.

A 2D mixed-lanthanide metal‒organic framework as dual-emitting luminescent sensor for ratiometric detection of tetracycline and nitrophenols

Solvothermal treatment of Gd(III)/Eu(III) salts with 2,3,5,6-tetrachloroterephthalic acid (H2tClbdc) and 1,10-phenanthroline (phen) afforded three two-dimensional lanthanide metal‒organic frameworks (MOFs), [Ln(tClbdc)(phen)(H2O)(NO3)]n (1-Ln, Ln = Gd, Eu, Eu0.03Gd0.97). The dual-emitting characteristic along with the excellent solution and photophysical stability of the mixed-lanthanide MOF 1-Eu0.03Gd0.97 make it a highly sensitive luminescent sensor to ratiometrically detect tetracycline (TC), picric acid (PA) and 4-nitrophenol (4-NP), with the limits of detection of 0.38 μM, 0.75 μM and 1.49 μM for TC, PA and 4-NP, respectively. The significant luminescence quenching of the lanthanide-based sensor by these organic pollutants might be ascribed to inner filtration effect (IFE), fluorescence resonance energy transfer (FRET) and hydrogen-bonding and/or electrostatic interactions between the sensor and phenolic analytes. More significantly, 1-Eu0.03Gd0.97 filled mixed-matrix membranes could be employed as an easy-to-use sensory tool for visual recognition of TC by the turn-off red emission signal.