Stern-Volmer Plots Research Articles

The novel mechanism on the inhibition of superoxide anion generating from xanthine oxidase in the presence of myricetin.

To gain an in-depth understanding of the process of myricetin (MY) inhibiting the generation of •O2- from Xanthine Oxidase (XOD) at a novel perspective, the inhibiting pathway is necessary to be re-elaborated through inhibitory type, thermodynamic analysis and molecular simulation. The results demonstrated that MY is indeed a potent inhibiting agent for •O2- producing from XOD, with the maximum value of 33.78 % in the inhibition of •O2-. Furthermore, the deprotonated form (De-MY) of MY was examined to be an effective agent for interacting with XOD, with the measurement of •O2- in productions from MY, XOD@MY and XAN-XOD@MY, as comparing to the XAN-XOD@ALL. On the inhibition kinetics, De-MY was witnessed to be on a mixed-type inhibition, with more competitive inhibition. In the thermodynamic analysis, the Stern-Volmer plots for De-MY obtained at 298 K, 303 K and 308 K, were polynomial-fitted to form curves approaching the X axis via the fluorescence quenching of XOD, which was against the reported with good linearity. It indicated that the interaction between De-MY and XOD occurred at the range of MY concentrations from 0 to 0.025 (×10-5 mol L-1), is dominated by a static quenching procedure, ascribing to the appearance of accessible interaction with corresponding f values less than 1. As well, via combining the synchronous fluorescence data, Molecular dynamics simulations showed that MY binding to the Trp 283, ARG-60 and Tyr 58 with H-binding interactions is an available access to block the transfer of free electrons from FADH2 to O2. Therefore, in this work, successfully re-elaborating the inhibition mechanism of •O2- generating from XOD by MY is benefited for MY in the future applications.

2-Methoxy-4-formylphenol suppresses methylglyoxal glycation mediated structural alterations and esterase activity of hemoglobin – A multi spectroscopic, biophysical and in-silico study

Glycation is the non-enzymatic reaction of glucose or its metabolites to proteins, causing irreversible changes. Methylglyoxal, a dicarbonyl, affects the structure and function of physiologically important proteins. Being a major circulatory protein, hemoglobin is highly prone to glycation. Current research focuses on identifying potent glycation inhibitors to prevent glycation and their impact on protein structure and function. The present study investigates the Advanced Glycation Endproducts (AGEs) inhibitory effects of 2-methoxy-4-formylphenol (Vanillin) against methylglyoxal mediated glycation of hemoglobin. The hemoglobin-vanillin glycation model exhibited inhibition of AGE formation, amyloid fibrils, aggregates and reduction in esterase activity. The fluorescence spectroscopic technique revealed efficient binding of vanillin and hemoglobin, with Stern Volmer plot indicating the presence of static quenching. The conformational stability of the vanillin and hemoglobin interaction was also evident from the molecular docking and dynamics studies. The proximal orientation of residues (H2 and K82 associated in esterase activity) of hemoglobin β1 chain and vanillin, supports the noted effect of reduced esterase activity in the presence of vanillin in glycated hemoglobin and the inhibition of the overall formation of AGE of hemoglobin in the presence of vanillin.

Selective Detection of Divalent Cations (Cu2+, Zn2+, Pb2+) and Anions (SO42-, S2-, CO32-) Using a pH-Sensitive Multi-functional Schiff Base inNeutralMedium.

A new Schiff base-based multi-cation/anion probe (L) has been synthesized and characterized using HR-MS, FT-IR, 1H, and 13C NMR techniques. The Schiff base motif provides specific binding sites that detect cations and anions by generating distinct optical output signals upon interaction. A noticeable color change of the probe solution was observed from pale yellow to various shades of yellow upon adding cations such as Cu2+, Zn2+, and Pb2+ and anions such as CO32⁻, S2⁻, and SO42⁻. This color change results from forming complexes like M3L2 with metal ions. Whereas origin of color in presence of anion were attributed due to the deprotonation of acidic proton in the ligand. Moreover, the complexes formed by Zn2+, S2/CO32⁻ ion with L are fluorescent, enabling the detection of Cu2+ and SO42⁻ using the Stern-Volmer plot, with a limit of detection (LODs) of 8.48µM and 10.47µM, respectively. Additionally, increasing the pH of the probe solution above 8 reveals a significant enhancement of fluorescence intensity due to the deprotonation of phenolic -OH and amide -NH in the presence of hydroxide ions. This emission in the basic medium is quenched by Cu2+ ions and restored when Cu2+ is complexed with EDTA. A logic gate has also been constructed for understanding the TURN-OFF-TURN-ON mechanism involving Cu2+ ions and EDTA. Overall, the versatile performance of a single probe L opens up new possibilities as a multifunctional sensor, making it highly suitable for practical applications.

Kinetic study on bimolecular photochemical quenching of tris(2,2'-bipyridyl)ruthenium(II) complex in water-ethylene glycol binary media.

The bimolecular photochemical quenching of the tris(2,2'-bipyridyl)ruthenium (II) complex by ferricyanide ions in water-ethylene glycol binary media was investigated using a spectrophotometric approach, as previously reported by our research group. Time-resolved spectroscopy revealed that dynamic photochemical quenching occurred via a diffusion-dominated pathway. The static quenching process was found to occur significantly when the concentration of ethylene glycol was greater than 40 wt%. The analysis of the Stern-Volmer plots revealed that the emitters and quenchers tended to show ionic associations in water-ethylene glycol compared to our previous results with a water-glycerol binary solvent system. This is attributed to hydrophobicity, which is consistent with pioneering works that report that the addition of ethylene glycol to pure water forms hydrophobic regions, leading to dehydration of the complex ions.

An Extension of the Stern-Volmer Equation for Thermally Activated Delayed Fluorescence (TADF) Photocatalysts.

Fluorescence quenching experiments are essential mechanistic tools in photoredox catalysis, allowing one to elucidate the first step in the catalytic cycle that occurs after photon absorption. Thermally activated delayed fluorescence (TADF) photocatalysts, however, yield nonlinear Stern-Volmer plots, thus requiring an adjustment to this widely used method to determine the efficiency of excited state quenching. Here, we derive an extension of the Stern-Volmer equation for TADF fluorophores that considers quenching from both the singlet and triplet excited states and experimentally verify it with fluorescence quenching experiments using the commonly employed TADF-photocatalyst 4CzIPN, and multiple-resonance TADF-photocatalyst QAO with three different quenchers in four solvents. The experimental data are perfectly described by this new equation, which in addition to the Stern-Volmer quenching constants allows for the determination of the product of intersystem and reverse intersystem crossing quantum yields, a quantity that is independent of the quencher.

Amide/urea-based simple fluorometric receptors for iodide and Hg2+ ions in aqueous medium: Aggregation induced emission and DFT studies

Herein, we report pyrene-tagged amide and urea-based sugar derivatives 1 and 2 in a simple synthetic pathway to recognize I− and Hg2+ ions. Both molecules showed absorbance and fluorescence selectivity towards iodide ions in THF/H2O (7/3, v/v) medium. The selectivity and sensitivity of 2 for iodide ions are superior to 1 due to more H-bond donors in 2. Interestingly, fluorometric receptor 2 exhibited aggregation-induced emission (AIE) at higher pH with a remarkable fluorometric color change. The AIE phenomenon might be explained by the self-association of 2 after forming imine functionality in the alkali medium. The Stern-Volmer plot showed the fluorescence quenching constant of each receptor with an iodide ion and indicated the quenching pathway. The LODs of 1 and 2 for iodide ions were evaluated as 0.84 and 0.17 µM, respectively. The 1:1 binding stoichiometry of 1 or 2 with iodide was found from the Job plot and verified by measuring the complex mass.Further, the complexes of each receptor with I− ions can detect Hg2+ ions selectively by fluorescence turn-on method with low sensitivities (LODs: 0.008 µM for 1 and 0.01 µM for 2). DFT results were used to understand the binding mode of receptors 1 and 2 with iodide ions and the quenching process in the aqueous THF medium. The real application of the receptors was established for the recovery of iodide and Hg2+ ions from natural water samples.

Highly sensitive detection of kojic acid in food samples using fluorescent carbon dots derived from pomegranate peel

Kojic acid (KA) has gained significant attention due to its widespread use in the food and cosmetics industries. However, concerns about its potential carcinogenic effects have heightened the need for sensitive detection methods. This study introduces a fluorescence-based optical sensor for the quantification of KA in food samples, utilizing fluorescent carbon dots (CDs) synthesized from pomegranate peel via a hydrothermal method. The Stern–Volmer plot demonstrated a linear response for KA in the range of 120 to 1200 µM, with a Pearson correlation coefficient (r) of 0.9999 and. The sensor exhibited a detection limit of 30 ± 0.04 µM and a limit of quantification (LOQ) of 90 ± 0.14 µM. Application of the developed method to soy sauce and vinegar samples yielded accurate KA determinations, with recoveries of 103.11 ± 0.96% and 104.45 ± 2.15%, respectively. These findings highlight the potential of the proposed sensor for practical applications in food quality and safety assessment, offering valuable insights into the presence of KA in food products.

Carbohydrate-modified simple efficient fluorometric probe for sensing Cu2+ions in aqueous solution

Triazole-appended pyrenyl-modified carbohydrate 1 was introduced in one step for detecting Cu2+ ions over various metal ions and anions in a 90 % aqueous acetonitrile medium. Selectivity of 1 towards Cu2+ ions was established from spectroscopic (absorbance and fluorescence) variations. Probe 1 is more effective in sensing Cu2+ ions within the pH range from 6 to 11. The quenched fluorescence of 1 with Cu2+ at a second was attributed to the reverse PET process from pyrene to electron-deficient Cu2+. The Stern-Volmer plot indicated static quenching at lower concentrations of Cu2+ ions, but both static and dynamic quenching processes were involved at higher concentrations. The ligand-metal ratio (1:1) was established from the Job plot and supported by the complex's HRMS data. The detection limit of 1 (0.08 µM) indicated that probe 1 can detect Cu2+ ions in the micromolar range. The binding mode of 1 with Cu2+ and HOMO-LUMO of 1 and 1-Cu2+ were discussed from DFT calculations. Finally, the practical use of the probe was established from the recovery of Cu2+ ions from natural water samples.

Tailoring the naphtho-[2,3]-furan framework for Pb2+ ion sensing through substitutional effect

This article describes the synthesis of naphthofuran-based probes NF, NNF, and BNFvia a multiple-step synthetic approach and their characterization using standard spectroscopic techniques such as FT-IR, 1H NMR, 13CNMR and HR-MS spectrometry. The inclusion complex (ICNNF) has also been synthesized by encapsulating the NNF molecule into the hydrophobic cavity of β-CD. The chemosensing properties of all these probes have been investigated using UV-visible and fluorescence spectroscopy. However, all these probes could interact with metal ions, only NNF showed chemoselectivity towards Pb2+ detection. The limit of detection (LOD) and binding constant were calculated to be 1.47 µM and 7.38 ⅹ 1010 M−2 for NNF using the Stern-Volmer and Bensi-Hiderland plots, respectively. Further studies revealed that the –NO2 group and furan oxygen in NNF simultaneously interacted with the empty orbital of Pb2+ to produce the "turn-on" spectra.

The effect of Cu(I)-doping on the photoinduced electron transfer from aqueous CdS quantum dots.

The doping of CdS quantum dots (QDs) with Cu(I) disrupts electron-hole correlation due to hole trapping by the dopant ion, post-photoexcitation. The present paper examines the effect of such disruption on the rate of photoinduced electron transfer (PET) from the QDs to methyl viologen (MV2+), with implications in their photocatalytic activity. A significantly greater efficiency of PL quenching by MV2+ is observed for the doped QDs than for the undoped ones. Interestingly, the Stern-Volmer plots constructed using PL intensities exhibit an upward curvature for both the cases, while the PL lifetimes remain unaffected. This observation is rationalized by considering the adsorption of the quencher on the surface of the QDs and ultrafast PET post-photoexcitation. Ultrafast transient absorption experiments confirm a faster electron transfer for the doped QDs. It is also realized that the transient absorption experiment yields a more accurate estimate of the binding constant of the quencher with the QDs, than the PL experiment.

Development of a fluorescent nano-sensing probe for atomoxetine analysis: Additional clinical pharmacokinetic study

Atomoxetine is a psychostimulant drug used for the treatment of attention-deficit/hyperactivity disorder (ADHD) symptoms in people with autism. Herein, eco-friendly fluorescent carbon quantum dots (CQDs) were synthesized using black-eyed pea beans and characterized for the purpose of quantifying atomoxetine in pharmaceutical capsules and human plasma. The selectivity of these CQDs towards atomoxetine was improved by functionalizing their surface with an atomoxetine-tetraphenylborate ion complex. The quantification of atomoxetine is based on measuring the fluorescence quenching of the functionalized CQDs in response to varying concentrations of atomoxetine. The Stern-Volmer plot was employed to investigate the mechanism through which atomoxetine quenches the fluorescence intensity of the CQDs. The outcomes indicated a dynamic quenching mechanism. The applied method was optimized and validated in compliance with ICH requirements, resulting in excellent linearity across the concentration range of 50–800 ng/mL. The developed method was successfully used to quantify atomoxetine in pharmaceutical dosage form and human plasma with acceptable accuracy and precision outcomes. In addition, the method was applied for clinical pharmacokinetic study of atomoxetine in the plasma of children diagnosed with both autism and ADHD. Atomoxetine was rapidly absorbed after a single oral dose of 10 mg, reaching maximum concentration within two hours and having a half-life (t1/2) of 3.11 h. Moreover, the method demonstrates a notable degree of eco-friendliness, as evidenced by two greenness evaluation metrics; Green Analytical Procedure Index (GAPI) and Analytical GREEnness (AGREE).

Fluorimetric determination of Vonoprazan via quenching of nitrogen and sulfur co-doped carbon quantum dots: A rapid and sustainable analytical approach.

In this study, an environmentally sustainable fluorimetric method for determination of Vonoprazan fumarate (VON) in dosage forms using nanoprobes consisting of nitrogen and sulfur co-doped carbon quantum dots (N, S-CQDs). The N, S-CQDs were prepared through a microwave-assisted method in 30 s. The resulting N, S-CQDs were characterized using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). They exhibit fluorescence emission at 460 nm after excitation at 385 nm with a high quantum yield (60%). The analytical approach for VON determination relies on the quenching effect exerted by VON on the native fluorescence intensity of CQDs. The quenching mechanism was investigated using Stern-Volmer plots. The proposed method demonstrates linearity across a concentration range 10-80 μM (4.6-36.8μg/mL) with corresponding limits of detection and quantitation calculated as 2.17 μM (0.99 μg/mL) and 6.58 μM (3.02 μg/mL), respectively. The method has been effectively utilized for the determination of VON in the pharmaceutical samples. Statistical comparison with reported RP-HPLC has been performed to verify the accuracy and precision of the developed method. The environmental sustainability of the developed method has been thoroughly examined through various greenness metrics.

Antimicrobial potential and protein binding affinity of a hybrid ternary nanocomposite matrix: Zinc oxide functionalization with poly(vinyl alcohol)-sulphonated graphene oxide-poly pyrrole

The present study focuses on the application of a ternary PVA/sGO/ZnO-NP/PP nanocomposite as an antibacterial and antifungal agent. The process involved utilizing a solution casting technique to fabricate the inorganic–organic blend material, where 4-sulfophthalic acid (SPTA) was used in the sulfonation of graphitic oxide (GO) sheets. The amalgamation of polyvinyl alcohol polymer (PVA) and sulphonated GO (sGO) was achieved through a chemical oxidation polymerization process carried out in a water-based environment. This process developed a PVA/sGO film, in which zinc oxide nanoparticles (ZnO-NP) and pyrrole monomers were introduced. The PVA/sGO film served as the initial stage for the in-situ deposition and formation of polypyrrole (PP), leading to the fabrication of PVA/sGO/ZnO-NP/PP membrane. The structure was stabilized by hydrogen bonding and electrostatic interactions between the components, while SPTA acted as a cross-linker and a sulphonating agent. The Fourier transform infrared (FTIR) spectra of the quad-component composite unraveled the presence of distinctive functional groups, including PVA, sGO, PP, and Zn-O bands. The UV–visible spectra of PVA/sGO/ZnO-NP/PP nanocomposite membrane revealed a peak in the UV-B region, while in-depth X-ray diffraction (XRD) analyses provided strong evidence of its amorphous nature. The scanning electron microscopy (SEM) image showed that the top surface of the organic film was adorned with PP polymeric chains. The membrane exhibited great water retention capabilities due to its high ion exchange capacity (IEC) value.Additionally, the minimal water loss observed underscores its extended shelf life. Due to their inherent hydrophilic properties, the ternary nanocomposite membranes exhibited enhanced hydrophilicity, porosity, zeta potential, and water uptake. The BET and BJH analyses revealed that PVA/sGO/ZnO-NP/PP nanocomposites had a substantial surface area. Remarkably, the nanocomposite membrane exhibited significantly improved antimicrobial efficacy against bacteria and fungi. The type of interactions between Human serum lysozyme (HSL) and nanocomposite at the molecular level was studied through fluorescence spectroscopy. Stern-Volmer plot revealed the occurrence of both static and dynamic quenching. However, the precise mechanisms underlying the antimicrobial and protein binding (HSL) studies of PVA/sGO/ZnO-NP/PP-based nanocomposites require further investigation.

Mango Leaves (Mangifera indica)-Derived Highly Florescent Green Graphene Quantum Dot Nanoprobes for Enhanced On-Off Dual Detection of Cholesterol and Fe2+ Ions Based on Molecular Logic Operation.

In the present study, we have engineered a molecular logic gate system employing both Fe2+ ions and cholesterol as bioanalytes for innovative detection strategies. We utilized a green-synthesis method employing the mango leaves extract to create fluorescent graphene quantum dots termed "mGQDs". Through techniques like HR-TEM, i.e., high-resolution transmission electron microscopy, Raman spectroscopy, and XPS, i.e., X-ray photoelectron spectroscopy, the successful formation of mGQDs was confirmed. The photoluminescence (PL) characteristics of mGQDs were investigated for potential applications in metal ion detection, specifically Fe2+ traces in water, by using fluorescence techniques. Under 425 nm excitation, mGQDs exhibited emission bands at 495 and 677 nm in their PL spectrum. Fe2+-induced notable quenching of mGQDs' PL intensity decreased by 97% with 2.5 μM Fe2+ ions; however, adding 20 mM cholesterol resulted in a 92% recovery. Detection limits were established through a linear Stern-Volmer (S-V) plot at room temperature, yielding values of 4.07 μM for Fe2+ ions and 1.8 mM for cholesterol. Moreover, mGQDs demonstrated biocompatibility, aqueous solubility, and nontoxicity, facilitating the creation of a rapid nonenzymatic cholesterol detection method. Selectivity and detection studies underscored mGQDs' reliability in cholesterol level monitoring. Additionally, a molecular logic gate system employing Fe2+ metal ions and cholesterol as a bioanalyte was established for detection purposes. Overall, this research introduces an ecofriendly approach to craft mGQDs and highlights their effectiveness in detecting metal ions and cholesterol, suggesting their potential as versatile nanomaterials for diverse analytical and biomedical applications.

Dual fluorescence response of calix[4]arene-1,8-naphthalimide derivatives towards Hg(II) /Cr(VI) and their antimicrobial studies of transparent biofilms with hyaluronic acid

In this study, 4-sulfo-1,8-naphthalimide calixarene of derivatives were prepared (3 and 4) then transparent biofilms of the Ag salts of these compounds were formed in the presence of hyaluronic acid (HA), and antimicrobial properties were investigated. In chemosensor studies, the sensing ability behavior of 3 and 4 towards some cations and anions was investigated by fluorescence spectroscopy. It was observed that the prepared chemosensors show selectivity towards Hg(II) and Cr(VI). Ligand-ion interaction occurs according to the photo-induced electron transfer (PET) mechanism. The stoichiometric ratio was calculated by using Stern-Volmer plot method and binding constant Ksv values were found as 5.2 × 107 M−1 and 5.5 × 107 M−1 for 3-Hg(II) and 4-Hg(II) complexes, respectively and 4.0 × 107 M−1 and 4.3 × 107 M−1 for 3-Cr(VI) and 4-Cr(VI) complexes. The detection limits of the complexes of 3-Hg(II) and 4-Hg(II) are 6.35 × 10−12and 6.81 × 10−12, while those of 3-Cr(VI) and 4-Cr(VI) are 1.41 × 10- 11and 8.37 × 10−12, respectively. As a result of the antimicrobial test performed with these compounds, it was observed that the most effective material was HA-3Ag, which showed a significant antibacterial effect against Sarcina lutea (S. lutea) at a minimum inhibitory concentration (MIC) value of 0.097 mg/mL.

Selective sensing of paraquat by simple off-the-shelf compounds: Applications using composite hydrogel beads and smartphone

The massive use of paraquat (PQ) in agricultural practices has posed serious threats to food safety and human health. Real-time monitoring of PQ remains an obstacle. Herein, a fluorometric as well as smartphone-based very cheap sensing assay is discussed for the detection of this non-selective contact herbicide PQ based on simple off-the-shelf commercially available dyes PTSA (1), HPTS (2) and Eosin Y (3) in pure aqueous media. Owing to their sensitivity towards PQ through electrostatic interactions, these dyes undergo a fluorescence quenching process. Dyes (2) and (3) show a rapid colorimetric change in the presence of PQ as shown by UV-Vis absorption spectral studies. 1 exhibits high sensitivity for PQ in comparison to 2 and 3 with the detection limit as low as 182 nM. All three probes exhibit high sensitivity, high selectivity for PQ over other analytes and excellent anti-interference properties. The Stern-Volmer plots and fluorescence lifetime studies confirm the static quenching process of the probes in the presence of PQ. Furthermore, sensor-coated paper-based test strips were successfully used for the ultrafast detection and quantification of PQ in spiked real water, fruit and vegetable samples. For the first time, silica-sodium alginate (SA) polymer hybrid hydrogel beads incorporated with probes 1, 2 and 3 were used for the detection and adsorption of PQ from water samples. For assessing the reliability of the proposed sensing system for the on-site detection of PQ, an easy-to-use portable test cassette kit integrated with a smartphone was used. The signal outputs were captured and analysed via RGB color value to use the probes for the practical application by using a smartphone as a portable analytical device for the rapid point-of-care monitoring of PQ.

Pyridine-2,6-Dicarboxylic Acid As a Facile and Highly Selective "Turn-Off" Fluorimetric Chemosensor for Detection of Cu (II) Ions in Aqueous Media.

Copper metal is third most abundant trace element in human body. Determination of Cu (II) ions is a burning topic in field of environment protection and food safety because of its significant impact on ecosystem. In this study, 2,6-pyridine dicarboxylic acid (PDA) has been explored as "turn-off" florescent probe for florescent detection of Cu (II) ions. This sensor showed highly selective complexing ability towards Cu (II) ions. Addition of aqueous solution of Cu (II) ions remarkably quenched the fluorescence intensity of PDA while, on contrary, there was no any prominent fluorescence quenching interference on addition of various metal ions. The binding mode of PDA and Cu (II) ions was determined as stoichiometry of 1:1 and it was further confirmed by single crystal XRD analysis. Mechanisms of static and dynamic quenching were confirmed by stern-volmer plot. Limit of detection (LOD) and limit of quantification (LOQ) for Cu (II) ions was calculated as 3.6 µM and 1.23 µM respectively, which is far below the acceptable value (31.5µM) according to the World Health Organization. The use of the sensor for detection of Cu (II) ions in real samples in aqueous media was also performed.

Efficient nanostructured Cs2CuBr2Cl2 perovskite as a fluorescent sensor for the selective “Switch Off” detection of nitrobenzene

Lead halide nanostructured perovskites are well known for their excellent photoluminescence and optoelectronic properties. However, lead toxicity and instability in moisture impedes its suitability for material use. Here we synthesized a highly efficient, lead free, economical, stable Cs2CuBr2Cl2 perovskite nanocrystals (PNCs) via Ligand Assisted Re-Precipitation (LARP) method which is less explored. The sensing application of the synthesized PNCs towards nitro explosives and other small organic compounds were studied. The probe exhibited high selectivity towards nitrobenzene with a lowest detection limit of 57.64 nM. The fluorescent emission intensity was drastically quenched upon the addition of 32 µM nitrobenzene. A Stern-Volmer plot was utilized for the quantification of fluorescence quenching. Further to investigate the quenching mechanism, time correlated single photon counting spectroscopy and other photoluminescence studies were performed pointing out the possibility of fluorescence resonance energy transfer. The work has been further extended to test the capability of the probe to detect nitrobenzene in real water samples and a good recovery percentage ranging from 93-98 % was obtained. Further, a paper strip assay was designed which successfully detected nitrobenzene and can be clearly noticed even with our naked eye making the probe an excellent sensor for nitrobenzene detection.

Nanostructured systems based on pluronics to carry gold nanoparticles and methylene blue aiming for multimodal therapy

The rise of multidrug-resistant microorganisms has become a cause of concern in the biomedical field. In this sense, this study focuses on the development of an effective treatment for infectious diseases mediated by Multimodal Therapy, combining Photodynamic Therapy (PDT), and Photothermal Therapy (PTT). The system involves the synthesis and stabilization of gold nanoparticles (AuNPs) in Pluronic® micelles of F-127 and P-84, combined with the Methylene Blue (MB) aiming effects against microorganisms. It is noteworthy that the AuNPs were synthesized in situ in the copolymer using the solid dispersion technique. These copolymers were strategically chosen for evaluation purposes with our study involving P-123 previously published in this journal. Thus, the effect of the length of the PEO and PPO blocks can be delineated concerning the synthesis of AuNPs. In this case, copolymer F127 has PPO blocks identical to P-123 while P-84 has PEO blocks compatible with P-123. Characterization of the formulations included electronic absorption spectroscopy, dynamic light scattering, and transmission electron microscopy. Fluorescence quenching studies by Stern Volmer plots indicated the location of the MB in the hydrophilic corona of the micelles. In general, was verified that reducing the PEO/PPO ratio favors the formation of AuNPs, possibly due to the greater number of reducing sites per unit mass of the polymer. The formulations remained stable for at least 15 days, and photothermal studies showed a temperature increase of at least 11 °C. The photothermal effect proved reversible after three heating–cooling cycles, revealing a synergy between MB and AuNPs in heat generation, hindered by increased irradiance and rapid photobleaching of MB. The in vitro susceptibility tests with Candida albicans and Staphylococcus aureus demonstrated effective inhibition of the microorganisms. The result shows that AuNPs for itself do not affect the fungal/bacteria lineage. However, the MB/AuNPs combination samples, showed excellent fungal and bacterial inhibition at low drug concentrations.

Highly sensitive detection of copper in aqueous media using a fluorescent probe developed from isophthaldehyde and (E)-1-(hydrazonomethyl) naphthlen-2-ol

A highly selective Schiff base PMB3 with AIEE activity was synthesized and characterized for detecting Cu2+ in aqueous media. The PMB3 aggregates exhibit a green fluorescence in the DMF-water mixed solvent, demonstrating a switch-off response specifically to Cu2+ ions over various other biologically significant metal ions. The quenching of fluorescence in PMB3 aggregates is likely attributed to the disassembly caused by the chelation of the imine-N atom and phenolic -O atom of PMB3 aggregates with Cu2+ ions. The molar ratio of the complex formed as per Job’s plot method was 1:1 between PMB3 and Cu2+. The fluorescence lifetime measurements confirmed the involvement of the dynamic quenching process in the reaction cycle. The analysis of the Stern-Volmer plot divulged a quenching constant of 3.75×1015 M−1. Remarkably, the limit of detection was determined to be 16.08×10−15 M (16.08fM), demonstrating a sensitivity far exceeding the permissible limit set by the World Health Organization.