In-Vitro Study of the Binding of Atorvastatin with Adenine using Multi-Spectroscopic Approaches.

Atorvastatin-an oral lipid regulating drug is a competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase), which is the rate determining enzyme for cholesterol synthesis. Adenine is a purine nucleobase that is found in deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) to generate genetic information. The binding mechanism of atorvastatin and adenine was studied for the first time utilizing various techniques, including UV-visible spectrophotometry, spectrofluorimetry, synchronous fluorescence spectroscopy (SF), Fourier transform infrared (FTIR), fluorescence resonance energy transfer (FRET), and metal ion complexation. The fluorescence spectra of the complex indicated that atorvastatin is bound to adenine via hydrophobic interaction through a spontaneous binding process, and the fluorescence quenching mechanism was found to be static quenching with a binding constant of 1.4893 × 104 Lmol-1 at 298 K. Various temperature settings were used to investigate thermodynamic characteristics, such as binding forces, binding constants, and the number of binding sites. The interaction parameters, including the standard enthalpy change (ΔHο) and standard entropy change (ΔSο) were calculated using Van't Hoff's equation to be 42.82 kJmol-1 and 208.9 Jmol-1K-1, respectively. The findings demonstrated that the adenine- atorvastatin binding was endothermic. Furthermore, the results of the experiments revealed that some metal ions (K+, Ca+2, Co+2, Cu+2, and Al+3) facilitate the binding interaction between atorvastatin and adenine. Slight changes are observed in the FTIR spectra of adenine, indicating the binding interaction between adenine and atorvastatin.

Microwave-assisted preparation of yellow fluorescent graphitic carbon nitride quantum dots for trace tetracycline-specific detection.

Tetracycline (TC) is extensively utilized in livestock breeding, aquaculture, and medical industry. TC residues seriously harm food security, the environment, and human health. There is an urgent need to exploit a highly efficient and sensitive testing method to monitor TC residue levels in aquatic environments. In this study, graphitic carbon nitride quantum dots (g-CNQDs) were successfully synthesized by a one-step microwave-assisted method using citric acid and urea as precursors. The as-prepared g-CNQDs with size of 1.25-3.75 nm exhibited bright yellow fluorescence at 523 nm when excited at 397 nm. Interestingly, this characteristic fluorescence emission of g-CNQDs could be selectively and efficiently quenched by TC. Based on this phenomenon, for TC detection was successfully explored and applied in real water samples. Wide linear scope of 7-100 µM, low detection limit (LOD) of 0.48 µM, satisfactory recovery of 97.77%-103.4%, and good relative standard deviation (RSD) of 1.05-5.87% were obtained. Mechanism investigations revealed that the static quenching and the inner filter effect (IFE) were responsible for this fluorescence quenching between g-CNQDs and TC. This work not only provided a facile approach for g-CNQDs synthesis but also constructed a g-CNQDs-based fluorescent sensor platform for the highly sensitive and selective detection of TC in aquatic environments.

Insights on multi-spectroscopic approaches for estimating the in vitro binding of favipiravir with adenine nucleotide.

Favipiravir (FVP) is an oral antiviral drug approved in 2021 for the treatment of COVID-19. It is a pyrazine derivative that can be integrated into anti-viral RNA products to inhibit viral replication. While, adenine is a purine nucleobase that is found in deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) to generate genetic information. For the first time, the binding mechanism between FVP and adenine was determined using different techniques, including UV-visible spectrophotometry, spectrofluorimetry, synchronous fluorescence (SF) spectroscopy, Fourier transform infrared (FTIR), fluorescence resonance energy transfer (FRET), and metal ion complexation. The fluorescence spectra indicated that FVP is bound to adenine via Van der Waals forces and hydrogen bonding through a spontaneous binding process (ΔGο < 0). The quenching mechanism was found to be static. Various temperature settings were used to investigate thermodynamic characteristics, such as binding forces, binding constants, and the number of binding sites. The reaction parameters, including the enthalpy change (ΔHο) and entropy change (ΔSο), were calculated using Van't Hoff's equation. The findings demonstrated that the adenine-FVP binding was endothermic. Furthermore, the results of the experiments revealed that some metal ions (K+, Ca+2, Co+2, Cu+2, and Al+3) might facilitate the binding interaction between FVP and adenine. Slight changes are observed in the FTIR spectra of adenine, indicating the binding interaction between adenine and FVP. This study may be useful in understanding the pharmacokinetic characteristics of FVP and how the drug binds to adenine to prevent any side effects.

Exploring the twin potential of nanostructured TiO2:SeO2 as a promising visible light photocatalyst and selective fluorosensing platform.

The present work describes the development of TiO2/SeO2 nanostructure as a potential candidate for visible light photocatalysis as well as selective fluorophore for the sensing of picric acid. The obtained nanostructure consists of uniform globular nanoparticles having approximate size of 170 nm and possess an optical band gap of 2.33 eV with absorption maxima at 473 nm. The photocatalyst was able to achieve 90.34% degradation efficiency for 2, 4-dichlorophenol (2,4-DCP) with rate constant of 0.0046 min-1 in the visible region. Further the nanostructure was able to serve as a selective fluorophore for sensing of Picric acid portraying more than 95% of fluorescence quenching when the concentration of PA is 10-4 M. Theoretical calculations indicate the interaction of organic pollutants with the nanostructure and reveal that both picric acid (- 66.21 kcal/mol) and 2,4-DCP (- 12.31 kcal/mol) possess more negative binding energy values demonstrating a strong interaction of both with the nanostructure, making it suitable for the degradation as well as sensing of organic pollutants. Thus this study explains the potential of prepared catalyst for waste water treatment.

Simultaneous sensing of carbidopa and levodopa by a novel strategy based on dual-emission ratiometric assay of modified carbon dots.

Rapid control of the content of Parkinson's drugs in biological fluids and pharmaceutical formulations is of great importance because changes in the concentration of these drugs affect their bioavailability and biopharmaceutical properties. Therefore, we presented a simple and convenient method for the ratiometric detection of carbidopa and levodopa for carbon dots (CDs) dual-fluorescent emission. Dual-emission CDs were prepared from chitosan using a microwave method, following which the surface was chemically modified with terephthalaldehyde. CDs had two strong well-separated peaks at 445 and 510 nm. The relative measurement of carbidopa and levodopa was based on the static extinction of CDs at 445 nm and increase at 510 nm, respectively. The linear range for carbidopa measurement was 2.5-300 nM, with a limit of detection (LOD) of 2.1 nM, and a relative standard deviation (RSD) of 1.68%. Further, the linear range for levodopa measurement was equal to 3.0-400 nM, with LOD and RSD% of 2.8 nM and 3.5%, respectively. Also, selectivity of ratiometric sensor in the presence of interferences was investigated, which showed that the recovery of carbidopa and levodopa in serum and urine samples has changed between 96.80% and 116.24% with RSD% 0.11-0.77. CDs also provided good results for the determination of carbidopa and levodopa in real samples, and had high selectivity in the presence of possible interferences.

pH-responsive dual-emission carbon dots for the ratiometric detection of organophosphorus pesticides in Brassica chinensis and Hg2+ in water.

Accurate and rapid monitoring of organophosphorus pesticides (OPs) residues is crucial for regulating food safety. Herein, dual-emission carbon dots (de-CDs) were fabricated for the ratiometric detection of OPs and Hg2+. The de-CDs exhibited two emission peaks at 678 and 485 nm when excited with visible light. Interestingly, the fluorescence at 678 nm was significantly quenched by Hg2+ mainly because of the static quenching effect, whereas that at 485 nm exhibited a slight change. More significantly, the quenched fluorescence of the de-CDs recovered remarkably after introducing omethoate, diazinon and malathion. Accordingly, the ratiometric detection of the three OPs and Hg2+ was achieved with high selectivity and robust performance. In addition, the OPs residues assay in Brassica chinensis was successfully performed with satisfactory results. This study not only provides an attractive tool for the simple and rapid assay of OPs but also offers new insights into the fabrication of multi-functional carbon dots.

Green one-step synthesis of N-doped carbon quantum dots for fluorescent detection of lemon yellow in soft drinks.

A new fluorescent sensor for the determination of lemon yellow was developed based on nitrogen-doped carbon quantum dots (N-CQDs), which were prepared via a hydrothermal method with dried pomelo peel and L-tyrosine. The N-CQDs exhibited the blue fluorescence with a quantum yield of 28 %. The sensing principle of N-CQDs was quenched by lemon yellow via static quenching. The potential interfering substances showed no influence on the detection of lemon yellow. The limit of detection was 0.023 mg/L and lower than that of national standard. Furthermore, the synthesized N-CQDs have been successfully applied to the measurement of lemon yellow in real samples. Hence, the N-CQDs would be a promising sensor in food analysis.

Investigation of the Application and Mechanism of Nitrogen and Phosphorus Co-doped Carbon Dots for Mercury Ion Detection.

In this paper, we obtained nitrogen and phosphorus co-doped carbon dots through a hydrothermal method using o-phenylenediamine and citric acid in a 40% phosphoric acid environment. The carbon dots emitted fluorescence at 476 nm under excitation at 408 nm and exhibited good selectivity and high sensitivity towards mercury ions. These carbon dots showed excellent dispersibility in water and maintained stable fluorescence even in high concentration salt environments. The interaction between mercury ions and functional groups on the carbon dots surface through electrostatic interaction resulted in static quenching. Simultaneously, by detecting the lifetime and transient absorption spectra of the carbon dots, we observed that the coordination of mercury ions with the carbon dots broadened the band structure of the carbon dots, and the existing photoinduced electron transfer process increased the non-radiative transition channel. The combined effect of dynamic quenching and static quenching significantly reduced the fluorescence intensity of the carbon dots at 476 nm. The carbon dots exhibited linear detection of mercury ions in the range of 0.01-1 µM, with a detection limit as low as 0.0245 µM. In terms of practical water environmental detection applications, these carbon dots were able to effectively detect mercury ions in tap water and lake water, demonstrating their broad application prospects in the field of environmental metal analysis.

Rapid chemical reduction synthesis of copper nanoclusters with blue fluorescence for highly sensitive detection of furazolidone.

Tannic acid (TA), as a stabilizing agent, was successfully utilized to establish blue-emitting copper nanoclusters (TA-Cu NCs) on the basis of a facile chemical reduction preparation method. Characterization results proved successful synthesis of TA-Cu NCs with uniform size and excellent stability. TA-Cu NCs exhibited a blue emission wavelength at 431 nm when excited at 364 nm. Interestingly, the as-prepared TA-Cu NCs were selectively quenched by furazolidone based on static quenching. In addition, this analysis platform for furazolidone detection had an excellent linear range from 0.5 to 120 µM with a detection limit of 0.074 µM (S/N = 3). Furthermore, the accuracy of this sensing method was successfully confirmed by detecting furazolidone in bovine serum samples, indicating that TA-Cu NCs had bright application prospects.

A dual-emitting fluoroprobe fabricated by aloe leaf-based N-doped carbon quantum dots and copper nanoclusters for nitenpyram detection in waters by virtue of inner filter effect and static quenching principles.

Fluorescence sensing technique has been used in environmental analysis due to its simplicity, low cost, and visualization. Although the fruit pulp-based biomass carbon quantum dots (CQDs) have excellent luminescent properties, aloe leaves possess the superiority of being easily accessible in all seasons compared to fruit pulp. Thus, we fabricated Aloe carazo leaf-based nitrogen doping-CQDs (N-CQDs) using a facile hydrothermal approach, which emitted bright blue fluorescence with a quantum yield of 21.4 %. By comparison, the glutathione-encapsulated copper nanoclusters (GSH-CuNCs) displayed strong red fluorescence. A blue/red dual emission based on the N-CQDs/CuNCs mixture was established for nitenpyram detection. At the 350-nm excitation, the N-CQD/CuNCs system produced dual-wavelength emitting peaks at 440 and 660 nm, respectively. Moreover, when nitenpyram was introduced into the system, the fluorescence intensities (FIs) of N-CQDs significantly decreased, whereas the FIs of GSH-CuNCs varied slightly; simultaneously, the solution color changed from bright blue to dark red. Both the spectral overlapping between nitenpyram's UV-Vis absorption and N-CQDs' excitation and almost unchanged fluorescence lifetimes indicated the occurrence of inner-filtering effect (IFE) in the dual-emitting fluoroprobe. In addition, the Stern-Volmer constant (Ksv = 6.92 × 103 M-1), temperature effect, as well as UV-Vis absorption of N-CQD/CuNCs before and after the addition of nitenpyram corroborated the static-quenching behavior. Consequently, the fluorescence-quenching of N-CQDs by nitenpyram was attributable to the joint IFE and static-quenching principles. A good linearity existed between the F660/F440 values and nitenpyram concentrations (0.5-200 µM) with a method detection limit of 0.15 µM. The dual-emitting fluoroprobe provided the satisfactory recoveries (95.0%-107.0 %) for nitenpyram detection in real-world waters, which were comparable with the results of traditional liquid chromatography coupled to tandem mass spectrometry method. Owing to its simple operations, low-cost, and adaptability for on-site outdoor monitoring, the newly developed dual-emitting fluoroprobe possesses great potential applications in routine monitoring of nitenpyram under field conditions.

Histidine-capped copper nanoclusters for in situ amplified fluorescence monitoring of doxycycline through inner filter effect.

There is a significant need to accurately measure doxycycline concentrations in view of the adverse effects of an overdose on human health. A fluorescence (FL) detection method was adopted and copper nanoclusters (CuNCs) were synthesized using chemical reduction technology. Based on FL quenching with doxycycline, the prepared CuNCs were used to explore a fluorescent nanoprobe for doxycycline detection. In an optimal sensing environment, this FL nanosensor was sensitive and selective in doxycycline sensing and displayed a linear relationship in the range 0.5-200 µM with a detection limit of 0.092 µΜ. A characterization test demonstrated that CuNCs offered active functional groups for identifying doxycycline using electrostatic interaction and hydrogen bonds. Static quenching and the inner filter effect (IFE) resulted in weakness in the FL of His@CuNCs with doxycycline with great efficiency. This suggested nanosensor was revealed to be a functional model for simple and rapid detection of doxycycline in real samples with very pleasing accuracy.

Preparation and p-phenylenediamine detection mechanism of a dialdehyde cellulose and a 7-amino-4-methylcoumarin-based fluorescent probe.

A novel fluorescent probe, fluorescent dialdehyde cellulose (FDAC), was prepared to detect p-phenylenediamine (PPD) in water samples conveniently and quickly. This was achieved by grafting 7-amino-4-methylcoumarin (AMC) onto dialdehyde cellulose (DAC) via an aldol-amine condensation reaction. This method is greener, more economical, and simpler than existing methods for preparing fluorescent probes. The probe was found to be more effective for PPD detection in polar solvents, with less interference from pH and other compounds present in the sample matrix. The photoluminescence of FDAC at λex/λem = 340/430 nm was statically quenched by PPD, allowing for accurate detection within the range of 10-100 µmol/L under optimal conditions, with a detection limit of 3.2 µmol/L (3 σ/s). Meanwhile, the Schiff base (-C=N- group) generated by the condensation of DAC and AMC increased the reaction activity of the fluorescent moiety and changed the AMC conjugated structure, making FDAC more susceptible to aminolysis with PPD than AMC. This study presents a promising solution for fluorescence detection of aniline compounds, with significant potential for application in fields such as environmental analysis.

Constructing an eco-friendly and ratiometric fluorescent sensor for highly efficient detection of mercury ion in environmental samples.

Mercury ion (Hg2+) is a highly toxic and ubiquitous pollutant, whose effective detection has aroused widespread concern. A novel ratiometric fluorescent sensor has been designed to rapidly and efficiently detect Hg2+ based on blue/red carbon dots (CDs) with environmental friendliness. This sensor was well characterized via TEM, FTIR, XPS, UV-vis, and zeta potential analysis and displayed excellent fluorescence properties and stability. The fluorescence of blue CDs at 447 nm was significantly quenched with the addition of Hg2+ resulted from the static quenching, whereas that of red CDs at 650 nm remained invariable. A sensitive method for Hg2+ determination was constructed in the range of 0.05-7.0 nmol mL-1 with optimal conditions, and the detection limit was down to 0.028 nmol mL-1. Meanwhile, compared to other 17 metal ions, the ratiometric fluorescent sensor exhibited high selectivity for Hg2+. Furthermore, satisfied recoveries had also been obtained for measuring trace Hg2+ in practical environmental samples. This developed ratiometric fluorescent sensor provided a reliable, environmental-friendly, rapid, and efficient platform for the detection of Hg2+ in environmental applications.

Spectroscopic Insights of an Emissive Complex between 4'-N,N-Diethylaminoflavonol in Octa-Acid Deep-Cavity Cavitand and Rhodamine 6G.

Excited-state chemistry relies on the communication between molecules, making it a crucial aspect of the field. One important question that arises is whether intermolecular communication and its rate can be modified when a molecule is confined. To explore the interaction in such systems, we investigated the ground and excited states of 4'-N,N-diethylaminoflavonol (DEA3HF) in an octa acid-based (OA) confined medium and in ethanolic solution, both in the presence of Rhodamine 6G (R6G). Despite the observed spectral overlap between the flavonol emission and the R6G absorption, as well as the fluorescence quenching of the flavonol in the presence of R6G, the almost constant fluorescence lifetime at different amounts of R6G discards the presence of FRET in the studied systems. Steady-state and time-resolved fluorescence indicate the formation of an emissive complex between the proton transfer dye encapsulated within water-soluble supramolecular host octa acid (DEA3HF@(OA)2) and R6G. A similar result was observed between DEA3HF:R6G in ethanolic solution. The respective Stern-Volmer plots corroborate with these observations, suggesting a static quenching mechanism for both systems.

Highly efficient ferric ion sensing and high resolution latent fingerprint imaging based on fluorescent silicon quantum dots.

Expanding the application of silicon based luminescent materials is a fast-growing interdisciplinary field. Herein, a novel fluorescent bifunctional probe based on silicon quantum dots (SiQDs) for highly sensitive Fe3+ sensing and high-resolution latent fingerprint (LFP) imaging was subtly devised. The SiQD solution was mildly prepared using 3-aminopropyl trimethoxysilane as the silicon source and sodium ascorbate as the reductant, showing green emission at 515 nm under UV irradiation with a quantum yield of 19.8%. As a highly sensitive fluorescent sensor, the SiQD was demonstrated to have a highly selective quenching with Fe3+ in the concentration range of 2-1000 µM with the LOD of 0.086 µM in water. The quenching rate constant and association constant of the SiQDs-Fe3+ complex was calculated to be 1.05 × 1012 mol/s and 6.8 × 103 L/mol, respectively, suggesting a static quenching effect between them. Moreover, to achieve high-resolution LFP imaging, a novel SiO2@SiQDs composite powder was further fabricated. The SiQDs were covalently anchored on the surface of silica nanospheres to conquer aggregation-caused quenching for the high-solid fluorescence. In the demonstration of LFP imaging, this silicon based luminescent composite exhibited high developing sensitivity, high selectivity and high contrast, indicating its practical value as a fingerprint developer at crime scenes.

A Novel and Sensitive Fluorescent Probe for Glyphosate Detection Based on Cu2+ Modulated Polydihydroxyphenylalanine Nanoparticles.

A novel and sensitive fluorescent probe based on Cu2+-modulated polydihydroxyphenylalanine nanoparticles (PDOAs) has been developed for the detection of glyphosate pesticides. Compared to conventional instrumental analysis techniques, fluorometric methods have obtained good results in the field of agricultural residue detection. However, most of the fluorescent chemosensors reported still have some limitations, such as long response times, the high limit of detection, and complex synthetic procedures. In this paper, a novel and sensitive fluorescent probe based on Cu2+ modulated polydihydroxyphenylalanine nanoparticles (PDOAs) has been developed for the detection of glyphosate pesticides. The fluorescence of PDOAs can be effectively quenched by Cu2+ through the dynamic quenching process, which was confirmed by the time-resolved fluorescence lifetime analysis. In the presence of glyphosate, the fluorescence of the PDOAs-Cu2+ system can be effectively recovered due to the higher affinity of glyphosate for Cu2+, and thus released the individual PDOAs. Due to the admirable properties such as high selectivity to glyphosate pesticide, "turn on" fluorescence response, and ultralow detection limit of 1.8 nM, the proposed method has been successfully applied for the determination of glyphosate in environmental water samples.

Selective detection of nitrofurantoin by histidine-capped silver nanoclusters with blue luminescence.

In view of the significance of nitrofurantoin, there is an urgent need for efficient analytical methods for accurate detection of nitrofurantoin. Considering their superior fluorescence performance and rarity of reports regarding nitrofurantoin detection by fluorescent silver nanoclusters (Ag NCs), Ag NCs with good stability and uniform size were synthesized through a simple method by protection of histidine (His) and reduction of ascorbic acid (AA). Based on the quenching by nitrofurantoin, Ag NCs were applied successfully in the detection of nitrofurantoin with high sensitivity. In the range of 0.5-150 µM, a linear relationship was found between ln(F0 /F) and nitrofurantoin amounts. Static quenching and inner filter effect were proved to be the main quenching mechanisms. Significantly superior selectivity and satisfactory recovery results in bovine serum indicate that Ag NCs provide a better choice for nitrofurantoin detection.

Selective determination of ellagic acid in aqueous solution using blue-green emissive copper nanoclusters.

Development of beneficial sensors to analyze ellagic acid concentrations is of great importance for food safety and human health. Herein, a facile and fast fluorescent probe was carried out for the excellently selective and sensitive measurement of ellagic acid in real samples through histidine protected copper nanoclusters (histidine@Cu NCs) as a nanosensor. This as-developed histidine@Cu NCs were performed through UV-vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy and fluorescence lifetime analysis. The TEM image revealed that this nanomaterial had spherical features with the average diameter of 2.5 ± 0.05 nm. The blue-green fluorescence of this Cu NCs was found under the UV light. Meanwhile, the maximum excitation and emission wavelength were located at 387 nm and 488 nm. After addition of ellagic acid, the fluorescence of histidine@Cu NCs was slowly weakened with excellent linear range of 0.5-300 µM and detection limit of 0.077 µM. The fluorescence weakening mechanism of this nanosensor were attributed to the inner filter effect (IFE) and static quenching. Finally, this as-established analysis platform was successfully employed to measure ellagic acid in real samples.

Hemin as a General Static Dark Quencher for Constructing Heme Oxygenase-1 Fluorescent Probes.

The development of small-molecule probes suitable for live-cell applications remains challenging yet highly desirable. We report the first fluorescent probe, RBH, for imaging the heme oxygenase-1 (HO-1) activity in live cells after discovering hemin as a universal dark quencher. Hemin works via a static quenching mechanism and shows high quenching efficiency (>97 %) with fluorophores across a broad spectrum (λex =400-700 nm). The favorable properties of RBH (e.g. long excitation/emission wavelengths, fast response rate and high magnitude of signal increase) enable its use for determining HO-1 activity in complex biological samples. As HO-1 is involved in regulating antioxidant defence, iron homeostasis and gasotransmitter carbon monoxide production, we expect RBH to be a powerful tool for dissecting its functions. Also, the discovery of hemin as a general static dark quencher provides a straightforward strategy for constructing novel fluorescent probes for diverse biological species.

Facile synthesis of non-modified yellow emission silicon quantum dots and their visualization of hydrogen sulfide in living cells and onion tissues.

Yellow fluorescent silicon quantum dots (y-SiQDs) with 22.2% fluorescence quantum yield were synthesized by a simple hydrothermal method using 3-glycidoxypropyl triethoxysilane (GOTS) and m-aminophenol. The excitation wavelength is 550 nm with an emission wavelength of 574 nm, which effectively avoids the interference of biological autofluorescence. Notably, the synthesis approach does not require any post-modification and the y-SiQDs can be directly used for hydrogen sulfide (H2S) quantification due to static quenching. It exhibits high sensitivity and excellent selectivity for H2S with a 0.2-10 µM (R2 = 0.9953) linear range and detection limit of 54 nM. y-SiQDs have excellent stability and biocompatibility and can be used for H2S imaging in living cells and onion tissues.