Determination of Tetracaine Hydrochloride by Fluorescence Quenching Method with Some Aromatic Amino Acids as Probes

Fluorescent hydrogen-bonded organic framework act as a multifunctional platform for Fe3+ and F- sensing, and for information encryption

Due to their exceptional optical properties and adjustable functional characteristics, hydrogen-bonded organic frameworks (HOFs) demonstrate significant potential in applications such as sensing, information encryption. However, studies on the synthesis of HOFs designed to construct multifunctional platforms are scant. In this work, we report the synthesis of a new fluorescent HOF by assembling melem and isophthalic acid (IPA), designated as HOF-IPA. HOF-IPA exhibited good selectivity and sensitivity towards Fe3+, making it suitable as a fluorescent sensor for Fe3+ detection. The sensor achieved satisfactory recoveries ranging from 97.79 % to106.42 % for Fe3+ sensing, with a low relative standard deviation (RSD) of less than 3.33 %, indicating significant application potential for HOF-IPA. Due to the ability of F- to mask the electrostatic action on the surface of Fe3+ and inhibit the photoelectron transfer (PET) of HOF-IPA, the HOF-IPA - Fe3+ system can be utilized as a fluorescent "off-on" sensor for F- detection. Additionally, owing to the colorless, transparent property of HOF-IPA in aqueous solution under sunlight and its blue fluorescence property under UV light (color) or microplate reader (fluorescence intensity), HOF-IPA based ink can be used for various types of information encryption, and all yielding favorable outcomes.

Eco-friendly approach for the determination of moxifloxacin in pharmaceutical formulations and biological fluids based on fluorescence quenching of l-tryptophan

A rapid, novel and cost-effective spectrofluorimetric method developed to determine moxifloxacin (MFX) in pharmaceutical preparations because MFX in a pH 10 medium could reduce the fluorescence intensity of l-tryptophan. The maximum fluorescence excitation and emission wavelengths were found to be 280 and 363 nm respectively. A range of factors affecting fluorescence quenching and the effect of co-existing substances were investigated. Fluorescence quenching values (ΔF = FL-tryptophan  - FMoxi-L-tryptophan ) displayed a strong linear relationship with the MFX concentration ranging from 0.2 to 8.0 μg/ml under optimum conditions. The limit of detection was found to be 6.1 × 10-4  μg/ml. The proposed method was shown to be suitable for MFX determination in pharmaceutical tablets and biological fluids by the linearity, recovery and limit of detection. The spectrofluorimetric approach that has been developed is extremely eco-friendly, as evidenced by the fact that all the experimental components and solvents were safe for the environment.

Environmentally friendly protocol for the determination of sitagliptin phosphate in pharmaceutical preparations and biological fluids using l-tyrosine as a fluorescence probe

A responsive spectrofluorometric method was developed for the determination of sitagliptin phosphate using l-tyrosine as a fluorescence probe. The fluorescence intensity of l-tyrosine was quenched with sitagliptin phosphate. The fluorescence intensity was recorded at 307 nm using a 272 nm excitation wavelength. The calibration plot between fluorescence intensity and the concentration of drug was linear in the range of 0.1 to 2.0 mM with a good correlation value of 0.997. The limit of detection and quantification were established to be 3.7 × 10-4 and 1.23 × 10-3  mM, respectively. Commonly used excipients did not interfere with sitagliptin phosphate measurement. The proposed method was used to measure the sitagliptin phosphate in its standard type, dosage form, and biological samples. The percent recovery ranged from 97.41-103.36%. The static quenching was shown to be responsible for quenching as indicated by the Stern-Volmer plot. The method was validated using ICH guidelines and profitably applied for the content uniformity test, resulting in a high percent recovery and small relative standard deviation. The proposed approach is effortless, susceptible, selective, economic, and provides a high precision and accuracy, and can be used to determine sitagliptin phosphate in the pharmaceutical industry.

Block catiomers with flanking hydrolyzable tyrosinate groups enhance in vivo mRNA delivery via π-π stacking-assisted micellar assembly

Messenger RNA (mRNA) therapeutics have recently demonstrated high clinical potential with the accelerated approval of SARS-CoV-2 vaccines. To fulfill the promise of unprecedented mRNA-based treatments, the development of safe and efficient carriers is still necessary to achieve effective delivery of mRNA. Herein, we prepared mRNA-loaded nanocarriers for enhanced in vivo delivery using biocompatible block copolymers having functional amino acid moieties for tunable interaction with mRNA. The block copolymers were based on flexible poly(ethylene glycol)-poly(glycerol) (PEG-PG) modified with glycine (Gly), leucine (Leu) or tyrosine (Tyr) via ester bonds to generate block catiomers. Moreover, the amino acids can be gradually detached from the block copolymers after ester bond hydrolyzation, avoiding cytotoxic effects. When mixed with mRNA, the block catiomers formed narrowly distributed polymeric micelles with high stability and enhanced delivery efficiency. Particularly, the micelles based on tyrosine-modified PEG-PG (PEG-PGTyr), which formed a polyion complex (PIC) and π-π stacking with mRNA, displayed excellent stability against polyanions and promoted mRNA integrity in serum. PEG-PGTyr-based micelles also increased the cellular uptake and the endosomal escape, promoting high protein expression both in vitro and in vivo. Furthermore, the PEG-PGTyr-based micelles significantly extended the half-life of the loaded mRNA after intravenous injection. Our results highlight the potential of PEG-PGTyr-based micelles as safe and effective carriers for mRNA, expediting the rational design of polymeric materials for enhanced mRNA delivery.

Sulfuric acid induced-synthesis coupled with ethanol extraction-water precipitation purification method for orange fluorescent carbon dots with dual-emission: Application for methyl blue detection and cell imaging

In this work, by adjusting the sulfuric acid content in reaction solvent of ethanol, orange fluorescent carbon dots (O-FCDs) with dual-emission wavelength and blue fluorescent carbon dots (B-FCDs) with single-emission wavelength were successfully prepared using 1,3-dihydroxynaphthalene as precursor. Coupling with ethanol extraction-water precipitation purification method, pure O-FCDs and B-FCDs with yields of 9.0 % and 21.3 %, quantum yields (QYs) of 43.0 % and 13.7 % were obtained, respectively. The structures and optical properties of O-FCDs and B-FCDs were investigated by TEM, AFM, Raman, FT-IR, XPS, UV-vis, fluorescence analysis etc. The results revealed that sulfuric acid promoted the carbonization and the oxidation of precursor in the reaction process. In comparison with the B-FCDs, O-FCDs showed narrower lattice spacing and band gap, demonstrating the important role of sulfur-doping in fluorescence tuning. Additionally, O-FCDs showed good sensitivity for methyl blue with a linear response range of 0.05-100 μM (LOD was 20 nM) and the satisfactory results were obtained when O-FCDs were applied to the detection of methyl blue in real fish sample. Moreover, two FCDs showed good biocompatibility and negligible cytotoxicity proved by MTT experiment, while, O-FCDs showed better cell imaging effects than that of B-FCDs. Therefore, the O-FCDs had a broad application prospect as sensing platform in detection of methyl blue and for imaging in biological field.

A highly sensitive dual-readout assay for perfluorinated compounds based CdTe quantum dots

Perfluorooctanoic acid (PFOA) and Perfluorooctane sulfonate (PFOS) are two typical perfluorinated compounds (PFCs) that poss potential ecological toxicity. In this work, a fluorescence and resonance light scattering (RLS) dual-readout strategy for the detection of PFCs at picomole level based on the water-soluble CdTe quantum dots (CdTe QDs) has been proposed. It is found that the CdTe QDs exhibit a quenching in the presence of PFCs and thus serve as useful probes for PFCs. The linear ranges are 0.032-10.0 nM with a limit of detection(LOD) of 32.02 pM for PFOA and 0.044-15.0 nM with a LOD of 43.96 pM for PFOS, respectively. Meanwhile, PFCs can form complexes with CdTe QDs in acid medium, resulting in remarkable RLS signals. The enhanced RLS intensities are in proportion to the concentrations of PFOA and PFOS, respectively. And the linear ranges are 0.048-5.0 nM with a LOD of 47.78 pM for PFOA, and 0.057-5.0 nM with a LOD of 56.72 pM for PFOS, respectively. This dual-mode detection increases the reliability of the measurement. The proposed method is simple, sensitive and cost-effective, with potential applications in environmental monitoring and assessment.

A Highly Sensitive and Selective Fluorescent Probe Using MPA-InP/ZnS QDs for Detection of Trace Amounts of Cu2+ in Water

Detection of copper (II) ions (Cu²⁺) in water is important for preventing them from entering the human body to preserve human health. Here, a highly sensitive and selective fluorescence probe that uses mercaptopropionic acid (MPA)-capped InP/ZnS quantum dots (MPA-InP/ZnS QDs) was proposed for the detection of trace amounts of Cu²⁺ in water. The fluorescence of MPA-InP/ZnS QDs can be quenched significantly in the presence of Cu²⁺, and the fluorescence intensity shows excellent linearity when the concentration of Cu²⁺ varies from 0–1000 nM; this probe also exhibits an extremely low limit of detection of 0.22 nM. Furthermore, a possible fluorescence-quenching mechanism was proposed. The MPA-InP/ZnS QDs probes were further applied to the detection of trace Cu²⁺ in real water samples and drink samples, showing good feasibility.

Deep eutectic solvent assisted synthesis of carbon dots using Sophora flavescens Aiton modified with polyethyleneimine: Application in myricetin sensing and cell imaging

Here, an efficient method for synthesizing carbon dots (CDs) using a deep eutectic solvent (DES) was developed. To investigate the influence of different DESs on the quantum yield of CDs, different hydrogen-bonding acceptors (HBAs) and hydrogen-bonding donors (HBDs) were used to synthesize the DES and prepare CDs. Using Sophora flavescens Aiton as precursor, CDs were prepared using choline chloride (ChCl)/urea based DES as reaction media and doping agent in the presence of water. The CDs showed strong blue fluorescence and were further modified with polyethyleneimine (CDs@PEI). The fluorescence intensity of CDs@PEI was selectively quenched by myricetin with a limit of detection (LOD) of 10 nM. Furthermore, CDs@PEI was used to analyze myricetin in the extracts that were fluorescent by DES with satisfactory performance of Abelmoschus manihot (Linn.) Medicus flowers, vine teas and blueberries. Finally, the bio-imaging application of CDs@PEI was tested and the results confirmed its potential application in bio-imaging.

Spectrofluorometric method for the determination of ascorbic acid in pharmaceutical preparation using l-tyrosine as fluorescence probe

Ascorbic acid is a vital nutrient and antioxidant that is commonly used as an additive in commercial products. Quantitation of ascorbic acid is highly desired in the medical, food, and cosmetic industries. A spectrofluorometric assay for sensitive determination of ascorbic acid was developed using l-tyrosine as a fluorescent probe. The native fluorescence intensity of tyrosine was quenched using ascorbic acid. The linear range was 0.03-30.00 μM, and the limit of detection was 0.01 μM. The method exhibited excellent precision, accuracy, specificity, and robustness. Components of pharmaceutical preparations that are commonly found with ascorbic acid did not interfere with detection. The procedure was successfully employed for determination of ascorbic acid content in pharmaceutical tablets, injections, and nutrient supplements with satisfactory results. A Stern-Volmer plot and fluorescence lifetime revealed that quenching was attributed to the inner filter effect and static quenching. Isothermal titration calorimetry confirmed the formation of a complex between tyrosine and ascorbic acid, with a binding constant of 1.68 × 10³ M^-1 and reaction stoichiometry of 0.94. Thermodynamic parameters suggested spontaneous complexation via hydrophobic interactions as the dominant binding force. This method is promising for the simple and rapid determination of ascorbic in the pharmaceutical industry.

Label-free, Water-soluble Fluorescent Peptide Probe for a Sensitive and Selective Determination of Copper Ions

This study aimed to develop a label-free, sensitive, selective, and environment-friendly fluorescent peptide probe His-His-Trp-His (HHWH) for determining the concentration of copper ion (Cu²⁺) in aqueous solutions. The results demonstrated that the designed HHWH has a high selectivity and sensitivity for monitoring the concentration of free Cu²⁺ via quenching of the probe fluorescence upon a binding of Cu²⁺. The fluorescence intensity of the HHWH had a linear relationship with the concentration of Cu²⁺ between 10 nM and 10 μM, and the detection limit was 8 nM. Furthermore, HHWH could be regenerated with sulfide ions at least five times. The concentrations of Cu²⁺ in three different real water samples were detected using this probe, and the results were consistent with the one detected using an atomic absorption spectrometer. Thus, HHWH can be used as an accurate and feasible fluorescent peptide probe for detecting Cu²⁺ in aqueous solutions.

Two New Mononuclear Copper(II)-Dipeptide Complexes of 2-(2'-Pyridyl)Benzoxazole: DNA Interaction, Antioxidation and in Vitro Cytotoxicity Studies

Two new mononuclear mixed ligand copper(II) complexes [Cu(PBO)(Gly-gly)(H₂O)]·ClO₄·1.5H₂O (1) and [Cu(PBO)(Gly-L-leu)(H₂O)]·ClO₄ (2) (PBO is 2-(2'-pyridyl)benzoxazole, Gly-gly and Gly-L-leu are Glycyl-glycine anion and Glycyl-L-leucine anion, respectively), have been prepared and characterized by various analytical and spectral techniques. The interactions of the complexes with DNA were investigated using multi-spectroscopic methods (absorption, emission, circular dichroism), viscometry and electrochemical titration as well as molecular docking technique. The results indicated that 1 and 2 are bound to calf thymus DNA (CT-DNA) through an intercalative mode. The thermodynamic analyses revealed that the reactions between the Cu(II) complexes with DNA are spontaneous with negative Gibbs free energy (ΔG). The positive changes of enthalpy (ΔH) and entropy (ΔS) suggested that the binding processes are dominated by hydrophobic interaction accompanying with endothermic. Also, the complexes exhibited efficient oxidative cleavage of pBR322 plasmid DNA in the presence of ascorbic acid, probably induced by •OH as reactive oxygen species. In addition, 1 and 2 displayed excellent antioxidant activities with the IC₅₀ values of 0.112 and 0.191 μM, respectively, using the mean of nitroblue tetrazolium (NBT) photochemical reduction under a nonenzymatic condition. Moreover, the complexes were screened for their in vitro cytotoxicity against three human carcinoma cell lines (HeLa, PC-3 and A549), in which 2 owns higher cytotoxicity, which was consistent with DNA binding and cleavage ability order of the complexes. This results showed the in vitro biochemical potentials of the Cu(II)-dipeptide complexes with aromatic heterocyclic, viz. effective metallopeptide-nucleases, SOD mimics and non-platinum chemotherapeutic metallopharmaceuticals and their structure-activity relationship, which may contribute to the rational molecular design of new metallopeptide based chemotherapeutic agents.

Electron transfer and fluorescence “turn-off” based CdTe quantum dots for vancomycin detection at nanogram level in aqueous serum media

Mode of interaction of GSH-CdTe QDs with vancomycin and the mechanism of the fluorescence “turn-off” process.

Detection of DNA using an “off-on” switch of a regenerating biosensor based on an electron transfer mechanism from glutathione-capped CdTe quantum dots to nile blue

A new DNA detection method, which relies on the “off-on” switch of a regenerated fluorescence biosensor based on an electron transfer mechanism from glutathione (GSH)-capped CdTe quantum dots (QDs) to nile blue (NB), is proposed.