Fluorometric determination of quercetin by using graphitic carbon nitride nanoparticles modified with a molecularly imprinted polymer

Water-soluble sulfur quantum dots as a potential sensitive fluorescent probe for quercetin detection and cell imaging

A simple fluorescent quenching probe based on polyethylene glycol-400 capped sulfur quantum dots (PEG-SQDs) was fabricated to determine quercetin (QT) quantitatively. As anticipated, the PEG-SQDs exhibited favourable luminescent properties, stability and low cytotoxicity. QT effectively quenched the fluorescence of the PEG-SQDs through static quenching and the inner filter effect. Moreover, the PEG-SQDs showed rapid QT detection within a linear range of 0.100-45.0 μM, with a limit of detection of 0.014 μM (3σ/k). This fluorescent probe successfully detected QT in human serum, quercetin supplement capsules and red wine, achieving a standard recovery of 92.6 %-105 %.

N-doped carbon dots coupled with molecularly imprinted polymers as a fluorescent sensor for ultrasensitive detection of genistein in soya products

Rapid detection of genistein in soya products has remained difficult. Current methods necessitate sample handling and use of costly instruments. Here, using a simple one-pot reverse microemulsion method, a sensor based on N-doped carbon dots conjugated molecularly imprinted polymers (N-CDs@MIPs) was synthesized to analyze genistein. N-doped carbon dots were used as fluorescent component, genistein as the template molecule, and molecularly imprinted polymers as the selective sorbent in this fluorescence sensor. The sensor was then examined and optical studies demonstrated that N-CDs@MIPs not only had strong fluorescence emission and outstanding optical stability, but also had good sensitivity (detection limit 35.7 nM) and selectivity to genistein. Furthermore, the N-CDs@MIPs materials were used to analyze genistein in soya products, and the findings (which ranged from 99.77% to 106.11%) show that the N-CDs@MIPs has high potential for quickly detecting the amount of genistein in complicated food samples.

Enhanced electrochemical determination of quercetin in a choline chloride-based ionic liquid

Electrochemical techniques have been applied to determine quercetin and to evaluate its antioxidant effect. Deep eutectic solvents as a new generation of green solvents are promising electrolyte catalytically active additives for electrochemical oxidation of quercetin. Herein, in this work, Au was directly electrodeposited on the surface of graphene-modified glassy carbon electrodes, and AuNPs/GR/GC electrodes were fabricated. Choline chloride-based ionic liquids as deep eutectic solvents were readily prepared and applied to detect quercetin in buffer solutions, allowing a detection enhancement. X-ray diffraction and scanning electron microscopy were carried out to characterize the morphology of AuNPs/GR/GCE. Fourier transform infrared spectroscopy was carried out to interpret the H-bond interactions between the DES and quercetin. This electrochemical sensor exhibited good analytical performance. The low detection limit was reduced to 0.5 μM in a 15% DES solution, which was 300% higher than the signal without DES. It proved to be fast and environmentally friendly for the determination of quercetin and the DES had no effect on antioxidant effects of quercetin. In addition, it has been successfully applied in real sample analysis.

Preparation and Application of Molecularly Imprinted Polymers for Flavonoids: Review and Perspective

The separation and detection of flavonoids from various natural products have attracted increasing attention in the field of natural product research and development. Depending on the high specificity of molecularly imprinted polymers (MIPs), MIPs are proposed as efficient adsorbents for the selective extraction and separation of flavonoids from complex samples. At present, a comprehensive review article to summarize the separation and purification of flavonoids using molecular imprinting, and the employment of MIP-based sensors for the detection of flavonoids is still lacking. Here, we reviewed the general preparation methods of MIPs towards flavonoids, including bulk polymerization, precipitation polymerization, surface imprinting and emulsion polymerization. Additionally, a variety of applications of MIPs towards flavonoids are summarized, such as the different forms of MIP-based solid phase extraction (SPE) for the separation of flavonoids, and the MIP-based sensors for the detection of flavonoids. Finally, we discussed the advantages and disadvantages of the current synthetic methods for preparing MIPs of flavonoids and prospected the approaches for detecting flavonoids in the future. The purpose of this review is to provide helpful suggestions for the novel preparation methods of MIPs for the extraction of flavonoids and emerging applications of MIPs for the detection of flavonoids from natural products and biological samples.

Non-conjugated polymer dots for fluorometric and colorimetric dual-mode detection of quercetin

Due to the biochemical and pharmacological activities, the convenient and effective detection of quercetin (Qc) is very important for biochemistry, pharmaceutical chemistry and clinical medicine. A kind of non-conjugated polymer dots (NCPDs) was used as a versatile and sensitive dual-mode optical output for Qc detection, which was synthesized by hyperbranched poly(ethylenimine) (PEI) and l-threonine via environmentallyfriendly way. The dual-mode method proposed in this work had high sensitivity and definiteselectivity for Qc detection. Additionally, it was convenient for the naked eyes to observe the fluorescence brightness and color change.

Nanomaterial Complexes Enriched With Natural Compounds Used in Cancer Therapies: A Perspective for Clinical Application

Resveratrol and quercetin are natural compounds contained in many foods and beverages. Reports indicate implications for the health of the general population; on the other hand the use of both compounds has interesting results for the treatment of many diseases as cardiovascular affections, diabetes, Alzheimer's disease, viral and bacterial infections among others. Based on their capacities described as anti-inflammatory, antioxidant, and anti-aging, resveratrol and quercetin showed antiproliferative and anticancer activity specifically in maligned cells. These molecular characteristics trigger the pharmacological repurposing of both compounds and improved its research for treating different cancer types with interesting results at in vitro, in vivo, and clinical trial studies. Meanwhile, the development of different systems of drug release in specific sites as nanomaterials and specifically the nanoparticles, potentiates the personal treatment perspective in conjunct with the actual cancer therapies; regularly invasive and aggressive, the perspective of nanomedicine as higher effective and lower invasive has gained popularity. Knowledge of molecular interactions of resveratrol and quercetin in diseases confirms the evidence of multiple benefits, while the multiple analyses suggested a positive response for the treatment and diagnostics of cancer in different stages, including at metastatic stage. The present work reviews the reports related to the impact of resveratrol and quercetin in cancer treatment and its effects when the antioxidants are encapsulated in different nanoparticle systems, which improve the prospects of cancer treatment.

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.

Fluorescence determination of trace level of cadmium with pyrene modified nanocrystalline cellulose in food and soil samples

Cadmium is one of the most toxic metal that accumulates in the human body via food chain, industrial/agricultural activites. It also has negative effects in organs such as the brain, liver and central nervous system. Therefore, International Agency for Research on Cancer is classified cadmium as "carcinogenic to humans" (group 1). In this work, novel pyrene modified nanocrystalline cellulose (NP-1) was designed as a fluorescence sensor for selective determination of Cd²⁺ in food and soil samples. FTIR, UV-Vis, SEM, TEM and TGA were used for structural, morphological characterizations and thermal properties of NP-1. The experimental conditions such as selectivity, pH, sensor concentration, photostability, time and interaction mechanism were examined and optimized. The LOD was determined as 0.09 μM (10.70 μg/L) which was lower than WHO's permissible limit of cadmium in plant with 0.10-60.00 μM linear working range. Validation of the present method was performed by spike/recovery test and ICP-MS, then fluorescence determination of Cd²⁺ in food and soil samples was succesfully applied. The results indicated that the proposed method based on "turn-on" fluorescence of NP-1 was a simple, sensitive and reliable for rapid determination of Cd²⁺ in real samples with high applicability and stability.

Application of micro/nanomaterials in adsorption and sensing of active ingredients in traditional Chinese medicine

Traditional Chinese medicine (TCM) has been widely applied for the prevention and cure of various diseases for centuries. Ingredient with pharmacological activity is the key to the application of TCM. Hence, it is of significance to separate and detect active ingredients in TCM effectively. Micro/nanomaterial is the promising candidate for adsorption and sensing due to its unique physical and chemical properties. For years, many efforts have been made to develop functional micro/nanomaterials to realize the effective adsorption or sensing of bioactive compounds in TCM. In this review, we discussed recent progresses in the application of various functional micro/nanomaterials for adsorption or detection (electrochemical detection, fluorescent detection, and colorimetric detection) of active ingredients. Based on the kind of matrix materials, micro/nano-adsorbents or sensors can be classified into following categories: metal-based micro/nanomaterials, porous materials, carbon-based materials, graphene/graphite-liked micro/nanomaterials and hybrid micro/nanomaterials.

Preparation of levofloxacin-imprinted nanoparticles using designed deep eutectic solvents for the selective removal of levofloxacin pollutants from environmental waste water

Designed deep eutectic solvents was applied to preparation of levofloxacin-imprinted nanoparticles as functional monomer. The nanoparticles using for the selective removal of levofloxacin pollutants from a natural environmental system.

Fluorometric detection of pH and quercetin based on nitrogen and phosphorus co-doped highly luminescent graphene-analogous flakes

Highly luminescent nitrogen and phosphorus co-doped graphene-analogous flakes (NPCGFs) were synthesized by a one-pot simple hydrothermal reaction using β-cyclodextrin (β-CD), vinylphosphoric acid (VPA), and o-phenylenediamine (oPD) as the precursors. VPA, as an important organic P-containing monomer, was selected as the phosphorus source to generate additional conjugated and effective binding sites on the surface of the NPCGFs. This synthetic strategy not only allows enhancement of structural rigidity, but also effectively eliminates surface traps of the NPCGFs, resulting in an improved fluorescence quantum yield (FL QY) of the NPCGFs. Additionally, oPD simultaneously acts as a nitrogen source and enables amino functionalisation of the NPCGF surface in the synthesis process. The NPCGFs (QY, 32.49%) are irregularly shaped with a typical diameter of approximately 54 nm and display strong fluorescence, with excitation/emission maxima of 360/445 nm. It was found that the NPCGFs can serve as a multifunctional FL probe for pH measurement and quercetin (Qc) detection. A linear relationship exists between the decrease in FL intensity and the concentration of Qc in the range from 0.35 to 30 μg mL-1 as well as the pH variation between 4.0 and 7.0. The probe was further applied to the determination of Qc in living cells.

One-pot green and simple synthesis of actinian nickel-doped carbon nanoflowers for ultrasensitive sensing of quercetin

In this contribution, a one-pot method possessing the advantages of easy preparation, rapidness, efficiency and environmental friendliness has been developed for the first time for the facile synthesis of highly fluorescent actinian nickel-doped carbon nanoflowers (Ni-CNFWs) by using nickel(ii)acetylacetonate as a metal-carbon source. Various characterization studies indicate that metal nickel atoms have been successfully doped into carbon nanoflower frameworks with a weight percentage of 1.46 wt%. The Ni-CNFWs showed a "shell-core" actinian structure with ∼400 nm diameter and highly efficient fluorescence quenching ability in the presence of quercetin (Qut) due to the formed Meisenheimer complexes via the conjugation effect of p, π-electrons between Ni-CNFWs and Qut, which allowed the analysis of Qut in a very facile method. Under the optimal conditions, the decreased fluorescence of Ni-CNFWs showed a good linear relationship with the concentration of Qut ranging from 0.5 to 300.0 μM, and the limit of detection was 0.137 μM (3σ/k). Finally, the content of Qut in bovine serum was successfully detected with the novel on-off sensor, and the recoveries were 97.3-101.9%, which indicate that the constructed on-off sensor has a high selectivity and accuracy.

Surface-imprinted β-cyclodextrin-functionalized carbon nitride nanosheets for fluorometric determination of sterigmatomycin

β-Cyclodextrin-functionalized carbon nitride nanosheets were modified with a molecularly imprinted polymer to obtain a fluorescent probe of type MIP@β-CD/CNNS which is shown to enable fluorometric determination of sterigmatocystin (STG). The material was characterized by transmission electron microscopy, infrared spectra, powder X-ray diffraction, X-ray photoelectron spectroscopy, and by absorption and emission spectra. The modified CNNSs have a good fluorescence quantum yield (13%), high sorption capacity for STG (86 mg·g^-1), fast adsorption rate (25 min), and superior adsorption selectivity (with an imprint factor 2.56). When used as an optical probe for STG, the CNNSs act as the chromophore, while β-CD and MIP act as the recognition groups. The blue fluorescence of MIP@β-CD/CNNS (with excitation/emission maxima at 368/432 nm) is quenched by STG. Fluorescence drops linearly in the 0.15 to 3.1 μM STG concentration range. The lower detection limit is 74 nM. The method was successfully applied to the determination of STG in spiked wheat extract. Conceivably, this detection scheme based on a combination of β-CD inclusion and molecular imprinting may be extended to the detection of various other organic compounds. Graphical abstractSchematic representation of the preparation of surface-imprinted β-cyclodextrin-functionalized carbon nitride nanosheets. These are used, along with a molecularly imprinted polymer, for fluorometric determination of sterigmatomycin.

Molecularly imprinted mesoporous silica incorporating C3N4 dots and CdTe quantum dots as ratiometric fluorescent probe for determination of Malachite Green

A new dual-emission ratiometric fluorescent probe was synthesized and successfully used for the determination of Malachite Green (MG) in fish farming water. The ratiometric fluorescent probe was successfully composited by sol-gel method using C₃N₄ and CdTe quantum dots as fluorescent materials combined with mesoporous molecularly imprinted polymers. MG quenches the red fluorescence of the CdTe QDs (with excitation/emission wavelengths at 350/680 nm) while the blue fluorescence of C₃N₄ (with excitation/emission wavelengths at 350/458 nm) remains unchanged. The change of fluorescence color and fluorescence intensity ratio can be successfully used for quantification of malachite green. In addition, the mesoporous structure has a large surface and good adsorption capacity for malachite green. The normalized intensity of fluorescence increases linearly in the 50-1000 ng·mL^-1 MG concentration range, and the detection limit is 10 ng·mL^-1. The imprinting factor is 3.2. The nanoprobe was applied to the determination of MG in fish farming water samples. Recoveries and relative standard deviations were 92.5-97.8% and 2.5-6.2%, respectively. Graphical abstract Schematic representation of synthesis of molecularly imprinted mesoporous silica ratiometric fluorescent probes incorporating C₃N₄ dots and CdTe quantum dots for determination of malachite green.

Excitation-independent emission carbon nanoribbon polymer as a ratiometric photoluminescent probe for highly selective and sensitive detection of quercetin

In this study, sulfur–nitrogen co-doped carbon nanoribbon (SNCNR) polymers with stable dual-emission fluorescence were synthesized using a one-step traditional hydrothermal method of 6-mercaptopurine in an aqueous methanol solution.