Preparation and use of tyrosine-capped copper nanoclusters as fluorescent probe to determine rutin

A facile synthesis of water-soluble copper nanoclusters as label-free fluorescent probes for rapid, selective and sensitive determination of alizarin red

Copper nanoclusters (FA@CuNCs) emitting blue fluorescence were successfully developed via a one-pot technique. In this method, the copper chloride, folic acid and hydrazine hydrate were applied as a precursor, protective agent and reducing agent, respectively. The absorption, fluorescence excitation and emission spectra of FA@CuNCs were carried out by using ultraviolet-visible and fluorescence spectrometry, respectively. The morphology, particle size, functional groups, oxidation states of elements of FA@CuNCs were discussed via using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The stability of FA@CuNCs was studied under various conditions, such as storage time at 25 ℃, ultraviolet radiation time, sodium chloride solutione and pH. The FA@CuNCs displayed blue fluorescence under the excitation wavelength of 361 nm, and the fluorescence quantum yield was 7.45 %. As a result of the inner filter effect, the alizarin red could significantly weaken the blue fluorescence of FA@CuNCs. Thus, the as-prepared FA@CuNCs could be utilized as fluorescence nanosensors for the trace determination of alizarin red. This platform suggested an excellent linear range for alizarin red varying from 0.5 to 200 μM with a fitting coefficient of 0.9955. The detection limit was calculated to be 0.064 μM in the light of the 3b/k (b and k refer to the standard deviation and slope of fitted curve, respectively). Furthermore, the as-developed FA@CuNCs could be used to detect the alizarin red in real samples and for the sensing of temperature.

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.

Highly photoluminescent tryptophan-coated copper nanoclusters based turn-off fluorescent probe for determination of tetracyclines

Employing cheap Cu nanoclusters to design a novel fluorescent probe have promising opportunities in the field of optical sensors. Here, we fabricated a highly photoluminescent D-tryptophan (D-Trp)-coated Cu nanoclusters (Trp-Cu NCs) by rapid microwave-assisted method to achieve precise quantification of tetracyclines (TC). Due to protecting groups of Trp, the synthesized Trp-Cu NCs have remarkable fluorescence stability with a quantum yield reached 12.5%. A distinct fluorescence quenching with the incremental addition of TC via the internal filtration effect (IFE). Based on turn-off fluorescence within 1 min, a detection method for detecting TC was constructed with a linear range of 0.3-120 μM and a limit of detection (LOD) of 0.12 μM. Besides, the proposed fluorescent probe has been employed for the determination of practical samples such as water samples, milk and honey, and exhibited satisfactory recoveries of 96.1%-108.2%, with relative standard deviations (RSD) lower than 5.0%. This is a sensitive, rapid and easily recognizable Trp-Cu NCs based sensing platform for the determination of TC, which could offer a powerful tool for ensuring food safety.

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.

Ionic liquid-based carbon dots as highly biocompatible and sensitive fluorescent probe for the determination of vitamin P in fruit samples

Vitamin P (VP) known as rutin is one of the common flavonoids, which widely exists in fruits and vegetables and often used as a dietary additive. The rapid and accurate detection of VP in food matrices is critical for evaluating food quality and guiding diet. Herein, a rapid, accurate, and selective detection scheme for VP in fruit samples was proposed for the first time using ionic liquid-based carbon dots (IL-CDs). The synthesized IL-CDs exhibited great biocompatibility and excellent optical properties including high fluorescence intensity, high quantum yield, and good fluorescence stability. Through an internal filtering effect (IFE), VP could greatly reduce the fluorescence of these CDs. In the present study, this probe demonstrated good sensitivity and excellent selectivity toward VP with a low detection limit of 60.0 nmol/L. Moreover, this approach was effectively applied to detect VP in food samples with a recovery range of 97 % to 119 %. More interestingly, the results of cell imaging suggested that IL-CDs were expected to be promising material for bioimaging.

Fluorescent folic acid-capped copper nanoclusters for the determination of rifampicin based on inner filter effect

Development of excellent sensors to determine trace concentrations of rifampicin is of intense importance for medicine analysis and human health. Herein, a facile and green fluorescent probe was established for the determination of rifampicin by using folic acid protected copper nanoclusters (FA-Cu NCs). Many characterization methods were applied for the analysis of the as-prepared FA-Cu NCs including UV-visible absorption spectra, fluorescence spectra, Fourier-transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), fluorescence lifetime and X-ray photoelectron spectroscopy (XPS). The TEM image suggested that the as-prepared FA-Cu NCs were highly dispersed. The as-synthesized FA-Cu NCs emerged blue fluorescence under UV light and demonstrated maximum emission wavelength at 446 nm under the maximum excitation wavelength of 358 nm. After the addition of rifampicin, the FL intensities of FA-Cu NCs were uncommonly quenched. The related experimental data intimated that the quenching mechanisms were assumed to the inner filter effect (IFE) and static quenching. The as-proposed probe platform displayed an obvious linear relationship with rifampicin concentrations varying from 0.5 to 100 µM, and the corresponding detection limit (LOD) was 0.073 µM (S/N = 3). Finally, the as-established detection platform was successfully employed to analyze trace concentrations of rifampicin in real samples.

Preparation of Nitrogen and Sulfur Co-Doped Fluorescent Carbon Dots from Cellulose Nanocrystals as a Sensor for the Detection of Rutin

The poor water solubility, large particle size, and low accessibility of cellulose, the most abundant bioresource, have restricted its generalization to carbon dots (CDs). Herein, nitrogen and sulfur co-doped fluorescent carbon dots (N, S-CDs) were hydrothermally synthesized using cellulose nanocrystals (CNC) as a carbon precursor, exhibiting a small particle size and excellent aqueous dispersion. Thiourea was selected as a nitrogen and sulfur dopant to introduce abundant fluorescent functional groups into N, S-CDs. The resulting N, S-CDs exhibited nanoscale size (6.2 nm), abundant functional groups, bright blue fluorescence, high quantum yield (QY = 27.4%), and high overall yield (16.2%). The excellent optical properties of N, S-CDs endowed it to potentially display a highly sensitive fluorescence "turn off" response to rutin. The fluorescence response for rutin allowed a wide linear range of 0-40 mg·L^-1, with a limit of detection (LOD) of 0.02 μM, which revealed the potential of N, S-CDs as a rapid and simple sensing platform for rutin detection. In addition, the sustainable and large-scale production of the N, S-CDs in this study paves the way for the successful high-value utilization of cellulose.

One-step synthesis of blue emission copper nanoclusters for the detection of furaltadone and temperature

Polyvinyl pyrrolidone (PVP), playing roles as a templating agent, can be applied to prepare blue-emitting copper nanoclusters (Cu NCs@PVP) on the basis of a rapid chemical reduction synthesis method. The Cu NCs@PVP displayed a blue emission wavelength at 430 nm and the corresponding quantum yield (QY) could reach 10.4%. Subsequently, the as-synthesized Cu NCs@PVP were used for the trace analysis of furaltadone based on the inner filter effect (IFE) between Cu NCs@PVP and furaltadone, which caused the fluorescence to be effectively quenched. Additionally, this proposed determination platform based on the Cu NCs@PVP for furaltadone sensing possessed an excellent linear range from 0.5 to 100 μM with a lower detection limit of 0.045 μM (S/N = 3). Meanwhile, the Cu NCs@PVP also could be applied for the sensing of temperature. Furthermore, the practicability of the sensing platform has been successfully verified by measuring furaltadone in real samples, affirming its potential to increase fields for the determination of furaltadone.

One facile fluorescence strategy for sensitive determination of baicalein using trypsin-templated copper nanoclusters

Herein, we established a fluorescent detection platform for baicalein (Bai) based on copper nanoclusters, which were prepared by using copper sulfate as the precursor, trypsin (Tryp) as the template and hydrazine hydrate as the reducing agent. The entire preparation and testing process were rapid, facile and green. Many characterization methods, such as UV-vis absorption spectroscopy, fluorescence spectroscopy, fourier transform infrared spectroscopy (FT-IR), fluorescence lifetime, transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS), were applied for the analysis of trypsin-templated copper nanoclusters (Cu NCs@Tryp). The Cu NCs@Tryp released green fluorescence at maximum emission wavelength of 457 nm under maximum excitation wavelength of 377 nm. More importantly, the fluorescence of Cu NCs@Tryp was efficiently quenched by Bai. According to this phenomenon, a facile, rapid and selective turn-off fluorescence probe for Bai sensing was developed. Under the optimized testing conditions, the ln(F₀/F) value and concentration of Bai displayed excellent linear relationship changing from 0.5 to 60 μM (R² = 0.9969), and the detection limit was 0.078 μM. Furthermore, the Cu NCs@Tryp has been successfully employed to measure the amount of Bai in bovine serum samples with satisfactory recoveries.

Highly fluorescent carbon dots from coix seed for the determination of furazolidone and temperature

In this work, blue emission fluorescent carbon dots (CDs) were fabricated by using the hydrothermal strategy from coix seed for the first time. We found that the prepared CDs possessed many excellent characteristics including excitation-dependent properties, good solubility and strong photostability. The optimal excitation and emission wavelength of CDs were 363 and 435 nm, respectively. Unbelievably, the fluorescence of CDs was selectively and effectively quenched with the addition of furazolidone (Fu). The quenching mechanisms might be assumed to the static quenching and inner filter effect (IFE). Based on this principle, a novel fluorescence probe was developed for the determination of Fu. At the same time, the proposed probe showed excellent sensitivity and selectivity towards Fu with a wide linear range from 0.5 to 100 μM, and the corresponding detection limit was 0.096 μM. Moreover, the CDs also could be applied for the sensing of temperature. The practical application of the CDs for Fu detection in real samples was also confirmed with the satisfactory recoveries changing from 96.6% to 108.5%, which provided huge possibility in the field of medical analysis.

Highly sensitive and selective fluorescence sensing of nitrofurantoin based on water-soluble copper nanoclusters

In this contribution, dopamine-protected copper nanoclusters as a novel fluorescent nanosensor was employed to detect nitrofurantoin (NFT) for the first time, which were prepared by using dopamine as the stabilizing agent and sodium borohydride (NaBH₄) and hydrazine hydrate (N₂H₄·H₂O) as the reducing agents. A series of methods were used to analyze the structure and optical properties of as-prepared Cu NCs, such as UV-Vis absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It possessed high dispersion, excellent water solubility, good photostability and strong green fluorescence under UV lamp (365 nm). Significantly, the FL intensities of Cu NCs were quenched with addition of NFT. The analytical method possessed good linear relationship between the relative fluorescence intensity (F₀/F) and the NFT concentrations (range from 5 to 120 μM), and the limit of detection (LOD) could reach 0.73 μM. The fluorescence detection mechanisms were attributed to the static quenching and inner filter effect (IFE). In addition, this proposed fluorescence sensor has been successfully used for the detection of NFT in bovine serum samples.

Discriminating detection of dissolved ferrous and ferric ions using copper nanocluster-based fluorescent probe

Discrimination and detection of specific metal ions that belong to the same metallic element with different valence states in a complex matrix is challenging. In the present work, a fluorescence method using polyvinylpyrrolidone stabilized copper nanocluster (CuNCs@PVP) as a probe for discriminating detection of ferrous (Fe³⁺) and ferric (Fe²⁺) ions was developed. The CuNCs@PVP exhibited an excellent selective response to Fe³⁺ ions in contrast to Fe²⁺ ions and other metal ions when the pH value of solution was less than 4.0. Furthermore, the fluorescence of the CuNCs@PVP could be more sensitively quenched by Fe²⁺ ions by virtue of Fenton reaction. The different response of CuNCs@PVP towards Fe³⁺ and Fe²⁺ ions under different conditions offered the potential for the discriminating detection of Fe³⁺ and Fe²⁺ ions. Based on detailed optimization of detection conditions, an excellent linear relationship between the fluorescence quenching efficiency (F/F₀) of the CuNCs@PVP and the concentration of Fe³⁺ ions over the range of 0.4-20.0 μM and of Fe²⁺ ions in the range of 0.01-0.4 μM were obtained, respectively. The detection limits for the Fe³⁺ and Fe²⁺ ions were 0.14 μM and 0.008 μM, respectively. The developed probe showed good selectivity and presented an alternative strategy for discriminating detection of Fe³⁺ and Fe²⁺ ions in complex samples.