Water-soluble polymer dots formed from polyethylenimine and glutathione as a fluorescent probe for mercury(II)

A highly sensitive and selective fluorescent biosensor for breast cancer derived exosomes using click reaction of azide-CD63 aptamer and alkyne-polymer dots

Exosomes have gained recognition as valuable reservoirs of biomarkers, holding immense potential for early cancer detection. Consequently, there is a pressing need for the development of an economical and highly sensitive exosome detection methodology. In this work, we present a fluorescence method for breast cancer-derived exosome detection based on Cu-triggered click reaction of azide-modified CD63 aptamer and alkyne functionalized Pdots. The detection threshold for the exosomes obtained from the breast cancer serum was determined to be 6.09 × 107 particles per μL, while the measurable range spanned from 6.50 × 107 to 1.30 × 109 particles per μL. The employed methodology achieved notable success in accurately distinguishing breast cancer patients from healthy individuals through serum analysis. The application of this method showcases the significant potential for early exosome analysis in the clinical diagnosis of breast cancer patients.

A polystyrene-based ESIPT fluorescent polymeric probe for highly sensitive detection of chromium(vi) ions and protein staining

A "two-step" preparation method of an excited-state intermolecular proton transfer (ESIPT) fluorescent polymer (f-PP) is reported here. The synthesis of f-PP involves the acetylation of polystyrene and a "multicomponent one pot" reaction. The as-prepared polymer bears a group of ESIPT fluorescent units, enabling it to exhibit high brightness, moderate solubility and ESIPT fluorescence. F-PP gives off tautomeric bright green fluorescence under UV-tamp and the dual-emission could be specifically suppressed by Cr(vi). This phenomenon cannot be elicited by other competing species. On this basis, an ESIPT polymeric probe-based method for the determination of Cr(vi) was developed, offering high sensitivity (19.5 nM) and selectivity. The f-PP was successfully used to detect Cr(vi) in real water samples by standard adding methods, indicating its application feasibility.

Multiple fluorescence polymer dots-based differential array sensors for highly efficient heavy metal ions detection

Water pollution caused by harmful heavy metal ions (HMIs) can significantly impact aquatic ecosystems and pose a high risk to human health. In this work, equipped with ultra-high fluorescence brightness, efficient energy transfer, and environmentally friendly performance, polymer dots (Pdots) were employed to construct a pattern recognition fluorescent HMIs detection platform. A single-channel unary Pdots differential sensing array was first developed to identify multiple HMIs with 100% classification accuracy. Then an "all-in-one" multiple Förster resonance energy transfer (FRET) Pdots differential sensing platform was constructed to discriminate HMIs in the artificial polluted water samples and actual water samples, exhibiting high classification accuracy in distinguishing HMIs. The proposed strategy leverages the compounded cumulative differential variation of diverse sensing channels for analytes, which is anticipated to find extensive applications in other fields for detection purposes.

Detection of mercury(II) and glutathione using a carbon dots-based "off-on" fluorescent sensor and the construction of a logic gate

In this paper, we proposed an efficient method for mercury(II) and glutathione detection using a fluorescent nanoprobe as a sensor. Carbon dots were synthesized from polyethyleneimine and ammonium citrate via a one-step hydrothermal method. The fluorescence of carbon dots was quenched since electron transfer occurred due to the interaction between mercury(II) and functional groups on the surface of carbon dots. Adding glutathione to the carbon dots-mercury(II) system, the fluorescence was recovered due to the stronger binding ability of glutathione to mercury(II). Based on the above-mentioned principle, this "off-on" fluorescent sensor can easily achieve the detection of mercury(II) and glutathione, which provided limits of detection of 22.45 nM and 61.89 nM, respectively. In this paper, the proposed method has been applied to detect mercury(II) and glutathione in real lake water and serum, respectively, and a logic gate for sensing glutathione was presented. The developed "off-on" fluorescent sensor with high sensitivity and selectivity has shown great potential for mercury(II) and glutathione detection in environmental and biosensing fields.

N-doped carbon dots as the multifunctional fluorescent probe for mercury ion, glutathione and pH detection

Recently, carbon dots (CDs) have exhibited promising applications in the fluorescence detection of various ions and biomolecules. In this work, one kind of nitrogen-doped CDs (N-CDs) with high fluorescence intensity was synthesized, characterized by transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, Fourier-transform infrared, UV-vis absorption spectra, and fluorescence spectra. The results show that the spherical and uniform N-CDs (quantum yield: 60.2%) have remarkable fluorescence properties and photostability, which makes N-CDs can be utilized as an 'on-off-on' sensor for Hg²⁺and glutathione (GSH). In addition, the pH-sensitive behavior of N-CDs makes it also applicable to H⁺detection under acid conditions (pKa = 3.53). The linear range of the 'turn-off' sensor detecting Hg²⁺was 0.014-50μM, with a 0.014μM limit of detection (LOD). GSH was detected by the fluorescence 'turn-on' method with a linear range of 0.125-60μM and a LOD of 0.125μM. The outstanding performance of N-CDs makes it potential applications in ecological pollution and biomolecule visualization monitoring.

Wet Process Phosphoric Acid Purification Using Functionalized Organic Nanofiltration Membrane

The utilization of phosphoric acid in various sectors, e.g., food industry, is controlled by the authorized concentration limit of impurities. However, industrial phosphoric acid is contaminated with undesirable impurities (such as F, Al, Fe, Mg, etc.). Herein, this study aimed to evaluate the efficiency of the membrane purification process of pretreated industrial phosphoric acid using a premodified nanofiltration membrane. We demonstrated that the prior pretreatment steps for industrial phosphoric acid allowed the elimination of sulfate, fluorine and arsenic. Further purification of the obtained pretreated phosphoric acid using membrane cells reduced the concentrations of Cd, Al, Fe and rare earth elements by 94.81, 99.30, 99.63 and 96.67%, respectively. The membrane is functionalized by a deposit of a high molecular weight polycationic polymer of polyethyleneimines in order to produce a highly charged membrane surface to enhance the separation efficiency, selectivity and stability of the membrane. We found that the purification process relies on electrostatic repulsion between the functionalized membrane and highly charged ions, and the reduction rate of metals is a cation charge-dependent parameter. The laboratory and industrial pilot scale results showed that this process allows the production of food-grade phosphoric acid.

Highly fluorescent N doped C-dots as sensor for selective detection of Hg2+ in beverages

In this work, nitrogen doped carbon dots (NCDs) were synthesized through one step hydrothermal reaction using citric acid and ethylenediamine as precursors. The prepared NCDs exhibit high quantum yield of 67.4%, good stability, excellent selectivity and sensitivity. It was found that the NCDs have potential as a fluorescence sensor for the detection of Hg²⁺. Under optimal conditions, good linearity between the change in NCDs fluorescence intensity and Hg²⁺ concentration was obtained in the range of 0.3 to 2.0 μM with a detection limit at 0.24 μM. The possible detection mechanism was static quenching of NCDs by Hg²⁺. The established method was successfully applied to the determination of Hg²⁺ in beverage samples. The results indicated that the NCDs-based sensor has potential for detection of Hg²⁺ in real beverage sample.

Photoluminescent Nanoparticles for Chemical and Biological Analysis and Imaging

Research related to the development and application of luminescent nanoparticles (LNPs) for chemical and biological analysis and imaging is flourishing. Novel materials and new applications continue to be reported after two decades of research. This review provides a comprehensive and heuristic overview of this field. It is targeted to both newcomers and experts who are interested in a critical assessment of LNP materials, their properties, strengths and weaknesses, and prospective applications. Numerous LNP materials are cataloged by fundamental descriptions of their chemical identities and physical morphology, quantitative photoluminescence (PL) properties, PL mechanisms, and surface chemistry. These materials include various semiconductor quantum dots, carbon nanotubes, graphene derivatives, carbon dots, nanodiamonds, luminescent metal nanoclusters, lanthanide-doped upconversion nanoparticles and downshifting nanoparticles, triplet-triplet annihilation nanoparticles, persistent-luminescence nanoparticles, conjugated polymer nanoparticles and semiconducting polymer dots, multi-nanoparticle assemblies, and doped and labeled nanoparticles, including but not limited to those based on polymers and silica. As an exercise in the critical assessment of LNP properties, these materials are ranked by several application-related functional criteria. Additional sections highlight recent examples of advances in chemical and biological analysis, point-of-care diagnostics, and cellular, tissue, and in vivo imaging and theranostics. These examples are drawn from the recent literature and organized by both LNP material and the particular properties that are leveraged to an advantage. Finally, a perspective on what comes next for the field is offered.

Ultra-high quantum yield nitrogen-doped carbon quantum dots and their versatile application in fluorescence sensing, bioimaging and anti-counterfeiting

The exploration of carbon quantum dots (CQDs) with ultra-high quantum yield, simple synthesis path, and satisfying output to facilitate their wide applications in numerous fields are always the research focus. In this work, nitrogen-doped carbon quantum dots (N-CQDs) with strong blue fluorescence were synthesized with a simple one-step hydrothermal method using citric acid and o-phenylenediamine as raw materials, and the absolute quantum yield was as high as 92.1%. The detailed research results demonstrate that the N-CQDs have outstanding fluorescence stability, high selectivity, and anti-interference in Hg²⁺ detection. The obtained N-CQDs also possess excellent biocompatibility, which can also be successfully applied in cell imaging and intracellular Hg²⁺ detection. Most importantly, due to their high quantum yield and excellent dispersibility, the N-CQDs solution can be used as a quick-drying fluorescent ink for ink-jet printing. Therefore, the as-prepared N-CQDs have great potential in fluorescence sensing, biomedical diagnosis, data encryption, and anti-counterfeiting.

Nitrogen-Doped Carbon Quantum Dots from Poly(ethyleneimine) for Optical Dual-Mode Determination of Cu2+ and l-Cysteine and Their Logic Gate Operation

In this work, nitrogen-doped carbon quantum dots from poly(ethyleneimine) (PQDs) were synthesized by a low-cost and facile one-step hydrothermal method without other reagents. A quantum yield (QY) of up to 23.2% with maximum emission at 460 nm under an excitation wavelength of 340 nm was ascribed to the high nitrogen doping (20.59%). The PQDs selectively form a blue complex with Cu²⁺ accompanied by strong quenching of the fluorescence emission. Meanwhile, the PQD-Cu²⁺ complex exhibited selective fluorescence recovery and color disappearance on exposure to l-cysteine (Cys). The electron transfer from amino or oxygen groups on the PQDs to Cu²⁺ leads to fluorescence quenching, and a chromogenic reaction of the cuprammonium complex results in a color change. The strong affinity between Cys and Cu²⁺ causes the detachment of Cu²⁺ from the surface of PQDs, so the color of the solution disappears and the fluorescence of PQDs recovers. Under the optimized condition, the proposed sensor was applied to detect Cu²⁺ in the linear range of 0-280 μM. A detection limit of 4.75 μM is achieved using fluorescence spectroscopy and 4.74 μM by monitoring the absorbance variation at 272 nm. For Cys detection, the linear range of 0-800 μM with detection limits of 28.11 μM (fluorescence determination) and 19.74 μM (peak shift determination at 272 nm) was obtained. Meanwhile, the PQD-Cu²⁺ system exhibits distinguishable responses to other biothiols such as l-glutathione (GSH) and dl-homocysteine (Hcy). Based on the multimode signals, an "AND" logic gate was constructed successfully. Interestingly, besides Cu²⁺, Fe³⁺ can also quench the fluorescence of PQDs and the PQD-Fe³⁺ system exhibits superior selectivity for Cys detection. Most importantly, the proposed assay is not only simple, cheap, and stable but also suitable for detecting Cu²⁺ and Cys in some real samples.

One-pot synthesis of fluorescent non-conjugated polymer dots for Fe3+ detection and temperature sensing

The facile preparation of highly fluorescent polymer dots (PDs) still attracts substantial interest. Here, temperature/Fe³⁺ dual-responsive PDs are synthesized under mild conditions via the amidation reaction and self-assembly between hyperbranched polyethyleneimine and 5-aminosalicylic acid. The prepared PDs display strong green fluorescence with quantum yield of 15.5% and 53.3% in water and dimethylsulfoxide, respectively. The PDs also possess unique features, including excellent solubility, solvent polarity-dependent emission, remarkable photostability, as well as good salt-tolerance. Interestingly, the fluorescence intensity of PDs exhibits a reversible and sensitive response to temperature within 20-65 °C, which renders the PDs useful as a thermometer probe. Importantly, Fe³⁺ ion has the specific coordination ability toward the surface groups of PDs, leading to the aggregation and fluorescence quenching of PDs. Thus, the PDs are employed as a fluorescence probe for sensitive detecting Fe³⁺. The fluorescent intensity linearly decreases with increasing Fe³⁺ from 2 to 60 μM. Besides, Fe³⁺ concentration in river water samples is successfully assayed with this developed probe. The non-conjugated PDs with facile preparation, sensitive response to temperature and Fe³⁺ may hold potential applications in environmental monitoring.

Polyethylenimine-Assisted Generation of Optical Nanoprobes for Biosensing Applications

Detection of analytes in biological systems is pivotal to explore their physiological roles and provide diagnostic and treatment options for related diseases, which however remains a great challenge. Optical nanoprobes that exhibit absorption or fluorescence signal changes in response to the targets of interest have emerged as a versatile class of biosensors in the field. Polyethylenimine (PEI) with abundant amine groups plays indispensable roles in the construction of optical nanoprobes and mediating the sensing processes. After interaction with analytes, PEI-based optical nanoprobes can be induced to form aggregates, be disassembled or separated into individual units, or undergo structure/component alterations. As such, the optical properties of these nanoprobes have corresponding changes, allowing for sensitive and selective detection of a wide variety of analytes in biological environment. Up to now, detections of reactive oxygen species, pH, metal ions, biothiols, neurotransmitters, therapeutic agents, oxygen levels, enzyme activities, and virus/bacteria have been successfully demonstrated using PEI-based optical nanoprobes. Herein, we summarize the recent developments of PEI-based optical nanoprobes for biosensing applications and highlight the probe designs and sensing mechanisms. The existing challenges and prospects regarding biosensing applications of PEI-based optical nanoprobes are also briefly discussed.

Fluorescent, colourimetric, and ratiometric probes based on diverse fluorophore motifs for mercuric(II) ion (Hg2+) sensing: highlights from 2011 to 2019

Though it has not been shown to deliver any biological importance, mercuric(II) ion (Hg²⁺) is a deleterious cation which poses grievous effects to the human body and/or the ecosystem, hence, the need for its sensitive and selective monitoring in both environmental and biological systems. Over the years, there has been a great deal of work in the use of fluorescent, colourimetric, and/or ratiometric probes for Hg²⁺ recognition. Essentially, the purpose of this review article is to give an overview of the advances made in the constructions of such probes based on the works reported in the period from 2011 to 2019. Discussion in this review work has been tailored to the kinds of fluorophore scaffolds used for the constructions of the probes reported. Selected examples of probes under each fluorophore subcategory were discussed with mentions of the typically determined parameters in an analytical sensing operation, including modulation in fluorescence intensity, optimal pH, detection limit, and association constant. The environmental and biological application ends of the probes were also touched where necessary. Important generalisations and conclusions were given at the end of the review. This review article highlights 196 references.

Chromium speciation by isophthalic acid-doped polymer dots as sensitive and selective fluorescent probes

Hexavalent chromium is a known carcinogen, among all species of chromium ions, for the respiratory tract in humans. In the present work, a new facile probe is developed for rapid and sensitive determination of Cr(VI) based on utilizing highly fluorescent conjugated poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(1,4-benzo-(2,1',3) thiadiazole)] (PFBT) polymer dots (PDs). The PDs are easily functionalized by doping of isophthalic acid (IPA) into the target PDs during a single step preparation. The prepared PDs with an average diameter of 30 nm illustrated a strong fluorescence with an emission peak centered at 530 nm (photo-excited at 480 nm). The strong fluorescence of PDs is selectively and significantly quench with Cr(VI), while it does not change by Cr(III) ion and, thus, can facilitate a chromium speciation process. The proposed mechanism is an inner filter effect (IFE) mechanism, in which the absorption bands of Cr(IV) overlaps with the emission and excitation bands of the modified PDs. The prepared PDs revealed a good linear relationship from 0.1 to 1000 μmol L^-1 for Cr(VI) with a detection limit of 0.03 μmol L^-1, which further used to track the Cr distribution in water samples. Finally, the IPA-doped PDs with excellent optical properties, biocompatibility, and high quantum yield showed promising potential in tracking Cr species and specifying of different Cr ions inside the human cells, which opening a new door toward getting a better insight into the cell function and metabolism in the presence of heavy metal ions, and especially chromium ions.

Fluorescence Emission of Polyethylenimine-Derived Polymer Dots and Its Application to Detect Copper and Hypochlorite Ions

Polymer dots with nonconjugated groups that are facile to synthesize and environmentally friendly generally attract substantial interest. However, their fluorescence-emitting mechanisms are not clear. In this paper, nonconjugated polymer dots (N-PDs) are synthesized by amidation reaction between polyethylenimine (PEI) and citric acid (CA), then self-assemble into rice-like dots in aqueous phase with a high fluorescence quantum yield. Such nitrogen-containing nonconjugated compounds N-PDs are believed to be inherently fluorescent, and the reported reasons for fluorescence-emitting are discussed. Importantly, these N-PDs can be used as an excellent fluorescent probe to detect Cu²⁺ and ClO^- in aqueous solutions. Cu²⁺ could combine with the PEI moiety of the N-PDs to form a copper amine complex and then quench the fluorescence by an internal filtration effect. ClO^- could oxidize the hydroxyl groups on the surface of the N-PDs to form a positive charge, blocking electron transfer between the hydroxyl groups and the chromophore groups. Finally, the sensor was successfully applied to the detection of Cu²⁺ and ClO^- in environmental water samples.

Ratiometric fluorometric determination of mercury(II) by exploiting its quenching effect on glutathione-stabilized and tetraphenylporphyrin modified gold nanoclusters

A ratiometric fluorometric assay for mercury(II) ion is described. It is making use of glutathione-stabilized gold nanoclusters (GSH-AuNCs) modified with tetraphenylporphyrin tetrasulfonic acid (TPPS). The resultant GSH-AuNC/TPPS nanocomposite displays dual emission (at 572 and 664 nm) under a single excitation wavelength of 365 nm. Mercury(II) ion intensively quenches the yellow fluorescence of GSH-AuNCs (peaking at 572 nm) but has a negligible effect on the red fluorescence of TPPS (at 664 nm). The ratio of fluorescence intensities at 572 and 664 nm drops linearly with Hg(II) ion concentration in the 0.02-2.0 μmol·L^-1 range, and the detection limit is 7 nmol·L^-1 (3s_b/S). The relative standard deviation (RSD) of the assay is 2.0% at a 0.5 μmol·L^-1 concentration level (n = 11). The method was successfully applied to the determination of Hg(II) ion in spiked water samples, with recoveries within the range of 87.5-107.5%. Graphical abstract Ratiometric fluorescence detection of mercury(II).

Hydrothermal synthesis of N-doped carbon dots from an ethanolamine–ionic liquid gel to construct label-free multifunctional fluorescent probes for Hg2+, Cu2+ and S2O32−

N-Doped carbon dots were synthesized and used to construct multifunctional fluorescent probes for Hg²⁺, Cu²⁺ and S₂O₃²⁻.