Carbon Dots with Spatially-Mediated-N/S-Co-Doping Enabling One-Year Stable Lubricant with Oil Leakage Detection Capability.

The dispersion stability of nano-lubricating additives is crucial for the shelf life of lubricant and its practical applications. Nitrogen-sulfur co-doped carbon dots (N,S@CDs) via a one-step hydrothermal method with nitropyrene and thiourea as raw materials are hereby presented. The N and S elements are selectively distributed throughout the entire carbon skeleton with a doping amount of 22.6 at%. The as-synthesized N,S@CDs exhibit excellent dispersion stability in PEG200 and maintain stability for over one year. The experiment results indicate that N,S@CDs significantly improve the anti-wear and friction reduction properties of PEG200, while the friction coefficient is reduced from 0.25 to 0.09 with 1.5 wt% N,S@CDs addition, and the wear volume, depth, and width are reduced by 68%, 52%, and 57%, respectively. The good lubrication performance is attributed to N,S@CDs excellent dispersion stability, enhanced filling and polishing effects, and complex tribochemical reactions caused by heteroatom doping to form a stable protective film on the worn surface. Furthermore, the as-prepared N,S@CDs exhibit intrinsic fluorescence intensity in PEG200 with the photoluminescence quantum yield (PLQY) of 12.5% and remain fluorescent stable during the long-term friction process, therefore the N,S@CDs have a potential application prospect in non-destructive detection of oil leakage via fluorescence labeling method.

Novel Metal-Free Synthesis of 3-Substituted Isocoumarins and Evaluation of Their Fluorescence Properties for Potential Applications.

A novel metal-free synthesis of 3-substituted isocoumarins through a sequential O-acylation/Wittig reaction has been established. The readily accessible (2-carboxybenzyl)-triphenylphosphonium bromide and diverse chlorides produced various 1H-isochromen-1-one in the presence of triethylamine, employing sequential O-acylation and an intramolecular Wittig reaction of acid anhydride. Reactions using these facile conditions have exhibited high functional group tolerance and excellent yields (up to 90%). Moreover, the fluorescence properties of isocoumarin derivatives were evaluated at the theoretical and experimental levels to determine their potential application in fluorescent materials. These derivatives have good photoluminescence in THF with a large Stokes shift and an absolute fluorescence quantum yield of up to 14%.

A Study of the Mechanisms and Characteristics of Fluorescence Enhancement for the Detection of Formononetin and Ononin.

In this work, the origins for the spectral difference between two isoflavones, formononetin (F) and ononin (FG), are revealed via a comparison study of the fluorescence molecular structure. The fluorescence enhancement of FG in hot alkaline conditions is reported for the first time. For F, there is almost no fluorescence under acidic conditions, but when the pH is >4.8, its fluorescence begins to increase due to the deprotonation of 7-OH. Under a pH between 9.3 and 12.0, the anionic form of F produces a strong and stable fluorescence. The fluorescence quantum yield (Yf) of F is measured to be 0.042. FG shows only weak fluorescence in aqueous solutions under a wide range of pH until it is placed in hot alkaline solutions, which is attributed to the cleavage reaction of the γ-pyrone ring in FG. The Yf of FG is determined to be 0.020. Based on the fluorescence sensitization methods of F and FG, the quantitative analysis and detection of two substances can be realized. The limit of the detections for F and FG are 2.60 ng·mL-1 and 9.30 ng·mL-1, respectively. The linear detection ranges of F and FG are 11.7~1860 ng·mL-1 and 14.6~2920 ng·mL-1, respectively. Although the structural relationship between F and FG is glycoside and aglycone, under hot alkaline conditions, the final products after the cleavage and hydrolysis reactions are essentially different. The different fluorescence characteristics between F and FG pave a way for further identification and a quantitative analysis of the corresponding components in Chinese herbal medicine.

Self-Assembled BODIPY Nanoparticles for Near-Infrared Fluorescence Bioimaging.

In vivo optical imaging is an important application value in disease diagnosis. However, near-infrared nanoprobes with excellent luminescent properties are still scarce. Herein, two boron-dipyrromethene (BODIPY) molecules (BDP-A and BDP-B) were designed and synthesized. The BODIPY emission was tuned to the near-infrared (NIR) region by regulating the electron-donating ability of the substituents on its core structure. In addition, the introduction of polyethylene glycol (PEG) chains on BODIPY enabled the formation of self-assembled nanoparticles (NPs) to form optical nanoprobes. The self-assembled BODIPY NPs present several advantages, including NIR emission, large Stokes shifts, and high fluorescence quantum efficiency, which can increase water dispersibility and signal-to-noise ratio to decrease the interference by the biological background fluorescence. The in vitro studies revealed that these NPs can enter tumor cells and illuminate the cytoplasm through fluorescence imaging. Then, BDP-B NPs were selected for use in vivo imaging due to their unique NIR emission. BDP-B was enriched in the tumor and effectively illuminated it via an enhanced penetrability and retention effect (EPR) after being injected into the tail vein of mice. The organic nanoparticles were metabolized through the liver and kidney. Thus, the BODIPY-based nanomicelles with NIR fluorescence emission provide an effective research basis for the development of optical nanoprobes in vivo.

Effect of pH on dissociation of casein micelles in yak skim milk.

The dissociation of yak casein (CN) micelles was evaluated by scanning electron microscopy, particle size, fluorescence properties, and soluble mineral and CN molecule content at pH 4.6 to 8.2. The results showed that the size of CN micelles remained constant with decreasing pH from 8.2 to 5.8 but sharply increased at pH ≤5.4. Casein micelles began to aggregate at pH 5.4, and the serum magnesium, potassium, iron, zinc, copper, and manganese levels had their minimum values at this pH level. During acidification, colloidal calcium phosphate dramatically disassociated from yak CN micelles, but the soluble CN monomer content decreased slightly. During alkalization, the soluble calcium and phosphorus content decreased below pH 6.8 but increased with pH increases from 6.8 to 8.2. However, the soluble CN content increased markedly during alkalization. The emission wavelength of 8-anilino-1-naphthalenesulfonic acid sodium salt fluorescence decreased during both acidification and alkalization from pH 6.6, whereas the opposite was found for intrinsic fluorescence.

Synthesis and Fluorescence Properties of a New Heterotrinuclear Co(II)-Ce(III)Complex Constructed from a bis(salamo)-Type Tetraoxime Ligand.

[Co2(L)Ce(OAc)3(CH3CH2OH)]·1.5CH3OH∙0.5CH2Cl2, a heterotrinuclear Co(II)-Ce(III) bis(salamo)-type complex with a symmetric bi(salamo)-type ligand H4L and an acyclic naphthalenediol moiety, was designed, synthesized and characterized by elemental analyses, FT-IR, UV-Vis and fluorescence spectroscopy and X-ray crystallography. The X-ray crystallographic investigation revealed the heterotrinuclear complex consisted of two Co(II) atoms, one Ce(III) atom, one (L)4‒ unit, three µ2-acetate ions, one coordinated ethanol molecule, one and half crystallization methanol molecule and half crystallization dichloromethane molecule. Two Co(II) atoms located in the N2O2 coordination spheres, are both hexacoordinated, with slightly distorted octahedral geometries. The Ce(III) atom is nine-coordinated and located in the O6 cavity possesses a single square antiprismatic geometry. In addition, supramolecular interactions exist in the Co(II)-Ce(III) complex. Two infinite 2D supramolecular structures are built via intermolecular O-H···O, C-H···O and C-H···π interactions, respectively.

Unprecedented Fluorescent Dinuclear CoII and ZnII Coordination Compounds with a Symmetric Bis(salamo)-Like Tetraoxime.

Two unprecedented homometallic CoII and ZnII coordination compounds, [M2(L)(OCH3)][M2(L)(OAc)] (MII = CoII (1) and ZnII (2)), with a novel symmetric bis(salamo)-like tetraoxime ligand H3L were synthesized and characterized by elemental analyses, infrafred (IR), ultraviolet⁻visible spectroscopy (UV-Vis), fluorescent spectra and single-crystal X-ray diffraction analyses. The unit cell of the two coordination compounds contains two crystallographically and chemically independent dinuclear coordination compounds. In the two coordination compounds, three metal ions are five-coordinated, formed two square pyramidal and a trigonal bipyramidal geometries, and the other metal ion is a hexacoordinate octahedral configuration. In addition, the coordination compound 1 forms a 3D supramolecular structure, and the coordination compound 2 forms a 0D dimer structure by the inter-molecular hydrogen bond interactions. Meanwhile, the fluorescence spectra of the coordination compounds 1 and 2 were also measured and discussed.

A Self-Assembled ZnII-NdIII Heterohexanuclear Dimer Based on a Hexadentate N2O4-Type Ligand and Terephthalic Acid: Synthesis, Structure, and Fluorescence Properties.

A self-assembled ZnII-NdIII heterohexanuclear coordination compound [Zn4Nd2(L)4(bdc)2]·2NO3 based on a hexadentate Salamo-like chelating ligand (H2L = 1,2-bis(3-methoxysalicylideneaminooxy)ethane]) and H2bdc (H2bdc = terephthalic acid) has been synthesized and characterized by elemental analyses, IR and UV/Vis spectra, and X-ray crystallography. Two crystallographically equivalent [Zn2Nd(L)2] moieties lie in the inversion center linked by two (bdc)2- ligands leading to a heterohexanuclear dimer in which the carboxylato group bridges the ZnII and NdIII atoms. The heteropolynuclear 3d-4f coordination compound includes four ZnII atoms, two NdIII atoms, four completely deprotonated (L)2- units, two fully deprotonated (bdc)2- units, and two crystalling nitrate ions. All of the ZnII atoms in the ZnII-NdIII coordination compound possess trigonal bipyramidal geometries and the NdIII atoms possess distorted bicapped square antiprism coordination arrangements. In addition, the fluorescence properties of the ligand and the ZnII-NdIII coordination compound were investigated.

Aldehyde Substituted Phthalocyanines: Synthesis, Characterization and Investigation of Photophysical and Photochemical Properties.

The new free and nickel phthalocyanine derivatives, tetrakis [(2-formylphenoxy)-phthalocyanine (4), tetrakis [(2-formylphenoxy)-phthalocyaninato]nickel(II) (5) have been synthesized via de-protection of tetra acetal-substituted phthalocyanines in acetic acid/FeCl3 system. The starting phthalocyanines, tetrakis [(2-(1,3-dioxolan-2-yl)phenoxy)-phthalocyanine (2) and tetrakis [(2-(1,3-dioxolan-2-yl)phenoxy)-phthalocyaninato]nickel (3), were prepared by the tetramerization of 4-(2-(1,3-dioxolan-2-yl) phenoxy) phthalonitrile (1). The new compounds have been characterized by the combination of FT-IR, (1)H NMR, UV-Vis, Mass spectra and elemental analysis. Compound 1 crystallizes in the Orthorhombic, space group Pbca with a = 9.2542 (4) Å, b = 13.3299 (5) Å, c = 23.2333 (11) Å, and Z = 8. Compound 1 is built up from two planar groups (phthalonitrile and phenoxy), with a dihedral angle of 69.693(36)° between them and non-planar dioxolane group. We report a combined experimental and theoretical study on molecule 1, as well. Geometric, spectroscopic and electronic properties of compound 1 has been calculated using B3LYP method and 6-311++G(dp) basis set. Fluorescence spectroscopy was applied to record the photoluminescence spectra of the prepared phthalocyanines and the photophysical and photochemical properties were examined in DMSO.

Cytocompatible and multifunctional polymeric nanoparticles for transportation of bioactive molecules into and within cells.

Multifunctional polymeric nanoparticles are materials with great potential for a wide range of biomedical applications. For progression in this area of research, unfavorable interactions of these nanoparticles with proteins and cells must be avoided in biological environments, for example, through treatment of the nanoparticle surfaces. Construction of an artificial cell membrane structure based on polymers bearing the zwitterionic phosphorylcholine group can prevent biological reactions at the surface effectively. In addition, certain bioactive molecules can be immobilized on the surface of the polymer to generate enough affinity to capture target biomolecules. Furthermore, entrapment of inorganic nanoparticles inside polymeric matrices enhances the nanoparticle functionality significantly. This review summarizes the preparation and characterization of cytocompatible and multifunctional polymeric nanoparticles; it analyzes the efficiency of their fluorescence function, the nature of the artificial cell membrane structure, and their performance as in-cell devices; and finally, it evaluates both their chemical reactivity and effects in cells.

Synthesis, crystal structure and fluorescence properties of terbium complexes with phenoxyacetic acid and 2,4,6-tris-(2-pyridyl)-s-triazine.

Two complexes of Tb(3+), Gd(3+) /Tb(3+) and one heteronuclear crystal Gd(3+)/Tb(3+) with phenoxyacetic acid (HPOA) and 2,4,6-tris-(2-pyridyl)-s-triazine (TPTZ) have been synthesized. Elemental analysis, rare earth coordination titration, inductively coupled plasma atomic emission spectrometry (ICP-AES) and thermogravimetric analysis-differential scanning calorimetry (TG-DSC) analysis show that the two complexes are Tb2 (POA)6 (TPTZ)2 · 6H2O and TbGd(POA)6 (TPTZ)2 · 6H2O, respectively. The crystal structure of TbGd(POA)6 (TPTZ)2 · 2CH3OH was determined using single-crystal X-ray diffraction. The monocrystal belongs to the triclinic system with the P-1 space group. In particular, each metal ion is coordinately bonded to three nitrogen atoms of one TPTZ and seven oxygen atoms of three phenoxyacetic ions. Furthermore, there exist two coordinate forms between C6H5OCH2COO(-) and the metal ions in the crystal. One is a chelating bidentate, the other is chelating and bridge coordinating. Fluorescence determination shows that the two complexes possess strong fluorescence emissions. Furthermore, the fluorescence intensity of the Gd(3+)/Tb(3+) complex is much stronger than that of the undoped complex, which may result from a decrease in the concentration quench of Tb(3+) ions, and intramolecular energy transfer from the ligands coordinated with Gd(3+) ions to Tb(3+) ions.

A facile assay to monitor secretory phospholipase A2 using 8-anilino-1-naphthalenesulfonic acid.

Secretory phospholipases A2 (sPLA2s) are present in snake venoms, serum, and biological fluids of patients with various inflammatory, autoimmune and allergic disorders. Lipid mediators in the inflammatory processes have potential value for controlling phospholipid metabolism through sPLA2 inhibition. Thus, it demands the need for screening of potential leads for sPLA2 inhibition. To date, sPLA2 activity has been assayed using expensive radioactive or chromogenic substrates, thereby limiting a large number of assays. In this study, a simple and sensitive NanoDrop assay was developed using non-fluorogenic and non-chromogenic phospholipid substrate 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 8-anilino-1-naphthalenesulfonic acid (ANS) as interfacial hydrophobic probe. The modified assay required a 10ng concentration of sPLA2. ANS, as a strong anion, binds predominantly to cationic group of choline head of DMPC through ion pair formation, imparting hydrophobicity and lipophilicity and resulting in an increase in fluorescence. Triton X-100 imparts correct geometrical space during sPLA2 catalyzing DMPC, releasing lysophospholipid and acidic myristoyl acid, which in turn alters the hydrophobic environment prevailing around ANS-DMPC, which leads to weakening of the electrostatic ion pair interaction between DMPC and ANS ensuing decrease in fluorescence. These characteristic fluorescence changes between DMPC and ANS in response to sPLA2 catalysis are well documented and validated in this study.

Novel imidazo[1,2,4] triazole derivatives: Synthesis, fluorescence, bioactivity for SHP1.

The Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP1) is a convergent node for oncogenic cell-signaling cascades. Consequently, SHP1 represents a potential target for drug development in cancer treatment. The development of efficient methods for rapidly tracing and modulating the SHP1 activity in complex biological systems is of considerable significance for advancing the integration of diagnosis and treatment of the related disease. Thus, we designed and synthesized a series of imidazo[1,2,4] triazole derivatives containing salicylic acid to explore novel scaffolds with inhibitory activities and good fluorescence properties for SHP1. The photophysical properties and inhibitory activities of these imidazo[1,2,4] triazole derivatives (5a-5y) against SHP1PTP were thoroughly studied from the theoretical simulation and experimental application aspects. The representative compound 5p exhibited remarkable fluorescence response (P: 0.002) with fluorescence quantum yield (QY) of 0.37 and inhibitory rate of 85.21 ± 5.17% against SHP1PTP at the concentration of 100 µM. Furthermore, compound 5p showed obvious aggregation caused quenching (ACQ) effect and had high selectivity for Fe3+ ions, good anti-interference and relatively low detection limit (5.55 µM). Finally, the cellular imaging test of compound 5p also exhibited good biocompatibility and certain potential biological imaging application. This study provides a potential way to develop molecules with fluorescent properties and bioactivities for SHP1.

Synthesis, spectral characterization, computational studies, antifungal, DNA interaction, antioxidant and fluorescence property of novel Schiff base ligand and its metal chelates.

Cobalt, Copper, Nickel and Zinc coordinated metal complexes were synthesized by novel thiazole Schiff base ligand 2-ethoxy-4-((5-methylthiazol-2-ylimino)methyl) phenol derived from 3-ethoxy-4-hydroxybenzaldehyde and 2-amino- 5-methylthiazol. The synthesized compounds were spectrochemically characterized by elemental analysis, molar conductance, FT-IR, UV-Vis, Mass spectral analysis, Powdered-XRD and cyclic voltammetry. The thermal stability of synthesized complexes were investigated by using thermogravimetric analysis (TGA). Theoretical computational study were performed for all the synthesized compounds utilizing the DFT/B3LYP method at the 6-31G basic set for Schiff base ligand whereas LANL2DZ basis set for metal complexes. Molecular Electrostatic Potential (MEP), HOMO-LUMO, Mulliken charges and global reactivity descriptors, including chemical potential (µ), global softness (S), chemical hardness (η), and electrophilicity index (ω) were measured and correlated with antimicrobial activity. The synthesized thiazole Schiff base ligand and its coordinated metal complexes shows good antifungal agreement against Fusarium Oxysporum and Aspergillus Niger species. These compounds also exhibit DNA binding, DNA cleaving and antioxidant activity. All the synthesized molecules indicate potential fluorescence property.

Detection of nosocomial pneumonia pathogens using a fluorescence-based device.

BACKGROUND: Early detection of nosocomial pneumonia pathogens is a significant factor in hospital-acquired pneumonia care. This study aimed to determine the autofluorescence properties of five nosocomial pneumonia pathogens using a fluorescence-based device and to establish evidence for clinical guidelines. METHODS: The following bacterial strains were assessed: Acinetobacter baumannii (AB), Escherichia coli (EC), Enterococcus faecalis (EF), Klebsiella pneumoniae (KP), and Staphylococcus aureus (SA). The bacteria were cultured separately on tryptic soy agar at 37 °C under aerobic conditions for 168 h. Fluorescence photographs of each species were captured every 24 h using a fluorescence-based device with fixed camera settings. The images were analyzed by measuring the red and green values (R/G ratio) at a central point in each colony, and the R/G ratios were analyzed using the Kruskal-Wallis non-parametric test. RESULTS: KP and SA showed red fluorescence with their R/G values, which were significantly higher than those of the other strains (p < 0.001). In particular, the R/G ratio of KP increased steadily until 72 h of incubation, peaking at 3.65. In addition, AB and EC showed orange fluorescence with higher red ratios than green ratios. EF and SA showed green fluorescence all through 168 h of incubation, with R/G ratio less than 1.0. CONCLUSIONS: Nosocomial pneumonia pathogens can be identified and classified via bacterial autofluorescence emission. It is possible to develop a rapid and easy-to-use identification technology based on bacterial autofluorescence for clinical applications.

Synthesis, characterization and antimicrobial property in vitro of supramolecular coordination polymers bearing brominated Schiff base ligand.

In this study, two supramolecular coordination polymers of Co(II) and Zn(II) based on brominated Schiff base (E)-4-bromo-2-((quinolin-6-ylimino)methyl)phenol (HL) were synthesized and characterized by using elemental analysis, IR spectroscopy and NMR spectroscopy. Furthermore, the crystal structures of HL, CoL2 (І) and ZnL2 (II) were determined by single crystal X-ray analysis. It was revealed that the bromine-related interaction played important role in the self-assembly of HL supramolecular network. The crystal structural investigations revealed that І and II were isomorphous with the same geometry around the metal atom and similar structural feature. The stable four-membered chelate structure resulted from coordination between the metal(II) ion and deprotonated bidentate ligand. And supramolecular coordination polymers of І and II formed diverse architecture through multiple hydrogen bondings, π···π interactions and halogen-related interactions. Antimicrobial activities of polymers were tested toward four bacteria and five phytopathogenic fungi. І and II showed higher activities toward the tested microorganisms than HL. Furthermore, the photoluminescence results indicated that HL and II accompanied with better fluorescence properties in the ultraviolet region.

Unravelling relationships between fluorescence spectra, molecular weight distribution and hydrophobicity fraction of dissolved organic matter in municipal wastewater.

The characteristics of dissolved organic matter (DOM) in the influent and secondary effluent from 6 municipal wastewater treatment plants (WWTPs) were investigated with a size exclusion chromatogram (SEC) coupled with multiple detectors to simultaneously detect ultraviolet absorbance, fluorescence, dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) as a function of molecular weight (MW). The SEC chromatograms showed that biopolymers (>6 kDa) and humic substances (0.5-6 kDa) comprised the significant fraction in the influent, while humic substances became the abundant proportion in the secondary effluent. Direct linkages between MW distribution and hydrophobicity of DOM in the secondary effluent were further explored via SEC analysis of XAD resin fractions. DON and DOC with different hydrophobicity exhibited significantly distinct MW distribution, indicating that it was improper to consider DOC as a surrogate for DON. Different from DOC, the order of averaged MW in terms of DON was hydrophobic neutral ≈ transphilic neutral > hydrophobic acid > transphilic acid > hydrophilic fraction. Fluorescence spectral properties exhibited a significant semi-quantitative correlation with MW and hydrophobicity of DOC, with Pearson's coefficients of -0.834 and 0.754 (p < 0.01) for biopolymer and humic substances. Meanwhile, regional fluorescence proportion was demonstrated to indicate the MW and hydrophobicity properties of DON at the semi-quantitative level. The fluorescence excitation-emission matrix (EEM) could be explored to provide a rapid estimation of MW distribution and hydrophobic/hydrophilic proportion of DOC and DON in WWTPs.

A New Zn(II) Two-dimensional Coordination Polymer: Synthesis, Structure, Highly Efficient Fluorescence and DFT Study.

A new two-dimensional coordinate polymer, {[Zn2(pbmpd)(H2O)4]·(H2O)}n (H4pbmpd = 1,1'-(1,4-phenylenebis(methylene))bis-(1H-pyrazole-3,5-dicarboxylic acid)), has been hydrothermally synthesized and characterized by IR spectrum, elemental analysis，TGA and X-ray single-crystal/powder diffraction. Structural analyses reveal that complex 1 exhibits a two-dimensional sheet structure in the crystal lattice. In complex 1, the carboxylic oxygen atoms and conjugated N atoms of pbmpd4- bridge zinc(II) ions form indefinitely zigzag shaped one-dimensional chains through p···p stacking interactions which are further connected by [ZnO6] units to form a novel two-dimensional structure. Finally, p···p stacking interactions and intermolecular hydrogen bonds assemble the two dimensional networks into a three-dimensional framework. Furthermore, the luminescent properties are also discussed. Interestingly, the solid state photoluminescence properties of the title polymer show the enhancement effect of spectrum. Density functional theory (DFT) calculations were used to support the experimental data.

Fluorescence Enhancement of Lignin-Based Carbon Quantum Dots by Concentration-Dependent and Electron-Donating Substituent Synergy and Their Cell Imaging Applications.

Black liquor is an important pollutant in the pulp industry, but it also has the potential for high-value utilization. In this study, lignin extracted from black liquor was hydrothermally prepared into lignin-based carbon quantum dots (L-CQDs) using a one-pot method. Physicochemical characterization suggested that the L-CQDs exhibited a lamellar core-shell multilayered graphene structure surrounded by oxygen-containing functional groups. The fluorescence intensity of the L-CQDs was strengthened depending on their own concentration dependence and the doping of external groups. The fluorescence intensity of L-CQDs varied between 89.09 and 183.66 under different concentrations, and the most intense fluorescence (183.66) was obtained at 0.1 mg mL-1. At hydroxyl and amino adsorption capacities of 11.08 and 0.98 mmol g-1, the hydroxylated RL-CQDs-5 and aminated NL-CQDs-3 exhibited the highest fluorescence intensities at 689.22 and 605.39, respectively. Moreover, when pristine L-CQDs were sequentially aminated and hydroxylated, the NRL-CQDs' fluorescence intensity reached 1224.92. Cell imaging experiments proved that cells cultivated with NRL-CQDs have brighter fluorescence compared with L-CQDs. The results will render L-CQDs more suitable for practical applications.

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.