Application of magnetic and core–shell nanoparticles to determine enrofloxacin and its metabolite using laser induced fluorescence microscope

A unique analytical method using nanoparticles and laser-induced fluorescence microscopy (LIFM) was developed to determine enrofloxacin in this work. For sample pretreatment, two different kinds of particles, i.e., synthesized dye-doped core–shell silica nanoparticles and magnetic micro-particles (MPs), were used for fluorescent tagging and concentrating the enrofloxacin, respectively. The antibody of enrofloxacin was immobilized on the synthesized FITC-doped core–shell nanoparticles, and the enrofloxacin target was extracted by the MPs. At this moment, the average number of antibodies on each core–shell silica nanoparticle was ∼0.9, which was determined by the fluorescence ratiometric method. The described method was demonstrated for a meat sample to determine enrofloxacin using LIFM, and the result was compared with enzyme-linked immunosorbent assay (ELISA). The developed technique allowed the simplified analytical procedure, improved the detection limit about 54-fold compared to ELISA.     

Synthesis and characterization of the water-soluble silica-coated ZnS:Mn nanoparticles as fluorescent sensor for Cu ions

Silica-coated ZnS:Mn nanoparticles were synthesized by coating hydrophobic ZnS:Mn nanoparticles with silica shell through microemulsion. The core–shell structural nanoparticles were confirmed by X-ray diffraction (XRD) patterns, high-resolution transmission electron microscope (HRTEM) images and energy dispersive spectroscopy (EDS) measurements. Results show that each core–shell nanoparticle contains single ZnS:Mn nanoparticle within monodisperse silica nanospheres (40 nm). Photoluminescence (PL) spectroscopy and UV–vis spectrum were used to investigate the optical properties of the nanoparticles. Compared to uncoated ZnS:Mn nanoparticles, the silica-coated ZnS:Mn nanoparticles have the improved PL intensity as well as good photostability. The obtained silica-coated ZnS:Mn nanoparticles are water-soluble and have fluorescence sensitivity to Cu²⁺ ions. Quenching of fluorescence intensity of the silica-coated nanoparticles allows the detection of Cu²⁺ concentrations as low as 7.3 × 10⁻⁹ mol L⁻¹, thus affording a very sensitive detection system for this chemical species. The possible quenching mechanism is discussed.     

An Efficient Near-Infrared Emissive Artificial Supramolecular Light-Harvesting System for Imaging in the Golgi Apparatus

Light-harvesting systems are an important way for capturing, transferring and utilizing light energy. It remains a key challenge to develop highly efficient artificial light-harvesting systems. Herein, we report a supramolecular co-assembly based on lower-rim dodecyl-modified sulfonatocalix[4]arene (SC4AD) and naphthyl-1,8-diphenyl pyridinium derivative (NPS) as a light-harvesting platform. NPS as a donor shows significant aggregation induced emission enhancement (AIEE) after assembling with SC4AD. Upon introduction of Nile blue (NiB) as an acceptor into the NPS-SC4AD co-assembly, the light-harvesting system becomes near-infrared (NIR) emissive (675 nm). Importantly, the NIR emitting NPS-SC4AD-NiB system exhibits an ultrahigh antenna effect (33.1) at a high donor/acceptor ratio (250:1). By co-staining PC-3 cells with a Golgi staining reagent, NBD C₆-ceramide, NIR imaging in the Golgi apparatus has been demonstrated using these NIR emissive nanoparticles.     

Electrochemical synthesis of core–shell nanoparticles by seed-mediated selective deposition

Conventional solvothermal synthesis of core–shell nanoparticles results in them being covered with surfactant molecules for size control and stabilization, undermining their practicality as electrocatalysts. Here, we report an electrochemical method for the synthesis of core–shell nanoparticles directly on electrodes, free of surfactants. By implementation of selective electrodeposition on gold cores, 1^st-row transition metal shells were constructed with facile and precise thickness control. This type of metal-on-metal core–shell synthesis by purely electrochemical means is the first of its kind. The applicability of the nanoparticle decorated electrodes was demonstrated by alkaline oxygen evolution catalysis, during which the Au–Ni example displayed stable catalysis with low overpotential.

Core–shell nanoparticles can be synthesized by pure electrochemical methods, and the size of the core and the thickness of the shell can be precisely controlled. The nanoparticle-decorated electrodes exhibited respectable oxygen evolution catalysis.     

A fluorescent and chemiluminescent difunctional mesoporous silica nanoparticle as a label for the ultrasensitive detection of cancer cells

A new kind of ultrabright fluorescent and chemiluminescent difunctional mesoporous silica nanoparticle (FCMSN) is reported. A luminescent dye, Rhodamine 6G or tris(2,2′-bipyridyl)dichlororuthenium(II) hexahydrate (Rubpy), is doped inside nanochannels of a silica matrix. The hydrophobic groups in the silica matrix avoid the leakage of dye from open channels. The amines groups on the surface of the FCMSN improve the modification performance of the nanoparticle. Because the nanochannels are isolated by a network skeleton of silica, fluorescence quenching based on the inner filter effect of the fluorescent dyes immobilized in nanochannels is weakened effectively. The Quantum Yield of obtained 90 nm silica particles was about 61%. Compared with the fluorescent core–shell nanoparticle, the chemiluminescence reagents can freely enter the nanoparticles to react with fluorescent dyes to create chemiluminescence. The results show that the FCMSN are both fluorescent labels and chemiluminescent labels. In biological applications, the NaIO₄ oxidation method was proven to be superior to the glutaraldehyde method. The amount of amino could affect the specificity of the FCMSN. The fluorescence microscopy imaging demonstrated that the FCMSN is viable for biological applications.     

Highly selective fluorescent chemosensor with red shift for cysteine in buffer solution and its bioimage: symmetrical naphthalimide aldehyde

A new fluorescent probe 1, N-butyl-4, 5-(p-aldehyde)phenyl-1,8-naphthalimide, was designed and synthesized for the determination of the cysteine (Cys). Upon addition of Cys, the emission of 1 was enhanced with about 25 nm red-shift in the emission maximum (from 455 to 480 nm), accompanied with the fluorescent color change from blue to cyan, which was attributed to the reaction of the aldehyde groups in 1 with cysteine to form very stable thiazolidines derivative. Compound 1 was highly selective for cysteine detection without the interference of other amino acids and can be used for bioimaging of Cys.     

An Efficient Near‐Infrared Emissive Artificial Supramolecular Light‐Harvesting System for Imaging in the Golgi Apparatus

Light‐harvesting systems are an important way for capturing, transferring and utilizing light energy. It remains a key challenge to develop highly efficient artificial light‐harvesting systems. Herein, we report a supramolecular co‐assembly based on lower‐rim dodecyl‐modified sulfonatocalix[4]arene (SC4AD) and naphthyl‐1,8‐diphenyl pyridinium derivative (NPS) as a light‐harvesting platform. NPS as a donor shows significant aggregation induced emission enhancement (AIEE) after assembling with SC4AD. Upon introduction of Nile blue (NiB) as an acceptor into the NPS‐SC4AD co‐assembly, the light‐harvesting system becomes near‐infrared (NIR) emissive (675 nm). Importantly, the NIR emitting NPS‐SC4AD‐NiB system exhibits an ultrahigh antenna effect (33.1) at a high donor/acceptor ratio (250:1). By co‐staining PC‐3 cells with a Golgi staining reagent, NBD C₆‐ceramide, NIR imaging in the Golgi apparatus has been demonstrated using these NIR emissive nanoparticles.     

New green fluorescent polymer sensors for metal cations and protons

A new 4-(N-methylpiperazine)-N-allyl-1,8-naphthalimide with intense yellow-green fluorescence has been synthesized. Then it has been copolymerized with styrene and methylmetacrylate. The photophysical characteristics of the fluorescent dye and its copolymers (poly(St-co-NI) and poly(MAA-co-NI)) have been determined viewing their sensor properties for protons and transition metal cations (Cu²⁺, Fe³⁺ and Zn²⁺). Fluorescence enhancement is the photophysical response of the 4-(N-methylpiperazine)-N-allyl-1,8-naphthalimide to the presence of metal cations and protons, while fluorescence quenching is observed for both copolymers.     

Aggregation-induced emission enhancement (AIEE)-active mechanofluorochromic tetraphenylethene derivative bearing a rhodamine unit

A novel tetraphenylethene derivative with a rhodamine unit was successfully synthesized via high-efficiency Suzuki coupling reaction. The highly solid-state emissive target fluorescent molecule exhibited significative aggregation-induced emission enhancement (AIEE) feature. Furthermore, the luminogen showed reversible mechanochromic luminescence behavior involving color change from orange to red. In addition, the powder X-ray diffraction (XRD) test results verified that the mechanofluorochromic phenomenon of luminogen 1 was attributed to a morphological transformation between the crystalline and amorphous states.     

Core–shell structured phosphorescent nanoparticles for detection of exogenous and endogenous hypochlorite in live cells via ratiometric imaging and photoluminescence lifetime imaging microscopy

We report a ratiometric phosphorescence sensory system for hypochlorite (ClO^–) based on core–shell structured silica nanoparticles. Two phosphorescent iridium(iii) complexes were immobilised in the inner solid core and outer mesoporous layer of the nanoparticles, respectively. The former is insensitive to ClO^– and thus serves as an internal standard to increase the accuracy and precision, while the latter exhibits a specific and significant luminogenic response to ClO^–, providing high selectivity and sensitivity. Upon exposure to ClO^–, the nanoparticles display a sharp luminescence colour change from blue to red. Additionally, intracellular detection of exogenous and endogenous ClO^– has been demonstrated via ratiometric imaging and photoluminescence lifetime imaging microscopy. Compared to intensity-based sensing, ratiometric and lifetime-based measurements are independent of the probe concentration and are thus less affected by external influences, especially in intracellular applications.     

A Novel Fluorescent Probe for Determination of pH and Viscosity Based on a Highly Water-Soluble 1,8-Naphthalimide Rotor

A novel highly water-soluble 1,8-naphthalimide with pH and viscosity-sensing fluorescence was synthesized and investigated. The synthesized compound was designed as a molecular device in which a molecular rotor and molecular “off-on” switcher were integrated. In order to obtain a TICT driven molecular motion at C-4 position of the 1,8-naphthalimide fluorophore, a 4-methylpiperazinyl fragment was introduced. The molecular motion was confirmed after photophysical investigation in solvents with different viscosity; furthermore, the fluorescence-sensing properties of the examined compound were investigated in 100% aqueous medium and it was found that it could be used as an efficient fluorescent probe for pH. Due to the non-emissive deexcitation nature of the TICT fluorophore, the novel system showed low yellow–green emission, which represented “power-on”/“rotor-on” state. The protonation of the methylpiperazine amine destabilized the TICT process, which was accompanied by fluorescence enhancement indicating a “power-on”/“rotor-off” state of the system. The results obtained clearly illustrated the great potential of the synthesized compound to serve as pH- and viscosity-sensing material in aqueous solution.     

Trace analysis of uranyl ion (UO2) in aqueous solution by fluorescence turn-on detection via aggregation induced emission enhancement effect

A sensitive fluorescence turn-on method for trace amounts of uranyl ion (UO₂²⁺) in solution has been developed in this study, based on aggregation induced emission enhancement (AIEE) characteristics of 4-pethoxycarboxyl salicylaldehyde azine (PCSA) induced by complex interaction between UO₂²⁺ and PCSA. Under optimized conditions, a fluorescence enhancement at 540 nm could be observed, which was linearly related to the concentration of UO₂²⁺ in the range of 1–25 ppb (part per billion). Analytical data showed that a detection limit of 0.2 ppb was achieved with the relative standard deviation (R.S.D.) 1.3% (n = 5). The proposed method was successfully utilized in quantifying UO₂²⁺ in fuel processing wastewaters.     

Aggregation-induced emission enhancement in poly(phenylene-ethynylene)s bearing aniline groups

Poly(phenylene ethynylene)s(P1) with 4-vinylaniline pendant groups were successfully prepared by the Sonogashira coupling polymerization between l,4-diethynyl-2,5-bis(pentyloxy)benzene and 4-[2-(2,5-dibromophenyl)vinyl]-aniline. In comparison with its analogue P2 without amino group,the emission of P1 is only enhanced by aggregation when adding n-hexane into its THF solution,exhibiting an aggregation-induced emission enhancement(AIEE) effect.When methanol or water instead of hexane was added into THF solution,P1,however,didn’t show AIEE.The results indicated that amino groups strengthen the inter-chain and intra-chain interactions in P1 and restrict the non-radiative energy transition. This strategy can provide a platform for developing highly sensitive and efficient bio- and chemosensors.     

Aggregation-Induced Emission-Based Sensing Platform for Selective Detection of Zn2+: Experimental and Theoretical Investigations

Fluorescent chemosensors with aggregation induced emission enhancement (AIEE) emerge as promising tools in the field of sensing materials. Herein, we report the design, synthesis and applicability of a Schiff base chemosensor 1-(benzo[1,3]dioxol-4-ylmethylene-hydrazonomethyl)-naphthalen-2-ol ( Hbdhn ) of AIE characteristics that exhibits highly effective and selective response towards Zn²⁺. The sensing effect of Hbdhn was evaluated by means of absorption/emission spectra and corresponding underlying photophysical mechanisms were proposed based on extensive quantum-chemical (TD)DFT calculations. The aggregated states in different DMSO/H₂O ratios and in a presence of Zn²⁺ were examined by fluorescence lifetime measurements, dynamic light scattering and scanning electron microscopy studies. The bioimaging abilities of Hbdhn were evaluated for Zn²⁺ in HepG2 cancer cells. The results demonstrate instant, stable in time and reproducible, colorimetric turn-on response with superb selectivity and sensitivity of Hbdhn towards Zn²⁺, based on chelation enhanced fluorescence mechanism. AIEE improves further Hbdhn properties, leading to strong, long-lived fluorescence, with appearance of rod-like particles, in 90 % of water in DMSO and only 10 % of water in DMSO in the presence of Zn²⁺. All these features combined with successful biomaging studies make Hbdhn one of the most promising candidate for practical applications among recently proposed related systems.     

Theoretical Study on the Electronic Structures and Spectral Properties of 1,8-Naphthalimide Derivatives

The molecular geometries, frontier molecular orbital properties, and absorption and emission properties of three 4-phenoxy-1,8-naphthalimide derivatives, namely 4-phenoxy-N-（2-hydroxyethyl）-1,8-naphthalimide（1）,4-（2-tert-butylphenoxy）-N-（2-hydroxyethyl）-1,8-naphthalimide（2）, and 4-[2,4-di（tert-butyl）]phenoxy-N-（2-hydroxyethyl）-1,8-naphthalimide（3）, are investigated by density functional theory（DFT） and time-dependent density functional theory（TD-DFT） calculations in conjunction with polarizable continuum models（PCMs）. Four functionals and ten basis sets are employed for 1 to calculate the electron transition energies, which were compared with the experimental observations. Our results reveal that the B3LYP/6-311＋G（d,p） method is the best choice to reproduce the experimental spectra. Moreover, the effects of substituents on the molecular geometries, electronic structures, absorption and emission spectra are also studied at the B3LYP/6-311＋G（d,p） level. We find that the gap between the highest occupied molecular orbital（HOMO） and the lowest unoccupied molecular orbital（LUMO） decreases with increasing the number of tert-butyl substituents onto the phenoxy groups, suggesting red-shift of the absorption and emission bands. This is related to the increase of conjugation from 1 to 2 and 3. Our calculations are in good agreement with the experimental results.     

Fluorescence properties of novel 6-butyl-2,3-dicyano-7-methyl-6H-1,4-diazepine styryl dyes containing ethyleneglycol units

The fluorescence properties of novel 6-butyl-2,3-dicyano-7-methyl-6H-1,4-diazepine styryl dyes having mono-, di-, tri-, and tetra(ethyleneglycol) units were examined. The mono(ethylenglycol) derivative was solid at room temperature, whereas the di-, tri-, and tetra(ethylenglycol) derivatives were oily. The monoethyleneglycol derivative showed weak aggregation-induced emission enhancement with fluorescence maximum at 649 nm, which comes from J-aggregates. The fluorescence of oily di-, tri-, and tetra(ethyleneglycol) derivatives in neat form was very weak. No aggregation-induced emission enhancement was observed for the oily derivatives.     

The AIEE properties and solid state fluorescence of 3-indolyl-4-indazolyl maleimide compounds: Synthesis and fluorescence characteristics

A range of 3-indolyl-4-indazolyl maleimide fluorescent compounds, including 2a, 2b, 2c, 3a and 3b, were synthesized efficiently. In different organic dissolvents, the photo-physical performance was checked, either in the aggregated state or in the solid state. When being in solid and in solution state, these fluorescent compounds showed high fluorescent intensity, indicating a highest fluorescence quantum efficiency of 45% accompanying a large Stokes Shift longer than 100 nm in toluene. Also, they can carry out a phenomenon of aggregation-induced emission enhancement (AIEE). TDDFT and DFT calculations were used to confirm the experimental findings.     

A ratiometric and exclusively selective Cu fluorescent probe based on internal charge transfer (ICT)

A new ratiometric and exclusively selective fluorescent probe N-butyl-4,5-di[N-(phenyl)-2-(amino)-acetamino]-1,8-naphthalimide (1) was designed and synthesized on the basis of the mechanism of internal charge transfer (ICT). The probe 1 showed exclusively selectivity for Cu^II in the presence of a variety of other metal ions in aqueous ethanol solutions and the binding mode of probe 1 with Cu^II was 1:1 metal-ligand complex. Fluorescent emission spectra of probe 1 in the presence of Cu^II showed a 50 nm blue shift, which is from 521 nm to 471 nm. Furthermore, probe 1 shows the same fluorescent change with the Cu^II in living cells.     

In situ small-angle X-ray scattering studies during the formation of polymer/silica nanocomposite particles in aqueous solution

This study is focused on the formation of polymer/silica nanocomposite particles prepared by the surfactant-free aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) in the presence of 19 nm glycerol-functionalized aqueous silica nanoparticles using a cationic azo initiator at 60 °C. The TFEMA polymerization kinetics are monitored using ¹H NMR spectroscopy, while postmortem TEM analysis confirms that the final nanocomposite particles possess a well-defined core–shell morphology. Time-resolved small-angle X-ray scattering (SAXS) is used in conjunction with a stirrable reaction cell to monitor the evolution of the nanocomposite particle diameter, mean silica shell thickness, mean number of silica nanoparticles within the shell, silica aggregation efficiency and packing density during the TFEMA polymerization. Nucleation occurs after 10–15 min and the nascent particles quickly become swollen with TFEMA monomer, which leads to a relatively fast rate of polymerization. Additional surface area is created as these initial particles grow and anionic silica nanoparticles adsorb at the particle surface to maintain a relatively high surface coverage and hence ensure colloidal stability. At high TFEMA conversion, a contiguous silica shell is formed and essentially no further adsorption of silica nanoparticles occurs. A population balance model is introduced into the SAXS model to account for the gradual incorporation of the silica nanoparticles within the nanocomposite particles. The final PTFEMA/silica nanocomposite particles are obtained at 96% TFEMA conversion after 140 min, have a volume-average diameter of 216 ± 9 nm and contain approximately 274 silica nanoparticles within their outer shells; a silica aggregation efficiency of 75% can be achieved for such formulations.

SAXS is used to study the formation of polymer/silica nanocomposite particles prepared by surfactant-free aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate in the presence of silica nanoparticles using a azo initiator at 60 °C.     

Fluorescence Emission Mediated by Metal-Dielectric-Metal Fishnet Metasurface: Spatially Selective Excitation and Double Enhancement

Enhancement of fluorescent radiation is of great importance for applications including biological imaging, high-sensitivity detectors, and integrated light sources. Strong electromagnetic fields can be created around metallic nanoparticles or in gap of nanostructures, where the local state density of radiating mode is then dramatically enhanced. While enhanced fluorescent emission has been demonstrated in many metallic nanoparticles and nanoparticle pairs, simultaneous mediation of absorption and emission processes of fluorescent emitters remains challenging in metallic nanostructures. Here, we investigate fluorescent emission mediated by metal-dielectric-metal fishnet metasurface, in which localized surface plasmon (LSP) and magnetic plasmon polaritons (MPPs) modes are coupled with absorption and emission processes, respectively. For absorption process, coupling of the LSP mode enables spatially-selective excitation of the fluorescent emitters by rotating the polarization of the pump laser beam. In addition, the polarization-dependent MPP mode enables manipulation of both polarization and wavelength of the fluorescent emission by introducing a rectangular fishnet structure. All the experimental observations are further corroborated by finite-difference time-domain simulations. The structure reported here has great potentialfor application to color light-emitting devices and nanoscale integrated light sources.