Anchoring Cu Nanoclusters on Melamine-Formaldehyde Microspheres: A New Strategy for Triggering Aggregation-Induced Emission toward Specific Enzyme-Free Methyl Parathion Sensing

Methyl parathion (MP) residues have aroused extensive attention on account of their significant threat to the environment and food safety. Currently reported fluorescent methods used for MP sensing largely depend upon an enzyme. Designing a facile and specific enzyme-free MP fluorescent sensor is in great demand, which remains a challenge. Here, negatively charged Cu nanoclusters (CuNCs) anchored on positively charged melamine-formaldehyde (MF) microspheres (MF@CuNCs) through an electrostatic interaction were prepared. MF microspheres triggered aggregation-induced emission (AIE) of CuNCs and successfully circumvented the shortcomings of poor stability and low luminescence of CuNCs. The fluorescence intensity of MF@CuNCs can be quenched by p-nitrophenol produced by MP under alkaline conditions. Accordingly, a specific enzyme-free MP sensing method was constructed with MF@CuNCs. In combination with a smartphone, visually quantitative analysis of MP in a fast and portable way was also achieved. For the first time, AIE of CuNCs used for enzyme-free MP sensing was successfully explored in this work, and it is believed that this method will open a new pathway for AIE of CuNCs to be applied in various applications.

Hydrophilic magnetic molecularly imprinted resin in PVDF membrane for efficient selective removal of dye

Selective removal of contaminants from water by membranes is of practical importance for water purification and environmental protection. In the present study, through an in-situ polymerization process, a novel composite of Fe₃O₄/molecularly imprinted resorcinol -formaldehyde-melamine resin (Fe₃O₄/MIRFMR) was synthesized. Then, the novel membrane was prepared from a tea filter bag (TFB) as a base substrate which was subsequently coated by a casting solution containing polyvinylidene fluoride (PVDF) matrix, Prunus scoparia gum as a hydrophilic agent and Fe₃O₄/MIRFMR as selective filler by phase inversion technique. Resorcinol as functional monomers with multiple hydrophilic groups such as -OH, -NH₂ and -NH-, were used for selective removal of Rhodamine B (RhB) as target molecule. The Fe₃O₄/MIRFMR/PVDF/TFB membranes were characterized by FE-SEM, XRD, FTIR, BET, VSM, water contact angle (WCA) and mechanical analysis. The filtration and adsorption of RhB on the prepared membrane was investigated parameters in a cross-module filtration setup. Casting solution containing 0.01 g of Fe₃O₄/MIRFMR as optimum value showed good wettability, high water flux (42.5 L/m² h), flux recovery ratio (88.9%), RhB removal efficiency (95.8%). The selectivity of 4.9, 3.3, 2.1 and 2.5 was found to be for RhB compared to AB, MG, EB, and TB dye. It seems that the fabricated membrane could be an effective and selective option for wastewater containing pollutants. The high removal efficiency, fouling resistance, good wettability and stability of the fabricated membrane are promising for use in practical water filtration, especially for selective removal of dyes.

A signal-off fluorescent strategy for deferasirox effective detection using carbon dots as probe and Cu2+ as medium

The content of deferasirox (DEF) in plasma is significant in β-thalassemia patient that needs long-term transfusion therapy, while the effective and simple strategy for DEF monitoring is still limited. The carbon dots (CDs) prepared from citric acid monohydrate and glutathione exhibit weakly modulated fluorescence intensity to several common metal ions containing Cu²⁺. Interestingly, the process of interaction of Cu²⁺ and DEF forms the chelation of Cu²⁺ and DEF (Cu-DEF) with the absorbance wavelength of DEF at 320 nm shifting to 332 nm for Cu-DEF. And the obtained Cu-DEF will effectively quench CDs through inner filter effect (IFE). Accordingly, a facile signal-off fluorescent method based on CDs as probe is developed for DEF detection using Cu²⁺ as medium. And the proposed method exhibits linear range of 0.5-20 μg/mL with the detection limit of 0.33 μg/mL for DEF under the optimized conditions. Moreover, the developed assay is further expanded to test the content of DEF in dispersible tablet and plasma with accuracy and reproducibility. Such cost-effective and sensitive fluorescent assay just through simple mixing operation present a valuable strategy for drug monitoring.

Light-Regulated Natural Fluorescence of the PCC 6803@ZIF-8 Composite as an Encoded Microsphere for the Detection of Multiple Biomarkers

The use of color-encoded microspheres for a bead-based assay has attracted increasing attention for high-throughput multiplexed bioassays. A fluorescent PCC 6803@ZIF-8 composite was prepared as a bead-based assay platform by a self-assembled zeolitic imidazolate framework (ZIF-8) on the surface of inactivated PCC 6803 cells. The composite fluorescence owing to the presence of pigment proteins in PCC 6803 could be gradually bleached with the prolongation of the ultraviolet light irradiation time. The composites with different fluorescence intensities were therefore obtained as encoded microspheres for the multiplexed assay. ZIF-8 provides a stable, rigid shell and a large specific surface area for composites, which prevent the composites from breakage during use and storage, simplify the protein immobilization procedure, reduce non-specific adsorption, and enhance the detection sensitivity. The encoded composites were successfully used to detect multiple DNA insertion sequences of Mycobacterium tuberculosis. The presented strategy offers an innovative color-encoding method for high-throughput multiplexed bioassays without the need of using chemically synthesized fluorescent materials.

Approaching Highly Leaching-Resistant Fire-Retardant Wood by In Situ Polymerization with Melamine Formaldehyde Resin

The objective of the work was to improve the leaching resistance of fire-retardant (FR) modified wood by the incorporation of a thermoset resin. Here, Scots pine (Pinus sylvestris L.) sapwood was impregnated with melamine formaldehyde (MF) resin and hydrophilic FRs guanyl-urea phosphate/boric acid by a vacuum-pressure treatment. Resistance to leaching of FR-modified wood was evaluated, after conducting an accelerated aging test according to European standard EN 84. Inductively coupled plasma analysis showed that the incorporation of MF resin significantly reduced the leachability of FRs. Scanning electron microscopy/energy-dispersive X-ray spectrometry revealed that the mechanism of water resistance was by doping the FRs into MF resin microspheres. Fourier transform infrared spectra showed the chemical functionality changes of FR-modified wood such as the formation of methylene bridges by drying the modified wood specimens. An increase in the thermal stability of FR-modified wood was confirmed by thermal gravimetric analysis. Excellent fire performance of FR-modified wood after leaching was affirmed by the limiting oxygen index and cone calorimeter tests.

Amplified fluorescence detection and adsorption of Au3+ by the fluorescent melamine formaldehyde microspheres incorporated with N and S co-doped carbon dots

Gold is one of the potential toxic heavy metals. In the present study, Au³⁺ was detected and removed by newly-designed fluorescent microspheres (MF-CDs), i.e. melamine formaldehyde microspheres incorporated with N and S co-doped carbon dots (N,S-CDs). N,S-CDs played the role as sensing unites and melamine formaldehyde microspheres (MF) as carriers. When MF-CDs were attempted as the fluorescence probe, enhanced fluorescence sensing performance towards Au³⁺ was achieved with wider linear range (0.05-2 μM) and lower limit of detection (31 nM) compared to the N,S-CDs probe. In addition, when MF-CDs were used as the adsorbent, the adsorption capacity towards Au³⁺ reached up to 1 mmol g^-1, about ten times more than that of MF. Moreover, the Au³⁺ adsorbed on the MF-CDs could be in-situ transferred to gold nanoparticle (AuNP), forming the immobilized nanocatalyst, i.e. MF-CDs-AuNP, which could further assist the reduction of 4-nitrophenol with acceptable reusability. This study paved an avenue to design the multifunctional materials for simultaneous detection, removal and recycling of environmental concerned pollutants.

Development of Ratiometric Fluorescence Sensors Based on CdSe/ZnS Quantum Dots for the Detection of Hydrogen Peroxide

In this study, carboxyl group functionalized-CdSe/ZnS quantum dots (QDs) and aminofluorescein (AF)-encapsulated polymer particles were synthesized and immobilized to a sol-gel mixture of glycidoxypropyl trimethoxysilane (GPTMS) and aminopropyl trimethoxysilane (APTMS) for the fabrication of a hydrogen peroxide-sensing membrane. CdSe/ZnS QDs were used for the redox reaction of hydrogen peroxide (H2O2) via a reductive pathway by transferring electrons to the acceptor that led to fluorescence quenching of QDs, while AF was used as a reference dye. Herein, the ratiometric fluorescence intensity of CdSe/ZnS QDs and AF was proportional to the concentration of hydrogen peroxide. The fluorescence membrane (i.e., QD-AF membrane) could detect hydrogen peroxide in linear detection ranges from 0.1 to 1.0 mM with a detection limit (LOD) of 0.016 mM and from 1.0 to 10 mM with an LOD of 0.058 mM. The sensitivity of the QD-AF membrane was increased by immobilizing horseradish peroxidase (HRP) over the surface of the QD-AF membrane (i.e., HRP-QD-AF membrane). The HRP-QD-AF membrane had an LOD of 0.011 mM for 0.1-1 mM H2O2 and an LOD of 0.068 mM for 1-10 mM H2O2. It showed higher sensitivity than the QD-AF membrane only, although both membranes had good selectivity. The HRP-QD-AF membrane could be applied to determine the concentration of hydrogen peroxide in wastewater, while the QD-AF membrane could be employed for the detection of α-ketobutyrate.

Preparation of Fluorescence-Encoded Microspheres Based on Hydrophobic Conjugated Polymer-Dye Combination and the Immunoassay

Fluorescent microspheres are greatly demanded in many applications based on high-throughput suspension array technology. To realize the multiplexed assay, microspheres should be encoded to identify the interaction between analytes and spheres. This study advanced a strategy for preparing fluorescence-encoded microspheres, employing two hydrophobic fluorophores, poly(p-phenyleneethylene) (PPE), and Nile Red (NR), as well as the monodisperse amino-modified porous substrate polymeric spheres, poly(glycidyl methacrylate) microspheres (APGMA). Loading the fluorophores sequentially onto the substrate spheres via adsorption by immersing the spheres in the dipping solution of fluorophores resulted in the APGMA-PPE-NR spheres. By varying the concentration and combination of fluorophores in the solution, an array of 64-code APGMA-PPE-NR spheres was obtained and could be easily individually decoded via flow cytometry. A 2D dot plot from the flow cytometry of a set of mixed spheres with four different codes could also be differentiated, coincident with the overlaid plots of the spheres' corresponding codes but measured individually. These spheres were found to have good stability against washing, photobleaching, and thermal treatment. In addition, a sandwich immunoassay for the detection of goat IgG was performed, and the capability of the encoded spheres to be used in suspension array technology was demonstrated.

The Morphology and Performance of Poly(Vinyl Chloride) Containing Melamine Schiff Bases against Ultraviolet Light

Five Schiff bases derived from melamine have been used as efficient additives to reduce the process of photodegradation of poly(vinyl chloride) films. The performance of Schiff bases has been investigated using various techniques. Poly(vinyl chloride) films containing Schiff bases were irradiated with ultraviolet light and any changes in their infrared spectra, weight, and the viscosity of their average molecular weight were investigated. In addition, the surface morphology of the films was inspected using a light microscope, atomic force microscopy, and a scanning electron micrograph. The additives enhanced the films resistance against irradiation and the polymeric surface was much smoother in the presence of the Schiff bases compared with the blank film. Schiff bases containing an ortho-hydroxyl group on the aryl rings showed the greatest photostabilization effect, which may possibly have been due to the direct absorption of ultraviolet light. This phenomenon seems to involve the transfer of a proton as well as several intersystem crossing processes.

White-Light-Emitting Melamine-Formaldehyde Microspheres through Polymer-Mediated Aggregation and Encapsulation of Graphene Quantum Dots

Graphene quantum dot (GQD) encapsulated melamine-formaldehyde (MF) polymer microspheres with uniform particle size and tunable high-quality white-light emissions are prepared via a polymer-mediated GQD assembly and encapsulation strategy. In solution, GQDs are first aggregated with MF prepolymer through electrostatic interaction and further encapsulated inside the microspheres formed by polymerization of MF prepolymer under acid catalysis and heating. During this process, the aggregated GQDs are fixed in the MF polymer matrix with their emission extended from blue to full visible range, presenting bright white luminescence under ultraviolet excitation. The prepared white-light-emitting GQD-MF microspheres exhibit uniform morphology with an average particle size of 2.0 ± 0.08 µm and their luminescence properties are effectively regulated by the doping concentration of GQDs in the MF polymer matrix. A series of white-light-emitting GQD-MF microspheres with quantum yields from 0.83 to 0.43, Commission Internationale de L'Eclairage coordinates from (0.28, 0.28) to (0.33, 0.32), and color rendering index from 0.75 to 0.88 are obtained with excellent photostability and thermal stability. By dispersing the GQD-MF microspheres in cross-linked polydimethylsiloxane matrix, flexible film with dual functions of high-quality white-light-emitting and light diffusion is obtained and successfully applied for white light-emitting diode fabrication.

Multifunctional Polystyrene Core/Silica Shell Microparticles with Antifouling Properties for Bead-Based Multiplexed and Quantitative Analysis

Commercial bead-based assays are commonly built upon polystyrene particles. The polymeric carrier can be encoded with organic dyes and has ideal material properties for cytometric applications such as low density and high refractive index. However, functional groups are conventionally integrated during polymerization and subsequent modification is limited to the reactivity of those groups. Additionally, polystyrene as the core material leads to many hydrophobic areas still being present on the beads' surfaces even after functionalization, rendering the particles prone to nonspecific adsorption during an application. The latter calls for several washing steps and the use of additives in (bio)analytical assays. In this contribution, we show how these limitations can be overcome by using monodisperse polystyrene (PS) core/silica (SiO₂) shell particles (SiO₂@PS). Two different hydrophobic BODIPY (boron-dipyrromethene) dyes were encapsulated inside a poly(vinylpyrrolidone) (PVP) -stabilized polystyrene core in different concentrations to create 5-plex arrays in two separate detection channels of a cytometer. A subsequent modification of the silica shell with an equimolar APTES/PEGS (aminopropyltriethoxysilane/polyethylene glycol silane) blend added multifunctional properties to the hybrid core/shell microparticles in a single step: APTES provides amino groups for the attachment of a caffeine derivative (as a hapten) to create antigen-coupled microspheres; the PEG moiety effectively suppresses nonspecific binding of antibodies, endowing the surface with antifouling properties. The particles were applied in a competitive fluorescence immunoassay in suspension, and a highly selective wash-free assay for the detection of caffeine in beverages was developed as a proof of concept.

Layer-by-layer fabrication of fluorescent microspheres using micelles as a spacer: simultaneously realizing fluorescence enhancement and introduction of bioconjugation sites

Fluorescent microspheres fabricated using a conjugated polymer and micelles are demonstrated to have strong emission and are effective for bioconjugation.

Ratiometric Nanothermometer Based on Rhodamine Dye-Incorporated F127-Melamine-Formaldehyde Polymer Nanoparticle: Preparation, Characterization, Wide-Range Temperature Sensing, and Precise Intracellular Thermometry

A series of fluorescent nanothermometers (FTs) was prepared with Rhodamine dye-incorporated Pluronic F-127-melamine-formaldehyde composite polymer nanoparticles (R-F127-MF NPs). The highly soluble Rhodamine dye molecules were bound with Pluronic F127 micelles and subsequently incorporated in the cross-linked MF resin NPs during high-temperature cross-link treatment. The morphology and chemical structure of R-F127-MF NPs were characterized with dynamic light scattering, electron microscopy, and Fourier-transform infrared (FTIR) spectra. Fluorescence properties and thermoresponsivities were analyzed using fluorescence spectra. R-F127-MF NPs are found to be monodispersed, presenting a size range of 88-105 nm, and have bright fluorescence and high stability in severe treatments such as autoclave sterilization and lyophilization. By simultaneously incorporating Rhodamine B and Rhodamine 110 (as reference) dyes at a doping ratio of 1:400 in the NPs, ratiometric FTs with a high sensibility of 7.6%·°C(-1) and a wide temperature sensing range from -20 to 110 °C were obtained. The FTs exhibit good stability in solutions with varied pH, ionic strengths, and viscosities and have similar working curves in both intracellular and extracellular environments. Cellular temperature variations in Hela cells during microwave exposure were successfully monitored using the FTs, indicating their considerable potential applications in the biomedical field.

Color Tuning of Core-Shell Fluorescent Microspheres by Controlling the Conjugation of Poly(p-phenylenevinylene) Backbone

A series of poly(p-phenylenevinylene) (PPV)-coated microspheres with varied fluorescent emission colors have been prepared by controlling the average length of the conjugated segments on the polymer backbone. A modified Wessling method was used for preparing PPV with different conjugation segments. The labile sulfonium groups of the initial polymer precursor of PPV (pre-PPV) were partly substituted by relatively stable methoxyl groups. A series of precursors with different degrees of substitution were prepared by controlling the time of reaction; these precursors were adsorbed onto the negatively charged substrate spheres. Subsequently, heterogeneous thermal treatment eliminated the sulfonium groups selectively to form the conjugated segments on the PPV backbone with varied average conjugation lengths. Under UV exposure, the as-prepared PPV-coated microspheres displayed emission colors ranging from blue to green; a 65 nm shift in the emission maximum was observed in the fluorescence spectra. The gradual color change in emission of spheres was also confirmed in a confocal microscopy study. Further characterizations indicated that these microspheres possessed clear core-shell structure, good monodispersity in size, smooth surfaces, uniform emission, and superior thermal and photo stability. Flow cytometry measurements indicated that these spheres have very different patterns of intensity combination from four-signal receiving channels. The simple method reported herein, which can effectively and efficiently tune the emission color of the fluorescent microspheres, is a promising approach for preparation of microspheres used as encoded signal carrier in flow cytometry and other high-throughput techniques.

A facile method for high-performance multicolor upconversion microrods for biological encoding

In this paper, we demonstrate a facile method for preparing high-performance multicolor upconversion (UC) microrods for biological encoding. Multicolor UC microrods were prepared through a one-step facile hydrothermal method. The as-prepared UC microrods were uniform in shape and size (about 2 μm in length). For bioconjugation, the UC microrods were functionalized by coating with an amino-terminated silica shell. In order to magnify the bioactive sites, poly (acrylic acid) was introduced to the surface of UC microrods. The optical micrographs displayed that the carboxylated UC microrods were bright enough for observation of single crystals by a conventional microscope. They also exhibited excellent fluorescence stability against time expansion and pH change. Furthermore, a conventional optical microscope can readout the results of a sandwich immunoassay that was conducted by the UC microrods. All the results indicated that the UC microrods exhibited great potential to be new encoding particles for biological molecules.