pH-Responsive Water-Soluble Polymer Carriers for Cell-Selective Metabolic Sialylation Labeling.

Cell-surface sialic acids can be metabolically labeled and subsequently modified using bioorthogonal chemistry. The method has great potential for targeted therapy and imaging; however, distinguishing the sialylation of specific cells remains a major challenge. Here, we described a cell-selective metabolic sialylation labeling strategy based on water-soluble polymer carriers presented with pH-responsive N-azidoacetylmannosamine (ManNAz) release. 2-Methacryloyloxyethyl phosphorylcholine contributed to increased water solubility and reduced nonspecific attachment to cells. Lactobionic acid residues, used for cell selectivity, recognized overexpressed receptors on target hepatoma cells and mediated cellular internalization. ManNAz caged by acidic pH-responsive carbonated ester linkage on the polymer was released inside target cells and expressed as azido sialic acid. Additionally, longer copolymer carriers enhanced the metabolic labeling efficiency of sialylation. This approach provides a platform for cell-selective labeling of sialylation and can be applied to high-resolution bioimaging and targeted therapy.

Fluorescent polymeric nanoparticle for ratiometric temperature sensing allows real-time monitoring in influenza virus-infected cells.

Temperature is a key indicator of infection and disease, however, it is difficult to measure at a cellular level. Nanoparticles are applied to measure the cellular temperature, and enhancement of the stability and reliability of the signal and higher biocompatibility are demanded. We have developed fluorescent polymeric nanoparticles loaded with temperature-sensitive units (as rhodamine B) and internal reference units (as coumarin) for imaging and ratiometric sensing of the cellular temperature in the physiological range. The fluorescence signal of the nanoparticles was stable in the bio-environment and the ratiometric sensing strategy could overcome the concentration effect of nanoparticles. The nanoparticles were endocytosed by cells and partially presented in mitochondria. The fluorescence intensity ratio of rhodamine B and coumarin using nanoparticles showed good linear correlations in buffer solutions, cell suspensions, and imaging of living cells. Using the fluorescent polymeric nanoparticles, the change of temperature of cells during influenza virus infection could be individually monitored.

High Dye-Loaded and Thin-Shell Fluorescent Polymeric Nanoparticles for Enhanced FRET Imaging of Protein-Specific Sialylation on the Cell Surface.

Nanoparticle-based probes have great potential for imaging specific biomolecules in signal distinguishing and amplification via Förster resonance energy transfer (FRET). Protein-specific sialylation plays key roles in the regulation of protein structure and function, as well as in various pathophysiological processes. Here, we developed a fluorescent polymeric nanoparticle with a biocompatible hydrophilic thin shell loaded with plentiful dye and used it as the donor to enhance the FRET imaging of cell surface protein-specific sialylation. The hydrophobic core decreased the self-quenching of loaded fluorescent molecules, while the hydrophilic thin shell ensured that the nanoparticles remained on the extracellular surface and guaranteed the FRET effect. Thus, the thin-shell polymeric nanoparticles enhanced the FRET imaging of protein tyrosine kinase-7-specific sialylation on the CCRF-CEM cell surface and showed high sensitivity under drug treatment. This nanoparticle has great potential for elucidating the relationship between dynamic specific glycosylation states and disease processes, as well as for the study of new cell surface imaging methodologies.

Silver nanoparticle plasmonic enhanced förster resonance energy transfer (FRET) imaging of protein-specific sialylation on the cell surface.

A large amount of proteins are post-translationally modified with a sialic acid terminal oligosaccharide, and sialylation directly affects the function of glycoproteins and adjusts relevant biological processes. Herein, we developed a method for imaging analysis of protein-specific sialylation on the cell surface via silver nanoparticle (AgNPs) plasmonic enhanced Förster resonance energy transfer (FRET). In this strategy, the target monosaccharide was labelled with the FRET acceptor of Cy5 via bioorthogonal chemistry. In addition, aptamer linked AgNPs were combined with the Cy3 fluorophore by DNA hybridization as the FRET donor probe, which could be conjugated to the target glycoprotein based on specific aptamer-protein recognition. The Cy5 fluorescence signal was obtained under the Cy3 excitation wavelength via FRET. Moreover, the FRET fluorescence signal was obviously enhanced owing to the plasmonic effect of AgNPs at an appropriate distance to Cy3 on the cell surface. Hence, the protein-specific sialic acids were detected with high contrast. The results showed that the AgNP plasmonic enhanced FRET method was not only superior to the bare FRET method but also can be used to evaluate the expression of sialoglycoproteins in different cell types under pharmacological treatments. The AgNP plasmonic enhanced FRET method provides a valuable tool in the research of glycan metabolism biological processes, the active site of glycoproteins and drug screening.

Intrinsic "Vacancy Point Defect" Induced Electrochemiluminescence from Coreless Supertetrahedral Chalcogenide Nanocluster.

A deep understanding of distinct functional differences of various defects in semiconductor materials is conducive to effectively control and rationally tune defect-induced functionalities. However, such research goals remain a substantial challenge due to great difficulties in identifying the defect types and distinguishing their own roles, especially when various defects coexist in bulk or nanoscale material. Hereby, we subtly selected a molecular-type semiconductor material as structural mode composed of supertetrahedral chalcogenide Cd-In-S nanoclusters (NCs) with intrinsic vacancy point defect at the core site and antisite point defects at the surface of supertetrahedron and successfully established the correlation of those point defects with their own electrochemiluminescence (ECL) behaviors. The multichannel ECL properties were recorded, and the corresponding reaction mechanisms were also proposed. The predominant radiation recombination path of ECL emission peak at 585 nm was significantly distinguished from asymmetrically broad PL emission with a peak at 490 nm. In addition, the ECL performance of the coreless supertetrahedral chalcogenide nanocluster can be modulated by atomically precise doping of monomanganese ion at the core vacant site. A relatively high ECL efficiency of 2.1% was also gained. Actually, this is the first investigation of ECL behavior of semiconductor materials based on supertetrahedral chalcogenide nanocluster in aqueous solution. Current research may open up a new avenue to probe the roles of various different defects with defined composition and position in the NC. The versatile and bright ECL properties of Cd-In-S NC combined with tunable ECL potential and ECL peak suggest that the new kind of NC-based ECL material may hold great promising for its potential applications in electrochemical analysis, sensing, and imaging.

Nitrogen-doped carbon nanoparticle modulated turn-on fluorescent probes for histidine detection and its imaging in living cells.

In this work, nitrogen-doped carbon nanoparticle (N-CNP) modulated turn-on fluorescent probes were developed for rapid and selective detection of histidine. The as synthesized N-CNPs exhibited high fluorescence quantum yield and excellent biocompatibility. The fluorescence of N-CNPs can be quenched selectively by Cu(II) ions with high efficiency, and restored by the addition of histidine owing to the competitive binding of Cu(II) ions and histidine that removes Cu(II) ions from the surface of the N-CNPs. Under the optimal conditions, a linear relationship between the increased fluorescence intensity of N-CNP/Cu(II) ion conjugates and the concentration of histidine was established in the range from 0.5 to 60 µM. The detection limit was as low as 150 nM (signal-to-noise ratio of 3). In addition, the as-prepared N-CNP/Cu(II) ion nanoprobes showed excellent biocompatibility and were applied for a histidine imaging assay in living cells, which presented great potential in the bio-labeling assay and clinical diagnostic applications.

Non-redox modulated fluorescence strategy for sensitive and selective ascorbic acid detection with highly photoluminescent nitrogen-doped carbon nanoparticles via solid-state synthesis.

Highly photoluminescent nitrogen-doped carbon nanoparticles (N-CNPs) were prepared by a simple and green route employing sodium alginate as a carbon source and tryptophan as both a nitrogen source and a functional monomer. The as-synthesized N-CNPs exhibited excellent water solubility and biocompatibility with a fluorescence quantum yield of 47.9%. The fluorescence of the N-CNPs was intensively suppressed by the addition of ascorbic acid (AA). The mechanism of the fluorescence suppression of the N-CNPs was investigated, and the synergistic action of the inner filter effect (IFE) and the static quenching effect (SQE) contributed to the intensive fluorescence suppression, which was different from those reported for the traditional redox-based fluorescent probes. Owing to the spatial effect and hydrogen bond between the AA and the groups on the N-CNP surface, excellent sensitivity and selectivity for AA detecting was obtained in a wide linear relationship from 0.2 µM to 150 µM. The detection limit was as low as 50 nM (signal-to-noise ratio of 3). The proposed sensing systems also represented excellent sensitivity and selectivity for AA analysis in human biological fluids, providing a valuable platform for AA sensing in clinic diagnostic and drug screening.