Quantum dots with phenylboronic acid tags for specific labeling of sialic acids on living cells

Aqueous synthesis of dual-targeting Gd-doped CuInS2/ZnS quantum dots for cancer-specific bi-modal imaging

CIGS/ZnS@FA|APBA q-dots were synthesized in an aqueous phase; these quantum dots exhibited great potential as dual-modal nanoprobes for optical/MR imaging.

Different expression levels of glycans on leukemic cells-a novel screening method with molecularly imprinted polymers (MIP) targeting sialic acid

Sialic acid (SA) is normally expressed on the cell membranes and is located at the terminal position of the sugar chains. SA plays an important role for regulation of the innate immunity, function as markers of the cells and can be recognized by a variety of receptors. Interestingly, the level of SA expression is increased on metastatic cancer cells. The availability of specific antibodies against SA is limited and, therefore, biomarker tools for detection of SA are lacking. We have recently presented a novel method for specific fluorescence labeling of SA molecular imprinted polymers (MIP). Here, we have performed an extended screening of SA expression by using SA-MIP and included four different chronic lymphocytic leukemia (CLL) cell lines, conveniently analyzed by flow cytometry and fluorescence microscopy. SA expression was detected in four cell lines at different levels, and the SA expression were verified with lectin-FITC. These results show that SA-MIP can be used as a plastic antibody for detection of SA using both flow cytometry and fluorescence microscopy. We suggest that SA-MIP can be used for screening of different tumor cells of various stages, including CLL cells.

Targeting and Imaging of Cancer Cells via Monosaccharide-Imprinted Fluorescent Nanoparticles

The recognition of cancer cells is a key for cancer diagnosis and therapy, but the specificity highly relies on the use of biorecognition molecules particularly antibodies. Because biorecognition molecules suffer from some apparent disadvantages, such as hard to prepare and poor storage stability, novel alternatives that can overcome these disadvantages are highly important. Here we present monosaccharide-imprinted fluorescent nanoparticles (NPs) for targeting and imaging of cancer cells. The molecularly imprinted polymer (MIP) probe was fluorescein isothiocyanate (FITC) doped silica NPs with a shell imprinted with sialic acid, fucose or mannose as the template. The monosaccharide-imprinted NPs exhibited high specificity toward the target monosaccharides. As the template monosaccharides used are over-expressed on cancer cells, these monosaccharide-imprinted NPs allowed for specific targeting cancer cells over normal cells. Fluorescence imaging of human hepatoma carcinoma cells (HepG-2) over normal hepatic cells (L-02) and mammary cancer cells (MCF-7) over normal mammary epithelial cells (MCF-10A) by these NPs was demonstrated. As the imprinting approach employed herein is generally applicable and highly efficient, monosaccharide-imprinted NPs can be promising probes for targeting cancer cells.

Robust Nanoparticle-DNA Conjugates Based on Mussel-Inspired Polydopamine Coating for Cell Imaging and Tailored Self-Assembly

We have demonstrated that mussel-inspired polydopamine can serve as an intermediate coating layer for covalently attaching oligonucleotides on nanostructures of diverse chemical nature, which are made possible by the universal adhesion and spontaneous reactivity of polydopamine. Our results have shown that polydopamine can strongly bond to representative nanoparticles (i.e., Au nanoparticles and magnetic polymer nanobeads) and form a thin layer of coating that allows for attachment of commercially available DNA with thiol or amine end functionality. The resulting DNA-nanoparticle conjugates not only show excellent chemical and thermal stability and high loading density of DNA, but the linked DNA also maintain their biological functions in directing cancer cell targeting and undergo DNA hybridization to form multifunctional magnetic core-plasmonic satellite assemblies. The generally applicable strategy opens new opportunities for easy adoption of DNA-nanoparticle conjugates for broad applications in biosensors and nanomedicine.

A novel Fe3O4/CdTe fluorescence probe for sialic acid detection based on a phenylboronic acid–sialic acid recognition system

A novel fluorescence method was established for detecting sialic acid (SA) by using phenylboronic acid (PBA)-functionalized Fe₃O₄/CdTe magnetic nanoparticles as fluorescence probe.

Boronic acid recognition based-gold nanoparticle-labeling strategy for the assay of sialic acid expression on cancer cell surface by inductively coupled plasma mass spectrometry

Sialic acids are special sugars widely expressed at the termini of glycan chains on the cell surface, and their expression level on the cancer cell surface is much higher than on the normal cell surface.

Two-photon fluorescence imaging of sialylated glycans in vivo based on a sialic acid imprinted conjugated polymer nanoprobe

We have designed and synthesized an SA-imprinted conjugated polymer nanoprobe with two-photon fluorescence properties, which exhibits specific recognition ability to the target SA and has been used for monitoring sialylated glycan levels selectively in vivo.

Sialic Acid-Imprinted Fluorescent Core-Shell Particles for Selective Labeling of Cell Surface Glycans

The expression of cell surface glycans terminating with sialic acid (SA) residues has been found to correlate with various disease states there among cancer. We here report a novel strategy for specific fluorescence labeling of such motifs. This is based on sialic acid-imprinted core-shell nanoparticles equipped with nitrobenzoxadiazole (NBD) fluorescent reporter groups allowing environmentally sensitive fluorescence detection at convenient excitation and emission wavelengths. Imprinting was achieved exploiting a hybrid approach combining reversible boronate ester formation between p-vinylphenylboronic acid and SA, the introduction of cationic amine functionalities, and the use of an NBD-appended urea-monomer as a binary hydrogen-bond donor targeting the SA carboxylic acid and OH functionalities. The monomers were grafted from 200 nm RAFT-modified silica core particles using ethylene glycol dimethacrylate (EGDMA) as cross-linker resulting in a shell thickness of ca. 10 nm. The particles displayed strong affinity for SA in methanol/water mixtures (K = 6.6 × 10(5) M(-1) in 2% water, 5.9 × 10(3) M(-1) in 98% water, B(max) ≈ 10 μmol g(-1)), whereas binding of the competitor glucuronic acid (GA) and other monosaccharides was considerably weaker (K (GA) = 1.8 × 10(3) M(-1) in 98% water). In cell imaging experiments, the particles selectively stained different cell lines in correlation with the SA expression level. This was further verified by enzymatic cleavage of SA and by staining using a FITC labeled SA selective lectin.

Versatile Microfluidic Platform for the Assessment of Sialic Acid Expression on Cancer Cells Using Quantum Dots with Phenylboronic Acid Tags

This work describes a versatile microfluidic platform for evaluation of cell-surface glycan expression at the single-cell level using quantum dots (QDs) tagged with phenylboronic acid. The platform was integrated with dual microwell arrays, allowing the introduction of cells in two states using the same cell culture chamber. The simultaneous analysis of cells in the same environment minimized errors resulting from different culture conditions. As proof-of-concept, the expressions of sialic acid (SA) groups on K562 cells, with or without 3'-azido-3'-deoxythymidine (AZT) treatment, were evaluated in the same chamber. 3-Aminophenylboronic acid functionalized CdSeTe@ZnS-SiO2 QDs (APBA-QDs) were prepared as probes to recognize SA groups on K562 cells with only one-step labeling. The results showed that the expression of SA moieties on K562 cells was increased by 18% and 31% after treatment with 20 and 40 μM AZT, respectively. Performing the drug treatment and control experiments simultaneously in the same chamber significantly improved the robustness and effectiveness of the assay. The strategy presented here provides an alternative tool for glycan analysis in a sensitive, high-throughput, and effective manner.

Phenylboronic acid-modified magnetic nanoparticles as a platform for carbon dot conjugation and doxorubicin delivery

We describe the preparation of phenylboronic acid-modified magnetofluorescent nanoparticles (NPs) consisting of MnFe₂O₄ magnetic NPs conjugated to fluorescent carbon dots (Cdots). These NPs are useful for both optical and magnetic resonance imaging (MRI) modalities and could also be used to deliver the water-insoluble chemotherapy drug, doxorubicin (Dox). In this study, hydrophobic MnFe₂O₄ NPs were transferred from organic media to water by coordinating with 4-carboxyphenylboronic acid ligands, which also act as a cancer cell-specific targeting ligand and a site for conjugation to fluorescent Cdots, allowing the preparation of phenylboronic acid-modified magnetofluorescent NPs. The NPs displayed colloidal stability at different pH values and salt concentrations, and exhibited negligible cytotoxicity against HeLa cancer cells with >85% cell viability at concentrations of up to 500 μg mL^-1. Confocal laser scanning microscopy showed the specificity of the magnetofluorescent NPs in HeLa cells. MRI experiments showed that the magnetofluorescent NPs were effective contrast enhancement agents in T₂-weighted MRI. Moreover, the NPs were also found to be effective fluorescent markers in an in vivo experiment in zebrafish embryos. Dox was attached to the NPs by π-π stacking interactions, and was delivered in a targeted manner. The results indicated that these magnetofluorescent NPs could deliver Dox efficiently and induce an anticancer effect in HeLa cells, as confirmed by confocal laser scanning microscopy and in vitro cytotoxicity assays.

A rationally designed peptidomimetic biosensor for sialic acid on cell surfaces

We have developed peptidomimetic sialic acid (Sia) biosensors using boronic acid and arginine groups on the peptide backbone. The designed peptides were conjugated to fluorescent streptavidin via biotin enabling the optical labeling of cells. This approach provides unique opportunities to detect Sia composition on the cell surfaces and filopodia.

Surface-enhanced Raman scattering imaging of cancer cells and tissues via sialic acid-imprinted nanotags

Sialic acid-imprinted nanotags were designed and synthesized for surface-enhanced Raman scattering for imaging of cancer cells and tissues.

Assessing the blinking state of fluorescent quantum dots in free solution by combining fluorescence correlation spectroscopy with ensemble spectroscopic methods

The current method for investigating the blinking behavior is to immobilize quantum dots (QDs) in the matrix and then apply a fluorescent technique to monitor the fluorescent trajectories of individual QDs. So far, no method can be used to directly assess the blinking state of ensemble QDs in free solution. In this study, a new method was described to characterize the blinking state of the QDs in free solution by combining single molecule fluorescence correlation spectroscopy (FCS) with ensemble spectroscopic methods. Its principle is based on the observation that the apparent concentration of bright QDs obtained by FCS is less than its actual concentration measured by ensemble spectroscopic method due to the QDs blinking. We proposed a blinking index (Kblink) for characterizing the blinking state of QDs, and Kblink is defined as the ratio of the actual concentration (Cb,actual) measured by the ensemble spectroscopic method to the apparent concentration (Cb,app) of QDs obtained by FCS. The effects of certain factors such as laser intensity, growth process, and ligands on blinking of QDs were investigated. The Kblink data of QDs obtained were successfully used to characterize the blinking state of QDs and explain certain experimental results.

High loading MnO2 nanowires on graphene paper: facile electrochemical synthesis and use as flexible electrode for tracking hydrogen peroxide secretion in live cells

Recent progress in flexible and lightweight electrochemical sensor systems requires the development of paper-like electrode materials. Here, we report a facile and green synthesis of a new type of MnO2 nanowires-graphene nanohybrid paper by one-step electrochemical method. This strategy demonstrates a collection of unique features including the effective electrochemical reduction of graphene oxide (GO) paper and the high loading of MnO2 nanowires on electrochemical reduced GO (ERGO) paper. When used as flexible electrode for nonenzymatic detection of hydrogen peroxide (H2O2), MnO2-ERGO paper exhibits high electrocatalytic activity toward the redox of H2O2 as well as excellent stability, selectivity and reproducibility. The amperometric responses are linearly proportional to H2O2 concentration in the range 0.1-45.4 mM, with a detection limit of 10 μM (S/N=3) and detection sensitivity of 59.0 μA cm(-2) mM(-1). These outstanding sensing performances enable the practical application of MnO2-ERGO paper electrode for the real-time tracking H2O2 secretion by live cells macrophages. Therefore, the proposed graphene-based nanohybrid paper electrode with intrinsic flexibility, tailorable shapes and adjustable properties can contribute to the full realization of high-performance flexible electrode material used in point-of-care testing devices and portable instruments for in-vivo clinical diagnostics and on-site environmental monitoring.

Aminophenylboronic-acid-conjugated polyacrylic acid-Mn-doped ZnS quantum dot for highly sensitive discrimination of glycoproteins

Discrimination of glycoproteins with different glycans is a significant but difficult issue. We presented here a new strategy for strengthening the discrimination of glycoproteins by introducing a new signaling channel, fluorescence polarization (FP), into a "single probe with three signaling channels" sensor array. The single probe was aminophenylboronic-acid-conjugated poly(acrylic acid)-Mn-doped ZnS quantum dots, and the three signaling channels were FP, room temperature phosphorescence and light scattering. Ten glycoproteins, including ovalbumin, fibrinogen, transferrin, horseradish peroxidase, vascular endothelial growth factor, immunoglobulin G, avidin, hyaluronidase, cellulase R-10, and glucose oxidase, were involved for evaluating the discriminating capability. The introduction of the FP signaling channel improved the discriminating power of the sensor array, so that the 10 glycoproteins at 0.15 μM could be well discriminated both in PBS buffer and in the presence of human serum sample. The identification accuracy of the unknown samples was 96.25% (77 out of 80) at the 0.15 μM level and 97.50% (78 out of 80) at the 0.2 μM level. The integration of the signaling patterns with different responsive principles was demonstrated as the promising way to enhance the discrimination power of the single-probe-based sensor arrays.

Facile synthesis of ionic liquid functionalized silica-capped CdTe quantum dots for selective recognition and detection of hemoproteins

Novel ionic liquid functionalized silica-capped CdTe quantum dots were fabricated and used for the selective recognition and detection of hemoproteins.

Boronic Acid-based approach for separation and immobilization of glycoproteins and its application in sensing

Glycoproteins influence a broad spectrum of biological processes including cell-cell interaction, host-pathogen interaction, or protection of proteins against proteolytic degradation. The analysis of their glyco-structures and concentration levels are increasingly important in diagnosis and proteomics. Boronic acids can covalently react with cis-diols in the oligosaccharide chains of glycoproteins to form five- or six-membered cyclic esters. Based on this interaction, boronic acid-based ligands and materials have attracted much attention in both chemistry and biology as the recognition motif for enrichment and chemo/biosensing of glycoproteins in recent years. In this work, we reviewed the progress in the separation, immobilization and detection of glycoproteins with boronic acid-functionalized materials and addressed its application in sensing.

Sensitive and visible detection of apoptotic cells on Annexin-V modified substrate using aminophenylboronic acid modified gold nanoparticles (APBA-GNPs) labeling

A new strategy for sensitive detection of early stage apoptosis was proposed based on silver-enhanced gold nanoparticle (GNP) label method. Annexin-V modified substrate was constructed via layer-by-layer (LBL) method for specific capture of early stage apoptotic Jurkat cells. A new kind of aminophenylboronic acid modified gold nanoparticle (APBA-GNP) was synthesized and utilized for labeling cells, followed by silver enhancement. Anodic stripping voltammetry (ASV) was applied to sensitive detection of Ag(+) dissolved from the deposited silver particles, which reflected the number of cells. A good linear range from 1 × 10(2) to 3.5 × 10(3) cells was achieved, with a detection limit of 38 apoptotic cells. Moreover, the gray color of silver enhancement could be observed by the naked eye, which could be used to tell apoptotic cells apart from normal cells. Therefore, using the silver-enhanced GNP label method, apoptotic cells could not only be sensitively detected via electrochemical technique, but also can be discriminated from normal cells by the naked eye.

In situ recognition of cell-surface glycans and targeted imaging of cancer cells

Fluorescent sensors capable of recognizing cancer-associated glycans, such as sialyl Lewis X (sLe(x)) tetrasaccharide, have great potential for cancer diagnosis and therapy. Studies on water-soluble and biocompatible sensors for in situ recognition of cancer-associated glycans in live cells and targeted imaging of cancer cells are very limited at present. Here we report boronic acid-functionalized peptide-based fluorescent sensors (BPFSs) for in situ recognition and differentiation of cancer-associated glycans, as well as targeted imaging of cancer cells. By screening BPFSs with different structures, it was demonstrated that BPFS₁ with a FRGDF peptide could recognize cell-surface glycan of sLe(x) with high specificity and thereafter fluorescently label and discriminate cancer cells through the cooperation with the specific recognition between RGD and integrins. The newly developed peptide-based sensor will find great potential as a fluorescent probe for cancer diagnosis.

Layered double hydroxides as carriers for quantum dots@silica nanospheres

Quantum dot-hydrotalcite layered nanoplatforms were successfully prepared following a one-pot synthesis. The process is very fast and a priori delamination of hydrotalcite is not a prerequisite for the intercalation of quantum dots. The novel materials were extensively characterized by X-ray diffraction, thermogravimetry, infrared spectroscopy, transmission electron microscopy, true color fluorescence microscopy, photoluminescence, and nitrogen adsorption. The quantum dot-hydrotalcite nanomaterials display extremely high stability in mimicking physiological media such as saline serum (pH 5.5) and PBS (pH 7.2). Yet, quantum dot release from the solid structure is noted. In order to prevent the leaking of quantum dots we have developed a novel strategy which consists of using tailor made double layered hydrotalcites as protecting shells for quantum dots embedded into silica nanospheres without changing either the materials or the optical properties.

Self-assembled plasmonic vesicles of SERS-encoded amphiphilic gold nanoparticles for cancer cell targeting and traceable intracellular drug delivery

We report the development of bioconjugated plasmonic vesicles assembled from SERS-encoded amphiphilic gold nanoparticles for cancer-targeted drug delivery. This new type of plasmonic assemblies with a hollow cavity can play multifunctional roles as delivery carriers for anticancer drugs and SERS-active plasmonic imaging probes to specifically label targeted cancer cells and monitor intracellular drug delivery. We have shown that the pH-responsive disassembly of the plasmonic vesicle, stimulated by the hydrophobic-to-hydrophilic transition of the hydrophobic brushes in acidic intracellular compartments, allows for triggered intracellular drug release. Because self-assembled plasmonic vesicles exhibit significantly different plasmonic properties and greatly enhanced SERS intensity in comparison with single gold nanoparticles due to strong interparticle plasmonic coupling, disassembly of the vesicles in endocytic compartments leads to dramatic changes in scattering properties and SERS signals, which can serve as independent feedback mechanisms to signal cargo release from the vesicles. The unique structural and optical properties of the plasmonic vesicle have made it a promising platform for targeted combination therapy and theranostic applications by taking advantage of recent advances in gold nanostructure based in vivo bioimaging and photothermal therapy and their loading capacity for both hydrophilic (nucleic acids and proteins) and hydrophobic (small molecules) therapeutic agents.

Coating graphene paper with 2D-assembly of electrocatalytic nanoparticles: a modular approach toward high-performance flexible electrodes

The development of flexible electrodes is of considerable current interest because of the increasing demand for modern electronics, portable medical products, and compact energy devices. We report a modular approach to fabricating high-performance flexible electrodes by structurally integrating 2D-assemblies of nanoparticles with freestanding graphene paper. We have shown that the 2D array of gold nanoparticles at oil-water interfaces can be transferred on freestanding graphene oxide paper, leading to a monolayer of densely packed gold nanoparticles of uniform sizes loaded on graphene oxide paper. One major finding is that the postassembly electrochemical reduction of graphene oxide paper restores the ordered structure and electron-transport properties of graphene, and gives rise to robust and biocompatible freestanding electrodes with outstanding electrocatalytic activities, which have been manifested by the sensitive and selective detection of two model analytes: glucose and hydrogen peroxide (H(2)O(2)) secreted by live cells. The modular nature of this approach coupled with recent progress in nanocrystal synthesis and surface engineering opens new possibilities to systematically study the dependence of catalytic performance on the structural parameters and chemical compositions of the nanocrystals.