Lectin-Tagged Fluorescent Polymeric Nanoparticles for Targeting of Sialic Acid on Living Cells

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.

Covalent and Noncovalent Conjugation of Degradable Polymer Nanoparticles to T Lymphocytes

Cells are attractive as carriers that can help to enhance control over the biodistribution of polymer nanomedicines. One strategy to use cells as carriers is based on the cell surface immobilization of the nanoparticle cargo. While a range of strategies can be used to immobilize nanoparticles on cell surfaces, only limited effort has been made to investigate the effect of these surface modification chemistries on cell viability and functional properties. This study has explored seven different approaches for the immobilization of poly(lactic acid) (PLA) nanoparticles on the surface of two different T lymphocyte cell lines. The cell lines used were human Jurkat T cells and CD4⁺ T_EM cells. The latter cells possess blood-brain barrier (BBB) migratory properties and are attractive for the development of cell-based delivery systems to the central nervous system (CNS). PLA nanoparticles were immobilized either via covalent active ester-amine, azide-alkyne cycloaddition, and thiol-maleimide coupling, or via noncovalent approaches that use lectin-carbohydrate, electrostatic, or biotin-NeutrAvidin interactions. The cell surface immobilization of the nanoparticles was monitored with flow cytometry and confocal microscopy. By tuning the initial nanoparticle/cell ratio, T cells can be decorated with up to ∼185 nanoparticles/cell as determined by confocal microscopy. The functional properties of the nanoparticle-decorated cells were assessed by evaluating their binding to ICAM-1, a key protein involved in the adhesion of CD4⁺ T_EM cells to the BBB endothelium, as well as in a two-chamber model in vitro BBB migration assay. It was found that the migratory behavior of CD4⁺ T_EM cells carrying carboxylic acid-, biotin-, or Wheat germ agglutinin (WGA)-functionalized nanoparticles was not affected by the presence of the nanoparticle payload. In contrast, however, for cells decorated with maleimide-functionalized nanoparticles, a reduction in the number of migratory cells compared to the nonmodified control cells was observed. Investigating and understanding the impact of nanoparticle-cell surface conjugation chemistries on the viability and properties of cells is important to further improve the design of cell-based nanoparticle delivery systems. The results of this study present a first step in this direction and provide first guidelines for the surface modification of T cells, in particular in view of their possible use for drug delivery to the CNS.

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.

Interdependency of influential parameters in therapeutic nanomedicine

Introduction:Current challenges to successful clinical translation of therapeutic nanomedicine have discouraged many stakeholders, including patients. Significant effort has been devoted to uncovering the reasons behind the less-than-expected success, beyond failures or ineffectiveness, of therapeutic nanomedicine products (e.g. cancer nanomedicine). Until we understand and address the factors that limit the safety and efficacy of NPs, both individually and in combination, successful clinical development will lag.Areas covered:This review highlights the critical roles of interdependent factors affecting the safety and therapeutic efficacy of therapeutic NPs for drug delivery applications.Expert opinion:Deep analysis of the current nanomedical literature reveals ahistory of unanticipated complexity by awide range of stakeholders including researchers. In the manufacture of nanomedicines themselves, there have been persistent difficulties with reproducibility and batch-to-batch variation. The unanticipated complexity and interdependency of nano-bio parameters has delayed our recognition of important factors affecting the safety and therapeutic efficacy of nanomedicine products. These missteps have had many factors including our lack of understanding of the interdependency of various factors affecting the biological identity and fate of NPs and biased interpretation of data. All these issues could raise significant concern regarding the reproducibility- or even the validity- of past publications that in turn formed the basis of many clinical trials of therapeutic nanomedicines. Therefore, the individual and combined effects of previously overlooked factors on the safety and therapeutic efficacy of NPs need to be fully considered in nanomedicine reports and product development.

Self-Assembled Nanorods of Phenylboronic Acid Functionalized Pyrene for In Situ Two-Photon Imaging of Cell Surface Sialic Acids and Photodynamic Therapy

Sialic acid (SA) plays important roles in various biological and pathological processes. Methods for monitoring and detection of SA are of great significance in terms of fundamental research, cancer diagnostics, and therapeutics, which are still limited until now. Here, a phenylboronic acid (PBA)-functionalized pyrene derivative, 4-(4-(pyren-1-yl)butyramido)phenylboronic acid (Py-PBA), was synthesized and used as a building block for self-assembling into hydrophilic nanorods. The Py-PBA nanorods (Py-PBA NRs) featured highly specific and efficient imaging of SA on living cells with the advantages of excellent fluorescence stability, good biocompatibility, and unique two-photon fluorescence properties. Meanwhile, the assembled Py-PBA NRs could efficiently generate ¹O₂ under two-photon irradiation, making it an excellent candidate for photodynamic therapy. This nanoplatform realized in situ recognition and two-photon imaging of SA on the cell surface as well as effective cancer cell therapy, providing a potential method for simple and selective analysis of SA in living cells and a new prospect for image-guided therapy.

Carbohydrate-based nanocarriers and their application to target macrophages and deliver antimicrobial agents

Many deadly infections are produced by microorganisms capable of sustained survival in macrophages. This reduces exposure to chemadrotherapy, prevents immune detection, and is akin to criminals hiding in police stations. Therefore, the use of glyco-nanoparticles (GNPs) as carriers of therapeutic agents is a burgeoning field. Such an approach can enhance the penetration of drugs into macrophages with specific carbohydrate targeting molecules on the nanocarrier to interact with macrophage lectins. Carbohydrates are natural biological molecules and the key constituents in a large variety of biological events such as cellular communication, infection, inflammation, enzyme trafficking, cellular migration, cancer metastasis and immune functions. The prominent characteristics of carbohydrates including biodegradability, biocompatibility, hydrophilicity and the highly specific interaction of targeting cell-surface receptors support their potential application to drug delivery systems (DDS). This review presents the 21^st century development of carbohydrate-based nanocarriers for drug targeting of therapeutic agents for diseases localized in macrophages. The significance of natural carbohydrate-derived nanoparticles (GNPs) as anti-microbial drug carriers is highlighted in several areas of treatment including tuberculosis, salmonellosis, leishmaniasis, candidiasis, and HIV/AIDS.

Graphitic carbon nitride quantum dots as analytical probe for viewing sialic acid on the surface of cells and tissues

The abnormal expression of sialic acids (SAs) on cells and tissues is closely related to various pathophysiological states. Here we applied phenylboronic acid (PBA) functionalized graphitic carbon nitride fluorescent quantum dots (PCQDs) with sizes from 3 to 5 nm in efficient and selective labeling SAs on the surface of living cells and tissues. With abundant PBA in their structure, the water soluble PCQDs showed the relative SA level on the cell surface via selectively and efficiently staining different cell lines in 30 min and revealed that M1 macrophages may express more SAs on their surfaces compared with M0 and M2. The distinct demarcation of cancerous and para-noncancerous areas on cancer tissue sections was showed by PCQDs staining. PCQDs with their high selectivity, stable photoluminescence, low cost, and nontoxicity can be an ideal SA fluorescent probe for living cells and tissues.

[Negative regulation of gastric proton pump by desialylation suggested by fluorescent imaging with the sialic acid-specific nanoprobe]

Gastric proton pump (H⁺,K⁺-ATPase) which is responsible for H⁺ secretion of gastric acid (HCl) in gastric parietal cells is the major therapeutic target for treatment of acid-related diseases. H⁺,K⁺-ATPase consists of two subunits, a catalytic α-subunit (αHK) and a glycosylated β-subunit (βHK). N-glycosylation of βHK is essential for trafficking and stability of αHK in apical membrane of gastric parietal cells. Terminal sialic acid residues on sugar chains have an important role in various cellular functions. Recently, we succeeded in visualizing the sialylation and desialylation dynamics of βHK using a fluorescence bioimaging nanoprobe consisting of biocompatible polymers conjugated with lectins for detecting sialic acid. In H⁺,K⁺-ATPase-expressing cell lines, rat gastric mucosa, and primary culture of rat gastric parietal cells, fluorescence imaging of sialic acid with the nanoprobe showed that sialylation of βHK is regulated by intragastric pH and that inhibition of gastric acid secretion induces desialylation of βHK. In biochemical and pharmacological studies, we revealed that enzyme activity of αHK is negatively regulated by desialylation of βHK. Our studies uncovered a novel negative-feedback mechanism of H⁺,K⁺-ATPase in which sialic acids of βHK positively regulates H⁺,K⁺-ATPase activity, and acidic pH decreases the pump activity by cleaving sialic acids of βHK. In this topic, we introduce the overview of our research using the bioimaging nanoprobe.

Detection of analytes in mitochondria without interference from other sites based on an innovative ratiometric fluorophore

Mitochondria are vital organelles that not only produce cellular energy but also participate in many biological processes. Recently, various fluorescent probes have been developed for mitochondrial imaging. However, due to the lack of suitable dyes or strategies, it is difficult for most reported mitochondrial targeting probes to prove whether the analytes they detected are from mitochondria. In addition, positive charge on mitochondrial probes can seriously affect the mitochondrial environment. To address these issues, we herein put forward a novel strategy for probe design based on a smart NIR dye (HDFL) for mitochondrial targeting detection. Compared to general mitochondrial targeting probes that are modified with a target site and a reaction site, the new strategy is to combine the two sites together for a mitochondrial probe that would provide accurate detection of analytes in mitochondria without interference. As a proof of concept, we synthesized a mitochondrial-targetable probe HDFL-Cys for cysteine. Bioimaging studies have shown that the new type of probe HDFL-Cys can first accumulate in mitochondria and then react with the analyte (cysteine) accompanied by the departure of the targeting group (lipophilic cation moieties). Thus, it can specifically detect the analyte in mitochondria without interference from extra-mitochondrial analytes. We anticipate that the new strategy based on the novel NIR dye HDFL may be a potential platform for developing desirable ratiometric fluorescent probes for mitochondrial imaging.

Dependence of Nanoparticle Toxicity on Their Physical and Chemical Properties

Studies on the methods of nanoparticle (NP) synthesis, analysis of their characteristics, and exploration of new fields of their applications are at the forefront of modern nanotechnology. The possibility of engineering water-soluble NPs has paved the way to their use in various basic and applied biomedical researches. At present, NPs are used in diagnosis for imaging of numerous molecular markers of genetic and autoimmune diseases, malignant tumors, and many other disorders. NPs are also used for targeted delivery of drugs to tissues and organs, with controllable parameters of drug release and accumulation. In addition, there are examples of the use of NPs as active components, e.g., photosensitizers in photodynamic therapy and in hyperthermic tumor destruction through NP incorporation and heating. However, a high toxicity of NPs for living organisms is a strong limiting factor that hinders their use in vivo. Current studies on toxic effects of NPs aimed at identifying the targets and mechanisms of their harmful effects are carried out in cell culture models; studies on the patterns of NP transport, accumulation, degradation, and elimination, in animal models. This review systematizes and summarizes available data on how the mechanisms of NP toxicity for living systems are related to their physical and chemical properties.

Lectin-conjugated pH-responsive mesoporous silica nanoparticles for targeted bone cancer treatment

A novel multifunctional nanodevice based in doxorubicin (DOX)-loaded mesoporous silica nanoparticles (MSNs) as nanoplatforms for the assembly of different building blocks has been developed for bone cancer treatment. These building blocks consists of: i) a polyacrylic acid (PAA) capping layer grafted to MSNs via an acid-cleavable acetal linker, to minimize premature cargo release and provide the nanosystem of pH-responsive drug delivery ability; and ii) a targeting ligand, the plant lectin concanavalin A (ConA), able to selectively recognize, bind and internalize owing to certain cell-surface glycans, such as sialic acids (SA), overexpressed in given tumor cells. This multifunctional nanosystem exhibits a noticeable higher internalization degree into human osteosarcoma cells (HOS), overexpressing SA, compared to healthy preosteoblast cells (MC3T3-E1). Moreover, the results indicate that small DOX loading (2.5 µg mL^-1) leads to almost 100% of osteosarcoma cell death in comparison with healthy bone cells, which significantly preserve their viability. Besides, this nanodevice has a cytotoxicity on tumor cells 8-fold higher than that caused by the free drug. These findings demonstrate that the synergistic combination of different building blocks into a unique nanoplatform increases antitumor effectiveness and decreases toxicity towards normal cells. This line of attack opens up new insights in targeted bone cancer therapy.

STATEMENT OF SIGNIFICANCE

The development of highly selective and efficient tumor-targeted smart drug delivery nanodevices remains a great challenge in nanomedicine. This work reports the design and optimization of a multifunctional nanosystem based on mesoporous silica nanoparticles (MSNs) featuring selectivity towards human osteosarcoma cells and pH-responsive antitumor drug delivery capability. The novelty and originality of this manuscript relies on proving that the synergistic assembly of different building blocks into a unique nanoplatform increases antitumor effectiveness and decreases toxicity towards healthy cells, which constitutes a new paradigm in targeted bone cancer therapy.

Development of Sialic Acid-coated Nanoparticles for Targeting Cancer and Efficient Evasion of the Immune System

Evading the reticuloendothelial system (RES) remains a critical challenge in the development of efficient delivery and diagnostic systems for cancer. Sialic acid (N-acetylneuraminic acid, Neu5Ac) is recognized as a "self" marker by major serum protein complement factor H and shows reduced interaction with the innate immune system via sialic acid-binding immunoglobulin-like lectin (Siglec), which is known as one of the significant regulators of phagocytic evasion. Accordingly, we prepared different surface-modified gold nanoparticles (AuNPs) and investigated the effects of sialic acid on cellular and immune responses of nanoparticles in vitro and in vivo. Sialic acid modification not only facilitates evasion of the RES by suppressing the immune response, but also enhances tumor accumulation via its active targeting ability. Therefore, sialic acid modification presents a promising strategy to advance nanotechnology towards the prospect of clinical translation.

An approach to the research on ion and water properties in the interphase between the plasma membrane and bulk extracellular solution

In vivo, cells are immersed in an extracellular solution that contains a variety of bioactive substances including ions and water. Classical electrophysiological analyses of epithelial cells in the stomach and small intestine have revealed that within a distance of several hundred micrometers above their apical plasma membrane, lies an extracellular layer that shows ion concentration gradients undetectable in the bulk phase. This “unstirred layer”, which contains stagnant solutes, may also exist between the bulk extracellular solution and membranes of other cells in an organism and may show different properties. On the other hand, an earlier study using a bacterial planar membrane indicated that H⁺ released from a transporter migrates in the horizontal direction along the membrane surface much faster than it diffuses vertically toward the extracellular space. This result implies that between the membrane surface and unstirred layer, there is a “nanointerface” that has unique ionic dynamics. Advanced technologies have revealed that the nanointerface on artificial membranes possibly harbors a highly ordered assembly of water molecules. In general, hydrogen bonds are involved in formation of the ordered water structure and can mediate rapid transfer of H⁺ between neighboring molecules. This description may match the phenomenon on the bacterial membrane. A recent study has suggested that water molecules in the nanointerface regulate the gating of K⁺ channels. Here, the region comprising the unstirred layer and nanointerface is defined as the interphase between the plasma membrane and bulk extracellular solution (iMES). This article briefly describes the physicochemical properties of ions and water in the iMES and their physiological significance. We also describe the methodologies that are currently used or will be applicable to the interphase research.

Targeted systemic mesenchymal stem cell delivery using hyaluronate - wheat germ agglutinin conjugate

A variety of receptors for hyaluronate (HA), a natural linear polysaccharide, were found in the body, which have been exploited as target sites for HA-based drug delivery systems. In this work, mesenchymal stem cells (MSCs) were surface-modified with HA - wheat germ agglutinin (WGA) conjugate for targeted systemic delivery of MSCs to the liver. WGA was conjugated to HA by coupling reaction between aldehyde-modified HA and amine group of WGA. The conjugation of WGA to HA was corroborated by gel permeation chromatography (GPC) and the successful surface modification of MSCs with HA-WGA conjugate was confirmed by confocal microscopy. The synthesized HA-WGA conjugate could be incorporated onto the cellular membrane by agglutinating the cell-associated carbohydrates. Fluorescent imaging for in vivo biodistribution visualized the targeted delivery of the HA-WGA/MSC complex to the liver after intravenous injection. This new strategy for targeted delivery of MSCs using HA-WGA conjugate might be successfully exploited for various regenerative medicines including cell therapy.

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.

Analysis of the Changes in Expression Levels of Sialic Acid on Influenza-Virus-Infected Cells Using Lectin-Tagged Polymeric Nanoparticles

Viral infections affect millions around the world, sometimes leading to severe consequences or even epidemics. Understanding the molecular dynamics during viral infections would provide crucial information for preventing or stopping the progress of infections. However, the current methods often involve the disruption of the infected cells or expensive and time-consuming procedures. In this study, fluorescent polymeric nanoparticles were fabricated and used as bioimaging nanoprobes that can monitor the progression of influenza viral infection through the changes in the expression levels of sialic acids expressed on the cell membrane. The nanoparticles were composed of a biocompatible monomer to prevent non-specific interactions, a hydrophobic monomer to form the core, a fluorescent monomer, and a protein-binding monomer to conjugate lectin, which binds sialic acids. It was shown that these lectin-tagged nanoparticles that specifically target sialic acids could track the changes in the expression levels of sialic acids caused by influenza viral infections in human lung epithelial cells. There was a sudden drop in the levels of sialic acid at the initial onset of virus infection (t = 0~1 h) and at approximately 4~5 h post-infection. The latter drop correlated with the production of viral proteins that was confirmed using traditional techniques. Thus, the accuracy, the rapidity and the efficacy of the nanoprobes were demonstrated. Such molecular bioimaging tools, which allow easy-handling and in situ monitoring, would be useful to directly observe and decipher the viral infection mechanisms.

Fluorescent Polymer Nanoparticles Based on Dyes: Seeking Brighter Tools for Bioimaging

Speed, resolution and sensitivity of today's fluorescence bioimaging can be drastically improved by fluorescent nanoparticles (NPs) that are many-fold brighter than organic dyes and fluorescent proteins. While the field is currently dominated by inorganic NPs, notably quantum dots (QDs), fluorescent polymer NPs encapsulating large quantities of dyes (dye-loaded NPs) have emerged recently as an attractive alternative. These new nanomaterials, inspired from the fields of polymeric drug delivery vehicles and advanced fluorophores, can combine superior brightness with biodegradability and low toxicity. Here, we describe the strategies for synthesis of dye-loaded polymer NPs by emulsion polymerization and assembly of pre-formed polymers. Superior brightness requires strong dye loading without aggregation-caused quenching (ACQ). Only recently several strategies of dye design were proposed to overcome ACQ in polymer NPs: aggregation induced emission (AIE), dye modification with bulky side groups and use of bulky hydrophobic counterions. The resulting NPs now surpass the brightness of QDs by ≈10-fold for a comparable size, and have started reaching the level of the brightest conjugated polymer NPs. Other properties, notably photostability, color, blinking, as well as particle size and surface chemistry are also systematically analyzed. Finally, major and emerging applications of dye-loaded NPs for in vitro and in vivo imaging are reviewed.

An overview of nanoparticles commonly used in fluorescent bioimaging

This article gives an overview of the various kinds of nanoparticles (NPs) that are widely used for purposes of fluorescent imaging, mainly of cells and tissues. Following an introduction and a discussion of merits of fluorescent NPs compared to molecular fluorophores, labels and probes, the article assesses the kinds and specific features of nanomaterials often used in bioimaging. These include fluorescently doped silicas and sol-gels, hydrophilic polymers (hydrogels), hydrophobic organic polymers, semiconducting polymer dots, quantum dots, carbon dots, other carbonaceous nanomaterials, upconversion NPs, noble metal NPs (mainly gold and silver), various other nanomaterials, and dendrimers. Another section covers coatings and methods for surface modification of NPs. Specific examples on the use of nanoparticles in (a) plain fluorescence imaging of cells, (b) targeted imaging, (c) imaging of chemical species, and (d) imaging of temperature are given next. A final section covers aspects of multimodal imaging (such as fluorescence/nmr), imaging combined with drug and gene delivery, or imaging combined with therapy or diagnosis. The electronic supplementary information (ESI) gives specific examples for materials and methods used in imaging, sensing, multimodal imaging and theranostics such as imaging combined with drug delivery or photodynamic therapy. The article contains 273 references in the main part, and 157 references in the ESI.

Conventional fluorophore-free dual pH- and thermo-responsive luminescent alternating copolymer

Herein, we have designed and synthesized a novel traditional fluorophore-free water-soluble fluorescent copolymer based on a poly(maleimide-alt-styrene) skeleton, which responds to both pH and temperature in aqueous medium.

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.