Saccharide-functionalized alkanethiols for fouling-resistant self-assembled monolayers: synthesis, monolayer properties, and antifouling behavior

New Insights on Biological Activities, Chemical Compositions, and Classifications of Marine Actinomycetes Antifouling Agents

Biofouling is the assemblage of undesirable biological materials and macro-organisms (barnacles, mussels, etc.) on submerged surfaces, which has unfavorable impacts on the economy and maritime environments. Recently, research efforts have focused on isolating natural, eco-friendly antifouling agents to counteract the toxicities of synthetic antifouling agents. Marine actinomycetes produce a multitude of active metabolites, some of which acquire antifouling properties. These antifouling compounds have chemical structures that fall under the terpenoids, polyketides, furanones, and alkaloids chemical groups. These compounds demonstrate eminent antimicrobial vigor associated with antiquorum sensing and antibiofilm potentialities against both Gram-positive and -negative bacteria. They have also constrained larval settlements and the acetylcholinesterase enzyme, suggesting a strong anti-macrofouling activity. Despite their promising in vitro and in vivo biological activities, scaled-up production of natural antifouling agents retrieved from marine actinomycetes remains inapplicable and challenging. This might be attributed to their relatively low yield, the unreliability of in vitro tests, and the need for optimization before scaled-up manufacturing. This review will focus on some of the most recent marine actinomycete-derived antifouling agents, featuring their biological activities and chemical varieties after providing a quick overview of the disadvantages of fouling and commercially available synthetic antifouling agents. It will also offer different prospects of optimizations and analysis to scale up their industrial manufacturing for potential usage as antifouling coatings and antimicrobial and therapeutic agents.

The immune-stealth polymeric coating on drug delivery nanocarriers: In vitro engineering and in vivo fate

Although essential nanosystems such as nanoparticles and nanocarriers are desirable options for transporting various drug molecules into the biological environment, they rapidly remove from the circulatory system due to their interaction with multiple in vivo barriers, especially the immune barrier, which will result in their short-term effects. In order to improve their effectiveness and durability in the circulatory system, the polymer coatings can use to cover the surface of nanoparticles and nanocarriers to conceal them from the immune system. Due to their different properties (like charge, elasticity, and hydrophilicity/hydrophobicity), these coatings can improve drug delivery nanosystem durability and therapeutic applications. The mentioned coatings have different types and are divided into various categories, such as synthetic polymers, polysaccharides, and zwitterionic polymers. Each of these polymers has unique properties based on its category, origin, and chemical structure that make them suitable for producing stealth drug delivery nanocarriers. In this review article, we have tried to explain the importance of these diverse polymer coatings in determining the fate of drug nanocarriers and then introduced the different types of these coatings and, finally, described various methods that directly and indirectly analyze the nanocoatings to determine the stability of nanoparticles in the body.

Synthesis of Structurally Defined Nitroxide Spin-Labeled Glycolipids as Useful Probes for Electron Paramagnetic Resonance (EPR) Spectroscopy Studies of Cell Surface Glycans

Four glycolipids carrying different glycans and a nitroxide free radical spin at the glycan non-reducing end were designed and synthesized from free glucose and maltooligosaccharides by an efficient and streamlined synthetic strategy. The main features of this synthetic strategy include regioselective functionalization of the free carbohydrates and coupling of the radical spin label with functionalized free glycans as the last synthetic step. These glycolipids are useful probes for the study of cell surface glycans by electron paramagnetic resonance spectroscopy. Moreover, the key synthetic intermediates, free glycolipids carrying a flexible azido group at the glycan non-reducing end, are widely useful platforms for accessing glycolipids with other molecular labels.

Effect of Multilayer Termination on Nonspecific Protein Adsorption and Antifouling Activity of Alginate-Based Layer-by-Layer Coatings

Layer-by-layer (LbL) assembly is a versatile platform for applying coatings and studying the properties of promising compounds for antifouling applications. Here, alginate-based LbL coatings were fabricated by alternating the deposition of alginic acid and chitosan or polyethylenimine to form multilayer coatings. Films were prepared with either odd or even bilayer numbers to investigate if the termination of the LbL coatings affects the physicochemical properties, resistance against the nonspecific adsorption (NSA) of proteins, and antifouling efficacy. The hydrophilic films, which were characterized using spectroscopic ellipsometry, water contact angle goniometry, ATR-FTIR spectroscopy, AFM, XPS, and SPR spectroscopy, revealed high swelling in water and strongly reduced the NSA of proteins compared to the hydrophobic reference. While the choice of the polycation was important for the protein resistance of the LbL coatings, the termination mattered less. The attachment of diatoms and settling of barnacle cypris larvae revealed good antifouling properties that were controlled by the termination and the charge density of the LbL films.

Amphiphilic Zwitterionic Acrylate/Methacrylate Copolymers for Marine Fouling-Release Coatings

Methacrylate and acrylate monomers are popular building blocks for antifouling (AF) and fouling-release (FR) coatings to counteract marine biofouling. They are used in various combinations and often combined into amphiphilic materials. This study investigated the FR properties of amphiphilic ethylene glycol dicyclopentenyl ether acrylate (DCPEA) and the corresponding methacrylate (DCPEMA) blended with 5 wt % zwitterionic carboxybetaine acrylate (CBA) and the corresponding methacrylate (CBMA). A series of (co)polymers with different acrylate/methacrylate compositions were synthesized and tested against the attachment of the diatom Navicula perminuta and in short-term dynamic field exposure experiments. The more hydrophobic methacrylate DCPEMA homopolymer outperformed its acrylate counterpart DCPEA. Incorporated zwitterionic functionality of both CBMA and CBA imparted ultralow fouling capability in the amphiphilic polymers toward diatom attachment, whereas in the real ocean environment, only the employment of CBMA reduced marine biofouling. Moreover, it was observed that CBA-containing coatings showed different surface morphologies and roughnesses compared to the CBMA analogues. Particularly, a high impact was found when acrylic CBA was mixed with methacrylic DCPEMA. While the wettability of the coatings was comparable, investigated methacrylates in general exhibited superior fouling resistance compared to the acrylates.

Layer-by-Layer Deposited Hybrid Polymer Coatings Based on Polysaccharides and Zwitterionic Silanes with Marine Antifouling Properties

Polyelectrolyte multilayer (PEM) assembly is a versatile tool to construct low-fouling coatings. For application in the marine environment, their structure needs to be stabilized by covalent linkage. Here, we introduce an approach for spin coating of silane-based sol-gel chemistries using layer-by-layer assembly of polysaccharide-based hybrid polymer coatings (LBLHPs). The silane sol-gel chemistry allows the films to be cross-linked under water-based and mild reaction conditions. Two different silanes were used for this purpose, a conventional triethoxymethyl silane and a de novo synthesized zwitterionic silane. The polysaccharide-silane hybrid polymer coatings were thoroughly characterized with spectroscopic ellipsometry, water contact angle (WCA) goniometry, attenuated total reflection-Fourier transform infrared spectroscopy, and atomic force microscopy. The coatings showed good stability in seawater, smooth surfaces, a high degree of hydration, and WCAs below or close to the Berg limit. LBLHPs showed low-fouling properties in biological assays against nonspecific protein adsorption, attachment of the diatom Navicula perminuta, and settlement of zoospores of the macroalga Ulva linza.

Sol-Gel-Based Hybrid Materials as Antifouling and Fouling-Release Coatings for Marine Applications

Hybrid materials (HMs) offer unique properties as they combine inorganic and organic components into a single material. Here, we developed HM coatings for marine antifouling applications using sol-gel chemistry and naturally occurring polysaccharides. The coatings were characterized by spectroscopic ellipsometry, contact angle goniometry, AFM, and ATR-FTIR, and their stability was tested in saline media. Marine antifouling and fouling-release properties were tested in laboratory assays against the settlement of larvae of the barnacle Balanus improvisus and against the settlement and removal of the diatom Navicula incerta. Furthermore, laboratory data were confirmed in short-term dynamic field assays in Florida, USA. All hybrid coatings revealed a superior performance in the assays compared to a hydrophobic reference. Within the hybrids, those with the highest degree of hydrophilicity and negative net charge across the surface performed best. Alginate and heparin showed good performance, making these hybrid materials promising building blocks for fouling-resistant coatings.

Red Algae-Derived Carrageenan Coatings for Marine Antifouling Applications

We report a facile approach for the fabrication of a marine antifouling coating using the red algae-derived polysaccharide, carrageenan (CAR). Because CAR is hydrophilic and negatively charged, we hypothesized that it would form strong hydration layers upon adsorption onto solid surfaces, thereby exhibiting marine antifouling properties. Although various types of CAR can be used for marine antifouling, a universally applicable coating method has not yet been developed; thus, a systematic study on the marine antifouling property of CAR coating is lacking. Here, we fabricated a versatile CAR coating via Zr^IV-mediated multiple cross-linking reactions between the sulfate groups of CAR and metal ions and successfully deposited κ-, ι-, and λ-CAR onto solid surfaces. Specifically, λ-CAR showed superior marine antifouling performance, as evidenced by the results of the marine diatom adhesion assays.

Anti-Biofouling Features of Eco-Friendly Oleamide-PDMS Copolymers

The biofouling of marine organisms on a surface induces serious economic damage. One of the conventional anti-biofouling strategies is the use of toxic chemicals. In this study, a new eco-friendly oleamide-PDMS copolymer (OPC) is proposed for sustainable anti-biofouling and effective drag reduction. The anti-biofouling characteristics of the OPC are investigated using algal spores and mussels. The proposed OPC is found to inhibit the adhesion of algal spores and mussels. The slippery features of the fabricated OPC surfaces are examined by direct measurement of pressure drops in channel flows. The proposed OPC surface would be utilized in various industrial applications including marine vehicles and biomedical devices.

Recent Developments in the Design of Non-Biofouling Coatings for Nanoparticles and Surfaces

Biofouling is a major issue in the field of nanomedicine and consists of the spontaneous and unwanted adsorption of biomolecules on engineered surfaces. In a biological context and referring to nanoparticles (NPs) acting as nanomedicines, the adsorption of biomolecules found in blood (mostly proteins) is known as protein corona. On the one hand, the protein corona, as it covers the NPs' surface, can be considered the biological identity of engineered NPs, because the corona is what cells will "see" instead of the underlying NPs. As such, the protein corona will influence the fate, integrity, and performance of NPs in vivo. On the other hand, the physicochemical properties of the engineered NPs, such as their size, shape, charge, or hydrophobicity, will influence the identity of the proteins attracted to their surface. In this context, the design of coatings for NPs and surfaces that avoid biofouling is an active field of research. The gold standard in the field is the use of polyethylene glycol (PEG) molecules, although zwitterions have also proved to be efficient in preventing protein adhesion and fluorinated molecules are emerging as coatings with interesting properties. Hence, in this review, we will focus on recent examples of anti-biofouling coatings in three main areas, that is, PEGylated, zwitterionic, and fluorinated coatings.

Plasmonic-based platforms for diagnosis of infectious diseases at the point-of-care

Infectious diseases such as HIV-1/AIDS, tuberculosis (TB), hepatitis B (HBV), and malaria still exert a tremendous health burden on the developing world, requiring rapid, simple and inexpensive diagnostics for on-site diagnosis and treatment monitoring. However, traditional diagnostic methods such as nucleic acid tests (NATs) and enzyme linked immunosorbent assays (ELISA) cannot be readily implemented in point-of-care (POC) settings. Recently, plasmonic-based biosensors have emerged, offering an attractive solution to manage infectious diseases in the developing world since they can achieve rapid, real-time and label-free detection of various pathogenic biomarkers. Via the principle of plasmonic-based optical detection, a variety of biosensing technologies such as surface plasmon resonance (SPR), localized surface plasmon resonance (LSPR), colorimetric plasmonic assays, and surface enhanced Raman spectroscopy (SERS) have emerged for early diagnosis of HIV-1, TB, HBV and malaria. Similarly, plasmonic-based colorimetric assays have also been developed with the capability of multiplexing and cellphone integration, which is well suited for POC testing in the developing world. Herein, we present a comprehensive review on recent advances in surface chemistry, substrate fabrication, and microfluidic integration for the development of plasmonic-based biosensors, aiming at rapid management of infectious diseases at the POC, and thus improving global health.

Lipid Bilayer-like Mixed Self-Assembled Monolayers with Strong Mobility and Clustering-Dependent Lectin Affinity

Glycans at the surface of cellular membranes modulate biological activity via multivalent association with extracellular messengers. The lack of tuneable simplified models mimicking this dynamic environment complicates basic studies of these phenomena. We here present a series of mixed reversible self-assembled monolayers (rSAMs) that addresses this deficiency. Mixed rSAMs were prepared in water by simple immersion of a negatively charged surface in a mixture of sialic acid- and hydroxy-terminated benzamidine amphiphiles. Surface compositions derived from infrared reflection-absorption spectroscopy (IRAS) and film thickness information (atomic force microscopy, ellipsometry) suggest the latter to be statistically incorporated in the monolayer. These surfaces' affinity for the lectin hemagglutinin revealed a strong dependence of the affinity on the presentation, density, and mobility of the sialic acid ligands. Hence, a spacer length of 4 ethylene glycol and a surface density of 15% resulted in a dissociation constant K_d,multi of 1.3 × 10^-13 M, on par with the best di- or tri-saccharide-based binders reported to date, whereas a density of 20% demonstrated complete resistance to hemagglutinin binding. These results correlated with ligand mobility measured by fluorescence recovery after photobleaching which showed a dramatic drop in the same interval. The results have a direct bearing on biological cell surface multivalent recognition involving lipid bilayers and may guide the design of model surfaces and sensors for both fundamental and applied studies.

Direct stimulation of cellular immune response via TLR2 signaling triggered by contact with hybrid glyco-biointerfaces composed of chitohexaose and cellohexaose

Recognition of carbohydrates by cell receptors activates various cell signaling processes. In this report, hybrid self-assembled monolayers (SAMs) of chitohexaose (βGlcNAc6) and cellohexaose (βGlc6) are prepared to induce a highly sensitive, glyco-density-dependent inflammatory response by HEK293 cells expressing toll-like receptor 2 (TLR2), which recognizes oligo-βGlcNAc moieties. Thiosemicarbazide-labeled βGlcNAc6 and βGlc6, as a bio-signal inducer and a spacer molecule, respectively, were immobilized on a gold substrate via spontaneous chemisorption to control the βGlcNAc6 density on the SAM surface. The βGlcNAc6 density ranged from 0 to 0.65 chains nm^-2. The inflammatory response of HEK293 cells varied as a function of the surface glyco-density, and the hybrid SAM with 0.146 chains nm^-2 of βGlcNAc6 induced a stronger response than pure βGlcNAc6-SAM with 0.654 chains nm^-2. Thus, direct activation of TLR2-mediated cellular stimulation triggered by as-designed glyco-biointerfaces was possible through a mutual interaction between the fittingly βGlcNAc6 moieties assembled on hybrid glyco-SAMs and TLR2 on the surface of HEK293 cells.

Mini-review: effect sizes and meta-analysis for antifouling research

It is widely recognised that findings from experimental studies should be replicated before their conclusions are accepted as definitive. In many research areas, synthesis of results from multiple studies is carried out via systematic review and meta-analysis. Some fields are also moving away from null hypothesis significance testing, which uses p values to identify 'significant' effects, towards an estimation approach concerned with effect sizes and confidence intervals. This review argues that these techniques are underused in biofouling and antifouling (AF) research and discusses potential benefits of their adoption. They enable comparison of test surfaces even when these are not tested simultaneously, and allow results from repeated tests on the same surfaces to be combined. They also enable the use of published data to explore effects of different variables on the functioning of AF surfaces. AF researchers should consider using these approaches and reporting results in ways that facilitate future research syntheses.

Sulfated glycopeptide nanostructures for multipotent protein activation

Biological systems have evolved to utilize numerous proteins with capacity to bind polysaccharides for the purpose of optimizing their function. A well-known subset of these proteins with binding domains for the highly diverse sulfated polysaccharides are important growth factors involved in biological development and tissue repair. We report here on supramolecular sulfated glycopeptide nanostructures, which display a trisulfated monosaccharide on their surfaces and bind five critical proteins with different polysaccharide-binding domains. Binding does not disrupt the filamentous shape of the nanostructures or their internal β-sheet backbone, but must involve accessible adaptive configurations to interact with such different proteins. The glycopeptide nanostructures amplified signalling of bone morphogenetic protein 2 significantly more than the natural sulfated polysaccharide heparin, and promoted regeneration of bone in the spine with a protein dose that is 100-fold lower than that required in the animal model. These highly bioactive nanostructures may enable many therapies in the future involving proteins.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

Functional Nanocomposites Based on Fibrous Clays

This chapter is focused on functional nanocomposites based on the use of the microfibrous clays sepiolite and palygorskite as efficient fillers for diverse types of polymer matrices, from typical thermoplastics to biopolymers. The main features that govern the interaction between the silicates and the polymer matrix are discussed. The introduction addresses the structural and textural features of the fibrous silicates, as well as the possible synthetic approaches to increase the compatibility of these nanofillers with the polymeric matrix. Additionally, these clays can be easily functionalized through their surface silanol groups based on chemical reactions or by anchoring of nanoparticles. This allows for the preparation of a wide variety of functional polymer–clay nanocomposites. Thereafter, some relevant examples of nanocomposites derived from conventional polymers are reported, as well as of those based on polymers that exhibit electrical conductivity. Lastly, selected works employing sepiolite or palygorskite as fillers in polymeric matrixes of natural origin are discussed, showing the wide application of these resulting nanocomposites as bioplastics, as well as in biomedicine, environmental remediation and the development of sensor devices.

Design and mechanisms of antifouling materials for surface plasmon resonance sensors

Surface plasmon resonance (SPR) biosensors have many possible applications, but are limited by sensor chip surface fouling, which blocks immobilization and specific binding by the recognizer elements. Therefore, there is a pressing need for the development of antifouling surfaces. In this paper, the mechanisms of antifouling materials were firstly discussed, including both theories (hydration and steric hindrance) and factors influencing antifouling effects (molecular structures and self-assembled monolayer (SAM) architectures, surface charges, molecular hydrophilicity, and grafting thickness and density). Then, the most recent advances in antifouling materials applied on SPR biosensors were systematically reviewed, together with the grafting strategies, antifouling capacity, as well as their merits and demerits. These materials included, but not limited to, zwitterionic compounds, polyethylene glycol-based, and polysaccharide-based materials. Finally, the prospective research directions in the development of SPR antifouling materials were discussed.

STATEMENT OF SIGNIFICANCE

Surface plasmon resonance (SPR) is a powerful tool in monitoring biomolecular interactions. The principle of SPR biosensors is the conversion of refractive index change caused by molecular binding into resonant spectral shifts. However, the fouling on the surface of SPR gold chips is ubiquitous and troublesome. It limits the application of SPR biosensors by blocking recognition element immobilization and specific binding. Hence, we write this paper to review the antifouling mechanisms and the recent advances of the design of antifouling materials that can improve the accuracy and sensitivity of SPR biosensors. To our knowledge, this is the first review focusing on the antifouling materials that were applied or had potential to be applied on SPR biosensors.

Self-Assembled Monolayers Generated from Unsymmetrical Partially Fluorinated Spiroalkanedithiols

Self-assembled monolayers (SAMs) were prepared on gold substrates from an unsymmetrical partially fluorinated spiroalkanedithiol adsorbate with the specific structure of [CH3(CH2)7][CF3(CF2)7(CH2)8]C[CH2SH]2 (SADT) and compared to SAMs formed from the semifluorinated monothiol F8H10SH [CF3(CF2)7(CH2)10SH] of analogous chain length and n-octadecanethiol. The adsorbate with two alkyl chains, one terminally fluorinated and the other nonfluorinated, was designed to form monolayers in which the bulky helical fluorocarbon segments assemble on top of an underlying layer of well-packed trans-extended alkyl chains. Different combinations of deposition solvents and temperatures were used to produce the bidentate SAMs. Characterization of the resulting monolayers revealed that SAMs formed in DMF at room temperature allow complete binding of the sulfur headgroups to the surface and exhibit higher conformational order than those produced using alternative solvent/temperature combinations. The reduced film thicknesses and enhanced wettability of the SADT SAMs, as compared to the SAMs generated from F8H10SH, suggest loose packing and an increase in the tilt of the terminal fluorocarbon chain segments. Nevertheless, the density of the underlying hydrocarbon chains of the SADT SAMs was higher than that of the F8H10SH SAMs, owing to the double-chained structure of the new adsorbate. The conformational orders of the SAM systems were observed to decrease as follows: C18SH > F8H10SH > SADT. However, the SAMs formed from this new double-chained bidentate adsorbate in DMF expose a fluorinated interface with a relatively low surface roughness, as determined by contact-angle hysteresis.

Superior Antifouling Performance of a Zwitterionic Peptide Compared to an Amphiphilic, Non-Ionic Peptide

The aim of this study was to explore the influence of amphiphilic and zwitterionic structures on the resistance of protein adsorption to peptide self-assembled monolayers (SAMs) and gain insight into the associated antifouling mechanism. Two kinds of cysteine-terminated heptapeptides were studied. One peptide had alternating hydrophobic and hydrophilic residues with an amphiphilic sequence of CYSYSYS. The other peptide (CRERERE) was zwitterionic. Both peptides were covalently attached onto gold substrates via gold-thiol bond formation. Surface plasmon resonance analysis results showed that both peptide SAMs had ultralow or low protein adsorption amounts of 1.97-11.78 ng/cm2 in the presence of single proteins. The zwitterionic peptide showed relatively higher antifouling ability with single proteins and natural complex protein media. We performed molecular dynamics simulations to understand their respective antifouling behaviors. The results indicated that strong surface hydration of peptide SAMs contributes to fouling resistance by impeding interactions with proteins. Compared to the CYSYSYS peptide, more water molecules were predicted to form hydrogen-bonding interactions with the zwitterionic CRERERE peptide, which is in agreement with the antifouling test results. These findings reveal a clear relation between peptide structures and resistance to protein adsorption, facilitating the development of novel peptide-containing antifouling materials.

Localized Surface Plasmon Resonance Biosensing: Current Challenges and Approaches

Localized surface plasmon resonance (LSPR) has emerged as a leader among label-free biosensing techniques in that it offers sensitive, robust, and facile detection. Traditional LSPR-based biosensing utilizes the sensitivity of the plasmon frequency to changes in local index of refraction at the nanoparticle surface. Although surface plasmon resonance technologies are now widely used to measure biomolecular interactions, several challenges remain. In this article, we have categorized these challenges into four categories: improving sensitivity and limit of detection, selectivity in complex biological solutions, sensitive detection of membrane-associated species, and the adaptation of sensing elements for point-of-care diagnostic devices. The first section of this article will involve a conceptual discussion of surface plasmon resonance and the factors affecting changes in optical signal detected. The following sections will discuss applications of LSPR biosensing with an emphasis on recent advances and approaches to overcome the four limitations mentioned above. First, improvements in limit of detection through various amplification strategies will be highlighted. The second section will involve advances to improve selectivity in complex media through self-assembled monolayers, “plasmon ruler” devices involving plasmonic coupling, and shape complementarity on the nanoparticle surface. The following section will describe various LSPR platforms designed for the sensitive detection of membrane-associated species. Finally, recent advances towards multiplexed and microfluidic LSPR-based devices for inexpensive, rapid, point-of-care diagnostics will be discussed.

Antifouling properties of oligo(lactose)-based self-assembled monolayers

The antifouling (AF) properties of oligo(lactose)-based self-assembled monolayers (SAMs), using four different proteins, zoospores of the green alga Ulva linza and cells of the diatom Navicula incerta, were investigated. The SAM-forming alkylthiols, which contained 1, 2 or 3 lactose units, showed significant variation in AF properties, with no differences in wettability. Non-specific adsorption of albumin and pepsin was low on all surfaces. Adsorption of lysozyme and fibrinogen decreased with increasing number of lactose units in the SAM, in agreement with the generally observed phenomenon that thicker hydrated layers provide higher barriers to protein adsorption. Settlement of spores of U. linza followed an opposite trend, being greater on the bulkier, more hydrated SAMs. These SAMs are more ordered for the larger saccharide units, and it is therefore hypothesized that the degree of order, and differences in crystallinity or stiffness between the surfaces, is an important parameter regulating spore settlement on these surfaces.

Grafting hyaluronic acid onto gold surface to achieve low protein fouling in surface plasmon resonance biosensors

Antifouling surfaces capable of reducing nonspecific protein adsorption from natural complex media are highly desirable in surface plasmon resonance (SPR) biosensors. A new protein-resistant surface made through the chemical grafting of easily available hyaluronic acid (HA) onto gold (Au) substrate demonstrates excellent antifouling performance against protein adsorption. AFM images showed the uniform HA layer with a thickness of ∼10.5 nm on the Au surface. The water contact angles of Au surfaces decreased from 103° to 12° with the covalent attachment of a carboxylated HA matrix, indicating its high hydrophilicity mainly resulted from carboxyl and amide groups in the HA chains. Using SPR spectroscopy to investigate nonspecific adsorption from single protein solutions (bovine serum albumin (BSA), lysozyme) and complex media (soybean milk, cow milk, orange juice) to an HA matrix, it was found that ultralow or low protein adsorptions of 0.6-16.1 ng/cm(2) (e.g., soybean milk: 0.6 ng/cm(2)) were achieved on HA-Au surfaces. Moreover, anti-BSA was chosen as a model recognition molecule to characterize the immobilization capacity and the antifouling performance of anti-BSA/HA surfaces. The results showed that anti-BSA/HA sensor surfaces have a high anti-BSA loading of 780 ng/cm(2), together with achieving the ultralow (<3 ng/cm(2) for lysozyme and soybean milk) or low (<17 ng/cm(2) for cow milk and 10% blood serum) protein adsorptions. Additionally, the sensor chips also exhibited a high sensitivity to BSA over a wide range of concentrations from 15 to 700 nM. Our results demonstrate a promising antifouling surface using extremely hydrophilic HA as matrix to resist nonspecific adsorption from complex media in SPR biosensors.

Hydration and chain entanglement determines the optimum thickness of poly(HEMA-co-PEG₁₀MA) brushes for effective resistance to settlement and adhesion of marine fouling organisms

Understanding how surface physicochemical properties influence the settlement and adhesion of marine fouling organisms is important for the development of effective and environmentally benign marine antifouling coatings. We demonstrate that the thickness of random poly(HEMA-co-PEG10MA) copolymer brushes affect antifouling behavior. Films of thicknesses ranging from 50 to 1000 Å were prepared via surface-initiated atom-transfer radical polymerization and characterized using infrared spectroscopy, ellipsometry, atomic force microscopy and contact angle measurements. The fouling resistance of these films was investigated by protein adsorption, attachment of the marine bacterium Cobetia marina, settlement and strength of attachment tests of zoospores of the marine alga Ulva linza and static immersion field tests. These assays show that the polymer film thickness influenced the antifouling performance, in that there is an optimum thickness range, 200-400 Å (dry thickness), where fouling of all types, as well as algal spore adhesion, was lower. Field test results also showed lower fouling within the same thickness range after 2 weeks of immersion. Studies by quartz crystal microbalance with dissipation and underwater captive bubble contact angle measurements show a strong correlation between lower fouling and higher hydration, viscosity and surface energy of the poly(HEMA-co-PEG10MA) brushes at thicknesses around 200-400 Å. We hypothesize that the reduced antifouling performance is caused by a lower hydration capacity of the polymer for thinner films, and that entanglement and crowding in the film reduces the conformational freedom, hydration capacity and fouling resistance for thicker films.

68Ga-labeled gold glyconanoparticles for exploring blood-brain barrier permeability: preparation, biodistribution studies, and improved brain uptake via neuropeptide conjugation

New tools and techniques to improve brain visualization and assess drug permeability across the blood-brain barrier (BBB) are critically needed. Positron emission tomography (PET) is a highly sensitive, noninvasive technique that allows the evaluation of the BBB permeability under normal and disease-state conditions. In this work, we have developed the synthesis of novel water-soluble and biocompatible glucose-coated gold nanoparticles (GNPs) carrying BBB-permeable neuropeptides and a chelator of the positron emitter (68)Ga as a PET reporter for in vivo tracking biodistribution. The small GNPs (2 nm) are stabilized and solubilized by a glucose conjugate. A NOTA ligand is the chelating agent for the (68)Ga, and two related opioid peptides are used as targeting ligands for improving BBB crossing. The radioactive labeling of the GNPs is completed in 30 min at 70 °C followed by purification via centrifugal filtration. As a proof of principle, a biodistribution study in rats is performed for the different (68)Ga-GNPs. The accumulation of radioactivity in different organs after intravenous administration is measured by whole body PET imaging and gamma counter measurements of selected organs. The biodistribution of the (68)Ga-GNPs varies depending on the ligands, as GNPs with the same gold core size show different distribution profiles. One of the targeted (68)Ga-GNPs improves BBB crossing near 3-fold (0.020 ± 0.0050% ID/g) compared to nontargeted GNPs (0.0073 ± 0.0024% ID/g) as measured by dissection and tissue counting.

Antifouling glycocalyx-mimetic peptoids

The glycocalyx of the cell is composed of highly hydrated saccharidic groups conjugated to protein and lipid cores. Although components of the glycocalyx are important in cell-cell interactions and other specific biological recognition events, a fundamental role of the glycocalyx is the inhibition of nonspecific interactions at the cell surface. Inspired by glycoproteins present in the glycocalyx, we describe a new class of synthetic antifouling polymer composed of saccharide containing N-substituted polypeptide (glycopeptoid). Grafting of glycopeptoids to a solid surface resulted in a biomimetic shielding layer that dramatically reduced nonspecific protein, fibroblast, and bacterial cell attachment. All-atom molecular dynamics simulation of grafted glycopeptoids revealed an aqueous interface enriched in highly hydrated saccharide residues. In comparison to saccharide-free peptoids, the interfacial saccharide residues of glycopeptoids formed a higher number of hydrogen bonds with water molecules. Moreover, these hydrogen bonds displayed a longer persistence time, which we believe contributed to fouling resistance by impeding interactions with biomolecules. Our findings suggest that the fouling resistance of glycopeptoids can be explained by the presence of both a 'water barrier' effect associated with the hydrated saccharide residues as well as steric hindrance from the polymer backbone.

Electrochemical characterization of globotriose-containing self-assembled monolayers on nanoporous gold and their binding of soybean agglutinin

Self-assembled monolayers (SAMs) of α-D-Gal-(1→4)-β-D-Gal-(1→4)-β-D-Glc-mercaptooctane (globotriose, Gb3-C8-SH) were prepared both as single-component SAMs and as mixed SAMs with either octanethiol (OCT) or 8-mercapto-3,6-dioxaoctanol (HO-PEG2-SH), on flat gold and on nanoporous gold (NPG) electrodes. The binding of soybean agglutinin (SBA) to the globotriose (Gb3) unit in the SAMs was then studied using electrochemical impedance spectroscopy (EIS), which is a label free method found to be quite sensitive to SAM composition and to the differences in SAM structure on NPG versus on flat Au. The affinity of SBA to the mixed SAM of HO-PEG2-SH and Gb3-C8-SH on NPG is found to be greater on NPG than on flat gold, and indicates a potential advantage for NPG as a substrate. The SAMs of HO-PEG2-SH were found to resist protein adsorption on either NPG or flat gold. The non-specific adsorption of SBA to OCT SAMs on flat Au was observed in EIS by the increase in charge transfer resistance; whereas, the increase seen on the NPG surface was smaller, and suggests that EIS measurements on NPG are less affected by non-specific protein adsorption. Atomic force microscopy (AFM) images of the SBA binding to mixed SAM of HO-PEG2-SH and Gb3-C8-SH on NPG showed a greater number of proteins on top of the OCT containing SAMs.

Adhesion of marine fouling organisms on hydrophilic and amphiphilic polysaccharides

Polysaccharides are a promising material for nonfouling surfaces because their chemical composition makes them highly hydrophilic and able to form water-storing hydrogels. Here we investigated the nonfouling properties of hyaluronic acid (HA) and chondroitin sulfate (CS) against marine fouling organisms. Additionally, the free carboxyl groups of HA and CS were postmodified with the hydrophobic trifluoroethylamine (TFEA) to block free carboxyl groups and render the surfaces amphiphilic. All coatings were tested with respect to their protein resistance and against settlement and adhesion of different marine fouling species. Both the settlement and adhesion strength of a marine bacterium (Cobetia marina), zoospores of the seaweed Ulva linza, and cells of a diatom (Navicula incerta) were reduced compared to glass control surfaces. In most cases, TFEA capping increased or maintained the performance of the HA coatings, whereas for the very well performing CS coatings the antifouling performance was reduced after capping.