Quantitative and reversible lectin-induced association of gold nanoparticles modified with alpha-lactosyl-omega-mercapto-poly(ethylene glycol)

Peptide-capped gold nanoparticle for colorimetric immunoassay of conjugated abscisic acid

The pentapeptide Cys-Ala-Leu-Asn-Asn (CALNN) has been proved to be a powerful tool to stabilize the AuNPs. These CALNN-capped AuNPs have been used to develop various bioanalysis platforms. In this paper, the CALNN-capped AuNPs are proved to be a robust tool for aggregation-based colorimetric immunoassays as well. A colorimetric immunoassay strategy based upon the antibody-induced assembly of functionalized AuNPs for Abscisic Acid glucose ester (ABA-GE) determination has been developed. The ABA-functionalized AuNPs aggregate in the presence of specific antibody, accompanied by a color change of the solution. The color change is competitively inhibited by ABA-GE. The interparticle distance in aggregates is small due to the thin peptide layer on the AuNPs surface, and it is determined by the "Y" shape antibody linker as well. As a result of that, an obvious color change in the immunoassays is observed. Under the optimized conditions, a linear response range from 5 nM to 10 μM for ABA-GE determination is obtained, and the limit of detection (LOD) is evaluated to be 2.2 nM. This method is simple, homogeneous, and has potential for visual detection of ABA-GE.

Synthetic polymer nanoparticle-polysaccharide interactions: a systematic study

The interaction between synthetic polymer nanoparticles (NPs) and biomacromolecules (e.g., proteins, lipids, and polysaccharides) can profoundly influence the NPs fate and function. Polysaccharides (e.g., heparin/heparin sulfate) are a key component of cell surfaces and the extracelluar matrix and play critical roles in many biological processes. We report a systematic investigation of the interaction between synthetic polymer nanoparticles and polysaccharides by ITC, SPR, and an anticoagulant assay to provide guidelines to engineer nanoparticles for biomedical applications. The interaction between acrylamide nanoparticles (~30 nm) and heparin is mainly enthalpy driven with submicromolar affinity. Hydrogen bonding, ionic interactions, and dehydration of polar groups are identified to be key contributions to the affinity. It has been found that high charge density and cross-linking of the NP can contribute to high affinity. The affinity and binding capacity of heparin can be significantly diminished by an increase in salt concentration while only slightly decreased with an increase of temperature. A striking difference in binding thermodynamics has been observed when the main component of a polymer nanoparticle is changed from acrylamide (enthalpy driven) to N-isopropylacryalmide (entropy driven). This change in thermodynamics leads to different responses of these two types of polymer NPs to salt concentration and temperature. Select synthetic polymer nanoparticles have also been shown to inhibit protein-heparin interactions and thus offer the potential for therapeutic applications.

Characterization of a new α-galactosyl-binding lectin from the mushroom Clavaria purpurea

A galactose specific lectin (CpL) was purified from the Clavaria purpurea mushroom by affinity chromatography. CpL agglutinated only trypsin-treated rabbit erythrocytes. On enzyme linked lectin sorbent assay (ELLSA), the lectin bound with thyroglobulin and asialo bovine submaxillary mucin (BSM). The fine sugar binding specificity of CpL was elucidated using inhibition of hemagglutination and sugar immobilized gold nano-particles (SGNP). The results indicated a preference of CpL towards α-galactosyl sugar chains. Among several monosaccharides and disaccharides assayed for dissociation effect on the SGNP-CpL complex, Galα1-3Gal and raffinose were the best inhibitors. The partial amino acid sequence showed two QXW motifs in CpL and similarity towards members of the ricin B superfamily.

Silica-modified oligonucleotide-gold nanoparticle conjugate enables closed-tube colorimetric polymerase chain reaction

A facile silica coating significantly enhances the thermal stability and polymerase chain reaction (PCR) compatibility of oligonucleotide-gold nanoparticle conjugates, thus enabling colorimetric detection of PCR results in a closed-tube format. This method is specific, sensitive, and generally applicable. Its simplicity, visual readout, and carryover contamination-free features hold promise for point-of-care or on-site DNA testing.

Effect of gold nanoparticle conjugation on the activity and stability of functional proteins

Immobilization of functional proteins such as enzymes on solid surfaces produces a variety of effects ranging from the reversal and strong inhibition to the enhancement of protein stability and function. Such effects are protein-dependent and are affected by the physical and chemical properties of the surfaces. Functional consequences of protein immobilization on the surface of gold nanoparticles (AuNPs) are protein-dependent and require thorough investigation using suitable functional tests. However, traditional approaches to making control samples, i.e., immobilized protein vs. protein in solution in absence of any nanoparticles do not provide sufficiently identical reaction conditions and complicate interpretation of the results. This report provides advice and methods for preparing AuNP-conjugated preparations generally suitable for studying the effects of immobilization on the activity and stability of different functional proteins. We use bovine catalase to illustrate our approach, but the methods are easily adaptable to any other enzyme or protein. The AuNP-immobilized enzyme showed increased stability at elevated temperatures compared to the same enzyme in solution.

Ag Nanoparticle-Poly(acrylic acid) Composite Film with Dynamic Plasmonic Properties

Poly(acrylic acid) (PAA) thin films with embedded Ag nanoparticles (AgNPs) prepared by UV photoreduction exhibited cyclically changeable optical absorbance properties during variation of ambient aqueous medium. The observed phenomenon is due to conformational changes in the polymer matrix which leads to variation in the 3D configuration of the AgNPs ensemble. Reversible variation of the distance between nanoparticles during swelling and shrinking processes within the PAA matrix changes the optical parameters of these plasmonic metamaterials and can be considered a useful feature for optoelectronic devices and sensors. The finite-difference time-domain method was used for modelling of light extinction of developed matrix structures in their swollen and shrunken states.

A conjugated aptamer-gold nanoparticle fluorescent probe for highly sensitive detection of rHuEPO-α

We present here a novel conjugated aptamer-gold nanoparticle (Apt-AuNPs) fluorescent probe and its application for specific detection of recombinant human erythropoietin-α (rHuEPO-α). In this nanobiosensor, 12 nm AuNPs function as both a nano-scaffold and a nano-quencher (fluorescent energy acceptor), on the surface of which the complementary sequences are linked (as cODN-AuNPs) and pre-hybridized with carboxymethylfluorescein (FAM)-labeled anti-rHuEPO-α aptamers. Upon target protein binding, the aptamers can be released from the AuNP surface and the fluorescence signal is restored. Key variables such as the length of linker, the hybridization site and length have been designed and optimized. Full performance evaluation including sensitivity, linear range and interference substances are also described. This nanobiosensor provides a promising approach for a simple and direct quantification of rHuEPO-α concentrations as low as 0.92 nM within a few hours.

Colorimetric biosensing using smart materials

In recent years, colorimetric biosensing has attracted much attention because of its low cost, simplicity, and practicality. Since color changes can be read out by the naked eye, colorimetric biosensing does not require expensive or sophisticated instrumentation and may be applied to field analysis and point-of-care diagnosis. For transformation of the detection events into color changes, a number of smart materials have been developed, including gold nanoparticles, magnetic nanoparticles, cerium oxide nanoparticles, carbon nanotubes, graphene oxide, and conjugated polymers. Here, we focus on recent developments in colorimetric biosensing using these smart materials. Along with introducing the mechanisms of color changes based on different smart materials, we concentrate on the design of biosensing assays and their potential applications in biomedical diagnosis and environmental monitoring.

Host-guest sensing by calixarenes on the surfaces

The present critical review reports on recent developments of optical nanoparticles based on the association of gold, silver, silica and quantum dots and calixarenes. These hybrid organic-inorganic compounds characterized by a thick organic layer self-assembled on the surface of a core of mineral surface atoms take advantage of the supramolecular recognition of luminescent calixarenes to fabricate nanodevices of nanoparticle size, capable of detecting metal cations, polyaromatic hydrocarbons and pesticides. Also presented is an explanation of the involvement of such nanoparticles in biochemical systems. This critical review provides an overview of their preparation, the manner in which they are characterized, and their use (108 references).

Beauty is skin deep: a surface monolayer perspective on nanoparticle interactions with cells and bio-macromolecules

Surface recognition of biosystems is a critical component in the development of novel biosensors and delivery vehicles, and for the therapeutic regulation of biological processes. Monolayer-protected nanoparticles present a highly versatile scaffold for selective interaction with bio-macromolecules and cells. Through the engineering of the monolayer surface, nanoparticles can be tailored for surface recognition of biomolecules and cells. This review highlights recent progress in nanoparticle-bio-macromolecule/cellular interactions, emphasizing the effect of the surface monolayer structure on the interactions with proteins, DNA, and cell surfaces. The extension of these tailored interactions to hybrid nanomaterials, biosensing platforms, and delivery vehicles is also discussed.

Functionalized Gold Nanoparticles and Their Biomedical Applications

Metal nanoparticles are being extensively used in various biomedical applications due to their small size to volume ratio and extensive thermal stability. Gold nanoparticles (GNPs) are an obvious choice due to their amenability of synthesis and functionalization, less toxicity and ease of detection. The present review focuses on various methods of functionalization of GNPs and their applications in biomedical research. Functionalization facilitates targeted delivery of these nanoparticles to various cell types, bioimaging, gene delivery, drug delivery and other therapeutic and diagnostic applications. This review is an amalgamation of recent advances in the field of functionalization of gold nanoparticles and their potential applications in the field of medicine and biology.

Iminodiacetic acid-functionalized gold nanoparticles for optical sensing of myoglobin via Cu2+ coordination

A novel gold nanoparticle (AuNP)-based optical sensing system has been developed for the detection of myoglobin (Mb), which is of significant importance for early disease diagnosis. Two thiol molecules containing an iminodiacetic acid moiety (IDA) were synthesized. This detection is based on the Mb-induced aggregation of IDA-functionalized AuNPs resulting from the structures of Mb sandwiched between the functionalized AuNPs via Cu(2+) bridges in the coordination interactions of IDA-Cu(2+)-histidine residues available on the Mb surface, which was confirmed by UV-vis spectroscopy, transmission electron microscopy, dynamic light scattering, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The induction aggregation resulted in a red shift in plasmon resonance band of the AuNPs concomitant with a change in solution color from red to purple. The qualitative and quantitative detections of Mb can be achieved by colorimetric observations and UV-vis spectral measurements, respectively. The selectivity of protein assay with the functionalized AuNPs was further investigated, and it is found that the optical sensing of histidine-rich proteins is closely related to number and distribution of surface histidine residues as well as size of proteins.

Polymer-functionalized gold nanoparticles as versatile sensing materials

In this brief review, gold nanoparticles conjugated with functional polymers are described from the viewpoint of application to sensing materials. The optical properties of gold nanoparticles, the synthesis of polymer-functionalized gold nanoparticles, and their analytical applications are discussed. Polymer-functionalized gold nanoparticles are categorized into two classes: biopolymer-conjugated gold nanoparticles and artificial-polymer conjugated gold nanoparticles. Fluorometric and colorimetric sensing using gold nanoparticles are focused; fluorometric detection enables us to exploit sensitive assays for practical use. Furthermore, chemical amplification using gold nanoparticles is also discussed for the sensitive probing.

Self-assembled and nanostructured siRNA delivery systems

A wide range of organic and inorganic materials have been used in the development of nano-scale self-assembling gene delivery systems to improve the therapeutic efficacy of nucleic acid drugs. Small interfering RNA (siRNA) has recently been recognized as a promising and potent nucleic acid medicine for the treatment of incurable genetic disorders including cancer; however, siRNA-based therapeutics suffer from the same delivery problems as conventional nucleic acid drugs such as plasmid DNA and antisense oligonucleotides. Many of the delivery strategies developed for nucleic acid drugs have been applied to siRNA therapeutics, but they have not produced satisfactory in vivo gene silencing efficiencies to warrant clinical trials. This review discusses recent progress in the development of self-assembled and nanostructured delivery systems for efficient siRNA-induced gene silencing and their potential application in clinical settings.

Colorimetric immunosensing via protein functionalized gold nanoparticle probe combined with atom transfer radical polymerization

A novel colorimetric immunosensing strategy based on protein-modified gold nanoparticle probes combined with atom transfer radical polymerization (ATRP) technology was proposed. Gold nanoparticles (GNPs, ∼15 nm) were functionalized with antibodies through an acylamide-bond between the carboxylic group of 11-mercaptoundecanoic acid that previously self-assembled on the surface of GNPs and the amino group of the protein (here, goat anti-rabbit immunoglobulim G (anti-IgG) used as model). The surface functionalized GNPs were used for IgG capture, which introduced initiator coupled anti-IgG (Ab2*) onto the surface of GNPs through immunoreactions. Subsequently triggered polymer growth resulted in the surface graft of preformed polymer chains onto nanoparticles that altered the optical property of GNPs. A distinct color change occurred. This could be designed for IgG detection. The spectrum absorption and colorimetric detection gave a linear range of 0.5-25 ng mL(-1) with a detection limit of 0.03 ng mL(-1) for IgG. The proposed approach showed high sensitivity from both visual and absorbance measurements. In spite of the limitations of available IgG antibodies, this approach could be easily extended to the detection of other biomarkers.

PEGylated inorganic nanoparticles

Application of inorganic nanoparticles in diagnosis and therapy has become a critical component in the targeted treatment of diseases. The surface modification of inorganic oxides is important for providing diversity in size, shape, solubility, long-term stability, and attachment of selective functional groups. This Minireview describes the role of polyethylene glycol (PEG) in the surface modification of oxides and focuses on their biomedical applications. Such a PEGylation of surfaces provides "stealth" characteristics to nanomaterials otherwise identified as foreign materials by human body. The role of PEG as structure-directing agent in synthesis of oxides is also presented.

Ionic liquids in oligosaccharide synthesis: towards mucin-type glycan probes

The present article provides an overview on mucins and their role in biological processes, while aiming to familiarize readers with the current tools available for the synthesis of structurally defined mucin-type glycan probes including the advantages and potential applications of using ionic liquids in the synthesis of this important class of oligosaccharides. Furthermore, we also highlight recent developments in glycoarray technology that can enable high-sensitivity and high-throughput analysis of this important class of protein-carbohydrate interactions.

Adsorbed Tween 80 is unique in its ability to improve the stability of gold nanoparticles in solutions of biomolecules

This report shows that, of the Tween series (Tween 20, Tween 40, Tween 60 and Tween 80) of nonionic surfactants adsorbed on gold nanoparticles (NPs), Tween 80 makes the NPs most stably dispersed in aqueous solutions with or without the presence of representative biological molecules, such as nucleic acids or proteins of different sizes, isoelectric points (pIs) and shapes. In addition, the stability of gold NPs already modified with poly(L-lysine)-graft-poly(ethylene glycol) (PLL-PEG) or hexa(ethylene glycol)-terminated undecanylthiol (HS(CH(2))(11)EG(6)OH) is further improved in solutions of proteins when Tween 80 is co-adsorbed on the gold NPs. This strategy is the most effective when adsorption of Tween 80 on gold NPs precedes the coating of PLL-PEG or HS(CH(2))(11)EG(6)OH on the NPs.

Engineering of poly(ethylene glycol) chain-tethered surfaces to obtain high-performance bionanoparticles

A poly(ethylene glycol)-b-poly[2-(N,N-dimethylamino)ethyl methacrylate] block copolymer possessing a reactive acetal group at the end of the poly(ethylene glycol) (PEG) chain, that is, acetal-PEG-b-PAMA, was synthesized by a proprietary polymerization technique. Gold nanoparticles (GNPs) were prepared using the thus-synthesized acetal-PEG-b-PAMA block copolymer. The PEG-b-PAMA not only acted as a reducing agent of aurate ions but also attached to the nanoparticle surface. The GNPs obtained had controlled sizes and narrow size distributions. They also showed high dispersion stability owing to the presence of PEG tethering chains on the surface. The same strategy should also be applicable to the fabrication of semiconductor quantum dots and inorganic porous nanoparticles. The preparation of nanoparticles in situ, i.e. in the presence of acetal-PEG-b-PAMA, gave the most densely packed polymer layer on the nanoparticle surface; this was not observed when coating preformed nanoparticles. PEG/polyamine block copolymer was more functional on the metal surface than PEG/polyamine graft copolymer, as confirmed by angle-dependent x-ray photoelectron spectroscopy. We successfully solubilized the C60 fullerene into aqueous media using acetal-PEG-b-PAMA. A C60/acetal-PEG-b-PAMA complex with a size below 5 nm was obtained by dialysis. The preparation and characterization of these materials are described in this review.

Diazirine-modified gold nanoparticle: template for efficient photoinduced interfacial carbene insertion reactions

Photolysis of a 3-aryl-3-(trifluoromethyl)diazirine-modified monolayer-protected gold nanoparticles (2-C(12)MPNs), with a core size of 1.8 ± 0.3 nm, in the presence of model carbene trapping reagents leads to efficient, essentially quantitative, modification of the interface via carbene insertion reactions. The utility of carbene insertion reactions as a general approach for the modification of Au-MPNs to provide a breadth of new structures available was demonstrated using acetic acid, methanol, benzyl alcohol, phenol, benzylamine, methyl acrylate, and styrene (10a-g, respectively) as electrophilic carbene trapping agents to form the corresponding modified 3a-g-C(12)MPNs. The 1.8 ± 0.3 nm gold nanoparticles bearing a diazirine group (2-C(12)MPNs) were synthesized using the ligand exchange reaction with the requisite 3-aryl-3-(trifluoromethyl)diazirinealkylthiol. The 2-C(12)MPNs and the resulting products of the reaction on the MPN (3a-g-C(12)MPN) were fully characterized by IR, (1)H NMR, and (19)F NMR spectroscopy and, when applicable, transmission electron microscopy (TEM). Verification for the 3a-g-C(12)MPNs was accomplished by comparison of the spectral data to those of obtained for the photoreactions of 3-(3-methoxyphenyl)-3-(trifluoromethyl)-3H-diazirine as a model with 10a-g.

Target: ligand interactions of the vascular endothelium. Implications for molecular imaging in inflammation

Molecular imaging refers to the non-invasive visualisation of biological processes at the molecular and cellular levels within a living organism, and offers a wide range of potential benefits to both clinical medicine and research into novel therapeutic agents. Inflammation plays an important role in a wide variety of pathological processes and imaging the molecular and cellular machinery that underlies chronic inflammation is attractive and feasible. In this review, we present an overview of molecular imaging of inflammation. We start by characterising molecular and cellular events in early inflammation, identifying current and potential future imaging targets. We focus on the imaging of endothelial cells, which mediate the important first steps in inflammation in any tissue, are readily accessible to imaging probes and which present an approach that can be applied across multiple modalities. We then review the generic requirements for imaging contrast agents and focus on the important considerations in respect of ligands, ligand-target interactions and contrast vehicles. We aim to provide an integrated view of current progress with a focus on promising recent developments in experimental and translational molecular imaging.

Kinetic analyses of bindings of Shiga-like toxin to clustered and dispersed Gb3 glyco-arrays on a quartz-crystal microbalance

One-, two-, four-, and eight-branched globotriaosyl saccharides (Gb(3): Gal-alpha1,4-Gal-beta1,4-Glc), whose reducing ends were biotinylated, were prepared (1Gb(3)-bio, 2Gb(3)-bio, 4Gb(3)-bio, and 8Gb(3)-bio, respectively). They are dispersively immobilized as a glyco-array in the matrix of biotinylated maltotriose (Glc(3)-bio) on a streptavidin-covered 27 MHz quartz-crystal microbalance (QCM). The binding kinetics of the verotoxin B subunit (VTB) to various branched Gb(3)-bio ligands in the Glc(3)-bio matrix could be obtained from frequency decreases (mass increases) of the QCM. VTB can recognize the Gb(3) unit but not the Glc(3) unit, where VTB is a pentamer having five binding sites for one Gb(3) unit per each B subunit (having a total of 15 binding sites for Gb(3)). By changing the Gb(3) multivalency, the Gb(3) packing density, and the Gb(3) cluster size in the Glc(3) matrix, association constants (K(a)), maximum amounts bound (Delta m(max)), and binding and dissociation rate constants (k(on) and k(off)) were obtained. When 15 sites of VTB were recognized by 16 Gb(3) units, K(a) was 100 times larger than that when 15 sites of VTB were recognized by only 2 Gb(3) units, with a 6-fold-larger k(on) and a 25-fold-smaller k(off). When the Gb(3) multivalency was changed by covering with two 1Gb(3)-bio, 2Gb(3)-bio, 4Gb(3)-bio, or 8Gb(3)-bio ligands on two pockets of one streptavidin, the K(a) values increased with increasing branch number from one to eight. When the Gb(3) cluster size was changed from eight 1Gb(3)-bio units to one 8Gb(3)-bio unit in the matrix, the K(a) values increased but the Delta m(max) values decreased with increasing cluster size from eight 1Gb(3)-bio units to one 8Gb(3)-bio unit. This is the first example of systematically obtaining all kinetic parameters of sugar-binding proteins to sugars on a glyco-array by changing the sugar multivalency, the sugar packing density, and the sugar cluster size in the matrix.

Nanofabrication of nonfouling surfaces for micropatterning of cell and microtissue

Surface engineering techniques for cellular micropatterning are emerging as important tools to clarify the effects of the microenvironment on cellular behavior, as cells usually integrate and respond the microscale environment, such as chemical and mechanical properties of the surrounding fluid and extracellular matrix, soluble protein factors, small signal molecules, and contacts with neighboring cells. Furthermore, recent progress in cellular micropatterning has contributed to the development of cell-based biosensors for the functional characterization and detection of drugs, pathogens, toxicants, and odorants. In this regards, the ability to control shape and spreading of attached cells and cell-cell contacts through the form and dimension of the cell-adhesive patches with high precision is important. Commitment of stem cells to different specific lineages depends strongly on cell shape, implying that controlled microenvironments through engineered surfaces may not only be a valuable approach towards fundamental cell-biological studies, but also of great importance for the design of cell culture substrates for tissue engineering. To develop this kind of cellular microarray composed of a cell-resistant surface and cell attachment region, micropatterning a protein-repellent surface is important because cellular adhesion and proliferation are regulated by protein adsorption. The focus of this review is on the surface engineering aspects of biologically motivated micropatterning of two-dimensional surfaces with the aim to provide an introductory overview described in the literature. In particular, the importance of non-fouling surface chemistries is discussed.

Rapid and selective lead (II) colorimetric sensor based on azacrown ether-functionalized gold nanoparticles

A gold nanoparticle (AuNPs)-based simple and fast colorimetric sensor for selective detecting of Pb(II) in aqueous solution has been developed. Monodisperse AuNPs (approx. 2.0 nm diameter) has been prepared facilely and further modified with an alkanethiol-bearing monoazacrown ether terminus. These AuNPs are shown to selectively sense Pb(2+) through color change, which is visually discernible by an appearance of the surface plasmon band (SPB) at 520 nm. The recognition mechanism is attributed to the unique structure of the monoazacrown ether attached to AuNPs and metal sandwich coordination between two azacrown ether moieties that are attached to separate nanoparticles. This inter-particle cross-linking results in an aggregation and apparent color change from brown to purple. Additionally, TEM experiments support the optical absorption data proving the aggregation between azacrown ether-capped gold nanoparticles. This AuNP-based colorimetric assay is a facile and robust method and allows fast detection of Pb(2+) at ambient temperatures. More importantly, the developed technique does not utilize enzymatic reactions, light-sensitive dye molecules, lengthy protocols or sophisticated instrumentation.