Immobilization of peroxidase glycoprotein on gold electrodes modified with mixed epoxy-boronic Acid monolayers

In-Line Characterization of the Temperature-Responsive Behavior of Surface-Bound Microgel Coatings by QCM-D: A Novel Strategy for Protein Repellence Evaluation

In this work, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to develop a new method to evaluate the protein repellency of microgel coatings. Compared to traditional protocols for surface analysis, QCM has the advantage of a real-time quantitative approach with high sensitivity, allowing us to describe variations of the adsorbed mass with unprecedented accuracy. To enable the detectability of the film throughout the whole operational temperature interval, a poly(N-isopropylacrylamide-co-glycidyl methacrylate) p(NIPAm-co-GMA) microgel monolayer with defined thickness and rigidity was designed. Covalent adhesion of the film to the silica surface was achieved by epoxy-thiol click chemistry and tested for repeated temperature cycles, showing substantial reproducibility. Further functionalization of microgel surfaces by grafting polyzwitterionic chains remarkably improved the protein repellence leaving the strong surface adhesion unaltered. Before and after exposure to fluorescein-tagged bovine serum albumin (FITC-BSA), the coatings showed identical responsive behavior, proving the absence of protein deposition. In nonrepellent coatings, QCM monitoring instead displayed a characteristic shift in the volume phase transition (VPT), pointing out the effect of adsorbed proteins on the swelling behavior of pNIPAm. The combination of QCM-D and UV-visible (UV-vis) was used to evaluate the effect of increasing surface coverage, enabling to distinguish between the protein deposition occurring over the coated and the uncoated portion of the sensor.

Transmetalation of boronic acids and their derivatives: mechanistic elucidation and relevance to catalysis

The Suzuki-Miyaura reaction (the cross-coupling reaction of boronic acids with organic halides catalysed by Pd complexes) has been recognised as a useful synthetic organic reaction that forms a C(sp²)-C(sp²) bond. The catalytic cycle of the reaction involves the transmetalation of aryl- and alkenylboronic acids with Pd(II) complexes. It migrates the aryl and alkenyl groups of boronic acid to Pd and produces a Pd-C bond. Many studies have investigated the mechanism of transmetalation. They elucidated the mechanism of the organometallic reaction and its role as a fundamental step in catalytic reactions. This perspective reviews studies on the transmetalation of aryl- and alkenylboronic acids with Pd(II) complexes. Emphasis was laid on the structures and chemical properties of the intermediate Pd complexes and the effects of OH^- on the pathways of the catalytic Suzuki-Miyaura reaction. The reactions of arylboronic acids with Rh(I)-OH complexes were investigated, which are relevant to the mechanism of Rh-catalysed addition of aryl boronic acids to enones and aldehydes. Recent studies on the transmetalation of boronic acids with other late transition metals such as Fe(II), Co(I), Pt(II), Au(III), and Au(I) are presented with the related catalytic reactions and their utilisation in the synthesis of aromatic molecules and π-conjugated materials.

KAT Ligation for Rapid and Facile Covalent Attachment of Biomolecules to Surfaces

The efficient and bioorthogonal chemical ligation reaction between potassium acyltrifluoroborates (KATs) and hydroxylamines (HAs) was used for the surface functionalization of a self-assembled monolayer (SAM) with biomolecules. An alkane thioether molecule with one terminal KAT group (S-KAT) was synthesized and adsorbed onto a gold surface, placing a KAT group on the top of the monolayer (KAT-SAM). As an initial test case, an aqueous solution of a hydroxylamine (HA) derivative of poly(ethylene glycol) (PEG) (HA-PEG) was added to this KAT-SAM at room temperature to perform the surface KAT ligation. Quartz crystal microbalance with dissipation (QCM-D) monitoring confirmed the rapid attachment of the PEG moiety onto the SAM. By surface characterization methods such as contact angle and ellipsometry, the attachment of PEG layer was confirmed, and covalent amide-bond formation was established by X-ray photoelectron spectroscopy (XPS). In a proof-of-concept study, the applicability of this surface KAT ligation for the attachment of biomolecules to surfaces was tested using a model protein, green fluorescent protein (GFP). A GFP was chemically modified with an HA linker to synthesize HA-GFP and added to the KAT-SAM under aqueous dilute conditions. A rapid attachment of the GFP on the surface was observed in real time by QCM-D. Despite the fact that such biomolecules have a variety of unprotected functional groups within their structures, the surface KAT ligation proceeded rapidly in a chemoselective manner. Our results demonstrate the versatility of the KAT ligation for the covalent attachment of a variety of water-soluble molecules onto SAM surfaces under dilute and biocompatible conditions to form stable, natural amide bonds.

Paper-Based Competitive Immunochromatography Coupled with an Enzyme-Modified Electrode to Enable the Wireless Monitoring and Electrochemical Sensing of Cotinine in Urine

This paper proposes a combined strategy of using paper-based competitive immunochromatography and a near field communication (NFC) tag for wireless cotinine determination. The glucose oxidase labeled cotinine antibody specifically binds free cotinine in a sample, whereas the unoccupied antibody attached to BSA-cotinine at the test line on a lateral flow strip. The glucose oxidase on the strip and an assistant pad in the presence of glucose generated H₂O₂ and imposed the Ag oxidation on the modified electrode. This enabled monitoring of immunoreaction by either electrochemical measurement or wireless detection. Wireless sensing was realized for cotinine in the range of 100-1000 ng/mL (R² = 0.96) in PBS medium. Undiluted urine samples from non-smokers exhibited an Ag-oxidation rate three times higher than the smoker's urine samples. For 1:8 diluted urine samples (smokers), the proposed paper-based competitive immunochromatography coupled with an enzyme-modified electrode differentiated positive and negative samples and exhibited cotinine discrimination at levels higher than 12 ng/mL. This novel sensing platform can potentially be combined with a smartphone as a reader unit.

Immobilization of Proteins on Gold Surfaces

Gold has been a widely used support for protein immobilization in a nonspecific way through electrostatic and hydrophobic interactions. As no tools are available to predict the binding of proteins of biological interest to gold supports-for either nano, micro, or macroscopic sizes-smart, reliable, and reproducible protein immobilization protocols on gold are sought. This chapter will focus on a synthetic strategy which allows for the development of a multiplicity of architectures on gold that may be used for protein immobilization. Because of its simplicity, both from a conceptual and a practical point of view, the strategy demonstrated by this step-by-step synthesis of a functionally self-assembled monolayer (SAM) of thiols on gold is accessible to most laboratories working on enzyme technology, even those with limited organic synthesis facilities.

A Facile Strategy for Immobilizing GOD and HRP onto Pollen Grain and Its Application to Visual Detection of Glucose

Pollen grain was explored as a new carrier for enzyme immobilization. After being modified with boric acid-functionalized titania, the pollen grain was able to covalently immobilize glycosylated enzymes by boronate affinity interaction under very mild experimental conditions (e.g., pH 7.0, ambient temperature and free of organic solvent). The glucose oxidase and horse radish peroxidase-immobilized pollen grain became a bienzyme system. The pollen grain also worked as an indicator of the cascade reaction by changing its color. A rapid, simple and cost-effective approach for the visual detection of glucose was then developed. When the glucose concentration exceeded 0.5 mM, the color change was observable by the naked eye. The assay of glucose in body fluid samples exhibited its great potential for practical application.

Regioselective SN2-Type Reaction for the Oriented and Irreversible Immobilization of Antibodies to a Glass Surface Assisted by Boronate Formation

Antibodies have exquisite specificities for molecular recognition, which have led to their incorporation into array sensors that are crucial for research, diagnostic, and therapeutic applications. Many of these platforms rely heavily on surface-bound reactive groups to covalently tether antibodies to solid substrates; however, this strategy is hindered by a lack of orientation control over antibody immobilization. Here, we report a mild electrophilic phenylsulfonate (tosylate) ester-containing boronic acid affinity ligand for attaching antibodies to glass slides. A high level of antibody coupling located near the Fc region of the boronated antibody complex could be achieved by the proximal nucleophilic amino acid driven substitution reaction at the phenylsulfonate center. This enabled the full-length antibodies to be permanently tethered onto surfaces in an oriented manner. The advantages of this strategy were demonstrated through the individual and multiplex detection of protein and serum biomarkers. This strategy not only confers stability to the immobilized antibodies but also presents a different direction for the irreversible attachment of antibodies to solid supports in an orientation-controlled way.

Robust Strategy for Antibody-Polymer-Drug Conjugation: Significance of Conjugating Orientation and Linker Charge on Targeting Ability

Antibody-drug conjugates have shown great promise in active targeting for cancer therapy. The existing chemical techniques for antibody conjugation generally lack efficiency or universality. In this article, a site-specific antibody conjugation was developed by using a mild reaction between a benzoboroxole (BB) functionality and cis-diol moiety of sugar units in the antibody fragment crystallizable region under neutral pH conditions. A BB/PEG/ICG-grafted poly(aspartic acid) comb-like functional polymer was first synthesized and conjugated with transferrin (Tf) to form a transferrin-polymer-drug conjugate [Tf-P(BB)], which showed 120% increase in HepG2 hepatoma (Tf receptor overexpression) cell uptake compared to a nontargeting protein-polymer-drug conjugate [HRP-P(BB)]. The universality of this method was further demonstrated by the enhanced uptake of trastuzumab (anti-Her2 antibody)-polymer-drug conjugates in MCF-7 (295%) and MDA-MB-435S (66.4%) (Her2 positive) cells. The positive charge of the linker had great influence on the targeting ability of the antibody-polymer-drug conjugates. The in vivo studies demonstrated the distinct targeting ability of Tf-P(BB) in the HepG2 xenograft tumor, and the tumor accumulation of the Tf-P(BB) testing group increased by 92% with respect to the control group [HRP-P(BB)]. More significantly, the HepG2 cell uptake amount of the antibody-oriented conjugate [Tf-P'(BB)] was 2.4-fold higher than that of the controlled group [Tf-P'(Hex)]. On the basis of this facile site-specific conjugation method, the conjugates are able to change the antibody species easily against various cancers, while maintaining the antibody integrity and targeting ability.

A Novel Surface Modification and Immobilization Method of Anti-CD25 Antibody on Nonwoven Fabric Filter Removing Regulatory T Cells Selectively

Anti-CD25 antibodies were immobilized on polypropylene (PP) nonwoven fabrics to specifically remove mouse regulatory T cells (Tregs) from mouse spleen cells. PP fibers were coated with peptide nanosheets, which were prepared by self-assembling of a mixture of X-poly(sarcosine)-b-(l-Leu-Aib)₆ (X: glycolic acid or a phenylboronic acid) and Y-poly(sarcosine)-b-(d-Leu-Aib)₆ (Y: glycolic acid or diazirine derivative). Anti-CD25 antibodies were immobilized by covalent linking between the sugar moiety of the antibody and the phenylboronic acid group on the peptide nanosheet. The removal rate of mouse Tregs from the mouse spleen cells was more than 95% only by passing the filters, while the nonspecific removal rates of other cells were less than 15%. The coating of peptide nanosheets on PP fibers was very effective to provide a suitable environment for the immobilized antibody to interact with the counterpart cells while the coating suppressed nonspecific adsorption of other cells.

Boronate affinity-based photoactivatable magnetic nanoparticles for the oriented and irreversible conjugation of Fc-fused lectins and antibodies

The utilization of immuno-magnetic nanoparticles (MNPs) for the selective capture, enrichment, and separation of specific glycoproteins from complicated biological samples is appealing for the discovery of disease biomarkers. Herein, MNPs were designed and anchored with abundant boronic acid (BA) and photoreactive alkyl diazirine (Diaz) functional groups to obtain permanently tethered Fc-fused Siglec-2 and antiserum amyloid A (SAA) mAb with the assistance of reversible boronate affinity and UV light activation in an orientation-controlled manner. The Siglec-2-Fc-functionalized MNPs showed excellent stability in fetal bovine serum (FBS) and excellent efficiency in the extraction of cell membrane glycoproteins. The anti-SAA mAb-functionalized MNPs maintained active Ab orientation and preserved antigen recognition capability in biological samples. Thus, the BA-Diaz-based strategy holds promise for the immobilization of glycoproteins, such as antibodies, with the original protein binding activity maintained, which can provide better enrichment for the sensitive detection of target proteins.

Capacitive Saccharide Sensor Based on Immobilized Phenylboronic Acid with Diol Specificity

A capacitive sensor for saccharide detection is described in this study. The detection is based on selective interaction between diols and aminophenylboronic acid (APBA) immobilized on a gold electrode. Glucose, fructose, and dextran (MW: 40 kDa) were tested with the system over wide concentration ranges (1.0 x 10-8 M - 1.0 x 10-3 M for glucose, 1.0 x 10-8 M - 1.0 x 10-2 M for fructose and 1.0 x 10-10 M - 1.0 x 10-5 M for dextran). The limits of detection (LODs) were 0.8 nM for glucose, 0.6 nM for fructose, and 13 pM for dextran. These data were comparable to the others reported previously. In order to demonstrate glycoprotein detection with the same sensor, human immunoglobulin G (IgG) as well as horseradish peroxidase were used as model analytes. The sensor responded to IgG in the concentration range of 1.0 x 10-13 M - 1.0 x 10-7 M with a LOD value of 16 fM. The performance of the assay of peroxidase was compared to a spectrophotometric assay by determining the enzymatic activity of a captured analyte. The results showed that the method might be useful for label-free, fast, and sensitive detection of saccharides as well as glycoproteins over a wide concentration range.

Acetylcholine-responsive cargo release using acetylcholinesterase-capped nanomaterials

Mesoporous silica nanoparticles capped with acetylcholinesterase, through boronic ester linkages, selectively release an entrapped cargo in the presence of acetylcholine.

Immuno-impedimetric Biosensor for Onsite Monitoring of Ascospores and Forecasting of Sclerotinia Stem Rot of Canola

Sclerotinia stem rot, caused by the fungal pathogen Sclerotinia sclerotiorum, is a destructive disease of canola and many other broadleaf crops. The primary inoculum responsible for initiating Sclerotinia epidemics is airborne ascospores released from the apothecia of sclerotia. Timely detection of the presence of airborne ascospores can serve as an early-warning system for forecasting and management of the disease. A major challenge is to develop a portable and automated device which can be deployed onsite to detect and quantify the presence of minute quantities of ascospores in the air and serves as a unit in a network of systems for forecasting of the epidemic. In this communication, we present the development of an impedimetric non-Faradaic biosensor based on anti-S. sclerotiorum polyclonal antibodies as probes to selectively capture the ascospores and sense their binding by an impedance based interdigitated electrode which was found to directly and unambiguously correlate the number of ascospores on sensor surface with the impedance response.

Acrylate-based poly-high internal phase emulsions for effective enzyme immobilization and activity retention: from computationally-assisted synthesis to pharmaceutical applications

PolyHIPE functional materials were chemically conjugated with a model enzyme. It retained its activity upon flow as demonstrated by the conversion of a specific substrate.

Bioinspired design of a hybrid bifunctional enzymatic/organic electrocatalyst for site selective alcohol oxidation

TEMPO and AdhD were chemically conjugated into a bifunctional catalyst that selectively oxidizes primary and secondary alcohols.

Facile Oriented Immobilization of Histidine-Tagged Proteins on Nonfouling Cobalt Polyphenolic Self-Assembly Surfaces

In this study, a completely green and facile protocol to oriented immobilization of histidine-tagged (His-tagged) proteins based on plant polyphenolic tannic acid (TA) is described. This is the first time that TA has been applied as ionic chelators to immobilize His-tagged proteins. To reduce the nonspecific interactions between the TA and immobilized proteins, we assembled nonfouling zwitterionic poly(sulfobetaine methacrylate) (PSBMA) on the TA surface. The use of PSBMA could maintain the high activity of the His-tagged proteins and inhibit the adsorption of untagged protein to the TA surface. Subsequently, the obtained TA/PSBMA film was further chelated with Co^II for specific binding to a His-tagged protein. As Co^III is more stable and inert than Co^II, the chelated Co^II was oxidized to Co^III. Using this approach, His-tagged Chitinase was anchored to TA/PSBMA/Co^III film as a catalyst for the hydrolysis of chitin. The loading capacity of the film for the His-tagged Chitinase can reach ∼4.0 μg/cm². Moreover, the oriented immobilized Chitinase had high catalytic activity and excellent thermal and storage stability as well as being more resistant to proteolytic digestion by papain. This low-cost and green protein-oriented immobilization strategy may serve as a versatile platform for a range of applications, such as biomaterials, biocatalysis, sensors, drug delivery, and so on.

Nano-in-Nano Approach for Enzyme Immobilization Based on Block Copolymers

We set up a facile approach for fabrication of supports with tailored nanoporosity for immobilization of enzymes. To this aim block copolymers (BCPs) self-assembly has been used to prepare nanostructured thin films with well-defined architecture containing pores of tailorable size delimited by walls with tailorable degree of hydrophilicity. In particular, we employed a mixture of polystyrene-block-poly(l-lactide) (PS-PLLA) and polystyrene-block-poly(ethylene oxide) (PS-PEO) diblock copolymers to generate thin films with a lamellar morphology consisting of PS lamellar domains alternating with mixed PEO/PLLA blocks lamellar domains. Selective basic hydrolysis of the PLLA blocks generates thin films, patterned with nanometric channels containing hydrophilic PEO chains pending from PS walls. The shape and size of the channels and the degree of hydrophilicity of the pores depend on the relative length of the blocks, the molecular mass of the BCPs, and the composition of the mixture. The strength of our approach is demonstrated in the case of physical adsorption of the hemoprotein peroxidase from horseradish (HRP) using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) with H₂O₂ as substrate. The large surface area, the tailored pore sizes, and the functionalization with hydrophilic PEO blocks make the designed nanostructured materials suitable supports for the nanoconfinement of HRP biomolecules endowed with high catalytic performance, no mass-transfer limitations, and long-term stability.

Multiplexed Electrochemical Immunosensors for Clinical Biomarkers

Management and prognosis of disease requires the accurate determination of specific biomarkers indicative of normal or disease-related biological processes or responses to therapy. Moreover since multiple determinations of biomarkers have demonstrated to provide more accurate information than individual determinations to assist the clinician in prognosis and diagnosis, the detection of several clinical biomarkers by using the same analytical device hold enormous potential for early detection and personalized therapy and will simplify the diagnosis providing more information in less time. In this field, electrochemical immunosensors have demonstrated to offer interesting alternatives against conventional strategies due to their simplicity, fast response, low cost, high sensitivity and compatibility with multiplexed determination, microfabrication technology and decentralized determinations, features which made them very attractive for integration in point-of-care (POC) devices. Therefore, in this review, the relevance and current challenges of multiplexed determination of clinical biomarkers are briefly introduced, and an overview of the electrochemical immunosensing platforms developed so far for this purpose is given in order to demonstrate the great potential of these methodologies. After highlighting the main features of the selected examples, the unsolved challenges and future directions in this field are also briefly discussed.

Gold Superparticles Functionalized with Azobenzene Derivatives: SERS Nanotags with Strong Signals

The surface-enhanced Raman spectroscopy (SERS) nanotag was proposed as a substitute for fluorescent dye for imaging and biosensors several decades ago. However, its weak signal and poor reproducibility has hindered its application. Here, we report a new strategy to form Au superparticles (AuSPs) with high SERS enhancement via one-pot formation and self-assembly of Au nanoparticles (NPs). An azobenzene-carrying Raman reporter was synthesized to exhibit a large Raman cross-section and multiple bands. The self-assembly of the Raman reporter on AuSPs generated SERS nanotags with intense signals. A Raman reporter carrying boronic acid and azobenzene groups displayed six distinctive bands. Its corresponding SERS nanotag demonstrated a high sensing ability toward glycoprotein through aggregation-induced SERS enhancement or as a substitute for labeled antibodies in an immunoassay of the glycoprotein.

Assembly of designed protein scaffolds into monolayers for nanoparticle patterning

The controlled assembly of building blocks to achieve new nanostructured materials with defined properties at different length scales through rational design is the basis and future of bottom-up nanofabrication. This work describes the assembly of the idealized protein building block, the consensus tetratricopeptide repeat (CTPR), into monolayers by oriented immobilization of the blocks. The selectivity of thiol-gold interaction for an oriented immobilization has been verified by comparing a non-thiolated protein building block. The physical properties of the CTPR protein thin biomolecular films including topography, thickness, and viscoelasticity, are characterized. Finally, the ability of these scaffolds to act as templates for inorganic nanostructures has been demonstrated by the formation of well-packed gold nanoparticles (GNPs) monolayer patterned by the CTPR monolayer.

Electronic communication of cells with a surface mediated by boronic acid saccharide interactions

The fabrication of a molecularly tailored surface functionalised with a saccharide binding motif, a phenyl boronic acid derivative is reported. The functionalised surface facilitated the transfer of electrons, via unique electronic interactions mediated by the presence of the boronic acid, from a macrophage cell line. This is the first example of eukaryotic cellular-electrical communication mediated by the binding of cells via their cell-surface saccharide units.

Fabrication of antibody microarrays by light-induced covalent and oriented immobilization

Antibody microarrays have important applications for the sensitive detection of biologically important target molecules and as biosensors for clinical applications. Microarrays produced by oriented immobilization of antibodies generally have higher antigen-binding capacities than those in which antibodies are immobilized with random orientations. Here, we present a UV photo-cross-linking approach that utilizes boronic acid to achieve oriented immobilization of an antibody on a surface while retaining the antigen-binding activity of the immobilized antibody. A photoactive boronic acid probe was designed and synthesized in which boronic acid provided good affinity and specificity for the recognition of glycan chains on the Fc region of the antibody, enabling covalent tethering to the antibody upon exposure to UV light. Once irradiated with optimal UV exposure (16 mW/cm(2)), significant antibody immobilization on a boronic acid-presenting surface with maximal antigen detection sensitivity in a single step was achieved, thus obviating the necessity of prior antibody modifications. The developed approach is highly modular, as demonstrated by its implementation in sensitive sandwich immunoassays for the protein analytes Ricinus communis agglutinin 120, human prostate-specific antigen, and interleukin-6 with limits of detection of 7.4, 29, and 16 pM, respectively. Furthermore, the present system enabled the detection of multiple analytes in samples without any noticeable cross-reactivities. Antibody coupling via the use of boronic acid and UV light represents a practical, oriented immobilization method with significant implications for the construction of a large array of immunosensors for diagnostic applications.

Non-covalent functionalization of carbon nanotubes with boronic acids for the wiring of glycosylated redox enzymes in oxygen-reducing biocathodes

Easy covalent binding and efficient electrical wiring of enzymes onto carbon nanotube deposits by pyrene-boronic acid derivatives.

Improved activity of immobilized antibody by paratope orientation controller: probing paratope orientation by electrochemical strategy and surface plasmon resonance spectroscopy

Electrochemical method and surface plasmon resonance (SPR) spectroscopic analysis are utilized herein to investigate antibody immobilization without and with orientation control for site-positioning paratopes (antigen binding site) of the antibody molecules. Biotin and its antibody were selected in current study as model. Such an approach employed thiophene-3-boronic acid (T3BA) as paratope orientation controller, (i) enabled site orientation of the antibody molecules reducing the hiding of paratopes, and (ii) maintained the activity of the captured antibodies, as confirmed by electrochemical and SPR analysis. Anti-biotin antibody (a glycoprotein) was covalently bound to a self-assembled monolayer of T3BA modified on a nanogold-electrodeposited screen-printed electrode through boronic acid-saccharide interactions, with the boronic acid units specifically binding to the glycosylation sites of the antibody molecules. The immunosensor functioned based on competition between the analyte biotin and biotin-tagged, potassium hexacyanoferrate(II)-encapsulated liposomes. The current signal produced by the released liposomal Fe(CN)6(4-), measured using square wave voltammetry, yielded a sigmoidally shaped dose-response curve that was linear over eight orders of magnitude (from 10(-11) to 10(-3)M). Furthermore this biosensing system fabricated based on T3BA approach was found to possess significantly improved sensitivity, and the limit of detection toward biotin was calculated as 0.102 ng mL(-1) (equivalent to 6 μL of 4.19 × 10(-10)M biotin).

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

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

Aptamer-based array electrodes for quantitative interferon-γ detection

Present work describes the methylene blue tagged thiolated aptamer-modified gold micro-array based biosensor for specific detection of IFN-γ. The microchips with the microelectrode array were fabricated using standard silicon microfabrication technologies, and modified with methylene blue tagged aptamer using standard gold thiol chemistry. Electrodes were characterized and tested using Cyclic Voltammetric (CV) and Square Wave Voltammetry (SQW) measurements in a standard three-electrode format at room temperature. On an aptamer modified electrode, aptamer density was estimated to be about 4.4 × 10(12)molecules/cm(2). In IFN-γ studies, oxidation peak currents were found to decrease and more than 50% signal suppression was achieved at 500 ng/ml. Further, the magnitude of signal suppression was found to be logarithmically proportional to the IFN-γ in the concentration range of 1-500 ng/ml, with a detection limit of 1.3 ng/ml (i.e. 0.8 fmol in used sample volume of 10 µl). Biosensor showed negligible signal changes (5%) in a very high non-specific protein background, while still able to differentiate target protein IFN-γ at 5 ng/ml. The results indicated that our sensor binds selectively to target molecules, and the non-specific binding where adsorption of BSA protein molecules may be effectively omitted from consideration.

Immobilization techniques in the fabrication of nanomaterial-based electrochemical biosensors: a review

The evolution of 1st to 3rd generation electrochemical biosensors reflects a simplification and enhancement of the transduction pathway. However, in recent years, modification of the transducer with nanomaterials has become increasingly studied and imparts many advantages. The sensitivity and overall performance of enzymatic biosensors has improved tremendously as a result of incorporating nanomaterials in their fabrication. Given the unique and favorable qualities of gold nanoparticles, graphene and carbon nanotubes as applied to electrochemical biosensors, a consolidated survey of the different methods of nanomaterial immobilization on transducer surfaces and enzyme immobilization on these species is beneficial and timely. This review encompasses modification of enzymatic biosensors with gold nanoparticles, carbon nanotubes, and graphene.

Self-propelled carbohydrate-sensitive microtransporters with built-in boronic acid recognition for isolating sugars and cells

A new nanomotor-based target isolation strategy, based on a "built-in" recognition capability, is presented. The concept relies on a poly(3-aminophenylboronic acid) (PAPBA)/Ni/Pt microtube engine coupling the selective monosaccharide recognition of the boronic acid-based outer polymeric layer with the catalytic function of the inner platinum layer. The PAPBA-based microrocket is prepared by membrane-templated electropolymerization of 3-aminophenylboronic acid monomer. The resulting boronic acid-based microengine itself provides the target recognition without the need for additional external functionalization. "On-the-fly" binding and transport of yeast cells (containing sugar residues on their wall) and glucose are illustrated. The use of the recognition polymeric layer does not hinder the efficient propulsion of the microengine in aqueous and physiological media. Release of the captured yeast cells is triggered via a competitive sugar binding involving addition of fructose. No such capture and transport are observed in control experiments involving other cells or microengines. Selective isolation of monosaccharides is illustrated using polystyrene particles loaded with different sugars. Such self-propelled nanomachines with a built-in recognition capability hold considerable promise for diverse applications.

Ultrasensitive detection of adrenocorticotropin hormone (ACTH) using disposable phenylboronic-modified electrochemical immunosensors

This work reports for the first time an electrochemical immunosensor for the determination of adrenocorticotropin hormone (ACTH). The immunoelectrode design involves the use of amino phenylboronic acid for the oriented immobilization of anti-ACTH antibodies onto screen-printed carbon modified electrode surfaces. A competitive immunoassay between the antigen and the biotinylated hormone for the binding sites of the immobilized antibody was performed. The electroanalytical response was generated by using alkaline phosphatase-labelled streptavidin and 1-naphtyl phosphate as the enzyme substrate. The electrochemical oxidation of the enzyme reaction product, 1-naphtol, measured by differential pulse voltammetry was employed to monitor the affinity reaction. Under the optimized working conditions, an extremely low detection limit of 18 pg/L was obtained. Cross-reactivity was evaluated against other hormones (cortisol, estradiol, testosterone, progesterone, hGH and prolactin) and the obtained results demonstrated an excellent selectivity. The developed immunosensor was applied to a human serum sample containing a certified amount of ACTH with good results.

Covalent immobilization of antimicrobial peptides (AMPs) onto biomaterial surfaces

Bacterial adhesion to biomaterials remains a major problem in the medical devices field. Antimicrobial peptides (AMPs) are well-known components of the innate immune system that can be applied to overcome biofilm-associated infections. Their relevance has been increasing as a practical alternative to conventional antibiotics, which are declining in effectiveness. The recent interest focused on these peptides can be explained by a group of special features, including a wide spectrum of activity, high efficacy at very low concentrations, target specificity, anti-endotoxin activity, synergistic action with classical antibiotics, and low propensity for developing resistance. Therefore, the development of an antimicrobial coating with such properties would be worthwhile. The immobilization of AMPs onto a biomaterial surface has further advantages as it also helps to circumvent AMPs' potential limitations, such as short half-life and cytotoxicity associated with higher concentrations of soluble peptides. The studies discussed in the current review report on the impact of covalent immobilization of AMPs onto surfaces through different chemical coupling strategies, length of spacers, and peptide orientation and concentration. The overall results suggest that immobilized AMPs may be effective in the prevention of biofilm formation by reduction of microorganism survival post-contact with the coated biomaterial. Minimal cytotoxicity and long-term stability profiles were obtained by optimizing immobilization parameters, indicating a promising potential for the use of immobilized AMPs in clinical applications. On the other hand, the effects of tethering on mechanisms of action of AMPs have not yet been fully elucidated. Therefore, further studies are recommended to explore the real potential of immobilized AMPs in health applications as antimicrobial coatings of medical devices.

Dual amplification strategy for the fabrication of highly sensitive interleukin-6 amperometric immunosensor based on poly-dopamine

An electrochemical immunosensor was studied for sensitive detection of Interleukin-6 (IL-6) based on a dual amplification mechanism resulting from Au nanoparticles (AuNP)-Poly-dopamine (PDOP) as the sensor platform and multienzyme-antibody functionalized AuNP-PDOP@carbon nanotubes (CNT). The stable and robust film, PDOP, was used to immobilize biomolecules not only for the construction of the sensor platform, but also for the signal labeling. Sensitivity was greatly amplified by using the special platform of AuNP-PDOP and synthesizing horseradish peroxidase (HRP)-antibody (Ab(2)) functionalized AuNP-PDOP@carbon nanotubes (CNT). A linear response range of IL-6 from 4.0 to 8.0 × 10(2) pg mL(-1) with a low detection limit of 1.0 pg mL(-1) was obtained by the amperometry determination. Measurements of IL-6 in human serum gave excellent correlations with standard ELISA assays. Moreover, the immunosensor exhibited high selectivity, good reproducibility, and stability.

Multivalent interaction-based carbohydrate biosensors for signal amplification

Multivalent interaction between boronic acids immobilized on quartz crystal microbalance (QCM) sensor surface and the carbohydrates modified Au-nanoparticle (AuNP) has been demonstrated for the development of a sensitive carbohydrate biosensor. Briefly, a boronic acid-containing polymer (boropolymer) as multivalent carbohydrate receptor was oriented immobilized on the cysteamine coated electrode through isourea bond formation. Carbohydrates were conjugated to AuNPs to generate a multivalent carbohydrates moiety to amplify the response signal. Thus, the binding of the carbohydrate conjugated AuNPs to the boropolymer surface are multivalent which could simultaneously increase the binding affinity and specificity. We systematically studied the binding between five carbohydrates conjugated AuNPs and the boropolymer. Our studies show that the associate constant (K(a)) was in the order of fucose Collapse

Key Words

• carbohydrate biosensor
• multivalent interaction
• boronic acid

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MESH Headings

• Biosensing Techniques/methods
• Boronic Acids
• Carbohydrate Metabolism
• Carbohydrates/chemistry
• Electrochemical Techniques
• Gold
• Metal Nanoparticles
• Molecular Structure
• Polymers/chemistry
• Quartz Crystal Microbalance Techniques

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Grants

• EB000672 NIBIB NIH HHS
• R21 EB009513 NIBIB NIH HHS
• R21 EB000672 NIBIB NIH HHS
• R33 EB000672 NIBIB NIH HHS
• R21 EB009513-01A1 NIBIB NIH HHS

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Affiliation(s)

Yanyan Wang Department of Chemistry, Oakland University, Rochester, Michigan 48309, USA The key Laboratory of Bioactive Materials Ministry of Education, College of Life Sciences, Nankai University, Tianjin 300071, China
Srinivas Chalagalla Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115
Tiehai Li College of Pharmacy, Nankai University, Tianjin 300071, China
Xue-long Sun Department of Chemistry, Cleveland State University, Cleveland, Ohio 44115
Wei Zhao College of Pharmacy, Nankai University, Tianjin 300071, China
Peng Wang College of Pharmacy, Nankai University, Tianjin 300071, China
Xiangqun Zeng Department of Chemistry, Oakland University, Rochester, Michigan 48309, USA

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