Sensing capabilities of colloidal gold modified with a self-assembled monolayer of a glucose-carrying polymer chain on a glass substrate

Recent Insights into Glucose-Responsive Concanavalin A-Based Smart Hydrogels for Controlled Insulin Delivery

Many efforts are continuously undertaken to develop glucose-sensitive biomaterials able of controlling glucose levels in the body and self-regulating insulin delivery. Hydrogels that swell or shrink as a function of the environmental free glucose content are suitable systems for monitoring blood glucose, delivering insulin doses adapted to the glucose concentration. In this context, the development of sensors based on reversible binding to glucose molecules represents a continuous challenge. Concanavalin A (Con A) is a bioactive protein isolated from sword bean plants (Canavalia ensiformis) and contains four sugar-binding sites. The high affinity for reversibly and specifically binding glucose and mannose makes Con A as a suitable natural receptor for the development of smart glucose-responsive materials. During the last few years, Con A was used to develop smart materials, such as hydrogels, microgels, nanoparticles and films, for producing glucose biosensors or drug delivery devices. This review is focused on Con A-based materials suitable in the diagnosis and therapeutics of diabetes. A brief outlook on glucose-derived theranostics of cancer is also presented.

Large patternable metal nanoparticle sheets by photo/e-beam lithography

Techniques for micro/nano-scale patterning of large metal nanoparticle sheets can potentially be used to realize high-performance photoelectronic devices because the sheets provide greatly enhanced electrical fields around the nanoparticles due to localized surface plasmon resonances. However, no single metal nanoparticle sheet currently exists with sufficient durability for conventional lithographical processes. Here, we report large photo and/or e-beam lithographic patternable metal nanoparticle sheets with improved durability by incorporating molecular cross-linked structures between nanoparticles. The cross-linked structures were easily formed by a one-step chemical reaction; immersing a single nanoparticle sheet consisting of core metals, to which capping molecules ionically bond, in a dithiol ethanol solution. The ligand exchange reaction processes were discussed in detail, and we demonstrated 20 μm wide line and space patterns, and a 170 nm wide line of the silver nanoparticle sheets.

Monitoring interfacial lectin binding with nanomolar sensitivity using a plasmon field effect transistor

By immobilizing glycopolymers onto the surface of the recently developed plasmonic field effect transistor (FET), the recognition between lectins and surface-immobilized glycopolymers can be detected over a wide dynamic range (10^-10 to 10^-4 M) in an environment that resembles the glycocalyx. The binding to the sensor surface by various lectins was tested, and the selectivities and relative binding affinity trends observed in solution were maintained on the sensor surface, and the significantly higher avidities are attributed to cluster-glycoside effects that occur on the surface. The combination of polymer surface chemistry and optoelectronic output in this device architecture produces amongst the highest reported detection sensitivity for ConA. This work demonstrates the benefits that arise from combining emerging device architectures and soft-matter systems to create cutting edge nanotechnologies that lend themselves to fundamental biological studies and integration into point-of-use diagnostics and sensors.

Electrochemical synthesis of nanostructured gold film for the study of carbohydrate-lectin interactions using localized surface plasmon resonance spectroscopy

Localized surface plasmon resonance (LSPR) spectroscopy is a label-free chemical and biological molecular sensing technique whose sensitivity depends upon development of nanostructured transducers. Herein, we report an electrodeposition method for fabricating nanostructured gold films (NGFs) that can be used as transducers in LSPR spectroscopy. The NGF was prepared by electrodepositing gold from potassium dicyanoaurate solution onto a flat gold surface using two sequential controlled potential steps. Imaging by scanning electron microscopy reveals a morphology consisting of randomly configured block-like nanostructures. The bulk refractive index sensitivity of the prepared NGF is 100±2 nmRIU(-1) and the initial peak in the reflectance spectrum is at 518±1 nm under N2(g). The figure of merit is 1.7. In addition, we have studied the interaction between carbohydrate (mannose) and lectin (Concanavalin A) on the NGF surface using LSPR spectroscopy by measuring the interaction of 8-mercaptooctyl-α-d-mannopyranoside (αMan-C8-SH) with Concanavalin A by first immobilizing αMan-C8-SH in mixed SAMs with 3,6-dioxa-8-mercaptooctanol (TEG-SH) on the NGF surface. The interaction of Con A with the mixed SAMs is confirmed using electrochemical impedance spectroscopy. Finally, the NGF surface was regenerated to its original sensitivity by removing the SAM and the bound biomolecules. The results from these experiments contribute toward the development of inexpensive LSPR based sensors that could be useful for studying glycan-protein interactions and other bioanalytical purposes.

Activity and safety of synthetic lectins based on benzoboroxole-functionalized polymers for inhibition of HIV entry

Lectins derived from plant and microbial sources constitute a vital class of entry inhibitors that target the oligomannose residues on the HIV envelope gp120. Despite their potency and specificity, success of lectin-based entry inhibitors may be impeded by high manufacturing costs, formulation and potential mitogenicity. Therefore, there exists a gap in the HIV microbicides pipeline that underscores the need for mass producible, synthetic, broad-spectrum, and biocomptabile inhibitors of HIV entry. Here, we present the development of a polymeric synthetic lectin, based on benzoboroxole (BzB), which exhibits weak affinity (∼25 M(-1)) for nonreducing sugars, similar to those found on the HIV envelope. High molecular weight BzB-functionalized polymers demonstrated antiviral activity that increased with an increase in ligand density and molecular weight of the polymer construct, revealing that polyvalency improves activity. Polymers showed significant increase in activity from 25 to 75 mol % BzB functionalization with EC(50) of 15 μM and 15 nM, respectively. A further increase in mole functionalization to 90% resulted in an increase of the EC(50) (59 ± 5 nM). An increase in molecular weight of the polymer at 50 mol % BzB functionalization showed a gradual but significant increase in antiviral activity, with the highest activity seen with the 382 kDa polymer (EC(50) of 1.1 ± 0.5 nM in CEM cells and 11 ± 3 nM in TZM-bl cells). Supplementing the polymer backbone with 10 mol % sulfonic acid not only increased the aqueous solubility of the polymers by at least 50-fold but also demonstrated a synergistic increase in anti-HIV activity (4.0 ± 1.5 nM in TZM-bl cells), possibly due to electrostatic interactions between the negatively charged polymer backbone and the positively charged V3-loop in the gp120. The benzoboroxole-sulfonic acid copolymers showed no decrease in activity in the presence of a seminal concentration of fructose (p > 0.05). Additionally, the copolymers exhibit minimal, if any, effect on the cellular viability, barrier properties, or cytokine levels in human reconstructed ectocervical tissue after 3 days of repeated exposure and did not show pronounced activity against a variety of other RNA and DNA viruses.

Emerging use of nanostructure films containing capped gold nanoparticles in biosensors

The localized surface plasmon resonance (LSPR) property of gold nanoparticles (GNP) has been exploited in a variety of optical sensor configurations including solution-based bioassays, paper-based colorimetric detection, surface-confined nanoparticle film/array-based sensing, etc. Amongst these, gold nanostructured films are of great interest because of their high stability, good reproducibility, robustness, and cost-effectiveness. The inherent optical characteristics of GNP, are attributed to parameters like size and shape (eg, nanospheres, nanorods, nanostars), eg, LSPR spectral location sensitivity to the local environment, composition (eg, gold-silver or silica-gold nanoshells), sensing volume, mesospacing, and multiplexing. These properties allow sensor tunability, enabling enhanced sensitivity and better performance of these biosensors. Ultrasensitive biosensor designs were realized using gold nanostructured films fabricated by bottom-up as well as top-down approaches. In this review, we describe the past, present, and future trends in the development of GNP-LSPR-based sensors, concentrating on both design (fabrication) and application. In the process, we have discussed various combinations of GNP size and shape, substrate, and application domains.

Binding of beta-secretase to a peptide inhibitor-carrying SAM

A novel disulfide, which carried a specific inhibitor for beta-secretase (KMI360) at both ends, was prepared by the coupling of 11,11'-dithiobisundecanoic acid (DTUA) with the inhibitor. The compound obtained (DTUA-KMI360) formed a self-assembled monolayer (SAM) on a gold electrode as proven by cyclic voltammetry (CV) using hydroquinone as a probe. Furthermore, DTUA-KMI360 could be accumulated as a SAM on a gold colloid deposited on a glass plate (Au colloid-glass chip) as proven by both the red-shift and the increase in absorbance of the gold colloid corresponding to localized surface plasmon resonance (LSPR). When the SAM-modified Au colloid-glass chip was immersed in a solution of aspartyl proteases, pepsin and beta-secretase, the absorbance of the chip at 550nm corresponding to LSPR of the gold colloid further increased and was slightly red-shifted, whereas coexistence of a free inhibitor obstructed these phenomena. Adsorption of the enzymes was promoted by the incorporation of a zwitterionic group into the SAM, while non-specific adsorption to the mixed SAM was significantly reduced. The optimal ratio of omega-zwitterionic alkanethiol, 3-[(6-mercaptohexyl)-N,N-dimethylamino]propane-1-sulfonic acid (C(6)-SPB), and DTUA-KMI360 in the SAM for the binding of enzymes was found to be DTUA-KMI360:C(6)-SPB=1:11 using polarization modulation infrared reflection absorption spectroscopy (PM-IR-RAS). From increasing profiles of absorbance of the Au colloid-glass chip, the association constant (K(assoc)) for pepsin with the inhibitor on the SAM was determined, whereas that for beta-secretase could not be due to the strong binding of the enzyme to the inhibitor, resulting in the absence of the dissociation process. The results suggested that the SAM of the enzyme inhibitor can be used for both investigation of enzymes and removal of target enzymes from biological fluids.

Anti-biofouling properties of a telomer brush with pendent glucosylurea groups

A thiol-group-carrying telomer with pendent D-glucosylurea groups [poly(glucosylureaethyl methacrylate)-SH (PolyGUMA-SH)] was obtained by reversible addition-fragmentation chain-transfer (RAFT) polymerization of GUMA in the presence of 4,4'-azobis(4-cyanopentanoic acid) (initiator) and 4-cyanopentanoic acid dithiobenzoate (chain-transfer agent) and subsequent reduction with NaBH4. The thiol-carrying telomer was accumulated on both a gold electrode and a colloidal gold-immobilized glass substrate as proven by cyclic voltammetry using hydroquinone as a probe, and the increase in absorbance at 550 nm was ascribable to localized surface plasmon resonance (LSPR), respectively. The adsorption of various proteins to the surface of the telomer brush was examined by the LSPR method, too. The PolyGUMA brush showed a significant resistance against nonspecific adsorption of proteins, such as lysozyme, bovine serum albumin, immunoglobulin G, and fibrinogen. Furthermore, sugar-binding proteins, concanavalin A (Con A, with an affinity for mannose and glucose) and wheat germ agglutinin (WGA, with an affinity for N-acetylglucosamine), were not adsorbed to the GUMA-carrying brush, which is in contrast with the prompt and distinct binding of these proteins to the telomer brushes composed of 2-methacryloyloxyethyl D-glucopyranoside (Con A) and 1-O-(6'-methacrylamido)hexyl-2-N-acetoamido-2-deoxy-D-glucopyranoside residues (WGA). The glucosylurea-group-carrying telomer brush prepared here might be quite useful to provide a "bio-inert (anti-biofouling)" surface in biomedical fields.

A label-free immunoassay based upon localized surface plasmon resonance of gold nanorods

Robust gold nanorod substrates were fabricated for refractive index sensing based on localized surface plasmon resonance (LSPR). The substrate sensitivity was 170 nm/RIU with a figure of merit of 1.3. To monitor biomolecular interactions, the nanorod surfaces were covered with a self-assembled monolayer and conjugated to antibodies by carbodiimide cross-linking. Interactions with a specific secondary antibody were monitored through shifts in the LSPR spectral extinction peak. The resulting binding rates and equilibrium constant were in good agreement with literature values for an antibody-antigen system. The nanorod LSPR sensors were also shown to be sensitive and specific. These results demonstrate that given a sufficiently stable nanoparticle substrate with a well defined chemical interface, LSPR sensing yields similar results to the surface plasmon resonance technique, yet with much simpler instrumentation.

Interaction of wheat germ agglutinin with an N-acetylglucosamine-carrying telomer brush accumulated on a colloidal gold monolayer

A disulfide-carrying telomer with many pendent N-acetylglucosamine (GlcNAc) residues (Cys-PMHGlcNAc) was obtained by photo-polymerization of 1-(6'-methacryloylaminohexyl)-2-N-acetoamido-2-deoxy d-glucopyranoside) (MHGlcNAc) using a benzyl N,N-diethyldithiocarbamoyl (BDC) derivative that shows abilities of initiation, transfer, and termination (iniferter). The disulfide-carrying telomer was accumulated on a monolayer of colloidal Au on a glass substrate, and the interaction of wheat germ agglutinin (WGA) with GlcNAc residue at the polymer brush-solution interface was examined by using the localized surface plasmon resonance (LSPR) technique. For comparison, an amphiphile carrying many pendent GlcNAc residues was also prepared with MHGlcNAc and a lipophilic radical initiator and was incorporated in a phospholipid liposome to examine interaction of the GlcNAc residue with WGA on the liposome surface using turbidity measurements. Both the colloidal gold optical device and the liposome showed a concentration-dependent specific binding of WGA, and the GlcNAc-carrying liposome had a detection limit of 100 nM for WGA, whereas that of the colloidal gold device was 10nM. The sugar-carrying telomer-coated device examined here is not only useful as a simple biosensor chip but is also expected to expand our knowledge of bio-related phenomena at the liquid-telomer brush interfaces on a colloidal Au.

Sensing characteristics of NIR localized surface plasmon resonances in gold nanorings for application as ultrasensitive biosensors

The optical responses of 75-150 nm diameter gold nanorings to changes in local refractive index have been quantified by near-infrared extinction spectroscopy and compared to DDA calculations and an analytical approach. The "bulk" refractive index sensitivities of gold nanorings are substantially (>5 times) larger than those of nanodisks with similar diameters. Nanorings retain a significantly larger sensitivity than nanodisks at the same spectral position, demonstrating a clear shape dependence that may correlate to a systematic difference in the influence of the dielectric substrate. The nanoring bulk refractive index sensitivity scales linearly with plasmon peak position. The spectral sensitivity to thin films of alkanethiols gave a shift of approximately 5.2 nm/CH2 unit while bulk sensitivities as high as 880 nm/RIU were observed, the highest such reported sensitivities. Both bulk and thin dielectric film sensitivities correlated well with theory. Real-time label-free monitoring of protein binding via molecular recognition was demonstrated.

Recognition of sugars on surface-bound cap-shaped gold particles modified with a polymer brush

A dithiolated random copolymer with pendent phenylboronic acid residues (Cys-Poly(3-acrylamidophenylboronic acid-co-2-dimethylaminopropyl methacrylamide), Cys-Poly(APBA-co-DMAPMA)) obtained by photo-iniferter method was accumulated as a polymer brush on a cap-shaped gold particles deposited on a vacuum-evaporated gold film, and the usefulness of the polymer brush as a sensing element for glycoprotein, ovalbumin (OVA), was examined by using UV-vis spectroscopy with a help of surface plasmon resonance. A similar system was constructed with a dithiolated mannose-carrying polymer, dithiolated-poly(2-methacryloyloxyethyl-D-mannopyranoside) (DT-PMEMan), prepared by the atom transfer radical polymerization (ATRP). The brush composed of this polymer was examined as a sensing element for lectin, concanavalin A (Con A). The sensor cells modified with Cys-Poly(APBA-co-DMAPMA) and DT-PMEMan showed a concentration-dependent binding of OVA and Con A, respectively, with a comparable detection limit to those with a monolayer of polymer brush-coated gold particle deposited on a glass substrate. Using this system, it can be expected to open a new perspective to various functional polymer brushes fixed to the cap-shaped gold particle on a solid substrate.

Facile preparation of glyconanoparticles and their bioconjugation to streptavidin

Well-defined glycopolymers containing linear and cyclic carbohydrate moieties as pendent groups were prepared by reversible addition fragmentation chain transfer polymerization (RAFT). The RAFT synthesized glycopolymers were used for the aqueous synthesis of stabilized glyconanoparticles. The in situ reduction of the glycopolymers and HAuCl4 resulted in the formation of highly stable modified gold nanoparticles with diameters ranging from 40 to 80 nm in aqueous media. Multifunctional glyconanoparticles were also generated in the presence of varying amounts of biotinylated-polyethyleneglycol (bio-PEG-SH) having terminal thiol groups. The gold nanoparticles underwent aggregation in the presence of streptavidin as revealed by UV-vis spectroscopy. The availability of the biotin for conjugation to streptavidin was also confirmed using surface plasmon resonance (SPR).

Resistance of surface-confined telomers with pendent glucosylurea groups against non-specific adsorption of proteins

A disulfide-carrying random telomer with pendent D-glucosylurea groups (Cys-poly(glucosylureaethyl methacrylate-r-ureaethyl methacrylate), Cys-Poly(GUMA-r-UMA)) was obtained by UV-irradiation of GUMA and UMA in the presence of benzyl N,N-diethyldithiocarbamoyl (BDC) derivative which shows the abilities of initiation, transfer, and termination (iniferter). The disulfide-carrying telomer was accumulated on a gold electrode and colloidal gold-immobilized glass substrate, and the binding of various proteins to the surface of the polymer brush was examined by both cyclic voltammetry (CV) with hydroquinone as a probe, and localized surface plasmon resonance (LSPR) absorption method. The Cys-Poly(GUMA-r-UMA) brush did not show a significant non-specific adsorption of proteins such as bovine serum albumin and egg white lysozyme. Furthermore, sugar binding proteins, concanavalin A (with an affinity for mannose and glucose) and wheat germ agglutinin (with an affinity for N-acetylglucosamine), were only slightly adsorbed to the GUMA-carrying brush, which is in contrast with the prompt and distinct binding of these proteins to the brushes composed of 2-methacryloyloxyethyl D-glucopyranoside and 1-(6'-methacrylamido)hexyl-2-N-acetoamido-2-deoxy-D-glucopyranoside, respectively. The glucosylurea group-carrying telomer brush prepared here might be useful to provide a "bio-inert" surface in bio-medical fields.

Sensing Capabilities of Colloidal Gold Monolayer Modified with a Phenylboronic Acid-Carrying Polymer Brush

A dithiolated random copolymer with pendent phenylboronic acid residues [Cys-poly(3-acrylamidophenylboronic acid-co-N,N-dimethylaminopropyl methacrylamide), Cys-poly(APBA-co-DMAPMA)] that shows the abilities of initiation, transfer, and termination (iniferter) was obtained by using a benzyl N,N-diethyldithiocarbamoyl (BDC) derivative. The obtained disulfide-carrying copolymer was accumulated on a colloidal gold-immobilized glass substrate, and the usefulness of the polymer brush as a sensing element for glycoproteins such as ovalbumin (OVA) was examined by UV-visible spectrophotometry with the help of localized surface plasmon resonance (LSPR). The sensor showed a concentration-dependent binding of OVA with a detection limit of 100 nM, and it had a very high stability at high ionic strength. The sensor chip could be used for a detection of another glycoprotein, avidin, as well. Furthermore, the binding of biotin-modified human serum albumin (biotinylated HSA) to the avidin-phenylboronic acid- (PBA-) carrying polymer brush complex and further specific binding of anti-HSA immunoglobulin G to the biotinylated HSA-avidin-PBA-carrying polymer brush ternary complex could clearly be observed. The polymer-brush-coated device examined here not only was useful as a simple sensor chip, but also is expected to open a new perspective on interfacial phenomena performed by various functional polymer brushes fixed to colloidal gold on glass substrates.

Facile in situ preparation of biologically active multivalent glyconanoparticles

Biologically active multivalent glyconanoparticles are prepared in an extremely simple method by reduction of well-defined glycopolymers, prepared by RAFT polymerisation, in an aqueous solution of HAuCl(4).

Size Effect of Polydiacetylene Vesicles Functionalized with Glycolipids on Their Colorimetric Detection Ability

In this paper, the size effect of the polydiacetylene vesicles functionalized with glycolipids on their colorimetric detection ability has been studied. Polydiacetylene vesicles in which were incorporated glycolipids acted as a model system for the affinochromatic property. Visible color changes from blue to red could be observed to the naked eye owing to Con A binding to the sugar moiety and be detected quantitatively by the visible absorption spectrum. In the experiment, small and uniform vesicles were obtained after extrusion through membranes with different pore sizes. The morphology and mean size distribution of the extruded vesicles were studied by transmission electron microscopy (TEM) and dynamic light scattering (DLS), respectively. Our work shows that the smaller the vesicles are, the stronger is the effect, making the detection of Con A easier. The results may apply to the sensitivity enhancement of polydiacetylene biosensors for the recognition of other biomolecules.

Inclusion of bisphenols by a self-assembled monolayer of thiolated calix[6]arene on a gold surface

The molecular recognition of various kinds of bisphenols (BPs) by a self-assembled monolayer (SAM) of thiolated calix[6]arene on a gold electrode was examined using cyclic voltammetry (CV). Based on the inhibitory effect of BPs on the inclusion of hydroquinone (HQ) as a probe bythe surface-confined calix[6]arene, the association constants (Kassoc) of BPs with the immobilized calix[6]arene were estimated. The Kassoc values for BPs with the SAM of thiolated hexasodium calix[6]arenehexasulfonic acid (thioSCX6) were much smaller than those in the free calix[6]arene derivative systems reported previously. The order of the Kassoc values for BPs with thioSCX6 was bisphenol A (BPA) > bisphenol S (BPS) > bisphenol B (BPB) > bisphenol F (BPF). The Kassoc values for BPA and BPS with thioSCX6 were larger than that for BPB, despite the larger hydrophobicity of BPB than that of BPA and BPS. This is probably because the inclusion phenomena in this system are not simply driven by the hydrophobic interaction, but are significantly affected by several steric and structural factors with immobilization of the host. Those are (1) a decrease in flexibility of the SCX6 cavity by the formation of SAM, (2) a decrease in inclusion ability of the SCX6 by the presence of Au surface just beneath it, and (3) a repulsion of hydrophobic guests bythe presence of sulfonate groups at the top of the SAM. Moreover, the association phenomena (adsorption and desorption processes) of a bisphenol with the SCX6 SAM were examined directly by using localized surface plasmon resonance spectroscopy.

Orientational effect of surface-confined cyclodextrin on the inclusion of bisphenols

The molecular recognition of various kinds of bisphenols (BPs) and a bisphenol A-polymer conjugate (BPA-polymer) by a self-assembled monolayer (SAM) of thiolated beta-cyclodextrin (CD) on a gold electrode was examined using cyclic voltammetry (CV). Based on the inhibitory effect of BPs on the inclusion of hydroquinone (HQ) as a probe by the surface-confined CD, the association constants (K(assoc)) of BPs with the immobilized beta-CD were estimated. The K(assoc) values for BPs with the SAM of 3-dithiobis(undecanoylamido)-3-deoxy-beta-cyclodextrin (DTUA-beta-CD) were smaller than those in the free beta-CD system reported previously. A similar tendency was obtained when 6-(lipoylamido)-6-deoxy-beta-cyclodextrin (LP-beta-CD) was used in place of DTUA-beta-CD. The K(assoc) values for all the BPs except for bisphenol B with the SAM of LP-beta-CD were always larger than those with the SAM of DTUA-beta-CD, due to a difference in the orientation of the beta-CD moiety in the SAMs. Furthermore, adsorption and desorption processes of the BPA-polymer from the surface-confined beta-CD was followed using local surface plasmon resonance spectroscopy.

Self-Assembled Monolayer of a Pepstatin Fragment as a Sensing Element for Aspartyl Proteases

A novel disulfide, which carried two pepstatin fragments at both ends, was prepared by the coupling of 11,11'-dithiobisundecanoic acid (DTUA) with a fragment (Val-Val-Sta) carrying a n-hexyl end (Pepsta(h)). The compound obtained (DTUA-Pepsta(h)) formed a self-assembled monolayer (SAM) on a gold electrode and vacuum-evaporated gold thin film as proven by cyclic voltammetry and reflection absorption infrared spectroscopy, respectively. When the SAM-modified gold electrode was incubated with a solution of aspartyl protease, pepsin, a decrease in both anodic and cathodic peak currents and an increase in potential difference were observed in the cyclic voltamogram of hydroquinone as a probe, whereas a coexistence of free pepstatin fragment inhibited these phenomena, indicating the specific binding of pepsin to the fragment at the exterior of the SAM. The binding rate of the enzyme to the SAM was largely dependent on the surface density of the fragment moiety in the SAM. Furthermore, when the SAM of DTUA-Pepsta(h) on a gold colloid array deposited on an amino group-modified glass plate was immersed in a pepsin solution, absorption of the glass plate at 550 nm corresponding to a localized surface plasmon resonance of the gold colloid abruptly increased and slightly red-shifted, and a further addition of pepstatin A gradually decreased the absorbance. From the increasing and decreasing profiles of absorbance, the association constant (K(assoc)) for pepsin with the fragment on the SAM was determined. Similar phenomena were observed upon immersion of the fragment-modified SAM in a solution of HIV-1 protease, suggesting a usability of the pepstatin fragment SAM for the detection and removal of the enzyme from biological fluids.

Resistance of zwitterionic telomers accumulated on metal surfaces against nonspecific adsorption of proteins

Telomers of N,N-dimethyl-N-(3-sulfopropyl)-3'-methacryloylaminopropanaminium inner salt (SPB), 2-methacryloyloxyethyl phosphorylcholine (MPC), and N,N-dimethyl-N-(1-carboxymethyl)-2'-methacryloyloxylethanaminium inner salt (CMB) were prepared by UV irradiation in the presence of N,N,N',N'-tetraethylthiuram disulfide and a disulfide-group-carrying iniferter (a compound which pursues initiation, chain transfer, and termination), Cys-BDC, which had been prepared by coupling N,N-diethyldithiocarbamoylmethylbenzoic acid succinimidyl ester with cystamine dihydrochloride. The telomers formed a self-assembled monolayer (SAM) on a gold electrode and a monolayer of colloidal gold deposited on a glass plate, as confirmed by the increase in potential difference (DeltaE(p)) of the voltammogram for hydroquinone as a probe using cyclic voltammetry (CV) and the increase in absorbance using localized surface plasmon resonance (LSPR) absorption spectroscopy, respectively. Nonspecific adsorption of various proteins onto the surfaces of various telomer SAMs was examined from the decrease in peak current (DeltaI) using CV and the absorption increase at 550 nm using LSPR absorption spectroscopy. The zwitterionic telomer SAM in general did not adsorb proteins significantly, suggesting the usability of zwitterionic polymer SAMs and brushes to coat various materials used in biomedical fields. The correlation between the structure of water in the vicinity of zwitterionic telomers and the resistance of the zwitterionic telomer SAMs against the nonspecific adsorption of proteins was discussed.