Platelet compatibility improvement by proper choice of acidic terminal functionality for mixed-charge self-assembled monolayers

In this study two different series of mixed-charge self-assembled monolayers (SAMs) prepared with -N(+)(CH(3))(3)-terminated alkanethiol and strong dissociated monovalent -SO(3)H acid-terminated or weaker dissociated divalent -PO(3)H(2) acid-terminated alkanethiol in pure ethanol were characterized. The influence of the acidity of the anionic functionality in the mixed-charge SAMs on the surface characteristics and platelet compatibility was investigated. X-ray photoelectron spectroscopy indicated that a nearly equivalent amount of countercharged terminal groups was noted on the surface of -SO(3)H/-N(+)(CH(3))(3) mixed SAMs, while "-N(+)(CH(3))(3) thiol poor" phenomena were found on -PO(3)H(2)/-N(+)(CH(3))(3) mixed SAMs instead. This was caused by the distinct differences in solvation capability between the acidic anionic functional groups and solvent molecules and/or the interactions among the terminal ends of the thiols. This acidity difference also affected other interfacial properties and the platelet compatibility. The mixed SAMs formed from the mixture of -SO(3)H- and -N(+)(CH(3))(3)-terminated thiols showed higher surface hydrophilicity and exhibited the least amount of platelets adhered, but these two mixed SAMs were all fairly negatively surface charged. The structure of the hydration layer near the surfaces was likely affected by the acidity of the anionic functionality, and this would cause such a distinct behavior in platelet compatibility. It was concluded that the hydrophilic surfaces with nearly equal amounts of surface positively and negatively charged components could exhibit better platelet compatibility. This work demonstrated that the nature of the acidic terminal ends of alkanethiol is also a key factor for preparing mixed-charge SAMs with good platelet compatibility.     

Protein interactions with model chromatographic stationary phases constructed using self-assembled monolayers

Model surfaces representative of chromatographic stationary phases were developed by immobilising an homologous series (C2-C18) of n-alkylthiols, mixed monolayers of C4/C18 and thioalkanes with alcohol, carboxylic acid, amino and sulphonic acid terminal groups onto a flat, silver-coated glass surface using self-assembled monolayer (SAM) chemistry. The processes of adsorption and desorption of serum albumins onto the monolayer surfaces was monitored in real-time using surface plasmon resonance (SPR). Alkyl-terminated SAMs all showed a strong adsorption of bovine serum albumin which was largely independent of alkyl chain length, the ratio of mixed C4/C18 SAMs or the solution pH/ionic strength. The adsorption of human serum albumin to carboxylic and amine terminated SAMs was shown to be predominantly via non-electrostatic interactions (hydrophobic or hydrogen bonding). However, sulphonic acid terminated SAMs showed almost exclusively electrostatic interactions with human serum albumin. This preliminary work using self-assembled monolayer chemistry confirms the usefulness of well characterised SAMs surfaces for investigating protein adsorption and desorption onto/from model chromatography surfaces and gives some guidance for selecting appropriate functionalities to develop better surfaces for chromatography and electrophoresis.     

Immunosensor interface based on physical and chemical immunoglobulin G adsorption onto mixed self-assembled monolayers

An immunosensor interface based on mixed hydrophobic self-assembled monolayers (SAMs) of methyl and carboxylic acid terminated thiols with covalently attached human Immunoglobulin G (hIgG), is investigated. The densely packed and organised SAMs were characterised by contact angle measurements and cyclic voltammetry. The effect of the non-ionic surfactant, Tween 20, in preventing nonspecific adsorption is addressed by ellipsometry during physical and covalent hIgG immobilization on pure and mixed SAMs, respectively. It is clearly demonstrated that nonspecific adsorption due to hydrophobic interactions of hIgG on methyl ended groups is totally inhibited, whereas electrostatic/hydrogen bonding interactions with the exposed carboxylic groups prevail in the presence of surfactant. Results of ellipsometry and Atomic Force Microscopy, reveal that the surface concentration of covalently immobilized hIgG is determined by the ratio of COOH / CH(3)-terminated thiols in SAM forming solution. Moreover, the ellipsometric data demonstrates that the ratio of bound anti-hIgG / hIgG depends on the density of hIgG on the surface and that the highest ratio is close to three. We also report the selectivity and high sensitivity achieved by chronoamperometry in the detection of adsorbed hIgG and the reaction with its antibody.     

Mixed charged zwitterionic self-assembled monolayers as a facile way to stabilize large gold nanoparticles

Here we report a facile way of stabilizing large gold nanoparticles (AuNPs) by mixed charged zwitterionic self-assembled monolayers (SAMs). The citrate-capped AuNPs with diameters ranging from 16 nm to even ～100 nm are well stabilized via a simple place exchange reaction with a 1:1 molar ratio mixture of negatively charged sodium 10-mercaptodecanesulfonic acid (HS-C10-S) and positively charged (10-mercaptodecyl)-trimethyl-ammonium bromide (HS-C10-N4). The 16 nm AuNPs protected by mixed charged zwitterionic SAMs not only show much better stability than the single negatively or positively charged AuNPs, but also exhibit exciting stability as well as those modified by monohydroxy (1-mercaptoundec-11-yl) tetraethylene glycol (HS-C11-EG4). Importantly, 16 nm AuNPs protected by mixed SAMs exhibit good stability in cell culture medium with 10% FBS and strong protein resistance, especially with excellent resistance against plasma adsorption. Moreover, the mixed charged zwitterionic SAMs are also able to well-stabilize larger AuNPs with a diameter of 50 nm, and to help remarkably improve their stability in saline solution compared with HS-C11-EG4 protected ones. When it comes to AuNPs with a diameter of 100 nm, the mixed charged zwitterionic SAM protected nanoparticles retain a smaller hydrodynamic diameter and even better long-term stability than those modified by mercaptopolyethylene glycol (M(w) = 2000, HS-PEG2000). The above results demonstrated that the mixed charged zwitterionic SAMs are able to have a similar effect on stabilizing the large gold nanoparticles just like the single-component zwitterionic SAMs. Concerning its ease of preparation, versatility, and excellent properties, the strategy based on the mixed charged zwitterionic SAM protection might provide a promising method to surface tailoring of nanoparticles for biomedical application.     

Mechanism underlying bioinertness of self-assembled monolayers of oligo(ethyleneglycol)-terminated alkanethiols on gold: protein adsorption, platelet adhesion, and surface forces

The mechanism underlying the bioinertness of the self-assembled monolayers of oligo(ethylene glycol)-terminated alkanethiol (OEG-SAM) was investigated with protein adsorption experiments, platelet adhesion tests, and surface force measurements with an atomic force microscope (AFM). In this work, we performed systematic analysis with SAMs having various terminal groups (-OEG, -OH, -COOH, -NH(2), and -CH(3)). The results of the protein adsorption experiment by the quartz crystal microbalance (QCM) method suggested that having one EG unit and the neutrality of total charges of the terminal groups are essential for protein-resistance. In particular, QCM with energy dissipation analyses indicated that proteins absorb onto the OEG-SAM via a very weak interaction compared with other SAMs. Contrary to the protein resistance, at least three EG units as well as the charge neutrality of the SAM are found to be required for anti-platelet adhesion. When the identical SAMs were formed on both AFM probe and substrate, our force measurements revealed that only the OEG-SAMs possessing more than two EG units showed strong repulsion in the range of 4 to 6 nm. In addition, we found that the SAMs with other terminal groups did not exhibit such repulsion. The repulsion between OEG-SAMs was always observed independent of solution conditions [NaCl concentration (between 0 and 1 M) and pH (between 3 and 11)] and was not observed in solution mixed with ethanol, which disrupts the three-dimensional network of the water molecules. We therefore concluded that the repulsion originated from structured interfacial water molecules. Considering the correlation between the above results, we propose that the layer of the structured interfacial water with a thickness of 2 to 3 nm (half of the range of the repulsion observed in the surface force measurements) plays an important role in deterring proteins and platelets from adsorption or adhesion.     

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

We describe the synthesis of a series of mono-, di-, and trisaccharide-functionalized alkanethiols as well as the formation of fouling-resistant self-assembled monolayers (SAMs) from these. The SAMs were characterized using ellipsometry, wetting measurements, and infrared reflection-absorption spectroscopy (IRAS). We show that the structure of the carbohydrate moiety affects the packing density and that this also alters the alkane chain organization. Upon increasing the size of the sugar moieties (from mono- to di- and trisaccharides), the structural qualities of the monolayers deteriorated with increasing disorder, and for the trisaccharide, slow reorganization dynamics in response to changes in the environmental polarity were observed. The antifouling properties of these SAMs were investigated through protein adsorption experiments from buffer solutions as well as settlement (attachment) tests using two common marine fouling species, zoospores of the green macroalga Ulva linza and cypris larvae of the barnacle Balanus amphitrite. The SAMs showed overall good resistance to fouling by both the proteins and the tested marine organisms. To improve the packing density of the SAMs with bulky headgroups, we employed mixed SAMs where the saccharide-thiols are diluted with a filler molecule having a small 2-hydroxyethyl headgroup. This method also provides a means by which the steric availability of sugar moieties can be varied, which is of interest for specific interaction studies with surface-bound sugars. The results of the surface dilution study and the low nonspecific adsorption onto the SAMs both indicate the feasibility of this approach.     

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

The development of bioelectronic enzyme applications requires the immobilization of active proteins onto solid or colloidal substrates such as gold. Coverage of the gold surface with alkanethiol self-assembled monolayers (SAMs) reduces nonspecific adsorption of proteins and also allows the incorporation onto the surface of ligands with affinity for complementary binding sites on native proteins. We present in this work a strategy for the covalent immobilization of glycosylated proteins previously adsorbed through weak, reversible interactions, on tailored SAMs. Boronic acids, which form cyclic esters with saccharides, are incorporated into SAMs to weakly adsorb the glycoprotein onto the electrode surface through their carbohydrate moiety. To prevent protein release from the electrode surface, we combine the affinity motif of boronates with the reactivity of epoxy groups to covalently link the protein to heterofunctional boronate-epoxy SAMs. The principle underlying our strategy is the increased immobilization rate achieved by the weak interaction-induced proximity effect between slow reacting oxyrane groups in the SAM and nucleophilic residues from adsorbed proteins, which allows the formation of very stable covalent bonds. This approach is exemplified by the use of phenylboronates-oxyrane mixed monolayers as a reactive support and redox-enzyme horseradish peroxidase as glycoprotein for the preparation of peroxidase electrodes. Quartz crystal microbalance, atomic force microscopy, and electrochemical measurements are used to characterize these enzymatic electrodes. These epoxy-boronate functional monolayers are versatile, stable interfaces, ready to incorporate glycoproteins by incubation under mild conditions.     

Bioinert surface to protein adsorption with higher generation of dendrimer SAMs

Interactions between proteins and biomaterial surfaces correlate with many important phenomena in biological systems. Such interactions have been used to develop various artificial biomaterials and applications, in which regulation of non-specific protein adsorption has been achieved with bioinert properties. In this research, we investigated the protein adsorption behavior of polymer brushes of dendrimer self-assembled monolayers (SAMs) with other generations. The surface adsorption properties of proteins with different pI values were examined on gold substrates modified with poly(amidoamine) dendrimer SAMs. The amount of fibrinogen adsorption was greater than that of lysozyme, potentially because of the surface electric charge. However, as the generations increased, protein adsorption decreased regardless of the surface charge, suggesting that protein adsorption was also affected by density of terminal group.     

Self-assembled monolayers of an oligo(ethylene oxide) disulfide and its corresponding thiol assembled from water: characterization and protein resistance

Self-assembled monolayers (SAMs) of the disulfide [S(CH2CH2O)6CH3]2 ([S(EO)6]2) on Au from 95% ethanol and from 100% water are described. Spectroscopic ellipsometry and reflection-absorption infrared spectroscopy indicate that the [S(EO)6]2 films are similar to the disordered films of HS(CH2CH2O)6CH3 ((EO)6) and HS(CH2)3O(CH2CH2O)5CH3 (C3EO5) at their protein adsorption minima. The [S(EO)6]2 SAMs exhibit constant film thickness (d) of 1.2 +/- 0.2 nm over long immersion times (up to 20 days) and do not attain the highly ordered, 7/2 helical structure of the (EO)6 and C3EO5 SAMs (d = 2.0 nm). Exposure of these self-limiting [S(EO)6]2 SAMs to bovine serum albumin show high resistance to protein adsorption.     

Molecular organization in SAMs used for neuronal cell growth

The attachment of cells onto solid supports is fundamental in the development of advanced biosensors or biochips. In this work, we characterize cortical neuron adhesion, growth, and distribution of an adhesive layer, depending on the molecular structure and composition . Neuronal networks are successfully grown on amino-terminated alkanethiol self-assembled monolayer (SAM) on a gold substrate without adhesion protein interfaces. Neuron adhesion efficiency was studied for amino-terminated, carboxy-terminated, and 1:1 mixed alkanethiol SAMs deposited on gold substrates. Atomic force microscopy and X-ray photoelectron spectroscopy were used to measure the roughness of gold substrate and thickness of SAM monolayers. Conformational ordering and ionic content of SAMs were characterized by vibrational sum frequency generation (VSFG) spectroscopy. Only pure amino-terminated SAMs provide efficient neuronal cell attachment. Ordering of the terminal amino groups does not affect efficiency of neuron adhesion. VSFG analysis shows that ordering of the terminal groups improves with decreasing surface roughness; however the number of gauche defects in alkane chains is independent of surface roughness. We monitor partial dissociation of carboxy groups in mixed SAMs that implies formation of NH3+ neighbors and appearance of catanionic structure. Such catanionic environment proved inefficient for neuron adhesion. Surface roughness of metal within the 0.7-2 nm range has little effect on the efficiency of neuron adhesion. This approach can be used to create new methods that help map structure-property relationships of biohybrid systems.     

吡咯烷二硫代氨基甲酸铵自组装膜对铜的缓蚀作用

吡咯烷二硫代氨基甲酸铵(APDTC)是一种环境友好型金属缓蚀剂, 以其在铜表面制备了自组装单分子膜(SAMs), 用电化学方法研究在0.5 mol·L-1 HCl介质中APDTC SAMs对铜的缓蚀作用及其吸附行为. 结果表明, APDTC分子易在铜表面形成稳定的APDTC SAMs, 改变了电极表面的双电层结构, SAMs同时抑制了铜的阳极氧化过程和阴极还原过程, 铜电极的电荷转移电阻明显提高, 双电层电容明显降低. 电化学阻抗和极化曲线测试结果显示, 在0.5 mol·L-1 HCl介质中, 铜表面APDTC SAMs表现出良好的缓蚀效果. 研究结果还表明, APDTC的吸附行为符合Langmuir吸附等温式, 吸附机理是介于化学吸附和物理吸附之间的一种吸附.     

Understanding the nonfouling mechanism of surfaces through molecular simulations of sugar-based self-assembled monolayers

This paper presents a molecular simulation study of the interactions of a protein (lysozyme) with self-assembled monolayers (SAMs) of mannitol and sorbitol terminated alkanethiols in the presence of explicit water molecules and ions. The all-atom simulations were performed to calculate the force generated on the protein as a function of its distance above the SAM surfaces. The structural and dynamic properties of water molecules both above the SAM surfaces and around the SAM head groups were analyzed to provide a better understanding of the nonfouling behavior of the sugar-based SAM surfaces. Results from this work suggest that both mannitol and sorbitol SAMs generate a tightly bound, structured water layer around the SAM chains. This hydration layer creates a repulsive force on the protein when it approaches the surface, resulting in a nonfouling surface despite the presence of hydrogen-bond donor groups. This work demonstrates the importance of strong surface-water interactions for surface resistance to nonspecific protein adsorption.     

Molecular simulation study of water interactions with oligo (ethylene glycol)-terminated alkanethiol self-assembled monolayers

Molecular simulations were performed to study a system consisting of protein (e.g., lysozyme) and self-assembled monolayers (SAMs) terminating with different chemical groups in the presence of explicit water molecules and ions. Mixed SAMs of oligo (ethylene glycol) [S(CH2)4(OCH2CH2)4OH, (OEG)] and hydroxyl-terminated SAMs [S(CH2)4OH] with a mole fraction of OEG at chiOEG = 0.2, 0.5, 0.8, and 1.0 were used in this study. In addition, methyl-terminated SAMs [S(CH2)11CH3] were also studied for comparison. The structural and dynamic behavior of hydration water, the flexibility and conformation state of SAMs, and the orientation and conformation of protein were examined. Simulation results were compared with those of experiments. It appears that there is a correlation between OEG surface resistance to protein adsorption and the surface density of OEG chains, which leads to a large number of tightly bound water molecules around OEG chains and the rapid mobility of hydrated SAM chains.     

Improving the surface biocompatibility with the use of mixed zwitterionic self-assembled monolayers prepared by a proper solvent

In this study, the mixed self-assembled monolayers (SAMs) containing the mixture of long-chain alkanethiol, SH(CH(2))(11)NH(2) and SH(CH(2))(10)SO(3)H, was prepared as a model surface to examine the interaction between the biological environment and artificial surface. The 10% (v/v) NH(4)OH ethanolic solution and DMSO were chosen as the solvents for the preparation of these mixed SAMs and the "solvent effect" was discussed. X-ray photoelectron spectroscopy (XPS) has indicated that -SO(3)H/-NH(2) mixed SAMs formed from 10% (v/v) NH(4)OH ethanolic solution were surface "-SO(3)H poor", while a nearly equivalent amount of surface -SO(3)H functionality was presented on the mixed SAMs formed from DMSO. This has resulted from the different solvation capability between solvent molecules and the alkanethiol. Such solvent effects were also reflected in various surface properties such as surface wettability and surface zeta potential. The mixed SAMs formed from DMSO were more surface hydrophilic and less negatively surface charged than from 10% (v/v) NH(4)OH ethanolic solution. In addition, these mixed SAMs formed from DMSO exhibited the least amount of protein adsorbed as well as a better platelet compatibility than its counterpart from 10% (v/v) NH(4)OH ethanolic solution. These findings indicated that choosing a proper solvent for mixed zwitterionic SAM can greatly affect its surface properties and biocompatibility, such as to form a surface with near neutrality for reducing protein adsorption and subsequent platelet adhesion and activation.     

Prediction of the orientations of adsorbed protein using an empirical energy function with implicit solvation

When simulating protein adsorption behavior, decisions must first be made regarding how the protein should be oriented on the surface. To address this problem, we have developed a molecular simulation program that combines an empirical adsorption free energy function with an efficient configurational search method to calculate orientation-dependent adsorption free energies between proteins and functionalized surfaces. The configuration space is searched systematically using a quaternion rotation technique, and the adsorption free energy is evaluated using an empirical energy function with an efficient grid-based calculational method. In this paper, the developed method is applied to analyze the preferred orientations of a model protein, lysozyme, on various functionalized alkanethiol self-assembled monolayer (SAM) surfaces by the generation of contour graphs that relate adsorption free energy to adsorbed orientation, and the results are compared with experimental observations. As anticipated, the adsorbed orientation of lysozyme is predicted to be dependent on the discrete organization of the functional groups presented by the surface. Lysozyme, which is a positively charged protein, is predicted to adsorb on its 'side' on both hydrophobic and negatively charged surfaces. On surfaces with discrete positively charged sites, attractive interaction energies can also be obtained due to the presence of discrete local negative charges present on the lysozyme surface. In this case, 'end-on' orientations are preferred. Additionally, SAM surface models with mixed functionality suggest that the interactions between lysozyme and surfaces could be greatly enhanced if individual surface functional groups are able to access the catalytic cleft region of lysozyme, similar to ligand-receptor interactions. The contour graphs generated by this method can be used to identify low-energy orientations that can then be used as starting points for further simulations to investigate conformational changes induced in protein structure following initial adsorption.     

An aqueous-based surface modification of poly(dimethylsiloxane) with poly(ethylene glycol) to prevent biofouling

We report a simple modification of poly(dimethylsiloxane) (PDMS) surfaces with poly(ethylene glycol) (PEG) through the adsorption of a graft copolymer, poly(l-lysine)-graft-poly(ethylene glycol) (PLL-g-PEG) from aqueous solution. In this approach, the PDMS surface was treated with oxygen plasma, followed by immersion into aqueous solution containing PLL-g-PEG copolymers. Due to the hydroxyl/carboxylic groups generated on the PDMS surface after oxygen plasma, the polycationic PLL backbone is attracted to the negatively charged surface and PEG side chains exhibit an extended structure. The PEG/aqueous interface generated in this way revealed a near-perfect resistance to nonspecific protein adsorption as monitored by means of optical waveguide lightmode spectroscopy (OWLS) and fluorescence microscopy.     

Protein adsorption on oligo(ethylene glycol)-terminated alkanethiolate self-assembled monolayers: The molecular basis for nonfouling behavior

A study of protein resistance of oligo(ethylene glycol) (OEG), HS(CH2)11(OCH2CH2)nOH (n = 2, 4, and 6), self-assembled monolayers (SAMs) on Au(111) surfaces is presented here. Hydroxyl-terminated OEG-SAMs are chosen to avoid the hydrophobic effect observed with methyl-terminated OEG-SAMs, particularly at high packing densities. The structure of the OEG-SAM surfaces is controlled by adjusting the assembly solvent. These SAMs were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Protein adsorption on these surfaces was investigated by surface plasmon resonance (SPR). OEG-SAMs assembled from mixed ethanol and water solutions show higher packing density on gold than those from pure ethanol solution. For EG2OH- and EG4OH-SAMs, proteins (i.e., fibrinogen and lysozyme) adsorb more on the densely packed SAMs prepared from mixed ethanol and water solutions, while EG6OH-SAMs generally resist protein adsorption regardless of the assembly solvent used.     

Synthesis and self-assembly of galactose-terminated alkanethiols and their ability to resist proteins

The synthesis of two galactose-terminated alkanethiols with the structural formula X-OC2H5NHCO(CH2)15SH (X = 2,3,4,6-tetra-O-methyl-beta-D-Gal or beta-D-Gal) is described. Single-component and mixed self-assembled monolayers (SAMs) of the methylated and nonmethylated compounds were prepared on gold and subsequently characterized with ellipsometry, contact angle goniometry, and infrared reflection-absorption spectroscopy. Studies of the irreversible protein adsorption onto the SAMs using ex-situ ellipsometry revealed very low levels of fibrinogen and lysozyme adsorption onto mixed SAMs displaying advancing water contact angles between 24 degrees and 45 degrees and below 45 degrees , respectively. A monomethylated compound (X = 6-O-methyl-beta-D-Gal) was also synthesized and assembled on gold. This particular compound was found to possess wettability properties corresponding to the low adsorption regime of the mixed SAMs, and the results from the same set of fibrinogen and lysozyme adsorption experiments showed very low levels of protein adsorption. Our findings suggest that the protein rejecting properties rely on a fine balance between the surface energy and/or hydrogen bond donating/accepting properties of the SAM surface.     

Molecular dynamics simulations of low-ordered alzheimer β-amyloid oligomers from dimer to hexamer on self-assembled monolayers

Accumulation of small soluble oligomers of amyloid-β (Aβ) in the human brain is thought to play an important pathological role in Alzheimer's disease. The interaction of these Aβ oligomers with cell membrane and other artificial surfaces is important for the understanding of Aβ aggregation and toxicity mechanisms. Here, we present a series of exploratory molecular dynamics (MD) simulations to study the early adsorption and conformational change of Aβ oligomers from dimer to hexamer on three different self-assembled monolayers (SAMs) terminated with CH(3), OH, and COOH groups. Within the time scale of MD simulations, the conformation, orientation, and adsorption of Aβ oligomers on the SAMs is determined by complex interplay among the size of Aβ oligomers, the surface chemistry of the SAMs, and the structure and dynamics of interfacial waters. Energetic analysis of Aβ adsorption on the SAMs reveals that Aβ adsorption on the SAMs is a net outcome of different competitions between dominant hydrophobic Aβ-CH(3)-SAM interactions and weak CH(3)-SAM-water interactions, between dominant electrostatic Aβ-COOH-SAM interactions and strong COOH-SAM-water interactions, and between comparable hydrophobic and electrostatic Aβ-OH-SAM interactions and strong OH-SAM-water interactions. Atomic force microscopy images also confirm that all of three SAMs can induce the adsorption and polymerization of Aβ oligomers. Structural analysis of Aβ oligomers on the SAMs shows a dramatic increase in structural stability and β-sheet content from dimer to trimer, suggesting that Aβ trimer could act as seeds for Aβ polymerization on the SAMs. This work provides atomic-level understanding of Aβ peptides at interface.     

Nanoscale Biomolecular Structures on Self‐Assembled Monolayers Generated from Modular Pegylated Disulfides

A solid‐phase synthetic strategy was developed that uses modular building blocks to prepare symmetric oligo(ethylene glycol)‐terminated disulfides with a variety of lengths and terminal functionalities. The modular disulfides, composed of alkyl amino groups linked by an amide group to oligoethylene chains were used to generate self‐assembled monolayers (SAMs), which were characterised to determine their applicability for biomolecular applications. X‐ray photoelectron spectroscopy (XPS) of the SAMs obtained from these molecules demonstrated improved stability towards displacement by 16‐hexadecanethiol, while surface plasmon resonance (SPR) analyses of SAMs prepared with the hydroxy‐terminated oligoethylene disulfide showed equal resistance to non‐specific protein adsorption in comparison to 11‐mercaptoundecyl tri(ethylene glycol). SAMs made from these adsorbates were amenable to nanoscale patterning by scanning near‐field photolithography (SNP), facilitating the fabrication of nanopatterned, protein‐functionalised surfaces. Such SAMs may be further developed for bionanotechnology applications such as the fabrication of nanoscale biological arrays and sensor devices.