Amine-terminated Self-assembled Monolayers Research Articles

Chemical-Structure Evolution Model for the Self-Assembling of Amine-Terminated Monolayers on Nanoporous Carbon-Doped Organosilicate in Tightly Controlled Environments.

Amine-terminated self-assembled monolayers are molecular nanolayers, typically formed via wet-chemical solution on specific substrates for precision surface engineering or interface modification. However, homogeneous assembling of a highly ordered monolayer by the facile, wet method is rather tricky because it involves process parameters, such as solvent type, molecular concentration, soaking time and temperature, and humidity level. Here, we select 3-aminopropyltrimethoxysilane (APTMS) as a model molecule of aminosilane for the silanization of nanoporous carbon-doped organosilicate (p-SiOCH) under tightly controlled process environments. Surface mean roughness (Ra) and the water contact angle (θ) of the p-SiOCH layers upon silanization at a 10% humidity-controlled environment behave similarly and follow a three-stage evolution: a leap to a maximum at 15 min for Ra (from 0.227 to 0.411 nm) and θ (from 25 to 86°), followed by a gradual decrease to 0.225 nm and 69o, finally leveling off at the above values (>60 min). The -NH3+ fraction indicating monolayer disorientation evolves in a similar fashion. The fully grown monolayer is highly oriented yielding an unprecedented low -NH3+ fraction of 0.08 (and 0.92 of upright -NH2 groups). However, while having a similar thickness of approximately 1.4 ± 0.1 nm, the molecular layers grown at 30% relative humidity exhibit a significantly elevated -NH3+ fraction of 0.42, indicating that controlling the humidity is vital to the fabrication of highly oriented APTMS molecular layers. A bonding-structure evolution model, as distinct from those offered previously, is proposed and discussed.

First-Principles Prediction of Surface Wetting.

We have developed a method for predicting the solvation contribution to solid-liquid interfacial tension (IFT) based on density functional theory and the implicit solvent model COSMO-RS. Our method can be used to predict wetting behavior for a solid surface in contact with two liquids. We benchmarked our method against measurements of contact angle from water-in-oil on silica wafers and a range of self-assembled monolayers (SAMs) with different compositions, ranging from oil-wet to water-wet. We also compared our predictions to literature data for wetting of a polydimethylsilane surface. By explicitly including deprotonation for silica surfaces and carboxylic acid SAMs, very good agreement was obtained with experimental data for nearly all surfaces. Poor agreement was found for amine-terminated SAMs, which could be the result of both method and model insufficiencies and impurities known to be present for such surfaces. Solid-liquid IFT cannot be measured directly, making predictions such as from our method all the more important.

Integration of colloidal silicon nanocrystals on metal electrodes in single-electron transistor

We develop a facile process to integrate colloidal silicon nanocrystals (Si NCs) with metal electrodes in a single-electron transistor by self-assembly. Gold (Au) surface is modified by an amine-terminated self-assembled monolayer to have a positive potential. All-inorganic boron (B) and phosphorus (P) codoped Si NCs, with a negative surface potential and size-controllability, are selectively adsorbed on an amine-terminated Au surface by electrostatic attraction. We demonstrate the fabrication of SETs consisting of electroless-plated Au nanogap electrodes and codoped Si NCs using this process and observation of clear Coulomb diamonds at 9 K.

Influence of pH and Surface Chemistry on Poly(l-lysine) Adsorption onto Solid Supports Investigated by Quartz Crystal Microbalance with Dissipation Monitoring

Poly(L-lysine) (PLL) adsorption onto various materials has been widely applied as a surface modification strategy and layer-by-layer fabrication method. Considering the role of electrostatic charges, a detailed understanding of the influence of solution pH on PLL adsorption process is important for optimization of PLL coating protocols. Herein, PLL adsorption onto different polar and hydrophilic substrates—silica, an amine-terminated self-assembled monolayer (SAM) on gold, and a carboxyl-terminated SAM on gold—across a range of pH conditions was investigated using the quartz crystal microbalance with dissipation. The adsorption kinetics consisted of an initial rapid phase, followed by a second phase where adsorption rate gradually decelerated. These features were interpreted by applying a mean-field kinetic model implying diffusion-limited adsorption in the first phase and reconfiguration of adsorbed PLL molecules in the second phase. The adsorption kinetics and uptake were found to be sensitive to the pH condition, surface chemistry, and flow rate. The strongest PLL adsorption occurred at pH 11 on all three surfaces while weak PLL adsorption generally occurred under acidic conditions. The surface morphology and roughness of adsorbed PLL layers were investigated using atomic force microscopy, and strong PLL adsorption is found to produce a uniform and smooth adlayer while weak adsorption formed a nonuniform and rough adlayer.

Adsorption of hyaluronic acid on solid supports: Role of pH and surface chemistry in thin film self-assembly

Owing to its biocompatibility, resistance to biofouling, and desirable physicochemical and biological properties, hyaluronic acid (HA) has been widely used to modify the surface of various materials. The role of various physicochemical factors in HA adsorption remains, however, to be clarified. Herein, we employed quartz crystal microbalance with dissipation (QCM-D) in order to investigate HA adsorption at different pH conditions onto three substrates—silicon oxide, amine-terminated self-assembled monolayer (SAM) on gold, and carboxylic acid-terminated SAM on gold. The QCM-D experiments indicated specific pH conditions where either strong or weak HA adsorption occurs. The morphology of the adsorbed HA layers was investigated by atomic force microscopy (AFM), and we identified that strong HA adsorption produced a complete, homogenous and smooth HA layer, while weak HA adsorption resulted in rough and inhomogeneous HA layers. The observed specifics of the kinetics of HA adsorption, including a short initial linear phase and subsequent long non-linear phase, were described by using a mean-field kinetic model taking HA diffusion limitations and reconfiguration in the adsorbed state into account. The findings extend the physicochemical background of design strategies for improving the use of passive HA adsorption for surface modification applications.

Boc-protected ω-amino alkanedithiols provide chemically and thermally stable amine-terminated monolayers on gold.

Four custom-designed bidentate adsorbates having either ammonium or Boc-protected amino termini and either methanethiol or ethanethioate headgroups were prepared for the purpose of generating amine-terminated self-assembled monolayers (SAMs) on evaporated gold surfaces. These adsorbates utilize a phenyl-based framework to connect the headgroups to a single hexadecyloxy chain, extending the amino functionality away from the surface of gold, providing two regions within the adsorbate structure where intermolecular interactions contribute to the stability of the fully formed thin film. The structural features of the resulting SAMs were characterized by ellipsometry, X-ray photoelectron spectroscopy, and polarization modulation infrared reflection-absorption spectroscopy. The collected data were compared to those of eight additional SAMs formed from analogous monodentate alkanethiols and alkanethioacetates having either a similar aromatic framework or a simple alkyl chain connecting the headgroup to the tailgroup. The analysis of the data obtained for the full set of SAMs revealed that both the tailgroup and headgroup influenced the formation of a well-packed monolayer, with the Boc-protected amine-terminated alkanethiols producing films with superior surface bonding and adsorbate packing as compared to those formed with ammonium tailgroups or alkanethioacetate headgroups. A comparison of the structural differences before and after deprotection of the Boc-protected amine-terminated thiolate SAMs revealed that the bidentate adsorbate was the most resistant to desorption during the Boc-deprotection procedure. Furthermore, solution-phase thermal desorption tests performed to evaluate the thermal stability of the Boc-deprotected amine-terminated alkanethiolate films provided further evidence of the enhanced stability associated with SAMs formed from these bidentate adsorbates.

Dissolved organic matter adsorption to model surfaces: adlayer formation, properties, and dynamics at the nanoscale.

Adlayers of dissolved organic matter (DOM) form on many surfaces in natural and engineered systems and affect a number of important processes in these systems. Yet, the nanoscalar properties and dynamics of DOM adlayers remain poorly investigated. This work provides a systematic analysis of the properties and dynamics of adlayers formed from a diverse set of eight humic and fulvic acids, used as DOM models, on surfaces of self-assembled monolayers (SAMs) of different alkylthiols covalently bound to gold supports. DOM adsorption to positively charged amine-terminated SAMs resulted in the formation of water-rich adlayers with nanometer thicknesses that were relatively rigid, irreversibly adsorbed, and collapsed upon air drying, as demonstrated by combined quartz crystal microbalance and ellipsometry measurements. DOM adlayer thicknesses varied only slightly with solution pH from 5 to 8 but increased markedly with increasing ionic strength. Contact angle measurements revealed that the DOM adlayers were relatively polar, likely due to the high water contents of the adlayers. Comparing DOM adsorption to SAM-coated sensors that systematically differed in surface charge and polarity characteristics showed that electrostatics dominated DOM-surface interactions. Laccase adsorption to DOM adlayers on amine-terminated SAMs served to demonstrate the applicability of the presented experimental approach to study the interactions of (bio)macromolecules and (nano)particles with DOM.

Multi-color microfluidic electrochemiluminescence cells

We demonstrated multi-color microfluidic electrochemiluminescence (ECL) cells. 5,6,11,12-Tetraphenylnaphthacene (rubrene), 9,10-diphenylanthracene (DPA), tetraphenyldibenzoperiflanthene (DBP)-doped rubrene, and 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) dissolved in a mixed organic solvent of 1,2-dichlorobenzene and acetonitrile in the ratio of 2:1 (v/v) were used as yellow, blue, red, and green ECL solutions, respectively. Light emissions were confirmed using simple-structured ECL cells consisting of two indium tin oxide (ITO) coated glass substrates with an SU-8 spacer of thickness varying from 0.9 to 6μm. The SU-8-based microfluidic ECL cells were fabricated using photolithography and heterogeneous bonding techniques through the use of epoxy- and amine-terminated self-assembled monolayers. The emitting layers were formed on-demand by injecting the chosen ECL solutions into the microchannels sandwiched between ITO anode and cathode pairs. Multi-color ECL was successfully obtained at the light-emitting pixels. The microfluidic ECL cells with DBP-doped rubrene solution showed a maximum luminance of 11.6cd/m2 and the current efficiency of ca. 0.32cd/A at 8V. We expect that the proposed microfluidic device will be a highly promising technology for liquid-based light-emitting applications.

Immobilization of carbon nanotubes on functionalized graphene film grown by chemical vapor deposition and characterization of the hybrid material

We report the surface functionalization of graphene films grown by chemical vapor deposition and fabrication of a hybrid material combining multi-walled carbon nanotubes and graphene (CNT–G). Amine-terminated self-assembled monolayers were prepared on graphene by the UV-modification of oxidized groups introduced onto the film surface. Amine-termination led to effective interaction with functionalized CNTs to assemble a CNT–G hybrid through covalent bonding. Characterization clearly showed no defects of the graphene film after the immobilization reaction with CNT. In addition, the hybrid graphene material revealed a distinctive CNT–G structure and p–n type electrical properties. The introduction of functional groups on the graphene film surface and fabrication of CNT–G hybrids with the present technique could provide an efficient, novel route to device fabrication.

Nanocrystalline chitin thin films

Elucidating the interactions between crystalline chitin and various biomacromolecules is of fundamental importance for designing and fabricating chitin-based biomaterials. This work highlights a simple method to prepare ultrathin films of chitin nanocrystals (chitin NC) by spincoating chitin NCs from a colloidal suspension onto a gold surface modified by an amine-terminated self-assembled monolayer. Atomic force microscopy confirmed that chitin NC films are reasonably smooth and homogeneous, and quartz crystal microbalance with dissipation monitoring (QCM-D) solvent exchange experiments demonstrated that chitin NC films have twice as much water as amorphous regenerated chitin (RChitin) films of similar thickness. QCM-D data also showed that chitinase-catalyzed hydrolysis of chitin NC films was much slower than that of RChitin films. Chitinase not only degraded, but also caused the swelling of the chitin nanocrystals. BSA adsorption studies demonstrated that chitin NC films have high protein loading capacity, and thus show potential applications for enzyme immobilization.

Immobilization of Iron Oxide Nanoclusters on Surface Functionalized Silicon Substrate and Their Catalytic Behavior to Synthesize Multi-Walled Carbon Nanotubes

Multi-walled carbon nanotubes (MWCNTs) were grown using iron oxide nanoclusters (Nc) assisted by self-assembled monolayer (SAM) on substrate. The amine-terminated SAM fabricated on silicon substrate (APTMS/SI) was carried out by UV-treatment and immersed into the FeCI3/HCI aqueous solution. Then, Nc were immobilized onto oxidized SAM silicon substrate (SAMs/Si) through electrostatic interaction between cationic Nc and anionic SAMs/Si. The characterization results clearly show that the well-graphitized MWCNTs were synthesized by using functionalized silicon substrate (Nc/SAMs/Si) as a template having appropriate density of catalyst. These consequences show that SAM containing template is important to achieve the effective layer of catalyst to synthesize MWCNTs in chemical vapor deposition (CVD).

Synthesis and Micropatterning of Photocatalytically Reactive Self-Assembled Monolayers Covalently Linked to Si(100) Surfaces via a Si–C Bond

Selective generation of an amine-terminated self-assembled monolayer bound to silicon wafers via a silicon-carbon linkage was realized by photocatalytically reducing the corresponding azide-terminated, self-assembled monolayers (Az-SAMs). The Az-SAM was obtained by thermal deposition of 11-chloroundecene onto a hydrogen-terminated silicon wafer followed by nucleophilic substitution of the chloride with the azide ion in warm N,N'-dimethylformamide (DMF). The presence of the terminal azide group on the SAM was confirmed by reflection absorption infrared spectroscopy (RAIRS), by X-ray photoelectron spectroscopy (XPS), and by detecting the formation of a triazole upon reaction of the azide with an activated alkyne. The desired terminal amine groups were generated by photocatalytic reduction of the Az-SAM with cadmium selenide quantum dots (CdSe Qdots) using λ > 400 nm. Analysis of the reduced SAM by XPS gave results that were consistent with those obtained with an amine-terminated surface obtained by reducing the Az-SAM with triphenylphosphine. To demonstrate the feasibility of using the Az-SAM for surface patterning, a sample was coated with adsorbed CdSe Qdots and exposed to the output of a diode laser at λ = 407 nm through a micropatterned mask. Using a SEM, the pattern formed in this manner was revealed after removing the CdSe Qdots and subsequently adsorbing 10 nm gold nanoparticles (AuNPs) to the positively charged terminal-amine groups. The formation of the pattern by CdSe-photocatalyzed reduction of the azide demonstrates a novel route to create features by selective modification of organic monolayers on silicon wafers.

Using Nitrile Functional Groups to Replace Amines for Solution-Deposited Single-Walled Carbon Nanotube Network Films

Amine-terminated self-assembled monolayers (SAMs) can be utilized to selectively adsorb semiconducting single-walled carbon nanotubes (S-SWNTs), but are not ideal. Formation of these monolayer films from silanes can be dramatically influenced by atmospheric and other processing conditions, resulting in poor-quality SAMs or irreproducible results. The surface sorting method of fabricating these semiconducting nanotube networks (SWNTnts) can become ineffective if the functionalized surface is not smooth with high amine density. However, by replacing the amine with a nitrile group, SAM formation can be made more controllable and reproducible. Upon SWNT deposition, the nitrile group was found to not only adsorb higher density SWNTnts but also sort the nanotubes efficiently, as shown by micro-Raman spectroscopy. Upon testing these SWNTnts for device performance, these thin-film transistors (TFTs) were also found to yield higher quality devices than those fabricated on amine surfaces. Overall, these results expand the applicability of surface sorting and SWNT adsorption to other organic functionalities for nanotube separation. This report provides an outline of the merits and characterization of using the nitrile functional group for the separation and adsorption of SWNTs and its integration in network TFTs.

Ambient-ageing processes in amine self-assembled monolayers on microarray slides as studied by ToF-SIMS with principal component analysis, XPS, and NEXAFS spectroscopy

We investigated the ageing of amine-terminated self-assembled monolayers (amine-SAMs) on different silica substrates due to exposure to different ambient gases, pressures, and/or temperatures using time-of-flight secondary ion mass spectrometry (ToF-SIMS) with principal component analysis and complementary methods of surface analysis as X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS). The goal of this study is to examine the durability of primary amine groups of amine-SAMs stored in a user laboratory prior to being used as supports for biomolecule immobilization and other applications. We prepared amine-SAMs on the native oxides of silicon wafers and glass slides using 3-aminopropyl triethoxysilane, by using optimized conditions such as anhydrous organic solvent and reaction time scale of hours to avoid multilayer growth. Selected commercial amine-SAM slides have been investigated, too. When the amine-SAMs are exposed to air, oxygen incorporation occurs, followed by formation of amide groups. The formation of oxygen species due to ageing was proved by ToF-SIMS, XPS, and NEXAFS findings such as CNO(-) secondary ion emission at m/z 42, observation of the N 1s HNC=O component peak at 400.2-400.3 eV in XPS, and, last but not least, by formation of a π*(HNC=O) resonance at 401 eV in the N K-edge X-ray absorption spectrum. It is concluded that the used multi-method approach comprising complementary ToF-SIMS, XPS, and NEXAFS analyses is well suited for a thorough study of chemical aspects of ageing phenomena of amine-SAM surfaces.

Development of PNA-Array Platforms for Detection of Genetic Polymorphism of Cytochrome P450 2C19

The selective and sensitive detection of target DNA is an important issue for clinical diagnostics, including identification of single nucleotide polymorphism (SNP), as well as for fundamental studies in molecular biology. The commonly used DNA-detection techniques are mainly based on the DNA microarrays, which present probe-DNA molecules immobilized onto a solid surface in an array format for the bio-specific hybridization with the unknown target-DNA fragments. Although the DNA microarrays have been utilized as a basic platform for the clinical detection, selectivity and sensitivity are still limited toward the singlenucleotide discrimination, which precludes the accurate analysis of SNP. In addition, duplexes between the target and probe DNAs exist in a stable form only in the presence of salt because of the electrostatic repulsion between negatively charged ribose-phosphate backbones of DNA; these salt conditions also induce the secondary and tertiary structures of DNA oligomers themselves, which could disturb the hybridization between the target and probe DNAs. On the other hand, peptide nucleic acid (PNA), an artificial nucleic acid analog, has been introduced to overcome the drawbacks of natural DNA in the aspects of specificity, sensitivity, and stability, and been as a molecular tool for the identification of SNP. The neutral backbone of PNA enhances the stability of PNA-DNA duplexes due to the absence of interstrand repulsion between the negatively charged phosphate groups of DNA. In addition, the unnatural structure makes PNA not degraded by enzymatic reactions. In this work, we generated a PNA-array platform to detect the SNP of cytochrome P450 2C19 (CYP2C19) gene. The CYP2C19 gene is known to play an important role in the metabolism of therapeutic drugs, including diazepam, proguanil, lansoprazole, and omeprazole. It is noteworthy that 15-20% of the Asians are genetically deficient in CYP2C19, failing to produce enzymes for the metabolism, compared with the occurrence of 3-5% of Caucasian populations. Specifically, there exist two variant alleles leading to the mutant types. The first varient is CYP2C19*2, which has a G → A nucleotide substitution at position 681, resulting in an aberrant splicing site; the second one, CYP2C19*3, which does a G → A substitution at position 636, resulting in a premature termination codon. According to the previous report, the frequency of CYP2C19*2 and CYP2C19*3 for Koreans is 0.21 and 0.12, respectively. Onto the silicon oxide surface were aldehyde groups introduced via imine formation between amine-terminated self-assembled monolayers (SAMs) and glutaldehyde. Another imine linkage was used for immobilizing the PNA probes, and unreacted aldehyde groups were passivated with 2(2aminoethoxy)ethanol. We designed four probe-PNAs based on the clinically important SNPs of CYP2C19, and denoted them 636W and 636M for the wild and mutant types of CYP2C19*3, and 681W and 681M for CYP2C19*2, respectively (Fig. 1). The linker of the PNA probes contained repetitive ethylene glycol groups and ended with several lysine groups. The immobilization of the probe PNAs was confirmed by hybridization of target DNAs. The target DNAs (T-636W, T-636M, T-681W, and T-681M), complementary to each of the PNA probes, were tagged with Cy3 (green) for wild type and Cy5 (red) for mutant type, respectively. The hybridization was performed for 1 h at 40 C with the DNA solution containing both T-636W and T636M (100 nM), and the same conditions were used for hybridization of T-681W/M. As shown in Fig. 2a, each DNA was selectively hybridized with its complementary probe-

Trapping and release of citrate-capped gold nanoparticles

An electrical method to trap and release charged gold nanoparticles onto and from the surface of gold electrodes modified by an alkanethiol self-assembled monolayer (SAM) is presented. To form electrodes coated with gold nanoparticles (GNPs), amine-terminated SAMs on gold electrodes were immersed in a solution of negatively charged citrate-capped GNPs. Accumulation of GNPs on the electrode surface was monitored by a decrease in the impedance of the SAM-modified electrode and by an increase in the electrochemical activity at the electrode as shown through cyclic voltammetry (CV). Electrostatic interactions between the GNPs and the amine-terminated SAM trap the GNPs on the electrode surface. Application of a subsequent negative bias to the electrode initiated a partial release of the GNPs from the electrode surface. Impedance spectroscopy, cyclic voltammetry, ultraviolet–visible (UV–Vis) spectroscopy and atomic force microscopy (AFM) were used to monitor and confirm the attraction of GNPs to and release from the aminealkanethiolated gold electrodes. This work describes a method of trapping and release for citrate-capped GNPs that could be used for on-demand nanoparticle delivery applications such as in assessing and modeling nanoparticle toxicology, as well as for monitoring the functionalization of gold nanoparticles.

Synthesis of carbon nanotubes with catalytic iron-containing proteins

We report a novel method for the growth of carbon nanotubes (CNTs) that uses the iron-containing proteins, hemoglobin, myoglobin, or cytochrome c. The proteins were adsorbed onto amine-terminated self-assembled monolayer (SAM) by peptide bonds between the amine groups of the SAMs and the carboxyl groups of the proteins. SAM films allow proteins to be adsorbed onto films with appropriate density that can initiate the growth of well-graphitized multi-walled CNTs with a diameter of approximately 10 nm. These results show that proteins that contain iron atoms in any form have the catalytic ability to initiate the growth of CNTs.

The effect of amine protonation on the electrical properties of spin-assembled single-walledcarbon nanotube networks

Amine-terminated self-assembled monolayers (SAMs) have been shown to selectivelyadsorb semiconducting single-walled carbon nanotubes (sc-SWNTs). Previous studies haveshown that when deposited by spin coating, the resulting nanotube networks (SWNTnts)can be strongly influenced by the charge state of the amine (primary, secondary, andtertiary). When the amine surfaces were exposed to varying pH solutions, the conductivityand overall quality of the resulting fabricated networks were altered. Atomic forcemicroscopy (AFM) topography had shown that the density of the SWNTnts was reducedas the amine protonation decreased, indicating that the electrostatic attraction between theSWNTs in solution and the surface influenced the adsorption. Simultaneously,μ-Raman analysis had suggested that when exposed to more basic conditions,the resulting networks were enhanced with sc-SWNTs. To directly confirmthis enhancement, Ti/Pd contacts were deposited and devices were tested inair. Key device characteristics were found to match the enhancement trendspreviously observed by spectroscopy. For the primary and secondary amines,on/off current ratios were commensurate with the Raman trends in metallic contribution, while notrends were observed on the tertiary amine (due to weaker interactions). Finally, differingSWNT solution volumes were used to compensate for adsorption differences andyielded identical SWNTnt densities on the various pH-treated samples to eliminatethe influence of network density. These results further the understanding of theamine–SWNT interaction during the spin coating process. Overall, we provide aconvenient route to provide SWNT-based TFTs with highly tunable electronic chargetransport through better understanding of the influence of these specific interactions.

Photooxidation of Amine-Terminated Self-Assembled Monolayers on Gold

Amine-terminated self-assembled monolayers (SAMs) on Au surfaces are commonly used to immobilize various types of molecules, including DNA and proteins. However, little is known about the stability of these types of surfaces. In this work, it was observed that the surface potential (as well as the isoelectric point) of amine-bearing SAMs on flat gold substrates changed significantly with time, indicating that the surface functional group is not stable under ambient conditions (standard temperature and pressure). Contact angle analysis indicated that after degradation, the polar component of the interfacial force decreased and the dispersion component increased. These results indicate that the surface has undergone a chemical transformation. X-ray photoelectron spectroscopy (XPS) was used to detect changes in the chemical state of the surface nitrogen atoms. The chemical shift of the binding energy indicates that the nitrogen is partially oxidized. Using time-of-flight secondary ion mass spectrometry (ToF-SIMS), the oxidation of the amino groups to nitroso groups was evident, as was the previously reported oxidation of the thiol groups to sulfonate groups. Two methods for retarding the oxidation of the amine functional group are presented in this work. By isolating the SAM from either light or air, the oxidation is suppressed and the surface properties are preserved. In other words, the shelf life of the amine-modified gold substrates is prolonged. This result suggests that the oxidation is either photocatalyzed or photoinduced.

Surface Functionalization of Carbon Micro Coils and Their Selective Immobilization on Surface-Modified Silicon Substrates

Surface functionalization of carbon micro coils (CMCs) was performed by acid treatment at different times. Nitric acid oxidation produced CMC with acidic functional groups, although morphology of CMCs was modified after the oxidation. The selective immobilization of as-prepared CMC from an aqueous dispersion was examined on differently surface-modified silicon substrates. It was confirmed that the acid-treated CMC was selectively immobilized on a silicon substrate by chemical bonding with amine-terminated self-assembled monolayers on a silicon substrate, while the pristine CMC was not.