Self-assembled Monolayers Of 16-mercaptohexadecanoic Acid Research Articles

Photothermal therapeutic ability of copper open-shell nanostructures that are effective in the second biological transparency window based on symmetry breaking-induced plasmonic properties.

In this study, a photothermal therapy agent that works efficiently in the second biological transparency window was developed based on the localized surface plasmon (LSP) resonance of symmetry-broken open-shell nanostructures of low-cost Cu (CuOSNs). The strong LSP resonance and superior photothermal conversion ability in the second biological transparency window were achieved by generating the dipolar bonding mode due to the plasmon hybridization between the nanoshell dipole and the nanohole dipole at the opening edge in CuOSNs derived from the symmetry breaking of a Cu nanoshell. Oxidative dissolution of CuOSNs in water was significantly suppressed by successive coating with the self-assembled monolayer of 16-mercaptohexadecanoic acid and a thin silica layer. Furthermore, the stability in phosphate buffered saline, which models the biological environment, was attained by further coating the nanoparticles with polyethylene glycol. It was demonstrated from in vitro cell tests using HeLa cells that the cytotoxicity of CuOSNs was effectively suppressed by the surface protection. The viability of HeLa cells incubated with CuOSNs was decreased under the irradiation of low intensity 1060 nm laser with increasing number of CuOSNs. These results demonstrate that low-cost symmetry-broken Cu-based nanostructures can act as an excellent photothermal therapy agent in the second biological transparency window.

Pushing the Sample-Size Limit of Infrared Vibrational Nanospectroscopy: From Monolayer toward Single Molecule Sensitivity.

While scattering-scanning near-field optical microscopy (s-SNOM) has demonstrated its potential to extend infrared (IR) spectroscopy into the nanometer scale, it has not yet reached its full potential in terms of spectroscopic sensitivity. We combine broadband femtosecond mid-IR excitation with an optimized spectral irradiance of ∼2 W/cm(2)/ cm(-1) (power/area/bandwidth) and a combination of tip- and substrate enhancement to demonstrate single-monolayer sensitivity with exceptional signal-to-noise ratio. Using interferometric time domain detection, the near-field IR s-SNOM spectral phase directly reflects the molecular vibrational resonances and their intrinsic line shapes. We probe the stretching resonance of ∼1000 carbonyl groups at 1700 cm(-1) in a self-assembled monolayer of 16-mercaptohexadecanoic acid (MHDA) on an evaporated gold substrate with spectroscopic contrast and sensitivity of ≲100 vibrational oscillators. From these results we provide a roadmap for achieving true single-molecule IR vibrational spectroscopy in s-SNOM by implementing optical antenna resonant enhancement, increased spectral pump power, and improved detection schemes.

Electroless deposition of Cu nanostructures on molecular patterns prepared by dip-pen nanolithography

Cu nanostructures deposited on the top of self-assembled molecular patterns prepared by Dip-pen Nanolithography (DPN) are investigated thoroughly in this study. 16-Mercaptohexadecanoic acid (MHA) molecular patterns are used as templates and CuSO4 is reduced by electroless deposition method. According to the SEM, EDS and AFM test results, it is found that the formation and the dimension of the Cu nanostructure array can be governed by reaction conditions and the size of molecular patterns. The non-specific growth of Cu can also be minimized in the present work. The method designed has demonstrated its capability in the synthesis of molecular junctions with high reproducibility. Distinct phenomena of underpotential deposition behaviors of Cu on polycrystalline gold substrates covered with self-assembled monolayers of 16-mercaptohexadecanoic acid and octadecanethiol are also studied and discussed.

Surface characterization and efficiency of a matrix-free and flat carboxylated gold sensor chip for surface plasmon resonance (SPR)

We report the preparation and characterization of a matrix-free carboxylated surface plasmon resonance (SPR) sensor chip with high sensing efficiency by functionalizing a bare gold thin film with a self-assembled monolayer of 16-mercaptohexadecanoic acid (SAM-MHDA chip). The self assembled monolayer surface coverage of the gold layer was carefully evaluated and the SAM was characterized by infrared reflection absorption spectroscopy, X-ray photoemission spectroscopy, atomic force microscopy, X-ray reflectivity-diffraction, and SPR experiments with bovine serum albumin. We compared the SPR signal obtained on this chip made of a dense monolayer of carboxylic acid groups with commercially available carboxylated sensor chips built on the same gold substrate, a matrix-free C1 chip, and a CM5 chip with a ~100 nm dextran hydrogel matrix (GE Healthcare). Two well-studied interaction types were tested, the binding of a biotinylated antibody (immunoglobulin G) to streptavidin and an antigen-antibody interaction. For both interactions, the well characterized densely functionalized SAM-MHDA chip gave a high signal-to-noise ratio and showed a gain in the availability of immobilized ligands for their partners injected in buffer flow. It thus compared favourably with commercially available sensor chips.

Interfacial energy of calcite-MHA/MUA self-assembled monolayers during nucleation

ABSTRACTThe interfacial energies between template-directed calcite nuclei and self-assembled monolayers of 16-mercaptohexadecanoic acid (MHA) and 11-mercaptoundecanoic acid (MUA) were measured. The results reveal that (1) the MHA and MUA significantly reduce the effective surface energy of calcite from about 97 mJ/m2 in solution to about 45.3 and 52.7 mJ/m2 on MHA and MUA respectively, providing a thermodynamic basis for the strong capacity of MHA and MUA to promote calcite nuclei; and (2) the barrier to nucleation is dominated by the free energy barrier which enhances the rate of surface nucleation on MHA and MUA.

Implementing chemical functionality into oriented films of metal–organic frameworks on self-assembled monolayers

The generation of thin films of oriented functionalized metal–organic frameworks (MOFs) on self-assembled monolayers was achieved via direct growth from solution. Specifically, the direct growth from solvothermally pretreated synthesis solutions of two different MOF structures with amino functionality was investigated: the flexible framework structure NH2–Fe–MIL-88B and the mesoporous MOF NH2–Fe–MIL-101 with its remarkably large unit cell. Both MOF structures can be grown in a highly oriented fashion on self-assembled monolayers of 16-mercaptohexadecanoic acid on gold. With the help of a quartz crystal microbalance we demonstrate that the introduction of amino groups into the framework strongly affects the host–guest interactions towards ethanol molecules: thin films of NH2–Fe–MIL-88B show a significantly higher uptake of ethanol than unfunctionalized Fe–MIL-88B films. In situXRD experiments during sorption of ethanol showed that the amino group does have an impact on the cell parameters of the structure, but the flexibility (“breathing”) during ad- and desorption of ethanol is similar for the functionalized and the unfunctionalized structures. It is anticipated that the implementation of chemical functionalities into oriented MOF films will lead to selective host–guest interactions that are of key importance for chemical sensing and other applications.

Sensitive voltammetric detection of clomipramine at 16-mercapto-hexadecanoic acid self-assembled monolayer modified gold electrode

Clomipramine, an effective and important antipsychotic drug with low redox activity and poor hydrophilicity, was found to effectively accumulate on hydrophobic 16-mercaptohexadecanoic acid (i.e. MHA) self-assembled monolayer (SAM) modified gold electrode (i.e. MHA/Au) and generating a sensitive anodic peak at about 0.86 V (vs. SCE) in 0.05 M Tris–HCl (pH = 8.1) buffer solution. Thus, quantitative measurement of clomipramine was established with high sensitivity under optimum conditions. The anodic peak current was linear to clomipramine concentration in the range from 1 × 10−6 to 5 × 10−5 M, with a detection limit of 6 × 10−9 M. This method was successfully applied to the detection of clomipramine in drug tablets and proved to be reliable compared to UV. The spectral features, electrochemical characteristics and wettability of MHA-SAM were also studied.

Reactivity of Acid Fluoride-Terminated Self-Assembled Monolayers on Gold

This report describes the reactivity of acid fluoride (AF)-terminated self-assembled monolayers (SAMs) on gold toward amine and alcohol compounds and the potentiality of AF as a reactive intermediate for surface functionalizations. The AF group was generated in situ on a gold surface by reacting the terminal carboxylic acid group in the SAM of 16-mercaptohexadecanoic acid with cyanuric fluoride and pyridine under the optimized conditions. AF was found to be highly reactive toward various amine groups, such as primary and secondary amines, but it did not react effectively with alcohol. In addition, the amide coupling reaction by microcontact printing (microCP) was compared with the solution-based reaction: when amine-derivatized ferrocene compound was used for 1-min microCP on the AF-activated surface, the surface coverage of the reaction product was about 83% of 3.45 x 1014 cm-2, the coverage obtained in the solution-based reaction. On the basis of the high reaction efficiency of microCP, the AF-activated surface was also used as a platform for patterning a biological ligand, biotin.

Sensitive detection of clozapine using a gold electrode modified with 16-mercaptohexadecanoic acid self-assembled monolayer

Clozapine, an effective antipsychotic drug, was found generating a pair of redox peaks at about 0.33–0.4 V (versus SCE) at 16-mercaptohexadecanoic acid (i.e. MHA) self-assembled monolayer (SAM) modified gold electrode (i.e. MHA/Au) in 0.05 mol L −1 Tris–HCl (pH 8.1) buffer solution. Sensitive and quantitative measurement of clozapine based on anodic peak was established under optimum conditions. The anodic peak current was linear to clozapine concentration in the range from 1 × 10 −6 to 5 × 10 −5 mol L −1 with the detection limit of 7 × 10 −9 mol L −1. This method was successfully applied to the detection of clozapine in drug tablets and proved to be reliable compared with ultraviolet spectrophotometry (UV). The MHA SAM was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), contact angle goniometry, electrochemical impedance spectroscopy (EIS) and electrochemical probe.

Direct patterning of negative nanostructures on self-assembled monolayers of16-mercaptohexadecanoic acid on Au(111) substrate via dip-pen nanolithography

Both bare and self-assembled monolayer (SAM) protected gold substrate could be etchedby allyl bromide according to atomic force microscopy (AFM), x-ray photoelectronspectroscopy (XPS) and inductively coupled plasma mass spectrometric (ICPMS) analysisresults. With this allyl bromide ink material, negative nanopatterns could be fabricateddirectly by dip-pen nanolithography (DPN) on SAMs of 16-mercaptohexadecanoic acid(MHA) on Au(111) substrate. A tip-promoted etching mechanism was proposed wherethe gold-reactive ink could penetrate the MHA resist film through tip-induceddefects resulting in local corrosive removal of the gold substrate. The fabricationmechanism was also confirmed by electrochemical characterization, energy dispersivespectroscopy (EDS) analysis and fabrication of positive nanopatterns via a used DPNtip.

Surface Modification of Functional Self-Assembled Monolayers on 316L Stainless Steel via Lipase Catalysis

Lipase catalyzed esterification of therapeutic drugs to functional self-assembled monolayers (SAMs) on 316L stainless steel (SS) after assembly has been demonstrated. SAMs of 16-mercaptohexadecanoic acid (-COOH SAM) and 11-mercapto-1-undecanol (-OH SAM) were formed on 316L SS, and lipase catalysis was used to attach therapeutic drugs, perphenazine and ibuprofen, respectively, on these SAMs. The reaction was carried out in toluene at 60 degrees C for 5 h using Novozyme-435 as the biocatalyst. The FTIR spectra after surface modification of -OH SAMs showed the presence of the C=O stretching bands at 1745 cm(-1), which was absent in the FTIR spectra of -OH SAMs. Similarly, the FTIR spectra after the reaction of the -COOH SAM with perphenazine showed two peaks in the carbonyl region, a peak at 1764 cm(-1), which is the representative peak for the C=O stretching for esters. The second peak at 1681 cm(-1) is assigned to the C=O stretching of the remaining unreacted terminal COOH. XPS spectra after lipase catalysis with ibuprofen showed a photoelectron peak evolving at 288.5 eV which arises from the carbon (C=O) of the carboxylic acid of the drug (ibuprofen). Similarly for -COOH SAMs, after esterifiation we see a small, photoelectron peak evolving at 286.5 eV which corresponds to the C in the methylene groups adjacent to the oxygen (C-O), which should evolve only after the esterification of perphenazine with the -COOH SAM. Thus, lipase catalysis provides an alternate synthetic methodology for surface modification of functional SAMs after assembly.

Tailoring the electrochemical property of self-assembled monolayer of 16-mercaptohexadecanoic acid on gold (1 1 1) electrode with covalently coupling ethylene diamine

This paper reports an approach to tailor the electrochemical properties of self-assembled monolayer of 16-mercaptohexadecanoic acid (HDA) on gold electrode with covalently coupling ethylene diamine. The electron transfer kinetics of electrode varies from blocking to radial diffusion and then to linear diffusion character by controlling the surface reaction period. However, when HDA monolayer reacts with propylamine or other diamine molecules with longer alkyl chains, such as 1,6-diaminehexan and 1,4-diaminebutane, only enhanced blocking behaviors are observed. This unusual behavior is explored by a series of experiments, and a possible reaction mechanism is proposed.

The Surface Chelate Effect

The presence of a surface chelate effect is established in the model system of Cu2+ adsorption on a self-assembled monolayer of 16-mercaptohexadecanoic acid (MHA) on Au. The formation constant of Cu2+ with the MHA surface was found to be 119 +/- 3.2 times greater than that of Cu2+ with succinic acid (HOOC-(CH2)2-COOH), and 213 +/- 4.0 times greater than that of Cu2+ with glutaric acid (HOOC-(CH2)3-COOH) in aqueous solutions. Both of these molecules are known to chelate to metal ions forming seven- and eight-membered rings. The greater surface chelate effect is attributed to the presence of the two-dimensional array of ligands on the surface. We believe the surface chelate effect demonstrated here is of general significance to adsorption on molecular surfaces and should depend strongly on chemical functionality and monolayer structure.

Fabrication of Stimulus-Responsive Polymeric Nanostructures by Proximal Probes

ABSTRACTThe triggered control of interfacial properties on the nanometer scale holds significant promise for actuation in bio-nanotechnology applications where polymeric actuators may manipulate the transport, separation, and detection of biomolecules. To fabricate patterned, stimulus-responsive polymer brushes we have developed several methods that combine surface initiated polymerization (SIP) with dip-pen nanolithography (DPN). Surface-confined, stimulus-responsive polymer brush nanopatterns were fabricated by amplification of DPN patterned, self-assembled monolayers of 16-mercaptohexadecanoic acid on gold surfaces by SIP of N-isopropylacrylamide (NIPAAm). While free radical polymerization yielded only short polymer brushes (DP<50), atom transfer free radical polymerization (ATRP) produced thick, uniform polymer brushes. For free radical polymerization the thickness of the polymer brush layer is a function of the lateral feature size and the initiator density and is maximal at pattern boundaries.

Chemical Deposition of PbS on Self-Assembled Monolayers of 16-Mercaptohexadecanoic Acid

The chemical deposition of PbS on self-assembled monolayers of 16-mercaptohexadecanoic acid formed on evaporated gold was investigated. In situ evaluation of the thickness of the crystalline film and of the kinetics of crystal growth was carried out by surface plasmon spectroscopy (SPS). The SPS measurements were correlated with structural and morphological data on the PbS films, as obtained by transmission electron microscopy and scanning electron microscopy, thus enabling the film structure at precise thicknesses to be identified. The applicability of SPS measurements to such a system was demonstrated. The microscopical analysis clearly showed that the film exhibited a marked structural change at a thickness of 25 nm. It was proposed that the film formed by an ion-by-ion mechanism.