16-mercaptohexadecanoic Acid Research Articles

Nanobiosensors based on tyrosinase with alkanethiols for detection commercial formulation of atrazine in artesian water samples applied in agriculture crop

This study aims to develop cantilever nanobiosensors functionalized with commercial tyrosinase enzymes and alkanethiols for the detection of a commercial formulation of atrazine in artesian water samples used in agricultural crops. Functionalization was carried out using the self-assembled monolayer (SAM) technique with different alkanethiols, namely, 16-mercaptohexadecanoic acid (16-MHDA) and 11-mercaptoundecanoic acid (11-MUA), in conjunction with commercial tyrosinase enzymes. Surface characterization techniques confirm the successful deposition of the sensing layer. The nanobiosensors exhibited the capability to detect various concentrations of atrazine in water, achieving high sensitivity with detection and quantification limits in the µg/L range, while maintaining 100 % reversibility. The enzyme retained 87 % and 80 % of its activity when immobilized on 16-MHDA and 11-MUA linkages, respectively. The response of cantilever nanobiosensors was stable after 13 min, with deflection values showing a direct proportional relationship with atrazine concentrations ranging from 0.001 to 100 µg/L. Both cantilever nanobiosensors demonstrated promising responses, with 11-MUA differing statistically (P<0.05) from 16-MHDA. The rapid detection of commercial atrazine was successfully conducted in real water samples collected directly during its application in crop fields. Consequently, the developed devices hold significant potential for practical use in the detection of atrazine in water, contributing to assessments of environmental quality.

In Situ Dynamic Spectroscopic Ellipsometry Characterization of Cu-Ligated Mercaptoalkanoic Acid "Molecular" Ruler Multilayers.

Hybrid strategies that combine conventional top-down lithography with bottom-up molecular assembly are of interest for a range of applications including nanolithography and sensors. Interest in these strategies stems from the ability to create complex architectures over large areas with molecular-scale control and precision. The molecular-ruler process typifies this approach where the sequential layer-by-layer assembly of mercaptoalkanoic acid molecules and metal ions are combined with conventional top-down lithography to create precise, registered nanogaps. However, the quality of the metal-ligated mercaptoalkanoic acid multilayer is a critical characteristic in generating reproducible and robust nanoscale structures via the molecular-ruler process. Therefore, we explore the assembly of alkanethiolate monolayers, mercaptohexadecanoic acid (MHDA) monolayers, and Cu-ligated MHDA multilayers on Au{111} substrates using atomic force microscopy and in situ dynamic spectroscopic ellipsometry. The chemical film thicknesses in situ dynamic spectroscopic ellipsometry agree with previous ex situ surface analytical methods. Moreover, in situ dynamic spectroscopic ellipsometry provides insight into the assembly process without interrupting the assembly process and potentially altering the characteristics of the resulting chemical film. By following the real-time dynamics of each deposition step, the assembly of the Cu-ligated MHDA multilayers can be optimized to minimize deposition time while having minimal impact to the quality of the chemical film.

The optimization of self-assembled monolayer of thiols on screen-printed gold electrode

&lt;span&gt;The activated gold-modified electrode surface for self-assembled monolayer (SAM) is suitable for N-(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDC), 16-mercaptohexadecanoic acid (16-MDA), and N-hydroxysuccinimide (NHS). The various substrates could potentially be used for surface functionalization that binds to one another. Using modified screen-printed gold electrodes, 16-MDA, EDC, and NHS, we developed a self-assembling monolayer. Different 16-MDA concentrations were applied to the surface of a screen-printed electrode surface to enhance the sensitivity of the working electrode. The impact of different EDC, NHS, and 16-MDA concentrations (0.4 M, 0.8 M, 1 M, 1.2 M, 1.4 M, and 1.8 M) and incubation times between 5 and 30 minutes were examined and compared. The binding surface of the screen-printed gold electrode was characterized using the differential pulse voltammetry (DPV) technique. It has been demonstrated that the substrate concentrations at 5 minutes and 30 minutes of incubation time used to have the highest surface coverage and electron transfer rates. This concentration would be utilized in the subsequent experiment to evaluate the binding of various bacterial species. These findings suggest that the SAM in a modified screen-printed gold electrode may be functionalized to detect microorganisms.&lt;/span&gt;

Separation of shifts in surface plasmon resonance into refractive index and thickness of deposited layers

Routine Surface Plasmon Resonance (SPR) measurements, which are widely applied in affinity (bio)sensors and surface science, do not allow one to separate the obtained SPR signals into the change of the refractive index and thickness of deposited layers. For thin layers the signal is proportional to the product of the layer thickness and the difference in the refractive indices of this layer and of the aqueous media. In this study, we suggest an approach to separate these parameters. It is performed by subsequent measurements in the presence and in the absence of polyethylene glycol (PEG), an inert additive which modifies the refractive index of the liquid phase but do not penetrate into the adsorbed layer. Both parameters were successively determined for human serum albumin (HSA) as well as for anti-HSA IgG in three different settings: i) HSA adsorbed directly onto a gold surface, ii) HSA chemically immobilized on a gold surface coated with a self-assembled monolayer of 1,16 mercaptohexadecanoic acid and iii) chemically immobilized HSA with additional monomolecular layer of anti-HSA IgG antibodies bond to this protein layer. The suggested approach can be applied in most SPR devices with a flow cell for analysis of various adsorbed layers.

Impact of Surface Functionalization and Deposition Method on Cu-BDC surMOF Formation, Morphology, Crystallinity, and Stability.

For direct integration into device architectures, surface-anchored metal-organic framework (surMOF) thin films are attractive systems for a wide variety of electronic, photonic, sensing, and gas storage applications. This research systematically investigates the effect of deposition method and surface functionalization on the film formation of a copper paddle-wheel-based surMOF. Solution-phase layer-by-layer (LBL) immersion and LBL spray deposition methods are employed to deposit copper benzene-1,4-dicarboxylate (Cu-BDC) on gold substrates functionalized with carboxyl- and hydroxyl-terminated alkanethiol self-assembled monolayers (SAMs). A difference in crystal orientation is observed by atomic force microscopy and X-ray diffractometry based on surface functionalization for films deposited by the LBL immersion method but not for spray-deposited films. Cu-BDC crystallites with a strong preferred orientation perpendicular to the substrate were observed for the films deposited by the LBL immersion method on carboxyl-terminated SAMs. These crystals could be removed upon testing adhesive properties, whereas all other Cu-BDC surMOF film structures demonstrated excellent adhesive properties. Additionally, film stability upon exposure to water or heat was investigated. Ellipsometric data provide insight into film formation elucidating 7 and 14 Å average thicknesses per deposition cycle for films deposited by the immersion method on 11-mercapto-1-undecanol (MUD) and 16-mercaptohexadecanoic acid (MHDA), respectively. In contrast, the films deposited by the spray method are thicker with the same average thickness per deposition cycle (21 Å) for both SAMs. While the spray method takes less time to grow thicker films, it produces similar crystallite structures, regardless of the surface functionalization. This research is fundamental to understanding the impact of deposition method and surface functionalization on surMOF film growth and to provide strategies for the preparation of high-quality surMOFs.

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.

Aggregation induced emission of surface ligand controlled gold nanoclusters employing imidazolium surface active ionic liquid and pH sensitivity

Gold nanoclusters (AuNCs) are one of the emerging materials due to their luminescence property, but their fluorescence intensity significantly gets quenched in aqueous medium due to the intramolecular vibration and rotation of the capping ligands. Herein, we have prepared long carbon chain containing mercaptan acids capped AuNCs, using 16-mercaptohexadecanoic acid (MHDA) and 11-mercaptoundecanoic acid (MUA) respectively, in aqueous medium with quantum yields (QYs) 3.01% and 6.27% respectively. These AuNCs are negatively charged particles confirmed by zeta potential measurements. After addition of positively charged long hydrocarbon chain containing imidazolium surface active ionic liquid (SAIL), 1-hexadecyl-3-methylimidazolium chloride (C16mimCl) in these aqueous AuNCs solutions, respective fluorescence intensities increase due to the formation of rigid aggregates with AuNC. The intramolecular vibration and rotation of these capping ligands (MHDA and MUA) are reduced due to the formation of these rigid aggregates and therefore, the QYs of these MHDA and MUA capped AuNCs increase to 5.78% and 6.87% respectively. Now the aggregation induced emission is strongly dependent on the concentration of added C16mimCl with the presence of three distinct regions (first turbid, precipitate and second turbid). The aggregation induced emission enhancement in case of MHDA capped AuNC becomes more prominent than MUA capped AuNC because of more hydrophobic interaction. Moreover, with decreasing the pH of the solution, the carboxylate (–COO-) groups of the capping ligands are protonated and therefore, the electrostatic interaction between AuNCs and C16mimCl no longer exist. This results the gradual decrement in emission intensity and this produces a linear relationship against pH of the solution within pH range 7.5 to 1.5.

Suppression of Impedimetric Baseline Drift for Stable Biosensing

Biosensors based on Electrochemical Impedance Spectroscopy (EIS) detect the binding of an analyte to a receptor functionalized electrode by measuring the subsequent change in the extracted charge-transfer resistance (RCT). In this work, the stability of a long chain alkanethiol, 16-mercaptohexadecanoic acid was compared to that of a polymer-based surface linker, ortho-aminobenzoic acid (o-ABA). These two classes of surface linkers were selected due to the marked differences in their structural properties. The drift in RCT observed for the native SAM functionalized gold electrodes was observed to correlate to the drift in the subsequent receptor functionalized SAM. This indicates the importance of the gold-molecule interface for reliable biosensing. Additionally, the magnitude of the baseline drift correlated to the percentage of thiol molecules improperly bound to the gold electrode as evaluated using X-ray Photoelectron Spectroscopy (XPS). Alternatively, the o-ABA functionalized gold electrodes demonstrated negligible drift in the RCT. Furthermore, these polymer functionalized gold electrodes do not require a stabilization period in the buffer solution prior to receptor functionalization. This work emphasizes the importance of understanding and leveraging the structural properties of various classes of surface linkers to ensure the stability of impedimetric measurements.

Functionalized gold nanoparticles and nanoplatelets synthesized using plant extract and their potential for surface-enhanced Raman spectroscopy

Gold nanoparticles are increasingly used in biomedical fields due to their biocompatibility and their optical properties, such as tunable absorption of light and their efficiency for light to heat conversion, leading to recent developments in applications like photothermal therapy. In this work, gold nanoparticles and nanoplatelets were synthesized using an Aloe Vera leaf extract, without any additional surfactant, and functionalized using 16-mercaptohexadecanoic acid or L-Cysteine. The latest grafted nanoparticles and nanoplatelets were also further functionalized using Alexa Fluor NHS ester, that covalently binds to the amine group of L-Cysteine. They were fully characterized using Scanning/Transmission Electron Microscopy, UV-vis-NIR absorption and Raman spectroscopy The synthesized gold particles possess a large diversity of shapes: platelets with a triangular or hexagonal profile, tetrahedra, decahedra, icosahedra and bipyramids, but also polycrystals made of the assembly of two or three crystals. Their dimensions and proportions are correlated to the plant extract concentration used during the synthesis: the lower the concentration of the plant extract, the bigger the particles. Finally, the particles exhibit localized surface plasmon resonances correlated to their shapes. More, at the vicinity of the functionalized particles, we show that the Raman signal of 2,2’-bipyridine molecules is greatly enhanced, proving their potential use in SERS applications.

How to Use Localized Surface Plasmon for Monitoring the Adsorption of Thiol Molecules on Gold Nanoparticles?

The functionalization of spherical gold nanoparticles (AuNPs) in solution with thiol molecules is essential for further developing their applications. AuNPs exhibit a clear localized surface plasmon resonance (LSPR) at 520 nm in water for 20 nm size nanoparticles, which is extremely sensitive to the local surface chemistry. In this study, we revisit the use of UV-visible spectroscopy for monitoring the LSPR peak and investigate the progressive reaction of thiol molecules on 22 nm gold nanoparticles. FTIR spectroscopy and TEM are used for confirming the nature of ligands and the nanoparticle diameter. Two thiols are studied: 11-mercaptoundecanoic acid (MUDA) and 16-mercaptohexadecanoic acid (MHDA). Surface saturation is detected after adding 20 nmol of thiols into 1.3 × 10−3 nmol of AuNPs, corresponding approximately to 15,000 molecules per AuNPs (which is equivalent to 10.0 molecules per nm2). Saturation corresponds to an LSPR shift of 2.7 nm and 3.9 nm for MUDA and MHDA, respectively. This LSPR shift is analyzed with an easy-to-use analytical model that accurately predicts the wavelength shift. The case of dodecanehtiol (DDT) where the LSPR shift is 15.6 nm is also quickly commented. An insight into the kinetics of the functionalization is obtained by monitoring the reaction for a low thiol concentration, and the reaction appears to be completed in less than one hour.

Evaluating effect of metallic ions on aggregation behavior of \u03b2-amyloid peptides by atomic force microscope and surface-enhanced Raman Scattering

BackgroundExcessive aggregation of β-amyloid peptides (Aβ) is regarded as the hallmark of Alzheimer’s disease. Exploring the underlying mechanism regulating Aβ aggregation remains challenging and investigating aggregation events of Aβ in the presence and absence of metallic ions at molecular level would be meaningful in elucidating the role of metal cations on interactions between Aβ molecules. In this study, chemical self-assembled monolayer (SAM) method was employed to fabricate monolayer of β-amyloid peptides Aβ42 on gold substrate with a bolaamphiphile named 16-Mercaptohexadecanoic acid (MHA). Firstly, the samples of gold substrate (blank control), the MHA-modified substrate, and the Aβ42-modified substrate were detected by X-ray photoelectron spectroscopy (XPS) to track the self-assembly process. Aggregation behaviors of Aβ42 before and after metallic ions (Zn2+, Ca2+, Al3+) treatment were monitored by atomic force microscopy (AFM) and the interaction between Aβ42 and metallic ions (Zn2+, Ca2+, Al3+) was investigated by surface-enhanced Raman Scattering (SERS).ResultsThe XPS spectra of binding energy of gold substrate (blank control), the MHA-modified substrate, and the Aβ42-modified substrate are well fitted with the corresponding monolayer’s composition, which indicates that Aβ42 monolayer is well formed. The recorded surface morphology of different experimental groups obtained by AFM showed markedly different nanostructures, indicating occurrence of aggregation events between Aβ42 molecules after adding metal ions to the solution. Compared to the control group, the presence of metallic ions resulted in the increased size of surface structures on the observed 3D topography. Besides, the intermolecular rupture force of Aβ42 increased with the addition of metallic ions. Further study by SERS showed that the Raman strength of Aβ42 changes significantly after the metal cation treatment. A considerable part of the amide bonds interacts with metal cations, leading to a structural change, which is characterized by the weakened β-fold Raman peak.ConclusionThe AFM imaging results suggest that aggregation events occurred between Aβ42 molecules with the addition of metal cations. In addition, the results of force tests indicate that the presence of metallic ions could promote adhesion between Aβ42 molecules, which is likely to be the trigger for aggregation behavior of Aβ42. Furthermore, the effect of metallic cations on the conformational change of Aβ42 studied by SERS supported the results obtained by AFM. Taken together, the results showed that the presence of substoichiometric metal cations promotes aggregation behavior between Aβ42 molecules on the substrate at pH 7.4.

The Emission Mechanism of Gold Nanoclusters Capped with 11-Mercaptoundecanoic Acid, and the Detection of Methanol in Adulterated Wine Model.

The absorption and emission mechanisms of gold nanoclusters (AuNCs) have yet to be understood. In this article, 11-Mercaptoundecanoic acid (MUA) capped AuNCs (AuNC@MUA) were synthesized using the chemical etching method. Compared with MUA, AuNC@MUA had three obvious absorption peaks at 280 nm, 360 nm, and 390 nm; its photoluminescence excitation (PLE) peak and photoluminescence (PL) peak were located at 285 nm and 600 nm, respectively. The AuNC@MUA was hardly emissive when 360 nm and 390 nm were chosen as excitation wavelengths. The extremely large stokes-shift (>300 nm), and the mismatch between the excitation peaks and absorption peaks of AuNC@MUA, make it a particularly suitable model for studying the emission mechanism. When the ligands were partially removed by a small amount of sodium hypochlorite (NaClO) solution, the absorption peak showed a remarkable rise at 288 nm and declines at 360 nm and 390 nm. These experimental results illustrated that the absorption peak at 288 nm was mainly from metal-to-metal charge transfer (MMCT), while the absorption peaks at 360 nm and 390 nm were mainly from ligand-to-metal charge transfer (LMCT). The PLE peak coincided with the former absorption peak, which implied that the emission of the AuNC@MUA was originally from MMCT. It was also interesting that the emission mechanism could be switched to LMCT from MMCT by decreasing the size of the nanoclusters using 16-mercaptohexadecanoic acid (MHA), which possesses a stronger etching ability. Moreover, due to the different PL intensities of AuNC@MUA in methanol, ethanol, and water, it has been successfully applied in detecting methanol in adulterated wine models (methanol-ethanol-water mixtures).

A stable naked-eye colorimetric sensor for monitoring release of extracellular gamma-aminobutyric acid (GABA) neurotransmitter from SH-SY5Y cells

A novel optical γ-aminobutyric acid (GABA)-based sensor was developed on interacting thiol compounds and o-phthalaldehyde (OPA) to form thiacetal compounds. Then, the thiacetal interacts with the GABA molecule to form an isoindole compound. The effects of four thiol compounds on the stability of the resulting isoindole compound were assessed. The 2-mercaptoethanol, “one of the most used derivatizing agents,” is unexpectedly the least stable; while, 16-mercaptohexadecanoic acid resulted in the most durable isoindole compound. The developed sensor showed the capability for detecting GABA within a wide concentration range spanning from 500 nmol L–1 to 100 µmol L–1. The detection limit was about 330 nmol L–1, which indicated the high sensitivity of the developed sensor compared with those previously reported. The findings illustrated the ability to detect GABA at the physiological pH (pH = 7.4) without adjusting the pH value, opening the door for real applications. Furthermore, the sensor could detect various GABA concentrations in human serum with good recovery percentages (98% to 101.4%). In addition, this assay was applied to monitor GABA release from the SH-SY5Y cell line to convert glutamate into GABA. This result indicates the capability of the proposed assay for visually monitoring the release of GABA neurotransmitters.

Formation of extraordinary density alkanethiol self-assembled monolayers on surfaces of digitally photocorroded (001) GaAs/AlGaAs nanoheterostructures

We report the formation of extraordinary density 16-mercaptohexadecanoic acid (MHDA) self-assembled monolayer (SAMs) on surfaces of freshly etched and re-etched bulk (001) GaAs and on GaAs surfaces of a (001) GaAs/Al0.35Ga0.65 As nanoheterostructure exposed by digital photocorrosion (DIP). Our results demonstrate the advantage of a 2-step thiolation process in achieving high-quality MHDA SAMs on (001) GaAs surfaces. However, the development of the systematically increasing quality SAMs, as suggested by the Fourier-transform infrared absorption (FTIR) data, has been observed on the surfaces of GaAs subsequently revealed by DIP of the GaAs/Al0.35Ga0.65 As nanoheterostructure. An MHDA SAM with the maximum absorbance intensity of the asymmetric -CH2 vibrations, νasym = 2919.6 cm−1, equal to 1.08 × 102 and characterized by the full-width-at-half-maximum of 20.3 cm−1, represents the best quality SAM ever obtained on the surface of (001) GaAs. The underlying mechanism has been explained in terms of the formation of nanostructured surfaces with the increasing concentration of low-coordination number surface atoms available for the interaction with MHDA thiolates. The increased surface density of highly-organized SAMs remains in a qualitative agreement with the proposed cone model of DIP nanostructured surfaces.

Specific Detection of PE-Included Vesicles Using Cyclic Voltammetry

The binding between cinnamycin and the phosphatidylethanolamine (PE)-included vesicles was monitored using cyclic voltammetry (CV) measurements and interpreted in terms of the composition of the vesicles and the monolayer binding site. The monolayer was composed of pure 11-mercapto-1-undecanol (MUD) to 90% MUD/10% 16-mercaptohexadecanoic acid (MHA) on a gold surface. Cinnamycin was immobilized on each monolayer. The vesicles, prepared at the desired ratio of the phospholipids, were injected on the cinnamycin-immobilized surface. CV experiments were performed for each step. For the pure-dipalmitoylphosphatidyl-choline (DPPC) vesicles on all of monolayers and the DPPC/dipalmitoylphosphatidyl-ethanolamine (DPPE) vesicles on the pure-MUD monolayer, the electric property of the surface was little changed. However, the vesicles made with 90% DPPC/10% DPPE on the monolayer prepared with 99% MUD/1% MHA to 90% MUD/10% MHA showed a consistent decrease in the CV response. Additionally, in the 95% DPPC/5% DPPE vesicles and the 99.5% MUD/0.5% MHA monolayer, variances in the responses were observed.

Effect of Dipole Orientation in Mixed, Charge-Equilibrated Self-assembled Monolayers on Protein Adsorption and Marine Biofouling.

While zwitterionic interfaces are known for their excellent low-fouling properties, the underlying molecular principles are still under debate. In particular, the role of the zwitterion orientation at the interface has been discussed recently. For elucidation of the effect of this parameter, self-assembled monolayers (SAMs) on gold were prepared from stoichiometric mixtures of oppositely charged alkyl thiols bearing either a quaternary ammonium or a carboxylate moiety. The alkyl chain length of the cationic component (11-mercaptoundecyl)-N,N,N-trimethylammonium, which controls the distance of the positively charged end group from the substrate's surface, was kept constant. In contrast, the anionic component and, correspondingly, the distance of the negatively charged carboxylate groups from the surface was varied by changing the alkyl chain length in the thiol molecules from 7 (8-mercaptooctanoic acid) to 11 (12-mercaptododecanoic acid) to 15 (16-mercaptohexadecanoic acid). In this way, the charge neutrality of the coating was maintained, but the charged groups exposed at the interface to water were varied, and thus, the orientation of the dipoles in the SAMs was altered. In model biofouling studies, protein adsorption, diatom accumulation, and the settlement of zoospores were all affected by the altered charge distribution. This demonstrates the importance of the dipole orientation in mixed-charged SAMs for their inertness to nonspecific protein adsorption and the accumulation of marine organisms. Overall, biofouling was lowest when both the anionic and the cationic groups were placed at the same distance from the substrate's surface.

Effective replacement of cetyltrimethylammonium bromide (CTAB) by mercaptoalkanoic acids on gold nanorod (AuNR) surfaces in aqueous solutions.

The highly packed cetyltrimethylammonium bromide (CTAB) bilayer built up on the surface of gold nanorods (AuNRs) when synthesized by the seed-mediated procedure hampers the complete ligand exchange under experimental conditions that preserves the stability of the dispersions. In the present work, a ligand exchange protocol by using carboxy-terminated alkanethiols of different chain lengths by means of a green approach that uses only aqueous solutions is presented. The protocol is based on the knowledge of the stability in the aqueous solution of both the starting CTAB-AuNRs and the final products that help in the choice of the experimental conditions used for ligand exchange. The characterization of the CTAB protective layer as well as the study of its colloidal stability in solution has helped us to design an appropriate methodology. Cyclic voltammetry of CTAB-AuNRs demonstrates the high stability of the bilayer showing the existence of a two-dimensional phase transition from a highly ordered to a less organized phase. Other techniques such as XPS, FT-IR and Raman spectroscopy provide information about the structure of the layer and UV-visible-NIR spectroscopy establishes the stability conditions in aqueous solution. We have chosen an exchange procedure for 11-mercaptoundecanoic acid (MUA) and 16-mercaptohexadecanoic acid (MHDA) based on a one-pot methodology under conditions where all the species involved are stable. The protocol, however, can be extended to different chemical functionalities that are considered useful to be applied in living systems. Under these conditions the complete exchange of CTAB by the mercaptoderivatives was successful as demonstrated by the different characterization techniques used: UV-visible-NIR, FT-IR, Raman, XPS spectroscopy, cyclic voltammetry and transmission electron microscopy (TEM).

Nanopatterning of Cu-Ligated Mercaptoalkanoic Acid Multilayers on Si Substrates via Atomic Force Lithography

Chemical self-assembly has garnered tremendous interest as a tool for generating nanometer-scale structures and devices. Organosilane self-assembled monolayers (SAMs) are of particular interest because of their ability to assemble on a wide range of substrates with varied chemical functionalities. Nanoshaving, an atomic force lithographic technique, has been demonstrated as a method to generate nanopatterns of organosilane SAMs. However, this method requires extremely high force setpoints, which rapidly dulls atomic force microscopy tips and degrades the resolution of the resulting nanopattern. In this work, we utilize Cu-ligated mercaptohexadecanoic acid (MHDA) multilayers to circumvent this limitation. Initially, a 10-undecenyltrichlorosilane (UTS) SAM is assembled onto a Si substrate, and the terminal olefin groups of the UTS SAM are oxidized to carboxyl groups. Subsequently, a Cu-ligated MHDA multilayer is assembled via the sequential deposition of Cu2+ ions and MHDA molecules. The interface between the oxidized UTS SAM and Cu-ligated MHDA multilayer serves as a natural low force breakpoint for nanoshaving. We demonstrate that the resulting nanopatterns can function as a chemical resist to fabricate metal nanostructures.

Antimicrobial warnericin RK peptide functionalized GaAs/AlGaAs biosensor for highly sensitive and selective detection of Legionella pneumophila

Detection of pathogenic Legionella pneumophila by culture-based methods is not efficient in predicting outbreaks of the Legionnaires’ disease. The main problem is the relatively slow time-to-result and the inability of some culture media to support the growth of viable bacteria. One strategy to alleviate these issues is developing biosensors functionalized with mammalian antibodies designed to capture bacteria. However, mammalian antibodies are known to suffer from batch-to-batch variations, as well as limited stability, which reduce the consistent utility of antibody-based biosensors. In an attempt to address this problem, we investigated antimicrobial peptides (AMPs) for capture of L. pneumophila with GaAs/AlGaAs biochips. The Fourier-transform infrared spectroscopy measurements revealed that the peptides were covalently immobilized on the 1-ethyl-3-(-3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide activated −COOH terminals of mercaptohexadecanoic acid self-assembled monolayer functionalized GaAs surface. The efficiency of the specific interaction between the peptide and L. pneumophila, E. coli, B. subtilis and P. fluorescens was investigated with fluorescence microscopy and a digital photocorrosion GaAs/AlGaAs biosensor. We found that the warnericin RK peptides exhibited ∼5 times greater binding affinity towards L. pneumophila than to the other bacteria investigated. Furthermore, detection level as low as 103 CFU/mL was possible with the proposed biosensor architecture. We argue that a biosensor based on warnericin RK AMP peptides offers an attractive alternative solution in comparison to antibody-based devices towards detection of L. pneumophila.

Heavy metals detection in river water with cantilever nanobiosensor

Heavy metals can be highly toxic depending on the dose and the chemical form. In this context, sensing devices such as nanobiosensors have been presented as a promising tool to monitor contaminants at micro and nanoscale. In this work, cantilever nanobiosensors with phosphatase alkaline were developed and applied to detect heavy metals (Pb, Ni, Cd, Zn, Co, and Al) in river water. The nanobiosensor surface was functionalized by the self-assembled monolayers (SAM) technique using 16-mercaptohexadecanoic acid, N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC) and N- hydroxysuccinimide (NHS), and phosphatase alkaline enzyme. The sensing layer deposited on the cantilever surface presented a uniform morphology, at nanoscale, with 80 nm of thickness. The nanobiosensor showed a detection limit in the ppb range and high sensitivity, with a stability of fifteen days. The developed cantilever nanobiosensor is a simple tool, suitable for the direct detection of contaminants in river water.