Self-assembled Monolayer Technique Research Articles

The Effect of the Interface Layer on the Electronic Parameters of the Light Emitting Electrochemical Cell (LEC) Device Based on Iridium (III) Complex that Calculated by Different Methods

We report a calculation of the electronic parameters and some optical measurement results of a light-emitting electrochemical cell (LEC), one of the most basic forms of electroluminescent films by modifying 4-(4-methoxy-N-naphthalen-1-ylanilino) benzoic acid (MA) as hole injection layer doped with an emissive layer that is ionic transition metal complex (Ir[dF(CF3)ppy]2(dtbpy))PF6-(Ir-iTMC). The electronic parameters of LEC device were computed using three different methods; Cheung and Cheung’s, Conventional Schottky and Norde, to evaluate the ideality factor (n), the barrier height () and the series resistance (Rs) of the LEC device. The formation on indium tin oxide (ITO) substrate was analyzed by Atomic Force Microscopy (AFM). The HOMO-LUMO energy level and electronic charge distribution of the MA molecule were computed theoretically using Chemissian software. The MA’s HOMO-LUMO energy level is determined to be EHOMO = −5.27 eV and ELUMO = −1.40 eV. The ITO surface has been modified with the Self-Assembled Monolayers (SAM) technique as an interlayer to improve the surface working function by simplifying hole injection from the ITO anode to the Hole Transport Layer (HTL) in the LEC. The Ir- iTMC complexes containing Π-conjugated bridging ligand shown better external quantum efficiency (EQE), reaching to 1.49%. The max luminance values of the bare-LEC and LEC-MA are measured as 145 cd m−2 and 1240 cd m−2, respectively.

Novel Glycolipid Chips with a Double Layer of Au Nanoparticles for Biological Toxin Detection.

Glycolipid chips having a double layer of Au nanoparticles are proposed for detection of biological toxins. The sugar-modified chips constitute an under and an upper layer of Au nanoparticles of 20-80 nm diameter on glass plates, and Au nanoparticles of each layer are linked with 1,8-octanedithiol by a self-assembled monolayer (SAM) technique. A tris-sialo glycosphingolipid, ganglioside GT1b, having lipoic amide at the sphingosine part was immobilized on the Au outside surface of the upper layer, and botulinum toxin (type A heavy chain) was detected by localized surface plasmon resonance (LSPR). The GT1b-Cer-coated chip having a double layer of Au nanoparticles enhanced the toxin detection by LSPR more than those with single monolayers. The LSPR response changed according to the sizes of Au nanoparticles in each under and upper layer. The combination of 60 and 40 nm Au nanoparticles in the under and upper layer, respectively, gave the best result, which enabled the toxin detection at concentrations below 5 ng/mL with the portable LSPR device.

Immobilization of Polymers to Surfaces by Click Reaction for Photocatalysis with Recyclability.

A surface-bound photocatalyst offers advantages of reusability and recyclability with ease. While it can be immobilized by spin coating or drop-casting, a more reliable and durable method involves the formation of a self-assembled monolayer (SAM) on a suitable surface using designer molecules. In this paper, we report devising a practical, durable, and recyclable photocatalytic surface using immobilized polytriazoles of diketopyrrolopyrrole (DPP). While the SAM formation techniques were utilized for superior results, conventional coatings of polymers on surfaces were performed for comparison. Different methods confirmed efficient immobilization and high grafting density for the SAM technique. Computational models suggested favorable energy parameters for active materials. Photocatalytic studies were performed using both immobilized polymers and polymers in solution for comparison. These findings are important for understanding various physicochemical characteristics of polytriazole-functionalized surfaces.

Electrodeposited Gold Nanoparticle (AuNP)-Film as a Nanoplatform for a Label-Free Electrochemical Strongyloidiasis Immunosensor

Strongyloidiasis is an intestinal helminth infection caused by Strongyloides stercoralis. Early detection of this infection in immunocompromised patients is crucial to avoid severe complications and fatality. Herein, we present the potential application of electrodeposited AuNP-film in developing a label-free electrochemical immunosensor for strongyloidiasis using our synthesized monoclonal antibody. Layer-upon-layer attachment of Strongyloides monoclonal recombinant antibody protein (rMAb23) onto AuNP-film was constructed, utilizing a thiol linker via a self-assembly monolayer (SAM) technique. The modified electrode was utilized to detect S. stercoralis recombinant NIE (rNIE) protein. Each successful modification step was tested in a 10 mM [Fe(CN)6]3−/4− redox couple solution utilizing cyclic voltammetric (CV) and electrochemical impedance spectroscopic (EIS) techniques. The developed immunosensor required 20 min of incubation with an rNIE solution. Specificity study showed no cross-reaction with three other helminth recombinant proteins. Utilizing EIS measurements on a concentration series of rNIE protein in phosphate-buffered saline (PBS), ranging from 1 μg mL−1 to 10 μg mL−1, we obtained a detection limit (LOD) of 0.182 μg mL−1. The electrochemical immunosensor was also successfully used to analyze serum samples of individuals with strongyloidiasis and healthy people. The results indicated that the immunosensor might offer an excellent diagnostic capability and a rapid and sensitive antigen detection of strongyloidiasis.

RGD Nanoarrays with Nanospacing Gradient Selectively Induce Orientation and Directed Migration of Endothelial and Smooth Muscle Cells.

Directed migration of cells through cell-surface interactions is a paramount prerequisite in biomaterial-induced tissue regeneration. However, whether and how the nanoscale spatial gradient of adhesion molecules on a material surface can induce directed migration of cells is not sufficiently known. Herein, we employed block copolymer micelle nanolithography to prepare gold nanoarrays with a nanospacing gradient, which were prepared by continuously changing the dipping velocity. Then, a self-assembly monolayer technique was applied to graft arginine-glycine-aspartate (RGD) peptides on the nanodots and poly(ethylene glycol) (PEG) on the glass background. Since RGD can trigger specific cell adhesion via conjugating with integrin (its receptor in the cell membrane) and PEG can resist protein adsorption and nonspecific cell adhesion, a nanopattern with cell-adhesion contrast and a gradient of RGD nanospacing was eventually prepared. In vitro cell behaviors were examined using endothelial cells (ECs) and smooth muscle cells (SMCs) as a demonstration. We found that SMCs exhibited significant orientation and directed migration along the nanospacing gradient, while ECs exhibited only a weak spontaneously anisotropic migration. The gradient response was also dependent upon the RGD nanospacing ranges, namely, the start and end nanospacings under a given distance and gradient. The different responses of these two cell types to the RGD nanospacing gradient provide new insights for designing cell-selective nanomaterials potentially used in cell screening, wound healing, etc.

In situ discrimination of polymorphs and phase transformation of sulfamerazine using quartz crystal microbalance

A novel strategy utilizing the quartz crystal microbalance (QCM) was developed for the in situ discrimination of polymorphic nucleation (form-I and form-II) and phase transformation of sulfamerazine (SMZ) in cooling crystallization. According to Ostwald's rule of stages, metastable form-I of SMZ is first nucleated and then shifted to stable form-II by solution-mediated phase transformation. Through surface modification with the self-assembled monolayer technique of a functional group, QCM distinctively detects the formation of the two polymorphs. The results indicated that –NH2 (among the several functional groups tested) selectively accommodated stable form-II on the QCM sensor's surface and completely prevented the adsorption of metastable form-I on the surface. Therefore, the–NH2-terminated QCM detected the formation of form-I only using the solution viscosity variation on the surface. However, it monitored the nucleation and growth of form-II via the solid mass change on the surface during the phase transformation of form-I to form-II. This strategy suggests a new and precise solution for in situ discrimination of SMZ polymorphs and their phase transformation.

Assembly of Glycochips with Mammalian GSLs Mimetics toward the On-site Detection of Biological Toxins.

According to our previously proposed scheme, each of three kinds of glycosphingolipid (GSL) derivatives, that is, lactosyl ceramide [Lac–Cer (1)] and gangliosides [GM1-Cer (2) and GT1b-Cer (3)], was installed onto the glass surface modified with Au nanoparticles. In the present study, we tried to apply microwave irradiation to promote their installing reactions. Otherwise, this procedure takes a lot of time as long as a conventional self-assembled monolayer (SAM) technique is applied. Using an advanced microwave reactor capable of adjusting ambient temperatures within a desired range, various GSL glycochips were prepared from the derivatives (1)–(3) under different microwave irradiation conditions. The overall assembling process was programed with an IC controller to finish in 1 h, and the derived GSL glycochips were evaluated in the analysis of three kinds of biological toxins [a Ricinus agglutinin (RCA120), botulinum toxin (BTX), and cholera toxin (CTX)] using a localized surface plasmon resonance (LSPR) biosensor. In the LSPR analysis, most of the irradiated GSL chips showed an enhanced response to the targeting toxin when they were irradiated under optimal temperature conditions. Lac–Cer chips showed the highest response to RCA120 (an agglutinin with β-D-Gal specificity) when the microwave irradiation was conducted at 30–35 °C. Compared to our former Lac–Cer glycochips with the conventional SAM condition, their response was enhanced by 3.6 times. Analogously, GT1b chips gained an approximately 4.1 times enhancement in their response to botulinum type C toxin (BTX/C) when the irradiation was conducted around at 45–60 °C. In the LSPR evaluation of the GM1-Cer glycochips using CTX, an optimal condition also appeared at around 30–35 °C. On the other hand, the microwave irradiation did not lead to a notable increase compared to the former GM1-Cer chips derived with the SAM technique. Judging from these experimental results, the microwave irradiation effectively promotes the installing process for all the three kinds of the GSL derivatives, while the optimal thermal condition becomes different from each other. Many bacterial and botanic proteinous toxins are composed of such carbohydrate binding domains or subunits that can discriminate both the key epitope structure and the dimension of glycoconjugates on the host cell surface. It is assumed that the optimal irradiation and thermal conditions are required to array these semi-synthetic GSL derivatives on the Au nanoparticles in a proper density and geometry for tight adhesion with each of the biological toxins.

Biosensor for electrochemical detection of biomarkers of osteoarthritis

Biosensor for electrochemical detection of biomarkers of osteoarthritis

Ionically Self-Assembled Monolayer pH Sensitive Films-Fabrication and their Long Term Response to Varying Temperature Conditions

This study presents the long time effects of varying temperature conditions on pH-responsive films deposited on glass slides. The films were fabricated from Brilliant Yellow and poly (allylamine hydrochloride) through ionically self-assembled monolayer technique using an automated slide strainer. The absorbance of the films was monitored and the effect of varying temperature on the optical properties of the films was studied. We found that as the films are maintained at increasing temperatures their absorbance slightly decreased. As the temperature increased the percent change decreased reaching a plateau. Films kept at low temperatures of 3.24 °C and below freezing (-9.02 °C) had a small increase in absorbance. Finally, we monitored the absorbance of films kept at room temperature over a long time (128 days) and found that the films showed decreased absorbance by 19%.

Experimental study of near-wall underexpanded jet impingement on a flat plate using temperature-insensitive semi-transparent pressure-sensitive paint

The aim of this study is to experimentally investigate the pressure field of underexpanded sonic jet impingement with a short nozzle–plate distance (L/Dn) and a large impingement angle (θ). The measurement of surface pressure is difficult using traditional non-transparent PSP due to optical obstruction. Here, a novel pressure-sensitive paint (PSP) with a high degree of transparency was used, which enabled back illumination and back imaging to resolve the issue of optical obstruction. The temperature sensitivity of the PSP was also greatly reduced using the self-assembled monolayer (SAM) technique, which reduced the effect of temperature variation on the impingement plate, as demonstrated via comparison with pressure tap data. With this technique, the effects of the nozzle–plate distance (L/Dn = 1, 2, and 3), impingement angle (θ = 90°, 60°, and 30°), and pressure ratio (PR = 1.2 and 1.5) on the pressure-field characteristics were evaluated in detail, with a focus on the fine flow structures near the impingement point. The surface pressure distribution in the wall jet region was found to be significantly influenced by the nozzle–plate distance, which could be related to variation in the flow field, based on a physical model of the sonic line. The obtained PSP results with a high spatial resolution revealed interesting flow physics that improve our understanding of high-speed near-wall jet impingement.

Analysis of ITO surface modified with aromatic-based self-assembled molecules

This study focuses on characterization and enhancement of indium tin oxide (ITO) surface by using a self-assembled monolayer (SAM) technique. It is generally used to establish a compatible interface and a good charge injection from ITO surface. New generation organic semiconductor molecules such as dibenzo[a,c]phenazine-11-carboxylic acid, 4-(9H-carbazol-9-yl) benzoic acid, 4-(2,5-di-2-thienyl-1H-pyrrol-1-yl) benzoic acid, 5-[(diphenyl) amino]isophthalic acid and 5-[(3-methylphenyl)(phenyl)amino]isophthalic acid were coated on ITO. The surface of ITO was characterized by scanning spreading resistance microscopy, Kelvin probe force microscopy, scanning tunnelling microscopy, X-ray photoelectron spectroscopy and cyclic voltammetry techniques to ensure the chemical bonding of SAM materials on it.

Mechanical and wear behaviour of Friction stir processed surface composite through Self-Assembled Monolayer Technique

In the present research study, Friction stir processing (FSP) has been utilized to prepare nano surface composites, AA7075 based matrix was reinforced with B4C nanoparticles (size <30 nm). The aim of this study is to form a thin layer of B4C over the surface of AA7075 based matrix material through Self-Assembled Monolayer (SAM) technique followed by Friction stir processing. The major advantage of SAM is to minimize the quantity of B4C nanoparticles used in the preparation of nano surface composites. Additionally, this research also investigates the effect of tool rotation speed of Friction stir processing on mechanical and wear properties of processed nano surface composite. The results observed a uniform dispersion of nanoparticles in the processed nano surface composite and an improved value of microhardness with maximum value was found to be 185 Hv of the sample processed at 1200 rpm, compared to base metal. For the constant load, as FSP tool rotation speed increases, wear resistance increases from 1000 to 1200 rpm and decreases slightly for 1400 rpm. Scanning Electron Microscope (SEM) micrograph, tensile test and Field Emission Scanning-Electron Microscope (FESEM) fractography image used to study microstructure and the mechanical properties of processed nano surface composite. The x-ray Diffraction (XRD) showed the presence of B4C nanoparticles. Processed nano surface composites can be used for aircraft and automobile industry applications.

Sensitive immunoassay of cardiac troponin I using an optimized microelectrode array in a novel integrated microfluidic electrochemical device.

A sensitive and portable microfluidic electrochemical array device (μFED) was developed for the immunoassay of trace amounts of human cardiac troponin I (cTnI), which is an attractive biomarker for acute myocardial infarction (AMI). The classical "sandwich" method was adopted for the immunoassay. The capture antibody was immobilized using a self-assembled monolayer (SAM) technique, and the process was reorganized to be compatible with the bonding process. The detection antibody was labeled with alkaline phosphatase (AP) for signal amplification. The performance of the μFED was improved by eliminating the shielding effect of the microelectrode array (MEA) integrated in the μFED. The effects of the interstice and the width of the MEA on the response peak current were analyzed and simulated. The concentration gradient, about 3% of the gradient at the surface, was considered as the criterion for estimation of the optimal interstice between electrodes, and its effectiveness was proved. A stable and miniaturized reference electrode was integrated in the μFED, and its potential deviation was less than 5mV in 15min. These efforts resulted in the enhanced immunoassay performance of the μFED. A low limit of detection of about 5pg/mL was obtained in serum samples, and the response current was proportional to the logarithm of concentration from 50pg/mL to 1μg/mL. The immunoassay process was accomplished in 15min. The μFED was thus qualified and is a promising candidate for point-of-care immunoassay of cTnI. Graphical abstract.

Electrochemical sensing by a covalently bonded biotin–avidin couple on a silver nanoparticle modified gold electrode

A gold electrode was modified with cysteamine by a self-assembly monolayer technique and covalently coupled with 3-mercaptopropionic acid functionalized silver nanoparticles. The free carboxylic acid groups of the 3-mercaptopropionic acid functionalized silver nanoparticles assembled on gold electrode were bonded with the amine groups of biotin or avidin trough amide linkages. The changes in the interfacial properties of gold electrode modified stepwise were examined by cyclic voltammetry and electrochemical impedance spectroscopy using the ferric/ferrous redox system. The electrochemical sensing properties of covalently bonded biotin or avidin on a gold electrode modified with silver nanoparticle were studied by cyclic voltammetry and electrochemical impedance spectroscopy by the varying concentrations of the bio-affinity molecules in the same redox system. The charge transfer resistance was directly proportional to the concentration of analyte while the response was weakly dependent upon the change in the respective peak anodic currents. The sensing mechanism was established to explain the role of the silver nanoparticles.

Constructing Dual-Molecule Junctions to Probe Intermolecular Crosstalk.

Understanding and controlling charge transport across multiple parallel molecules are fundamental to the creation of innovative functional electronic components, as future molecular devices will likely be multimolecular. The smallest possible molecular ensemble to address this challenge is a dual-molecule junction device, which has potential to unravel the effects of intermolecular crosstalk on electronic transport at the molecular level that cannot be elucidated using either conventional single-molecule or self-assembled monolayer (SAM) techniques. Herein, we demonstrate the fabrication of a scanning tunneling microscopy (STM) dual-molecule junction device, which utilizes noncovalent interactions and allows for direct comparison to the conventional STM single-molecule device. STM-break junction (BJ) measurements reveal a decrease in conductance of 10% per molecule from the dual-molecule to the single-molecule junction device. Quantum transport simulations indicate that this decrease is attributable to intermolecular crosstalk (i.e., intermolecular π-π interactions), with possible contributions from substrate-mediated coupling (i.e., molecule-electrode). This study provides the first experimental evidence to interpret intermolecular crosstalk in electronic transport at the STM-BJ level and translates the experimental observations into meaningful molecular information to enhance our fundamental knowledge of this subject matter. This approach is pertinent to the design and development of future multimolecular electronic components and also to other dual-molecular systems where such crosstalk is mediated by various noncovalent intermolecular interactions (e.g., electrostatic and hydrogen bonding).

Effects of different chemical groups on behaviors of bladder cancer cells.

Chemical groups of microenvironment play an important role in the adhesion, proliferation, and apoptosis of tumor cells. The different chemical groups (CH3 , OH, COOH) were grafted on the surfaces with the same density by self-assembly monolayer (SAM) technique to introduce the influence of different microenvironments of the human bladder cancer (5637) cells. The results indicated that the 5637 cells on COOH surface exhibited the lowest proliferation rate and the highest apoptosis rate on the first and fifth day because of negative charge and polarity of the COOH group, which might help optimize biomedicine materials and find new methods to treat bladder cancer.

CORROSION INHIBITION OF CASEIN AS A NATURAL PROTEIN FOR 316L STAINLESS STEEL IN SIMULATED BODY FLUID

The importance of biomaterials is increased steadily with the augmentation of population and aging. In this research, casein, a protein present in milk, used to modify the 316L stainless steel (316L SS) alloy surface, used in medical application, against corrosion in the corrosive body fluid. Due to the presence of hetero-atoms in its moiety, casein has the ability to form a protective thin layer. Self-assembled monolayers (SAMs) technique is a common tool providing a well ordered thin film on the metallic surface. Casein was assumed to form SAMs on the 316L SS surface and the corrosion inhibition efficiency was examined electrochemically. The results proved the formation of SAMs and displayed that casein reduce the corrosion rate and serves as a mixed type inhibitor. The inhibition efficiency is increased by increasing the casein’s concentration and immersion time in the casein’s solution. A maximum inhibition efficiency obtained at 1000 ppm with immersion time equals 120 minutes. Further modification is undertaken to increase the inhibition efficiency.

Establishment of a 1, 4, 7, 10-tetraazacyclododecane-1,4,7,10-tetraacetic acid mono-N-hydroxysuccinimide ester (DOTA–NHS–ester) based lectin microarray for efficiently detecting serum glycans in gastric cancers

Development of cancers is involved in changes of a variety of glycans. Lectin microarray is one of the most powerful methodologies for investigation of glycan alterations in biological samples with its advantages of high through-put, selectivity and specificity of the technique. However, utilization of lectin microarrays available commercially keeps of great challenges. In this study, we took use of the molecular self-assembled monolayer technique to modify a gold surface with the reagent 1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid mono-N-hydroxysuccinimide ester (DOTA–NHS–ester) in combination with 16-amino-1-hexadecanethiol hydrochloride. Cross-linking effect of DOTA–NHS–ester is brought about via activating three –OH ends to three terminals of succinylimidines, making selective binding of the terminal amino groups in proteins possible. We immobilized ten commercial lectins on the platform and measured changes of serum lectin-matched glycans in patients with gastric cancer. The results demonstrated that this biochip modification platform conferred impressive chemical surface stabilization, sensitivity and geometric images. We observed that all the serum glycans tested in the patients were significantly higher than those in the controls (P < 0.05). The biochip would provide a versatile platform for investigation of potential glycan biomarkers in making tumor diagnosis decision and analyzing escape of tumors from immunity.

Detección de Salmonella enterica sobre sustratos de silicio biofuncionalizados con IgG anti-Salmonella, analizados por espectroscopía FTIR

Foodborne diseases are considered a health problem, Salmonella is part of the main microorganisms that generate this type of diseases, so its detection requires a short period of time, biosensors can be a good option to meet this need. In this work, three substrates (crystalline and amorphous silicon, hydrogenated amorphous silicon carbide) were biofunctionalized applying self-assembled monolayers technique, presence of characteristic functional groups of the assembly was verified by Fourier transform infrared spectroscopy (FTIR). Anti-Salmonella IgG antibodies against whole bacteria were generated. Second derivative of each FTIR detection spectrum was obtained, having modifications in the zone between 1600-1700 cm-1 given by the secondary structure of proteins, being crystalline silicon and hydrogenated amorphous silicon carbide platforms, which presented the most notorious bands. Detection was performed on flat substrates with a specific area (25 mm2), a detection time of 60 min was stablished and a concentration of 500 CFU/mL was detected. With this, the three silicon and derivatives biofunctionalized may have future applications in food microbial quality monitoring.

Effect of the Interface Improved by Self-Assembled Aromatic Organic Semiconductor Molecules on Performance of OLED

This work focuses on characterization the performance of enhanced interface of organic light emitting diode (OLED) device by Self-assembled Monolayer (SAM) technique. SAM technique is popular in order to overcome the weak bonding at the organic/inorganic interface in OLED. New generation of SAM molecules, phenyl-benzoic-acid (PBA, 4-(9H-carbazol-9-il) benzoic acid (MZ39), 4-(2,5-di-2thienyl-1H-pyrrol-1-il) benzoic acid (MZ25) were coated on between Indium Tin Oxide (ITO). The two configuration of ITO/SAM/TPD/Al and ITO/TPD/Al diode were fabricated as hole-only device to show the contribution of SAM layer on the hole mobility calculated by Space Charge Limited Current (SCLC) technique. The optical characterization of OLED devices with configuration ITO/TPD/Alq3/Al and ITO/SAM/TPD/Alq3/Al was performed to see the effect of aromatic SAM molecules on the luminance and quantum efficiency. Especially, the SAM modified OLED has a maximum luminance of 397 cd m−2. All devices containing SAM layer showed better performance than reference one.