Atomic Force Microscopy Characterization Research Articles

Thiolated polymer nanocarrier reinforced with glycyrrhetinic acid for targeted delivery of 5-fluorouracil in hepatocellular carcinoma.

The present work investigates the targeting efficacy of a novel thiolated polymer-based nanocomposite reinforced with glycyrrhetinic acid (GA) and loaded with 5-fluorouracil in hepatocellular carcinoma (HCC). The thiolated polymers were synthesized by EDAC-mediated conjugation reactions and lyophilization. The nanoparticles were prepared by solvent diffusion and high-pressure homogenization method. The prepared nanocomposite was characterized by Fourier transform infrared (FTIR) radiation, x-ray diffraction (XRD), dynamic light scattering (DLS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. Pharmacological evaluation of the formulation was carried out on a rat model of diethylnitrosamine (DEN), and carbon tetrachloride (CCl4)-induced HCC and MTT assay was carried out with HEP-G2 cell line. In silico studies were conducted to investigate the probable mechanistic pathway of the nanocomposite. FTIR and XRD analysis indicated the successful thiolation of the polymers and confirmed the formation of the nanocomposite without any incompatibilities. DLS, SEM/EDX and AFM characterization confirmed that the nanoparticles were within the nano-size range. MTT assay implied the cytotoxic nature of the nanocomposite against hepatic carcinoma cells. The in vivo study revealed that serum SGOT, SGPT, ALP, GGT and total bilirubin levels were significantly reduced, in comparison with disease control and the result was confirmed by histopathology studies. The results of the HPLC analysis of liver homogenate confirmed the liver targeting ability of the nanocomposite. In silico studies exhibited significant binding affinity of GA and thiolated Eudragit towards liver homolog receptor-1 (LRH-1) suggesting that the developed nanocomposite could be a potential material for the treatment of HCC.

Atomic Force Microscopy Reveals that the Drosophila Telomere-Capping Protein Verrocchio Is a Single-Stranded DNA-Binding Protein.

Atomic force microscopy (AFM) is a scanning probe technique that allows visualization of biological samples with a nanometric resolution. Determination of the physical properties of biological molecules at a single-molecule level is achieved through topographic analysis of the sample adsorbed on a flat and smooth surface. AFM has been widely used for the structural analysis of nucleic acid-protein interactions, providing insights on binding specificity and stoichiometry of proteins forming complexes with DNA substrates. Analysis of single-stranded DNA-binding proteins by AFM requires specific single-stranded/double-stranded hybrid DNA molecules as substrates for protein binding. In this chapter we describe the protocol for AFM characterization of binding properties of Drosophila telomeric protein Ver using DNA constructs that mimic the structure of chromosome ends. We provide details on the methodology used, including the procedures for the generation of DNA substrates, the preparation of samples for AFM visualization, and the data analysis of AFM images. The presented procedure can be adapted for the structural studies of any single-stranded DNA-binding protein.

Atomic force microscopy characterization of β-casein nanoparticles on mica and graphite

The morphology and size distribution of β-casein nanoparticles adsorbed on mica and graphite were determined using atomic force microscopy. The height of the dried nanoparticles on graphite was about twice as smaller as that on mica, and the cross-sectional profiles of particles were different for these substrates. It is due to the hydrophobic interaction of nanoparticles with the graphite surface.

Facile Li-Al layered double hydroxide films on Al alloy for enhanced hydrophobicity, anti-biofouling and anti-corrosion performance

In this work, lithium (Li)-aluminum (Al) layered double hydroxide (LDH) films modified by 4-amino-2-((hydrazine methylene) amino)-4-oxobutanoic acid (denoted as AOA acid) and/or 1H,1H,2H,2H-perfluorooctyltriethoxysilane were prepared on 6N01 Al alloy by a facile, in-situ growth method with enhanced hydrophobicity, anti-biofouling and anti-corrosion performance. The preparation is low energy consumptive and environment friendly, relying on self-assembly at ambient temperature. The structure, molecular weight and functional groups of the synthesized AOA acid were characterized by NMR spectrometer, ESI-MS spectrometer and Fourier transform infrared (FT-IR) spectroscopy. And the compositions, structure and morphology of the films were characterized by Fourier transform infrared (FT-IR) spectroscopy, glancing-angle X-ray diffraction (GA-XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and energy-dispersive x-ray spectrum (EDS). Water contact angle measurements (CA) and atomic force microscopy (AFM) characterization show that the films possess a micro/nanostructure with an improved hydrophobicity. Immersion test, neutral salt tests (NSS) and electrochemical impedance spectroscopy (EIS) conducted in 3.5 wt.% NaCl solutions demonstrate the improved corrosion resistance of the films over bare Al alloy. Meanwhile, the films also possess an excellent anti-bacterial property to Escherichia coli, Bacillus subtilis and sulfate-reducing bacteria.

Effect of nitrogen (N2) flow rate over the tribological, structural and mechanical properties diamond-like carbon (DLC) thin film

In this article, nitrogen (N2) doped diamond-like carbon (N-DLC) coatings are deposited by Atmospheric pressure chemical vapor deposition (APCVD) technique at varying N2 flow rates and are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, nanoindentation (NI) and nano scratch (NS) characterization. The wear rate (WR) and coefficient of friction (μ) of the N-DLC thin films increase from 1.32 × 10−4 to 3.11 × 10−4 μm2 and 0.05 to 0.15 with the increase of load from 40 to 70 mN at 70 sccm N2 flow rate. The results showed that there is a significant improvement in the tribological and mechanical properties of the APCVD synthesized DLC film as compare to the other PVD deposited DLC film.

Ultrasensitive detection of interleukin 1α using 3-phosphonopropionic acid modified FTO surface as an effective platform for disposable biosensor fabrication

In this study, we utilized a carboxyalkylphosphonic acid covered fluorine doped tin oxide (FTO) as an electrode material for fabrication of Interleukin 1α (IL-1α) immunosensor. For this aim, anti-IL-1α antibodies were attached on the 3-phosphonopropionic acid (PHP) modified FTO surface covalently. Electrochemical (electrochemical impedance spectroscopy and cyclic voltammetry) and morphological (scanning electron microscopy and atomic force microscopy) characterizations were performed to monitor the successful fabrication of immunoelectrodes. After incubation of anti-IL-1α antibody immobilized FTO electrodes in IL-1α antigen solutions, increases were seen in impedimetric responses. IL-1α antigen was determined in a linear detection range from 0.02 to 2 pg/mL by EIS. The detection limit of the suggested immunosensor was 6 fg/mL. The applicability of the designed biosensor was tested by using human serum and saliva samples and acceptable results were obtained. In addition, high sensitivity, good specificity, low detection limit made the proposed immunosensor a potential technique for IL-1α antigen determination in routine clinical analysis.

Hierarchical Self-Assembly Mechanism of Ladder-Like Orientated Aβ40 Single-Stranded Protofibrils into Multistranded Mature Fibrils.

The complex self-assembly processes in three dimensions of Alzheimer's β-peptide (Aβ) amyloid protofibrils into polymorphic mature fibrils, particularly the relative protofibril orientation and packing mechanism, are poorly understood. We report here the identification and quantification of the hierarchical self-assembly details among distinct Aβ40 fibrils, particularly the winding pictures of two, three, and four individual single-stranded protofibrils into two-, three-, and four-stranded mature fibrils, respectively, via cross-sectional analysis of atomic force microscopy (AFM) images. The statistical polymer physics analysis of fibril flexibilities from AFM characterizations as well as molecular dynamics (MD) simulations reveal a ladder-like packing mechanism rather than a closed-packing manner for the interprotofibril association into Aβ40 mature fibrils. Moreover, our MD results show atomic packing polymorphism at the well-packing interfaces even within the same multistranded fibril. This work provides mechanistic insights into the polymorphic transition of single-stranded Aβ40 protofibrils into multistranded mature fibrils at the mesoscopic level, which is useful for a more comprehensive understanding of Alzheimer's β-peptide amyloidosis.

Synthesis of large-area MoS2 films by plasma-enhanced chemical film conversion of solution-processed ammonium tetrathiomolybdate

The synthesis of large-area molybdenum disulfide (MoS2) films is desired for many emerging electronic and optical applications. A typical approach is to deposit films from vapor-phase precursors either by thermal- or plasma-activated chemistry. Here, we show that MoS2 films exhibiting excellent crystallinity and smooth surfaces are produced by plasma conversion of solution-deposited precursor films. Films containing a single-source precursor for MoS2, ammonium tetrathiomolybdate, were spin coated and converted by an atmospheric-pressure dielectric barrier discharge with substrate heating at 500 °C. X-ray diffraction and micro-Raman spectroscopy show that the plasma is necessary to successfully convert the precursor to MoS2. Further enhancements in the crystallinity and surface roughness were obtained by annealing the films, as revealed by high-resolution transmission electron microscopy and atomic force microscopy (AFM). Insights into the role of the plasma were provided by AFM characterization and a “plasma-trigger” experiment, which suggest that a nanocone surface morphology facilitates the growth of the films.

Replica molding of cicada wings: The role of water at point of synthesis on nanostructure feature size.

Many natural surfaces, including the wings of cicada insects, have shown to display bactericidal properties as a result of surface topography. Moreover, the size and distribution of the surface features (on the nano- and microscale) are known to influence the efficacy of the surface at inhibiting bacterial cell growth. While these types of natural surfaces illustrate the effect of structure on the bactericidal activity, a deeper understanding can be achieved by creating surfaces of different feature sizes. This is essential in order to understand the effects of changes of surface topography on bacteria-surface interactions. To this end, we have performed a series of replica molding processes of the wings of the Megapomponia Intermedia cicada to prepare wing replicas in polyethylene glycol (PEG), which possess the topographical features of the wing surface, with a minimum loss of feature resolution. Atomic force microscopy characterization of these patterned surfaces in both air and aqueous environments shows that by controlling the swelling characteristics of the PEG, we can control the ultimate swollen dimensions of the nanopillar structures on the surface of PEG. As a result, by using a single wing with an average nanopillar height of 220 nm, different patterned PEG samples with nanopillar heights ranging from 180 to 307 nm were produced.

Damage mechanism of graphene nanoribbons field effect transistors during focused ion beam etching

The fabrication of graphene nanoribbons (GNRs) is a familiar method to open the band gap of graphene. As one of the most novel means, focused ion beam (FIB) etching is expected to become the mainstream of GNRs production. Monte Carlo analysis is devoted to simulate the process of ion scattering in FIB etching GNRs. In the process of scattering, charged ions collide with solid materials continuously, which changes the direction and energy of ions in solid. Therefore, the information such as the motion track of the scattered ions, the damage of recoil atoms and the sputtering of surface atoms can be obtained, through the calculation of the scattering angle as well as nuclear energy loss of the charged ions. Combined with Raman spectroscopy and atomic force microscope (AFM) characterization, it is revealed that FIB etching indirectly induces the structure defects on GNRs and affects electrical performance.

Facile preparation of self-assembled black phosphorus-based composite LB films as new chemical gas sensors

In recent years, the researches on the modification and functionalization of black phosphorus (BP) materials have attracted more and more attention. In this study, few-layers BP nanosheets (BPNS) were prepared by a simple liquid exfoliation method. However, BPNS has the disadvantages of easy oxidation and poor stability, which will also affect the performance of BP. Therefore, 4-azidobenzoic acid was used to modify the BPNS to improve the stability of BP. In addition, 4-azidobenzoic acid modified BPNS (f-BPNS) and dye molecules can form a composite Langmuir-Blodgett (LB) film through electrostatic interaction or π-π stacking forces. UV–vis, Atomic force microscopy (AFM) and other characterizations were used to prove the successful preparation of the f-BPNS-dye composite LB film. It should be noted that the obtained uniform and dense composite films showed good sensitivity to acid and alkali gas. Moreover, the f-BPNS-dye composite films can still maintain high performance after 10 cycles of acid-alkali tests, indicating that the prepared films have high stability. This work provides a new direction for the preparation of new two-dimensional composite materials and their application in gas sensors.

Electrochemical Detection of Tetracycline on Highly Sensitive Benzene Sourced CVD Graphene‐Gold Nanoparticles Nanointerfaces

AbstractThe development of sensitive, fast and efficient nanointerfaces as platforms for electrochemical sensing devices for the detection of environmental pollutant including antibiotic pollutant has become a matter of priority for public safety. We report herein a benzene sourced graphene‐gold nanoparticle sensor for the detection of tetracycline using chronoamperometry. Structural analysis using Raman Spectroscopy and x‐ray diffraction spectroscopy (XRD) confirmed the presense of few‐layer graphene. Atomic force (AFM) and scanning electron microscopy (SEM) characterization results confirmed the synthesized graphene to be thin flat sheet‐like material with wide surface area and a thickness of less than 1 nm. Cyclic voltammetry characterization of the fabricated modified electrodes showed diffusion controlled process for the oxidation of tetracycline. The modified electrode exhibited a fast response to the detection of tetracycline and a sensitivity of 1,86×102 μA/mM/cm2.The theoretical detection limit (S/N=3) was 1,60×10−1 μM and the linear dynamic range was from 2,90×101 μM to 1.53×103 μM.

Green Preparation of Aqueous Graphene Dispersion and Study on Its Dispersion Stability.

The large-scale preparation of stable graphene aqueous dispersion has been a challenge in the theoretical research and industrial applications of graphene. This study determined the suitable exfoliation agent for overcoming the van der Waals force between the layers of expanded graphite sheets using the liquid-phase exfoliation method on the basis of surface energy theory to prepare a single layer of graphene. To evenly and stably disperse graphene in pure water, the dispersants were selected based on Hansen solubility parameters, namely, hydrophilicity, heterocyclic structure and easy combinative features. The graphene exfoliation grade and the dispersion stability, number of layers and defect density in the dispersion were analysed under Tyndall phenomenon using volume sedimentation method, zeta potential analysis, scanning electron microscopy, Raman spectroscopy and atomic force microscopy characterization. Subsequently, the long-chain quaternary ammonium salt cationic surfactant octadecyltrimethylammonium chloride (0.3 wt.%) was electrolyzed in pure water to form ammonium ions, which promoted hydrogen bonding in the remaining oxygen-containing groups on the surface of the stripped graphene. Forming the electrostatic steric hindrance effect to achieve the stable dispersion of graphene in water can exfoliate a minimum of eight layers of graphene nanosheets; the average number of layers was less than 14. The 0.1 wt.% (sodium dodecylbenzene sulfonate: melamine = 1:1) mixed system forms π–π interaction and hydrogen bonding with graphene in pure water, which allow the stable dispersion of graphene for 22 days without sedimentation. The findings can be beneficial for the large-scale preparation of waterborne graphene in industrial applications.

How Nanotopography-Induced Conformational Changes of Fibrinogen Affect Platelet Adhesion and Activation.

The conformational state of adsorbed human plasma fibrinogen (HPF) has been recognized as the determinant factor in platelet adhesion and thrombus formation on blood-contacting biomaterials. Studies have highlighted the ability to control the HPF conformation merely by tailoring surface nanotopographical features. However, a clear relationship between the conformational changes of adsorbed HPF and the degree of platelet adhesion and activation achieved with different surface nanotopographies is still unclear. Here, we examined HPF assembly characteristics on nanostructured polybutene-1 (PB-1) surfaces with nanosized lamellar crystals (LCs), needle-like crystals (NLCs), and a nanostructured high-density polyethylene (HDPE) surface with shish-kebab crystals (SKCs), at a biologically relevant HPF concentration. By exposing the nanostructured surfaces with preadsorbed HPF to human platelets, significant differences in platelet response on LCs/SKCs and NLCs were identified. The former presented a uniform monolayer in the advanced stage of activation, whereas the latter exhibited minimal adhesion and the early stage of activation. Distinct platelet response was related to the postadsorption conformational changes in HPF, which were confirmed by topography-dependent shifts of the amide I band in attenuated total reflection-Fourier transform infrared (ATR-FTIR) analysis. Supported by atomic force microscopy (AFM) characterization, we propose that the mechanism behind the nanotopography-induced HPF conformation is driven by the interplay between the aspect ratios of polymeric crystals and HPF. From the biomedical perspective, our work reveals that surface structuring in a nanoscale size regime can provide a fine-tuning mechanism to manipulate HPF conformation, which can be exploited for the design of thromboresistant biomaterials surfaces.

A 2D tungsten disulphide/diamond nanoparticles hybrid for an electrochemical sensor development towards the simultaneous determination of sunset yellow and quinoline yellow

We present the development of an electrochemical sensor towards the simultaneous analysis of a mixture of food additives: sunset yellow (SY) and quinoline yellow (QY) dyes. The sensor is based on the synergetic effect observed between diamond nanoparticles (DNPs) and WS2 nanosheets obtained by liquid exfoliation. The prepared TMDs were characterized using Raman spectroscopy, X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM). The AFM characterization showed isolated WS2 flakes with different lateral dimensions scattered over the flat background. The combination of WS2 and DNPs allows resolution of the oxidation signals of the analytes, which overlap working with the bare glassy carbon (GC) electrode. The best electroanalytical response was obtained with a sensor containing both nanomaterials deposited employing the drop-casting method in a sequential manner, a first layer of WS2 and a second layer of DNPs (GC/WS2/DNPs). Electrochemical impedance spectroscopy experiments showed that for the GC/WS2/DNPs system the charge transfer is clearly improved. Under optimized differential pulse voltammetry conditions, the GC/WS2/DNPs sensor allows the determination of SY at +100 mV and QY at +850 mV with detection limits of 0.086 and 3.4 μM respectively, with relative errors ≤ 8.40 % and a relative standard deviation ≤ 12.6 %. The proposed methodology was applied to the determination of SY and QY in commercial throat lozenge samples with very good recoveries on average: 93 %, for QY and 106 % for SY.

2D-MoS2/BMN Ceramic Hybrid Structure Flexible TFTs with Tunable Device Properties.

Two-dimensional (2D) layered semiconductor materials have emerged as prospective channel materials in flexible thin-film field effect transistors (TFTs) recently because of their unique electrical and mechanical characteristics. Meanwhile, high-quality ceramics, with outstanding dielectric property and fabrication process compatible with low-cost flexible substrates, have become one of the best candidates of gate dielectric layers in flexible TFTs. In this work, 2D MoS2 and dielectric ceramic Bi2MgNb2O9 (BMN) were utilized to fabricate flexible TFTs on low-cost polyethylene terephthalate substrates. The MoS2/BMN hybrid structure exhibited good quality by Raman, X-ray photoelectron spectroscopy, and atomic force microscopy characterizations. In addition, the flexible MoS2/BMN TFTs indicated good performances with a small gate voltage. More importantly, with the modulation of gate voltage, the flexible TFTs surprisingly exhibited three different device types, that is, multilayer MoS2/BMN n-type TFT (device type 1), homojunction MoS2/BMN TFT (device type 2), and thick MoS2/BMN p-type TFT (device type 3). In particular, with different bias conditions, the homojunction TFT showed bipolarity of transfer characteristics and forward/backward rectifications of output characteristics similar to p-n/n-n junctions. The high dielectric constant and high quality of the BMN ceramic layer enabled the gate to effectively modulate these different structures of MoS2 channels. The operation mechanisms of these three types of flexible TFTs were investigated. Additionally, the flexible MoS2/BMN TFTs showed good flexibility and performance stability with external strains. The results prove the great potential of integration of 2D materials, high-quality dielectric ceramics, and low-cost plastic substrates for high-performance flexible TFTs and further applications of flexible electronics.

Toward Sustainable Tackling of Biofouling Implications and Improved Performance of TFC FO Membranes Modified by Ag-MOF Nanorods.

In this work, nanorods with high antibacterial properties were synthesized with silver acetate as the metal source and 2-aminoterephthalic acid as the organic linker and were then embedded into thin-film composite (TFC) membranes to amend their performance as well as to alleviate biofouling. Silver metal-organic framework (Ag-MOF) nanorods with a length smaller than 40 nm were incorporated within the polyamide thin selective layer of the membranes during interfacial polymerization. The interaction of the synthesized nanorods with the polyamide was favored because of the presence of amine-containing functional groups on the nanorod's surface. The results of X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and atomic force microscopy characterizations proved the presence of Ag-MOF nanorods in the selective layer of thin-film nanocomposite (TFN) membranes. TFN membranes demonstrated improved water permeance, salt selectivity, and superior antibacterial properties. Specifically, the increased hydrophilicity and antibacterial potential of the TFN membranes led to a synergetic effect toward biofouling mitigation. The number of live bacteria attached to the surface of the neat TFC membrane decreased by more than 92% when a low amount of Ag-MOF nanorods (0.2 wt %) was applied. Following contact of the TFN membrane surface with Escherichia coli and Staphylococcus aureus, full inactivation, and degradation of bacteria cells were observed with microscopy, colony-forming unit tests, and disc inhibition zone analyses. This result translated to a negligible amount of the biofilm formed on the active layer. Indeed, the incorporation of Ag-MOF nanorods decreased the metal-ion release rate and therefore provided prolonged antibacterial performance.

Quantitative analysis based on atomic force microscopy characterization of interfacial properties between carbon fibers and epoxy resin subjected to hygrothermal and thermal treatments

It has been proved the interface between fibers and resin matrix suffers from severe service conditions, but it was rarely explored how to directly and quantitatively evaluate those negative effects. In this work, a novelly-designed quantitative analysis method was established via atomic force microscopy (AFM) based on shrinkage degree of resin matrix, and was further applied to assess the effects of hygrothermal and thermal treatment on the interfacial adhesion property of carbon fibers/epoxy composites (CFRPs). This method presented that the shrinkage extent of resin around carbon fibers after treatment could in a certain extent reflect the interfacial properties at the stability and linear constraint region. Furthermore, interlaminar shear strength and interfacial shear strength measurements demonstrated the validity of this novel method for interfacial properties, and revealed that the interface was more susceptible to hygrothermal than thermal treatment. This method is believed promising for studies on the interface of fibers/resin composites.

InVivo Bioengineering of Fluorescent Conductive Protein-Dye Microfibers.

SummaryEngineering protein-based biomaterials is extremely challenging in bioelectronics, medicine, and materials science, as mechanical, electrical, and optical properties need to be merged to biocompatibility and resistance to biodegradation. An effective strategy is the engineering of physiological processes in situ, by addition of new properties to endogenous components. Here we show that a green fluorescent semiconducting thiophene dye, DTTO, promotes, in vivo, the biogenesis of fluorescent conductive protein microfibers via metabolic pathways. By challenging the simple freshwater polyp Hydra vulgaris with DTTO, we demonstrate the stable incorporation of the dye into supramolecular protein-dye co-assembled microfibers without signs of toxicity. An integrated multilevel analysis including morphological, optical, spectroscopical, and electrical characterization shows electrical conductivity of biofibers, opening the door to new opportunities for augmenting electronic functionalities within living tissue, which may be exploited for the regulation of cell and animal physiology, or in pathological contexts to enhance bioelectrical signaling.

Staircase-like transfer characteristics in multilayer MoS2 field-effect transistors

Layered semiconductors, such as MoS2, have attracted interest as channel materials for post-silicon and beyond-CMOS electronics. Much attention has been devoted to the monolayer limit, but the monolayer channel is not necessarily advantageous in terms of the performance of field-effect transistors (FETs). Therefore, it is important to investigate the characteristics of FETs that have multilayer channels. Here, we report the staircase-like transfer characteristics of FETs with exfoliated multilayer MoS2 flakes. Atomic force microscope characterizations reveal that the presence of thinner terraces at the edges of the flakes accompanies the staircase-like characteristics. The anomalous staircase-like characteristics are ascribable to a difference in threshold-voltage shift by charge transfer from surface adsorbates between the channel center and the thinner terrace at the edge. This study reveals the importance of the uniformity of channel thickness.