Summary of ISO/TC 201 International Standard ISO 18516:2019 Surface chemical analysis—Determination of lateral resolution and sharpness in beam-based methods with a range from nanometres to micrometres and its implementation for imaging laboratory X-ray photoelectron spectrometers (XPS)

ISO 18516:2019 Surface chemical analysis—Determination of lateral resolution and sharpness in beam-based methods with a range from nanometres to micrometres revises ISO 18516:2006 Surface chemical analysis—Auger electron spectroscopy and X-ray photoelectron spectroscopy—Determination of lateral resolution. It implements three different methods delivering parameters useful to express the lateral resolution: (1) the straight edge method, (2) the narrow line method and (3) the grating method. The theoretical background of these methods is introduced in ISO/TR 19319:2013 Surface chemical analysis—Fundamental approaches to determination of lateral resolution and sharpness in beam-based methods. The revised International Standard ISO 18516 delivers standardized procedures for the determination of the (1) effective lateral resolution by imaging of square-wave gratings, the (2) lateral resolution expressed as the parameter D_12–88 characterizing the steepness of the sigmoidal edge spread function (ESF) determined by imaging a straight edge and (3) the lateral resolution expressed as the full width of half maximum of the line spread function (LSF), w_LSF, determined by imaging a narrow line. The last method also delivers information on the shape of the LSF, which characterizes an individual imaging instrument. Finally, the implementation of all three standardized methods in the field of imaging laboratory X-ray photoelectron spectroscopy (XPS) is shortly presented. This part of the letter is based on the use of a new test sample developed at ETH Zurich, Switzerland. This test sample displays a micrometre scaled pattern motivated by the resolving power of recent imaging XPS instruments.     

Summary of ISO/TC 201 Standard: ISO 29081: 2010, surface chemical analysis—Auger electron spectroscopy—reporting of methods used for charge control and charge correction

This international standard specifies the minimum amount of information required for describing the methods of charge control and charge correction in measurements of Auger electron transitions from insulating specimens by electron‐stimulated AES to be reported with the analytical results. Information is provided in an Annex on methods that have been found useful for charge control prior to or during AES analysis. The Annex also includes a summary table of methods or approaches, ordered by simplicity of approach. A similar international standard has been published for XPS (ISO 19318: 2003(E), Surface chemical analysis—XPS—reporting of methods used for charge control and charge correction. Copyright © 2010 John Wiley & Sons, Ltd.     

Oxidation‐Induced C—H Functionalization: A Formal Way for C—H Activation

Cross‐coupling reactions have developed widely and provided a powerful means to synthesize a variety of compounds in each chemical field. The compounds which have C—H bonds are widespread in fossil fuels, chemical raw materials, biologically active molecules, etc. Using these readily‐ available substances as substrates is high atom‐ and step‐economy for cross‐coupling reactions. Over the past decades, our research group focused on finding and developing new strategies for C—H functionalization. Compared with classical C—H activation methods, for example, C—H bonds are deprotonated by strong base or converted into C—M bonds, oxidation‐induced C—H functionalization would be another pathway for C—H bond activation. This perspective shows a brief introduction of our recent works in this oxidation‐induced C—H functionalization. We categorized this approach of these C—H bond activations by the key intermediates, radical cations, radicals and cations.     

Aptamer Laden Liquid Crystals Biosensing Platform for the Detection of HIV-1 Glycoprotein-120

We report a label-free and simple approach for the detection of glycoprotein-120 (gp-120) using an aptamer-based liquid crystals (LCs) biosensing platform. The LCs are supported on the surface of a modified glass slide with a suitable amount of B40t77 aptamer, allowing the LCs to be homeotropically aligned. A pronounced topological change was observed on the surface due to a specific interaction between B40t77 and gp-120, which led to the disruption of the homeotropic alignment of LCs. This results in a dark-to-bright transition observed under a polarized optical microscope. With the developed biosensing platform, it was possible to not only identify gp-120, but obtained results were analyzed quantitatively through image analysis. The detection limit of the proposed biosensing platform was investigated to be 0.2 µg/mL of gp-120. Regarding selectivity of the developed platform, no response could be detected when gp-120 was replaced by other proteins, such as bovine serum albumin (BSA), hepatitis A virus capsid protein 1 (Hep A VP1) and immunoglobulin G protein (IgG). Due to attributes such as label-free, high specificity and no need for instrumental read-out, the presented biosensing platform provides the potential to develop a working device for the quick detection of HIV-1 gp-120.     

Characterizing stability properties of supported bilayer membranes on nanoglassified substrates using surface plasmon resonance

Supported bilayer membranes (SBMs) formed on solid substrates, in particular glass, provide an ideal cell mimicking model system that has been found to be highly useful for biosensing applications. Although the stability of the membrane structures is known to determine the applicability, the subject has not been extensively investigated, largely because of the lack of convenient methods to monitor changes of membrane properties on glass in real time. This work reports the evaluation of the stability properties of a series of SBMs against chemical and air damage by use of surface plasmon resonance spectroscopy and nanoglassified gold substrates. Seven SBMs composed of phosphatidylcholine and DOPC+, including single-component, mixed, protein-reinforced SBMs (rSBMs) and protein-tethered bilayer membranes (ptBLMs), are studied. The stability properties under various conditions, especially the effects of surfactants, organic solvents, and dehydration damage on the bilayers, are compared. PC membranes are found to be easily removed from the glassy surfaces using relatively low concentrations of the surfactants, while DOPC+ is markedly more stable toward nonionic surfactant. DOPC+ membranes also demonstrated remarkable air stability while PC films exhibited considerable damage from dehydration. Doping of cholesterol does not improve PC's stability against SDS and Triton but changes the lipid membrane packing enough to protect against dehydration damage. Although rSBMs and ptBLMs improve air stability to a certain degree, they are still quite susceptible to significant damage/removal from ionic and nonionic surfactants at lower concentrations. Overall, DOPC+ has noted higher stability on glass, likely due to the favorable electrostatic interaction between the silicate surface and the lipid headgroup, making it a good candidate for application. Nanoglassy SPR proves to be an attractive platform capable of rapidly screening film stability in real-time, providing critical information for future work using supported membranes for sensing applications.     

Recent Advances on Electrochemical Biosensing Strategies toward Universal Point‐of‐Care Systems

A number of very recently developed electrochemical biosensing strategies are promoting electrochemical biosensing systems into practical point‐of‐care applications. The focus of research endeavors has transferred from detection of a specific analyte to the development of general biosensing strategies that can be applied for a single category of analytes, such as nucleic acids, proteins, and cells. In this Minireview, recent cutting‐edge research on electrochemical biosensing strategies are described. These developments resolved critical challenges regarding the application of electrochemical biosensors to practical point‐of‐care systems, such as rapid readout, simple biosensor fabrication method, ultra‐high detection sensitivity, direct analysis in a complex biological matrix, and multiplexed target analysis. This Minireview provides general guidelines both for scientists in the biosensing research community and for the biosensor industry on development of point‐of‐care system, benefiting global healthcare.     

Particle Network Self-Assembly of Similar Size Sub-Micron Calcium Alginate and Polystyrene Particles Atop Glass

Particle-mediated self-assembly, such as nanocomposites, microstructure formation in materials, and core-shell coating of biological particles, offers precise control over the properties of biological materials for applications in drug delivery, tissue engineering, and biosensing. The assembly of similar-sized calcium alginate (CAG) and polystyrene sub-micron particles is studied in an aqueous sodium nitrate solution as a model for particle-mediated self-assembly of biological and synthetic mixed particle species. The objective is to reinforce biological matrices by incorporating synthetic particles to form hybrid particulate networks with tailored properties. By varying the ionic strength of the suspension, the authors alter the energy barriers for particle attachment to each other and to a glass substrate that result from colloidal surface forces. The particles do not show monotonic adsorption trend to glass with ionic strength. Hence, apart from DLVO theory—van der Waals and electrostatic interactions—the authors further consider solvation and bridging interactions in the analysis of the particulate adsorption-coagulation system. CAG particles, which support lower energy barriers to attachment relative to their counterpart polystyrene particles, accumulate as dense aggregates on the glass substrate. Polystyrene particles adsorb simultaneously as detached particles. At high electrolyte concentrations, where electrostatic repulsion is largely screened, the mixture of particles covers most of the glass substrate; the CAG particles form a continuous network throughout the glass substrate with pockets of polystyrene particles. The particulate structure is correlated with the adjustable energy barriers for particle attachment in the suspension.     

Surface‐Independent and Oriented Immobilization of Antibody via One‐Step Polydopamine/Protein G Coating: Application to Influenza Virus Immunoassay

For the construction of high‐performance biosensor, it is important to interface bioreceptors with the sensor surface densely and in the optimal orientation. Herein, a simple surface modification method that can optimally immobilize antibodies onto various kinds of surfaces is reported. For the surface modification, a mixture of polydopamine (PDA) and protein G was employed. PDA is a representative mussel‐inspired polymer, and protein G is an immunoglobulin‐binding protein that enables an antibody to have an optimal orientation. The surface characteristics of PDA/Protein G mixture‐coated substrates are analyzed and the PDA/protein G ratio is optimized to maximize the antibody binding efficiency. Moreover, the antibody‐immobilized substrates are applied to the detection of influenza viruses with the naked eye, providing a detection limit of 2.9 × 10³ pfu mL^‐1. Importantly, the several substrates (glass, SiO₂, Si, Al₂O₃, polyethylene terephthalate, polyethylene, polypropylene, and paper) can be modified by simple incubation with the mixture of PDA/protein G, and then the anti‐influenza A H1N1 antibodies can be immobilized on the substrates successfully. Regardless of the substrate, the influenza viruses are detectable after the sandwich immunoreaction and silver enhancement procedure. It is anticipated that the developed PDA/protein G coating method will extend the range of applicable materials for biosensing.     

Development of standards for reliable surface analyses by ISO technical committee 201 on surface chemical analysis

The need for reliable surface analyses together with quality‐management requirements for analytical laboratories led the International Organization for Standardization (ISO) to form its Technical Committee (TC) 201 on Surface Chemical Analysis in 1991. This article describes the organization of TC 201, the strategies that have been found useful for identifying and assessing possible projects for new international standards, and the 57 international standards and other documents prepared to date by TC 201. Standards have now been developed for Auger‐electron spectroscopy, glow‐discharge spectroscopy, various types of scanning probe microscopy, secondary‐ion mass spectrometry, sputter‐depth profiling, total‐reflection X‐ray fluorescence spectroscopy, X‐ray photoelectron spectroscopy, and X‐ray reflectometry. In addition, standards have been developed with definitions of terms used in surface chemical analysis; the handling, preparation of specimens for surface analysis; information and data‐transfer formats; and methods for determining the lateral resolution of beam‐based methods of surface analysis. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermoplastic microfluidic devices and their applications in protein and DNA analysis

Microfluidics is a platform technology that has been used for genomics, proteomics, chemical synthesis, environment monitoring, cellular studies, and other applications. The fabrication materials of microfluidic devices have traditionally included silicon and glass, but plastics have gained increasing attention in the past few years. We focus this review on thermoplastic microfluidic devices and their applications in protein and DNA analysis. We outline the device design and fabrication methods, followed by discussion on the strategies of surface treatment. We then concentrate on several significant advancements in applying thermoplastic microfluidic devices to protein separation, immunoassays, and DNA analysis. Comparison among numerous efforts, as well as the discussion on the challenges and innovation associated with detection, is presented.     

Hardness Equation for Ormosils

Hardness of ormosils coating on various kinds of substrates is important, and by considering recent progresses in understanding the hardness of ionic crystals or covalent crystals, new hardness equations for calculating the hardness of glasses or ormosils from chemical compositions were derived. When we applied an indenter to the surface of glass or sol-gel coatings, the surface of indenter is a declined one to the flat surface of glass or coating, thus the applied force should be analyzed by using the shear modulus, S, and Young's modulus, E. This is now well accepted for the analysis of hardness of ionic or covalent bonding inorganic materials. For example, by considering the binding energy and plastic deformation, Gilman showed that Hv of NaCl crystal can be calculated by an equation including elastic stiffness which indicated a good agreement between calculated and observed value. For covalent crystals he reported that the strength of chemical bonds could be correlated with the glide (shear) activation energy for covalent crystals quantitatively. These explanations are basically applied to the hardness of silicate glasses and ormosils. By considering both shear modulus and Young's modulus we have derived equations for calculating the hardness of glasses or ormosils from chemical composition, which includes packing density of atoms and bond energy per unit volume has been taken account. The agreements between calculated and observed hardness values for ormosils were comparatively good.     

Metal-enhanced fluorescence using anisotropic silver nanostructures: critical progress to date

In this critical and timely review, the effects of anisotropic silver nanostructures on the emission intensity and photostability of a key fluorophore that is frequently used in many biological assays is examined. The silver nanostructures consist of triangular, rod-like, and fractal-like nanoparticles of silver deposited on conventional glass substrates. The close proximity to silver nanostructures results in greater intensity and photostability of the fluorophore than for fluorophores solely deposited on glass substrates. These new anisotropic silver nanostructure-coated surfaces show much more favorable effects than silver island films or silver colloid-coated substrates. Subsequently, the use of metal-enhanced fluorescence (MEF) for biosensing applications is discussed.     

Biological sensing using transmission surface plasmon resonance spectroscopy

Ultrathin gold island films evaporated on transparent substrates offer promising transducers for chemical and biological sensing in the transmission surface plasmon resonance (T-SPR) mode. In the present work, the applicability of T-SPR-based systems to biosensing is demonstrated, using a well-established biological model system. Au island films were evaporated on polystyrene slides and modified with a biotinylated monolayer via a multistep surface reaction, the latter assisted by the good adhesion of metal islands to polystyrene. The biotin-derivatized Au island film was then used as a biological recognition surface for selective sensing of avidin binding, distinguishing between specific and nonspecific binding to the substrate. Transduction of the binding event into an optical signal was achieved by T-SPR spectroscopy, using plasmon intensity measurements, rather than wavelength change, for maximal sensitivity and convenience. T-SPR spectroscopy of Au island films is shown to be an effective tool for monitoring the binding of biological molecules to receptor layers on the Au surface and a promising approach to label-free optical biosensing.     

玻璃上基于自组装和喷墨打印的选位金属沉积

采用氨基硅烷自组装分子对玻璃表面进行修饰; 借助喷墨打印技术, 按照设计好的线路图形把引发化学镀的催化剂“墨水”喷射在上述修饰表面上. 由于自组装分子具有朝向面外的氨基末端能吸附作为催化剂的溶胶或离子, 因而可以起到“有机浆糊”的作用, 使图形化的催化剂层固定在表面上以充当模板, 由于化学镀只在催化剂模板上发生, 从而可获得与设计一致的, 且与基底牢固结合的金属沉积图形. 将该方法拓展应用到玻璃基底上, 着重优化自组装条件, 提高了结合力, 首次实现了玻璃表面上包括金、铜以及镍硼合金在内的多种金属直接成型.     

Application of monofluorophosphate/alkaline phosphatase system in flow injection analysis

Monofluorophosphate was found to be a specific substrate for alkaline phosphatase (EC 3.1.3.1) forming novel biosensing schemes with potentiometric detection. Several utilities of this substrate/enzyme system in analytical chemistry will be demonstrated. The system is useful for direct detection of enzymes and substrates as well as for indirect determination of enzyme inhibitors and cofactors using common potentiometric instrumentation. The analytical values of reported biosensing schemes are significantly improved by their implementation into flow injection analysis. This paper presents recent developments in this area and suggests important prospects for further investigations and applications.     

Zinc oxide-potassium ferricyanide composite thin film matrix for biosensing applications

Thin film of zinc oxide-potassium ferricyanide (ZnO-KFCN) composite has been deposited on indium tin oxide (ITO) coated corning glass using pulsed laser deposition (PLD). The composite thin film electrode has been exploited for amperometric biosensing in a mediator-free electrolyte. The composite matrix has the advantages of high iso-electric point of ZnO along with enhanced electron communication due to the presence of a redox species in the matrix itself. Glucose oxidase (GOx) has been chosen as the model enzyme for studying the application of the developed matrix to biosensing. The sensing response of the bio-electrode, GOx/ZnO-KFCN/ITO/glass, towards glucose was studied using cylic voltammetry (CV) and photometric assay. The bio-electrode exhibits good linearity from 2.78 mM to 11.11 mM glucose concentration. The low value of Michaelis-Menten constant (1.69 mM) indicates an enhanced affinity of the immobilized enzyme towards its substrate. A quassireversible system is obtained with the composite matrix. The results confirm promising application of the ZnO-KFCN composite matrix for amperometric biosensing applications in a mediator-less electrolyte that could lead to the realization of an integrated lab-on-chip device.     

A novel biosensing interfacial design produced by assembling nano-Au particles on amine-terminated plasma-polymerized films

A novel biosensing interfacial design strategy has, for the first time, been produced by assembling nano-Au particles on amine-terminated plasma-polymerized films (PPF). A quartz-crystal microbalance (QCM) as a model transducer was deposited with PPF of n-butylamine by use of a glow discharge and then treated with nano-Au particles. The kinetic assembly process and conditions were studied using the real-time-output device and the surface topology of the resulting crystal was characterized by atomic force microscopy (AFM) imaging. Based on analysis of the experimental data, including the association constant of Au–amine interaction, the assembly mechanism is considered to be partly or even mainly chemical adsorption. Moreover, immobilization of anti-human IgM antibody (IgM Ab), as an example, on the developed PPF-Au interface was investigated. It was found that antibody molecules immobilized by the proposed procedure had higher immunological activity than those immobilized by the conventional glutaraldehyde (GLU) cross-linking procedure or the direct gold-attachment procedure. The newly developed sensor had a better response, with a detection limit of IgM concentration as low as ~1.00 g mL^–1. In particular, the extremely high stability of both PPF and nano-Au monolayer formulated allows the designed biosensing interface to withstand harsh regeneration treatment, making it reusable.     

Sensitive Detection of Small Molecule–Protein Interactions on a Metal–Insulator–Metal Label‐Free Biosensing Platform

The need to develop label‐free biosensing devices that enable rapid analyses of interactions between small molecules/peptides and proteins for post‐genomic studies has increased significantly. We report a simple metal–insulator–metal (MIM) geometry for fabricating a highly sensitive detection platform for biosensing. MIM substrates consisting of an Au–PMMA–Ag nanolayer were extensively studied using both theoretical and experimental approaches. By monitoring reflectivity changes at the normal incidence angle, we observed molecular interactions as the thickness of the biolayer increased on the substrate surface. These interactions included the adsorption of various proteins (Mw=6–150 kD) and interactions between small molecules (Mw≤2 kD) and the immobilized proteins. The interaction of designed monosaccharide‐modified designed peptides with various lectins was also clearly detected. These interactions could not be detected by the conventional Au‐only substrate. Thus, the MIM approach affords a powerful label‐free biosensing device that will aid our understanding of protein interactions and recognition.     

Application of surface analysis methods to nanomaterials: summary of ISO/TC 201 technical report: ISO 14187:2011 – surface chemical analysis – characterization of nanomaterials

The ISO technical report 14187 provides an introduction to (and examples of) the information that can be obtained about nanostructured materials by using surface analysis tools. In addition, both general issues and challenges associated with characterizing nanostructured materials and the specific opportunities and challenges associated with individual analytical methods are identified. As the size of objects or components of materials approaches a few nanometers, the distinctions among ‘bulk’, ‘surface’, and ‘particle’ analysis blur. This technical report focuses on issues specifically relevant to surface chemical analysis of nanostructured materials. The report considers a variety of analysis methods but focuses on techniques that are in the domain of ISO/TC 201 including Auger electron spectroscopy, X‐ray photoelectron spectroscopy, secondary ion mass spectrometry, and scanning probe microscopy. Measurements of nanoparticle surface properties such as surface potential that are often made in a solution are not discussed. Copyright © 2012 John Wiley & Sons, Ltd.