Graphene nano-ink biosensor arrays on a microfluidic paper for multiplexed detection of metabolites

The development of a miniaturized and low-cost platform for the highly sensitive, selective and rapid detection of multiplexed metabolites is of great interest for healthcare, pharmaceuticals, food science, and environmental monitoring. Graphene is a delicate single-layer, two-dimensional network of carbon atoms with extraordinary electrical sensing capability. Microfluidic paper with printing technique is a low cost matrix. Here, we demonstrated the development of graphene-ink based biosensor arrays on a microfluidic paper for the multiplexed detection of different metabolites, such as glucose, lactate, xanthine and cholesterol. Our results show that the graphene biosensor arrays can detect multiple metabolites on a microfluidic paper sensitively, rapidly and simultaneously. The device exhibits a fast measuring time of less than 2 min, a low detection limit of 0.3 μM, and a dynamic detection range of 0.3–15 μM. The process is simple and inexpensive to operate and requires a low consumption of sample volume. We anticipate that these results could open exciting opportunities for a variety of applications.     

Synthesis and Evaluation of 2,2‐Dimethylchroman Derivatives as Inhibitors of ICAM‐1 Expression on Human Endothelial Cells

We herein report the synthesis of novel 2,2‐dimethylchroman analogs and their effect on the modulation of tumor necrosis factor‐α‐induced expression of intercellular adhesion molecule‐1 in human endothelial cells. These compounds were found to be potent inhibitors of tumor necrosis factor‐α‐induced expression of intercellular adhesion molecule‐1 on human endothelial cells at very low concentration. The structure–activity relationship of these compounds has been studied. The IC₅₀ and maximum tolerable dose value of the lead compound 7d (X═NH, R═4Cl) of this study was found to be 9.5 and 150 μM, respectively. The present results indicate that our novel compound is potentially effective and therefore could be useful for further pharmaceutical studies.     

Potential of Gelatin‐Zinc Oxide Nanocomposite as Ascorbic Acid Sensor

We report on the studies relating to fabrication of gelatin B (GB) and zinc oxide (ZnO) based nanocomposite (GB‐ZnO) film deposited on indium‐tin‐oxide (ITO) glass plate, and used for the immobilization of ascorbate oxidase (AsOx) which was further used for ascorbic acid (AA) detection. The structural and morphological studies of GB‐ZnO, and AsOx/GB‐ZnO/ITO bioelectrodes were carried out using XRD, SEM and FTIR techniques. This bioelectrode showed a broad range of linearity (5–500 mg/dL), low detection limit (1 mg/dL), higher sensitivity (0.106 µA mg/dLcm^?2) and low value of the apparent Michaelis? Menten constant (K_m^app=0.35 mg/dL) for AA. Efforts are being made to utilize this electrode for sensing AA in real samples in a bid to develop a strip based sensor.     

Molybdenum doping of semiconducting vanadium phosphate glasses

The DC conductivity and dielectric properties of glasses of composition (70 ? x) V₂O₅ : x MoO₃ : 30 P₂O₅ have been measured as a function of temperature and frequency for O × 5 mol %. An increase in conductivity by two orders of magnitude is observed for 1 mol % MoO₃ and this is correlated with changes in activation energy and dielectric constant. The results can be explained in terms of small polaron theory, with the main interaction being through the local electronic polarizability at any site. The results indicate that percolation considerations have to be taken into account in describing the electrical properties of transition metal glasses.     

Toxicity assessment of nanomaterials: methods and challenges

The increasing use of nanomaterials in consumer and industrial products has aroused global concern regarding their fate in biological systems, resulting in a demand for parallel risk assessment. A number of studies on the effects of nanoparticles in in vitro and in vivo systems have been published. However, there is still a need for further studies that conclusively establish their safety/toxicity, due to the many experimental challenges and issues encountered when assessing the toxicity of nanomaterials. Most of the methods used for toxicity assessment were designed and standardized with chemical toxicology in mind. However, nanoparticles display several unique physicochemical properties that can interfere with or pose challenges to classical toxicity assays. Recently, some new methods and modified versions of pre-existing methods have been developed for assessing the toxicity of nanomaterials. This review is an attempt to highlight some important methods employed in nanomaterial toxicology and to provide a critical analysis of the major issues/challenges faced in this emerging field.     

Structural and stability studies of CdS and SnS nanostructures synthesized by various routes

CdS nanorods and SnS nano-flakes have been synthesized by solvothermal process and CdS nanoparticles have been synthesized by aqueous media process. Structural properties of these nanocomposites are performed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Chemical purity of these nanocomposites has been confirmed by energy dispersive analysis of X-ray (EDAX). Thermal stability of these nanocomposites is investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Different parameters such as activation energy (E) for the degradation, Arrhenius parameter (A) and the entropy change (ΔS) have been calculated by Coats-Redfern and Satava model. It is observed that the activation energy of the CdS nanorods is much higher compared to that of CdS nanoparticles and SnS nano-flakes.     

Ion beam sputter deposited W/Si multilayers: Influence of re-sputtering on the interface structure and structure modification at ultra short periods

X-ray multilayer mirrors of period ranging from 9.6 to 1.7 nm, deposited using ion beam sputtering, have been examined using grazing incidence X-ray reflectivity (GIXRR) and grazing incidence X-ray diffraction. Detailed analysis of GIXRR data revealed that significant amount of re-sputtering of Si layer takes place while W deposition is underway. Re-sputtering is mainly due to bombardment of high-energy neutrals getting reflected from the W target. Due to re-sputtering interface of the multilayer becomes asymmetric. This puts a major hindrance in avoiding the intermixing and achieving sharp interfaces at shorter periods. Maximum thickness of Si which gets lost due to re-sputtering during deposition is ∼0.8 nm. The shortest period multilayer estimated, that could be deposited without intermixing, was 2.7 nm. These results are of significance for developing low period W/Si multilayers.     

Coatings of polyethylene glycol for suppressing adhesion between solid microspheres and flat surfaces

This article describes the development and the examination of surface coatings that suppress the adhesion between glass surfaces and polymer microspheres. Superparamagnetic doping allowed for exerting magnetic forces on the microbeads. The carboxyl functionalization of the polymer provided the means for coating the beads with polyethylene glycol (PEG) with different molecular weight. Under gravitational force, the microbeads settled on glass surfaces with similar polymer coatings. We examined the efficacy of removing the beads from the glass surfaces by applying a pulling force of ~1.2 pN. The percent beads remaining on the surface after applying the pulling force for approximately 5 s served as an indication of the adhesion propensity. Coating of PEG with molecular weight ranging between 3 and 10 kDa was essential for suppressing the adhesion. For the particular substrates, surface chemistry and aqueous media we used, coatings of 5 kDa manifested optimal suppression of adhesion: that is, only 3% of the microbeads remained on the surface after applying the pulling magnetic force. When either the glass or the beads were not PEGylated, the adhesion between them was substantial. Addition of a noncharged surfactant, TWEEN, above its critical micelle concentrations (CMCs) suppressed the adhesion between noncoated substrates. The extent of this surfactant-induced improvement of the adhesion suppression, however, did not exceed the quality of preventing the adhesion that we attained by PEGylating both substrates. In addition, the use of surfactants did not significantly improve the suppression of bead-surface adhesion when both substrates were PEGylated. These findings suggest that such surfactant additives tend to be redundant and that covalently grafted coatings of PEGs with selected chain lengths provide sufficient suppression of nonspecific interfacial interactions.     

Angle-dependent resonance of localized and propagating surface plasmons in microhole arrays for enhanced biosensing

The presence of microhole arrays in thin Au films is suited for the excitation of localized and propagating surface plasmon (SP) modes. Conditions can be established to excite a resonance between the localized and propagating SP modes, which further enhanced the local electromagnetic (EM) field. The co-excitation of localized and propagating SP modes depends on the angle of incidence (θ _exc) and refractive index of the solution interrogated. As a consequence of the enhanced EM field, enhanced sensitivity and an improved response for binding events by about a factor of 3 to 5 was observed with SPR sensors in the Kretschmann configuration for a set of experimental conditions (λ _SPR, θ _exc, and η). Thus, microhole arrays can improve sensing applications of SPR based on classical prism-based instrumentation and are suited for SP-coupled spectroscopic techniques.

An Experimental Study for Enhanced Availability of Free-Space Optics Systems over Hybrid Free-Space Optics/Radio Frequency Systems Using Switching Scheme Based on On–Off Keying and Multiple Pulse Position Modulation Schemes with Variable Data Rates

Abstract

Free-space optic links are degraded by such weather conditions as rain, fog, and atmospheric scintillation. The inherent advantages of free-space optic communication—providing higher data rates, security, and easy redeployment ability—motivate the avoidance of switching over free-space optic links to low bandwidth radio frequency links. This article establishes viable alternatives over free-space optics/radio frequency hybrid links to achieve higher capacity operation exploiting on–off keying and multiple pulse position modulation schemes with variable data rates to overcome the effect of fading due to adverse weather conditions. Results of an experimental free-space optical link at 1,550 nm are presented.