Real-Time Electrochemical Monitoring of Adenosine Triphosphate in the Picomolar to Micromolar Range Using Graphene-Modified Electrodes

We report on a competitive electrochemical detection system that is free of wash steps and enables the real-time monitoring of adenosine triphosphate (ATP) in a quantitative manner over a five-log concentration range. The system utilizes a recognition surface based on ATP aptamer (ATPA) capture probes prebound to electroactive flavin adenine dinucleotide (FAD) molecules, and a signaling surface utilizing graphene (Gr) and gold nanoparticle (AuNP) modified carbon paste electrode (Gr–AuNP–CPE) that is optimized to enhance electron-transfer kinetics and signal sensitivity. Binding of ATP to ATPA at the recognition surface causes the release of an equivalent concentration of FAD that can be quantitatively monitored in real time at the signaling surface, thereby enabling a wide linear working range (1.14 × 10^–10 to 3.0 × 10^–5 M), a low detection limit (2.01 × 10^–11 M using graphene and AuNP modified glassy carbon), and fast target binding kinetics (steady-state signal within 12 min at detection limit). Unlike assays based on capture probe-immobilized electrodes, this double-surface competitive assay offers the ability to speed up target binding kinetics by increasing the capture probe concentration, with no limitations due to intermolecular Coulombic interactions and nonspecific binding. We utilize the real-time monitoring capability to compute kinetic parameters for target binding and to make quantitative distinctions on degree of base-pair mismatch through monitoring target binding kinetics over a wide concentration range. On the basis of the simplicity of the assay chemistry and the quantitative detection of ATP within fruit and serum media, as demonstrated by comparison of ATP levels against those determined using a standard high-performance liquid chromatography (HPLC)-UV absorbance method, we envision a versatile detection platform for applications requiring real-time monitoring over a wide target concentration range

Enhanced Quality CVD-Grown Graphene via a Double-Plateau Copper Surface Planarization Methodology

Two-dimensional (2D) nanomaterials have been of intense interest in recent years because of their exceptional electronic, thermal, and mechanical properties. Tailoring these novel properties toward their intrinsic potential requires precise control of the atomic layer growth process and the underlying catalytic growth substrate, as the morphology and purity of the catalytic surface plays a critical role on the shape, size, and growth kinetics of the 2D nanomaterial. In this work, we present a systematic study on the role of the catalytic surface morphology and interface properties on the subsequent carrier mobility properties of CVD-grown graphene. A modified electropolishing methodology results in a dramatic reduction of over 99% in Cu surface roughness that enhances the carrier mobility of the CVD-grown graphene by as much as 125% compared to unpolished and lower planarization level growth substrates, providing a clear correlation between the smoothness of the Cu growth substrate and the resulting electrical properties of the graphene. Mobility measurements also reveal a systematic and controllable reduction in carrier concentration for increased electropolishing time. In addition to enhanced transport properties, the 100-fold reduction in the copper surface roughness leads to the ability to grow high-quality graphene at lower process temperatures

Growth of Large Single-Crystalline Two-Dimensional Boron Nitride Hexagons on Electropolished Copper

Hexagonal-boron nitride (h-BN) or “white graphene” has many outstanding properties including high thermal conductivity, high mechanical strength, chemical inertness, and high electrical resistance, which open up a wide range of applications such as thermal interface material, protective coatings, and dielectric in nanoelectronics that easily exceed the current advertised benefits pertaining to the graphene-based applications. The development of h-BN films using chemical vapor deposition (CVD) has thus far led into nucleation of triangular or asymmetric diamond shapes on different metallic surfaces. Additionally, the average size of the triangular domains has remained relatively small (∼0.5 μm²) leading to a large number of grain boundaries and defects. While the morphology of Cu surfaces for CVD-grown graphene may have impacts on the nucleation density, domain sizes, thickness, and uniformity, the effects of the decreased roughness of Cu surface to develop h-BN films are unknown. Here, we report the growth and characterization of novel large area h-BN hexagons using highly electropolished Cu substrate under atmospheric pressure CVD conditions. We found that the nucleation density of h-BN is significantly reduced while domain sizes increase. In this study, the largest hexagonal-shape h-BN domain observed is 35 μm², which is an order of magnitude larger than a typical triangular domain. As the domains coalesce to form a continuous film, the larger grain size offers a more pristine and smoother film with lesser grain boundaries induced defects

<i>In situ</i> Synthesis of Fluorescent Gold Nanoclusters by Nontumorigenic Microglial Cells

To date, the directed <i>in situ</i> synthesis of fluorescent gold nanoclusters (AuNCs) has only been demonstrated in cancerous cells, with the theorized synthesis mechanism prohibiting AuNC formation in nontumorigenic cell lines. This limitation hinders potential biostabilized AuNC-based technology in healthy cells involving both chemical and mechanical analysis, such as the direct sensing of protein function and the elucidation of local mechanical environments. Thus, new synthesis strategies are required to expand the application space of AuNCs beyond cancer-focused cellular studies. In this contribution, we have developed the methodology and demonstrated the direct <i>in situ</i> synthesis of AuNCs in the nontumorigenic neuronal microglial line, C8B4. The as-synthesized AuNCs form <i>in situ</i> and are stabilized by cellular proteins. The clusters exhibit bright green fluorescence and demonstrate low (<10%) toxicity. Interestingly, elevated ROS levels were not required for the <i>in situ</i> formation of AuNCs, although intracellular reductants such as glutamate were required for the synthesis of AuNCs in C8B4 cells. To our knowledge, this is the first-ever demonstration of AuNC synthesis in nontumorigenic cells and, as such, it considerably expands the application space of biostabilized fluorescent AuNCs