Kyle R. Ratinac

Carbon Nanomaterials in Biosensors: Should You Use Nanotubes or Graphene?

From diagnosis of life-threatening diseases to detection of biological agents in warfare or terrorist attacks, biosensors are becoming a critical part of modern life. Many recent biosensors have incorporated carbon nanotubes as sensing elements, while a growing body of work has begun to do the same with the emergent nanomaterial graphene, which is effectively an unrolled nanotube. With this widespread use of carbon nanomaterials in biosensors, it is timely to assess how this trend is contributing to the science and applications of biosensors. This Review explores these issues by presenting the latest advances in electrochemical, electrical, and optical biosensors that use carbon nanotubes and graphene, and critically compares the performance of the two carbon allotropes in this application. Ultimately, carbon nanomaterials, although still to meet key challenges in fabrication and handling, have a bright future as biosensors.

Three-dimensional electrodes for dye-sensitized solar cells: synthesis of indium?tin-oxide nanowire arrays and ITO/TiO2 core?shell nanowire arrays by electrophoretic deposition

Dye-sensitized solar cells (DSSCs) show promise as a cheaper alternative to silicon-based photovoltaics for specialized applications, provided conversion efficiency can be maximized and production costs minimized. This study demonstrates that arrays of nanowires can be formed by wet-chemical methods for use as three-dimensional (3D) electrodes in DSSCs, thereby improving photoelectric conversion efficiency. Two approaches were employed to create the arrays of ITO (indium-tin-oxide) nanowires or arrays of ITO/TiO(2) core-shell nanowires; both methods were based on electrophoretic deposition (EPD) within a polycarbonate template. The 3D electrodes for solar cells were constructed by using a doctor-blade for coating TiO(2) layers onto the ITO or ITO/TiO(2) nanowire arrays. A photoelectric conversion efficiency as high as 4.3% was achieved in the DSSCs made from ITO nanowires; this performance was better than that of ITO/TiO(2) core-shell nanowires or pristine TiO(2) films. Cyclic voltammetry confirmed that the reaction current was significantly enhanced when a 3D ITO-nanowire electrode was used. Better separation of charge carriers and improved charge transport, due to the enlarged interfacial area, are thought to be the major advantages of using 3D nanowire electrodes for the optimization of DSSCs.

Cancer-cell-specific cytotoxicity of non-oxidized iron elements in iron core-gold shell NPs

UNLABELLED Gold-coated iron nanoparticles (NPs) selectively and significantly (P <0.0001) inhibit proliferation of oral- and colorectal-cancer cells in vitro at doses as low as 5 μg/mL, but have little adverse effect on normal healthy control cells. The particle treatment caused delay in cell-cycle progression, especially in the S-phase. There was no significant difference in the NP uptake between cancer and control cells, and cytotoxicity resulted primarily from the iron core, before oxidation, rather than from the Fe ions released from the core. In contrast with magnetic NPs that usually serve as drug carriers, diagnostic probes or hyperthermia media, the iron, before oxidation, in the NPs selectively suppressed cancer cell growth and left healthy control cells unaffected in vitro and in vivo. This novel nanomaterial holds great promise as a therapeutic tool in nanomedicine. FROM THE CLINICAL EDITOR Gold-coated iron nanoparticles (NPs) selectively suppressed squamous cell carcinoma (SCC) and colorectal cancer (CRC) cell growth, but left healthy control cells unaffected both in vitro and in vivo. The particles were equally uptaken by all cells, but delayed cell progression only for cancer cells. The origin is related to the iron core: neither iron ions nor the oxidized NPs have the same outcome.

Correlative microscopy: providing new understanding in the biomedical and plant sciences.

Correlative microscopy is the application of two or more distinct microscopy techniques to the same region of a sample, generating complementary morphological, structural and chemical information that exceeds what is possible with any single technique. As a variety of complementary microscopy approaches rather than a specific type of instrument, correlative microscopy has blossomed in recent years as researchers have recognised that it is particularly suited to address the intricate questions of the modern biological sciences. Specialised technical developments in sample preparation, imaging methods, visualisation and data analysis have also accelerated the uptake of correlative approaches. In light of these advances, this critical review takes the reader on a journey through recent developments in, and applications of, correlative microscopy, examining its impact in biomedical research and in the field of plant science. This twin emphasis gives a unique perspective into use of correlative microscopy in fields that often advance independently, and highlights the lessons that can be learned from both fields for the future of this important area of research.

High-flux ceramic membranes with a nanomesh of metal oxide nanofibers

Traditional ceramic separation membranes, which are fabricated by applying colloidal suspensions of metal hydroxides to porous supports, tend to suffer from pinholes and cracks that seriously affect their quality. Other intrinsic problems for these membranes include dramatic losses of flux when the pore sizes are reduced to enhance selectivity and dead-end pores that make no contribution to filtration. In this work, we propose a new strategy for addressing these problems by constructing a hierarchically structured separation layer on a porous substrate using large titanate nanofibers and smaller boehmite nanofibers. The nanofibers are able to divide large voids into smaller ones without forming dead-end pores and with the minimum reduction of the total void volume. The separation layer of nanofibers has a porosity of over 70% of its volume, whereas the separation layer in conventional ceramic membranes has a porosity below 36% and inevitably includes dead-end pores that make no contribution to the flux. This radical change in membrane texture greatly enhances membrane performance. The resulting membranes were able to filter out 95.3% of 60-nm particles from a 0.01 wt % latex while maintaining a relatively high flux of between 800 and 1000 L/m2.h, under a low driving pressure (20 kPa). Such flow rates are orders of magnitude greater than those of conventional membranes with equal selectivity. Moreover, the flux was stable at approximately 800 L/m2.h with a selectivity of more than 95%, even after six repeated runs of filtration and calcination. Use of different supports, either porous glass or porous alumina, had no substantial effect on the performance of the membranes; thus, it is possible to construct the membranes from a variety of supports without compromising functionality. The Darcy equation satisfactorily describes the correlation between the filtration flux and the structural parameters of the new membranes. The assembly of nanofiber meshes to combine high flux with excellent selectivity is an exciting new direction in membrane fabrication.

Ceramic Membranes for Separation of Proteins and DNA through In Situ Growth of Alumina Nanofibres inside Porous Substrates

Ceramic membranes were fabricated by in situ synthesis of alumina nanofibres in the pores of an alumina support as a separation layer, and exhibited a high permeation selectivity for bovine serum albumin relative to bovine hemoglobin (over 60 times) and can effectively retain DNA molecules at high fluxes.

A novel method for practical temperature measurement with carbon nanotube nanothermometers

This work presents an oxidation-assisted approach to measurement of temperatures with carbon nanotubes that contain liquid gallium (Ga). When a Ga-filled carbon nanotube is heated in air for an appropriate length of time, an oxide marker is formed on the inner wall of the carbon nanotube due to partial oxidation of the Ga. Thus, the temperature to which the nanotube was exposed can be retrieved by progressively heating the carbon nanotube until the liquid Ga reaches the oxide marker. Compared with previous methods, this novel approach provides a simpler and, importantly, a far more reliable way to measure temperatures over a moderate temperature range at the nanometre scale.

Multi-dimensional correlative imaging of subcellular events: combining the strengths of light and electron microscopy

To genuinely understand how complex biological structures function, we must integrate knowledge of their dynamic behavior and of their molecular machinery. The combined use of light or laser microscopy and electron microscopy has become increasingly important to our understanding of the structure and function of cells and tissues at the molecular level. Such a combination of two or more different microscopy techniques, preferably with different spatial- and temporal-resolution limits, is often referred to as ‘correlative microscopy’. Correlative imaging allows researchers to gain additional novel structure–function information, and such information provides a greater degree of confidence about the structures of interest because observations from one method can be compared to those from the other method(s). This is the strength of correlative (or ‘combined’) microscopy, especially when it is combined with combinatorial or non-combinatorial labeling approaches. In this topical review, we provide a brief historical perspective of correlative microscopy and an in-depth overview of correlative sample-preparation and imaging methods presently available, including future perspectives on the trend towards integrative microscopy and microanalysis.

Atom Probe Microscopy of Self-Assembled Monolayers: Preliminary Results

We have achieved three-dimensional imaging of decanethiol self-assembled monolayers (SAMs) on metal surfaces by atom probe tomography (APT). The present Letter provides preliminary results on Ni [001] and Au [111], shows the analytical potential of APT analysis of SAMs, and details developments in specimen preparation and in data-treatment methodologies. Importantly, the investigation of the mass spectra from analysis of the SAMs revealed no combination of sulfur and hydrogen at the interface between the metal substrates and the organic materials, potentially providing insight about the bonding of the thiols on the substrate.

Imaging fluorescently labeled complexes by means of multidimensional correlative light and transmission electron microscopy: practical considerations.

These days the common ground between structural biology and molecular biology continues to grow thanks to the biomolecular insights offered by correlative microscopy, even though the vision of combining insights from different imaging tools has been around for nearly four decades. The use of correlative imaging methods to dissect the cells internal structure is progressing faster than ever as shown by the boom in the number of methodological approaches available for correlative microscopy studies, each designed to address a specific scientific question. In this chapter, we will present a relatively straightforward approach to combining information from fluorescence microscopy and electron microscopy at the supramolecular level. The method combines live-cell and/or confocal laser microscopy with classical sample preparation for transmission electron microscopy (TEM), thereby allowing the integration of dynamic details of subcellular processes with insights about the organelles and molecular machinery involved. We illustrate the applicability of this multidimensional correlative microscopy approach on cultured Caco-2 colorectal cancer cells exposed to fluorescently labeled cisplatin, and discuss how these methods can deepen our understanding of key cellular processes, such as drug uptake and cell fate.