Integrating Carbon Nanomaterials with Metals for Bio-sensing Applications

Age structure in most developed countries is changing fast as the average lifespan is increasing significantly, calling for solutions to provide improved treatments for age-related neurological diseases and disorders. In order to address these problems, a reliable way of recording information about neurotransmitters from in vitro and in vivo applications is needed to better understand neurological diseases and disorders as well as currently used treatments. Likewise, recent developments in medicine, especially with the opioid crisis, are demanding a swift move to personalized medicine to administer patient needs rather than population-wide averages. In order to enable the so-called personalized medicine, it is necessary to be able to do measurements in vivo and in real time. These actions require sensitive and selective detection of different analytes from very demanding environments. Current state-of-the-art materials are unable to provide sensitive and selective detection of neurotransmitters as well as the required time resolution needed for drug molecules at a reasonable cost. To meet these challenges, we have utilized different metals to grow carbon nanomaterials and applied them for sensing applications showing that there are clear differences in their electrochemical properties based on the selected catalyst metal. Additionally, we have combined atomistic simulations to support optimizing materials for experiments and to gain further understanding of the atomistic level reactions between different analytes and the sensor surface. With carbon nanostructures grown from Ni and Al + Co + Fe hybrid, we can detect dopamine, ascorbic acid, and uric acid simultaneously. On the other hand, nanostructures grown from platinum provide a feasible platform for detection of H2O2 making them suitable candidates for enzymatic biosensors for detection of glutamate, for example. Tetrahedral amorphous carbon electrodes have an ability to detect morphine, paracetamol, tramadol, and O-desmethyltramadol. With carbon nanomaterial-based sensors, it is possible to reach metal-like properties in sensing applications using only a fraction of the metal as seed for the material growth. We have also seen that by using nanodiamonds as growth catalyst for carbon nanofibers, it is not possible to detect dopamine and ascorbic acid simultaneously, although the morphology of the resulting nanofibers is similar to the ones grown using Ni. This further indicates the importance of the metal selection for specific applications. However, Ni as a continuous layer or as separate islands does not provide adequate performance. Thus, it appears that metal nanoparticles combined with fiber-like morphology are needed for optimized sensor performance for neurotransmitter detection. This opens up a new research approach of application-specific nanomaterials, where carefully selected metals are integrated with carbon nanomaterials to match the needs of the sensing application in question.

Electrochemical Activity Assay for Protease Analysis Using Carbon Nanofiber Nanoelectrode Arrays

There is a strong demand for bioanalytical techniques to rapidly detect protease activities with high sensitivity and high specificity. This study reports an activity-based electrochemical method toward this goal. Nanoelectrode arrays (NEAs) fabricated with embedded vertically aligned carbon nanofibers (VACNFs) are functionalized with specific peptide substrates containing a ferrocene (Fc) tag. The kinetic proteolysis curves are measured with continuously repeated ac voltammetry, from which the catalytic activity is derived as the inverse of the exponential decay time constant based on a heterogeneous Michaelis-Menten model. Comparison of three peptide substrates with different lengths reveals that the hexapeptide H2N-(CH2)4-CO-Pro-Leu-Arg-Phe-Gly-Ala-NH-CH2-Fc is the optimal probe for cathepsin B. The activity strongly depends on temperature and is the highest around the body temperature. With the optimized peptide substrate and measuring conditions, the limit of detection of cathepsin B activity and concentration can reach 2.49 × 10-4 s-1 and 0.32 nM, respectively. The peptide substrates show high specificity to the cognate proteases, with negligible cross-reactions among three cancer-related proteases cathepsin B, ADAM10, and ADAM17. This electrochemical method can be developed into multiplex chips for rapid profiling of protease activities in cancer diagnosis and treatment monitoring.

Electrical Transport and Power Dissipation in Aerosol-Jet-Printed Graphene Interconnects

This paper reports the first known investigation of power dissipation and electrical breakdown in aerosol-jet-printed (AJP) graphene interconnects. The electrical performance of aerosol-jet printed (AJP) graphene was characterized using the Transmission Line Method (TLM). The electrical resistance decreased with increasing printing pass number (n); the lowest sheet resistance measured was 1.5 kΩ/sq. for n = 50. The role of thermal resistance (RTH) in power dissipation was studied using a combination of electrical breakdown thermometry and infrared (IR) imaging. A simple lumped thermal model ([Formula: see text]) and COMSOL Multiphysics was used to extract the total RTH, including interfaces. The RTH of AJP graphene on Kapton is ~27 times greater than that of AJP graphene on Al2O3 with a corresponding breakdown current density 10 times less on Kapton versus Al2O3.

Integrated Carbon Nanostructures for Detection of Neurotransmitters

Carbon-based materials, such as diamond-like carbon (DLC), carbon nanofibers (CNFs), and carbon nanotubes (CNTs), are inherently interesting for neurotransmitter detection due to their good biocompatibility, low cost and relatively simple synthesis. In this paper, we report on new carbon-hybrid materials, where either CNTs or CNFs are directly grown on top of tetrahedral amorphous carbon (ta-C). We show that these hybrid materials have electrochemical properties that not only combine the best characteristics of the individual "building blocks" but their synergy makes the electrode performance superior compared to conventional carbon based electrodes. By combining ta-C with CNTs, we were able to realize electrode materials that show wide and stable water window, almost reversible electron transfer properties and high sensitivity and selectivity for detecting dopamine in the presence of ascorbic acid. Furthermore, the sensitivity of ta-C + CNF hybrids towards dopamine as well as glutamate has been found excellent paving the road for actual in vivo measurements. The wide and stable water window of these sensors enables detection of other neurotransmitters besides DA as well as capability of withstanding higher potentials without suffering from oxygen and hydrogen evolution.

Optimization of Parameters to Achieve High Yield and Purity Single-Walled Carbon Nanotube by Thermal and Chemical Oxidation and Its Effect on Conductivity

Single wall carbon nanotubes due to their unique structural and electronic characteristics have revolutionized the field of nanotechnology and are widely used the field of transistors, drug delivery, and nanocomposities. For improved efficiency of these applications, the utilized tubes must of preeminent purity. Here, we report key parameters that are optimized to achieve their highest purity upto 98 wt%, and yield as high as 50 wt% by thermal and chemical oxidation. The as-produced SWCNT were heated in air at 470 °C, for 90 min, and later subjected to chemical oxidation. The chemical oxidation involved the treatment of thermally treated SWCNT with different concentrations of HCl (4N, 6N, 8N) and 30% H₂O₂, for different time periods (4 hr, 6 hr). This method does not cause damage to the walls of the tubes, observing no loss of nanotubes. The sheet resistance of as-produced and purified tubes was measured and the conductivity was calculated.

Three-dimensional wax patterning of paper fluidic devices

In this paper we describe a method for three-dimensional wax patterning of microfluidic paper-based analytical devices (μPADs). The method is rooted in the fundamental details of wax transport in paper and provides a simple way to fabricate complex channel architectures such as hemichannels and fully enclosed channels. We show that three-dimensional μPADs can be fabricated with half as much paper by using hemichannels rather than ordinary open channels. We also provide evidence that fully enclosed channels are efficiently isolated from the exterior environment, decreasing contamination risks, simplifying the handling of the device, and slowing evaporation of solvents.

Agarose gel tailored calcium carbonate nanoparticles-synthesis and biocompatibility evaluation

In this study, a novel approach to tailor the calcium carbonate nanoparticles was exploited based on agarose gel as polymer medium. The size of nanoparticles formed was governed by ionic diffusion and affected by weight percent of agarose and reaction temperature. The size, shape, purity, composition and allotropy of the synthesized nanoparticles were analyzed by different characterization techniques. Purity of nanoparticles as small as 37 nm demonstrates their suitability for broad range of industrial applications. The exposure of rat lung epithelial cells to these nanoparticles even at a higher concentration (50 microg/ml) did not induce considerable oxidative stress or cell death authenticating their fidelity to potential applications in the field of biotechnology and medicine. Through the simple and economic method of synthesis adopted in this study, separation of nanoparticles from the gel was easy, and process parameters could be optimized to control the particle size.

Neuromodulation: selected approaches and challenges

The brain operates through complex interactions in the flow of information and signal processing within neural networks. The 'wiring' of such networks, being neuronal or glial, can physically and/or functionally go rogue in various pathological states. Neuromodulation, as a multidisciplinary venture, attempts to correct such faulty nets. In this review, selected approaches and challenges in neuromodulation are discussed. The use of water-dispersible carbon nanotubes has been proven effective in the modulation of neurite outgrowth in culture and in aiding regeneration after spinal cord injury in vivo. Studying neural circuits using computational biology and analytical engineering approaches brings to light geometrical mapping of dynamics within neural networks, much needed information for stimulation interventions in medical practice. Indeed, sophisticated desynchronization approaches used for brain stimulation have been successful in coaxing 'misfiring' neuronal circuits to resume productive firing patterns in various human disorders. Devices have been developed for the real-time measurement of various neurotransmitters as well as electrical activity in the human brain during electrical deep brain stimulation. Such devices can establish the dynamics of electrochemical changes in the brain during stimulation. With increasing application of nanomaterials in devices for electrical and chemical recording and stimulating in the brain, the era of cellular, and even intracellular, precision neuromodulation will soon be upon us.

Optimization of process parameters of polymer solution mediated growth of calcium carbonate nanoparticles

With the advent of nanotechnology, many methods of synthesis of nanoparticles have come into practice and the 'polymer mediated growth' technique is among them. In this route, ions of one of the reactants are allowed to diffuse from an external solution into a polymer matrix where the other reactant is complexed and bound. The exact role of ionic diffusion in the formation of nanoparticles was investigated in the current study by studying the patterns of kinetics of nanoparticle formation using UV vis spectroscopy. Typically, calcium carbonate nanoparticles were formed by the aforementioned technique using polyethylene glycol solution. The particle size was calculated using Scherrer's formula on x-ray diffraction plots and was reconfirmed with field emission scanning electron microscope and transmission electron microscope images. Energy-dispersive x-ray analysis was used to study the composition and purity of the nanoparticles formed. The reactant to polymer ratio, reaction temperature and molecular weight of polyethylene glycol affected the size of the particles formed. Through this knowledge we optimized these parameters to obtain particles as small as 20 nm and confirmed that this technique can be used to control the size of nanoparticles.

Self-organization of a new fluorous porphyrin and C60 films on indium-tin-oxide electrode

The highly fluorinated alkyl moieties of a new porphyrin drive the self-organization of thin films with C(60) on ITO electrodes.

Ultrasensitive label-free DNA analysis using an electronic chip based on carbon nanotube nanoelectrode arrays

We report the detection of DNA PCR amplicons using an ultrasensitive label-free electronic technique based on multiwalled carbon nanotube (MWNT) nanoelectrode arrays embedded in an SiO(2) matrix. Specific PCR amplicons are reliably detected using electrochemical (EC) methods through allele-specific oligonucleotide hybridization. The inherent guanine bases in the DNA amplicon target of [Formula: see text] bases serve as signal moieties with the aid of Ru(bpy)(3)(2+) mediators, providing an amplified anodic current associated with the oxidation of guanine groups at the nanoelectrode surface. The reduced size and density of the nanoelectrode array provided by MWNTs dramatically improves the sensitivity of EC detection. In addition, the abundant guanine bases in target DNA produce a large signal. Less than [Formula: see text] target amplicons can be detected on a microspot, approaching the sensitivity limit of conventional laser-based fluorescence techniques. This method also eliminates the labelling requirement and makes the measurements much simpler. This platform can be employed for developing highly automated electronic chips with multiplex nanoelectrode arrays for quick DNA analysis.

Topography and transport properties of oligo(phenylene ethynylene) molecular wires studied by scanning tunneling microscopy

Conjugated phenylene(ethynylene) molecular wires are of interest as potential candidates for molecular electronic devices. Scanning tunneling microscopic study of the topography and current-voltage (I-V) characteristics of self-assembled monolayers of two types of molecular wires are presented here. The study shows that the topography and I-Vs, for small scan voltages, of the two wires are quite similar and that the electronic and structural changes introduced by the substitution of an electronegative N atom in the central phenyl ring of these wires does not significantly alter the self-assembly or the transport properties.