Radim Hrdý

Atmospheric pressure barrier discharge at high temperature: Diagnostics and carbon nanotubes deposition

Atmospheric pressure dielectric barrier discharge (DBD) in Ar/H2 gas feed with C2H2 or CH4 admixture was studied at room and high temperature of 680 °C by plasma diagnostics (electrical measurements, fast camera imaging, and optical emission spectroscopy). It was shown that filamentary DBD in pure Ar or Ar/H2 can be converted into homogeneous discharge by an acetylene admixture. Fast intensified charge-coupled device (ICCD) camera proved that this homogeneous discharge is an atmospheric pressure glow discharge (APGD) at room temperature whereas at high temperature the discharge mode switches at every half-period between APGD and atmospheric pressure Townsend discharge. The high temperature discharges (610–710 °C) in Ar/H2/C2H2 and Ar/H2/CH4 were also investigated with respect to a surface bound deposition of carbon nanotubes using 5 nm thick iron layer as a catalyst. CNTs were deposited without any dedicated catalyst pretreatment phase. The quality of CNTs, namely, their density, vertical alignment, and w...

Portable Lock-in Amplifier-Based Electrochemical Method to Measure an Array of 64 Sensors for Point-of-Care Applications

We present a portable lock-in amplifier-based electrochemical sensing system. The basic unit (cluster) consists of four electrochemical cells (EC), each containing one pseudoreference electrode (PRE) and one working electrode (WE). All four ECs are simultaneously interrogated, each at different frequencies, with square wave pulses superposed on a sawtooth signal for cyclic voltammetry (CV). Lock-in amplification provides independent read-out of four signals, with excellent noise suppression. We expanded a single cluster system into an array of 16 clusters by using electronic switches. The chip with an array of ECs was fabricated using planar technology with a gap between a WE and a PRE of ≈2 μm, which results in partial microelectrode-type behavior. The basic electrode characterization was performed with the model case using a ferricyanide-ferrocyanide redox couple (Fe2+/Fe3+) reaction, performing CV and differential pulse voltammetry (DPV). We then used this system to perform cyclic lock-in voltammetry (CLV) to measure concurrently responses of the four ECs. We repeated this method with all 64 ECs on the chip. The standard deviation of a peak oxidation and reduction current in a single channel consisting of 13 ECs was ≈7.46% and ≈5.6%, respectively. The four-EC configuration in each measured spot allows determination of nonperforming ECs and, thus, to eliminate potential false results. This system is built in a portable palm-size format suitable for point-of-care applications. It can perform either individual or multiple measurements of active compounds, such as biomarkers.

Nanostructured Surface Effect of Electrode on Doxorubicin Determination

In this study, we compared two types of nanostructured electrodes with gold nanocolumns and flat gold electrodes by measurements with doxorubicin. Nanostructured electrodes were fabricated by electrochemical anodic oxidation followed by deposition of gold to the porous alumina. Flat gold electrodes were fabricated by physical evaporation of gold layer to the silicon substrate. All electrodes were characterized by electrochemical impedance spectroscopy and then the electrochemical determination of doxorubicin was studied by differential pulse voltammetry. The impedance spectroscopy measurements proved a bigger electroactive area for nanostructured electrodes. The gold nanocolumns have been found as an important factor in increasing of electrodes active area. This fact is very important for sensors sensitivity. Fabricated electrodes were successfully used for determination of doxorubicin.

Gold Nanostructured Surface for Electrochemical Sensing and Biosensing: Does Shape Matter?

ABSTRACT The construction of an electrochemical sensor based on a gold working electrode modified with gold nanostructures was achieved by galvanic deposition into an anodic alumina nanoporous template. Two approaches were investigated to fabricate the nanostructures of various sizes and shapes. First, gold deposition was performed through a thin alumina template resulting in the production of nanorods. In the second approach, alumina pores were widened to form cup-shaped nanostructures. The detailed topography of the nanostructured surfaces was characterized by scanning electron microscopy. The lengths and the diameters of the nanostructures were anticipated to have a significant influence on the surface area and thus on the capacity to promote electron-transfer reactions. This dependence was investigated by electrochemical impedance spectroscopy and cyclic voltammetry. The functionalization of electrode surface with 11-mercaptoundecanoic acid provided a basis for further bonding with analytes. A modified Randles equivalent circuit model with a constant phase element was used to interpret the impedance spectra. The interfacial properties of the modified electrodes were also evaluated by cyclic voltammetry in the presence of the Fe(CN)63−/4− redox couple as a probe. The results showed that the voltammetric behavior of the probe was influenced by surface modification. The accumulation of 11-mercaptoundecanoic acid on the nanostructured electrode surface did not result in the expected increase in charge-transfer resistance and the decreased capacitance, unlike the cup-shaped nanostructured electrode.

Biosensing Surfaces Based on Quantum Dots Array

The fabrication of self-ordered semiconductor (TiO2) and noble metal (Au) QDs arrays was successfully achieved by advanced nonlithographic template based method, namely using nanoporous alumina template. The emphasis was placed on the successful preparation of QDs arrays with the desired size, homogeneous distribution and optical (especially fluorescence) properties. Titania and gold QDs characterization by SEM, EDX and fluorescence spectroscopy was performed in order to verify their surface topography, chemical composition and emission properties in UV/VIS range of spectra, respectively. The surface biofunctionalization of QDs was realized via simple physical adsorption of glutathione tripeptide, which makes these arrays suitable for potential biosensing application, mainly in optical and electrochemical detection of biomolecules in vitro.

Chemical Separation on Silver Nanorods Surface Monitored by TOF-SIMS

The article introduces a possible chemical separation of a mixture of two compounds on the metal nanorods surface. A silver nanorods surface has been prepared by controlled electrochemical deposition in anodic alumina oxide (AAO) template. Rhodamine 6G and 4-aminothiophenol have been directly applied to the sampling point on a silver nanorods surface in an aliquot mixture. The position of the resolved compounds was analysed by time-of-flight secondary ion mass spectrometry (TOF-SIMS) which measured the fragments and the molecular ions of the two compounds separated on the silver nanorods surface. Rhodamine 6G has been preconcentrated as 1.5 mm radial from the sampling point while 4-aminothiophenol formed a continuous self-assembled monolayer on the silver nanorods surface with a maximum molecular ion intensity at a distance of 0.5 mm from the sampling point. The separation of the single chemical components from the two-component mixture over the examined silver nanostructured films could clearly be shown. A fast separation on the mentioned nanotextured films was observed (within 50 s). This procedure can be easily integrated into the micro/nanofluidic systems or chips and different detection systems can be applied.