Ronan Baron

Concatenated logic gates using four coupled biocatalysts operating in series

The assembly of three concatenated enzyme-based logic gates consisting of OR, AND, XOR is described. Four biocatalysts, acetylcholine esterase, choline oxidase, microperoxidase-11, and the NAD+-dependent glucose dehydrogenase, are used to assemble the gates. Four inputs that include acetylcholine, butyrylcholine, O2, and glucose are used to drive the concatenated-gates system. The cofactor NAD+, and its reduced 1,4-dihydro form, NADH, are used as a reporter couple, and these provide an optical output for the gates. The modulus of the absorbance changes of NADH is used as a readout signal.

Biomolecule–nanoparticle hybrids as functional units for nanobiotechnology

Biomolecule-metal or semiconductor nanoparticle (NP) hybrid systems combine the recognition and catalytic properties of biomolecules with the unique electronic and optical properties of NPs. This enables the application of the hybrid systems in developing new electronic and optical biosensors, to synthesize nanowires and nanocircuits, and to fabricate new devices. Metal NPs are employed as nano-connectors that activate redox enzymes, and they act as electrical or optical labels for biorecognition events. Similarly, semiconductor NPs act as optical probes for biorecognition processes. Double-stranded DNA or protein chains that are modified with metallic nanoclusters act as templates for the synthesis of metallic nanowires. The nanowires are used as building blocks to assemble nano-devices such as a transistor or a nanotransporter.

Two coupled enzymes perform in parallel the ‘AND’ and ‘InhibAND’ logic gate operations

The coupled activation of two enzymes: glucose dehydrogenase (GDH) and horseradish peroxidase (HRP), is used to construct the parallel-operating AND and InhibAND logic gates. The added substrates for the respective enzymes, glucose and H(2)O(2), act as the gate inputs, while the biocatalytically generated NADH and gluconic acid provide the output signals that follow the operations of the gates. The two gates are generated in the same vial, thus allowing the logic operations to take place in parallel, and the simultaneous readout of the functions of the gates.

Investigating the reactive sites and the anomalously large changes in surface pKa values of chemically modified carbon nanotubes of different morphologies

“Bamboo-like” multiwalled (b-MWCNT), “hollow-tube” multiwalled (h-MWCNT) and single-walled carbon nanotubes (SWCNT), chemically modified with 1-anthraquinonyl (AQ) or 4-nitrophenyl (NP) groups, are characterized using voltammetric, electron microscopic and Raman spectroscopic techniques. The pKa values of the AQ-modified CNTs are found to be shifted by greater than three units when compared to the pKa values of anthrahydroquinone (AHQ, the reduced form of AQ) in aqueous solution to beyond pH 14. These large changes in the surface pKa values of the modified CNTs are explored further by comparing the pKa values of CNTs modified with an anthraquinonyl-2-carboxylic acid group. These groups are attached to the CNT surface via the formation of an amide bond with an aminophenyl “spacer” unit derived from the chemical reduction of NP modified CNTs. The location of reactive sites on the CNT surface is investigated and their influence on the pKa of the modified materials is discussed. Comparison with modified pyrolytic graphite electrodes exposing pure edge-plane or pure basal-plane crystal faces indicates that the modifying aryl groups are predominantly located on edge-plane like defects at the tube ends of MWCNTs. The effect of polymer formation on electron transfer kinetics of b-MWCNTs and h-MWCNTs is also discussed. In contrast SWCNTs show both significant side-wall functionalisation and fast electron transfer kinetics which is attributed to their different electronic structure.

Electrochemical detection of arsenic on a gold nanoparticle array

The detection of As(III) was investigated on a gold nanoparticle array. At the first stage, gold nanoparticles were synthesized on glassy carbon microspheres. The resulting hybrid material was characterized by SEM and the sizes of the nanoparticles were found to be in the range 20–200 nm. At the second stage, glassy carbon microspheres decorated with Au nanoparticles were abrasively attached to the surface of a basal-plane pyrolytic electrode. The resulting gold nanoarray was characterized by the reduction of surface gold oxides. Furthermore, it was found to have good characteristics for the sensing of arsenic via anodic stripping voltammetry with a limit of detection of 0.8 μM and a sensitivity of 0.91 C M−1.

Magnetically moveable bimetallic (nickel/silver) nanoparticle/carbon nanotube composites for methanol oxidation

Multi-walled carbon nanotubes (CNTs) functionalized both by nickel and silver nanoparticles were obtained using a single step chemical deposition method in an ultrasonic bath. The new composite material was characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) and cyclic voltammetry (CV). The electroactivity of the bi-functionalized CNTs multi-walled carbon nanotubes was assessed in respect to the electrooxidation of methanol. It was found that the carbon nanotube supported silver nanoparticles have significantly higher catalytic properties than the bulk metal of the same surface area. Furthermore, it was shown that the presence of only a very small proportion of magnetic nickel nanoparticles (1.5% of the total number of metallic nanoparticles) allows the bi-functionalized carbon nanotubes to be moved magnetically in solution, making them easily recoverable after use whilst keeping an optimal electrocatalytic surface area.

The expansion/contraction of gold microparticles during voltammetrically induced amalgamation leads to mechanical instability

The mechanical stability of gold microparticles during anodic stripping voltammetric (ASV) detection over a large range of mercury concentrations was investigated. Mercury was detected at gold microparticles chemically deposited onto glassy carbon microspheres using ASV. Oxidation was observed at 0.5 and 0.8 V vs. SCE. Which peak was observed was dependent on the concentration of mercury and the deposition potential. The formation of the amalgam was of interest. As mercury was deposited for longer time intervals, scanning electron microscopy (SEM) analysis showed the microparticles increasing in size from 0.76 ± 0.03 μm (initial) to 1.51 ± 0.14 μm (Hg2+ deposited for 1980 s at 0.35 V) in diameter. In order to ascertain if multiple expansion and contraction cycles damaged the gold microparticles, cyclic voltammetry was used to monitor the amount of gold on the electrode as mercury was deposited and stripped repeatedly. It was seen that the area under the cathodic gold peak decreased with repetitive scans. SEM analysis revealed that the mechanical stress of repetitive deposition and stripping cycles of mercury caused the gold microparticles to fracture, appearing as irregular cuboid crystals rather than as the orderly polycrystallite formations seen initially. Energy dispersive X-ray (EDX) analysis indicated that the composition of the microparticles changed over the course of repetitive deposition and stripping cycles from gold to an Au–Hg amalgam, which may not be in electrical contact with the carbon support.