A novel technique for fabrication of micro- and nanofluidic device with embedded single carbon nanotube

This paper describes a novel technique for fabrication of micro- and nanofluidic device that consists of a carbon nanotube (CNT) and a polydimethylsiloxane (PDMS) microchannel. Single CNT was placed at desired locations using dielectrophoresis (DEP) and PDMS microchannel was constructed on the aligned CNT via photolithography and soft lithography techniques. This technique enables a CNT to be seamlessly embedded in a PDMS microchannel. Moreover, controlling the PDMS curing condition enables the construction of the device with or without a CNT (the device without CNT has a trace nanochannel in PDMS). Preliminary flow tests such as capillary effect and pressure-driven flow were performed with the fabricated devices. In the capillary effect tests, the flow stopped at the nanochannel in both devices. In the pressure-driven flow lower flow resistance was observed in the device with a CNT.     

Selective voltammetric determination of electroactive neuromodulating species in biological samples using iron(II) phthalocyanine modified multi-wall carbon nanotubes paste electrode

Iron(II) phthalocyanine (FePc) modified multi-wall carbon nanotubes paste electrodes (MWCNTPEs) were used as voltammetric sensors to selectively detect dopamine (DA) in the presence of serotonin (5-HT). The electrochemical behavior of DA at the new modified electrode was investigated using CV. The enhanced current response of DA indicates that FePc modification of the MWCNTPE surface results in a high catalytic activity for the redox reaction of DA. Differential pulse voltammetry was applied in detection of DA and 5-HT at FePc-MWCNTPE. The method parameters were optimized. Detection limit of 2.05 × 10⁻⁷ M was obtained for DA by using the electrocatalytic oxidation signal corresponding to the Fe^II/Fe^III redox process. The separation between the peak potentials of DA and 5-HT is 170 mV which is large enough for the simultaneously, selective determination of the two chemical species in their mixtures. There was no electrochemical response for ascorbic acid (AA) added in the sample. The monoamine neurotransmitter measuring method has been tested in analyzing deproteinized serum samples.     

Fabrication of carbon nanotubes/poly(1,2-diaminobenzene) nanoporous composite via multipulse chronoamperometric electropolymerization process and its electrocatalytic property toward oxidation of NADH

A novel method was proposed for fabrication of a carbon nanotubes/poly(1,2-diaminobenzene) nanoporous composite based electrode. The poly(1,2-diaminobenzene) was deposited onto the surface of a glassy carbon electrode (GCE) modified with multi-wall carbon nanotubes (MWNTs) via multipulse chronoamperometric electropolymerization (MCE) process. Compared with the composite prepared by conventional electropolymerization (CE), the electronic and ionic transport capacity of the MCE-based composite were significantly improved due to its unique nanoporous structure. The surface of the composite-modified GCE was characterized with scanning electron microscopy (SEM) and cyclic voltammetry (CV). The nanoporous MCE-based electrode was applied to determination of NADH at a much low potential of 70 mV, and a linear range from 2.0 μM to 4.0 mM was observed with fast response (within 5 s) and a lower detection limit of 0.5 μM (based on S/N = 3). In comparison, a narrow linear range from 5.0 μM to 2.0 mM, slower response (up to 15 s) and a higher detection limit of 3.0 μM (based on S/N = 3) was obtained with the electrode prepared by CE. The wider linear range, lower detection limit and fast response of the MCE-based electrode implies that the new method proposed can provide more excellent platforms for sensitive electrochemical sensing and biosensing.     

Simultaneous determination of N-acetylcysteine and acetaminophen by voltammetric method using N-(3,4-dihydroxyphenethyl)-3,5-dinitrobenzamide modified multiwall carbon nanotubes paste electrode

A new dopamine-derivative, i.e. N-(3,4-dihydroxyphenethyl)-3,5-dinitrobenzamide (N-DHPB), was synthesized and its application was investigated for the simultaneous determination of N-acetylcysteine (NAC) and acetaminophen (AC) using modified multiwall carbon nanotubes paste electrode. This modified electrode exhibited a potent and persistent electron mediating behavior followed by well separated oxidation peaks of NAC and AC. The peaks current of differential pulse voltammograms of NAC and AC increased linearly with their concentration in the ranges of 0.5-200 μmol L⁻¹ NAC and 15.0-270 μmol L⁻¹ AC. The detection limits for NAC and AC were 0.2 μmol L⁻¹ and 10.0 μmol L⁻¹, respectively. The relative standard deviation for seven successive assays of 1.0 and 30.0 μmol L⁻¹ NAC and AC were 1.7% and 2.2%, respectively. The proposed sensor was successfully applied for the determination of NAC in human urine, tablet, and serum samples.     

Composites of carboxylate-capped TiO2 nanoparticles and carbon black as chemiresistive vapor sensors

Titanium (IV) dioxide (TiO₂) nanoparticles (NPs) with a 1-5 nm diameter were synthesized by a sol-gel method, functionalized with carboxylate ligands, and combined with carbon black (CB) to produce chemiresistive chemical vapor sensor films. The TiO₂ acted as an inorganic support phase for the swellable, organic capping groups of the NPs, and the CB imparted electrical conductivity to the film. Such sensor composite films exhibited a reproducible, reversible change in relative differential resistance upon exposure to a series of organic test vapors. The response of such chemiresistive composites was comparable to, but generally somewhat smaller than, that of thiol-capped Au NPs. For a given analyte, the resistance response and signal-to-noise ratio of the capped TiO₂-NP/CB composites varied with the identity of the capping ligand. Hence, an array of TiO₂-NP/CB composites, with each film having a compositionally different carboxylate capping ligand, provided good vapor discrimination and quantification when exposed to a series of organic vapors. Principal components analysis of the relative differential resistance response of the sensor array revealed a clear clustering of the response for each analyte tested. This approach expands the options for composite-based chemiresistive vapor sensing, from use of organic monomeric or polymeric sorbent phases, to use of electrically insulating capped inorganic NPs as the nonconductive phase of chemiresistive composite vapor sensors.     

On the complex formation of CdCl2 with 1-furoylthioureas: Preconcentration and voltammetric behavior of Cd(II) at carbon paste electrodes modified with 3-monosubstituted and 3,3-disubstituted derivatives

Two series of 1-furoylthioureas were used as modifiers of carbon paste electrodes (CPE). The preconcentration of Cd(II) at CPE modified with these 3-monosubstituted and 3,3-disubstituted 1-furoylthioureas and its subsequent voltammetric determination was studied with Cd(II) test solution. The preconcentration of cadmium at the surface of the modified CPE varied with the steric and electronic nature of the present CS neighboring groups. This is in accord with the changes observed in the Raman spectra of the ligands after complexation with CdCl₂, and with the chemical yields of the complexes obtained.     

Nonlinear model identification and adaptive control of CO2 sequestration process in saline aquifers using artificial neural networks

In recent years, storage of carbon dioxide (CO₂) in saline aquifers has gained intensive research interest. The implementation, however, requires further research studies to ensure it is safe and secure operation. The primary objective is to secure the CO₂ which relies on a leak-proof formation. Reservoir pressure is a key aspect for assessment of the cap rock integrity. This work presents a new pressure control methodology based on a nonlinear model predictive control (NMPC) scheme to diminishing risk of carbon dioxide (CO₂) back leakage to the atmosphere due to a fail in the integrity of the formation cap rock. The CO₂ sequestration process in saline aquifers is simulated using ECLIPSE-100 as black oil reservoir simulator while the proposed control scheme is realized in MATLAB software package to prevent over-pressurization. A modified form of growing and pruning radial basis function (MGAP-RBF) neural network model is identified online for prediction of reservoir pressure behaviors. MGAP-RBF is recursively trained via extended Kalman filter (EKF) and unscented Kalman filter (UKF) algorithms. A set of miscellaneous test scenarios has been conducted using an interface program to exchange ECLIPSE and MATLAB in order to demonstrate the capabilities of the proposed methodology in guiding saline aquifer to follow some desired time-dependent pressure profiles during the CO₂ injection process.