Electrodes MWCNT-modified

Zhang L, Tian DB, Zhu JJ (2008) Third generation biosensor based on myoglobin-TiOV MWCNTs modified glassy carbon electrode. Chin Chem Lett 19 965-968... 

In another protocol [42], the MWCNTs-modified electrode was prepared by using MWCNTs (obtained by CVD) previously treated by refluxing in... 

Other methodology proposed the preparation of MWCNTs-modified electrode by casting a gold surface previously cycled between 0.0 and 1.5 V in 0.5 M sulfuric acid with 5 pL of a black suspension of CNTs prepared by dispersing the oxidized MWCNTs in double distilled water (0.5 mg/mL) [42]. The electrode was then dried imder vacuum at about 50 °C. 

Figure 18. (A) Cyclic voltammograms for MWCNTs-modified gold electrode treated with 2 mg/mL dsDNA with EDC/NFIS activation at different times in the presence of 10 mM K4Fc(CN)6 and 10 mM KjFeCCFOe contaimng 0.1 MNaCl. (a) 0 h (b) 0.8 h (c) 1.8 h (d) 2.8 h (e) 4.8 h. (B) Changes of the anodic peak current of Fe(CN)6 / Fe(CN)6 " redox couple at MWCNTs-modified electrode immobilized with dsDNA ( ) and ssDNA ( ) for different time intervals. From reference 42.

Figure 19. Nyquist plots (Zim vs. Zre) for different electrodes in 10 mM K4Fe(CN)6 +10 mM K3Fe(CN)6 + 0.1 M NaCl aqueous solutions, (a) MWCNTs-modified gold electrode (b,c) MWCNTs-modified gold electrode treated with 2 mg/mL dsDNA with and without EDC/NHS activation, respectively (d,e) MWNTs-modified gold electrode treated with 2 mg/mL ssDNA with and without EDC/NHS activation, respectively. From reference 42.

The electrode preparation, the enzyme immobilization procedure was described as follows. About two mg of acid treated MWCNTs was ultrasonicated in 1 pL of N, N dimethylformamide (DMF) until a black suspension was obtained. About 15 pi of this MWCNTs suspension was casted on the working area of SPE surface and dried in an oven at 80 °C for 30 min. About 10 pi of AChE solution (0.132 U) was dropped on the MWCNTs modified electrode surface and dried at room temperature under a current of air and used. Hydrodynamic voltammetric studies results shows that significant response was observed at MWCNT-SPE towards 2mM thiocholine, whereas the response was poor at the unmodified electrode (Fig. 2). The linear response of the MWCNT-SPE modified sensor was found to be between 5 pM - 430 pM (r2 = 0.999) with a sensitivity of 6.018 mA/M. In contrast, the response of AChE/SPE modified electrode was only 5 % and thus this result further reveals the contribution of MWCNTs in improving the sensitivity. 

Figure 7.3 Label-free voltammetry of 10 nM IgE on a multiwalled carbon nanotube (MWCNT)-modified screen-printed carbon electrode (solid line) and on a bare screen-printed carbon electrode (dashed line). Experimental conditions for differential pulse voltammetry were as described in Figure 7.2. MWCNTs (1 mg) were dispersed with the aid of ultrasonic agitation in 10 mL of N, Ai-dimethylformamide to give a 0.1-mg mL black solution. MWCNT film was prepared by pipetting a 2- xL drop of MWCNT solution onto the carbon working electrode of the screen-printed electrode and then evaporating the solvent at room temperature.

N. Zhu et al [32] reported in 2005 the use of Pt-NPs combined with nafion-solubilized MWCNTs as electrode-surface modifiers for fabricating sensitivity-enhanced electrochemical DNA biosensor. The hybridization events were monitored by DPV measurements of the intercalated daunomycin (Fig. 5.5). Due to the ability of MWCNTs to promote electron-transfer reactions and the high... 

Electrochemical AC impedance measurements provided another label-free approach to DNA hybridization detection on a DNA probe-doped polypyrrole film on MWCNT-modified electrodes... 

A non-enzymatic H2O2 sensor based on Prussian Blue (PB], also known as an artificial peroxidase, was accomplished by step-by-step electrodeposition of polyaniline on a glassy carbon electrode (GCE] modified with MWCNTs followed by potentiostatic deposition of PB [42]. By using PB instead of peroxidase, the linear calibration range could be improved and interference due to oxygen prevented. A non-enzymatic H2O2 sensor based on PANI-SWCNT electropolymerized in the ionic liquid (IL]... 

Amperometric detection of bisphenol A (BPA), which is used in the production of epoxy resins and polycarbonate plastics, was done with the pencil graphite electrode (PGE) modified with PANI nanorods and MWCNTs [50]. The BPA determination was comparable with the gas chromatographic method coupled with mass spectroscopy, but PANI-c-MWCNT-chitosan-PGE sensor had shorter analysis time and cheaper anal)ftical costs. Another... 

Another amperometric DA sensor based on PPyox-MWCNT composite was developed by T i et al. [73]. In this work, the deposition of PPyox-MWCNT film on gold substrate was carried out potentiostatically in a solution containing p3rrrole and functionalized MWCNTs dispersed in water. The overoxidation of the PPy in the composite was carried out in a NaOH solution using CV. The PPyox-MWCNT modified electrode shows good sensitivity, selectivity and stability with a LOD of 1.7 nM. 

Afkhami et al. [162] used a graphite paste electrode containing MWCNT modified by the electrodeposition of gold NPs from a HAuCl solution to successfully determine cefixime, methadone [163], and nitrite [164] in a pharmaceutical form, in urine and saliva in several food stuffs and water samples, respectively. Fe203... 

Ma Q, Ai S, Yin H, Chen Q, Tang T. Towards the conception of an amperometric senso- of L-tyrosine based on Hemin/PAMAM/MWCNT modified glassy carbon electrode. Electro-chim Acta 2010 55 6687-94. 

Kerman et al, 2004 also described the label-free electrochemical detection of DNA based on the direct attachment of adenine probes to the sidewall and end of functionalized MWCNTs. The MWCNTs were attached onto the carbon paste electrode surface modified with thymine probes by hybridization between adenine and thymine. The combination of sidewall and end functionalization of MWNT showed enhancement of the guanine oxidation signal in the direct measurement compared to the ones from only end-modified MWCNT. 

Using a glass carbon electrode (GCE) modified with MWCNTs, Cai et al. ° observed an enhanced sensitivity for electrochemical DNA biosensor based on CNTs. Figure 6.22 schematically shows the steps for constructing the nanotube-DNA biosensor. To start, carboxylic acid functionalized MWCNTs (COOH-MWCNTs) were dropped on a GCE electrode, single-strand DNA oligonucleotides (ss-DNAs) were then covalently bonded onto the COOH-MWCNTs via amide formation. The hybridization reaction on the electrode was monitored by differential pulse voltammetry (DPV) using an electroactive daunomycin intercalator as the indicator. 

In a somewhat related but separate study, Guo et al. used electrochemical impedance spectroscopy to investigate the process of the electrostatic assembly of calf thymus DNA on MWCNTs-modified gold electrodes in the presence of a cationic polyelectrolyte PDDA (polydiallyldimethylammo-nium chloride). The gold electrode modified with carboxylic acid functionalized MWCNTs was... 

The impedance spectra for the MWCNT-modified microelectrode after adsorption of different layer numbers of PDDA/DNA are given in Figure 6.24B, which shows an increase in the semicircle diameter with increasing layer number for the adsorbed multilayer film. The linear relationship between and the cycle number shown in Figure 6.24C suggests the formation of a uniform PDDA/DNA multilayer film on the MWCNT-modified gold electrode. 

It has been shown [M.C. Henstridge et al, Sensor. Actuat. B 145 (2010) 417] that the effect of a porous thin layer on cyclic voltammetry can be easily confused with electrocatalytic behaviour, since both effects cause a shift of peak potential to lower overpotentials. Such a thin layer may exist in, for instance, a multi-walled carbon nanotube (MWCNT)-modified electrode where the MWCNTs form a dense mesh across the substrate, a system which is also often associated with electrocatalysis. 

Hu et al. reported an electrochemical sensor based on self-assembly MWCNTs-clindamycin molecularly imprinted sol-gel with a linear response ranging from 5.0 X 10 to 8.0 X 10 M, and the LOD of 2.44 X 10" M, and its application to the determination of clindamycin in human urine [422]. In another work, Zhang et al. have recently reported an assembly of molecularly imprinted sol-gel on an MWCNT modified gold electrode for the selective recognition of the same. The sensor showed a linear reponse towads the concentration of the analyte in almost the same range as the previous work (i.e., 5.0 X 10" M to 8.0 X 10" M), and the same limit of detection (i.e., 2.44 x 10 M) [393]. 

The working electrode was modified by pipetting a controlled amount of BiFePc/MWCNT and Nafion ink onto the electrode surface, resulting in a formation of a thin layer comprising of Nafion bonded catalyst (BiFePc/MWCNT/Nafion ). The pipetted solution is then prepared by ultrasoni-cally mixing the BiFePc/MWCNT in a Nafion ionomer solution. 

The BiFePc and BiFePc/MWCNT modified electrode were then used to detect oxygen in 0.5 mol dm H2SO4 solution in the presence and absence of 0.5 methanol. Figure 31 shows cyclic voltammograms results for BiFePc (Fig. 31a) and BiFePc/MWCNT (Fig. 31b) modified electrodes. 

CVs (Fig. 31) in O2 saturated solution (in the presence and absence of methanol) a large O2 reductive peak at 0.66 V was observed for BiFePc/MWCNT electrodes. The BiFePc/MWCNT modified electrodes was found to show resistance to methanol oxidation, which is a desirable property for a cathode catalyst in direct methanol fuel cells (DMFCs) technology. The above show that combination of BiFePc and MWCNT have excellent synergistic elfect. 

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