Interdigital microelectrodes coated

Figure 6. Generation/collection experiments for different fixed collector potentials in an interdigitated array of microelectrodes coated with poly(I) in CH3CN/O.I 14 [n-Bu4N]PF6. The potential of the collector electrodes is held at 0.0 V, -0.50 V, -0.59 V, -0.62 V, or -0.80 V vs. Ag+/Ag while the potential of the generator electrodes is swept between 0.0 V and -0.9 V vs. Ag+/Ag at 20 mV/s.

Figure 7. Cyclic voltammetry of an interdigitated array of microelectrodes coated with poly(I) in CH3CN/0.I H [n-Bu NlPFg (a) The potential of all eight electrodes is scanned together at 10 mV/s. (b) The potential of electrodes 2,4,6, and 8 is scanned at 10 mV/s while the potential of electrodes 1,3,5, and 7 is held at 0 V vs. Ag+/Ag.

Figure 8. Generation/colleotion experiments as a function of temperature at an interdigitated array of microelectrodes coated with poly(I) at 50 mV/s in CH3CN/O.I H [n-B NIPFg.

Figure 1. Schematic representations and dimensions of interdigital microelectrodes that were coated with phthalocyanines.

Anion detection at microelectrodes has not been studied widely. Amongst the first was the work of de Beer et al. [ 111 ] who manufactured a nitrite sensor with a tip just a few microns in diameter, which could detect nitrite ions down to 1 pM. This proved to be suitable for profiling the concentrations of nitrite anion within biofilms less than 1-mm thick inside water treatment plants. Other workers have found that use of an interdigitated microelectrode array [ 112] allows measurement of iodide via monitoring of its redox peak down to sub-micromole levels, making it a suitable technique for analysing mineral water. Carbon nanotubes coated onto Pt microdiscs have been utilised to make a nitrite sensor [113,114] with detection levels of 0.1 pM. Sulphide has also been detected at nickel microdiscs (50 pm diameter) [115]. 

Heterogeneous immunoassay has also been conducted with the antibody immobilized on beads. For instance, mouse IgG (50-100 ng/mL) was detected by ELISA in a glass chip. First, mouse IgG (antigen) was captured by magnetic beads coated with sheep anti-mouse antibody (1.02 x 107 beads/mL). Then the secondary antibody, which was rat anti-mouse conjugated with alkaline phosphatase (0.7 pg/mL), was delivered. Thereafter the substrate, PAPP, was added. It was enzymatically converted to p-aminophenol (PAP), which was electrochem-ically detected by the on-chip interdigital microelectrodes [1016]. 

Regarding NT-based conductometric gas sensors, one can say that chemiresistors based on MNPs were first demonstrated in 1998 by Wohltjen and Snow (1998). They fabricated a chemiresistor by deposition of a thin film of octanethiol-coated AuNPs (tf 2 mn) onto an interdigitated microelectrode. A rapid decrease in the conductance due to film swelling was observed in the presence of toluene, tetrachloroethylene, 1-propanol, and water vapor with a detection limit of -1 ppm. 

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