Ultrasensitive Detection of Dopamine Using a Carbon Nanotube Network Microfluidic Flow Electrode

Abstract

The electrochemical measurement of dopamine (DA), in phosphate buffer solution (pH 7.4), with a limit of detection (LOD) of ∼5 pM in 50 μL (∼ 250 attomol) is achieved using a band electrode comprised of a sparse network of pristine single-walled carbon nanotubes (SWNTs), which covers <1% of the insulating substrate. The SWNT electrodes are deployed as amperometric (anodic) detectors in microfluidic cells, produced by microstereolithography, designed specifically for flow injection analysis (FIA). The flow cells, have a channel (duct) geometry, with cell height of 25 μm, and are shown to be hydrodynamically well-defined, with laminar Poiseuille flow. In the arrangement where solution continuously flows over the electrode but the electrode is only exposed to the analyte for short periods of time, the SWNT electrodes do not foul and can be used repeatedly for many months. The LOD for dopamine (DA), reported herein, is significantly lower than previous reports using FIA-electrochemical detection. Furthermore, the SWNT electrodes can be used as grown, i.e., they do not require chemical modification or cleanup. The extremely low background signals of the SWNT electrodes, as a consequence of the sparse surface coverage and the low intrinsic capacitance of the SWNTs, means that no signal processing is required to measure the low currents for DA oxidation at trace levels. DA detection in artificial cerebral fluid is also possible with a LOD of ∼50 pM in 50 μL (∼2.5 fmol).

In Situ Optimization of pH for Parts-Per-Billion Electrochemical Detection of Dissolved Hydrogen Sulfide Using Boron Doped Diamond Flow Electrodes

“…This is as expected for this design of flow cell. 28,39 Even though the residence time of electroanalyte in contact with the detector electrode is greatly reduced in FIA and under flow potential fouling products can be washed away downstream, 28 for HS − oxidation, repeat injections at a fixed concentration (25 μM) and V f = 1 cm 3 min −1 showed a decrease in peak current (data not shown), suggesting electrode passivation, most likely with electrodeposited sulfur (vide infra). The mobile phase contained 0.1 M KNO 3 , adjusted to pH 10 through the use of potassium hydroxide.…”

Chemical reactions confined within carbon nanotubes

“…88 In an attempt to replace expensive platinum catalysts for the oxygen reduction reaction in fuel cells, carbon nanotube supports have been investigated as potential catalysts in this extremely useful process. 111 A novel demonstration of electrochemical carbon nanoreactors was reported by McSweeney et al by the encapsulation of methylcyclopentadienyl manganese tricarbonyl, Cp Me Mn(CO) 3 , within narrow SWCNT. However, in this case, the encapsulation of iron nanoparticles 86 and phosphorus 87 dopants alters the electronic properties and the catalytic activity of the carbon nanotube external surface, demonstrating the influence that confined species can have on the host carbon nanotube and highlighting the symbiotic nature of such host-guest interactions.…”

Carbon nanotubes in microfluidic lab-on-a-chip technology: current trends and future perspectives

“…They showed that the ultra-high porosity arrays resulting from this CVD technique gave enhanced particle interception and subsequently allowed microfluidic cell separation (equivalent to cell sorting). In order to fabricate SWCNT electrodes that could be used to detect dopamine in a flow stream, Sansuk et al (2012) successfully formed a two-dimensional sparse network of SWCNTs on an insulating Si/ SiO 2 substrate via a catalyzed CVD technique. It was shown that this detector effectively improved dopamine detection.…”