Improving sensitivity of electrochemical sensors with convective transport in free-standing, carbon nanotube structures

Abstract

High-aspect-ratio, porous membrane of vertically-aligned carbon nanotubes (CNTs) were developed through a templated microfabrication approach for electrochemical sensing. Nanostructured platinum (Pt) catalyst was deposited onto the CNTs with a facile, electroless deposition method, resulting in a Pt-nanowire-coated, CNT sensor (PN-CNT). Convective mass transfer enhancement was shown to improve PN-CNT sensor performance in the non-enzymatic, amperometric sensing of hydrogen peroxide (H 2 O 2). In particular, convective enhancement was achieved through the use of high surface area to fluid volume structures and concentration boundary layer confinement in a channel. Stir speed and sensor orientation especially influenced the measured current in stirred environments for sensors with through-channel diameters of 16 µm. Through-flow sensing produced drastically higher signals than stirred sensing with over 90% of the H 2 O 2 being oxidized as it passed through the PN-CNT sensor, even for low concentrations in the range of 50 nM to 500 µM. This effective utilization of the analyte in detection demonstrates the utility of exploiting convection in electrochemical sensing. For through-flow at 100 µL s-1 , a sensitivity of 24,300 µA mM-1 cm-2 was achieved based on the frontal projected area (871 µA mM-1 cm-2 based on the nominal microchannel surface area), with a 0.03 µM limit of detection and a linear sensing range of 0.03-500 µM.

CIP2A immunosensor comprised of vertically-aligned carbon nanotube interdigitated electrodes towards point-of-care oral cancer screening

“…The high-aspect-ratio VANTAs were subsequently grown on the IDE patterned iron layer using a chemical vapor deposition (CVD) method followed by an amorphous carbon infiltration process for structural support according to our previous work (Figure 1d) (Brownlee et al, 2017;Marr et al, 2015). The VANTA IDEs exhibited a height to width ratio of approximately 3 to 1 as the CNT height measured approximately 75 µm.…”

3D Interdigitated Vertically Aligned Carbon Nanotube Electrodes for Electrochemical Impedimetric Biosensing

“…Planar Cr electrical leads underneath Al 2 O 3 can be seen in Figure B as the lighter region on the substrate. VACNTs were grown by chemical vapor deposition (CVD) similar to previously published protocols. , After VACNT growth, amorphous carbon was added to strengthen the VACNTs and create mechanically sturdy, porous microstructures (see Figure B,C). It should be noted that while VACNTs are generally vertically aligned, they are not perfectly straight and often exhibit some waviness (see Figure C) that is possibly due to edge effects caused by the iron catalyst and general strain on the VACNTs during growth and carbon infiltration. , Additional scanning electron microscopy (SEM) images showing magnified views of the VACNTs are found in Figure S1 (Supporting Information).…”

“…VACNTs were grown by chemical vapor deposition (CVD) similar to previously published protocols. [30][31] After VACNT growth, amorphous carbon was added to strengthen the VACNTs and create mechanically sturdy, porous microstructures (see Figure 2B and C). It should be noted that while VACNTs are generally vertically aligned, they are not perfectly straight and often exhibit some waviness (see Figure 2C) that is possibly due to edge effects caused by the iron catalyst and general strain on the VACNTs during growth and carbon infiltration.…”

“…VACNT growth methods were similar to previously published protocols. , VACNTs were grown by chemical vapor deposition (CVD) in a 1 in. diameter Lindberg/Blue M tube furnace with flowing hydrogen (H 2 , 311 sccm) and ethylene (C 2 H 4 , 338 sccm) at 750 °C for 5, 30, or 120 s. The temperature was then increased to 900 °C, and the C 2 H 4 flow rate was decreased to 193 sccm to infiltrate (coat) the VACNTs with amorphous carbon for 60 s. The electrodes were oxygen plasma etched (250 W, 300 mTorr, 30–60 s) until the two electrodes were electrically isolated using a Technics Planar Etch II machine.…”

Electrochemical Glucose Sensors Enhanced by Methyl Viologen and Vertically Aligned Carbon Nanotube Channels

“…Thus, a 20-minute wait time was chosen for all subsequent experiments.3.3. Flow RateFlow rate greatly influences the sensitivity of flow sensors and can provide linearly varying current with flow rate 15. Figure 4 shows the measured current density for 100 µM glucose at different volumetric flow rates (0.5 to 8 mL/min; average velocities: 0.283 to 4.53 mm/s) for each of the glucose sensors (MV, GOx-in-stream, EDC/NHS, and PEDOT; see Figure 2) in the large flow cell.…”