Functionalized Single‐Walled Carbon Nanotubes Modified Microsensors for the Selective Response of Epinephrine in Presence of Ascorbic Acid

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Abstract
Modified stainless steel microelectrodes (microwire diameter: 300 μm) were assembled using functionalized single‐walled carbon nanotubes (SWCNTs) deposited by the EPD method (electrophoretical deposition process). The functionalized SWCNTs, which covered the microelectrode surfaces, showed an improved sensitivity and selectivity toward the electrochemical detection of epinephrine. These chemical sensors hampered the voltammetric responses of ascorbic acid (AA) and uric acid (UA), while the electrochemical oxidation of epinephrine was significantly enhanced. Using the differential pulse voltammetry (DPV) technique, epinephrine showed a very well resolved peak centered around 240 mV, while 1 mM of AA (present in the same solution) was not detected. The corresponding permeability and permselectivity parameters were also evaluated for ascorbic acid and uric acid. To investigate the sensor selectivity, a comparative study performed using microsensors assembled with non functionalized carbon nanotubes, deposited on the microelectrode surfaces by a chemical vapor deposition (CVD) technique, was also carried out. This study was useful to highlight that the presence, or the absence of electrostatic barriers on SWCNT's walls (due to the presence of some chemical functional groups), can be able to control the electrochemical response of these sensors. This optimization resulted in microsensors with a good linear range (2–100 μM) epinephrine; a good sensitivity (28.1 A M−1 cm−2) and interelectrodes reproducibility (RSD%=7.0, n=6), a detection of limit (LOD=3σ) of 2 μM; a response time of 6 s; a significant operational stability (of 13 hours in continuous working conditions) and long term stability (1 month).

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