Electrochemical enzymatic biosensors using carbon nanofiber nanoelectrode arrays
2012
The reduction of electrode size down to nanometers could dramatically enhance detection sensitivity and
temporal resolution. Nanoelectrode arrays (NEAs) are of particular interest for ultrasensitive biosensors. Here
we report the study of two types of biosensors for measuring enzyme activities using NEAs fabricated with
vertically aligned carbon nanofibers (VACNFs). VACNFs of ~100 nm in average diameter and 3-5 μm in
length were grown on conductive substrates as uniform vertical arrays which were then encapsulated in SiO2
matrix leaving only the tips exposed. We demonstrate that such VACNF NEAs can be used in profiling
enzyme activities through monitoring the change in electrochemical signals induced by enzymatic reactions to
the peptides attached to the VACNF tip. The cleavage of the tetrapeptide with a ferrocene tag by a cancerrelated
protease (legumain) was monitored with AC voltammetry. Real-time electrochemical impedance
spectroscopy (REIS) was used for fast label-free detection of two reversible processes, i.e. phosphorylation by
c-Src tyrosine kinase and dephosphorylation by protein tyrosine phosphatase 1B (PTP1B). The REIS data of
phosphorylation were slow and unreliable, but those of dephosphorylation showed large and fast exponential
decay due to much higher activity of phosphatase PTP1B. The kinetic data were analyzed with a
heterogeneous Michaelis-Menten model to derive the “specificity constant” k cat /K m , which is 8.2x10 3 M -1 s -1
for legumain and (2.1 ± 0.1) x 10 7 M -1 s -1 for phosphatase (PTP1B), well consistent with literature. It is
promising to develop VACNF NEA based electrochemical enzymatic biosensors as portable multiplex
electronic techniques for rapid cancer diagnosis and treatment monitoring.
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