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submitted on 02.10.2019, 13:56 and posted on 03.10.2019, 21:07by Mark D. Holtan, Subramaniam Somasundaram, Niamat Khuda, Christopher Easley
One of the key factors limiting sensitivity in many
electrochemical assays is the non-faradaic or capacitive current. This is particularly true in modern assay
systems based on DNA monolayers at gold electrode surfaces, which have shown
great promise for bioanalysis in complex milieu such as whole blood or serum. While various changes in analytical parameters,
redox reporter molecules, DNA structures, probe coverage, and electrode surface
area have been shown useful, background reduction by hardware subtraction has
not yet been explored for these assays.
Here, we introduce new electrochemistry hardware that considerably
suppresses non-faradaic currents through real-time analog subtraction during
current-to-voltage conversion in the potentiostat. This differential potentiostat (DiffStat)
configuration is shown to suppress or remove capacitance currents in
chronoamperometry, cyclic voltammetry, and square-wave voltammetry measurements
applied to nucleic acid hybridization assays at the electrode surface. The DiffStat makes larger electrodes and higher
sensitivity settings accessible to the user, providing order-of-magnitude
improvements in sensitivity, and it also significantly simplifies data
processing to extract faradaic currents in square-wave voltammetry (SWV). Since two working electrodes are used for
differential measurements, unique arrangements are introduced such as
converting signal-OFF assays to signal-ON assays, or background drift
correction in 50 % human serum. Overall,
this new potentiostat design should be helpful not only in improving the
sensitivity of most electrochemical assays, but it should also better support adaptation
of assays to the point-of-care by circumventing complex data processing.