Solid-State Nanopore Sensors: Analyte Quantification by Event Frequency Analysis at High Voltages

Solid state nanopores have emerged as an important electrical
label-free
single-molecule detection platform. While much effort has been spent
on analyzing the current trace to determine size, shape and charge
of the translocating species, a less studied aspect is the number
of events and how this relates to analyte concentration. In this work
we systematically investigate how the event frequency depends on voltage
applied across the pore and show that this dependence can be utilized
to determine target concentration. Importantly, this method does not
require any calibration or any additional species added to the solution.
Data analysis algorithms are introduced to accurately count events
also for high voltages (up to 1 V). For double stranded DNA as model
analyte, we find a linear relation between event frequency and voltage
for pores 10 nm or more in diameter. For smaller pores, the majority
of events are dockings rather than translocations and the linear relation
is lost, in agreement with theory. Our model also predicts that the
electrophoretic mobility of the species will influence event frequency,
while diffusivity does not, which we confirm by using two different
sizes of DNA. The analyte concentration determination is found to
be remarkably accurate (10% error) when taking the average of multiple
(∼4) experiments. If based on a single experiment, the predictive
power is lower, but the method still provides a useful estimate (<30%
error). This study should be useful as a guide when performing experiments
at higher voltages and may serve as a method to extract analyte concentration
in bioanalytical applications of nanopore sensors.