UC Irvine

This thesis describes research conducted on the physics and applications of micro- and

nanoscale ion-conducting channels. Making use of the nanoscale physics that takes place

in the vicinity of charged surfaces, there is the possibility that nanopores, holes on the order

of 1 nm in size, could be used to make complex integrated ionic circuits. For inspiration on

what such circuits could achieve we only need to look to biology systems, immensely com-

plex machines that at their most basic level require precise control of ions and intercellular

electric potentials to function. In order to contribute to the ever expanding field of nanopore

research, we engineered novel hybrid insulator-conductor nanopores that behave analagously

to ionic diodes, which allow passage of current flow in one direction but severely limit the

current in the opposite direction. The experiments revealed that surface polarization of the

conducting material can induce the formation of an electrical double layer in the same way

static surface charges can. Furthermore, we showed that the hybrid device behaved similar to

an ionic diode, and could see potential use as a standard rectifying element in ionic circuits.

Another application based on ion conducting channels is resistive pulse sensing, a single par-

ticle detection and characterization method. We present three main experiments that expand

the capacity of resistive pulse sensing for particle characterization. First, we demonstrate

how resistive pulse sensing in pores with longitudinal irregularities can be used to measure

the lengths of individual nanoparticles. Then, we describe an entirely new hybrid approach

to resistive pulse sensing, whereby the electrical measurements are combined with simulta-

neous optical imaging. The hybrid method allows for validation of the resistive pulse signals

and will greatly contribute to their interpretability. We present experiments that explore

some of the possibilities of the hybrid method. Then, building off the hybrid method we

present experiments performed to measure single particle deformability with resistive pulse

sensing. Using a novel microfluidic channel design, we were able to reproducibily induce

bidirectional deformation of cells. We describe how these deformations could be detected

with the resistive pulse signal alone, paving the way for resistive pulse sensing based cell

deformability cytometers.