Solid State Nanopores for Selective Sensing of DNA - Nanopores: Sensing and Fundamental Biological Interactions - page 108

5.1 Introduction

Solid stare nanopores show great promise for application as biosensors. Though
nanopores can be created by way of a bio-protein channel, solid state nanopores
have the advantage of being easier to mass produce on a wide and inexpensive
scale. Solid state nanopores could be used to rapidly sequence DNA, thus greatly
reducing the time it takes to do so currently and reducing the workload of super-
computers tasked with this. They also have the potential to detect anomalies in a
DNA strand, giving vital forewarning to doctors about a patient's susceptibility
to diseases like cancer.
Methods of fabricating and functionalizing solid state nanopores for various
purposes have already been developed. They can be fabricated on wafers using
photolithography and many special techniques. Though they can then be functio-
nalized with a variety of ways, this chapter discusses functionalization of solid state
nanopores for the purpose of acting as selective DNA sensors through the use
of DNA probe hairpin loops. It has already been shown that this functionalization of
nanopores has the ability to discriminate between perfect complementary and
single-base-mismatch DNA sequences [ 1 ]. This illustrates that there is indeed
the possibility of creating a reliable DNA sensor.
The goal of this chapter is to explore and explain the current techniques
and methods which are currently being or have been used in order to create and
functionalize solid state nanopores for selective sensing of DNA. A synopsis
of fabrication is given at start followed by descriptions of ways to shrink the
nanopores. After this is a discussion of DNA-nanopore molecular dynamics,
which is necessary knowledge in order to understand DNA translocation through
nanopores. Next a review is provided on DNA translocation and what has been
done to functionalize solid state nanopores to accomplish this. The chapter
then closes with an overview of biological applications of the functionalized
nanopores.

5.2 Fabrication Processes

In the last decade or so, researchers have used different processes to fabricate
solid state nanopores (SSNs). In one report, Li et al. at Harvard University made
use of an Ar + ion beam to drill a SSN in Si 3 N 4 membranes [ 2 , 3 ]. They found that
ion interactions with the thin membrane simultaneously involved two physical
processes. One is surface erosion, which results in the opening of the pore. The
other is surface diffusion, which involves matter transportation resulting in
the shrinking of the pore. Both of the processes depend on temperature. Since
then a number of techniques have emerged such as electron beam sculpting [ 4 ],
laser heating [ 5 ], feedback controlled chemical etching [ 6 ], and etching of silicon-
on-insulator (SOI) wafers [ 7 ].