Biomedical Engineering Reference
In-Depth Information
role in offering the possibility of performing reliable diagnosis even before the
appearance of any symptoms of a disease. Small variations in the genome affect
our predisposition to diseases, such as cancer and congenital genetic diseases [
4
,
5
]. In environmental and food areas, the detection of specific DNA sequences can
be used for the monitoring of genetically modified organism (GMO) or pathogenic
bacteria [
6
].
Biosensors refer to self-containing integrated devices, being capable of provid-
ing specific quantitative or semiquantitative analytical information using a biologi-
cal recognition element which is followed by contact with a transduction element.
Major processes involved in a biosensor are specific target recognition event and
signal transduction [
7
]. The first successfully developed DNA biosensor achieved
rapid screening of toxic substances. The biosensor was constructed by immobiliz-
ing a double helix DNA (Calf Thymus DNA) onto screen-printed electrodes and
then used for the determination of the toxicity of different kinds of common sur-
factants based on the height of the guanine oxidation peak. The interactions with
toxic substances raise structural and conformational modifications of DNA caus-
ing decrease in guanine peak [
8
]. Except such kind of direct oxidation of guanine,
the DNA probe must be thus chemically or enzymatically labeled with radioac-
tive material, chemiluminophore, fluorophore, electrochemical, or photoelectro-
chemical materials to generate signal because the nucleic acid itself are not able
to provide any signal. Quantum dots (QDs) emerge as excellent fluorescent nano-
materials possessing great potentials in DNA biosensor fabrication. Up to now,
different types of DNA biosensors based on amperometric [
9
,
10
], potentiometric
[
11
,
12
], piezoelectric [
13
,
14
], thermal [
15
,
16
], and optical techniques [
17
,
18
]
have been developed. In this topic, we will focus on those DNA biosensors fabri-
cated by taking advantages of properties of QDs (optical, electrochemical lumines-
cence, electrochemical, and photoelectrochemical). Firstly, we overview different
types of QDs. Preparation methods and functionalization of QDs were presented
in
Chap. 2
. This provides a basis for the fabrication of QD-based DNA biosensors.
Then, based on the properties of QDs (optical, electrochemiluminescence, elec-
trochemical, and photoelectrochemical), we numerate these QD-based DNA and
1.2 Overview of Quantum Dots
Quantum dots (QDs or Qdots) are colloidal semiconductor nanocrystals and have
been developed for more than 30 years. Since discovered in glass crystals by
Russian physicist Alexei Ekimov in 1980 [
19
], QDs have attracted great interests
from researchers, demonstrated by the large number of scientific publications in
this area (Fig.
1.1
). QDs' excellent fluorescent, electrochemical, and photoelectro-
chemical properties have been widely applied in various research areas, ranging
from in vitro biosensing to intracellular and in vivo imaging.
