DISSERTATION

______________________________________________________________________ Introduction
beacon are complementary and form a loop through self-hybridization. Coupling of a
fluorophore and a quencher on opposite ends of a beacon results in quenching of fluorescence
when the beacon is closed and a fluorescence signal when the beacon is opened due to
hybridization with a target DNA. Another optical technique commonly used for DNA detection
is surface plasmon resonance, based on the change in the refractive index of a thin metal
substrate modified with a biorecognition interface upon hybridization. Nevertheless, the
required equipment for optical detection is sophisticated and relatively expensive and therefore
not suitable for clinical purposes and point-of-care diagnostics but rather for laboratory
applications. Furthermore, inconsistent yields of target synthesis and labelling as well as nonuniform
rates of photobleaching can result in insufficient readout accuracy required for patient
diagnosis 54 .
Figure 1.13. Optical DNA detection using molecular beacons.
Piezoelectric DNA sensors rely on the mass change upon hybridization with a target DNA that
is correlated with an increase in the fundamental resonance frequency of a crystal 55 . Quartz
crystal microbalance is the most commonly used technique for the real-time monitoring of the
hybridization process 56 . Different strategies to increase the mass change upon hybridization
were used in order to increase the sensitivity, usually by using bulky labels 57,58 .
Point-of-care diagnostics requires fast response, high sensitivity and selectivity, and operation
simplicity. These, coupled with portability, low cost and possibility of miniaturization, are
characteristics of electrochemical DNA sensors, which makes them very attractive for mass
production. Unlike bulky optical readout systems, electrochemical detection can be integrated
1.4 Hybridization detection 22