Biomedical Engineering Reference
In-Depth Information
sandwiched by reporter and capture probes, which brings the QD donor and fluo-
rophore or quencher acceptor close proximity causing the FRET phenomenon. The
detection of decreased fluorescence emission of QDs or increased fluorescence
emission intensity of acceptor indicates the presence of target DNA, and their quan-
tification can also be realized. A simple example was demonstrated by Asahi. They
developed a sandwich structure for DNA and antigen detection based on self-assem-
bly of multiwalled carbon nanotubes (CNTs) and CdSe quantum dots (QDs) via
oligonucleotide hybridization. QDs and CNTs were conjugated with different DNA
oligos, which were both complementary to the target DNA. In the presence of target
complementary oligonucleotides, QDs and CNTs assembled into nanohybrids via
DNA hybridization bringing a fluorescence response to the target DNA amount and
a 0.2-pM DNA detection limit was achieved [
9
]. Huang et al. described a nucleic
acid sandwich hybridization assay with a QD-induced FRET reporter system, as
shown in Fig.
3.3
. Hemagglutinin H5 sequences (60-mer DNA and 630-nt cDNA
fragment) of avian influenza viruses were chosen as the target. Two oligonucleo-
tides (16 mers and 18 mers) that complement to the two separate, but neighboring
regions of the target sequence were designed as the capturing and reporter probes,
respectively. They were conjugated with QD655 (donor) and Alexa Fluor 660 dye
(acceptor) at first. The sandwich hybridization occurred once the existence of target
Fig. 3.3
Schematic illustration of the sandwich hybridization assay with a QD-induced FRET
reporter system for H5 target DNA detection.
a
Sandwich hybridization with H5 sequence (tar-
get) by the capturing probes conjugated on QD655 (FRET donor) and the reporter probes labeled
with Alexa Fluor 660 (FRET acceptor);
b
FRET emission shift before and after the sandwich
hybridization. Reproduced with permission from Ref. [
10
]. Copyright 2012, MDPI AG
