A polymer microspheres carried DNA probe, which was based on resonance energy transfer, was presented in this paper
when CdTe quantum dots(QDs) were as energy donors, Au nanoparticles were as energy accepters and poly(4-
vinylpyrindine-co-ethylene glycol dimethacrylate) microspheres were as carriers. Polymer microspheres with functional
group on surfaces were prepared by distillation-precipitation polymerization when ethylene glycol dimethacrylate was as
crosslinker in acetonitrile. CdTe QDs were prepared when 3-mercaptopropionic acid(MPA) was as the stabilizer in
aqueous solution. Because of the hydrogen-bonding between the carboxyl groups of MPA on QDs and the pyrindine
groups on the microspheres, the QDs were self-assembled onto the surfaces of microspheres. Then, the other parts of
DNA probe were finished according to the classic method. The DNA detection results indicated that this novel
fluorescent DNA probe system could recognize the existence of complementary target DNA or not.
CdTe/CdS core-shell quantum dots (QDs) with 12 nm in diameters were synthesized in water, and Au nanoparticles
(AuNPs) with 25nm in diameters were prepared by reduction of sodium citrate. Compared with the fluorescent of CdTe
core QDs, the fluorescent of CdTe/CdS core-shell QDs was increased about one times, which suggested the advantage of
CdTe/CdS core-shell QDs in fluorescence application. It was confirmed that the fluorescence emission spectrum of
CdTe/CdS QDs and the UV-Vis absorption spectrum of AuNPs had an obvious overlap, which indicated that a novel
DNA probe based on fluorescence resonance energy transfer (FRET) from CdTe/CdS QDs donors to AuNPs acceptors
could be designed. 3'-SH-DNA were assembled onto the surface of AuNPs by Au-S bond (Au-DNA), and CdTe/CdS
QDs were linked to 5'-NH2-DNA (partly complementary with 3'-SH-DNA) by Schiff's reaction (CdTe/CdS-DNA).
Then, the distance between donors and acceptors of DNA probe was controlled within 1-10 nm by hybridization of
CdTe/CdS-DNA and Au-DNA, which resulted in a FRET from CdTe/CdS QDs to AuNPs according to Forster theory, so
the fluorescent of probe was extremely decreased compared with CdTe/CdS-DNA. The detection ability of this novel
probe was investigated by fluorescence emission spectrum when target DNA (completely complementary with
3'-SH-DNA) existed.
KEYWORDS: Quantum dots, Luminescence, Nanocrystals, System on a chip, Americium, Fluorescence resonance energy transfer, Quantum efficiency, Biosensing, Nanoparticles, Tellurium
Concerns on quantum dots (QDs) have been continuously increasing because of their advantages on photophysical
properties. Water soluble CdTe/CdS core-shell and CdTe/CdS/ZnS multi-layer QDs were synthysized with
mercaptopropanoic acid (MPA) as stabilizer in aqueous phase in the current research. The obtained QDs were
characterized with fluorescence spectrum (FS), and quantum yields (QYs) was calculated base on the resulting data from
FS. Comparing with CdTe core, red-shift of maximum emission wavelength (MEW) of CdTe/CdS was observed, which
indicated the growth of QDs size. To obtain high QYs of CdTe/CdS core-shell QDs, several methods and different
reaction conditions were investigated and discussed, such as dependence of Cd2+ concentration, dependence of pH,
influence of S2-:Te2-, and effect of Cd2+:S2- etc. Among all of discussed methods, QYs of core-shell CdTe/CdS is
generally degressive with refluxing time elapsing. The best QYs of 79.8% can be achieved when pH was set at 8.5,
Cd2+:S2-=1:0.1 (mol ratio). Moreover, CdTe/CdS/ZnS multi-layer QDs was prepared, and results via FS indicated a
further red-shift from 554 nm to 646 nm comparing with CdTe/CdS QDs, but QYs decreased to 14.0%. QDs currently
discussed in this research are easily synthesized, and safe to organism, i.e. biocompatible. They will be useful in
applications of biolabeling, imaging, and biosensing based on fluorescence resonance energy transfer (FRET).
KEYWORDS: Fluorescence resonance energy transfer, Luminescence, Gold, Nanoparticles, Absorption, Nanocrystals, Semiconductors, Americium, System on a chip, Quantum dots
CdTe semiconductor nanocrystals with 2.5 nm in diameters, as energy donors, were prepared in water. Narrow-disperse
Au nanoparticles with 16 nm in diameters, as energy acceptors, were prepared from gold chloride by reduction. It was
confirmed that the emission spectrum of CdTe ODs and the absorption spectrum of AuNPs had an appreciable overlap.
Therefore, a DNA fluorescence probe system based on fluorescence resonance energy transfer (FRET) from CdTe
quantum dots donors to gold nanoparticles acceptors was designed. CdTe QDs were linked to 5'-NH2-DNA through 1-
ethyl-3-(dimethylaminopr opyl) carbodi-imide hydrochloride (EDC) as a linker, and the 3'-SH-DNA was self-assembled
onto the surface of Au nanoparticles. The hybridization of complementary DNA bound to the QDs and Au nanoparticles
(CdTe-DNA-Au) determined the FRET distance of CdTe QDs and Au nanoparticles. Compared with the fluorescence of
CdTe-DNA, the fluorescence of CdTe-DNA-Au conjugates decreased extremely, which indicated that the FRET
occurred between CdTe ODs and Au nanoparticles. The fluorescence change of this conjugates was depended on the
ratio of Au-DNA and CdTe-DNA, when the AuNPs-DNA to QD-DNA ratio is 5:1, the FRET efficiency reached a
maximum. If a complementary single stranded DNA was add to the CdTe-DNA-Au conjugates, the fluorescence of the
probe system would have a certain degree recovery, this showed that the distance between CdTe QDs and Au
nanoparticles was increased.
A novel electrochemical DNA biosensor system based on methylene blue (MB) as hybridization indicator for DNA
hybridization detection was presented in this paper. 5' end -SH modified DNA (HS-DNA) as nucleotide probes were
self-assembled onto the surface of Au electrode. The complementary single stranded DNA (ssDNA) was hybridized with
this nucleotide probes to form double-stranded DNA (dsDNA) system in Tris-HCl buffer solution (pH=8.0). Compared
with the electrochemical signal of HS-DNA electrode, the electrochemical signal of dsDNA electrode system was
decreased after the hybridization program. When the methylene blue, as hybridization indicator, was introduced into this
system, the cathodic peak current (ΔIp) of Au electrode with dsDNA was increased significantly after the hybridization
program. If the target was a mismatching base-pair DNA sequence, the electrochemical signal of electrode would have
no changes almost. This result showed that this DNA biosensor system had an excellent sensitivity with a complete
complementary DNA sequence. When the target DNA concentration was 5.0×10 -10 mol/L to 1.8×10-9 mol/L, the
cathodic peak current of Au electrode system with the MB as indicator was linearly related, and the detection limit was
about 5.0×10-10 mol/L.
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