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Toxoplasma Gondii infection is widespread in humans worldwide and reported infection rates range from 3%-70%,
depending on the populations or geographic areas, and it has been recognized as a potential food safety hazard in our
daily life. A magnetic molecular beacon probe (mMBP), based on theory of fluorescence resonance energy transfer
(FRET), was currently reported to detect Toxoplasma Gondii DNA. Nano-sized Fe3O4 were primarily prepared by coprecipitation
method in aqueous phase with NaOH as precipitator, and was used as magnetic core. The qualified coreshell
magnetic quantum dots (mQDs), i.e. CdTe(symbol)Fe3O4, were then achieved by layer-by-layer method when mol ratio of
Fe3O4/CdTe is 1/3, pH at 6.0, 30 °C, and reactant solution was refluxed for 30 min, the size of mQDs were determined to
be 12-15 nm via transmission electron microscopy (TEM). Over 70% overlap between emission spectrum of mQDs and
absorbance spectrum of BHQ-2 was observed, this result suggests the synthesized mQDs and BHQ-2 can be utilized as
energy donor and energy acceptor, respectively. The sensing probe was fabricated and a stem-loop Toxoplasma Gondii
DNA oligonucleotide was labeled with mQDs at the 5' end and BHQ-2 at 3' end, respectively. Target Toxoplasma gondii
DNA was detected under conditions of 37 °C, hybridization for 2h, at pH8.0 in Tris-HCl buffer. About 30% recovery of
fluorescence intensity was observed via fluorescence spectrum (FS) after the Toxoplasma gondii DNA was added, which
suggested that the Toxoplasma Gondii DNA was successfully detected. Specificity investigation of the mMBP indicated
that relative low recovery of fluorescence intensity was obtained when the target DNA with one-base pair mismatch was
added, this result indicated the high specificity of the sensing probe. Our research simultaneously indicated that mMBP
can be conveniently separated from the unhybridized stem-loop DNA and target DNA, which will be meaningful in
DNA sensing and purification process.
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