Electrochemiluminescent Biosensor Based On Magnetic Nanoparticles Functionalized By Nanomaterials And Aptamer

(1) An electrochemiluminescence （ECL） DNA bisensor based on Fe₃O₄/Aucore/shell nanoparticle films modified magnetic controlled glassy carbon electrode（MCGCE） was developed by using quantum dots （QDs） as labels of reporter probeDNA. The DNA biosensor was based on a sandwich detection strategy, whichinvolves5’-SH capture probe immobilized on magnetic nanoparticles （MNPs）,target and5’-NH₂reporter probe NH₂-3’. After hybridization reaction, thioglycollicacid-capped CdTe QDs are attached to the end amino group of the sandwich hybrids.The fabrication and hybridization process of the DNA biosensor were characterizedby cyclic voltammetric methods. The responsive ECL intensity was linearly relatedto the target nucleic acid concentration in the range of1.0×10^-131.0×10^-11mol/L,with the detection limit of1.8×10^-14mol/L. In addition, the ECL biosensorexhibited high sensitivity, good selectivity, satisfying stability, reproducibility andrepeatability.（2） PDTPA-EG and PDTPA-EG@CdTe were synthesized in the assay.According to the hybrid theory of the DNA （or ss-DNA）, a DNA electrochemicalsensor was fabricated based on the electrochemiluminescence of the quantum dots.On the surface of the magnetic controlled golden electrode （MCGE）,5’-SH-ssDNA,the capture probe, got on to the Fe₃O₄/Au magnetic nanoparticles by self-assemblyand it could couple with the complementary end of the target DNA chine to form thedsDNA; the complex could then combine with the signal probe3’-NH₂-ssDNA toform the sandwich type hybrid DNA; at last the PDTPA-EG@CdTe nanoparticleswere fabricated on the hybrid DNA. cyclic voltammogram（CV） and electrochemicalimpedance spectroscopy （EIS） method were employed to determine the fixation,hybridization of the DNA and the characterization of the PDTPA-EG@CdTe nano-composites. The linear range between the concentration of the target DNA and theresponse ECL signals is1.0×10^-161.0×10^-14mol/L with the detection limit of3.0×10^-17mol/L. The sensitivity of the biosensor is dramatically enhanced with the helpof PDTPA-EG@CdTe.（3） A layer of Aptamer probe with hairpin structure was modified on thesurface of Fe₃O₄/Au magnetic nanoparticles （Fe₃O₄/Au-Aptamer）."stem-loop"structure of hairpin aptamer was opened when adding Pb²⁺. Then G-quadruplex wasformed, exposing3’-NH₂, which bound to CdTe quantum dots. Thus the magneticnanoparticles were separated and enriched on the surface of the magnetic controlled gold electrode （MCGE）. By this means,"Turn-on" electrochemiluminescence （ECL）sensor for Pb²⁺detection using quantum dots was constructed. The changes of thestructure of aptamer were characterized by cyclic voltammetry, AC impedance, andUV-Vis absorption spectroscopy. Pb²⁺concentration and ECL signal presented alinear relationship in the range of2.0×10^-101.0×10^-8mol/L. The detection limitwas1.08×10^-11mol/L. In addition, the biosensor showed good selectivity, stabilityand reproducibility.（4） A layer of Aptamer probe with duplex structure was modified on thesurface of Fe₃O₄/Au magnetic nanoparticles （Fe₃O₄/Au-dsDNA）.Pb²⁺-driven Aptamerprobe which is constructed based on a DNA duplex-quadruplex exchange is utilizedfor the highly selective and sensitive detection of Pb²⁺. The power of thisFe₃O₄/Au-dsDNA device originates from the excellent efficiency of Pb²⁺forstabilizing G-quadruplexes, which makes the DNA duplex unwind thereby driving thedevice. This device can be reset to the original state by addition of a strong Pb²⁺chelator EDTA,endowing the device with good reusability. In the whole process,thesignal readout is modulated via a Ru（phen）₃²⁺probe binding to and being releasedfrom the DNA druplex. Such a Fe₃O₄/Au-dsDNA device can serve as a novelelectrochemiluminescence sensor for Pb²⁺detection with high selectivity andsensitivity.