Establishment And Evaluation Of Novel Electrical Aptasensors For Amyloid Oligomers Based On Triple Helix Molecular Switch

Objective Amyloid oligomers?A?Os?,the core biomarker of Alzheimer's disease?AD?,were selected as the target in this paper.Based on the special structure design of aptamers and the regulation/amplification of electrical detection signals,a series of simple and rapid methods for detecting A?Os with high sensitivity and specificity had beed established.A?Os electrochemical aptasensors faced many problems such as simple aptamer configuration,old sensing strategy,and poor specificity and sensitivity.It provided an efficient and accurate methodological basis for the identification and quantitative detection of trace substances in biological samples,and a new idea for the detection of A?with low concentration and different aggregate morphology.Methods In this paper,the aptamers were used as bioreceptors of A?Os,and two DNA sequences were rationally designed:A?Os aptamer?Apt?containing two symmetric short arms and a signal transduction probe?STP?complementary to the symmetric two arms.Firstly,Apt was immobilized on gold electrode and palladium modified electrode by Au-S and Pd-S bonds,and then hybridized with STP labeled with three different metal nanomaterials including Au nanoparticles?AuNPs?,Ru?bpy?₃²⁺-CuNPs doped gold core-shell luminescent nanocomposites?RuCu@AuNPs?and AuNPs-doped Cu metal organic framework?AuNPs@CuMOF?.In this case,a triple-stranded DNA structure on the electrode surface was formed,producing strong electrochemical and electrochemiluminescence?ECL?signal?switch"on"?.Finally,Apt specifically bound to A?Os,and STP was displaced away from the electrode surface,weakening significantly the signal?switch“off”?.Three-helix molecular switch?THMS?was used to control the signal before and after the addition of A?Os.Three kinds of electrical aptasensors of A?Os were established.Modified electrodes and metal nanomaterials were characterized by scanning,transmission electrons,atomic force and fluorescence inverted microscope.Moreover,properties of metal nanomaterials were also characterized by ultraviolet,infrared,energy dispersive X-ray spectroscopy and X-ray diffraction.The sensitive detection of A?Os was achieved by cyclic voltammetry?CV?,electrochemical impedance spectroscopy?EIS?,differential pulse voltammetry?DPV?,and ECL.The analytical performance of the three sensors was systematically studied by methodological evaluation and feasibility verification.Results Under the optimal conditions,the linear ranges of the three A?Os electrochemical aptasensors were 1¹000 fmol/L,1¹000 fmol/L and 0.5⁵00 fmol/L,respectively.The detection limits?LOD?were 0.5 fmol/L,0.5 fmol/L and 0.25 fmol/L.The sensitivity was magnified by about 3 times compared with the double helix strategy.Systematic methodological evaluation and feasibility verification confirmed that the three sensing systems have good stability,repeatability and selectivity.They were also applied to detect serum samples and artificial cerebrospinal fluid.The recoveries were between 95.8%and 102.3%,and the RSDs were less than 4.04%,which were in good agreement with the ELISA results.Conclusion In this paper,A?Os,the core biomarker of AD,were used as the target,and three different metal nanoparticles were utilized to label STP to realize various electrochemical signal detections.A series of novel electrochemical aptamer sensors for detecting A?Os had been established coordinate with THMS strategy to regulate signal changes.The strategy organically combined the advantages of three-strand DNA structure,label-free aptamer and target trigger-chain replacement model.These sensors have excellent analytical performance for distinguishing different aggregation forms of A?to achieve specific detection.They also provide a new idea for monitoring the occurrence and development of AD disease course,thus having a good application prospect.