Ultrasensitive Amperometric Determination Of PSA Based On A Signal Amplification Strategy Using Nanoflowers Composed Of Single-strand DNA Modified Fullerene And Methylene Blue,and An Improved Surface-initiated Enzymatic Polymerization

Objective:PSA（Prostate specific antigen）is the most reliable tumor marker for early diagnosis of prostate cancer.However,the fluctuating range of PSA in the patient is even lower on the nanogram scale.Therefore,the traditional method is not enough to meet the detection requirements.A new type of highly sensitive detection method is needed.This study establishes an accurate and sensitive new method,immunosensor,for the detection of PSA,allowing early screening of related diseases.Methods:1.Improved surface-initiated enzymatic polymerization（SIEP）:single-stranded DNA is extended under the action of terminal deoxynucleotidyl transferase（TdT）,Combined with the role of electrochemical indicator,this method can effectively amplify electrochemical detection signals.2.Synthesis of novel electrochemical reaction Indicator C₆₀/MB Complex:the C₆₀ nanoparticles and methylene blue can form a flower complex in aqueous solution.As a new type of electrochemical indicator,C₆₀/MB complex is used in the construction of biosensors,effectively improving the detection performance of the sensor.3.Gold electrode is used as a reaction substrate and a phosphate buffer solution is used as a reaction liquid.After the key experimental conditions are optimized,differential pulse voltammetry is used to electrochemically detect PSA with different concentration gradients.According to the test results,a standard curve is drawn and the performance of the constructed sensor is evaluated.Results:1.The improved SIEP exhibit prominent effects in signal amplification of the biosensor.And its successful extension and the effect of signal amplification are verified by Gel electrophoresis and electrochemical methods,respectively.2.The C₆₀/MB complex is successfully synthesized.The procedure and synthesis products are characterized by UV spectrophotometer,particle size analysis and transmission electron microscopy.The results are satisfactory.3.The constructed immunosensor has a linear correlation between the logarithm of the electrical signal and the target concentration in the range from 15 pg mL^-1 to 8 ng mL^-1.The detection limit is 1.7 pg mL^-1（S/N=3）.4.The immunosensor has superiorly performance,good specificity and stability.Conclusion:Through the combination of improved SIEP technology and the new electrochemical indicator C₆₀/MB,the electrochemical signal has been double amplified.The detection performance of the constructed sandwich immunosensor has been greatly improved,and it is sufficient for detection of low concentrations of PSA.This signal amplification strategy is expected to be applied to the construction of other biosensors.