Constuction Of Signal Amplified Electrochemical Aptasensor For The Detection Of Cancer Biomarkers

Substances expressed excessively or abnormally in the body are usually selected as the indicator for early screening and diagnosis of cancer.However,the amount of these biomarkers is extremely low in the early stages of cancer.Therefore,the sensitive detection of cancer biomarkers is essential for the early diagnosis of cancer.Electrochemical aptasensor is regarded as one of the most promising devices to analyze and detect cancer biomarkers because of the following merits:low cost,good stability,specific recognition capacity and easy to operate.However,the sensitivity of electrochemical aptasensor still needs to be improved.Currently,the improvement of sensitivity of electrochemical aptasensors is achieved by adopting signal amplification strategies,such as,enzyme catalyzed signal amplification,nucleic acid signal amplification and nanomaterial signal amplification.Inspired by the above strategies,this article intends to use the following two methods to improve the sensitivity of electrochemical aptasensors:1)Finding new functional nanomaterials,which can amplify the signal and improve the detection sensitivity of electrochemical aptasensors;2)combining exonuclease III（Exo III）assisted cycle amplification,catalytic hairpin assembly and enzyme catalytic strategies to achieve amplification of the detection signal and further increase the sensitivity of aptasensor.The details are as follows:（1）Construction of dual-mode electrochemical aptasensor based on the catalysis of Fe-ZIF-950 to detect the vascular endothelial growth factor（VEGF165）:Fe,N-doped carbon materials（Fe-ZIF-950）was prepared by a simple one-step pyrolyzing Fe-doped ZIF-8 particles.The as-prepared material contained highly dispersed Fe N_x coordination structure,which can be used as an efficient catalyst to generate electrochemical signal.In the absence of VEGF165,biotin-modified aptamer could hybridize with C-DNA,and then the streptavidin（SA）-modified Fe-ZIF-950 binded to aptamer.Fe-ZIF-950 could catalyze the oxidation of 3,3’,5,5’-tetramethylbenzidine（TMB）with the presence of hydrogen peroxide（H₂O₂）to amplify the current signal;and also oxidize 3,3’-diaminobenzidine（DAB）form insoluble precipitates（IPs）,which amplified the electrochemical impedance signal.By contrast,with the presence of VEGF165,Fe-ZIF-950 will not be fixed on the electrode surface,consequently resulting in a weaker electrochemical signal.Based on this material,a dual-mode electrochemical aptasensor was designed to detect VEGF165.The detection range of the aptasensor toward VEGF165 was0.1-1×10³ ng m L^-1,and the detection limits were 71.9 pg m L^-1 and 67.7 pg m L^-1,respectively.Furthermore,the dual-mode electrochemical aptasensor has the potential of practical application.（2）Construction of electrochemical aptasensor based on triple signal amplification for detection of mucin 1（MUC1）:Three kinds of signal amplification methods（exonuclease III（Exo III）assisted amplification,catalytic hairpin assembly and enzyme catalysis strategy）were overlaid to construct an aptasensor,which was applied to detect MUC1 sensitively.Firstly,with the help of Exo III,MUC1 and aptamer could be recycled during the cycle I,the single stranded DNA（S-1）was produced during the process and was introduced to the hybride reaction on the electrode.Secondly,during the cycle II,catalytic hairpin assembly was triggered on the electrode with the adding of hairpin DNA-2（H-2）.Thirdly,after the Au NPs-DNA-HRP conjugates hybrided with the H-2 on the electrode,the Au NPs-DNA-HRP could catalyze3,3’,5,5’-tetramethylbenzidine（TMB）to produce current signal in the presence of hydrogen peroxide（H₂O₂）.The as-obtained electrochemical aptasensor exhibited high sensitivity and rapid response in the concentration ranging from 0.1 pg m L^-1 to 10 ng m L^-1.Meanwhile,the aptasensor gave a detection limit as low as 0.04 pg m L^-1,which shows a promising application prospect in clinical diagnosis.