| Nowadays,cancer is a disease with a high mortality rate,so the detection of cancer markers has an extraordinary significance in early screening,early diagnosis,efficacy monitoring and postoperative prognosis of cancer.As an emerging quantitative detection method,photoelectrochemical?PEC?sensing holds the advantages of rapidity,simplicity,sensitivity,and wide detection range.The application of PEC sensors in the detection of cancer markers is promising.However,in the light of the detection of cancer markers in complex real serum samples,the selectivity and stability of PEC sensors still need to be improved.In this work,superparamagnetic Fe3O4,Fe3O4@SiO2,Fe3O4@SiO2@CdS,silver nanoparticles and quantum dots were prepared for the construction of high-performance PEC sensing for the detection of carcinoembryonic antigen?CEA?and microRNAs.The specific research tasks are as follows:?1?Superparamagnetic Fe3O4@SiO2@CdS core-shell structures were used to construct CEA PEC biosensor.Specifically,the amino groups were introduced on the surface of Fe3O4@SiO2@CdS by chitosan,and then Fe3O4@SiO2@CdS was connected with the NH2-DNA through glutaraldehyde to form Fe3O4@SiO2@CdS-DNA1 particles.ThenAu nanoparticles were anchored on the surface of SiO2,and connected with SH-DNA to form SiO2-Au-DNA2 structures.According to the principle of complementary base pairing,the structures of Fe3O4@SiO2@CdS-DNA1 and SiO2-Au-DNA2 were connected with the CEA aptamer,so that the Fe3O4@SiO2@CdS-DNA1-CEA aptamer-DNA2-Au-SiO2 sandwich-like composite was formed,and it was used for the construction of a PEC biosensor.Intiallly,the photocurrent of the sensor was weak because the large-sized SiO2-Au-DNA2 nanoparticles hindered the electron transfer between Fe3O4@SiO2@CdS-DNA1 and the electrode.As CEA aptamers continue to capture CEA,SiO2-Au-DNA2 and Fe3O4@SiO2@CdS-DNA1 were separated,then the steric hindrance effect was weakened,and the photocurrent was gradually strengthened.Superparamagnetic Fe3O4@SiO2@CdS can effectively separate the target from the complex biological environment,and achieve the measurement of CEA concentration in pure buffer solution.This PEC biosensor has been successfully applied to the detection of CEA in human serum samples.In addition,the as-designed sensor also has excellent performance in terms of easy operation,high sensitivity and good selectivity.?2?MicroRNAs are important biomarkers for early prediction and treatment of various cancers,so sensitive detection of microRNA expression in the human body is of great significance for the early diagnosis and treatment of tumors.Different from the combination of antibodies,the combination of DNA and microRNA is based on the principle of complementary base pairing,which enhances the selectivity of the biosensor.However,due to the low-abundance expression of microRNA in the human body,improving the sensitivity of microRNA detection has always been a significant research topic.In this work,according to the principle of entropy driving,we promoted the autonomous circulation of microRNA in system,which realized the amplification of biological signals,effectively enhancing the sensitivity of microRNA detection.First of all,we utilized the EDC-NHS classic coupling reaction to convert the DNA strand L and D coupling with Fe3O4@SiO2 and CdSe QDs,respectively.Then the three DNA strands L,D,and R were assembled into structure?I?.Subsequently,the target microRNA-155?T?was introduced.According to the strand replacement reaction,the DNA strand R was replaced by T and recovered by magnetic attraction.After adding the DNA strand F,the structure?II?was generated,T was detached and automatically put into the next cycle,The strand D linked with CdSe QDs was also replaced and reused.Compared with structure?I?,the photocurrent intensity of structure?II?is significantly weakened,which is caused by the detachment of CdSe QDs.Separating and washing the structure?II?from the complex system would not only effectively improve the selectivity of the sensor,but also reuse the replace DNA strands,so that no waste was generated in the entire system.As a result,the PEC sensor can be successfully applied to the detection of miRNA-155 in human serum samples.In addition to the excellent selectivity and sensitivity,the designed PEC sensor has the advantages of low cost,easy manufacturing,and reproducibility.?3?DNA nanomachine is a DNA nanostructure with DNA as the main element or a composite nanostructure combined with nanomaterials.It can convert a certain external power into mechanical energy and simulate the movement of the machine to complete specific biological functions on the nanometer scale.In this work,a novel enzyme-free,entropy-driven DNA walker was developed and applied to the detection of microRNA-141.Protection probe was firstly bound to target microRNA-141 and released the special DNA walking probe to impel walking probe three-dimensional walking on the surface of SiO2 nanoparticles.And due to the entropy-driven strand displacement reaction,the output DNAs were continuously released as a result of the amplified biological signals.Subsequently,the capture probe modified on the superparamagnetic material Fe3O4@SiO2 hybridized with the output DNA,and was detached from the complex reaction system by magnetic attraction.Then,based on the principle of complementary base pairing,the output DNA was complementary to the cytosine-rich signal probe H,which was coupled with CdTe@ZnS core-shell QDs.Strand H coordinated with Ag+ions,and which were reduced to Ag nanoparticles by hydroquinone.At this time,Ag nanoparticles accelerated the charge transfer of CdTe@ZnS QDs and enhanced the photoelectric signal.The DNA walker amplified the biological signal expression of the target.The photoelectric signal of CdTe@ZnS core-shell QDs is also far superior to that of single quantum dots.The resulting Ag particles have obvious signal-sensitizing effect on CdTe@ZnS QDs.Therefore,the triple signal amplification-based PEC biosensor holds an amazing performance in detection of microRNA-141. |
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