Aptasensor For Breast Cancer Markers Based On Ionic Liquid Functionalized Metal-organic Framework

Photoelectrochemical（PEC）biosensing systems often use light as the excitation source,electrochemical responses as output signals,biomolecules as recognition elements.As targets are specifically recognized on the PEC biosensing interfaces,the photoelectrochemical signals will change accordingly and will be linearly related to their concentrations,thus achieving the determination of biomolecules.Due the excitation source and the detection signal are totally different,the photoelectrochemical biosensing system provides an ultra-low background signal,and shows higher sensitivity than conventional electrochemical biosensors.As the core element of photoelectrochemical biosensing system,the photoelectroactive materials are the most important elements for the conversion of light to electrical signal,and should possess excellent photoelectric conversion efficiency and high stability.In addition,the strategies for the immune recognition and the signal amplification will determine the performances of photoelectrochemical biosensors.Therefore,the development of photoelectroactive materials with superior performances and sensitive sensing strategies will be helpful for improving the sensing performances of photoelectrochemical biosensors.In this dissertation,ionic liquid functionalized metal-organic frameworks integrated with noble metal nanoparticles were used as photoelectroactive materials to construct PEC aptasensing systems for the high-performance determination of breast cancer markers.The main contents of this dissertation were detailed as follows:（1）A single tumor marker may correspond to a variety of diseases,and a specific disease often requires the joint detection of multiple tumor markers for improving the accuracy of diagnoses.Herein,ionic liquid functionalized Zn-MOF,spherical gold nanoparticles and triangular silver nanosheets were successfully synthesized.The ionic liquid functionalized Zn-MOF was modified onto a glassy carbon electrode surface and was used as a substrate to immobilize the aptamers（Ab1）for CEA and CA153.The gold nanoparticles and triangular silver nanosheets labeled with the aptamer（Ab2）were used as the beacon substances to construct a dual-wavelength response sandwich-type photoelectrochemical aptasensor.Due to the localized surface plasmon resonance effect of noble metal nanoparticles,gold nanoparticles and triangular silver nanosheets can be excited by light sources with different excitation wavelengths（520 nm and 808 nm）to generate two photoelectronic signals respectively,enabling the simultaneous detection of CEA and CA153 tumor markers.Under the optimized conditions,CA153 and CEA at the concentrations of 0.05～25 U m L^-1 and 0.005～5 ng m L^-1 were detected by the PEC aptasensor.Detection limits calculated for CA153 and CEA determinations were 0.0275 U m L^-1 and 2.85 pg m L^–1（S/N=3）,respectively.CA153 and CEA in serum samples were detected by the PEC aptasensor,and their concentrations were well consistent with that obtained from ELISA.In addition,the PEC aptasensor exhibited a recovery rate of 96.42%～102.5%,and a relative standard deviation of 1.1%～3.6%,indicating good accuracy and precision,further confirming its potential for clinical diagnosis.（2）The low photon energy and deep penetrating ability of near-infrared（NIR）light make it an ideal light source for PEC immunosensing system.Absorption wavelengths of metal-organic frameworks（MOFs）can be regulated by adjusting the conjugation degree of ligands and metal ions.Herein,ionic liquid with a large conjugated structure was synthesized and was used as a ligand to coordinate with Nd ion to prepare Nd-MOF rods with a bandgap of 1.26 e V.Nd-MOF rods show good absorption property in the wavelength range from 200 to 980 nm.A photoelectrochemical platform was constructed by using Nd-MOF rods as the photoelectroactive element.A double-stranded DNA labeled with alkaline phosphatase（ALP）which is specific to VEGF165 was immobilized onto the PEC sensing interface,after blocking unspecific active sites with bovine albumin,a PEC aptasensing system was developed for VEGF165.After being incubated in a mixture of VEGF165,vitamin C magnesium phosphate（AAP）,and chloroauric acid,the aptamers for VEGF165 will be detached from the PEC aptasensing interface,thus resulting in the charge transfer resistance decrease and the photocurrent response increase.The shedding of aptamers makes ALP close to the electrode surface,thus catalyzing the reduction of AAP to produce ascorbic acid（AA）.Subsequently,AA can in-situ reduce chloroauric acid to produce gold nanoparticles on the Nd-MOF rods-based sensing interface.With excellent conductivity and localized surface plasmon resonance effect,the gold nanoparticles can promote the separation of electron-hole pairs generated from Nd-MOF rods,thus promoting the photoelectric conversion efficiency and achieving signal amplification.Under optimized conditions,the photoelectrochemical responses linearly related to VEGF165 concentrations in the range of 0.01～100 ng m L^-1 and presents a low detection limit of 3.51 pg m L^-1（S/N=3）.VEGF165 in serum samples was detected by the PEC aptasensor,and their concentrations were well consistent with that obtained from ELISA.In addition,the PEC aptasensor exhibited a recovery rate of 97.10%～104.0%,and a relative standard deviation within 5%,indicating good accuracy and precision,further confirming its potential for clinical diagnosis.