| Early diagnosis and treatment of diseases can effectively reduce the trauma of treatment and even reduce the mortality rate,which is critical for the cure of diseases like cancer.Therefore,the sensitive detection of biomarkers for early diagnosis of diseases is of great significance.Assays for a range of human disease biomarkers are emerging.Among the analytical methods,electrochemical sensors have attracted extensive attention due to the high sensitivity,low cost,and high efficiency.However,the biofouling of the sensing interface poses a serious challenge to their application in real biological samples.Contaminants such as nonspecific proteins in serum can cover the electrochemically effective surface of the electrode and cause a series of adverse effects,such as low sensitivity,long response time,and low accuracy of quantitative analysis.Currently,various anti-fouling materials have been introduced into the construction of biosensing interfaces to reduce the effects of biofouling in complex media.Although these materials are harmless to the human body and can form an antifouling layer at the sensing interface,for the construction materials of biosensors,excellent biocompatibility is also required,which can keep the immobilized biomolecules in high biological activity.Therefore,it remains a great challenge to develop antifouling materials with higher biocompatibility and stability.Peptide hydrogels,as three-dimensional（3D）porous materials,have great application potential due to their good biocompatibility and physical similarity with biological tissues.As a class of soft matter,hydrogels are widely used in biomedical fields serving as key materials for sensing,tissue engineering,wound dressings,3D cell culture,and cancer therapy.In this thesis,based on the hydrogel materials with excellent properties,peptide hydrogels were designed and prepared,which were then successfully used in the construction of electrochemical biosensors.The biocompatible cross-linked network formed by hydrogels effectively maintained the activity of attached biomolecules.Besides,the adjustable properties and good hydrophilicity of hydrogels facilitate their application in antifouling biosensors.By further combining with conducting polymer materials which provided a stable conductive substrate for biosensor construction and maked up for the poor conductivity of peptide hydrogels,sensitive and accurate detection of disease markers in complex biological samples such as human serum was achhieved.This thesis mainly includes the following three parts:（1）Supramolecular hydrogels based on fluorenemethoxycarbonyl N-terminal modified peptides（Fmoc-FEKF）were designed.The hydrogel has a microstructure of nanofiber network,which forms a perfect supramolecular network with shear-thinning properties and excellent biocompatibility.Introducing the antibiotic ciprofloxacin（CIP）as the loaded drug and prepared Fmoc-FEKF/CIP hydrogel with excellent bacteriostatic effect,which could effectively inhibit the growth and reproduction of common bacteria such as Staphylococcus aureus,Escherichia coli,and Pseudomonas aeruginosa.Meanwhile,Fmoc-FEKF hydrogels with nanofibrous structure were used to construct electrochemical sensors by doping gold nanoparticles（Au NPs）to enhance the specific surface area and electrical conductivity for the catalysis of the neurotransmitter dopamine（DA）.Furthermore,antibacterial electrochemical sensors based on FEKF/Au NPs/CIP composite hydrogels were prepared.The constructed antibacterial sensor maintained excellent catalytic effect and biocompatibility,simultaneously had the characteristics of inhibiting the growth of bacteria,which was expected to achieve infection-free detection of biomolecules in the human body.（2）A novel,antifouling,and ultrasensitive electrochemical biosensor for the detection of human epidermal growth factor receptor 2（HER2）was constructed based on peptide hydrogels and conducting polymer poly（3,4-ethylenedioxythiophene）（PEDOT）.The designed peptide hydrogels served as the antifouling interface and a matrix for the immobilization of HER2 antibodies.Nonrigid hydrogels with large specific surface area can reduce steric hindrance,enhance the immobilization of biomolecules and the binding with target molecules,and their biocompatible crosslinked network can effectively maintain the activity of attached biomolecules.In addition,the hydrophilicity of the hydrogel facilitates the formation of a hydration layer,thereby alleviating the nonspecific adhesion of biomacromolecules on the sensing interface.The prepared sensor could detect the target HER2 with high sensitivity,basically maintain the original signal in a series of concentrations of serum,and exhibited good antifouling ability in complex biological environment to detect HER2 in human serum,which has broad application prospects in biochemical analysis and clinical diagnosis.（3）In order to solve the problem of biofouling for prostate-specific antigen（PSA）detection in complex biological systems and obtain biosensors with better antifouling performance,an electroneutral peptide was designed;and used for the preparation of zwitterionic peptide hydrogels through its self-assembly and an antifouling biosensor for the detection of PSA was further constructed based on the hydrogel.With the electrodeposition of PEDOT and Au NPs,a stable sensing substrate was formed,and the designed peptide chain with the cysteine modified at its end was immobilized on the Au NPs modified surface through the Au-S bonds,and the antibodies were further immobilized to construct the antifouling biosensor.The conducting polymer PEDOT facilitated the increase of effective electrode surface area for electron transfer,while the Au NPs supported the formation of Au-S bonds for hydrogel immobilization.The peptide hydrogel was able to resist nonspecific protein adsorption and cell adhesion,and it showed excellent antifouling performance in complex environments such as serum.The low-fouling sensing system based on the zwitterionic peptide hydrogel was successfully applied to the detection of PSA in complex biological fluids,providing a new view for diseases diagnosis. |
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