Study On The Photoelectrochemical Biosensor Based On Carbohydrate-Protein Interactions

Carbohydrate-protein interactions are the fundamentals of many cellular processes, such as signal transduction, cell adhesion, viral/bacterial infection, proliferation, differentiation and immune response, which are of great significance in life sciences. The glycosylation profile (glycosignature) on the cell surface is dynamic and its alterations are indicative of changes in cellular environment and physiology. Most chronic and immunological diseases and their progression are accompanied by corresponding glycosignature changes of affected cells and circulatory proteins. The alteration in glycosignatures associated with malignant transformation, tumor progression, and metastasis is very well documented. The determination of the carbohydrate components of glycoconjugates is challenging because of the chemical complexity of glycan chains. Through monitoring corresponding antibody, we can get a good solution for early clinical diagnoses. In this paper, based on carbohydrate-protein interactions, a new photoelectrochemical (PEC) biosensor for ultrasensitive detection of antibody against tumor-associated carbohydrate antigen was developed.(1) In this work, mannose-concanavalin A (Con A) and galactose-peanut agglutinin (PNA) were used as models. A photoelectrochemical biosensor for carbohydrate-lectin interactions was developed. Poly(dimethyl-diallylammonium chloride)(PDDA) functionalized graphene was synthesized to construct CdSe QDs sensitized sensing interface. The resulting modified electrodes were tested for lectin through the recognition of monosaccharide, which was covalently bound to the electrode. The quantitative behavior of the photoelectrochemical biosensor was assessed by measuring the dependence of the changed photocurrent intensity (ΔI) before and after incubated with different concentration of lectin. Photocurrent intensity decreased as the concentration of lectin increased. Under optimal condition, the detection limit for both lectins was about10ng/mL. This method has high sensitivity and selectivity, and provides a theoretical basis for subsequent detection for antibody against tumor-associated carbohydrate antigen.(2) In this experiment breast tumor-associated carbohydrate antigens Tn (GalNAc-a-Ser/Thr) was used as a model and a new photoelectrochemical immunosensor for high sensitive detection of antibody against Tn (anti-Tn) was developed. After the covalent attachment of Tn on the photoactive films (PDDA-G/CdSe QDs), the biosensor can recognise different concentrations of antibodies. After recognition with the horseradish peroxidase labeled secondary antibodies (Ab2-HRP), a sandwich-type photoelectrochemical immunosensor interface was fabricated. To enhance the sensitivity, HRP catalyzed precipitation product as an isolating barrier for the electron-transfer was introduced. The oxidation of4-Chloro-1-naphthol catalyzed by HRP would yield insoluble product on the photoelectrode surface, on the basis of which the photocurrent was decreased greatly. The detection limit of1.2×10-11g/mL for the determination of anti-Tn was achieved.(3) Functional graphene oxide (GO) has been extensively investigated as a nanocarrier to enhance the sensitivity, a new photoelectrochemical biosensor for ultrasensitive detection of antibody against Tn was developed. To synthesize GO nanocomposites (GO-Ab2-HRP), HRP and Ab2were both covalent attached to GO nanofilm for more enzyme loading. Though formation of immunocomplexes and the insoluble biocatalytic precipitation (BCP) product, photocurrent intensity was decreased more. The decrease of photocurrent intensity was linearly related to the concentration of anti-Tn in the range from0.5to500pg/mL. The regression equation was ΓI (μA)=0.13+0.261gC (pg/mL), with a detection limit of1.0×10-13g/mL, At the same time, this work showed acceptable selectivity and could be used in the complex matrix. This PEC biosensor showed high sensitivity and selectivity, and thus provides another platform to monitor the immune response to carbohydrate epitopes at different stages during differentiation, metastasis, or treatment.