The Sudy Of Polyoxometalates In The Colorimetric Immunoassay

Early detection of cancer biomarkers plays an important role in early diagnosisof cancer and clinical research. Multiplexed colorimetric immunoassay has theadvantages of simplified analytical procedure, shortened analysis time, improveddetection efficiency, decreased sample volume and reduced costs. In colorimetricimmunoassay, an horseradish peroxidase-labeled （HRP-labeled） secondary antibodyneeds to be used to assess the oxidation of3,3′,5,5′-tetramethylbenzidine （TMB）.However, some drawbacks need to be improved for the above method: HRP oftenloses its peroxidase activity when denatured; hydrogen peroxide decomposes uponprolonged storage and losses its ability to oxidize the TMB in the presence of HRP.More stable and convenient immunoassay methods are needed for extensive clinicalapplications.FA is familiar to amino acid and the structure. Amino acids or cationic dipeptidehad been used as building blocks in the construction of defined supramolecularpolyoxometalates （POMs） structures. TMB is a dye, which is used as （HRP） substratein various bioassays upon the oxidation form of blue and had been used todemonstrate the peroxidase-like activity of Fe3O4nanopaticles and single-walledcarbon nanotube. Herein, we selected PMV and Fe₂SiW₁₀as inorganic parts andfolate as an organic group to self-assemble folate-POMs hybrid particles FA-PMVand FA-Fe₂SiW₁₀.And we studied the catalytic activity of FA-PMV and FA-Fe₂SiW₁₀in facilitatingthe oxidation of substrate TMB. It was found that inorganic-organic hybridnanoparticles FA-PMV and FA-Fe₂SiW₁₀both had intrinsic oxidase-like activity atacidic and neutral pH values, which can quickly oxidize TMB without using O2orH₂O₂. The purpose of using folate is to enhance the biocompatibility and target totumor cells of FA-PMV and FA-Fe₂SiW₁₀hybrid, which could provide immunoassaybased on folate-expressing cancer cells and catalytic oxidation of sensitivecolorimetric substrates （such as TMB）.It is more and more important to detecing concentration of glucose in our society.To evaluate the performance of POMs as peroxidase mimetics, three POMs had beenchosen to study their catalytic activity in detecting H₂O₂（Figure S2）, such asH3PW₁₂O40(PW₁₂), H4SiW₁₂O40(SiW₁₂), and H3PMo₁₂O40(PMo₁₂). The result showsthat PW₁₂present the best activity. Therefore, PW₁₂was selected as the catalyst in our detecting system from the above comparison. It is known that the pH and temperatureare the important parameters for the H₂O₂detection. The pH-dependent responsecurve and temperature-dependent response curves were shown.1. Preparation of FA-functionalized POMs: FA-PMV and FA-Fe₂SiW₁₀nanoparticles, and were characterized by IR、UV、XRD、TEM、EDS et al.2. The study of the catalytic activity of FA-PMV and FA-Fe₂SiW₁₀nanoparticles.3. FA-PMV and FA-Fe₂SiW₁₀were used to detect folate-expressing cancer cells.4. Preparation of POMs: PW₁₂, SiW₁₂and PMo₁₂.5. The study of the catalytic activity of PW₁₂, SiW₁₂and PMo₁₂.6. PW₁₂is used to detect concentration of H₂O₂and glucose.