Preparation of fractioned DNA aptamer–Pt complex through ultrafiltration and the colorimetric sensing of thrombin

DNA aptamers were combined with platinum complexes to form DNA–Pt complexes, which exhibited peroxidase enzymatic activity while retaining the specific binding ability of aptamers. The DNA–Pt complexes were fractioned by size through ultrafiltration membranes having several molecular weight cut-offs, and the peroxidase enzymatic activities of these fractions were compared. The enzymatic activity was highest in the filtrate of DNA–Pt complex solutions prepared with cisplatin and K2[PtCl4] after ultrafiltration through membranes having MWCO = 300,000. These showed 1.2-fold and 1.6-fold higher activity, respectively, than the corresponding unfractioned complexes. Sandwich-type DNAzyme-linked aptamer assays (DLAAs) using unfractioned or fractioned DNA–Pt complexes successfully detected the target protein thrombin. DLAAs incorporating a DNA–Pt (K2[PtCl4]) complex fractioned through ultrafiltration membranes having MWCO = 300,000 showed the highest sensitivity among DLAAs made using fractioned DNA–Pt complexes, and had a 13-fold higher sensitivity than those made with unfractioned DNA–Pt complexes.