Al3+-directed self-assembly and their electrochemistry properties of three-dimensional dendriform horseradish peroxidase/polyacrylamide/platinum/single-walled carbon nanotube composite film

A novel general methodology for protein immobilization and third-generation biosensor construction is demonstrated, which involves Al3+-directed polyacrylamide (PAM) self-assembly into an ordered dendriform structure, easily immobilizing enzymes and nanoparticles. Platinum/single-walled carbon nanotube (Pt/SWCNT) heterojunction nanomaterials were for the first time fabricated via an EDTA-directed synthesis strategy. The Pt/SWCNTs were employed as a supporting matrix to explore a novel immobilization and biosensing platform of redox proteins through cooperating Al3+-directed PAM self-assembly. Compared with the almost single-layer horseradish peroxidase (HRP)/PAM film electrode, multilayer HRP/PAM/Pt/SWCNT film electrode exhibited a pair of much stronger redox peaks at −0.22 V (vs. Ag/AgCl). Moreover, with advantages of the ordered multilayer HRP/PAM/Pt/SWCNT film, facilitated direct electron transfer of the metalloenzymes with an apparent heterogeneous electron transfer rate constant (ks) of 14.94 ± 1.36 s−1 and smaller peak-to-peak separation (ΔEp) of about 37 mV was acquired on the PAM/Pt/SWCNT-based enzyme electrode. The PAM/Pt/SWCNT-based biosensor demonstrated significant electrocatalytic activity for the reduction of hydrogen peroxide with a small apparent Michaelis–Menten constant (87 μM), wide linear range (1–270 μM), very low detection limit (0.08 μM, S/N = 3), and high sensitivity (372 mA cm−2 M−1). Together, these indicated that the Al3+-directed HRP/PAM/Pt/SWCNT film was one of ideal candidate materials for direct electrochemistry of redox proteins and the construction of the related enzyme biosensors, and may find potential applications in biomedical, food, and environmental analysis and detection.