We developed a simple method to prepare gold-nanoparticle-doped titanium dioxide (GTD) sol–gel solution. The optimized GTD sol–gel solutions were a mixture of TEA, titanium (IV) butoxide, HAuCl4, and deionized water in 0.3:1:0.5:3 volume ratios at room temperature. Using this sol–gel solution, we fabricated the GTD photonic crystal structure by infiltrating this solution by dip-coating into a polystyrene (PS) template. It was found that high quality of thin films was obtained by infiltrating twice the PS templates with the synthesized GTD sol–gel solutions. Energy dispersive X-ray spectroscopy and X-ray photoelectron spectra revealed the doping of TiO2 and Au in the GTD photonic crystals. X-ray diffraction showed that TiO2 and Au existed as anatase phase and metallic Au phase, respectively, in the GTD photonic crystals. The results indicated that the gold nanoparticles were doped into the framework of the photonic crystals.

The three-dimensionally ordered macroporous gold-nanoparticle-doped titanium dioxide (3DOM GTD) film was modified on the indium-tin oxide (ITO) electrode surface. Hemoglobin (Hb) has been successfully immobilized on the 3DOM GTD film and the fabrication process was characterized by Raman and UV–vis spectra. The results indicated that the Hb immobilized on the film retained its biological activity and the secondary structure of Hb was not destroyed. The direct electrochemistry and electrocatalysis of Hb immobilized on this film have been investigated. The Hb/3DOM GTD/ITO electrode exhibited two couples of redox peaks corresponding to the Hb intercalated in the mesopores and adsorbed on the external surface of the film with the formal potential of −0.20 and −0.48 V in 0.1 M PBS (pH7.0), respectively. The Hb/3DOM GTD/ITO electrode exhibits an excellent eletrocatalytic activity, a wide linear range for H2O2 from 5.0 μM to 1.0 mM with a limit of detection of 0.6 μM, high sensitivity (144.5 μA mM−1), good stability and reproducibility. Compared with the TiO2 nanoneedles modified electrode, the GTD modified electrode has higher sensitivity and response peak current. The 3DOM GTD provided a good matrix for bioactive molecules immobilization, suggesting it has the potential use in the fields of H2O2 biosensors.

Gold nanoparticles have been introduced into the wall framework of titanium dioxide photonic crystals by the colloidal crystal template technique. The three-dimensionally ordered macroporous gold-nanoparticle-doped titanium dioxide (3DOM GTD) film was modified on the indium-tin oxide (ITO) electrode surface and used for the hydrogen peroxide biosensor. The direct electron transfer and electrocatalysis of horseradish peroxidase (HRP) immobilized on this film have been investigated. The 3DOM GTD film could provide a good microenvironment for retaining the biological bioactivity, large internal area, and superior conductivity. The HRP/3DOM GTD/ITO electrode exhibited two couples of redox peaks corresponding to the HRP intercalated in the mesopores and adsorbed on the external surface of the film with the formal potential of −0.19 and −0.52 V in 0.1 M PBS (pH 7.4), respectively. The HRP intercalated in the mesopores showed a surface-controlled process with a single proton transfer. The direct electron transfer between the adsorbed HRP and the electrode is achieved without the aid of an electron mediator. The H2O2 biosensor displayed a rapid eletrocatalytic response (less than 3 s), a wide linear range from 0.5 μM to 1.4 mM with a detection limit of 0.2 μM, high sensitivity (179.9 μA mM−1), good stability and reproducibility. Compared with the free-Au doped titanium dioxide photonic crystals modified electrode, the GTD modified electrode could greatly enhance the response current signal, linear detection range and higher sensitivity. The 3DOM GTD provided a new matrix for protein immobilization and direct transfer study and opened a way for low conductivity electrode biosensor.

The DNA–thionine–carbon nanotube (DNA–Th–CNT) nanocomposites were prepared by immobilizing DNA on the surface of carbon nanotubes (CNTs) via thionine (Th). The fabrication process was characterized by Raman spectroscopy, UV–vis spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM). The results indicated that Th could facilitate the immobilization of DNA molecules onto the surface of CNTs, and DNA retained its native secondary conformational structure after it was immobilized. These demonstrated that Th may be served as an effective mediator for immobilization of DNA on CNTs. The nanocomposites were immobilized on the surface of glassy carbon (GC) electrode forming the DNA–Th–CNTs/GC electrode. The electrode was used to study the interaction between Co(bpy)33+ probe and the immobilized DNA by cyclic voltammetry, whose results indicated that Co(bpy)33+ could be electrostatically bound onto the immobilized DNA. The method of the present work has the advantages of rapid and facile CNTs functionalization, high immobilization efficiency. The nanocomposites have a good electrochemical response with a long-term stability, suggesting they have the potential use in the fields of DNA biosensors.