Hollow TiO₂ modified reduced graphene oxide microspheres encapsulating hemoglobin for a mediator-free biosensor

Hollow TiO₂ modified reduced graphene oxide microspheres (hollow TiO₂-rGO microspheres or H-TiO₂-rGO MS) have been synthesized and then be used to immobilize hemoglobin (Hb) to fabricate a mediator-free biosensor. The morphology and structure of hollow TiO₂-rGO microspheres were characterized by scanning electron microscopy, transmission electronic microscopy and X-ray diffraction. Results of spectroscopy and electrochemistry tests revealed that hollow TiO₂-rGO microsphere is an excellent immobilization matrix with biocompatibility for redox protein, affording good protein bioactivity and stability. The hollow TiO₂-rGO microspheres with special structure and component enhance the immobilization efficiency of proteins and facilitate the direct electron transfer, which result in the better H₂O₂ detection performance-the wide linear range of 0.1-360μM for H₂O₂ (sensitivity of 417.6 μA mM^-1 cm^-2) and the extremely low detection limit of 10nM for H₂O₂. Moreover, the hollow microsphere can provide a protective microenvironment for Hb to make the as-prepared biosensor improve long-term stability. The as-prepared biosensor retains 95.4% of the initial response to H₂O₂ after 60-d storage. Hence, this work suggests that if can be fabricated a mediator-free biosensor, hollow TiO₂-rGO microspheres will find wide potential applications in environmental analysis and biomedical detection.