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A novel organ-like MXene-Ti 3 C 2 nanomaterial was successfully prepared by etching Al from Ti 3 AlC 2 in HF at room temperature and then used to immobilise hemoglobin (Hb) to fabricate a mediator-free biosensor with an oxidized surface. MXene-Ti 3 C 2 and its morphology were well characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and the physical and electrochemical properties of as-obtained samples were studied by UV-vis diffuse reflectance spectra (DRS) and the electrochemical workstation. Spectroscopic and electrochemical results confirmed that MXene-Ti 3 C 2 exhibited an excellent enzyme immobilization ability with biocompatibility for redox protein, displaying good protein bioactivity and stability. Due to the special structure and properties of MXene-Ti 3 C 2 , the direct electron transfer of Hb is facilitated and the prepared biosensors displayed good performance for the detection of H 2 O 2 with a wide linear range of 0.1-260 μM for H 2 O 2 , as well as an extremely low detection limit of 20 nM (based on a signal-to-noise ratio of 3) for H 2 O 2 . The immobilization of proteins onto the surface of MXene-Ti 3 C 2 is shown to be an efficient method for the development of a new class of sensitive, stable, and promising electrochemical biosensors.To accomplish the direct electron transfer (DET) between an enzyme and an electrode is of great importance in fabrication of mediator-free electrochemical biosensors. 1 Because the redox-active center of proteins is embedded in its protein shell deeply, DET between the protein and the electrode surface is generally difficult. 2-6 Moreover, the enzyme usually loses its bioactivity that adsorbed directly onto the electrode surface. 1,7 These problems make it difficult to transfer electrons directly at traditional electrodes. 1 Therefore, to employ nanomaterials is an efficient way to facilitate the direct electron transfer and retain the bioactivity of immobilized enzymes. 1,[8][9][10][11][12][13][14][15][16][17] And among them, two-dimensional layered nanomaterials such as graphene 18-26 and MoS 2 , 27-29 have attracted extensive attention to being used for immobilization of biomolecules onto electrode surface due to large specific surface areas, excellent electronic transport properties, and good biocompatibility.However, as far as we know, the application of the novel graphene-like MXene-Ti 3 C 2 nanomaterial, for constructing mediatorfree biosensor has rarely been reported. In our study, MXene-Ti 3 C 2 was successfully prepared by etching Al from Ti 3 AlC 2 in HF at room temperature. [30][31][32] In general, Ti 3 AlC 2 is a promising member of a large family of layered hexagonal (space group P6 3 /mmc) ternary metal carbides and nitrides referred to as the M n+1 AX n phases, where "M" is an early transition metal, "A" is an A-group element (mostly groups 13 and 14), "X" is carbon or nitrogen, and n = 1, 2, 3, 4, 5 or 6. 33,34 This structure comprises Ti 6 C octahedra, interleaved with layers of Al atoms. Immersing Ti 3 AlC 2 phase in ...

Porous Co3O4 hexagonal nanosheets (PCHNSs) with a well-defined morphology have been synthesized successfully via a hydrothermal process and followed by calcinations. Co3O4 nanosheets immobilizing horseradish peroxidase (HRP), together with reduced graphene oxide, have been used to modify glassy carbon electrode to fabricate a mediator-free biosensor. The morphology and structure of PCHNSs are studied by XRD, FESEM, and HRTEM techniques. Spectroscopic and electrochemical results reveal that Co3O4/rGO composite film is an excellent immobilization matrix with biocompatibility for enzymes, affording good enzymes' bioactivity and stability. Meanwhile, due to the unique structure of the modified electrode, the direct electron transfer of HRP is facilitated and the prepared nitrite biosensors display good performance---a wide linear range of 1 to 5400 μM, an extremely low limit of detection (LOD) as 0.21 μM and a limit of quantification as (LOQ) as 0.58 µM. This work suggests that Co3O4/rGO composite film is a potential matrix for enzymes' immobilization and biosensors' preparation.

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Hollow TiO modified reduced graphene oxide microspheres (hollow TiO-rGO microspheres or H-TiO-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 TiO-rGO microspheres were characterized by scanning electron microscopy, transmission electronic microscopy and X-ray diffraction. Results of spectroscopy and electrochemistry tests revealed that hollow TiO-rGO microsphere is an excellent immobilization matrix with biocompatibility for redox protein, affording good protein bioactivity and stability. The hollow TiO-rGO microspheres with special structure and component enhance the immobilization efficiency of proteins and facilitate the direct electron transfer, which result in the better HO detection performance-the wide linear range of 0.1-360μM for HO (sensitivity of 417.6 μA mM cm) and the extremely low detection limit of 10nM for HO. 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 HO after 60-d storage. Hence, this work suggests that if can be fabricated a mediator-free biosensor, hollow TiO-rGO microspheres will find wide potential applications in environmental analysis and biomedical detection.