Sol–gel hydrothermal synthesis and enhanced biosensing properties of nanoplated lanthanum-substituted bismuth titanate microspheres

Abstract

Nanoplated lanthanum-substituted bismuth titanate (Bi_3.25La_0.75Ti₃O₁₂, BLTO) microspheres constructed with tens of BLTO nanoplates were synthesized by a sol–gel hydrothermal method. Using nanoplated BLTO microspheres, a novel third-generation H₂O₂ biosensor was fabricated with loading of myoglobin (Mb) and chitosan (Chi). Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) measurements reveal that partial Bi ions of bismuth titanate (BTO, Bi₄Ti₃O₁₂) are successfully substituted with La ions by the sol–gel hydrothermal method. UV-visible (UV-vis) and Fourier-transform infrared (FTIR) spectra show that Mb encapsulated in the Mb–Chi–BLTO film can retain its bioactivity well. Comparative experiments witness that the Mb–Chi–BLTO biosensor, compared with the Mb–Chi–BTO biosensor, not only has enhanced direct electron-transfer capacity (e.g., stronger redox peak currents (approximately 3-fold) and a larger heterogeneous electron-transfer rate constant of 12.8 ± 3.3 s⁻¹), but also exhibits a wider linear response to H₂O₂ in the concentration range of 2–490 μM, higher sensitivity (88 mA cm⁻² M⁻¹), a lower Michaelis–Menten constant (0.55 mM) and detection limit (0.14 μM), a shorter response time (2.8 s), and better reproducibility and stability. These results imply that La doping greatly improves electrochemical and electrocatalytic properties of the Mb–Chi–BLTO biosensor, which will open up a new idea for the design of third-generation electrochemical biosensors, and the BLTO-based biosensors are also expected to find potential applications in many areas such as clinical diagnosis and food and environmental detection.