2.3 Scanning electron microscopy
BL21 (DE3) and BL21 (DE3-lac1G) cells harboring the pET24a-GDH expression vector were cultured as described above, and samples were collected at 24h and 43h, respectively. Samples were fixed overnight at 4°C in 2.5% glutaraldehyde in 0.1 M cacodylate buffer (pH 7.2) and then stained with 2% OsO4 in the same buffer. Then, samples were dried at critical point and coated with platinum. Observations were made using a Tecnai FEG ESEM Quanta 200 microscope (FEI Corp, USA), and images were recorded using SIS iTEM software (Olympus Corp, Japan).