Laser particle size analyzer

Expression and purification of OmpA were performed as described previously [16 (link)]. Briefly, the OmpA expression strain was cultured overnight and transferred to 600 mL LB medium until OD₆₀₀ nm = 0.5. Isopropyl-β-d-thiogalactoside (IPTG) was then added and induced at 20 ℃ for 24 h. Bacterial cells were harvested by centrifugation and disrupted by sonication with an ice bath. Finally, OmpA was purified with the Ni-NTA flow resin (Sigma, St. Louis, MO, USA).
The OmpA nanoparticles (NP-OmpA) were prepared by CS encapsulation. Briefly, tripolyphosphate (TPP) (3 mL, 1 mg/mL) was added dropwise to a CS solution (10 mL, 1 mg/mL), and stirred for 10 min at 700 r/min. After centrifugation (15 min at 9500 r/min), the precipitate was added to 25 mL of water and subjected to ultrasound (2 min at 50% power). Then 3 mL of OmpA was added dropwise. After centrifugation, 10 mL of water was added to the precipitate to obtain the NP-OmpA. Nanoparticle diameter and zeta potential were analyzed using a Laser Particle Size Analyzer (Beckman, Fullerton, CA, USA), and the morphology was observed using a scanning electron microscope (Phenom Pro, Eindhoven, The Netherlands) [17 (link)].