Thermoresponsive protein nanocapsules were prepared via in situ precipitation polymerization using protein bovine serum album (BSA) as the model protein

N-isopropyl acrylamide (NIPAM) as the monomer

and N

N'-methylene bis-acrylamide (BIS) as the crosslinker.To synthesize such nanocapsules

BSA was first attached with polymerizable groups through reacting with N-acryloxysuccinimide (NAS)

and the degree of reaction was examined using MALDI-TOF mass spectrometer.By adjusting the NIPAM/BSA ratio

BSA nanocapsules (nBSA) with different sizes (7.4 nm to 17 nm) were synthesized successfully and confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM).Thermoresponsive behavior of nBSA was studied by monitoring the size-temperature trending test through DLS.Reversible thermoresponsive property of obtained nBSA was observed from DLS test

with responsive temperatures ranging from 33℃ to 41℃ accordingly of different sized protein nanocapsules synthesized from various NIPAM/BSA ratios.There is an obvious particle size increase of all synthesized BSA nanocapsules after their exposure to higher temperatures above their responsive ones.The observed particle sizes of nBSA at higher temperatures were increased by 16 to 33 times accordingly.By observing the HeLa cell viability after incubation with the nanocapsules at different concentrations for 24 h

the result shows the nanocapsules exhibit low cytotoxicity.This work provides a new synthesis method of thermoresponsive protein nanocapsules for various applications.