Temperature-Responsive Poly(N-isopropylacrylamide) Modified Gold Nanoparticle–Protein Conjugates for Bioactivity Modulation

It is important to effectively maintain and modulate the bioactivity of protein-nanoparticle conjugates for their further and intensive applications. The strategies of controlling protein activity via "tailor-made surfaces" still have some limitations, such as the difficulties in further modulation of the bioactivity and the proteolysis by some proteases. Thus, it is essential to establish a responsive protein-nanoparticle conjugate system to realize not only controllable modulations of protein activity in the conjugates by incorporating sensitivity to environmental cues but also high resistance to proteases. In the work reported here, Escherichia coli (E. coli) inorganic pyrophosphatase (PPase) and poly(N-isopropylacrylamide) (pNIPAM) were both fabricated onto gold nanoparticles (AuNPs), forming AuNP-PPase-pNIPAM conjugates. The bioactivity-modulating capability of the conjugates with changes in temperature was systematically investigated by varying the molecular weight of pNIPAM, the PPase/pNIPAM molar ratio on AuNP, and the orientation of the proteins. Under proper conditions, the activity of the conjugate at 45 °C was approximately 270% of that at 25 °C. In the presence of trypsin digestion, much less conjugate activity than protein activity was lost. These findings indicate that the fabrication of AuNP-protein-pNIPAM conjugates can both modulate protein activity on a large scale and show much higher resistance to protease digestion, exhibiting great potential in targeted delivery, controllable biocatalysis, and molecular/cellular recognition.