Enhanced green fluorescence protein/layered double hydroxide composite ultrathin films: bio-hybrid assembly and potential application as a fluorescent biosensor

Protein immobilization is of significant interest for applications in biosensing, drug delivery and bioconversion, and challenges still remain for the in vitro immobilization and application of proteins. Due to it being non-specific to species, easy to express in cells and able to exhibit fluorescence after expression without the need for cofactors or chaperones, green fluorescent protein (GFP), together with its differently colored mutants, has been widely studied and applied. This article reports the fabrication of enhanced green fluorescent protein (EGFP)/layered double hydroxide nanosheet (EGFP/LDH)(n) ultrathin films (UTFs) via a layer-by-layer assembly technique based on electrostatic and hydrogen-bond interactions, and this realized the immobilization of EGFP. The obtained UTFs show a long-range-ordered periodic layered stacking structure and strong fluorescence originating from EGFP, which also retains its predominant beta-barrel structure well in the LDH laminates. The inorganic LDH laminates play an important role in protecting and improving the structure and properties of the EGFP in the UTFs. Furthermore, the UTFs exhibit a reversible fluorescence response between different pH environments or different wet or dry environments, and also could detect some small biological medicine molecules such as protoporphyrin, and thus they have the potential to be a novel type of biological fluorescence sensor.