Polyphosphonate induced coacervation of chitosan: Encapsulation of proteins/enzymes and their biosensing

•The ionotropic crosslinking interactions result in the coacervation of chitosan.•A phosphonate-assisted encapsulation of proteins in chitosan matrix is introduced.•The encapsulated proteins retain their bioactivity.•The encapsulation method can be used to fabricate various chitosan-based biosensors.

Based on the polyphosphonate-assisted coacervation of chitosan, a simple and versatile procedure for the encapsulation of proteins/enzymes in chitosan–carbon nanotubes (CNTs) composites matrix was developed. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectrum (EDS) mapping demonstrated the hemoglobin (Hb) uniformly distributed into chitosan–CNTs composites matrix. Raman measurements indicated the CNTs in composites matrix retained the electronic and structural integrities of the pristine CNTs. Fourier transform infrared (FT-IR), ultraviolet–visible (UV–vis) and circular dichroism (CD) spectroscopy displayed the encapsulated Hb preserved their near-native structure, indicating the polyphosphonate–chitosan–CNTs composites possessed excellent biocompatibility for the encapsulation of proteins/enzymes. Electrochemical measurements indicated the encapsulated Hb could directly exchange electron with the substrate electrode. Moreover, the modified electrode showed excellent bioelectrocatalytic activity for the reduction of hydrogen peroxide. Under optimum experimental conditions, the fabricated electrochemical sensor displayed the fast response (less than 3 s), wide linear range (7.0 × 10−7 to 2.0 × 10−3 M) and low detection limit (4.0 × 10−7 M) for the determination of hydrogen peroxide. This newly developed protocol was simple and mild and would certainly find extensive applications in biocatalysis, biosensors, bioelectronics and biofuel cells.

Graphical abstractBased on the coacervation of chitosan via the ionotropic crosslinking interaction, proteins/enzymes can be encapsulated in situ into chitosan matrix.Figure optionsDownload full-size imageDownload as PowerPoint slide