Plasma chemical modification of hydroxyapatite surface to immobilise bioreceptors for biosensor applications

Introduction: Biosensors are instruments capable of providing quantitative or semi-quantitative analytical information from an identifier in the form of a bioreceptor linked to signal transduction. Nanosized hydroxyapatite (nHA) is often used as an immobilisation matrix component due to its excellent biocompatibility and high adsorption capacity. Successful immobilisation of bioreceptor molecules on the surface of the working electrode is the key to achieving high sensitivity of the biosensor. To achieve better binding of biomolecules to the nHA matrix, plasma chemical surface modification is used in the present work.

Methods: The synthesis of nHA was carried out by the chemical precipitation method. The obtained powder was characterised by XRD, FTIR, TEM, and BET, and the zeta potential was measured. To study the adsorption properties and surface modification, the nHA powder was pressed into 10 mm diameter tablets. To obtain carboxyl functional groups on the surface of the material, a perfected mode of plasma deposition from CO₂/C₂H₄/Ar gas mixture on a ZP-COVANCE-RFPE-3MP unit was used. The treated materials were investigated by SEM, EDX analysis, XPS, and WCA. The adsorption capacity was investigated using glucose oxidase enzyme as an example. Cross-linking by carbodiimide chemistry was carried out to immobilise glucose oxidase.

Results: Plasma modification resulted in successful immobilisation of glucose oxidase on the nHA surface. According to XPS data, the spectra obtained indicated the presence of carboxyl compounds on the surface of the modified samples. Plasma chemical treatment was shown to increase the bond strength between the nHA substrate and immobilised glucose oxidase molecules.

Conclusions: An approach to immobilise biomolecules on hydroxyapatite matrix has been developed, which is promising for applications in biosensors.

Funding: This work was supported by the Russian Science Foundation (grant №20-19-00120-P).