Analytical Sciences

Tyrosinase-mediated Peptide Conjugation with Chitosan-coated Gold Nanoparticles

Naomi SAKONO,* Kosuke NAKAMURA,* Tatsuki OHSHIMA,** Ryoto HAYAKAWA,** and Masafumi SAKONO**

*Department of Applied Chemistry and Chemical Engineering, National Institute of Technology, Toyama College, 13 Hongo, Toyama, Toyama 939-8630, Japan
**Department of Applied Chemistry, Faculty of Engineering, University of Toyama, 3190 Gofuku, Toyama, Toyama 930-8555, Japan

The conjugation of biomolecules, such as protein, sugar, and DNA, with metal nanoparticles is an important technique for bioassay and biomaterial preparation. In this study, we aim to enzymatically immobilize a functional peptide on gold nanoparticles (AuNPs) using a single-step reaction. We used tyrosinase, a catechol oxidase, to immobilize an enzymatic peptide. We performed immobilization experiments of a fluorescent compound-linked caspase-3 substrate peptide using tyrosinase on chitosan-coated AuNPs. Peptides were effectively immobilized onto the AuNPs depending on the presence of tyrosine within the sequence, which suggests the DOPA-quinone produced from tyrosine, via tyrosinase, is connected to the chitosan amino group. Although fluorescent emission from the immobilized capase-3 substrate was quenched by AuNPs, fluorescence intensity recovery occurred due to the addition of caspase-3. Thus, we were able to easily prepare functional AuNPs that can be used for a caspase-3 activity assay. Our results indicate that the tyrosinase-mediated peptide link to chitosan-coated particles is a useful technique for preparing functionalized nanoparticles.

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