Gold nanozyme as an excellent co-catalyst for enhancing the performance of a colorimetric and photothermal bioassay

Abstract

Advanced oxidation processes (AOPs) have recently proposed for advancing colorimetric sensing applications, owing to their excellent performance of sensitive color readout that generated from the oxidation of chromogenic substrates like 3,3',5,5'-tetramethylbenzidine (TMB) by reactive oxygen species (ROS) of AOPs such as ·OH and ·O₂^- radicals. However, the efficiency of ROS generation and the related H₂O₂ decomposition in most AOPs is quite low especially at neutral pH, which greatly hampered the practical sensing applications of the AOPs. We herein communicated that β-cyclodextrin (β-CD)-capped gold nanoparticles (β-CD@AuNPs) can promote catalysis at neutral pH for AOP as an excellent co-catalyst. In this strategy, inorganic pyrophosphate (PPi) ions was first used to coordinate with Cu²⁺ and form Cu²⁺-PPi complex. In the presence of hydrogen peroxide, target inorganic pyrophosphatase (PPase) can hydrolyze PPi into inorganic phosphate (Pi) and release free Cu²⁺ simultaneously, resulting in a Cu²⁺-triggered Fenton-like AOP reaction. The introduced β-CD@AuNPs acts as a co-catalyst, analogous to mediators in the most co-catalyzed system, to enhance the rate-limiting step of Cu²⁺/Cu⁺ conversion in Cu²⁺/H₂O₂ Fenton-like AOP and resulting in an efficient generation of ·OH and ·O₂^- radicals, which further producing an intense blue color by oxidizing TMB into its oxidation product (TMBox) within a short time. Finally, this reaction system was used to simply detecting target PPase with the colorimetric and photothermal readout based on the in-situ generated TMBox indicator. More significantly, we successfully demonstrated nanozyme can serve as a co-catalyst to promote the AOP catalysis at neutral pH, and inspire other strategies to overcome the pH limitation in the AOP catalysis and expand its colorimetric and photothermometric application.

Keywords: Co-catalyst; Colorimetric; Gold nanoparticles; Nanozyme; Photothermal.