Ultrasensitive Stimulation Effect of Fluoride Ions on a Novel Nanozyme–SERS System

Abstract

Recently, nanomaterial-based enzyme mimics (nanozymes) have captured extensive interest owing to their high stability and low cost compared with natural enzymes. The mechanism of the stimulation effect of external substances on the nanozymes and their sensing applications are significantly attractive. In this study, we have constructed an excellent nanozyme−SERS system based on reduced MnCo 2 O 4 /Au nanotubes (R-MnCo 2 O 4 /Au NTs) through a selfreduction process with the assistance of oxygen vacancies. In the R-MnCo 2 O 4 /Au NTs, R-MnCo 2 O 4 possesses rich oxidation states of Mn 2+ / Mn 3+ and Co 2+ /Co 3+ , giving them excellent peroxidase-like catalytic activity; on the other hand, Au NPs on the surface of R-MnCo 2 O 4 NTs contribute to their favorable SERS activity. Meanwhile, the important contribution of •OH and O 2•− radicals in the catalytic mechanism of nanozymes was proposed. Furthermore, the peroxidase-like activity of the R-MnCo 2 O 4 /Au NTs is reduced with the introduction of fluoride, which is related to the inhibition of the formation of •OH radicals. Owing to the inhibition effect, an ultrasensitive sensing platform for fluoride detection was developed. The work in this study provides a deep insight into the mechanism of the catalytic activity of nanozymes and opens up broad promising prospects in biosensing.

Defect engineering in semiconductor-based SERS

“…In another example, Wen et al have studied the nanoenzyme properties of reduced MnCo 2 O 4 with the aid of Au NPs to boost its SERS activity. 126 They also reported a SERS-kinetic model which monitored the oxidation of tetramethylbenzidine (TMB), based on reduced MnCo 2 O 4 nanotubes, which had the double function of the SERS substrate and oxidase ( Fig. 8d ).…”

“…The production of *OH species is identied in situ, which is attributed to the oxygen vacancies on the CuO surface which act as absorption and activation sites for H 2 O 2 . In another example, Wen et al have studied the nanoenzyme properties of reduced MnCo 2 O 4 with the aid of Au NPs to boost its SERS activity 126. They also reported a SERS-kinetic model which monitored the oxidation of tetramethylbenzidine (TMB), based on reduced MnCo 2 O 4 nanotubes, which had the double function of the SERS substrate and oxidase (Fig.8d) 127.…”

Nanozyme Applications: A Glimpse of Insight in Food Safety

“…The nanozyme probe showed a linear range of 1–100 nM and a LOD of 0.1 nM using the TMB/H 2 O 2 system. Besides, Wen et al developed a nanozyme–SERS system for detection of fluoride based on reduced MnCo 2 O 4 /Au nanotubes, which revealed the key roles of •OH and O 2 •– radicals in the catalytic mechanism of nanozymes ( Wen et al, 2020 ). The constructed methods are adopting the inhibition principle of heavy metal ions (Cu 2+ ) or anion (F − ) toward the catalytic activity of nanozymes.…”

“…•radicals in the catalytic mechanism of nanozymes (Wen et al, 2020). The constructed methods are adopting the inhibition principle of heavy metal ions (Cu 2+ ) or anion (F − ) toward the catalytic activity of nanozymes.…”

SERS Resolving of the Significance of Acetate on the Enhanced Catalytic Activity of Nanozymes

“…Surface-enhanced Raman spectroscopy (SERS) has been widely used in biosensing, environmental monitoring, and food safety due to its particular advantages of single-molecule-level detection sensitivity from spectral fingerprint information. − Recently, SERS technology has shown a promising application to study a variety of nanozyme-based catalytic systems, presenting a highly sensitive in situ monitoring capacity . However, due to the weak SERS activity of some TMO materials while with high peroxidase-like activities, it is necessary to introduce SERS-active materials such as Au and Ag, to achieve a synergistic enhancement of SERS and catalytic activity through manipulating their compositions and architecture. − Recently, Zhu and co-workers proposed a SERS-borrowing strategy for direct determination of reactive oxygen species (ROS), opening the prelude to directly determine the catalytic intermediates of nanozymes through the SERS technology . It is time to use SERS technology to directly clarify the internal catalytic mechanism of nanozymes in HAc-NaAc buffer environment.…”