Honeycomb-like mesoporous Fe-N-C single-atom nanozyme with excellent POD-like activity: Preparation, properties, and application as a sensor array for discrimination of phenolic acids.

A colorimetric sensor array based on a mesoporous Fe-N-C single-atom nanozyme (mFeSAzyme) was fabricated for the rapid detection and discrimination of phenolic acids. Wherein, mFeSAzyme was prepared through a coordination-assisted polymerization assembly strategy, and it showed spherical morphology with uniform size distribution and honeycomb-like mesoporous structure. A large surface area (537.87 m2/g) and an abundant of Fe-N sites render mFeSAzyme to have an excellent POD-like activity. The Km values were 0.43 mM and 1.32 mM for TMB and H2O2, and the corresponding Vmax values were 49.02 × 10-8 Ms-1 and 16.42 × 10-8 Ms-1, respectively. The POD-like activity of mFeSAzyme can be regulated though various pH conditions. The significant structural differences between phenolic acids resulted in different inhibition for the POD-like activity. Given these differences, mFeSAzyme sensor array was developed using pH (3.0, 4.0, and 5.0) as three channels for five phenolic acids (rosmarinci acid, sinapic acid, gallic acid, caffeic acid, and ferulic acid) discrimination. The mFeSAzyme sensor array exhibited good discriminated capabilities even at low concentration (0.5 μM). Meanwhile, this sensor array possessed high sensitive detection for these phenolic acids. Owing to its high catalytic activity, the developed mFeSAzyme proved effective as the basis for a sensor array. This array successfully identified and measured phenolic acids in authentic samples (juice and beer) with satisfactory accuracy and precision, as evidenced by good recoveries and low RSDs. The study therefore provides a proof-of-concept for using this nanozyme to facilitate the detection and discrimination of phenolic acids in real matrices.