High sensitive and discriminating colorimetric assay for S overload in adaptogenic herbs utilizing ZnS nanoparticle-enhanced S, N-doped eggshell membrane-derived biochar.

Background: With the rapid development of industrialization, the excessive emission of S have become increasingly serious, leading to a surge in the content of S in nature. Rapid and accurate detection of S contamination in natural adaptogens is crucial for food safety. Annually, discarded eggshell waste, rich in organic and inorganic materials, poses environmental risks if landfilled. Utilizing waste eggshell membrane biomass for S detection is cost-effective, yet designing biochar materials for sensors requires balancing catalytic enhancement and anti-interference capabilities. Improving the catalytic performance of biochar for colorimetric S detection without metal ion interference presents a challenging issue.

Results: We first modified biochar (EBc) derived from waste eggshell membranes using a combination of thiourea and ZnS nanoparticles, fabricating ZnS-decorated, S-N co-doped biochar (ZnS-SN-EBc) nanozymes, which were applied for the colorimetric assay detection of S contamination. The addition of thiourea significantly increases the proportion of pyridinic-N in biochar, enhancing the peroxidase-like activity of the nanozyme. The growth of ZnS nanoparticles on the biochar not only enhances the catalytic performance by increasing the S content but also reduces the content of oxidized S, thereby improving resistance to interference. The detection range for S was expanded from 0.1 to 45 μM for EBc to 0.05-225 μM for ZnS-SN-EBc, and the limit of detection improved to 0.0397 μM. Additionally, ZnS-SN-EBc significantly enhanced metal ion interference resistance. S detection in five types of adaptogenic herbs verified the accuracy and practicality of the colorimetric assay, with recovery rates comparable to national standards.

Significance: We innovatively repurposed waste eggshell membranes to develop a selective and catalytic peroxidase-like nanozyme, ZnS-decorated S-N co-doped biochar (ZnS-SN-EBc). The developed colorimetric assay utilizing ZnS-SN-EBc demonstrates significant potential for the detection of sulfur ions in adaptogenic herbs, thus contributing to both waste resource utilization and the advancement of food safety detection technologies.