A smartphone-assisted on-site colorimetric sensing for total amount determination of leuco-malachite green and malachite green based on nanozyme selected oxidation strategy

The total amount of malachite green (MG) and leuco-malachite green (LMG) is the safety target for evaluating MG residues in aquatic products. In this work, we propose for the first time a nanozyme oxidation strategy for rapid detection of the total amount of MG and LMG. Nanozymes Poly (sodium 4-styrenesulfonate) (PSS) doped metal-organic frameworks ZIF-67 (PSS/ZIF-67) was fabricated and used as oxidizing agent. PSS/ZIF-67 could rapidly and selectively on-site oxidate LMG into MG. Based on this oxidative transformation and the typical absorption of MG at 618 nm, a colorimetric sensing for the total amount of MG and LMG detection was established. This method not only achieves the simple and rapid determination of total MG residue, but also avoids interference from the sample matrix. The whole procedure from extraction to detection end was no more than 10.0 min. Furthermore, with test strip immobilization technology and mobile phone, a portable visual strip platform for total amount of LMG and MG in fish also was fabricated. Such a nanozyme oxidation strategy supplied new avenue for high throughput market monitoring of aquatic products.