The colorimetric assay of diamine oxidase activity with high sensitivity based on calixarene derivative-capped gold nanoparticles

Diamine oxidase (DAO) is involved in regulating ingested or endogenous histamine, several types of human cancer, and the cell mass during embryonic development. Furthermore, DAO is a potential indicator of intestinal mucosa damage in inflammatory and neoplastic diseases or after chemotherapy. Therefore, developing a biosensor is urgently needed to assay DAO activity. In this work, a simple but sensitive colorimetric biosensor is developed for DAO assay and inhibitor screening. The biosensor is based on host-guest interactions between the amine group on the terminal of 1,6-hexanediamine (HMD) and p-sulfonatocalix[6]arene (pSC₆). These interactions may aggregate pSC₆ modified gold nanoparticles (AuNPs) and induce the corresponding color change of the test solution. Specifically, AuNP aggregation is affected because coordination reactivity does not exist between oxidized HMD and pSC₆ during HMD oxidation by DAO. Therefore, a simple colorimetric method with high sensitivity for the assay of DAO activity is proposed. A linear relationship is presented under optimized experimental conditions in a range of 0.15 mU mL⁻¹ to 4.5 mU mL⁻¹ with the lowest detection limit of 0.062 mU mL⁻¹. Moreover, the inhibition effect of guanidine on DAO activity is tested with the IC₅₀ value of 2.4 μM using the proposed biosensor. Therefore, this biosensor has great potential not only for the detection of DAO activity but also for inhibitor screening in future.