A selective dual-response biosensor for tyrosinase monophenolase activity based on lanthanide metal-organic frameworks assisted boric acid-levodopa polymer dots

Tyrosinase (TYR) monophenolase activity plays a key role in the development of diseases such as melanoma. The selective and sensitive detection of TYR monophenolase activity is a persistent challenge. Here, by integrating fluorescent polymer dots and a luminescent lanthanide metal-organic framework (Ln-MOF), we proposed an on-off dual-response biosensor for the sensitive and selective detection of TYR monophenolase. The Ln-MOF was prepared with Eu3+ and monoaromatic ligand dipicolinic acid (DPA), and it plays multiple functions such as fluorescent internal standard, chromaticity shift enhancement and fluorescence sensing. In alkaline boric acid (BA) buffer, L-tyrosine is converted into BA-levodopa by TYR monophenolase. Then, with the assistance of Eu-DPA, BA-levodopa is initiated by diethylaminepropyltrimethoxysilane (DAMO) to generate BA-levodopa polymer dots, which turn on strong blue fluorescence (crosslink-enhanced emission) and meanwhile quench the red fluorescence of Eu-DPA through enhanced photo-induced electron transfer. Thus, the sensitive and selective dual-response sensing to TYR monophenolase is achieved. Both DAMO and BA play significant roles in the synthesis of strong fluorescence polymer dots, and another key role of BA is to inhibit TYR diphenolase activity. Furthermore, chromaticity shift value-based quantification greatly improves the response linearity. The linear range is 0.05-2 U mL-1 (r = 0.9966), and the limit of detection is 0.004 U mL-1. The precise and accurate quantification of TYR monophenolase activity in saliva samples is realized (recovery of 96.9-102.0%, relative standard deviation < 9.56%). To our knowledge, it is the first highly-sensitive double-response biosensor for TYR monophenolase activity.