Exponential Amplification Using Photoredox Autocatalysis

Abstract

Exponential molecular amplification such as the polymerase chain reaction is a powerful tool that allows ultrasensitive biodetection. Here we report a new exponential amplification strategy based on photoredox autocatalysis,\nwhere eosin Y, a photocatalyst, amplifies itself by activating a non-fluorescent eosin Y derivative (EYH2) under green light.\nThe deactivated photocatalyst is stable and rapidly activated under low intensity light, making the eosin Y amplification\nsuitable for resource-limited settings. Through steady-state kinetic studies and reaction modeling, we found that EYH2 is\neither oxidized to eosin Y via one-electron oxidation by triplet eosin Y and subsequent 1e─/H+ transfer, or activated by\nsinglet oxygen with the risk of degradation. By reducing the rate of the EYH2 degradation, we successfully improved EYH2-\nto-eosin Y recovery, achieving efficient autocatalytic eosin Y amplification. Additionally, to demonstrate its flexibility in\noutput signals, we coupled the eosin Y amplification with photo-induced chromogenic polymerization, enabling sensitive\nvisual detection of analytes. Finally, we applied the exponential amplification methods in developing bioassays for detection\nof biomarkers including SARS-CoV-2 nucleocapsid protein, an antigen used in the diagnosis of COVID-19