A Fluorescent Self-Assembled Chemosensor Array on Paper for Saccharides and Carboxylic Acids in Fermented Rice Mash during a Sake Brewing Process

The taste of Japanese rice wine (sake) is significantly affected by the production process that involves concentration changes in sake components (i.e., saccharides and carboxylic acids). We herein propose a self-assembled fluorescent chemosensor array made of a paper substrate to simultaneously detect sake components in fermented rice mash during the sake brewing process. The chemosensors are formed by self-assembling building blocks (i.e., esculetin as a fluorophore and 3-nitrophenylboronic acid and a cobalt(II) ion as target-binding sites). The detection mechanism relies on competitive interactions between sake components and the building blocks of the chemosensors, which provide various optical patterns on the paper device. Indeed, the paper device has achieved not only qualitative detection of nine types of analytes (glucose, maltose, pyruvic acid, acetic acid, pyroglutamic acid, lactic acid, succinic acid, malic acid, and citric acid) with an 89% classification rate but also semiquantitative discrimination of glucose and pyruvic acid with 100% correct classification. In this regard, its limits of detection for glucose and pyruvic acid were estimated to be 2.1 and 0.62 mM, respectively. Furthermore, recovery rates of glucose and pyruvic acid in fermented rice mash were 95–104% and 97–110%, respectively.