Discovery of Surface‐Induced Resonance Shift of 4‐Nitrophenol Enabling Direct Monitoring of an Enzymatic Reaction

Chromogenic and fluorogenic substrates are important for the detection of enzymatic activity. Conjugates of 4‐nitrophenol are among the earliest investigated classes of molecules and have been used in diagnostic applications, including those for type‐2 diabetes. The detection of 4‐nitrophenol under physiological conditions enables real‐time monitoring of glucosidase activity. This becomes possible when the resonance structure of 4‐nitrophenol is altered, making it distinguishable from its precursor chromogenic substrate. One of the surface‐modified silica materials, comprising an acetyl‐protected mannoside along with precipitated byproducts such as acyl‐urea and urea formed during carbodiimide coupling, induces a unique resonance shift in 4‐nitrophenol upon interaction. Raman microscopic analysis can distinguish the phenol‐type band at 1330 cm −1 and the quinone‐type band at 860 cm −1 , thereby enabling monitoring of the α‐glucosidase reaction.