Metal free bioimaging reagent for intracellular citrate in prostate cancer cells using aryl boronate derivative

Abstract A boronate group integrated on a triphenylimidazoleoxadiazolephenyl (TPIOP) moiety exhibited unusual sensing and detection abilities towards citrate. TPIOP boronate exhibited a bathochromic shift in its fluorescence emission upon interaction with citrate. Quantification of trace levels of citrate ions in the human body may aid in the diagnosis of prostate cancer and kidney malfunctions. Herein, a novel, metal-free sensing strategy for citrate was developed based on fluorimetric detection with TPIOP boronate. The fluorescence of TPIOP boronate increased linearly and was gradually red-shifted upon addition of citrate. The enhanced emission intensity was attributed to aggregation induced emission. The vacant ‘p’ orbital of boron in TPIOP boronate acts as a Lewis acid, and accepts electrons from citrate, which is a Lewis base. Upon binding, the hybridization geometry of boron changes from sp 2 trigonal planar to sp 3 tetrahedral. The TPIOP boronate-citrate aggregates increase the polarity of TPIOP-boronate, which caused the red shift in the fluorescence. Citrate could be detected visually using a UV lamp, as the probe changed from blue to green upon interaction with the analyte. The developed probe was applied for the visualization of endogenous citrate in PC3 live cells.