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  • Self-Assembled Near-Infrared Dye Nanoparticles as a Selective Protein Sensor by Activation of a Dormant Fluorophore

Self-Assembled Near-Infrared Dye Nanoparticles as a Selective Protein Sensor by Activation of a Dormant Fluorophore

Design of selective sensors for a specific analyte in blood serum,which contains a large number of proteins, small molecules, and ions, isimportant in clinical diagnostics. While metal and polymeric nanoparticleconjugates have been used as sensors, small molecular assemblies have rarelybeen exploited for the selective sensing of a protein in blood serum. Herein wedemonstrate how a nonspecific small molecular fluorescent dye can beempowered to form a selective protein sensor as illustrated with a thiolsensitivenear-IR squaraine (Sq) dye (λabs= 670 nm, λem= 700 nm). The dyeself-assembles to form nonfluorescent nanoparticles (Dh = 200 nm) whichselectively respond to human serum albumin (HSA) in the presence of otherthiol-containing molecules and proteins by triggering a green fluorescence.This selective response of the dye nanoparticles allowed detection andquantification of HSA in blood serum with a sensitivity limit of 3 nM. Notably,theSq dye in solution state is nonselective and responds to any thiolcontainingproteins and small molecules. The sensing mechanism involves HSA specific controlled disassembly of the Sqnanoparticles to the molecular dye by a noncovalent binding process and its subsequent reaction with the thiol moiety of theprotein, triggering the green emission of a dormant fluorophore present in the dye. This study demonstrates the power of a self-assembledsmall molecular fluorophore for protein sensing and is a simple chemical tool for the clinical diagnosis of blood serum.J. Am. Chem. Soc.2014, 136, 13233−13239