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

Abstract

Design of selective sensors for a specific analyte in blood serum, which contains a large number of proteins, small molecules, and ions, is important in clinical diagnostics. While metal and polymeric nanoparticle conjugates have been used as sensors, small molecular assemblies have rarely been exploited for the selective sensing of a protein in blood serum. Herein we demonstrate how a nonspecific small molecular fluorescent dye can be empowered to form a selective protein sensor as illustrated with a thiol-sensitive near-IR squaraine (Sq) dye (λabs= 670 nm, λem= 700 nm). The dye self-assembles to form nonfluorescent nanoparticles (Dh = 200 nm) which selectively respond to human serum albumin (HSA) in the presence of other thiol-containing molecules and proteins by triggering a green fluorescence. This selective response of the dye nanoparticles allowed detection and quantification of HSA in blood serum with a sensitivity limit of 3 nM. Notably, the Sq dye in solution state is nonselective and responds to any thiol-containing proteins and small molecules. The sensing mechanism involves HSA specific controlled disassembly of the Sq nanoparticles to the molecular dye by a noncovalent binding process and its subsequent reaction with the thiol moiety of the protein, triggering the green emission of a dormant fluorophore present in the dye. This study demonstrates the power of a self-assembled small molecular fluorophore for protein sensing and is a simple chemical tool for the clinical diagnosis of blood serum.

D-amino acid-containing supramolecular nanofibers for potential cancer therapeutics

“…Among these, self-assembling peptides have attracted increasing attentions in recent years due to their easiness in design and synthesis [15-19]. Moreover, their readily modifiable and known functional motifs, good biocompatibility, low immunogenicity, minimal toxicity, inherent biodegradability, and fast responses to external stimuli have resulted in the applications of self-assembling peptides in various biomedical applications, such as three dimensional cell culture [20-24], drug delivery [25-33], cancer therapy [34-37], immune boosting [38-41], regenerative medicine [20, 42-44], and detection of important analytes (e.g., enzymes, metal ions, bacteria) [4, 45-52]. In order to form nanostructures, a stimulus, such as heating-cooling cycle [53], sonication [54, 55], pH adjustment [22, 56, 57], assistance of organic solvent [58-60], light irradiation [61-63], chemical fuels [64, 65], as well as enzymatic reaction [66-69], usually is needed [70].…”

A protein–dye hybrid system as a narrow range tunable intracellular pH sensor

“…24 Recently, we have shown that Sq nanoparticles (SqNPs) specifically interact with serum albumin proteins (SAP), resulting in BSA and HSA specific sensors. 25 In the present work, we report a unique two-component hybrid pH sensor whose sensitivity range can be tuned for narrow pH windows by choosing different ratios of the individual components, for monitoring minute pH variations in live cells. These nanosensors have a fast and variable fluorescence response that is ideal for measuring minor pH variations with a linear response.…”

Aggregation induced Raman scattering of squaraine dye: Implementation in diagnosis of cervical cancer dysplasia by SERS imaging

“…However, in general it has the tendency to form aggregates under aqueous conditions which restricts their use in bioimaging due to the strong fluorescence quenching. (Anees et al, 2014, Gassensmith et al, 2009Sreejith et al, 2012).…”