Aggregation-Induced Emission (AIE)-Labeled Cellulose Nanocrystals for the Detection of Nitrophenolic Explosives in Aqueous Solutions.

Xiu Ye,Haoying Wang,Lisha Yu,Jinping Zhou

doi:10.3390/nano9050707

Abstract

Aggregation-induced emission (AIE) active cellulose nanocrystals (TPE-CNCs) were synthesized by attaching tetraphenylethylene (TPE) to cellulose nanocrystals (CNCs). The structure and morphology of TPE-CNCs were characterized by FT-IR, XRD, ζ-potential measurements, elemental analysis, TEM, atomic force microscopy (AFM), and dynamic laser light scattering (DLS). Fluorescent properties of TPE-CNCs were also further studied. Unlike aggregation-caused quenching (ACQ), TPE-CNCs emitted weak fluorescence in the dilute suspensions, while emitting efficiently in the aggregated states. The AIE mechanism of TPE-CNCs was attributed to the restriction of an intramolecular rotation (RIR) process in the aggregated states. TPE-CNCs displayed good dispersity in water and stable fluorescence, which was reported through the specific detection of nitrophenolic explosives in aqueous solutions by a fluorescence quenching assay. The fluorescence emissions of TPE-CNCs showed quantitative and sensitive responses to picric acid (PA), 2,4-dinitro-phenol (DNP), and 4-nitrophenol (NP), and the detection limits were 220, 250, and 520 nM, respectively. Fluorescence quenching occurred through a static mechanism via the formation of a nonfluorescent complex between TPE-CNCs and nitrophenolic analytes. A fluorescence lifetime measurement revealed that the quenching was a static process. The results demonstrated that TPE-CNCs were excellent sensors for the detection of nitrophenolic explosives in aqueous systems, which has great potential applications in chemosensing and bioimaging.

Highlights

As sustainable materials obtained from renewable sources, cellulose nanocrystals (CNCs) have drawn greater attention during the past few decades because of their uniform nanorod-like shape, excellent mechanical properties, high specific surface areas, large aspect ratios, sustainability, biocompatibility, biodegradability, and low cost as a well-defined nanomaterial [1,2,3,4]
As far as we know, conventional organic dyes and fluorophores are quenched at a high concentration or in a solid state, which is known as the aggregation-caused quenching (ACQ) effect
The results indicated that TPE-CNCs are excellent sensors of nitrophenolic explosives in aqueous solutions, which has promising applications for bioimaging and chemosensing

Summary

Introduction

As sustainable materials obtained from renewable sources, cellulose nanocrystals (CNCs) have drawn greater attention during the past few decades because of their uniform nanorod-like shape, excellent mechanical properties, high specific surface areas, large aspect ratios, sustainability, biocompatibility, biodegradability, and low cost as a well-defined nanomaterial [1,2,3,4]. Fluorescent dye-labeled CNCs have been reported for fluorescence sensing, bioimaging, and drug delivery [5]. Nielsen et al reported dual fluorescent labeling of CNCs that had pH-sensitive properties and could be used as sensing nanomaterials [6]. Huang et al reported a mild approach for producing pH-sensitive fluorescent CNCs by labeling dye-containing groups with L-leucine amino acids [7]. As far as we know, conventional organic dyes and fluorophores are quenched at a high concentration or in a solid state, which is known as the aggregation-caused quenching (ACQ) effect. Aggregation-induced emission (AIE) fluorophores show luminous properties opposite to the common ACQ effect [17]. An AIE fluorogen is nonemissive when molecularly dissolved, but appears as strong fluorescence in an aggregated state [18,19,20]

Methods

Results

Conclusion