Real-time Monitoring of Turbidity Changes of Solution Induced by Polymer Nanoparticle Using Fluorescent Probes

Abstract

Although numerous fluorophores have been developed for visual detection of viscosity in homogeneous systems, the real-time monitoring of turbidity variations in heterogeneous systems using fluorescent probes remains a significant challenge—particularly when the suspended particles are non-emissive and nanometer size. Here, we report a phenanthridine-based fluorophore (PTF2) capable of in situ tracking turbidity changes arising from polymer chain assembly, nucleation, and subsequent particle growth through discernable fluorescence changes. Specifically, the intrinsic blue fluorescence of PTF2 in a homogeneous polymer solution undergoes a pronounced bathochromic shift as the polymer chains begin assembling into nanoscale aggregates. Continued growth of these aggregates results in further redshifts in emission (exceeding 100 nm), enabling a good correlation between emission wavelength and particle size. Notably, even subtle increases in aggregate size—on the order of tens of nanometers—elicit significant emission changes. Mechanistic investigations reveal that the strong polar-π interactions and molecular orbital energy alignment between the fluorophore and polymer assemblies underpin this sensing capability. This work provides a robust and sensitive platform for real-time detection of turbidity changes that are beyond the reach of conventional methods and offers great potential in tracking the nanoplastic pollution in a variety of water bodies including oceans, lakes, and rivers.