Towards a microscale characterization of TEP-like organic aggregates: a comprehensive suite for image analysis of two-dimensional and three-dimensional structures

Abstract

Transparent exopolymer particles (TEP) are abundant gel-like colloids pivotal in marine carbon cycling and water treatment processes. Their environmental roles are governed by hierarchical architectures, yet in-situ structural characterization remains challenging due to transparency, fragility, and polymorphism. To address this, we developed an integrated image analysis suite combining advanced processing with statistical modeling, enabling simultaneous 2D/3D quantification of TEP morphology and intra-particle heterogeneity. This framework generates multidimensional descriptors (e.g., fractal dimensions, density gradients) for individual aggregates and assemblies. Applied to cation-mediated aggregation, it revealed divergent bridging behaviors. Mg²⁺ induced moderate size changes (2.99–4.08 μm), while Ca²⁺ drove exponential growth (1.81–187.76 μm) when ionic strength increasing from 1 to 5 mmol/L. Concurrent form factor reductions (Mg: 0.31 to 0.16; Ca: 0.44 to 0.19) quanti-tatively distinguish aggregation pathways. The method deciphers ion-specific assembly mechanisms and resolves subtle colloidal interactions, establishing a paradigm for colloidal system analysis with possible applications extending beyond TEP research to other subjects such as microplastic aggregation.

Graphical abstract

Keywords

Transparent exopolymer particles / Image analysis / Morphological features / 2D and 3D modelling

Highlight

	● A suite processes for quantitative characterization of dyed TEPs is presented.
	● The suite was employed to assess the influence of Ca2+ and Mg2+ on the TEP.
	● The result indicates significant difference of Ca2+ and Mg2+ in bridging effect.
	● This method can provide indications for other transparent organic aggregations.

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