# Size- and Concentration-Resolved Detection of PET Microplastics in Real Water via Excitation–Emission Matrix Fluorescence Quenching of Polyamide-Derived Carbon Quantum Dots

## TL;DR

A new method uses carbon quantum dots to detect PET microplastics in water, overcoming interference from other substances and particle size differences.

## Contribution

A fluorescence-based method using PACQDs enables size- and concentration-resolved detection of PET microplastics in real water.

## Key findings

- PACQDs show a fluorescence 'turn-off' response to PET microplastics, with sensitivity varying by particle size.
- Multivariate EEM analysis distinguishes true quenching from optical interferences like scattering and inner-filter effects.
- The method achieves reliable detection of small PET microplastics in tap water with high recovery rates.

## Abstract

What are the main findings?
Polyamide-derived carbon quantum dots enable size- and concentration-resolved fluorescence detection of PET microplastics.Excitation–emission matrix analysis with PCA/PARAFAC separates true quenching from scattering and inner-filter effects.

Polyamide-derived carbon quantum dots enable size- and concentration-resolved fluorescence detection of PET microplastics.

Excitation–emission matrix analysis with PCA/PARAFAC separates true quenching from scattering and inner-filter effects.

What are the implications of the main findings?
Multivariate EEM fluorescence improves reliability of microplastic sensing in complex water matrices.The approach supports selective, matrix-robust detection of small PET microplastics in real water samples.

Multivariate EEM fluorescence improves reliability of microplastic sensing in complex water matrices.

The approach supports selective, matrix-robust detection of small PET microplastics in real water samples.

The selective detection of microplastics (MPs) in aquatic environments is hindered by particle size diversity and matrix-induced interferences. This study reports an excitation–emission matrix (EEM) fluorescence sensing platform using polyamide-derived carbon quantum dots (PACQDs; 0.5–2.6 nm) for the size- and concentration-resolved detection of polyethylene terephthalate MPs (PETMPs). PACQDs exhibited a pronounced fluorescence “turn-off” response upon PETMP interaction, governed by particle size (10–149 μm) and loading (4–8 g L−1). Small PETMPs (10 μm) followed linear Stern–Volmer behavior, achieving a detection limit of 1.67 mg L−1 in deionized water. Conversely, larger particles induced non-linear optical effects, including scattering-driven enhancement and inner-filter effects. Multivariate analysis using PCA and PARAFAC resolved three distinct components associated with surface-state quenching, scattering-mediated redistribution, and surface area-driven binding. Component-specific scores confirmed that PACQDs are most sensitive to small PETMPs, while larger particles primarily introduce optical interference. Selectivity tests showed distinct discrimination of PETMPs over polyamide and polypropylene. In tap water, significant matrix effects were corrected via matrix-matched calibration, achieving recoveries within 80–120%. This study establishes EEM-based multivariate fluorescence as a mechanism-informed strategy for PETMP sensing, highlighting the robust applicability of PACQDs for monitoring small PETMPs in real-world water matrices.