# Two-Step Non-Food Valorization of Phaleria macrocarpa Fruit Lignin into Lignin Nanoparticles and Quantum Dots for Antibacterial and Bioimaging Applications

## TL;DR

Researchers converted lignin from Phaleria macrocarpa fruit into useful nanomaterials that can be used for imaging and fighting bacteria.

## Contribution

A two-step, green method to convert non-food lignin into photoluminescent lignin quantum dots with antibacterial and bioimaging properties.

## Key findings

- Lignin quantum dots (LQDs) were produced with a narrow size distribution (3–5 nm) and blue–green fluorescence.
- LQDs showed high cytocompatibility and were internalized by cells for live-cell imaging.
- The LQDs demonstrated antibacterial activity against both Gram-positive and Gram-negative strains.

## Abstract

Lignin from Phaleria macrocarpa (Mahkota Dewa) fruit, a bioactive-rich cultivated medicinal biomass, was employed as a renewable precursor for lignin quantum dots (LQDs). A simple, aqueous, catalyst-free two-step route (lignin to lignin nanoparticles to LQDs) is demonstrated, enabling the valorization of non-food lignin into photoluminescent nanomaterials. The resulting LQDs were predominantly amorphous with short-range graphitic ordering and a narrow particle size distribution (3–5 nm). Structural and chemical analyses indicated a partially graphitized carbon framework enriched with oxygenated surface functionalities, which is consistent with their bright blue–green emission (λem of 490 nm; average fluorescence lifetime of 4.51 ns). Hydrothermal carbonization induced a blue shift in the UV–Vis absorption profile, resulting in a main band at 288 nm with a shoulder at 312 nm. The LQDs exhibited high cytocompatibility toward L929 mouse fibroblasts (93.1 ± 6.5% viability at 24 h) and were readily internalized by cells, facilitating green fluorescence live-cell imaging as a proof-of-concept. Antibacterial activity was observed against both Gram-positive and Gram-negative strains, supporting dual biofunctional performance. Overall, this study established a green and scalable route for converting P. macrocarpa fruit lignin into multifunctional LQDs, with potential applications in circular-bioeconomy such as antimicrobial/active coatings and optical sensing in agro-industrial contexts.