# Design, Synthesis, and Characterization of N‑Doped Carbon Dots from a Ternary System of Citric Acid, Urea, and (E)‑2-(2,5-Dimethoxyphenyl)methylenebutane-1,4-dioic Acid

## TL;DR

Researchers created new nitrogen-doped carbon dots using a green method, showing they are stable, emit blue light, and have antibacterial properties suitable for biomedical uses.

## Contribution

A new type of nitrogen-doped carbon dot (ARI-NCDs) is synthesized using a ternary system with aryl itaconic acid, offering enhanced properties for biomedical applications.

## Key findings

- ARI-NCDs show bright blue emission and higher quantum yield compared to control CDs.
- They exhibit superior thermal stability and consistent surface charge at neutral pH.
- ARI-NCDs demonstrate low cytotoxicity and strong antibacterial activity against both Gram-positive and Gram-negative bacteria.

## Abstract

Synthesizing carbon
dots (CDs) using therapeutic compounds
as precursors
has emerged as a promising strategy for biomedical applications, enabling
simultaneous utilization of the beneficial properties of both nanoparticles
and bioactive molecules without additional modification. In this work,
we report the synthesis of novel CDs (ARI-NCDs) using citric acid,
urea, and (E)-2-(2,5-dimethoxyphenyl)­methylenebutane-1,4-dioic
acid via a green, one-step hydrothermal process at 200 °C for
10 h. Control CDs prepared from citric acid and urea (U-NCDs) were
synthesized identically. Comprehensive characterization by TEM, FT-IR,
Raman, XRD and XPS confirmed nitrogen-doped, oxygen-rich surfaces
and successful aryl functionalization. ARI-NCDs exhibited bright,
nearly excitation-independent blue emission and a higher quantum yield
than U-NCDs. TGA revealed the enhanced thermal stability of ARI-NCDs
compared with U-NCDs. Zeta potential measurements across pH 4–10
indicated a single well-defined negative surface charge for ARI-NCDs
at neutral pH, consistent with superior colloidal stability and dispersion
homogeneity, while U-NCDs displayed charge heterogeneity. In vitro
assays using HeLa cells demonstrated efficient cellular internalization
of ARI-NCDs and low cytotoxicity, highlighting their suitability for
live cell imaging and other biomedical applications. Additionally,
ARI-NCDs displayed pronounced antibacterial activity against both
Gram-positive and Gram-negative bacteria with larger inhibition zones
and lower minimum inhibitory concentrations relative to U-NCDs, attributable
to the functional groups and structural attributes imparted by the
aryl itaconic acid precursor. These findings underscore the versatility
of ARI-NCDs for multifunctional biomedical applications, combining
imaging capability with antimicrobial efficacy.