Carbon-based nanomaterials, particularly carbon dots (C-dots) have emerged as outstanding candidates for several areas such as biomedicine, (bio)sensors, photocatalysis, optoelectronics and bioimaging, due to their excellent luminescence, photostability, small size, low cytotoxicity, and biocompatibility.

C-dots can be prepared by several procedures (top-down and bottom-up methods), using various carbon sources. Bottom-up green approaches based on the use of renewable biomass precursors for producing C-dots are particularly attractive since an effective reduction of environmental impacts of those wastes can be foreseen, while high-valued nanomaterials can be obtained, contributing to a circular economy.

In this work, we highlight recent green synthesis of C-dots from Porphyridium cruentum biomass, a red marine microalga, expecting that the
as-synthesized nanoparticles have good luminescence, biocompatibility, and antioxidant capabilities. The obtained nanomaterials were characterized regarding surface functional groups by FTIR spectroscopy and optic properties using UV-Vis and fluorescence spectroscopies. Antioxidant properties were explored through the ABTS assay, and their cytotoxicity was evaluated against Vero and HeLa cell-lines.

Fluorescence microscopy images were acquired and showed that C-dots have good interaction with the cell plasma membrane, encouraging their use on bioimaging.