Nitrogen-doped carbon dots prepared from bovine serum albumin to enhance algal astaxanthin production

The aim of this work was to use green and simply synthesized nitrogen-doped carbon dots (N@CDs) based on carbonized bovine serum albumin (BSA) to boost the accumulation of astaxanthin in microalgae. The BSA carbon dots revealed a high blue emission having a quantum yield of up to 44%, which is superior to all previously reported carbon dots. By directly adding the N@CDs at low concentrations (1 mg L^{− 1}) to the algal culture of Haematococcus pluvialis, astaxanthin production increased more than two-fold (66 mg L^{− 1}), compared to the control (29 mg L^{− 1}), in a shorter time of 1 week instead of 2 weeks at the reddening stage. After 1 month of continuous irradiation, the HRTEM images and fluorescence spectra of N@CDs looked similar to as-prepared N@CDs, suggesting their photostability and reusability. Our novel N@CDs could be a promising tool for the future industry of natural astaxanthin and other value-added products from microalgae.