Detection of yeast Saccharomyces cerevisiae with ionic liquid mediated carbon dots

Hydrophobic nitrogen-doped carbon dots are prepared with energetic ionic liquid (1,3-dibutylimidazolium dicyandiamide, BbimDCN) as carbon source. A yield of as high as 58% is obtained for the carbon dots, shortly termed as BbimDCN-OCDs, due to the presence of thermal-instable N(CN)₂^- moiety. BbimDCN-OCDs exhibit favorable biocompability and excellent imaging capacity for fluorescence labelling of yeast cell Saccharomyces cerevisiae. In addition, chitosan-modified Dy³⁺-doped magnetic nanoparticles (shortly as Chitosan@Fe_2.75Dy_0.25O₄) with superparamagnetism are prepared. The electrostatic attraction between positively charged magnetic nanoparticles and negatively charged yeast cells facilitates exclusive recognition/isolation of S. cerevisiae. In practice, S. cerevisiae is labelled by BbimDCN-OCDs and adhered onto the Chitosan@Fe_2.75Dy_0.25O₄. The yeast/ BbimDCN-OCDs/Chitosan@Fe_2.75Dy_0.25O₄ composite is then isolated with an external magnet and the fluorescence from BbimDCN-OCDs incorporated in S. cerevisiae is monitored. The fluorescence intensity is linearly correlated with the content of yeast cell, showing a calibration graph of F = 3.01log[C]+11.7, offering a detection limit of 5×10² CFU/mL. S. cerevisiae content in various real sample matrixes are quantified by using this protocol.