Turn-off-on fluorescence probe based on 3-mercaptopropionic acid-capped CdS quantum dots for selective and sensitive lysozyme detection

In this work, we presented a novel biosensor for rapid detection of lysozyme. The novel biosensor was based on the fluorescent "turn off-on" of 3-mercaptopropionic acid-capped CdS quantum dots (MPA-CdS QDs). Positively charged hemoglobin (Hb) could bind to MPA-CdS QDs via electrostatic interaction, which leads to the fluorescence of MPA-CdS QDs to "turn off". Lysozyme is also positively charged, and it can replace Hb on the surface of MPA-CdS QDs. In the presence of lysozyme, the fluorescence of MPA-CdS QDs could be restored due to the displacement of Hb by lysozyme. The relative fluorescence intensity ratio F/F-0 (F and F-0 is the intensity of the MPA-CdS QDs-Hb system in the presence and absence of lysozyme respectively) showed a good linear relationship with the lysozyme concentration in the range of 15-600 nmol L (1) with a detection limit of 6.3 nmol L (1), the method exhibited remarkable selectivity for lysozyme in the presence of several other proteins. The presented method was cost-effective, convenient, and does not require any complicated synthetic procedures.