Fig. 6

a Fluorescence intensity schematic presentation of PLL-protected Ti₃C₂ MQDs in 10 mM tris–HCl buffer (black); PLL-protected Ti₃C₂ MQDs and trypsin (80.0 μg mL⁻¹) (red); PLL-protected Ti₃C₂ MQDs and cyt-c (40.0 μM) (green); PLL-protected Ti₃C₂ MQDs, cyt-c (40.0 μM) and trypsin (80.0 μg mL⁻¹) (blue). b Fluorescence intensity schematic presentation of the mixture containing PLL-protected Ti₃C₂ MQDs and cyt-c (40.0 μM) in the presence of different concentrations of trypsin (from bottom to top: 0, 0.5, 2.5, 5.0, 10.0, 20.0, 40.0, 60.0, 80.0, 160.0, 250.0 μg mL⁻¹. c The relationship schematic presentation between the change in fluorescence intensity of the mixture and the trypsin concentration. A linear relationship between changes in fluorescence intensity and trypsin concentration [trypsin] = 0.5, 2.5, 5.0, 10.0, 20.0, 40.0, 60.0, 80.0 μg mL⁻¹. Error bars represent standard deviations from triplicate measurements. d Effect of different proteins (100 μM) on the fluorescence intensity of Ti₃C₂ MQDs. e) The selectivity of the PLL-protected Ti₃C₂ MQDs toward trypsin using ALP, lysozyme, bovine serum albumin (BSA), pepsin, thrombin and IgG. The concentration of trypsin was 80 μg mL⁻¹, and other substances are 200 μg mL⁻¹. Reproduced with permission from Ref. [93], © Springer Nature 2019