They are responsible for the enhanced PL intensity of RNase A@C-dots [33]. Figure 3 XPS and FTIR spectra and zeta potential. (a) XPS C 1 s spectrum. (b) XPS O 1 s spectrum. (c) XPS N 1 s of RNase A@C-dots. (d) FTIR spectra of RNase A@C-dots. (e) Zeta potential of RNase A@C-dots. The average zeta potential of C-dots (Figure 3e) is 0.02 mV, slightly beyond zero. Considering the fact that cells are with positive charges, a zeta potential of no less than zero is definitely favorable in cell labeling and imaging. (The

influence of BAY 80-6946 mw microwave condition on PL of carbon dots was also investigated, as shown in Additional file 1: Figure S5). Effects of pH on PL properties of RNase A@C-dots Although the mechanism of PL properties of C-dots is still unclear and debatable, there is solid evidence of lower quantum efficiency of C-dots that is caused by the fast recombination of excitations located at surface energy traps [8]. BAY 11-7082 Therefore, after modifying the surface of C-dots using different OTX015 supplier surface passivation reagents, the PL properties of the C-dots

can be significantly improved [7, 8, 34]. In this work, we firstly introduce the bioactive enzyme RNase A to synthesize C-dots by one-step micro-assisted synthesis method. The mechanism of the PL enhancement could be explained by following two reasons: Firstly, we propose that the electron-donating effect which resulted from the abundant amino acid groups on the surface of RNase A, especially those amino acids with benzene rings, might contribute a lot to the much enhanced Farnesyltransferase PL intensity of the C-dots. To test our assumption, we select tryptophan and thenylalanine as replacements of RNase A to synthesize C-dots in the same conditions. As shown in Additional file 1: Figure S5b, both tryptophan and thenylalanine can greatly enhance the PL intensity. Secondly, we think that in the microware heating reaction, RNase A acts as a N doping reagent that causes the PL enhancement of the C-dots. The data of IR and XPS can also support the point. In the biological application, pH is a very important factor that we

firstly take into consideration. Herein, the influence of pH values over the PL of the RNase A@C-dot clusters is indicated in Figure 2d. The fact that pH values could affect the PL intensity has been seen in quite a few studies [10, 21, 32, 35]. Generally, PL intensity reaches its maximum at a certain pH values, 4.5 [35] or 7 [21]. At the same time, a slight redshift in the emission peak was identified with the increase of pH value [35]. Interestingly, the pH value played a unique role upon the PL of RNase A@C-dots. There was a noticeable redshift in the emission peak when the pH went from 2.98 to 11.36. However, the PL intensity decreases continuously as pH values increase. Specifically, the C-dots lost about 25% of its PL intensity when the pH increases from 2.98 to 7.32 and retain only 40% of its intensity when the pH value comes to 11.36.