The phycocyanin content increased throughout the growth cycle, reaching a maximum on day 65, and then began to decrease. Two-dimensional correlation was calculated for the changes of phycocyanin content during the growth cycle, and the synchronous and asynchronous two-dimensional correlation fluorescence spectra of microalgae phycocyanin were obtained. Figure 4.6(c) shows that there is only one autocorrelation peak on the main diagonal, and there is no cross peak outside the main diagonal. CQDs were used as probes to analyze the fluorescence changes of phycocyanin content at different growth stages, and the excitation wavelengths were all 370 nm, so no cross peak existed outside the main diagonal because there was no obvious interference in the system. In Figure 4.6(d), an asynchronous cross-peak appeared at 465 nm outside the main diagonal. The asynchronous cross-peak appeared here reflected that the excitation at 370 nm would get an emission peak at 465 nm, which was consistent with the results shown in the previous 1D fluorescence spectra, and the distribution of the algal cyanobacterial protein content at different stages measured by the system was clear and well correlated.
Figure 5 Variation of phycocyanin content in algal cells (a) (b); 2D synchronous correlated fluorescence spectra (c); 2D asynchronous correlated fluorescence spectra (d)
3.3 SOD content changes
As shown in Figure, SOD enzyme content showed an upward trend and reached a maximum at 65 days. 2-D synchronous correlation fluorescence spectra plots, it can be seen that there is only one autocorrelation peak on the main diagonal, no cross peaks exist on the outside of the main diagonal, the situation of the fluorescence change of SOD enzyme content is probed by using CQDS as the probe, the excitation wavelength is all 370 nm, the synchronous fluorescence change plot of SOD enzyme all the peaks are synchronous changes; Since there was no significant interference within the system, no cross peaks outside the main diagonal existed. The asynchronous cross peak appears at 465 nm outside the main diagonal, and the asynchronous cross peak presented here reflects that excitation at 370 nm gives an emission peak at 465 nm, which is consistent with the results shown in the previous one-dimensional fluorescence spectrogram, and this system measures the SOD content change at different growth stages, and the SOD enzyme content distribution at different stages is clear and well correlated.