## 3 Results  
### Biocidal Efficiency  
The analysis of the three different systems--the free biocides, not-loaded nanocontainers, and loaded nanocontainers--showed multiple differences. For the free biocide, the optical microscopy images at the 8 th week show a higher efficiency of MBT than ZS, which does not highlight evidence of biocidal activity in both concentrations (Figure 2a). Indeed, it is clear in the images of both concentrations of ZS that no fluorescence reduction is evident. Instead, the MBT biocide shows a higher efficiency in 3 mg concentration than 1 mg, as expected, even if the chlorophyll's fluorescence has not completely disappeared by the 8 th week. The quantitative analysis, performed with the cell count, confirms the qualitative data obtained by the optical microscope observation. The graph (Figure 2b) highlights that the vitality of the cells treated with MBT is reduced by about 50% after the first week for both concentrations but with different rates of reduction, with a rate of reduction of 0.88% and 4.7% in the 4 th week, and 2.7% and 20.37 % in the 8 th week for 1 mg and 3 mg, respectively. All the nanocontainers (loaded and not loaded) present an initial reduction in chlorophyll autofluorescence, which can be noted with a color change of fluorescence from red to green, different to the pure biocide, which, after 1 week, did not show this effect. Figure 2: Evaluation of _Zostera_ sodium salt (ZS) and 2-mercaptoethanolthiazolole (MBT) efficiency applied as free biocides in different concentrations (3 mg and 1 mg). (**a**) Optical microscope image in blue channel fluorescent light at the 8 th week. The loss of fluorescence of chlorophyll (red) highlights the efficiency of the biocide. (**b**) Graph of red fluorescence percentage of culture treated with different concentrations of both free biocides. The decrease in fluorescent cells’ percentage highlights the efficiency of products. The non-loaded nanosystems highlighted a clear reduction in chlorophyll autofluorescence of the photosynthetic microorganisms already after the first week and, almost complete disappearance of chlorophyll fluorescence after the 6 th week. Indeed, the optical image at the 8 th week shows the complete disappearance of chlorophyll fluorescence and only a few cells with very low green fluorescence. The quantitative analysis of non-loaded nanocontainers highlighted a very high efficiency rate, reducing the vitality of the cells at about 2% in only 4 weeks (Figure 3a). Finally, the nanosystems loaded with different biocides highlighted a higher efficiency for the mesoporous systems (MNP) than the nanocapsules (NC). Indeed, in the optical images, it is clear that both MBT-NC and ZS-NC at the 8 th week show complete disappearance of red fluorescence but a few cells with low green fluorescence, different to MBT-MNP and ZS_MNP that show complete disappearance of fluorescence. Figure 3: Evaluation of biocide efficiency of nanocontainers not loaded (NC; MNP) and loaded with the biocides (NC_ZS; NC_MBT; MNP_MBT; NC_MBT), where the decrease in fluorescent cells’ percentage highlights the efficiency of products. (**a**) Graph of red fluorescence percentage of culture treated with non-loaded nanocontainers. (**b**) Graph of red fluorescence percentage of culture treated with loaded nanocontainers. Moreover, confirming the qualitative data from a quantitative point of view, it is also evident that nanocontainers loaded with the commercial biocide are more efficient than the green product. Indeed, Figure 3b shows that in the 4 th week, MBT_MNP has a redution rate of 31.63% in comparison with 23.08% for ZS-MNP. Comparing the biocide efficiency of pure biocide with the biocide loaded in the nanosystems, it is highlighted that there is a quantity reduction in biocide used of 10 and 12%, respectively, for MBT-NC and MBT-MNP, and 47.6 and 12.6%, respectively, for ZS-NC and ZS-MNP. This reduction is linked to an efficiency increase of 71 % and 50%, respectively, for 3 mg and 1 mg MBT, and of 100% for both nanocontainers with ZS.