Fluorescence Analysis of Biocide Efficiency in Antifouling Coatings against Cyanobacteria

Novel technique for the ultra-sensitive detection of hazardous contaminants using an innovative sensor integrated with a bioreactor

This study introduces an evaluation methodology tailored for bioreactors, with the aim of assessing the stress experienced by algae due to harmful contaminants released from antifouling (AF) paints. We present an online monitoring system equipped with an ultra-sensitive sensor that conducts non-invasive measurements of algal culture's optical density and physiological stage through chlorophyll fluorescence signals. By coupling the ultra-sensitive sensor with flash-induced chlorophyll fluorescence, we examined the dynamic fluorescence changes in the green microalga Chlamydomonas reinhardtii when exposed to biocides. Over a 24-h observation period, increasing concentrations of biocides led to a decrease in photosynthetic activity. Notably, a substantial reduction in the maximum quantum yield of primary photochemistry (FV/FM) was observed within the first hour of exposure. Subsequently, we detected a partial recovery in FV/FM; however, this recovery remained 50% lower than that of the controls. Integrating the advanced submersible sensor with fluorescence decay kinetics offered a comprehensive perspective on the dynamic alterations in algal cells under the exposure to biocides released from antifouling coatings. The analysis of fluorescence relaxation kinetics revealed a significant shortening of the fast and middle phases,  along with an increase in the duration of the slow phase, for the coating with the highest levels of biocides. Combining automated culturing and measuring methods, this approach has demonstrated its effectiveness as an ultrasensitive and non-invasive tool for monitoring the physiology of photosynthetic cultures. This is particularly valuable in the context of studying microalgae and their early responses to various environmental conditions, as well as the potential to develop an AF system with minimal harm to the environment.

The interaction between titanium dioxide nanoparticles and light can have dualistic effects on the physiological responses of plants

The model plant Arabidopsis thaliana was exposed to combined stress factors, i.e., titanium dioxide nanoparticles (TiNPs) and high light. The concentrations of TiNPs used for irrigation were 250, 500, and 1000 μg/mL. This study shows that TiNPs alter the morphology and nanomechanical properties of chloroplasts in A. thaliana, which leads to a decrease in membrane elasticity. We found that TiNPs contributed to a delay in the thermal response of A. thaliana under dynamic light conditions, as revealed by non-invasive thermal imaging. The thermal time constants of TiNP-treated plants under excessive light are determined, showing a shortening in comparison to control plants. The results indicate that TiNPs may contribute to an alleviation of temperature stress experienced by plants under exposure to high light. In this research, we observed a decline in photosystem II photochemical efficiency accompanied by an increase in energy dissipation upon exposure to TiNPs. Interestingly, concentrations exceeding 250 µg/mL TiNPs appeared to mitigate the effects of high light, as shown by reduced differences in the values of specific OJIP parameters (FV/FM, ABS/RC, DI0/RC, and Pi_Abs) before and after light exposure.