Betaine-Modified Green Carbon Dot for Cr(VI) Sensing, in Vivo Cr(VI) Imaging, and Growth Promotion in the Rice Plant

Hexavalent chromium is a toxic environmental pollutant that damages plants due to disruption of nutrient uptake, photosynthesis metabolism, and oxidative stress, which suppresses the growth and development of the plant. In this work, we have developed a betaine-modified carbon dot (BT@CD) sensor for monitoring Cr(VI) in water and plants. Fluorescent carbon dots have been synthesized using jamun juice (Syzygium cumini) as the carbon source subjected to surface modification with betaine (BT@JCD). This BT@JCD exhibits strong blue fluorescence, which significantly decreases in the presence of Cr(VI) due to the inner filter effect in a range of 5–450 nM with a detection limit of 0.033 μM. Due to its easy translocation in the vascular bundles, these fluorescence nanosensors can be applied to detect Cr(VI) in rice plants Oryza sativa) through fluorescence confocal imaging. The treatment of rice plants with BT@JCDs in the concentration range of 0.2 to 1g/mL not only triggered photophysical parameters such as carbohydrates, chlorophyll, and carotenoids but also enhanced the antioxidant enzyme activity promoting plant growth.