## 1 Introduction  
The widespread use of AlNPs leads to their possible escape into the environment [1] while enhancing the need for immediate attention to be directed to seed germination and plant growth. The industrial use of nanoparticles has rapidly increased in the fields of cosmetics, pharmaceuticals, textiles, electronics, biosensors, catalysts, etc. Ref. [2] owing to their special physicochemical characteristics, such as small size, large specific surface area, and surface energy compared to bulk materials. Aluminium oxide or AlNPs are frequently utilized in explosives and rocket propellants, catalysis, electensors and electonanalysis, coatings, high-performance ceramics, sunscreens, etc. [1]. In addition to their use as fillers and packaging materials [3], they find unique uses in wastewater treatment technology through the creation of ultrafiltration membranes with smaller pore sizes [4] that contribute to a better performance index. AlNPs also serve as a solid phase extraction material to remove heavy metal and other pollutants from wastewater through the processes of absorption and adsorption [5]. There are limited investigations about the impact of alumina nanoparticles on the growth of seedlings and seed germination. Some studies have concluded by identifying negative effects [6], positive effects [7], or no effect for different plant species [1]. The effect of aluminium ions (Al3+) and alumina nanoparticles on cabbage seedlings were compared [8]. The results of that study imply the strong adverse effect of aluminium ions and the positive effect of a low concentration of alumina nanoparticles. However, the biochemical parameters and nitrate reductase activities of the treated seedlings were negatively impacted by the greater dosages of AlNPs. Moreover, the effect of AlNPs and aluminium ions on plant growth were further studied using lettuce (_Latuca sativa_ L). In that study, AlCl3 was used to observe the effect of aluminium ions. Interestingly, a positive effect of AlNPs on root elongation was observed, whereas a low concentration of alumina was able to enhance the biomass compared to control conditions. The results of that study emphasize that the AlNPs can absorb root hair and promote the uptake of macronutrients, but the micronutrient uptake was reduced by AlNPs [9]. Moreover, the effects of alumina nanoparticles and macroparticles on _Trigonella foenum-graceum_ L. were observed with the help of growth parameters and antioxidative stress parameters [10]. The results of that study emphasize that low concentrations of alumina nanoparticles do not induce a negative effect on plant growth, even at those concentrations for which alumina microparticles could induce negative effects. Therefore, the results obtained by this study provide a clear idea of the allowed amount of alumina NPs that can be exposed to the terrestrial environment without causing any detrimental effects is higher than that of alumina microparticles. Nevertheless, the high concentrations of alumina nanoparticles could alter the soybean growth by affecting the cell wall structure and lignin composition [11]. However, the methods used in most of the studies are destructive, highly time-consuming, and do not enable the observation of the effect at an early stage. Therefore, in this study, we propose the biospeckle optical coherence tomography (bOCT) developed by researchers to study the germination of lentil seeds under the exposure of AlNPs. Optical coherence tomography (OCT) is a non-destructive, in vivo, image modality that maps 2D or 3D depth-resolved tomographic images of internal tissue structures with high speed, quality, and spatial resolution when compared to existing image modalities.