Plants have been used for their beneficial compounds especially therapeutic and medicinal properties over the centuries. Various applications of plants in industry and medicine are related to their distinct phytochemical molecules called secondary metabolites (bioactive chemicals). In reaction to stress, plants produce secondary metabolites that serve numerous physiological functions. Their complex chemical compositions make them valuable across various industries, including food, agriculture, cosmetics, and pharmaceuticals. The chemicals are efficacious and have been deemed an optimal candidate for commercialization. From several decades ago, studies have suggested that elicitation is an effective strategy to increase the production of secondary metabolites in plants. This could help overcome the limitations of plant cell technology for commercial use. An external stimulus may enhance the synthesis of secondary metabolites by triggering various biosynthetic pathways, activating specific genes associated with defense or non-defense functions, stimulating distinct enzymes, and modifying proteins via phosphorylation or dephosphorylation. Upon new findings, it has found that nanoparticles (NPs) might stimulate the production of bioactive molecules, particularly secondary metabolites in plants. This review will highlight in vivo and in vitro studies using different carbon and metal nanoparticles as nano-elicitors to stimulate secondary metabolite production in various plants.
