## 1 Introduction  
Homeopathic plants are the ideal source of medicinal compounds that enhance the quality and longevity of life. _Gymmema sylvestre_ (Retz.) R. Br. (Family: Asclepiadaceae) is a woody climbing shrub that has medicinal value because of the presence of various bioactive compounds like gymnemic acids (GA) and phenolic compounds (PC), which are used to treat diabetes mellitus [1]. The plant is also used as an ingredient of tea, confections, and many food preparations for the regulation of sugar homeostasis and to control obesity and the level of blood cholesterol [2]. The pharmacologic potential of GA includes antimicrobial, antihypercholesterol, hepatoprotective and anti-saccharine activities [3]. GA selectively suppresses the urge for sweet flavors in humans. The leaves of _G. sylvestre_contain triterpen saponins, such as oleananes (e.g., GA) and dammarane (gymnemasides), which are considered the active constituents [4]. The medicinal value of _G. sylvestre_ could lead to its overharvesting. In vitro plant tissue culture or cell suspension culture (CSC) techniques are eco-friendly biotechnological methods for the production of phytochemicals that are an alternative to overexploitation of naturally growing _G. sylvestre_ sources. The phytochemicals derived using these techniques can be used as food additives, nutraceuticals, and pharmaceuticals [5]. Elicitation is one of the most effective biotechnological approaches to increase the production of phytochemicals in tissue culture or CSC [6]. Elicitors are biological and non-biological molecules that recognize receptors on the cytoplasmic membrane of plant cells. The binding of the compounds to the receptors elicits a signal that stimulates the expression of genes involved in the synthetic pathway of plant secondary metabolites. Elicitors can stimulate defensive responses in cells, tissues, organs, and plants because of the alteration of various biosynthetic pathways. Thus, the production of preferred phytochemicals requires elicitor-mediated external stimuli [7]. Enhanced accumulation of secondary metabolites by the addition of elicitors to the CSCs has been reported [8; 9]. Application of elicitors to improve the production of GA from _G. sylvestre_ has been accomplished using callus and CSC methods [10; 11; 12]. Copper (Cu) is a vital micronutrient for plant development and a co-factor in various physiological processes that include cell wall metabolism, photosynthesis and lignification. However, Cu is toxic at higher levels [13]. Cu is also present in catalytic enzymes, assists in protein transport, and functions in the transcription of some genes [14]. Elicitation of CuSO\({}_{4}\) increases the content of phytochemicals that include bacoside, betacyanin, and phenylpropanoids during in vitro tissue culture of _Bacopa monmieri_[15], _Alternanthera philoseroides_[16], and _Ocimum basilicum_[14]. Cu is essential in plant growth and stimulates phytochemical production. Nanotechnology is an advanced technology that has diverse scientific applications. Recent developments in nanotechnology and extensive uses of engineered nanoparticles (NPs) have advanced biotechnology. Reflecting this importance, the manufacture of engineered NPs is predicted to increase from 0.27 million tons in 2012 to 1.663 million tons by 2020 [17]. Nanotechnology also has huge benefits in agriculture for the control of diseases and in crop production [18]. Nanomaterials with a diameter from 1 to 100 nm are often used commercially. A recent focus has been on the use of nanomaterials as an elicitor to evaluate the stress responses in different economically and medicinally important plants. NPs are extensively used as abiotic elicitors in plant biotechnology to enhance the production of valuable bioactive compounds [19]. In the past several years metallic NPs have become popular due to their enhanced physical and chemical properties [20]. Nanoscale nutrients and insecticides are being increasingly used in agriculture.