## 1 Introduction  
There is currently a strong interest in human food quality--specifically in foods' bioactive compound contents. These compounds may help to prevent chronic and degenerative diseases and generate positive effects to promote and restore the physiological functions of the human organism. Therefore, it is important to generate healthier and better food quality. The tomato fruit (_Solanum lycopersicum_ L.) has been identified as a functional and nutraceuticalal food [1]. This fruit is an important source of bioactive compounds such as vitamins, carotenoids, and phenolic compounds, which produce a greater antioxidant activity that represents a direct benefit to human health [2]. Besides its importance to the human diet, it is the second most commercially consumed vegetable after the potato [3]. The currently available technology affords several approaches to increasing crop production and crop nutraceuticalal quality. One of these is the application of nanotechnology to improve productivity [4; 5]. In recent years, nanotechnology has been used by means of the application of nanomaterials such as nanofertilizers, nanoparticles, or nanopesticides for nutrient management, genetic improvement, plant disease treatment, and plant growth promotion [4]. Nanoparticles (NPs) and nanomaterials (NMs) are materials with at least one dimension less than 100 nm. This small size gives rise to properties different from those exhibited by the bulk of the material of the same composition. Indeed, for metallic elements such as Cu, Fe, Ce, Ti, and Ag, the cellular responses are very different when induced by ionic forms compared to the nanometric forms [6]. These new properties provide the material with an added value that has multiple applications in the automotive, energy, pharmaceutical, medical, and agricultural industries, among others [7]. These nanomaterials can induce a faster germination, or help plants tolerate biotic and abiotic stresses, favoring a more efficient management of nutrients and increasing plant growth while reducing the environmental impact in comparison with traditional methods [8]. Recently, the use of nanoparticles such as insecticides, fungicides, and nanofertilizers has been investigated [9]. It has been shown that the impact of NPs on plants depends on many factors, such as the composition, concentration, size, the physical and chemical properties, and even the plant species under study [10]. A concentration of NPs above the optimal ranges of Zn, Cu, Ag, Ce, and Ti, among others, produces stress and/or toxicity, generating reactive oxygen species (ROS) and resulting in the disruption of cellular metabolism. Under these conditions, plants produce antioxidant enzymes and non-enzymatic components that protect the cellular and subcellular system from ROS cytotoxic effects [11]. Cu nanoparticles (Cu NPs) have properties linked to their small size and high specific surface area which provides them with a physical resistance, chemical reactivity, electrical conductivity, magnetism, and optical effects [12]. Low doses of Cu NPs (5-20 mg Cu per plant) generate metabolic effects due to the Cu accumulation and ROS generation [13]. CuO NPs applied in _Arabidopsis thaliana_ (L.) [PERSON]. increased the flavonoid content at concentrations of 5 mg L\({}^{-1}\). A significant induction of genes related to the responses to oxidative stress, sulfur assimilation, glutathione, and proline biosynthesis has also been shown under CuO NPs stress [14]. While the CuO NPs (0-200 mg L\({}^{-1}\)) applied to the leaves in cucumber plants significantly reduced the firmness of the fruit [15], it has also been shown that when applied to the substrate, Cu NPs (0.006 mg L\({}^{-1}\)) increased the total phenols and modified the concentration of the enzymatic and non-enzymatic compounds in tomato fruits [16]. Similar results were obtained in jalapeno peppers with Cu NPs + Chitosan-polyvinyl alcohol (Cs-PVA) (0-10 mg L\({}^{-1}\)) applied on the substrate [17].