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malignant melanoma therapy. When HIF‐1α is upregulated, transcription is activated that results in angiogenesis. Small interfering RNA (siRNA) are pieces of double‐stranded RNA that can interfere with the translation of proteins and inhibit angiogenesis when used against HIF‐1α. The double‐stranded RNA alone did not achieve the antiangiogenesis activity, thus HIF‐1α siRNA vector is an excellent vehicle that can load siRNA and protect it from degradation [44]. Another method of delivering anticancer drugs, such as quercetin, is a lecithin‐based mixed polymeric micelle. Although quercetin (Que) is a well‐known and successful anticancer drug, its low solubility and low oral bioavailability (BA) hinders its use in clinical settings. A micelle as a delivery system is quite useful in this case because its hydrophobic core and hydrophilic shell provide a safe passage for low soluble drugs. To increase the solubility of drugs, the more hydrophobic material is added to the micelle, which increases the space in the hydrophobic core and provides more space for drugs to be solubilized. Lecithin is a hydrophobic mixture of organic phospholipids that help in the absorption of drugs. In this case, lecithin helps increase the BA of Que. These micelles not only are able to increase drug solubility and BA but also, due to their nanosize, are able to enter and gather in tumor sites [45].

Even though most of the drug delivery methods are focused on cancer treatments, some specialize in other problematic areas of the human body. Skin is the largest organ of the body and the stratum corneum is the main barrier that drugs need to penetrate to get into the deeper layer of the skin. In the case of antifungals, drugs should be able to get through this layer but are not always able to do so. The development of nanosized colloidal carriers can be used as vehicles for drug delivery. Studies done on naftifine‐loaded microemulsion colloidal carriers showed that the carriers were an effective way of delivering naftifine, an antifungal drug, to deeper layers of the skin. Additionally, the method of delivery was shown to have low levels of cytotoxicity [46].

      1.2.3 Biosensors

      Biosensors are tools used to detect and analyze biological elements. Conventional biosensors have their advantages, but they also exhibit several limitations. Nanotechnology, however, eliminates the limitations of conventional methods. In fact, as the material dimensions are minimized, the applicability of biosensors is improved [47]. There are several nanoparticle‐based biosensors that can help detect pathogenic viruses. For example, the development of quantum dots‐based imaging and capturing systems for selective capturing and detection of the HIV in whole blood. It is a dual‐stain imaging system for the detection of HIV1 gp120 envelope glycoprotein. It is also capable of obtaining countable imaging. This system can work with 10 μl of a blood sample, is portable, and is highly cost‐effective compared to other methods [48]. For the detection of multiple viruses, the fluorescence characteristic of AgNPs is quite useful for optical biosensors. Using silver nanoclusters, biosensors have been prepared for the detection of specific DNA sequences of HIV, hepatitis B virus (HBV) and human T‐lymphotropic virus type I (HTLV‐I) gene. Before binding to the DNA sequence, these nanoclusters exhibited high fluorescence activity. After attaching to the sequence, however, the fluorescence intensity decreased, allowing the target sequences to be detected [49]. Additionally, magnetic nanoparticles have also been utilized for virus detection. Amino functional carbon‐coated magnetic nanoparticles, for example, have been used to distinguish hybridization of HBV nucleic acids [50, 51].

      MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression by inhibiting translation and play a role in RNA degradation [52–54]. Currently, miRNA detection has several limitations such as sensitivity and selectivity [55]. Additionally, the current methods of miRNA detection, including northern blotting, microarray analysis, and RT‐PCR, are high in cost, complicated to handle, and do not produce stable results [56]. Tumor‐derived miRNA‐141 deregulation in human plasma is an important biomarker for blood‐based detection of various cancers, such as prostate [57], colons [58], and ovarian [59]. An electrochemical immunosensor composed of modified gold electrodes, reduced graphene oxide, and CNTs has been developed for the detection of the miR‐141 gene. With this method, the detection limit was down to 10fM [60]. Similar to miRNA‐141, miRNA‐155 is another biomarker for diagnosis of diffuse large B‐cell lymphoma [61]. Oligo‐hybridization‐based electrochemical biosensors can be used for its detection. These biosensors utilized GNPs on sheets of graphene oxide situated on glassy carbon electrodes. This particular biosensor exhibited higher selectivity as it was able to distinguish between complementary target miRNAs, three‐base mismatch, and noncomplementary miRNAs.

      It also was capable of directly detecting miR‐155 in plasma without any need for sample preparation, extraction, and amplification [62]. Another example of a useful biomarker is miRNA‐21, the most frequently upregulated miRNA in breast cancer and can also be used for early diagnosis and drug development for cardiovascular disease [63]. An electrochemical biosensor based on a metal ion functionalized titanium phosphate nanospheres is a sensitive and selective tool for detecting miR‐21. The addition of cadmium ion to titanium phosphate nanosphere exhibited improvement of the electrochemical signals by five times [64, 65].

1.3 Food and Agriculture

      Advocates of global sustainability recognize and emphasize the importance of sustainable development of agriculture and food [66]. Currently, agriculture is one of the largest causes of global environmental change. The process of food production alone contributes to 30% of the global greenhouse gas emissions [67], occupies 40% of the land [68], uses 80% of the freshwater [69], and is one of the largest factors contributing to species extinction [70]. There are several aspects of the food sector that can be enhanced to prevent and minimize the negative consequences of the current system. Using nanotechnology in food and agriculture can not only increase the safety of the product and protect the environment but can also be used to improve the mechanisms of food distribution.

      1.3.1 Fertilizers

Chemical‐based conventional fertilizers may have worked previously but have been deemed unsustainable since the beginning of the green revolution [71]. Current fertilizers cause a loss of nutrients. Nitrogen is an essential mineral required for the growth of crops. It is lost through processes of nitrate leaching, denitrification, and ammonia volatilization. This loss of nitrogen not only affects plant growth but also contributes to pollution, global warming, and causes a huge economic loss [72]. This and other problematic results of conventional fertilizers can be prevented by using nanofertilizers. Nanofertilizers can enhance nutrient use efficiency by causing a higher uptake of nutrients. This is accomplished by the smaller surface area of nanomaterials, which is known to increase the nutrient surface interaction. Nanomaterials can also be used to enhance the results of conventional fertilizers. Slow‐release chemical‐based fertilizers, for example, can be coated with nanoparticles and significantly reduce the results of nitrate leaching and denitrification [73]. Compared to conventional fertilizers, nanofertilizers have many advantages. Where conventional fertilizers work rapidly, nanofertilizers feed the crops gradually in a controlled manner. They are highly effective in nutrient absorption by plants and result in a lower loss of essential nutrients. This is due to their nanosized pores and their ability to utilize various ion channels within the plants. In addition, polymer‐coated fertilizers are able to avoid contact with the soil and water due to the coating encapsulating the nanoparticles. This ensures that the nutrients and minerals are available for the plant to uptake when it is ready to do so. This also minimizes the unnecessary loss of nutrients [74].

      1.3.2 Application in Food Science

      Due to public apprehension and the regulatory agencies not reaching upon agreement, the application of nanotechnology in food preparation does not have any worldwide applicable rules and, hence, is still in the developmental phase [75–77]. There are various aspects needed to be explored in the relationship between nanotechnology and food preparation. Application, for one, is certainly a matter of discussion [78]. Nanotechnology can have various possible applications in food science. For example, nanomaterials can be used in food products to increase its freshness and improve its taste. This can be done through methods of nanoencapsulation. SiO₂ nanomaterials, for example, can act as carriers for flavors in food

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