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 [79]. In addition, the functionality of these applications should also be the focus development of this field. What are the reasons for using nanomaterials? Protection against biological deterioration, chemicals, and enhancement of physical properties can be few of the reasons. Furthermore, the safety of using nanomaterials over conventional materials and methods should be assessed, for example, what are the results of these applications in in vivo and in vitro experiments, or do nano‐enhanced food contribute to food allergies? [78]
Healthy and sustainable food is certainly a goal for the future, especially to achieve global sustainability. Sustainability of food is a bit tricky because food has a shelf life and for most items, it is not very long. A reason for that is biological pathogens. Silver nanoparticles and nanocomposites have been identified as antimicrobials by the US FDA. The Ag+ ions in AgNPs are responsible for binding to cause morphological changes and generation of reactive oxygen species by binding to membrane proteins of bacteria. This causes damage to cells and death due to oxidative stress [80, 81]. Even though some nanomaterials are used to cause oxidative stress, there is some that act as antioxidant carriers. A developed example of this is SiO₂‐gallic acid nanoparticles that contain a high capacity of 2,2‐diphenyl‐1‐picrylhydrazyl radicals, a compound used to measure antioxidant activity [82]. Nano‐delivery materials can also be used to increase the BA of bioactive compounds in food products. Depending on the type of bioactive compound, there are many nano‐carries available. For instance, coenzyme Q10 is a lipophilic compound and is not very soluble in water, which is the cause of its low BA. A lipid‐free nano‐CoQ10 system is modified with various surfactants, which improve the solubility and BA of coenzyme Q10 in oral administration [83].
1.3.3 Food Packaging
Similar to its contribution to food science, nanotechnology’s contribution to food packaging focuses on increasing the shelf life of food and improving its safety. Currently, polymer‐based materials, synthetic and organic, are widely used in biomedical sciences and agriculture. However, polymers alone cannot achieve the required performance of an innovative packaging; hence, nanomaterials such as CNTs, nano clay, and biocomposites have been used to manipulate the polymers and improve their performance [83]. In food packaging, the combination of polymers and nanomaterials has developed intelligent and active packaging systems. The basis of each packaging system is the mimicking of biological processes, which preserves the integrity of the package and foods in food chain systems [84].
1.3.3.1 Intelligent Packaging
An intelligent packaging system focuses on monitoring the conditions and quality of food products during the distribution and storage stage of the supply chain and intends on delivering this information to the consumer of the product. Intelligent packaging systems can be distributed in four categories: data carriers, quality indicators, sensors, and others such as organic light‐emitting diodes (OLEDs) and holograms [84]. Nano‐based communication devices such as Radio Frequency Identification (RFID) tags and a barcode with wireless sensors could be used to provide product authenticity, anti‐theft, anti‐counterfeiting [85], and product traceability [86]. For instance, a wireless RFID sensor tag consisting of two planar inductor‐capacitor resonators to monitor relative humidity has shown a sensitivity range of 20–70%.
This system could be integrated into the RFID sensors of conventional packaging machines [87]. ZnO nanoparticle and polyvinylpyrrolidone (PVP)‐based luminescent films also showed the capability of sensing the status of food substrates by the intensity of their luminescence [88]. In addition, the use of quantum dots and graphene to develop a chip‐based sensor to detect oil samples exhibits the capability to differentiate between various oil samples in a laboratory setting. Compared to the conventional methods of high‐performance liquid chromatography (HPLC), this system was able to discriminate between eight different unknown oil samples with an accuracy of 92.5% [89].
1.3.3.2 Active Packaging
In active packaging systems, food products, packaging materials, and the environment are interacting together to extend the shelf life, quality, and
