use of nanomaterials leads to decrease the size of the biosensor; to increase its sensitivity, selectivity, reproducibility of the assay, and enable its incorporation into multiplexed, transportable, and portable devices for assessment of food quality (Otles and Yalcin 2012; Ríos‐Corripio et al. 2020).
Figure 1.4 Schematic representation of the operating principle of the biosensor.
Nanosensors use nanoparticles of different chemical nature: carbon nanomaterials (graphene, CNTs, carbon fibers, fullerenes, etc.) (Kurbanoglu and Ozkan 2018), nanoparticles of metals (gold, silver, copper, silicon; metal oxides; quantum dots) (Li et al. 2019), and branched polymers (dendrimers) (Abbasi et al. 2014). GNPs are used most often, due to their resistance to oxidation, low toxicity, and ability to amplify the biosensor signal. The application of such particles leads to increased sensitivity and detection limits up to one molecule (Vigneshvar et al. 2016). An important positive point of using nanosensors is also shorter assay time, especially when pathogenic microorganisms in food are detected. There are many reports available which involved the use of biosensors based on nanoparticles for screening for pathogens, toxins, and allergen products in food matrices (Warriner et al. 2014; Inbaraj and Chen 2016; Prakitchaiwattana and Detudom 2017).
Many modern applications of nanosensors are based on the observed changes of color, which occur with solutions of metal nanoparticles in the presence of an analyte of interest. For instance, aggregation of GNPs caused by mercury (II) ions (Hg2+) is the main sensor mechanism resulting in a significant redshift in the absorption band, with color changing to blue (Chansuvarn et al. 2015). Ma et al. (2018) reported that with the presence of tobramycin in the sample, the DNA aptamer will bind exactly to it, separating from GNPs, and their aggregation will lead to a color change from red to purple‐blue. According to Ramezani et al. (2015) in the presence of an analyte (tetracycline) GNPs remain stable and do not aggregate under the action of the salt; as a result, the color changes from blue (in the absence of the analyte) to red (in the presence of the analyte). Immunosensors also based on GNPs non‐aggregation have been developed for the assay of β‐lactams in milk (Chen et al. 2015) and for the simultaneous detection of benzimidazoles and metabolite residues in milk samples (Guo et al. 2018). A general scheme of similar colorimetric nanosensors is given in Figure 1.5.
Kaur et al. (2019) presents not only advantages of using nanoparticles but also restrictions associated with the cost of their production, preparation of samples, sensitivity to other substances occurring in the sample, lack of self‐standardization, and validation with real samples, as well as with the toxicity of used nanomaterials and ways of utilizing spent sensors. Despite the negative aspects of using nanoparticles in sensor systems, this direction is actively developed. Investigators working with nanomaterials have yet to solve many problems associated both with leveling off their negative characteristics and developing methods of fabricating and using nanoparticles in various regions of the economy.
Figure 1.5 A general scheme of similar colorimetric nanosensors.
1.3.2 In Drug Delivery and Treatment
Nanotechnologies have enabled novel solutions for the treatment of various diseases. Nano‐drug delivery systems present some advantages over conventional (non‐targeted) drug delivery systems such as high cellular uptake and reduced side effects (Singh et al. 2019). Figure 1.6 represents the comparison between untargeted and targeted drug delivery systems. The development of drug delivery systems by using nanotechnology for various diseases, particularly for cancer treatment, is making revolutionary changes in treatment methods and handling side effects of chemotherapy (Zhao et al. 2018). Furthermore, nanotechnology allows for selective targeting of disease‐ and infection‐containing cells and malfunctioning cells. Nanotechnology has also opened a new era in implantable delivery systems such as those used in bone cement, nano‐needle patches, etc., which are preferable than using other modes of direction like injections and oral delivery. Therefore, nano‐based drug delivery systems have attracted a great of attention due to novel and promising properties like enhanced bioavailability and stability of the drug.
Figure 1.6 Schematic representation of comparison between untargeted and targeted drug delivery systems.
Moreover, antimicrobials are one of the most important therapeutic discoveries in the history of medicine. Some projections suggest that by 2050 the annual deaths caused by multidrug‐resistant bacterial infections will reach up to 10 million per year (de Kraker et al. 2016). Nanotechnology provides an innovative platform to address this challenge, because of their small size and various other physical, chemical, and optical properties. As mentioned above, numerous nanomaterials are reported to have significant antimicrobial efficacies and hence such nanomaterials can be used as next‐generation antimicrobials against various multidrug‐resistant organisms and also in the treatment of different infectious diseases (Rai et al. 2012; Beyth et al. 2015; Rai et al. 2016).
The bioavailability of a drug within the body depends on some factors like the size of the drug molecules and solubility factors (Kesharwani et al. 2018). The conventional dosage system consequently faces some challenges in reaching the target site at an appropriate dose. For example, highly water‐soluble drugs cause fluctuations in drug concentration in the body due to high disintegration properties, and also result in quicker clearance of the drug from the bloodstream. However, some medicines are fat‐soluble and when such drugs are taken in the form of conventional dosage, they face bioavailability difficulties. Similarly, patients suffering from chronic diseases like diabetes need to take painful insulin injections regularly. Likewise, cancer patients regularly have to undergo powerful chemotherapy, which involves quite severe side effects as the anticancer drugs target cancer cells and normal cells equally. Therefore, proper platforms to deliver the drugs at targeted sites without losing their efficacies, and while limiting the associated side effects, are highly required (Mura et al. 2013).
Many novel technologies for developing effective drug delivery systems came into existence in this context, among which nanotechnology platforms for achieving targeted drug delivery are gaining prominence. Research in this field includes the development of drug nanoparticles, polymeric and inorganic biodegradable nanocarriers for drug delivery, and surface engineering of carrier molecules (Senapati et al. 2018). These nanocarriers help in solubilizing the lipophilic drugs, protecting fragile drugs from enzymatic degradation, pH conditions, etc., and targeting specific sites with triggered release of drug contents.
To date, a wide range of nanomaterials enlisted above has been developed and used for applications in nano‐drug delivery. There are many reports on the usage of metallic nanoparticles in drug delivery and diagnostic applications. It mainly includes the applications of silver, gold, and iron‐based superparamagnetic nanoparticles as nanocarriers for controlled and targeted delivery of potential drugs and genes for enhanced clinical efficacy. In addition, nanosuspensions or nanodispersions, which are theoretically considered the simplest form of nanomedicine, contain two specific components, the active pharmaceutical ingredients nanoparticle and the adsorbed surface stabilizer(s), which have been also effectively used in the treatment of various diseases (Adeyemi
