17.1 Introduction

Nanotechnology is the branch of science (nanoscience) that deals with manipulating and tailoring nanosized particles for the desired applicability. The building block of nanotechnology is the nanoparticles (NPs), and this new innovative technology offers an edge over conventional diagnostics and therapeutic approaches (Yetisgin et al. 2020). The properties such as optimal shape, size, larger surface area, biodegradability, biocompatibility, and immune-compatibility make nanomaterials attractive to researchers (Gurunathan et al. 2020). This technology has enabled better bioimaging and improved diagnostic devices, which have further increased therapy success rates in the medical field (Ibrahim 2020). Nanotechnology in agricultural industries has potential applications in crop production, crop improvement, assurance of healthy food, pathogen identification, and removal (Ghorbanpour et al. 2020). Invention like “Nanosensors” can detect and measure the material derived from bacterial growth and metabolism. Thus, nanosensors can check bacterial and viral toxicity at extremely low concentrations (Rahmati et al. 2020; Kumar et al. 2020). Nanotechnology can also provide solutions for a clean and green environment. A nano fabric towel can absorb 20 times its weight in oil utilized for clean-up purposes (Jin et al. 2018). The use of water-repellent magnetic NPs in oil spills can remove the oil from the water mechanically. Nanotechnology promises an efficient and cost-effective waste-water treatment and thus can help cope with the ever-increasing water demands in the human population. Graphene oxide NPs are increasingly used to filter out air pollutants and purify the air. New NPs-based catalyst has the efficiency to minimize the effect of air pollutants from industrial plants and automobiles (Skinder and Hamid 2020).

NPs are useful in cosmetics, paints, automobiles, space science, and sports utilities. The use of NPs in textiles and fabrics makes them stain resistant, increases sustainability, enhances the quality of food packaging material, and increases the food preservation period, accordingly (Thangadurai et al. 2020). An overview of various applications of nanotechnology is shown in Fig. 17.1. The antimicrobial properties of NPs are of particular interest to researchers. The characteristic of NPs to restrict the growth and metabolism of microbes better than their macroscale counterparts has proved advantageous to overcome the multidrug-resistant mechanism (Wang et al. 2020). For example, cerium oxide NPs cause oxidative stress to eliminate microorganisms (Farias et al. 2018). NPs can serve as antibacterial, antifungal, and antiviral agents (Gudkov et al. 2021; Chen and Liang 2020; Mba and Nweze 2020) both in metallic and biogenic forms (Saleem et al. 2019; Bagchi and Chauhan 2018). This chapter, in particular, elaborates on the current understanding of NP-based technology for its use as antimicrobial agent.

Fig. 17.1
A chart depicts the applications of Nanoparticles. It consists of the following fields. Biomedical, environment, electronics, and agriculture. Some of the applications are listed for each field.

Various applications of nanotechnology

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17.2 Nanoparticles: An Overview

According to the international organization for standardization (ISO), NPs are defined as nano entities that have all three dimensions (3D) in the nanoscale (Sudha et al. 2016). NPs can be formed of several elements, primarily metals, polymers, metal oxides, ceramics, and organic molecules, having salient features that make them desirable for various industrial and pharmaceutical applications (Gharpure et al. 2020). These can be synthesized by chemical processes or environment-friendly methods such as microbes, enzymes, and plants (Hasan 2014). The best-explored applications of NPs include early diagnosis, treatment, and cure of diseases such as cancer, diabetes, and cardiovascular diseases.

17.2.1 Nanoparticles as Drug Carriers

The traditional drug delivery system possesses various constraints such as insolubility of drug, low permeability to the plasma membrane, high dosage of injections, and adverse side effects. The nanotechnology-based drug delivery approach is a novel and emerging concept to overcome the pitfalls of conventional drug delivery approaches (Patra et al. 2018). One can encapsulate the drugs in the internal cavity of the NPs through non-covalent interactions and accomplish the administration of such nanomaterials-based drugs passively. After reaching its target position, the encapsulated structure unfolds, releasing the desired drug to the absolute target. Alternatively, in the self-delivery method, the drug is directly conjugated to the nanocarrier. For target drug delivery, special consideration is necessary during the early drug designing process itself. The coupling between the drug and the carrier NPs is crucial. It has to ensure that the drug does not dissociate too early from the nanocarrier, or else it will be cleared from the body without reaching its required destination. Also, if the drug is not cleaved from its nanocarrier at the optimum time, it will reduce its biological efficacy significantly (Lu et al. 2016). The following section describes the different forms of nanocarriers used for drug delivery with pictorial representation shown in Fig. 17.2.

Fig. 17.2
An illustration depicts the different forms of nanocarriers in drug delivery. It includes natural polymers, liposomes, solid lipid, polymeric, dendrimers, quantum data, metallic, and carbon based nanoparticles. The pictorial form is used to represent all nanoparticles.

Various forms of nanoparticles used for drug delivery purposes

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17.2.1.1 Chitosan

It is a biopolymer extracted from the chitinous shells of sea crustaceans. It is a nontoxic, stable, non-immunogenic, biodegradable polymer employed for the drug delivery process (Ahmad et al. 2021).

17.2.1.2 Alginate

It is a natural polysaccharide derived from the cell walls or intracellular compartments of brown algae, namely Ascophyllum nodosum and Laminaria digitata. With excellent stability, biocompatibility, biodegradability, and reduced toxicity, alginate is a proven agent for various pharmaceutical applications (Hariyadi and Islam 2020).

17.2.1.3 Liposomes

These are the spherical vesicles consisting of an inner aqueous core encapsulated around a phospholipid bilayer. Both water-loving (hydrophilic) and water-repelling (hydrophobic) drugs can form liposomes. Due to their structural similarity with the cell membrane phospholipids and superior pharmacokinetics, liposomes are attractive drug delivery tools in therapeutics (Xing et al. 2016). Apart from making the compound more stable, liposomes fulfill the 3Bs—biodegradable, biocompatible, and biodistribution. However, they are costly to produce (Yadav et al. 2017).

17.2.1.4 Solid Lipid Nanoparticles

As a substitute to conventional carrier systems, namely liposomes, emulsification, and polymeric NPs, solid lipid NPs are another form of nanocarriers for precise drug administration, non-degenerative, and a budget-friendly approach. It consists of a solid lipid matrix, a surfactant such as an emulsifier, a co-surfactant such as water or solvent, and active ingredients, particularly drugs (Basha et al. 2020). Formulations of solid lipid NPs are possible for oral, dermal, and parenteral administration.

17.2.1.5 Polymeric Nanoparticles

The 10–100 nm diametric amphiphilic solid colloidal particles formed of block copolymers hydrophobic core containing hydrophobic drug and water-soluble hydrophilic shell balancing the core are called polymeric nanoparticles. The use of polymeric nanocarriers reduces cytotoxicity and improves the stability and solubility of the drug in the bloodstream. While chitosan and dextran are natural polymers, polyamide, polyesters, and polyphosphazene are synthetic polymers (Lu et al. 2016). Polymeric micelles have a core and a shell that are hydrophilic. The hydrophilic drug is loaded in the core region of micelles.

Similarly, polymeric nanovesicles have an aqueous core and amphiphilic shell. Thus, nanovesicles can integrate both hydrophobic and hydrophilic materials like proteins, genes, and drugs. However, these structures dissociate into the linear form below its critical micelle concentration; therefore, the nanogel—a more stable polymeric nanoparticle form—is in better demand (Lu et al. 2016).

17.2.1.6 Dendrimers

The term is derived from two Greek words, “dendron” and “meros,” which means trees and the parts, respectively (Heera and Shanmugam 2015). Dendrimers indeed are highly branched nanostructures widely used for cancer treatment and bioimaging. With the properties like symmetrical molecular structure and numerous functional groups that can be modified desirably, this becomes a useful candidate for various therapeutics and drug delivery (Abbasi et al. 2014). However, the positively charged dendrimers can alter the cellular membranes and become poisonous to the cell.

17.2.1.7 Quantum Dots

Quantum dots are mini beads of free electrons possessing unique electronic and optical properties. It is a luminescent semiconductor nanocrystal with a 2–10 nm nano-diametric range (Cartaxo 2016). They are generally of two types: simple or core quantum dots (composed of a single material) and core-shell quantum dots (in which the material with a wider energy gap is enclosed by a material having a smaller energy gap). The commonly used material for quantum dots are indium phosphide, cadmium selenide, cadmium telluride, zinc sulfide, and indium arsenide (Ilaiyaraja et al. 2018). These tiny devices are reportable therefore suitable for therapeutic, biosensing, bioimaging, and protein-specific applications or targeting (Riyaz et al. 2019).

17.2.1.8 Metallic Nanoparticles

Metallic NPs consist of metals such as silver, titanium, and gold, metal oxides such as ZnO, magnetic oxides, and semiconductors such as CdS. These are easily transported to the cells due to their appropriate size (10–100 nm) and are not affected by the in vivo environment (Ojea-Jimenez et al. 2013). They are efficient in drug delivery and possess antioxidant properties (Khiev et al. 2021).

17.2.1.9 Carbon-Based Nanoparticles

The different allotropic forms of Carbon are helpful for pharmaceutical applications. Carbon-based NPs include carbon nanotubes, fullerene, and nanodiamonds. Fullerene is a highly symmetrical icosahedron having 60 carbons. Carbon nanotubes are single-walled or multi-walled nanotubes. These have a wide range of applications as they exhibit unique properties, namely elasticity, rigidity, electric conductivity, and thermal conductivity (Wilczewska et al. 2012).

17.2.2 Advantages of Drug Administration Employing Nanoscience

Nanostructure-mediated drug delivery comes with increased solubility, more surface area, high dissociation rates, decreased dosage amount reducing toxicity, improved stability, and many more benefits. Nanoparticle-based therapeutics exhibit better efficiency and site-specific drug release due to their nano size and bioavailability to specific tissue/organs. Also, it reduces the side effects of various drugs (Pardhiya and Paulraj 2016). It prolongs the circulation time of the drug, and increases drug penetration. Nanocarriers are generally biodegradable in nature, and, thus, are risk-free. It also protects the drug from premature degradation, increasing its life span. Particle size and surface characteristics of NPs can be easily manipulated to achieve both passive and active drug targeting after parenteral administration (Mitchell et al. 2020).

17.2.3 Disadvantages of Drug Administration Employing Nanoscience

The advantages provided by the NPs are immense, yet some of the limitations need mention and may not be ignored. The large surface area of nanosized particles makes these particles highly sensitive to the biological environment. Similarly, some NPs, such as polymeric NPs, have limited drug-loading capacity, which is a serious disadvantage. Some forms of NPs may cause systemic toxicity, which is an important consideration for clinical use. The small size and increased surface area may also lead to the accumulation of particles, making the physical management of NPs difficult both in dry and liquid states (Mohanraj and Chen 2006). Nanoparticle synthesis may not be economical and may require sophisticated technology and skilled human resource for large-scale manufacturing.

17.3 Applications of Nanoparticles

17.3.1 Nanoparticles as Antibacterial Agents

At least 1% of the bacteria present in the ecosystem are responsible for causing illness in humans. What might appear small percentage includes a plethora of highly infectious organisms, including but not limited to Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Mycobacterium tuberculosis, Staphylococcus aureus, and Clostridioides difficile. The frequent and prolonged use of commonly available antibiotics has led to antibiotic resistance in bacteria, making them less effective and creating a major public health problem. The pipeline for new drugs has been static for quite a while; therefore, there is a desperate need to find creative solutions to bacterial infections and combat antimicrobial resistance. According to the WHO’s 2020 annual review of the clinical and preclinical antibacterial pipelines (World Health Organization 2021), five key criteria were highlighted: (a) Target priority pathogens, (b) Overcome existing resistance, (c) Address a public health need, (d) Preserve effectiveness, and (e) Make accessible to all. Metal NPs with antibacterial activity meet all these criteria and have emerged as non-traditional but promising antibacterial agents. Different synthesis methods can produce NPs of varied shapes and dimensions, which shows strong and extended antimicrobial activity against a broad-spectrum of infectious bacteria (Correa et al. 2020). It has also been theorized that the ability of NPs to target multiple biomolecules in an organism can potentially bring the evolution of resistant bacteria to a standstill (Slavin et al. 2017). A diagrammatic representation of various mechanisms of action and targets of metal NPs in a bacterial cell is shown in Fig. 17.3. This chapter summarizes the latest understanding of the antimicrobial potential of NPs, wherein we have outlined the most recent and most cited papers that progressively endorse metallic NPs as the new antibiotic alternatives.

Fig. 17.3
A diagram represents the antibacterial mechanisms of metallic nanoparticles. It includes cell membrane invasion and disruption, E T C blocked, base intercalating agent, attachment to 30 S subunit and protein synthesis inactivation, damage to proton efflux pumps, biofilm inhibition, and oxidation of cellular components.

Mechanisms of action and targets of metallic NPs in a bacterial cell. (A) Bacterial cell walls have an overall negative charge on them, attracting metal ions released from NPs to the membrane. The ions penetrate the membrane, creating pores and destabilizing its structure. (B) Mitochondrial toxicity by causing a loss in membrane potential and inhibiting ATPases thereby blocking the electron transport chain (ETC) and ATP generation. (C) The metal ions released from NPs enter the bacterial genome and intercalate between bases by attaching to their S or P groups leading to cytotoxic mutations. (D) Ions released from amassed NPs in the cytoplasm denature the ribosomal subunits and hinder protein synthesis. (E) NPs block the proton efflux pumps on bacterial membranes and thereby prevent them from extruding toxins. (F) NPs affect biofilm integrity by inhibiting EPS production and interrupting bacterial communication required for quorum sensing. (G) NPs can induce oxidative stress in the bacterial cell by generating reactive oxygen species, which oxidize glutathione, leading to suppression of the bacterial antioxidant defense system and allowing the metal ions to freely interact with cellular organs and disrupt their functions, leading to cell death

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Silver (Ag) is the most sought-after metal for synthesizing NPs. In a study by Mohanta’s group (2020), spherical silver NPs were synthesized in conjugation with fresh leaf extracts from three plants Semecarpus anacardium (SA), Glochidion lanceolarium (GL), and Bridelia retusa (BR). Successful synthesis was confirmed by observing a color change in the solution from the pale-yellow mixture of leaf extract to a deep brown color. Results from SEM micrographs determined their size range as 52–96 nm. The particles exhibited antibacterial and antibiofilm activity against three pathogenic bacteria: E. coli, P. aeruginosa, and S. aureus. SA-AgNPs showed the best antibacterial and antibiofilm with minimum inhibitory concentration (MIC) values. Antibacterial MICs are as follows, E. coli: 23.49 μg/mL, P. aeruginosa: 12.9 μg/mL, S. aureus: 33.72 μg/mL, and antibiofilm MICs are E. coli: 23.42 μg/mL, P. aeruginosa: 12.9 μg/mL, S. aureus: 33.77 μg/mL, respectively. Comparative analysis also indicated that GL-AgNPs were more active against gram-positive organisms (S. aureus), whereas SA-AgNP and BR-AgNPs had the most potent activity against gram-negative organisms (P. aeruginosa and E. coli) (Table 17.1). In a similar study, Ahmed’s group (2020) involved green synthesis of silver NPs using the culture of silver-resistant Bacillus safensis TEN12 strain. UV-Vis spectroscopy was used to confirm the formation of AgNPs at an absorption peak at 426.18 nm, and FTIR analysis revealed that the AgNPs were stabilized by capping proteins and alcohols. The NPs were spherical, with sizes ranging between 20 and 45 nm, as confirmed by SEM and TEM. Disk diffusion and dilution assays revealed antibacterial activity against S. aureus with a zone of inhibition (ZOI) of 20.35 mm along with ~78% growth reduction and in E. coli ZOI was 19.69 mm and ~75% reduced growth. MTT assay with the NPs on the HepG2 cell line reported ~36% viability of cells. Both studies clearly showcase the strong potential of AgNPs as antibacterial therapeutic agents.

Table 17.1 Nanoparticles as antibacterial agents
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Rozilah’s group (2020) reported the production of antibacterial polymer films made of sugar palm starch biopolymer composite films and AgNPs (0%, 2%, 3%, 4%). At higher AgNPs percentages, there was a noted increase in film elasticity and reduced molecular mobility of matrix, making the nanocomposite films more resistant to breaks, wear, and tear. FE-SEM was used to characterize the nanostructures of films, and the average size of AgNPs was 67.73 ± 6.39 nm. The nanocomposites with thickness ranging from 0.180 to 0.250 ± 0.05 mm were cut into circular disks and immersed in bacterial cultures to determine their activity against S. aureus, E. coli, and S. cholerasuis. Maximum inhibitory activity (ZOI ranging from 7 to 8 mm) was observed against gram-negative bacteria using bio-composite films with 3–4% AgNPs, which can further be explored to prepare films with food packaging applications. In retrospect, silver is a metal with attractive antibacterial potential, and therefore AgNPs must be pushed forward as commercial broad-spectrum antibacterial therapeutic agents. The anti-infective activity of AgNPs inspired the exploration of other metals for similar properties against infectious bacteria. Al-Musawi’s group (2020) developed gold nanofibers by conjugating Honey/tripolyphosphate/chitosan (HTCs) fibers with Capsicum annuum (CA) and gold NPs. FE-SEM analysis revealed a size range of 351 ± 78 nm and a fibrous, dense, smooth, clear, and bead-free morphology. Disk diffusion assay confirmed antibacterial activity against P. multocida: 34 mm (HTC-CA/AuNPs), K. rhinoscleromatis: 31.5 mm (HTC-CA/AuNPs), S. pyogenes: 30.5 mm (HTC-CA/AuNPs), V. vulnificus: 34 mm (HTC-CA/AuNPs). Although, HTC-CA and HTC-AuNPs showed better results for P. multocida, K. rhinoscleromatis. MTT assay for HTC-CA/AuNP showed 61% cell viability, over 20% greater than the other nanofibers. HTC-CA/AuNP also demonstrated superior wound healing abilities compared to HTC-CA and HTC-AuNPs dressings thereby indicating the multi-pronged potential of these nanofibers.

Roy’s group (2020) developed an antibacterial biofilm from Edible biopolymer (pullulan/carrageenan), d-limonene (DL) and copper sulfide NPs (CuSNPs). The CuSNPs and DL fillers enhanced the UV-light shielding and mechanical properties of the film without altering the thermal stability and transparency. The greenish films showed a reduction of 7 log cycles for E. coli and about 2 log cycles for L. monocytogenes, a common pathogenic food microbe. In another study, Gabrielyan’s group (2020) demonstrated citric acid-coated Ag and iron oxide NPs with antagonistic activity towards two strains of E. coli K12 (Wild type) and pARG25 (kanamycin-resistant) and Salmonella typhimurium. AgNPs effect was more pronounced on all the strains but iron oxide NPs also suppressed the bacterial growth rate of E. coli wild type, E. coli (kanamycin-resistant), and S. typhimurium by 1.3-, 2.5-, and 4-folds, respectively. A study on zinc NPs by Basri’s group (2020) explored an exciting approach of conjugating zinc NPs with pineapple peel waste under temperature control and embedding zinc NPs in starch films to test for their antibacterial activity. Morphological experiments by SEM and TEM showed the non-heated (28 °C) zinc NPs as a mixture of spherical and rod-shaped (8–45 nm), whereas the heated (60 °C) zinc NPs were flower rod shapes (73–123 nm), and the zinc-starch nanocomposite films were 6 mm in diameter. The nanocomposite films prepared with non-heated zinc NPs showed higher efficacy than heated zinc NPs against B. subtilis at three NP concentrations 1%, 3%, and 5%. B. subtilis lawn indicated that films formed with 3% zinc non-heated and heated NPs showed the best antibacterial activity with ZOI of 15 and 12.33 mm, respectively. Therefore, this strategy could be further explored as a narrow-spectrum antibacterial agent. An intriguing study by Rehman’s group (2020) illustrated the synthesis of titanium NPs in combination with intracellular extract of a wild mushroom, Fomes fomentarius. FE-SEM showed titanium NPs as aggregated, irregularly shaped with a rough surface in the size range of 80–120 nm. Antibacterial disk diffusion assay showed promising titanium NPs against E. coli (ZOI: 15 mm) and S. aureus (ZOI: 11 mm). Other recent studies using Silica, Selenium, and Zinc NPs with conjugates significantly indicate their antibacterial potential against E. coli and S. aureus (Joyce et al. 2020; Huang et al. 2020; Naseer et al. 2020). The NPs in these studies could be strong prospects of broad-spectrum antibacterial agents against the most commonly observed, virulent gram-positive and gram-negative microorganisms.

17.3.2 Nanoparticles as Antifungal Agents

Fungal pathogens are the most common cause of bloodstream infections in hospitalized patients (Pfaller et al. 2020). The fungal toxins cause severe and life-threatening infections in humans and animals, leading to hepato- and nephrotoxicity, pulmonary infections, immunosuppression, and cancer (Khatoon et al. 2015; Claeys et al. 2020). Severe fungal infections begin with fungal colonization followed by microbial colonies leading to complex multicellular biofilms, which are very hard to fight off with conventional antifungal agents (Paul et al. 2018; Guerra et al. 2020). The use of several antifungal agents for the treatment of fungal infections has been proposed, but most of them are not approved due to limited clinical data (Arastehfar et al. 2020; Wall and Lopez-Ribot 2020). The production and characterization of NPs synthesized using a variety of metallic/nonmetallic components, and variable sizes and shapes have diversified their applications in healthcare and the food sector (Shakibaie et al. 2015). NPs facilitate efficient, targeted delivery of active ingredients with slow-release and long-lasting effectiveness (Silva Viana et al. 2020). Several research groups have evaluated the use of metal NPs alone and as conjugates with antifungal drugs, algal extracts having antifungal properties (Guerra et al. 2020; Cleare et al. 2020; Sattary et al. 2020). Silver is the most commonly applied metal for antifungal assessment, owing to its broad antimicrobial spectrum and less toxicity in mammals (Guerra et al. 2020; Silva Viana et al. 2020). However, the use of other metals like gold, zinc, titanium, and selenium (Pariona et al. 2019; Osonga et al. 2020), and nonmetallic substances like silica and chitosan has also been described (Kalagatur et al. 2018). Discussed below are relevant studies from the past year as available on PubMed, which reported a high antifungal potential of NPs and conjugates (Table 17.2).

Table 17.2 Nanoparticles as antifungal agents
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Guerra’s group (2020) tested the effectiveness of AgNPs against pathogenic Candida tropicalis and nonpathogenic probiotic Saccharomyces boulardii. The rationale behind the study was to search nanomaterials with significant inhibition of the growth of pathogen microorganisms without eradicating other nonpathogenic species like S. boulardii. Synthesized AgNPs have a polygonal-like shape with an average size of 35 ± 15 nm having 1.2% weight of metallic silver stabilized with 18.8% weight of polyvinylpyrrolidone (PVP) in 80% weight of distilled water. The results revealed that 25 μg/mL AgNPs are sufficient to inhibit 90% of the C. tropicalis cell growth in comparison to 60% by Fluconazole at 35 μg/mL and 95% inhibition by Amp B at 5 μg/mL. The results indicate selective inhibition of pathogenic fungi by AgNPs as approximately 50% of the S. boulardii cell population remains viable in the presence of AgNPs, which can initiate further cell multiplication. Hosseini’s group (2020) investigated the antifungal effect of zinc oxide (ZnO) NPs and Nystatin on inhibiting the growth of C. albicans isolates, causing vulvovaginal candidiasis (VVC). All isolates were susceptible to treatment at the lowest MIC value of ZnO-NPs (0.02 μg/mL) and Nystatin (0.6 μg/mL), respectively. The results indicate that both ZnO-NPs and Nystatin might be suitable inhibitors of Candida sp., with the highest sensitivity to ZnO at MIC 90, ≥0.5 μg/mL compared to the non-treated control samples. Therefore, ZnO can act as a potential agent for the control, prevention, and treatment of VVC. Similar observations against Amp B-resistant C. albicans are recorded using gold, silver, and selenium NPs (Lotfali et al. 2021). Piktel’s group (2020) demonstrated a significant reduction in filament formation following the incubation of conidia with average survival rates of 16.50 ± 11.12%, 10.8 ± 13.25%, 1.67 ± 0.19%, and 0.9 ± 0.51% for the tested C. albicans, C. glabrata, C. tropicalis, and C. krusei isolates at a dose of 1 ng/mL. No hemolytic activity was recorded at fungicidal doses, along with a reduction in biofilm formation at relatively low doses of 0.5–5 ng/mL. Cleare’s group (2020) also demonstrated significant growth inhibition of Candida auris strains and a >70% decrease in biofilm viability after treatment with 10 mg/mL of nitric oxide NPs. Green synthesized gold NPs synthesized using algae Chlorella sorokiniana displayed prominent activity against Candida tropicalis, C. glabrata, and C. albicans (Gürsoy and Öztürk 2021). The effectiveness of metallic NPs against Aspergillus sp. is also widely explored. Although lower than the conventional fluconazole antifungal drug, tungsten trioxide-doped zinc oxide NPs are found effective against Aspergillus sp. (A. niger and A. flavus) and Penicillium notatum (Arshad et al. 2020). Further, improvements with such rarely used metal NPs can be made by optimizing the metal concentration and reaction conditions.

Apart from the human pathogenic fungi, the use of antifungal NPs has overcome the persistent limitations of using conventional chemical fungicides in the management of plant diseases. Studies have reported the antifungal activity of metal NPs against a soil-borne plant pathogen, Fusarium oxysporum. A reduction in colony diameter of phytopathogenic fungal strains of Fusarium (F. oxysporum DSM 62338 and F. oxysporum DSM 62060) that affect tomato production was recorded when treated with chitosan-stabilized gold (AuNPs) and Carbon (CNPs) (Lipșa et al. 2020). A mycelial growth inhibition rate of 100% was achieved in the case of F. oxysporum DSM 62060 using 5 mL of three different concentrations of NPs (AuNP25, AuNP50, AuNP75). However, maximum growth inhibition of 54.1% was observed in the case of F. oxysporum DSM 62338. CNPs resulted in maximum inhibition of 42.4% and 36.5% for F. oxysporum DSM 62338 and F. oxysporum DSM 62060. Another study by Kalia’s group (2021) reported extensive leakage of the cytoplasmic material from the hyphal tissue along with the swelling of the hyphae cells in the tested fungal species (Fusarium oxysporum > Curvularia lunata > Macrophomina phaseolina) at a 40 mg/L concentration of zinc oxide NPs. Wheat rust caused by Ustilago tritici is responsible for global losses in wheat production and harvesting. Irshad’s group (2020) has reported a high antifungal potential of green synthesized titanium dioxide-based NPs, especially those produced using C. quinoa extract. Similarly, phytopathogenic Setosphaeria turcica is responsible for severe foliar disease in maize crops. Spherical AgNPs with an average size of 13 nm, synthesized with Ligustrum lucidum leaf extract, effectively against S. turcica with IC50 of 170.20 μg/mL (Huang et al. 2020). Sattery’s group (2020) reported antifungal effects of the mesoporous silica NPs encapsulated with lemongrass and clove oil increased threefold after encapsulation into NPs with a 70% disease control confirmed by in vivo studies. One of the most delicious tropical fruit, mango, suffers severe damage due to anthracnose produced by phytopathogenic Colletotrichum gloeosporioides (Kamle and Kumar 2016). Anthracnose is responsible for huge (sometimes up to 100%) postharvest loss for mangoes produced under wet or humid conditions. A promising dose-dependent antifungal activity of copper NPs in the size range of 100–300 nm has been reported against C. gloeosporioides with 100% growth inhibition at 200 ppm copper (Nguyen et al. 2020). Hashem’s group (2021) reported antifungal activity of selenium NPs against Rhizoctonia solani RCMB 031001 both in vitro and in vivo with minimum inhibition and minimum fungicidal concentrations of 0.0625 and 1 mM, respectively. A decrease in the severity of root rot disease was noted after treatment. Another report (Akpomie et al. 2021) on plant pathogenic fungi describes a maximum inhibition of Alternaria sp. and F. oxysporum after treatment with zinc NPs. The largest zone (25.09–36.28 mm) against A. alternata CGJM 3006 was observed at a concentration of 0.002–5 mg/mL, followed by F. verticilliodes CGJM 3823 (23.77–34.77 mm) and A. alternata CGJM 3078 (22.73–30.63 mm) in comparison to a positive control (5% bleach). Lastly, copper NPs have shown promising activity against A. niger, F. oxysporum, and A. alternata (Shende et al. 2021).

17.3.3 Nanoparticles as Antiviral Agents

Viruses are the disease-causing agent and have been the causative agent of various diseases in humans. They have a global presence and are responsible for pandemics and epidemics in the past. Viral infections have high morbidity and mortality rate as more than half a million (0.69 million) people died from AIDS-related illnesses in 2019 (Mahy et al. 2019). Respiratory viral infections are easily transmissible and result in a high death rate. Since the exposure of Corona virus disease 2019 (COVID-19), 50 million people were affected, and 3.15 million deaths were observed until April 2021, making it the highest pandemic of the century (Riffe and Acosta 2021). They also cause severe infections, as seen in the case of the Zika virus that results in encephalopathy and meningitis (Nunes et al. 2016). This also affects socioeconomic ratios and impacts the quality of life, as we have seen in the recent pandemic of COVID-19. Considering how prevalent these viral infections are, there is a smaller number of antiviral drugs available. The available vaccines need to be upgraded as the virus mutates rapidly, leading to a new strain, making the available vaccine less effective. Although the search and development of new antiviral are difficult but new and promising therapies have been suggested. NPs have very compelling properties that include optimal size, shape, immuno-compatibility, biodegradability, slow release in bloodstream, and importantly can cross blood-air as well as the blood–brain barrier thus can be precise for a target. NPs alone or in conjugation with antiviral drugs seem to be potential antiviral therapy candidates (Jiao et al. 2018; Szunerits et al. 2015; Gurunathan et al. 2018). The snapshot of antiviral mechanisms of NPs is presented in Fig. 17.4. Thus, to explore the role of the potential impact of NPs in antiviral therapy, we have discussed past 1-year studies retrieved from PubMed using keywords as antiviral and nanoparticles in the advance search option (Table 17.3).

Fig. 17.4
A diagram represents nanoparticles antiviral mechanism. It consists of 2 types, indirect, which acts at host, and direct, which acts at virus. The mechanism of the antiviral nanoparticles is presented in detail below.

Pictorial representation of NPs as antiviral agents

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Table 17.3 Nanoparticles as antiviral agents
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The study done by Bharti’s group (2021) explored the potential of colloidal and immobilized glass silver NPs against water-borne bacteriophages. The particles were synthesized using a chemical reduction approach and immobilized by post-immobilized method on a glass substrate having amines as a functional group. SEM and TEM platforms characterized NPs. Colloidal silver NPs inactivated the T4 bacteriophage and MS2 at the concentration of 60 μg/mL, making the drinking water free from these viruses. As the COVID pandemic is going on, there is an urgent need for a vaccine. So, many NPs emerged as potential candidates against SARS-CoV2. In a study done by Wang’s group (2021), cell membrane-based NPs were formed by the classical extrusion method, in which HEK-293 T-hACE2 cells were used for experimentation. These NPs exhibit affinity towards ACE2 receptors to attach to S1 of spike protein,-making the virus less available to HK-2 cells and reducing the infection. The TEM analysis revealed a diameter of size 100 nm. The conjugated NPs efficiently reduced the adherence of severe acute respiratory syndrome corona virus 2 (SARS-CoV2) and its mutant D614G-S1 (which is prevalent globally) to HK-2 cells. IC50 to neutralize the SARS-CoV2 pseudovirions is 431.2 ng/mg. It is nontoxic, both in vitro and in vivo, making it a potential candidate against the virus. A similar study against SARS-CoV2 by Rao’s group (2020) has taken membrane vesicle nanodecoy with 100 nm in size analyzed by TEM. They have shown that it binds and neutralizes inflammatory cytokines, including interleukin 6 (IL-6) and granulocyte-macrophage colony-stimulating factor (GM-CSF). In vivo study also showed that it suppresses pneumonia in mice models. In an interesting study done by Jeremiah’s group (2020), to determine the size and concentration at which silver NPs inhibit the SARS-CoV2. They have taken different sizes and concentrations and found that at around 10 nm, a concentration ranging from 1 to 10 ppm showed an inhibitory effect. The concentration above 20 ppm causes cytotoxicity in veroE6 cells/TMPRS22, and they also showed that AgNPs inhibit the viral entry by destroying the integrity of the virus, confirmed by luciferase-based assay. Surnar’s group (2020) using ivermectin drug loaded with poly(lactide-co-glycolide)-b-poly(ethylene glycol)-maleimide (PLGA-b-PEG-Mal) polymer and tagged with Fc immunoglobulin fragment. Ivermectin is a clinically antiviral-approved drug, but its single dose is toxic to the body, and fast clearance results in the noneffectiveness of the drug. So, the NPs are loaded with medicine cause it is slowly released into the bloodstream. Further attachment to Fc helps in crossing the gut epithelial barrier to reach the bloodstream. It has been shown in the study that free ivermectin is less effective in inhibiting or reducing the expression of pseudo-SARS-CoV2 as well as HEK293T expressing spike protein than ivermectin NPs. There are other studies also which proposed that Silver NPs are a potential candidate for inhibiting SARS-CoV2 shown by homology modeling and other bioinformatics studies (Pilaquinga et al. 2021; Varahachalam et al. 2021). Plants extract with known antiviral properties has been taken in nano form against Hepatitis C virus, as seen in a study by Al-Ansari’s group (2021). Traditional medicine formed from the herbal mineral Linga chenduram was used. It consists of mercury and sulfur elements in large amounts, but other metals like silver, iron, and molybdenum were also present in trace amounts shown by EDAX analysis. The particles are in the range of 9.71–18.40 nm, having spherical, but other shapes like triagonal, cubic, and hexagonal also exist. The inhibitory effect was seen on Huh-7 hepatoma cell line, showing a strong impact in a dose-dependent manner. It is nontoxic to the cell line and in vivo in the male albino rat. In a study against the ZIKA virus, curcumin is used, which has antiviral antibacterial activity. The NPs are made using Poly-lactic-co-glycolic acid (PLGA) as a polymer matrix. The size of the NP is 210 ± 40 nm, as observed from SEM, whereas DLS shows 780 nm size. This difference arises due to the aggregation of NPs in DLS as performed at 25 °C. In an in vitro study, in Vero cells, the E50 value was 3.7 ± 0.05 mm. The antiviral activity of PLGA-curcumin is more than free curcumin. Also, the synthesis of virus protein in Vero cells reduces as there has been a reduction of 68% in E-protein synthesis when incubating with PLGA-curcumin compared to only 20% reduction seen with free curcumin (Pacho et al. 2021). In a fascinating study done by Bianchin’s group (2021), they made children-friendly drugs for HIV using monoolein-based NPs containing indinavir drug, a particle size of 155 ± 7 nm. The monoolein successfully masked the bitter taste of the known anti-HIV drug indinavir, making it suitable for children to eat. Another study against the influenza virus done by Kiseleval’s group (2020) using silver NPs reported that it lowers the oxidase activity, prevents the lesion, and increases the life expectancy of female CBA mice. The characterization is done by TEM with a mean average size of 20–25 nm.

17.3.4 Nanoparticles as Anti-leishmanial Agents

Leishmaniasis is a widespread neglected tropical disease caused by protozoan parasites belonging to the genus Leishmania. Clinically, the disease is classified into three primary forms, cutaneous, mucocutaneous, and visceral leishmaniasis. Among them, visceral leishmaniasis is the fatal one and annually, 20,000–30,000 deaths occur due to this disease. Treatment regimens rely upon a few numbers of drugs such as pentavalent antimonials, Amp B, Miltefosine, and Paromomycin (Singh et al. 2016; Altamura et al. 2020). With increasing drug resistance and toxicities against these drugs, it is the need of the hour to improve the drug delivery approach to fight against leishmaniasis. In the following section, we have tried to discuss the last 1-year research publications retrieved from PubMed, which elucidate the role of NPs in anti-leishmanial therapy (Table 17.4).

Table 17.4 Nanoparticles as anti-leishmanial agents
Full size table

Saqib’s group (2020) assessed the anti-leishmanial activity of polycaprolactone (NPs) containing Amp B against two strains of the parasite (L. donovani and L. tropica KWH23). NPs formed were spherical with an average size of 183 nm and encapsulation efficiency of ~86% analyzed by UV-visible spectrophotometer. Macrophages cell line (J774) was infected with L. donovani and L. tropica KWH23 parasites, and anti-leishmanial activities of NPs, Amp B, and Ambisome were evaluated in a dose-dependent manner. As reported, inhibitory concentration (IC50) of NPs, Amp B, and Ambisome against L. donovani are 0.23, 0.21, and 0.28, respectively, and against L. tropica KWH23 these values are 0.03, 0.19, and 0.25 μg/mL, respectively. IC50 of NPs against L. tropica KWH23 was significantly lower as compared to the standard drugs. Thus, this formulation can provide a novel option for treating cutaneous infections caused by the L. tropica parasite. In another study, Almayouf’s group (2020) determined the effect of silver NPs against cutaneous infection of leishmaniasis in female Balb/c mice. Silver NPs containing Fig and Olive extracts were biosynthesized, and TEM studies confirmed the spherical shape of NPs, along with size ranging from 50 to 100 nm. Infection in Balb/c mice was developed by giving a subcutaneous injection of L. tropica parasites above the tail area. After the completion of 3 weeks, the mice group which were pretreated with NPs reported significantly reduced skin lesions as compared to the untreated group. Pretreatment with NPs also reduced oxidative stress and increased antioxidant enzyme activities in L. major infected Balb/c mice. NPs pretreated mice group also showed a marked decrease in the mRNAs expression levels of interleukin (IL)-1β and tumor necrosis factor (TNF)-α. In another study, Awad’s group (2021) synthesized silver NPs using Commiphora molmol (myrrh) and performed in vitro and in vivo assays against L. major. Dose-dependent reduction in the growth of L. tropica promastigotes was observed during in vitro studies and in vivo studies in BALB/c mice also reported complete healing of the skin lesions within 3 weeks of infection. In both studies mentioned above, lesion healing was significantly better as compared to the standard drug pentostam. Other recent studies also signify the protective efficacy of NPs against cutaneous infection caused by the Leishmania parasite (Bahraminegad et al. 2021; Riezk et al. 2020; Sepulveda et al. 2020; Silva Viana et al. 2020). In an interesting study, Javed’s group (2020a) explored the role of non-oxidative biocompatible silver NPs synthesized from an aqueous extract of Mentha arvensis against L. tropica. The average size of NPs was 20–100 nm, and they were structurally anisotropic, confirmed by SEM and AFM studies. Biocompatible NPs were highly effective against L. tropica promastigotes as 10 μg/mL dose of NPs killed ~50% of the parasite. In a similar study by the same group (Javed et al. 2020b), silver NPs were phyto-synthesized from an aqueous extract of Mentha longifolia. They reported dose-dependent killing of L. tropica parasites, with 10 μg/mL dose of NPs killing ~67% of the parasite. Both silver, as mentioned earlier NPs were also effective in killing various plant bacterial pathogens (Javed et al. 2020a, b).

As the drug resistance cases against the current treatment regimen for visceral leishmaniasis are on the rise, Alti’s group (2020) synthesized biogenic bimetallic NPs using herbal leaf extracts to evaluate the anti-leishmanial effect against promastigote and amastigote forms of L. donovani. TEM and EDX studies confirmed that NPs formed were well separated, spherical, and had an average size of 10–12 nm. As reported, IC50 of bimetallic NPs against promastigote was significantly lower (0.035 μg/mL) than the standard drug miltefosine (10 μg/mL). Bimetallic NPs were also successful in reducing the amastigote form of the parasite by 30–45% in L. donovani infected THP-1 cell line. Mechanistic studies revealed that parasite cell death occurred due to reactive oxygen species-induced apoptosis.

Similarly, Kumar’s group (2019) also reported improved anti-leishmanial efficacy (~5 folds) of gold NPs conjugated with Amp B compared to Amp B alone during ex vivo studies. The above studies suggest that the metallic NPs-based drug delivery approach can be explored as an alternative option to the available standard drugs. In an attempt to increase the bioavailability of Amp B, Ray’s group (2020) developed enteric-coated guar gum NPs containing natural bioenhancer (piperine) and Amp B suitable for oral administration. These NPs displayed controlled drug release and also protected the drug from the acidic pH of the stomach. In vitro studies of these NPs against promastigotes and amastigotes of L. donovani parasites exhibited two to threefolds higher IC50 than Amp B drug alone. Golden hamster animal model infected with L. donovani also showed significant anti-leishmanial activity with ~90% parasite clearance along with enhanced drug bioavailability confirmed by pharmacokinetics and biodistribution studies. In another study, Parvez’s group (2020a) reported the use of 2-hydroxypropyl-β-cyclodextrin (HPCD)-based solid lipid NPs composed of Amp B and paromomycin as an oral drug delivery approach. NPs were spherical with an average size of 141 ± 3.2 nm, confirmed by SEM and TEM studies. The safety and biocompatibility of formulated NPs were confirmed by cytotoxicity studies performed in the J774A.1 macrophage cell line and Swiss albino mice model. Ex vivo studies reported the inhibition of growth of L. donovani amastigotes with an IC50 value of 0.013 μg/mL, and in vivo experiments performed in BALB/c mice infected with L. donovani also showed a 70–90% decrease in parasite burden. In a similar study by the same group (Parvez et al. 2020b), the use of chitosan-based NPs containing Amp B and paromomycin drugs proved effective in inhibiting the growth of the L. donovani parasite. Thus, the above studies suggest that NPs-based oral drug delivery approach is the way forward to fight against leishmaniasis.

17.4 Conclusion and Future Perspectives

It is evident from the above context that the synergistic effect of nanotechnology with nanoscience has revolutionized the path of therapeutics approaches. With the excellent efficacy of NPs as antibacterial, antifungal, antiviral, and anti-leishmanial candidates, it is the future ray of hope in overcoming drug resistance and enhancing the killing efficacy of the drug. The use of metallic, liposomal, solid lipid NPs and polymeric micelles aided in on-point drug delivery, treatment shortening controlled drug release, and reduced considerable toxicity. The major action mechanisms employing NPs are enhancing oxidative/nitrosative production in parasites and bacteria, inhibiting biofilm formation in fungi and bacteria, and remodeling viral capsid proteins to disrupt its function and halt replication machinery of the virus. However, NPs are mostly restricted to the study and do not enter clinical trials owing to extensive cost, complicated synthesis mechanism, and low drug loading capacity. Despite these limitations, NPs carry significant potential pertaining to drug delivery approaches. Developing improved preclinical animal models along with a well-versed biological concept can improve the NPs-mediated drug delivery system. Eventually, alliance with theoretical and experimental researches across academia, pharmaceutical industry, and medicine will assist in taking forward these discoveries from research laboratories to the standard population. Therefore, there is an imperative urge to overdue these downfalls and explored realistic applications of NPs for next-generation drug delivery platforms.