Keywords

12.1 Introduction

Gold nanoparticle (GNP) bioconjugation has emerged as an important method for the advanced identification of pathogens (Pissuwan et al., 2010). Unique optical and surface properties and consistency make GNPs an unavoidable vessel for bioconjugation. Many scientists have studied the antibody bioconjugation of GNP to apply as a detector to find specific type of bacteria. Recently, antibody-conjugated GNPs have been synthesized for the detection of protein markers via tissue imaging and immune capture assays. In antibody-conjugated GNPs, antigens were tagged and noted from gold ions generated by laser ionization mass spectroscopy (El-Sayed & Huang, 2005). According to the researchers, GNPs can be applied as adjuvants to increase the effectiveness of vaccines (Dykman, 2020). It has been done by stimulating antigen-presenting cells and controlled antigen release. According to the reports, GNPs have been applied to synthesize antibodies and vaccines against more than 45 types of pathogens of viral, bacterial, and parasitic infections. GNPs as carriers and as adjuvants help increase the immune response and support vaccine design. GNPs have been used as antigen carriers for immunization and vaccination in the last few decades. Due to their low toxicity, simple preparation, and unique physicochemical properties, they are applied in the biomedical field. According to the earlier reports, adjuvant characteristics are inherited in GNPs. This chapter discusses their synthesis, functionalization, and applications (Fig. 12.1).

Fig. 12.1
A schematic of gold nanoparticle with its structures, functionalization, characterization, and applications. The structures have spheres, stars, rods, cubes, and plates. Therapeutic and diagnostic applications are depicted. The characterization has U V-V I S, X R D E D X, S A X S, and F T-I R.

Structure, characterization, functionalization, and applications of GNPs

Full size image

12.2 Synthesis and Properties of GNPs for the Synthesis of Antibodies and Vaccine Development

12.2.1 Synthesis of GNPs

There are two methods for synthesizing GNPs: the top-down and bottom-up methods.

12.2.1.1 Top-Down Approach

It is a subtractive method, beginning with the segregation of bulk materials and ending with self-assembled nanoscale objects, for example, micropatterning and photolithography (Fu et al., 2018). The top-down approach is fast, but the main concern is about achieving a uniform size during the synthesis. Recently developed micro-contact deprinting overcomes the limitation. It is a fast and cheap method to synthesize NPs on a wide range of substrates. Other methods such as pyrolysis, lithography, radiation-induced method, and thermolysis are also used for synthesis.

12.2.1.2 Bottom-Up Approach

The bottom-up approach is an emerging method. It involves three types of syntheses.

  1. I.

    Physical Approach: It involves microwave irradiation, ultrasound irradiation, ultraviolet irradiation, laser ablation, ion implantation, and gamma irradiation (Bandi et al., 2023).

  2. II.

    Chemical Approach: It involves chemical irradiation of metal ions in solution by adding stabilizing agents, chemical agents, etc. Stabilizing agents include sodium borohydride, sodium hydroxide, lithium aluminum hydroxide, and ethylene glycol (Huang & Yang, 2004).

  3. III.

    Biological Approach: In this approach, intracellular and extracellular extracts of eukaryotic and prokaryotic cells and various extracts from the parts of the plants are used (Patil & Kim, 2017).

12.2.2 Properties of GNPs

GNPs are used to synthesize antigen carrier systems for immunization. They are easy to synthesize and exhibit unique physicochemical properties. GNPs are used in different therapeutics and other applications as they can convert electromagnetic radiation to heat. GNPs display a unique surface area, size, and shape. They also possess high uptake efficiency (Jain et al., 2006). Therefore, they can penetrate into blood vessels and tissue barriers and reach the targeted sites. GNPs possess a large surface area and can be effectively applied in biomedical applications. They are applied in drug delivery, therapeutics, photothermal, and gene transfer agents. GNPs possess properties such as biocompatibility and can be easily conjugated with other main biological materials. In recent decades, they have been used in designing vaccines and other functionalizations. The main advantage of using GNPs in vaccine development is their ease of usage and functionalization only. These vaccines exhibit promising outcomes and can be used to treat diseases ranging from infections to cancers. Due to their biocompatibility, they can be used for in vitro and in vivo applications (Jia et al., 2017). When GNPs are allowed to bind with biomolecules, a new version of facile tracking of desired targets in aqueous samples can be obtained.

GNPs are applicable as an efficient antigen carrier system for immunization. Size, shape, geometry, and functionalization affect GNP functions. GNPs have unique properties such as biocompatibility and large surface area. They deliver antigens to dendritic cells. This facilitates the immune response. GNPs are less toxic and inert in nature. They can be easily modified with proteins, peptides, and enzymes. For vaccine development, GNPs are used as adjuvants to enhance the immune response. GNPs show less toxicity in mammals (Murphy et al., 2008). They can be used as vaccine delivery vehicles. This is because of their biocompatibility and easy functionalization with antigens.

12.3 Functionalization of GNPs

GNPs are functionalized in numerous ways, which helps to design antibodies in vaccine development or in drug delivery systems. In general, GNPs covalently bind to the drug through cleavable bonds. The method used for drug delivery is very important. More important is the modification of the monolayer of GNPs. Presently, functionalization of GNPs includes the addition of functionalization of groups such as polyethylene glycol (PEG), bovine serum albumin (BSA), oligonucleotide, albumin, amino acid, and antibiotics (Tiwari et al., 2011). In PEGylation, GNPs are conjugated with PEG alone or with some molecules to confirm the cellulose uptake of GNPs effectively. Functionalized GNPs are very efficiently used for targeted drug delivery. Similarly, GNPs are conjugated with peptide/amino acids for targeted delivery systems. They include aspartic acid, lysine, glutamic acid, phenylalanine, and L-cysteine (Wangoo et al., 2008). Ammonium ions in the amino acids exhibit higher targeted drug delivery. Functionalization of GNPs with different molecules (Fig. 12.2) helps to increase the multilevel characteristics, physicochemical characteristics, etc.

Fig. 12.2
An illustration of G N P functionality contains several labels around a circle. The labels are as follows. Drugs, S i R N A, dyes, proteins, p D N A, antibiotics, peptides, and enzymes.

Functionalization of GNPs

Full size image

GNPs have more applications in vaccinology. They can act as adjuvants and delivery agents and enhance the immune response with less toxicity (Table 12.1).

Table 12.1 Morphology and application of functionalized GNPs
Full size table

12.4 Characterization of GNPs Functionalized with Antibiotics

GNP characterization can be observed by a visual color change. The characterization of GNPs is done by two methods: (a) spectroscopic methods and (b) microscopy methods. Spectroscopic methods include techniques such as ultraviolet–visible (UV/Vis) spectrophotometry, X-Ray diffraction (XRD) analysis, energy-dispersive X-ray spectroscopy (EDXS), small-angle X-ray scattering (SAXS), and Fourier transform infrared (FT-IR) spectroscopy (Balasubramanian et al., 2010). Microscopic methods involve scanning electron microscopy (SEM), tunneling electron microscopy (TEM), high-resolution TEM (HR-TEM), and atomic force microscopy (AFM). FT-IR spectroscopy was used to analyze the nature of binding of antibiotics to GNPs. Dynamic light scattering is used to analyze the size distribution of GNPs, and the purity and the crystalline nature are confirmed by XRD analysis. It also provides the data to find the particle size. Chemical composition of GNPs is confirmed by EDXS. EDXS and SAXS are used to measure the interparticle distance of GNPs. They help in tumor imaging and tissue engineering. Surface morphology, shape, and size of the particle are analyzed by SEM, TEM, and AFM. SEM gives information about the particle at the nanoscale, and TEM gives information about the material layer composition, size, volume, and shape of NPs. HR-TEM is used to measure the size, shape, and crystalline structure of NPs. AFM gives information about the topography of NPs.

12.5 Applications of GNPS

Vaccination plays an important role in the protection of the immune system against different infections caused by pathogens. Here mainly used diagnosis method is called the immunochemical method (Dykman & Bogatyrev, 2007). It completely depends on the use of pathogen-specific antibodies. Recently, the most demanded antigen nanocarrier for vaccination and immunization has been only GNPs. It is mainly due to their low toxicity, high specificity, and ease of synthesis. GNPs are used to synthesize antibodies and vaccines against bacterial, viral, and parasitic infections (Carabineiro, 2017),

12.5.1 Designing Antibacterial Vaccines

Due to the emergence of drug resistance in bacterial pathogens, researchers are trying to find an alternative for antibiotics or new antibacterial agents (Roshmi et al., 2015). The development of nanoparticle-based therapeutic medications helps to provide treatment for drug-resistant bacteria. They include gold, silver, titanium, copper, and zinc oxide (ZnO). GNPs are mostly preferred due to their surface properties, low toxicity, high stability, optical properties, etc. They are successfully applied against bacterial and fungal infections (Santhakumar & Koperuncholan, 2019). GNPs are good drug carriers due to their antibacterial properties. They display photothermal effects that can kill bacteria within a short span of time. Surface functionalization of GNPs increases their properties, and it also increases their antibacterial characteristics (Vijayakumar & Ganesan, 2012). Antibacterial drugs can bind with GNPs through covalent and noncovalent bonds and act as antibacterial agents that display high antibacterial properties. The main advantage of GNPs is that, at certain concentrations, they did not show any toxic effects on normal cells. GNPs also exhibit antibacterial properties against multidrug-resistant bacteria.

12.5.2 Use of GNPs in Antiviral Immunization

GNPs are a major tool of virologists and are used for the synthesis of antiviral vaccines.

12.5.2.1 Human Immunodeficiency Virus (HIV)

For treating HIV, 2G12 antibiotics called GP120 are used. GNPs were efficient to bind to this antibiotic. GNPs carried with thiol-terminated oligosaccharides have been used for synthesizing HIV vaccines (Dykman, 2020).

12.5.2.2 Hepatitis B

For this HBs Antigen DNA coated with GNP was injected to the epidemic cells for the cure. GNPs act as adjuvants and help to trigger fast antibody production (Negahdari et al., 2019).

12.5.2.3 Hepatitis C

The hepatitis C vaccine was synthesized by using plasmonic GNPs activated by an electrical discharge. It helps to increase pore formation on the cell membrane (Paul et al., 2014).

12.5.2.4 Dengue

GNPs in different sizes such as 20 nm, 40 nm, and 80 nm are used against dengue viruses (Fig. 12.3). GNP conjugation with small interfering ribonucleic acid (siRNA) helps to promote the stability and delivery of siRNA and develops a high immune response (Sengupta et al., 2022).

Fig. 12.3
A schematic of G N P shapes exhibits the following shapes. Nanosphere, nanocage, nanorods, nano shell, nano cube, nanoplates, and nano stars.

Different shapes of GNPs

Full size image

12.5.3 Application of GNPs in Anti-parasitic Immunization

GNP-based antibiotics and vaccines in parasitic diseases are still being explored. In general, parasitic infections are caused by Plasmodium falciparum and cause deaths worldwide. GNP-conjugated antigens with GNP nanovaccine formation help to treat this type of infection.

12.5.4 Therapeutics

The main issue is bacterial resistance toward antibacterial drugs. GNPs are taken up by immune cells because of their strong cell affinity. These GNPs specifically deliver at the infected area, enhancing bacterial inhibition, and cause damage to the microbial pathogens. GNPs are used as antioxidants too. They block the formation of reactive oxygen species (ROS) and increase the antioxidant activity of defensive enzymes. For cancer therapy, photothermal treatment (PTT) is used wherein GNPs are embedded within the tumor and produce heat in response to the laser effect. PTT is an important method for cancer treatment (Riley & Day, 2017).

12.6 Recent Developments in the Experimental and Theoretical Areas of Antibiotic GNP Functionalization

Bacterial resistance is a major issue in global public health concerns. It leads to finding new antibacterial agents accordingly. In recent decades, nanomaterials have been proven to be highly effective for antibacterial applications. GNPs have got a special attention due to their less toxicity, easy fabrication, and biological inertness. Now, major studies are related to antibiotic functionalized GNPs and their advantages toward antibiotic-resistant bacterial cells. It was found that antibiotic functionalization helps to increase the photothermal stability (Pattani & Tunnell, 2012).

Antibiotics are used against bacterial infections. They either prevent or kill bacterial cells, for example, in diabetic patients, chemopatients, and arthritis patients (El Domany et al., 2018; Sekar et al., 2022; Lima & Reis, 2015). Bacterial cells develop resistance towards some antibiotics, which is a large threat to the human health. The main reason behind antibiotic resistance is the misuse and overuse of antibiotics and the absence of new drugs. Variation in antibiotic concentration is also the reason behind antibiotic resistance, which causes changes in gene expression, horizontal gene transfer (HGT), etc. (Chen et al., 2014; Das & Patra, 2017; Shwartz et al., 2017).

12.7 Application of GNPs in Medicine and Antibiotic Developments

Colloidal GNPs are very efficient in the application of biological and medical studies. There are other nanomaterials that can be used as antibacterial agents. They include ZnO, titanium dioxide (TiO2), silver, etc. (Zhang et al., 2008; Xu et al., 2020; Kim et al., 2016). GNPs are highly preferred due to their good functionalization with thiol-, amino-, and carboxyl-containing antibiotic molecules (Lin et al., 2004; Ghosh et al., 2008; Liu et al., 2005). Real GNPs do not show any antibacterial activity. Surface functionalization with different molecules makes them good antibacterial agents. This functionalization involves two approaches: ex situ and in situ (Table 12.2).

Table 12.2 Characteristics of ex situ and in situ functionalization
Full size table

12.8 Drug Delivery by GNPs

Nanomedicine exhibits good clinical performance with less tissue toxicity. GNPs are very efficient nanocarriers for different drugs such as plasmid deoxyribonucleic acid (pDNA), siRNA, proteins, and peptides (Song et al., 2010; Kim et al., 2013; Huo et al., 2014). The surface area of GNPs is increased by the functionalization of GNPs with different methods such as carboxylation, amination, and sulfonation (Chen et al., 2010; Garaiova et al., 2021).

12.8.1 Plasmid Deoxyribonucleic Acid (pDNA) Vector Delivery

Here, GNPs are conjugated with functionalized DNA. These DNA–GNP conjugates are very efficient as drug carriers and applied in biosensors and drug delivery (Ross et al., 2012; Miao et al., 2017; Tatumi & Fujihara, 2005). DNA is covalently bonded with GNPs, which enriches their stability. Functionalization of GNPs with oligonucleotides helps to develop NP dimers and trimers that contain a sequence drug carrier pattern (Xu et al., 2006; Giljohann et al., 2007; Pei et al., 2012). The GNP–DNA covalent linkage helps to increase their stability under DNA denaturing.

12.8.2 Ribonucleic Acid (RNA) Delivery

RNA is used against HIV, cancer, etc. Cancer has been treated by micro-RNA–GNP drug delivery to the targeted affected area (Sánchez-Visedo et al., 2020; Yin et al., 2016; Eissa et al., 2014). GNPs are used to deliver RNA to the targeted site. Small interfering RNA (SiRNA) delivery needs a vector system that has a specific target system and excellent biocompatibility (Lytton-Jean et al., 2011). GNPs help to cover siRNA from enzymatic degradation and mediate gene silencing. Peptides can be easily conjugated to Au–S bonds and can be used effectively due to low toxicity (Rajchakit & Sarojini, 2017).

12.9 Advantages of GNPs as Future Smart Materials

Some of the major advantages of using GNPs in biomedical field include the following:

  • Simple and easy synthesis.

  • Easy surface functionalization to graft and modify an array of ligands for multiple functionalities such as targeted delivery.

  • For the application of contrast imaging and thermal ablation, the physicochemical properties of gold core are ideal.

  • Well-engineered GNPs encompass the capability for early disease identification.

12.10 Limitations of GNPs

GNPs are considered promising materials for nanovaccine development. The major concern associated with nanomaterials is their biosafety. GNPs are nonbiodegradable products that cause many side effects. Literature reports suggest that the disruption of cellular metabolism is due to the precipitation of GNPs in cells and their organelles. GNPs can be surface-functionalized easily. However, it harms their histocompatibility. Therefore, GNP variants must be characterized individually before being applied in therapeutics and clinical applications. Positively and negatively charged GNPs are harmful to the DNA and other cell membranes. The melting point of GNPs changes with the variation in the size of the particles. GNPs have high efficiency in the field of application in drug delivery but have serious side effects too. This includes nonspecific targeting, negatively affecting the host immune system.

12.11 Conclusions and Future Applications

In this chapter, we have analyzed the synthesis, properties, functionalization, and application of GNPs in the synthesis of antibodies against infections. GNPs are very efficient for the development of antibodies and carriers for drug delivery due to their special characteristics such as tunable size and shape, easy functionalization, and less toxicity. There are many methods and possibilities for tuning the surface of GNPs, including PEGylation, with amino acids, peptides, and antibodies. In this chapter, we mainly discussed the efficiency of GNPs for vaccine development for defeating deadly infections. GNPs are safely used to treat many diseases and for the development of antibiotics ranging from infections to cancers. GNPs possess inherent adjuvant potential. They exhibit a higher surface area-to-volume ratio. GNPs display multifunctionalization properties. There are still gaps in studies related to the influence of GNPs and their association with photothermal stability. GNPs can be modified effectively to improve antibacterial, antiviral, and antiparasitic properties. They can be used to synthesize antibodies and vaccines against different pathogens. Among the GNPs available in different shapes such as nanorods, nanocages, nanocubes, nanospheres, nanoprisms, nanostars, and nanoclusters, nanospheres are the best with a high antigen-carrying capacity. In general, antibody proliferation happens while immunization with GNP–antigen conjugates. It enhances the secretion of cytokines. Hence, GNPs that have inherent adjuvant efficiency can be used as effective tools in the design of antibiotics against infectious diseases.

GNPs are highly considered for the development of vaccines and other therapeutic purposes. However, before being widely applied, certain issues are to be addressed. There is an essential need to analyze the influence of GNPs on immune cells. Similarly, the impact of GNPs on off-target cells and organs should be analyzed, and GNPs with polymer coating and application should also be analyzed. GNPs with thermal and optical properties in inflammatory responses should be studied.