The advent of molecular biology and biotechnology has given ease and comfort for the screening and detection of different animal diseases caused by bacterial, viral, and fungal pathogens. Furthermore, detection of antibiotics and its residues has advanced in recent years. However, most of the process of animal disease diagnostics is still confined in the laboratory. The next step to conduct surveillance and prevent the spread of animal infectious diseases is to detect these diseases in the field. Through the discovery and continuous development in the field of nanobiotechnology, it was found that incorporation of noble metal nanoparticles to biotechnology tools such as the loop-mediated isothermal amplification (LAMP), lateral flow assays (LFAs) and dipsticks provided a promising start to conduct point-of-care diagnostics. Moreover, the modification and application of nanoparticle noble metals has increased the stability, effectiveness, sensitivity and overall efficacy of these diagnostic tools. Thus, recent advances in disease diagnostics used these noble metals such as gold, silver and platinum.
- Animal Diseases
- Noble Metals
The fastest growing and expanding agricultural sectors worldwide are the livestock, poultry and aquaculture industries. These industries need to grow and expand fast to sustain the needs of the growing population. However, this massive growth is in constant threat of outbreak of different infectious and/or zoonotic diseases . Furthermore, the globalization of animal trade can further contribute to the spread of diseases such as spread of
The application of molecular tool such as Polymerase Chain Reaction (PCR) has become one of the most important routine diagnostic procedure in the laboratory . Furthermore, the development of Loop-mediated isothermal amplification (LAMP) by Japanese researchers further advanced disease diagnostics with its simplicity and cost-effectiveness . However, even with the new PCR or LAMP techniques developed to detect different animal diseases, still, most of animal diseases are not properly diagnosed. Thus, development of methods and techniques that are more sensitive, specific, cost-effective, and can be used under field conditions are of paramount importance.
Noble metals are metals that have outstanding resistance to corrosion and oxidation at elevated temperature. These metals have a long and rich history and was reported to be used as early as the First Egyptian Dynasty. Noble metals include the metals of groups VIIb, VIII and 1b of the second and third transition series of the periodic table such as rhodium (Rh), ruthenium (Ru), palladium (Pd), silver (Ag), osmium (Os), iridium (Ir), platinum (Pt) and gold (Au) . These metals belong to a group of elements with wide variety of use and applications in fields of aerospace, electronics and most significantly, health .
Nanotechnology is an emerging science and is the study of matter with one or more dimensions in between 1 to 100 nm. The combination of nanoscience and biotechnology has created a new growing field of research in the form of nanobiotechnology with massive opportunities  to further improve healthcare, medical treatments, therapeutics and biomedical  uses such as radiotherapy enhancers [8, 9, 10], drug and gene delivery vehicles, and highly specific and sensitive diagnostic assays [11, 12].
Among all noble metals, gold (Au) and silver (Ag) are the most extensively studied due to the well-established synthesis routes, their relatively higher content in the earth’s crust and better safety profile. Furthermore, gold and silver nanoparticles demonstrated the most fascinating properties for biosensing. Gold nanoparticles (AuNPs), commonly known as colloidal gold or gold colloids, are the most stable metal nanoparticle. AuNPs present distinctive characteristics like size-related optical, electronic and magnetic properties, individual particle behavior and specially, compatibility with biomolecules [10, 11]. These characteristics of AuNPs attracted researchers from the field of human and animal medicine to apply these properties in a point-of-care or field diagnosis of various infectious diseases. In 1996, it was originally reported the capability of nucleotide functionalized AuNP can detect DNA colorimetrically [11, 13]. Moreover, AuNPs had been used for the detection of pathogenic DNA, single nucleotide polymorphisms and sequence discrimination [11, 14]. Researchers used AuNP in the development of numerous disease detection or screening platforms or techniques. This made gold as the most used noble metal in the field of point-of-care or field diagnostics .
AuNPs remain the most studied noble metal for disease diagnostics due to its biocompatibility and chemical stability [10, 16, 17, 18]. However, silver nanoparticles (AgNPs) are reported to habitually result in better sensitivity compared to AuNPs [18, 19]. Furthermore, Ag has higher thermal and electrical conduciveness, and more efficient to transfer electron than gold with shaper extinction band and AgNPs are more stable in water and air. Thus, the use of Ag has also attracted researchers to be used in drug delivery, environmental, electronics, antimicrobial agents and in diagnostics. Furthermore, AgNPs have been prominent in the field of biosensor and imaging .
Aside from Au and Ag, platinum (Pt) is another noble metal that has been noteworthy scientific tool explored by researchers in the field of biotechnology, nanomedicine and pharmacology .
In this book chapter, the different routes of synthesis and application of noble metal nanoparticles were discussed in order to give an overview on the recent advances and/or point-of-care animal disease diagnostics using these noble metals.
2. Advances in animal disease diagnostics
2.1 Synthesis of Noble metal nanoparticles
Throughout the emergence of nanotechnology, there have been many techniques developed on how to synthesize nanoparticles which include physical, chemical, and biological approaches. Among the three, synthesis of nanoparticles from physical and chemical methods are considered the best methods for they can provide more uniform-sized nanoparticles with long-term stability. Biological approach on the other hand is also used to lessen the production of toxic by-products from physical and mostly from chemical approaches .
2.1.1 The Turkevich method
The most common method of synthesis of nanoparticles is probably through the Turkevich method used to make spherical gold and silver nanoparticles . This method is a chemical approach which makes use of a single phase water-based reduction where gold or silver salt undergo reduction by citrate (sodium tri-citrate) at boiling temperature (100°C). The citrate ions, which serves as both reducing and non-aggregation agent, stabilize the nanoparticles by providing negatively charged ions which gets absorbed onto the surface of each particle (see Figure 1). Individual particles which are now stabilized and surrounded by negative charges will tend to repel each other causing a more stable nanoparticle dispersion and preventing them from aggregation .
Furthermore, the concentration of the citrate ions used in the solution determines the average size of the nanoparticles. Higher concentration of citrate ions (citrate to gold ratio) produces smaller nanoparticle size (average of 10 nm) due to higher stabilization and particle repulsion. On the other hand, reducing the concentration of sodium tri-citrate limits the number of citrate ions that will stabilize the particles. This causes aggregation and forms bigger particles (>15 nm) .
2.1.2 Physical methods of synthesizing nanoparticles
Several ways of producing nanoparticles using physical methods are already reported [25, 26]. Generally, some of these methods are using Plasma, Chemical Vapor Deposition, Microwave Irradiation, Pulsed Laser, Sonochemical Reduction and Gamma Radiation.
2.1.3 Green synthesis of nanoparticles
Green synthesis or biological synthesis are alternative pathways to produce nanoparticles in an eco-friendly way. This approach (in comparison with the physical and chemical methods) has lower energy consumption, lower cost, and less harmful to the environment. This pathway utilizes the use of microorganisms or plants (phytosynthesis) as source of reducing agents . The main limitation of this approach is how to control the size and shape of the product. Different phyto-chemical compositions from organic sources have different influences on the particles’ size and shape which can be attributed to purity of the extract used as reducing agents .
2.2 Characterization of synthesized gold nanoparticles
Synthesis of nanoparticles are verified mainly through their size and shape using Scanning Electron or Transmission Electron Microscopes (SEM/TEM). Additional characterization methods include spectroscopic analysis (UV–Vis Spectroscopy), dynamic light scattering (DLS), Zeta Potential, Inductively-coupled Plasma Mass Spectroscopy (ICP-MS), dark field microscopy, and more [28, 29]. Aside from their size and shapes, nanoparticles can have other unique properties based on their method of synthesis and precursor metals. These characteristics affect how they react with light due to surface plasmon resonance . A good example on how to demonstrate the effect of size of nanoparticle on how they interact with light can be seen in Figure 2 .
2.3 Advances in animal disease diagnostics using Noble metals
Serological (e.g. Enzyme-linked immunosorbent assay – ELISA) and molecular detection (e.g. PCR) of different animal pathogens has been one of the routine diagnostic techniques is most animal disease diagnostics. However, this requires well-trained laboratory technicians and expensive, sophisticated equipment . Thus, the LAMP method developed by Japanese researchers that is claimed to be cost-effective without sacrificing sensitivity and specificity became a promising point-of-care molecular method . However, this technique still has drawbacks such as less versatility compared to PCR, cannot be used in cloning purposes, limitation in multiplexing and difficulty in primer designing.
Colorimetric-based nanoparticle DNA detection is an eye-catching method due to its rapidity and cost-effectiveness compared to current generation of DNA detection or amplification. This method enables a direct or visual detection of amplified DNA even without expensive, sophisticated equipment. The incorporation of nanoparticles in platforms such as LAMP addresses the issue with regards to false positive results due to the addition of intercalating dyes as amplification indicators. Furthermore, hybridizations of nanoparticles with complementary DNA make this method more specific and overcoming the weaknesses of test format such as LAMP. Thus, LAMP and other point-of-care diagnostic tools coupled with nanoparticle has become a promising, sensitive, specific, cost-effective and rapid animal disease diagnosis techniques.
2.3.1 Point-of-care animal disease diagnosis using gold nanoparticles (AuNPs)
AuNPs are the most studied nanoparticle and has a fascinating property for biosensing. Furthermore, AuNPs can be synthesized to gold nanoprobes (AuPr) for detection of colorimetric detection of different animal diseases.
22.214.171.124 Bacterial diseases
Paratuberculosis or Johne’s Disease, caused by
126.96.36.199 Viral diseases
Foot-and-Mouth Disease (FMD) is one of the most devastating and highly contagious disease of cloven-hoofed animals (e.g. ruminants and swine) that may threaten food security . The causative agent, Foot-and-Mouth Disease virus (FMDV) has multiple modes of transmission, fast replication rate and viral excretion that makes FMD one of the acute and highly contagious diseases of cloven-hoofed animals [34, 35]. Southeast and East Asian countries such as Cambodia, Laos, Thailand, Vietnam and China show varying FMD prevalence . Eradication and control strategy for FMD is mainly controlled by vaccination. However, discrimination between naturally infected versus immunized animals against FMD is a must especially in the event of mass importation of cloven-hoofed animals. Furthermore, the rapidity of development of antibody against FMD and the differentiation of naturally infected vs. immunized animals are important in the disease control and prevention strategies. Conventionally, serological methods such as FMD structural proteins (SPs)-based virus neutralization test (VNT), liquid phase blocking enzyme-linked immunosorbent assay (LPB-ELISA) and solid-phase competition ELISA (SPCE) can evaluate the antibody level and non-structural proteins (NSPs)-based ELISA can discriminate naturally infected from immunized animals. However, with the advent and success of immunochromatographic strip (ICS) in the field due to its high specificity, sensitivity, rapidity, low cost and portability for field detection and high sample throughput, Yang
Bluetongue disease (BTD) is an arthropod-borne viral disease that affects ruminants worldwide. Bluetongue can cause massive socio-economic effects and is one of OIE listed diseases [36, 37]. Diagnosis of BTD includes viral isolation, serology and molecular diagnostics. In 2011, Yin
Caprine arthritis encephalitis virus (CAEv) is one of the economically important diseases of goats that causes mostly polyarthritis in adults and progressive paresis (leukoencephalomyelitis) in kids. However, other clinical manifestations include interstitial pneumonia, mastitis and chronic wasting diseases that lead to eventual death of the animal. Detection of CAEv infection is mostly done through serological testing such as Agar Gel Immunodiffusion (AGID) and Enzyme-linked immunosorbent assay (ELISA) [39, 40]. However, application of polymerase chain reaction to detect CAEv became a routine assay due to its rapidity and ability to detect CAEv in early stage of the disease . Furthermore, Huang
Acute hepatopancreatic necrosis disease (AHPND) is one viral disease that causes devastating economic effects due to 100% mortality that occurs at 35 days after stocking of shrimp post-larvae in ponds [44, 45, 46]. De Guia
188.8.131.52 Fungal diseases
Epizootic ulcerative syndrome (EUS) also known as mycotic granulomatosis, red spot disease or ulcerative mycosis is an economically important disease of wild and cultured fresh-water and estuarine finfish species . This disease is caused by a fungus,
184.108.40.206 Parasitic diseases
Visceral Leishmaniasis, caused by
220.127.116.11 Antibiotics and antibiotic residues
Antimicrobial resistance has emerged as one of the most essential problems in public health for the 21st century. This phenomenon is a threat to the effective disease prevention and treatment as increasing number of pathogens gain resistance to common medicines that used to treat them. In recent years, steady increase and intensification of animal production due to the increasing demand for animal protein has also lead to the increase in the use of antimicrobials as growth promoters in addition the specific use of antibiotics to treat specific diseases and to prevent the spread of particular diseases. This practice has been an essential contributor to the development and spread of resistance. On the other side of the coin, the livestock industry cannot support the growing demand for animal protein to the growing population without this modern miracle – antibiotics.
Research groups around the world has developed aptamer nanoparticle-based detection of antibiotics and its derivatives. Point-of-care detection of antibiotics is important in One Health approach as tainted products with antibiotics and its derivatives can be intercepted before penetrating the market and table of consumers.
Oxytetracycline (OTC) is one of the most commonly used tetracyclines (TCs) in veterinary medicine. TCs are extensively used as growth promoters that can lead to bioaccumulation in livestock products and by-products. This bioaccumulation of antibiotics may lead to serious human health issues ranging from allergies to incurable disease such as aplastic anemia, however, still the greatest threat is antimicrobial resistance. Thus, point-of-care detection for antimicrobials and its derivative is important to prevent the development and spread of antimicrobial resistance. Kim
Kanamycin is one the frequently used aminoglycoside antibiotics produced by
2.3.2 Point-of-care animal disease diagnosis using silver nanoparticles (AgNPs)
18.104.22.168 Antibiotics and antibiotic residues
Aminoglycosides (AMG) antibiotics are known for their broad-spectrum activities to gram-negative aerobic bacteria . However, the discrepancy of administered AMG and the presence in blood is an important concern . Thus, emergence of AMG-resistant bacteria is a pressing concern due to its abuse in animal husbandry and agricultural practices [73, 74, 75]. One of the important AMG is Streptomycin, an effective antibiotic for gram-negative bacterial treatment and is used not only for human diseases but also for diseases of veterinary concern [76, 77]. The presence of streptomycin residues in animal-derived products is a threat to human health due to its nephrotoxicity, ototoxicity and allergic reactions [77, 78]. The European Commission has set a MRL for streptomycin of 500 and 200 μg kg −1 for meat and milk, respectively [77, 79]. Thus, development of sensitive and selective detection of streptomycin residues in animal derived products is vital to ensure food quality and safety and one health. Ghodake
2.3.3 Point-of-care animal disease diagnosis using platinum nanoparticles (PtNPs)
22.214.171.124 Drug residues
β2-adrenergic receptor agonists (β2-agonists) is a drug group which is usually used for the treatment of pulmonary diseases in animals [81, 82]. However, they can promote animal growth and increase feed efficiency by enhancing protein accretion and reducing fat deposition producing “lean meats” [82, 83, 84]. The use of this drug group in veterinary medicine is illegal since prolonged consumption of residues in animal-derived products can cause headache, chest tightness, nausea, and more. One of this β2-agonists is ractopamine (RAC), however RAC is a derivative of clenbuterol which causes high blood pressure and heart disease in human. Thus, the use of RAC is illegal in Europe and China but RAC is still used around the world due to its effectiveness and low cost . Thus, detection of RAC and its residue using simple and accurate method is important. Sun
In conclusion, this review has provided the application of noble metals (gold, silver and platinum) in the advances in animal disease diagnostics. The versatility of these noble metals to be able to detect virtually all types of animal pathogens such as bacteria, virus, fungi, parasites to detecting drug and its residues is a promising foundation for point-of-care diagnostics/field diagnostics of animal diseases in the near future.
We would like to thank Philippine Carabao Center and Department of Agriculture-Biotechnology Program Office for the support and technical assistance.
Conflict of interest
The authors declare no conflict of interests.