key: cord-0835080-vucdmomb
authors: Ayipo, Yusuf Oloruntoyin; Bakare, Ajibola Abdulahi; Badeggi, Umar Muhammad; Jimoh, Akeem Adebayo; Lawal, Amudat; Mordi, Mohd Nizam
title: Recent advances on therapeutic potentials of gold and silver nanobiomaterials for human viral diseases
date: 2022-02-01
journal: Current Research in Chemical Biology
DOI: 10.1016/j.crchbi.2022.100021
sha: e551b7b3c7a481e1269695e7f7e6e7b08d83f3b9
doc_id: 835080
cord_uid: vucdmomb

Viral diseases are prominent among the widely spread infections threatening human well-being. Real-life clinical successes of the few available therapeutics are challenged by pathogenic resistance and suboptimal delivery to target sites. Nanotechnology has aided the design of functionalised and non-functionalised Au and Ag nanobiomaterials through physical, chemical and biological (green synthesis) methods with improved antiviral efficacy and delivery. In this review, innovative designs, as well as interesting antiviral activities of the nanotechnology-inclined biomaterials of Au and Ag, reported in the last 5 years were critically overviewed against several viral diseases affecting man. These include influenza, respiratory syncytial, adenovirus, severe acute respiratory syndromes (SARS), rotavirus, norovirus, measles, chikungunya, HIV, herpes simplex virus, dengue, polio, enterovirus and rift valley fever virus. Notably identified among the nanotechnologically designed promising antiviral agents includeAuNP-M2e peptide vaccine, AgNP of cinnamon bark extract and AgNP of oseltamivir for influenza, PVP coated AgNP for RSV, PVP-AgNPs for SARS-CoV-2, AuNRs of a peptide pregnancy-induce hypertension and AuNP nanocarriers of antigen for MERS-CoV and SARS-CoV respectively. Others are AgNPs of collagen and Bacillus subtilis for rotavirus, AgNPs labelled Ag30-SiO 2 for murine norovirus in water, AuNPs of Allium sativum and AgNPs of ribavirin for measles, AgNPs of Citrus limetta and Andrographis Paniculata for Chikungunya, AuNPs of efavirenz and stavudine, and AgNPs-curcumin for HIV, NPAuG3-S8 for HSV, AgNPs of Moringa oleifera and Bruguiera cylindrica for dengue while AgNPs of polyethyleneimine and siRNA analogues displayed potency against enterovirus. The highlighted candidates are recommended for further translational studies towards antiviral therapeutic designs.

Viruses are the smallest microbes proven to be of great threat to human well-being with no known cure for a high number of their taxonomical strains [1, 2] . They are responsible for most human pathogenic infections and are difficult to manage for health practitioners. Several viruses such as influenza, hepatitis, Ebola, Zika virus, human immunodeficiency virus (HIV), herpes simplex virus (HSV), Hepatitis C virus (HCV) and recently coronaviruses (CoVs) have been identified as a serious threat to humanity through disease outbreaks and pandemics [3, 4] .

For instance, the coronavirus 2019 (COVID-19) pandemic overwhelmed the world healthcare and economic systems, infecting millions of people, with a higher mortality rate amongst the vulnerable. Governments and health bodies across the globe had to devise various effective strategies to prevent the spread of the virus, which remains a big struggle. Till this moment, scientific efforts are being made by researchers to find a vaccine and effective treatment options for the infection with limited success [5] . Generally, despite the enormous efficacious potentials of some topical virucidal agents, toxicity, the resistance of the pathogens and suboptimal delivery of the agents to target sites contributively limit their real-life clinical successes [6, 7] . These make the treatment of viral diseases remain a challenging task.

Among the strategies for mitigating the limitations, the application of nanotechnology through further modifications of active biomaterials into functionalised and non-functionalised nanoparticles (NPs) facilitate the designs of nano-biomaterials with promising advantages over larger particles in terms of efficacy, enhanced delivery to targets, safety, cost-effectiveness and environmental friendliness [8, 9] . The functionalised types are usually comprising organicbased NPs or organic-capped analogues of metals such as Ag, Au, Pt, Fe, Cu and Zn with antiviral effects traceable to ligand-receptor chemical interactions while the non-functionalised counterparts are mostly pure inorganic materials such as the NPs of SiO2, ZnO, CuCl2, TiO2 and CeO2 [10] [11] [12] [13] . The nano-sized biomaterials have been designed through various techniques J o u r n a l P r e -p r o o f including physical, chemical and biological (i.e. algae, fungi and bacteria) with advantages of morphologies, favouring pharmacokinetics at target sites [9] . Consequently, some formulated gold-based nanobiomaterials with in vivo activities have been recently overviewed and suggested for the development of antibodies against bacterial, parasitic and viral infection upon further study [14] . Similarly, based on their interesting performances in experimental models, few others are suggestively worthy of exploration as potential adjuvant/stand-alone vaccines against the dengue virus [15] , foot and mouth disease [16] , rift valley fever [17] , HIV [18] and respiratory syncytial virus [19] .

Nanotechnology has been gaining a great deal of scientific attention as a means of delivering medicinally attractive NPs with promising performances associated with synthetic accessibility, solubility, stability, release pattern and cell penetration and uptake [4] . [20] [21] [22] [23] [24] [25] . Moreover, the technology steadily features various scientific and allied disciplines including biology, chemistry, medicine, engineering, computational and material sciences as an integral part of modern interdisciplinary sciences [26] . Although, few of the recently documented literature reflects the biomedical potentials of some topical NPs [27] [28] [29] [30] , while some others were focused on antiviral potentials of nanoparticles generally without specificity on Au and Ag NPs [31] [32] [33] . Additionally, Babaei and co-researchers also reported an overview of antiviral activities of AuNPs experimented in vitro [34] , with less focus on AgNPs and their performances in vivo, where physiological side effects could be critically observed. However, the extensive coverage of the convenient methods of the nanotechnological designs of the nanobiomaterials of Au and Ag and their interesting efficacy specifically over a broad spectrum of human viral diseases remain underscored. In this review, innovative designs, as well as interesting antiviral activities of the nanotechnology-inclined J o u r n a l P r e -p r o o f biomaterials of Au and Ag, reported in the last 5 years were critically overviewed with more attention on synthetic accessibility and promising efficacy against several viral diseases affecting man.

Although there are several methods through which metal nanoparticles (MNPs) such as Au and AgNPs are synthesized, these are categorized basically into three main groups as physical, chemical and biological methods [35] . The physical methods such as sonochemical and laser ablation use the top-down approach and mostly produce monodispersed NPs. Unfortunately, so much waste is generated in addition to the required sophisticated resources. These limit their use, especially for certain biomedical applications [7] .

The chemical method such as hydrothermal synthesis, on the other hand, uses the bottom-up approach, leading to the production of NPs of well-defined dimensions, structures and sizes.

In this approach, metal ions such as those of Au and Ag are reduced by reducing agents. The reductants could be organic or inorganic agents. Often, stabilizing agents such as organic solvents, synthetic or natural polymers are employed to prevent the NPs from aggregation.

Alternatively, surfactants containing specific functionalities (e.g. nitrogen and oxygencontaining groups) have also acted as stabilizers, protecting the NPs from agglomeration or sedimentation. Comparatively to the physical methods, these techniques are more fascinating and economical. Despite these qualities, the chemical methods may not be without some disadvantages such as environmental pollution due to the toxic nature of the chemicals that might have been employed. Hence, some of the NPs from this route may not be suitable for certain biomedical applications [7] .

The biological method also known as the green synthesis depends on the bottom-up approach, employing unicellular and extracellular biological organisms (e.g. bacteria, algae and plants).

This technique is relatively simple, cost-effective and environmentally friendly. Biogenic NPs are biocompatible, easily scalable to large quantities, eco-friendly, however, challenged with size and shape moderation. Several factors such as pH, temperature, type, concentration of the reducing agent and synthesis time among others influence their size, morphology and stability.

The NPs synthesized through the green (biological) method are relatively safer and associated with fewer toxic by-products [36] , making them more preferable for biomedical applications.

The extract of several plants parts such as leaves, roots, stem bark, flowers and seeds have been used in the fabrication of both metal NPs. For instance, Citrus limetta peels [8] , aqueous extract J o u r n a l P r e -p r o o f of Cinnamon cassia [37] , Allium sativum [38] , Pelargonium sidoides [39] , Leucosidea sericea (procyanidins) [40, 41] have been used for the biological synthesis of both Au and Ag NPs.

Additionally, the green synthesis entails the use of microorganisms such as bacteria, fungi, and viruses for producing metal NPs of immense biological functions. There are numerous advantages in the use of biological methods, considering biocompatibility, safety to the environment, easy production in addition to avoiding carcinogenicity and cytotoxicity. Thus, biological methods are more preferred to physical and chemical methods.

Another important aspect of the preparation of MNPs is the determination of their physicochemical properties. Understanding the characteristic features such as size, shape, surface charge, morphology and distribution are of utmost importance as most applications are dependent on the parameters [42] . The ultra-violet visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD), dynamic light scattering (DLS), energy dispersive X-ray (EDX) spectroscopy are among the commonly applied techniques to determine absorbance, size and morphology, crystallinity, polydispersity, hydrodynamic size, and zeta potential (ZP) of MNPs [43] [44] [45] [46] . The surface plasmon resonance (SPR) of NPs may depend on the metal involved among other factors. For instance, while AgNPs possess SPR at about 320-500 nm, the Au counterparts appear at 500-600 nm [21] . From the TEM micrographs, the morphology and size of the MNPs can be determined. Although usually bigger than that measured by the TEM analysis, the DLS measurement also provides information on the size alongside the polydispersity index (PDI), used to determine the degree of homogeneity of the particles in colloidal solutions [47] . The ZP shows the extent of stability of the colloidal solutions. The ZP values could be positive or negative depending on the type of ions surrounding the surface of the NPs. However, the degree of stability is dependent on the magnitude of the ZP value and not the charge [47] . Several studies have employed XRD in conjunction with SAED to confirm the crystallinity of MNPs [48] . The EDX has been used to further confirm the type of MNPs that has been synthesized since it can detect heavy metals such as Au and Ag [49] .

Chloroauric acid was reduced by trisodium citrate (Na3C6H5O7.2H2O) to synthesize AuNPs using the Turkevich method. The synthesised NPs were characterised using UV-Vis spectroscopy, then PEGylated and subjected to a colloidal stability test. The PEGylated AuNPs J o u r n a l P r e -p r o o f were reacted with linker N-succinimidyl 3-(2-pyridyldithio) propionate molecule, while the subsequent product was conjugated with RNA before being coated with polyethyleneimine.

Size, polydispersity, concentration and ZP of the NPs were tested for at the end of each synthesis step. The characterization results indicated mean core diameters of the NPs between 30 -40 nm, λmax 527 -530 nm and ZPs in the range of -21.4 and 13.5 mV [7] . Malik [50] . Acyclovir was dispersed in an equimolar amount of (sulfobutyl ether-β-cyclodextrin) SBE-β-CD-containing water, stirred at room temperature for 24 h. The mixture was filtered on reaching equilibrium and the filtrate freeze-dried for 16 h. The drug-loaded nanodroplets were formed by dissolving the freeze-dried ACV-SBE-β-CD inclusion complex in distilled water, followed by the addition of chitosan nanodroplets under magnetic stirring. The resulting nanodroplets were characterized with FTIR spectroscopy indicating the participation of ACV functional groups, an average diameter of 400 nm, while their PDI and ZP were recorded as 0.20 and 19.98 mV respectively [51] . Gold NP capped with citrate was synthesized by the citrate reduction method of chloroauric acid.

Chloroauric acid was heated to boiling and stirred with prepared citrate solution added quickly leading to a change of colour from yellow to colourless and finally to deep red showing the formation of AuNP. The resulting solution was left to cool to room temperature. PEGlation of J o u r n a l P r e -p r o o f the citrated AuNP was done after the solution turned purple at the end of PEGlation. The redshift in UV-Vis λmax (from 520 to 529 nm) between the citrated and PEGlated AuNPs supported a successful PEGlation. The TEM image indicated the particle size of ≈12 and ≈15 nm for citrated and PEGlated AuNPs while their respective ZPs were recorded as -12.3 and -38 mV [52] .

Chloroauric acid was added to Oscillatoria sp. and Spirulina platensis respectively to biosynthesize AuNPs of the respective algae. It was observed during the biosynthesis of the NPs that the microalgae could either produce NPs extracellularly or reduce the metallic ions intracellularly. Mechanical mashing for 1h at room temperature was applied to disrupt the cells Prepared extract of garlic (A. sativum) and chloroauric acid (HAuCl4) were used to synthesize AuNP following the Turkevich method. The NPs were purified through a 0.2 µm filter, characterized with SPR at 537 nm, the average size of 6 nm, ZP of 21.2 mV while the TEM image indicated spherical shapes [38] . Two types of AuNPs were synthesized and coupled with silica. They were annotated as type "a" which was a sol-gel and a powdered type "b" with different diameters at 12-30 nm and 50-200 nm respectively and consequently, varied activity against adenoviruses [10] . Series of AuNPs, annotated as NPAuG1-S2, NPAuG2-S3 and NPAuG3-S8 with differing generation numbers 1-3 and some charge numbers of 2, 4 and 8 respectively were prepared. Although little was reported about their characterization, however, their impressive activity in cancer, cellular disruption and immunotherapy inspired the evaluation against the herpes simplex virus [25] . with AuNPs, with sCpG acting as a soluble adjuvant, taking advantage of interesting gold-thiol chemistry which aided the conjugation. Although little was reported of the characterization of the antibody, however, its immunogenicity significantly improved upon formulation into AuNP-M2e+sCpG [56] . Two AuNPs conjugates (AuNP+ Hex and AuNP+Hex+Tat) were synthesized using a coupling reaction to link hexapeptide and Tat peptide to the surface of the AuNPs. The AuNP and its corresponding formulated product, AuNP+Hex+Tat showed UV-Vis λmax of 500-600 nm, indicating the presence of Au and change in absorbance due to NP formation. They were further characterised, depicting sizes of 37.4 and 49.2 nm, and ZP of -22.9 and -13.7 mV respectively [12] . Flupep ligand was used to functionalize AuNPs by adding the ligand mixture to AuNPs. The resultant NPs were observed under UV-Vis with maximum absorption at 520 nm while their average diameter was recorded as 10 nm. It was explored as a delivery system for Flupep and increased antiviral activity [57] . Other synthesized AuNPs of interesting alkaloids such as the β-carboline and their extracts were not overviewed due to their reported off-scope applications as anticancer and antibacterial, though, the alkaloids possess antiviral potentials [58, 59] . Nevertheless, the alkaloids have been documented with interesting pharmacology as antiviral and anticancer, vast in natural products and possess good synthetic accessibility and bioavailability [60, 61] , worthy of exploration through the design into NPs.

The biological method represents the most explored for the design of the NPs possibly due to its cost-effectiveness, convenient synthetic approach and safety to the environment. The summary of the synthetic method and physicochemical properties of the overviewed AuNPs is presented in Table 1 . were synthesized. Scanning electron microscopy (SEM) was used to determine the molecular size and morphology of the nanorods while FTIR spectra showed the presence of the nanorods conjugation between 400-4000 cm -1 . The spectra peak at 2571 cm -1 attributed to the S-H stretch supported the attachment of MES to AgNPs. The quantity of sodium 2-mercaptoethane sulfonate on the surface of Ag was determined using thermogravimetric analysis in the range of 25-700 ºC [62] .

Huy and co-researchers applied the electrochemical method to synthesise AgNPs with trisodium citrate as a reagent and stabilizer. The first sign of the nanoparticle formation was a colour change from transparent to yellow. An absorption peak of 406 nm was recorded using a UV-Visible spectrophotometer. The AgNPs were mostly spherical and homogenous and had a size range between 4 to 9 nm. The EDX confirmed the presence of elemental silver between 2.5 and 4 keV [63] . Chitosan was used as a stabilizer in the synthesis of AgNP using the chemical reduction method. A colour change to yellow was noticed on the addition of sodium borohydride (NaBH4), while UV-Vis with a λmax 401 nm supported the formation of AgNPs.

The TEM indicated spherical NPs with an average diameter of ≈14 nm. The EDX showed highly crystalline particles with a d-spacing of 0.23 attributed to the metallic silver [64] . Using radiochemical synthesis, some AgNPs were designed to be immobilized on textile fabrics by 10% Ag load per gram of GO sheets and a thickness distribution of 0.6 -9.0 nm [66] . Similarly, adsorption of AgNPs on the surface of graphene oxide sheets was applied to prepare some graphene-based Ag composites. The AgNPs were uniformly adsorbed onto the surface of GO with sizes distributed between 30 -50 nm in form of well-dispersed aqueous colloidal hybrids [67] . Joe and co-workers applied a spark discharge generation (SDG) system to prepare AgNPs coated air filter with a geometric standard deviation and mode diameter of approximately 1.5

and 11 nm respectively. The coating efficiency of the filter sample for AgNO3 was reported to be ≈41.7% in mass base and ≈89.6% in number base [68] .

Avilala & Golla used AgNO3 and actinomycetes isolated from mangrove soil in the biosynthesis of AgNPs of Nocardiopsis alba extract. The formation of the NPs was confirmed with a colour change from colourless to brown. UV-Vis absorption peak of 420 nm indicated the presence of AgNPs coupled with FTIR band at 564 cm -1 which was assigned to AgNP vibration. The XRD and TEM also indicated the formation of spherical crystalline AgNPs of 20 -60 nm with an average size of 32.5 nm [69] . AgNPs of collagen was also prepared by mixing 40% 1 mM of AgNPs with 40% (v/v) collagen, 10% (v/v) PBS, 6.4% of 0.2 M NaOH and 3.6% H2O on ice. The AgNPs were confirmed using electron microscopy and much focus was on their interesting biological applications [70] . Some AgNPs were biosynthesized from pure honey and AgNO3. The result of the UV-Vis spectrophotometer depicted an absorption peak at around 340 nm. Results from TEM showed spherical NPs with sizes ranging from 20-50 nm in diameter [71] . In another study, amantadine, an antiparkinson drug was used to synthesize AgNPs by mixing Vitamin C, AgNO3 and Amantadine. The NPs were sonicated before passing through the filter.

Using TEM to characterize, the NPs showed uniform and monodisperse spherical morphology,

with AgNPs and AgNPs of amantadine having 3 and 2 nm average particle size respectively.

The ZP of Ag-amantadine was found to be -29 mV, which was lower compared to -14 mV recorded for AgNPs [84] . Similar research was conducted in the same year by the author using oseltamivir instead of amantadine and vitamin C to reduce AgNO3 followed by the addition of oseltamivir, similarly to the earlier procedure. The NPs were characterized by TEM, showing J o u r n a l P r e -p r o o f uniform, monodispersed spherical particles with an average size between 2-3 nm. ZP of -16 mV was recorded for AgNPs which was higher than -27 mV recorded for Ag-Oseltamivir [85] .

In a green synthesis involving protein biomolecules, AgNO3 was reduced using vitamin C, with the resulting NPs added to PEI and (small interfering RNA) siRNA to form silver nanocomposites of PEI and siRNA. The PEI and siRNA were used to cap the AgNPs, with the formation of nanocomposites shown by a strong absorption band at 420 nm through UV-Vis spectroscopy. TEM images showed Ag-PEI-siRNA to be uniform and spherical. The ZP of AgNPs, Ag-PEI and Ag-PEI-siRNA are -18 mV, 40 mV and 17 mV respectively. The PDI value of 0.065 was recorded for Ag-PEI-siRNA and a positively charged ZP of +18 [86] .

Commercially available poly-vinyl pyrrolidone coated AgNPs (PVP-AgNPs) of the size distribution of 8 to 12 nm, absorption peak of 390 nm, optimal density of 155 cm -1 and mass concentration of 1 mg/mL were reported as well of those with 10 nm at 20 ppm stock [87, 88] .

Ramadan et al. reacted an aqueous extract of Melaleuca alternifolia and AgNO3 to produce reddish-brown AgNPs with turbidity standard determined as 600 nm. The green NPs were characterized using TEM, PDI and ZP. Results derived from TEM analysis showed the NPs to be spherical with a mean size of 11.56 nm. A negative value of ZP at -28 mV was recorded alongside a PDI of 0.172 [89] . The summary of the synthetic method and physicochemical properties of the overviewed AuNPs is presented in Table 2 .

J o u r n a l P r e -p r o o f 18 

Influenza virus, popularly referred to as flu, is responsible for contagious influenza in some mammals and birds and is characterized by a non-segmented negatively sensed RNA genome.

Its main subtypes are A, B and C with subtype A being the most virulent, widespread and pinpointed in influenza outbreaks [87] . The two AuNPs-SiO2 showed anti-adenoviral activity with varying degrees of inhibition of the virus reproduction, especially the type 'b' even at low concentrations (Table 3 ) [10] . 

Rhesus rotavirus (RRV) strain MMU 18006 was introduced in MA104 cells with plaque assay method to quantify anti-RRV effects of some AgNPs. Using mice infected with biliary atresia, a viral infection associated with the neonatal system, a close to a total reduction of biliary epithelial cells at 9 and 12 days of RRV inoculation and a significant increase in survival in mice, reduction in jaundice and weight loss was recorded for the NP-treated group (Fig. 7) . 

The antiviral effects of AgNPs labelled Ag30-SiO2 particles were evaluated against bacteriophage MS2 and murine norovirus (MNV) in four different types of water at 5 ºC and 20 ºC respectively. Higher inhibition at more than 3 log10 reductions of bacteriophage MS2 was recorded for the particles in distilled water and tap water at 5 ºC while no significant reduction was observed on surface or groundwater. At 20 ºC, > 4 log10 reductions of MS2 was recorded after 24 h of exposure for the four water types. Antiviral activities of the silver NPs were also reported to be excellent against MNV. The AgNPs exhibited high activity against MNV in the four different types of water under consideration [95] . Cumulatively with another experimental investigation where filtration efficiency of AgNPs coated glass filter was recorded as 99.99% against MS2, T1 and T4 viruses [96] . This indicates the potentials of the AgNPs as effective disinfectants for treating viral-bound water, amenable for water treatment upon further evaluation. [11] . Although, a more experimental investigation is required especially in vivo for a better understanding of their mechanisms of action, however, AgNPs of A. paniculata could provide economic, safe and effective therapeutic options against CHIKV whose treatment options remain challenging.

The antiviral effect of green AgNPs of C. papaya leaves was evaluated against CHIKV. The activity was measured in terms of CPE and increase of percentage viability. Using MTT assay, the inhibition of CHIKV have been observed as 39% and 52% inhibition when treated with 62.5 and 125 µg/mL, representing ½ MNTD and MNTD respectively of the NPs. The interesting results were supported by the cell viability which increased by 14% upon application of ½ MNTD of the NPs [97] . The results further buttress the promising potentials of the green AgNPs for effective treatment of CHIKV which demand further scientific attention.

The human immunodeficiency virus (HIV) continues to pose threat to global wellbeing while the search for an effective therapeutic strategy lasts. The few available medications including J o u r n a l P r e -p r o o f the highly active antiretroviral therapy (HAART) are complicated with hypersensitivity, unpleasant aftereffects and contraindications, toxicity and incessant resistance, and the challenges of high viral mutation [12, 98] . Immune cells are renowned targets for the viral-host infusion, thereby forming a therapeutic target [55] . Other implicated therapeutic targets for HIV include the viral integrase enzyme for replication [12] . Lately, some negatively charged Au-based glyconanoparticles reportedly displayed interesting potentials for modulating and stabilising the secondary structure of a gp120 V3 loop peptide implicated in the pathogenesis of HIV. They are therefore suggested for further study as HIV vaccine candidates [18] .

Delivery of drug molecules to target host cells, resistance and toxicity contributively limit the efficacious applicability of most antiretroviral medications for treating HIV/AIDS infections.

Efaverinz enhanced the delivery through mannosylated niosomes and protein-carbohydrate intermolecular interactions between the lectins and mannan on gp-120 of HIV host cells and receptor respectively to improve antiviral effects. Quantitatively, the IC50 of AuNPs was reportedly higher than that of nanoparticle-inclined Efaverinz at 185.3 and 94.6 µg/mL respectively. The results demonstrate an enhanced delivery of the drug molecules through mannosylated niosomes by 42.6% compared to non-liganded noisome. The in vitro cumulative release, permeation and mucosal retention of both Au-loaded Efaverinz (EGNz) and the mannosylated type (manEGNz) were also demonstrated [6] , a potential for overcoming the challenges of delivery associated with antiretroviral agents. Single-stranded RNA molecules were reportedly delivered through PEGylated AuNP analogue linked covalently to thiolmodified oligoribonucleotide using a cleavable linker group, N-succinimidyl 3-(2pyridyldithio) propionate. The coatings of the NPs with polyethyleneimine enhance cell entry and endosomal escape, resulting in the uptake of ≈45000 RNA strands per lymphocyte. An extracellular aggregation was observed for the NPs with an only occasional presence within the cytoplasmic vesicle (Fig. 8) . The modified NPs demonstrate a nanotechnology-dependent delivery, although, no antiviral activity was recorded when subjected to MTT cytotoxicity assay and antiviral assay against HIV suggestively due to inadequate intracytoplasmic delivery of the RNA molecules [7] . An improved delivery of stavudine, an antiretroviral medication was demonstrated through Au nanocarriers. The AuNPs of stavudine reportedly activated a typical proinflammatory signal implicated in antiviral effects of macrophages, show better antiviral activity than the NPs of Au or stavudine separately [55] . The nanotechnology-based J o u r n a l P r e -p r o o f innovation supported by an earlier hypothesis of the hosting of AuNPs by human macrophages represents a potential therapeutic approach for HIV, deserving further exploration. The conjugates of AuNP/hexapeptide and AuNP/hexapeptide/Tat peptide (where Tat = transactivator of transcription) synthesized by Singh et al. were investigated for cellular entry potential and integrase-mediated activity against HIV replication and cytotoxicity using MTT assay. The study provided fundamental in vitro data supporting the potency of the hexapeptide conjugates and more insights into the applicability of functionalised AuNPs but showed no significant inhibitory activity against HIV [12] . The antiviral activity of sodium 2mercaptoethane sulfonate mediated AgNPs (Ag-MES) was determined by testing their ability to inhibit HIV and HSV-1 replication. HIV replication was inhibited more than HSV-1 on the application of the nanorods. Up to 50% of HIV virion growth was inhibited on the application of 5µg/mL silver nanorods while almost the entire viral cells were inhibited from replication at 10 µmol/mL of the biomaterial. Although the sensitivity was more favoured by the HIV, the nanorods also demonstrated about 90% inhibitory potential against the HSV and thus suggested J o u r n a l P r e -p r o o f as a promising antiviral candidate for further study (Fig. 9A) [62] . Curcumin-stabilized AgNPs were evaluated for antiretroviral efficacy through immunomodulatory activity observed in ACH-2 cells infected latently with the HIV-1 virus. The NPs significantly inhibited the expressions of HIV-1 long terminal repeat (LTR), p24 antigen, interleukin-1β (IL-1β), Tumour necrosis factor-alpha (TNF-αα), IL-6 and nuclear factor-kappa B (NF-kB) by -73% p<0.01, -57% p<0.05, -61% p<0.01, -54% p<0.05, -68% p<0.01 and -79% p<0.0001 respectively. More interestingly, it also inhibited pro-inflammatory responses induced by HIV-1 infection and showed no toxic effect [80] . The study supports the therapeutic potency of curcumin-capped AgNPs amenable for translational studies.

The infections caused by the Herpes simplex virus (HSV) are human lifelong infections primarily characterized by the periodical reactivation of the viral site of infection. Its transmission occurs predominantly through oral-oral contact and more recently reported oralgenital contact. It causes genital herpes as such categorized among the sexually transmitted infections (STIs) [51, 99] and oftentimes associated with the neurodegenerative disease through deregulation of amyloidogenic and non-amyloidogenic pathways resulting in the aggregation of amyloid-β-peptides [25] . In 2016, an estimate of 13.2% of the global population within 15-49-years of age was living with HSV type-2 while the treatment remains difficult [99, 100] . 

Hepatitis C virus remains an earmarked health challenge globally through the hepatitis disease due to its virulent action primarily on the liver, complications, resistance and limited treatment options despite concerted scientific strategies [83] . Generally, symptoms of acute HCV infection are mild and vague, however, it becomes chronic leading to liver damage, cirrhosis and hepatocellular carcinoma when left untreated. Prevention of severe complications from HCV can be achieved by early detection and treatment of the infection [4] . Some AgNPs of total and petroleum ether extracts of Amphimedon were evaluated in vitro against HCV NS3 helicase and protease activity. The AgNPs of petroleum ether fraction showed more activity against the NS3 helicase IC50 value of 0.11 ±0.62 compared to AgNPs of total extract, AgNO3 and ribavirin whose values are recorded as 1.52 ±1.18, 77.72 ± and 4.66 ±0.29 respectively.

Similarly, against the NS3 protease, the AgNPs of petroleum represents the most potent inhibitor with IC50 of 2.38 ±0.57 µg/mL compared to other agents including the drug controls whose IC50 values were in the range of 4.77 ±0.26 -52.67 ±0.33 µg/mL [83] . Although the mechanisms of activity remain understudied, the AgNPs of petroleum extract of Amphimedon demonstrated promising efficacy against HCV, worthy of further translational study.

Dengue virus (DEN-2) is an arthropod-borne, single positive-stranded RNA virus with renowned transmission within the tropical and sub-tropical regions of the world through Aedes J o u r n a l P r e -p r o o f aegypti, its primary mosquito vector which spreads the disease during blood-feeding [78] . No specific treatment has been identified for the virulent disease, as such most effective strategy has been focused on prevention through the control of its vector [75, 78] . Recently, some AuNPs demonstrated a size-dependent neutralising potentials on the dengue virus and as such suggested for further translational design into DEN-2 vaccine [15] . Series of nanobiomaterials have been prepared with prophylaxis and treatment potentials against the deadly disease.

Biosynthesized AgNPs of Moringa oleifera seed extract exhibited in vitro antiviral activity against DEN-2, reducing the viral titer loads quantitatively from 7 log10 in AgNP-free control Although, further investigational studies, especially in vivo animal models are required to validate the real-life observation of the pharmaco-physiological effects. Similarly, the effective experimental results of some golden-star nanoparticles in animal model by Teng and coworkers led to the suggestion of the nanobiomaterials as adjuvants and immunoprotective agents against HFMD, subject to further evaluation [16] .

Vero cell cultures. The NPs showed limited activity when applied post-infection, while they showed higher activity against the infection when applied pre-infection. Incubating 12µg/mL of Argovit with the virus leads to a 98% reduction in infection while 60% inhibition was recorded on inoculation with 1.2 µg/mL [102] . Progressively, some AuNPs were demonstrated J o u r n a l P r e -p r o o f to induce immunohistochemical and histological changes in rat spleen, as such, suggested for further studies as potential adjuvant vaccine against the RVFV [17] .

Several NPs of Au and Ag have been reported with potentials for viral diagnosis through testing and detection within living and non-living entities with sensitivity depending on the natures of the NP cores [2] . Consequently, various respiratory viruses with a proclivity for a pandemic such as the influenza virus, SARS-CoVs and MERS-CoV have been reportedly detected using nanobiosensors, most of which are DNA-or antibody-dependent with an electrochemical, field-effect transistor or optical transduction [103, 104] . For instance, double-stranded DNA, MERS-CoV was experimentally detected through label-free colourimetric assay incorporating self-assembly shielded AuNP in the presence of positive electrolytes. The viral presence was verified using localized SPR, (LSPR) [105] , supporting the extended applications of AuNP as a biosensor.

Nanotechnology has aided the design of functionalised and non-functionalised Au and Ag nanobiomaterials through physical, chemical and biological (green synthesis) methods. In this review, the innovative designs, as well as interesting antiviral activities of the nanotechnology- In summary, this review represents a model for an efficient design of nanobiomaterials and identifies promising candidates recommended for further translational studies towards therapeutic designs for the prevention and treatment of human viral diseases.

The authors declare no conflict in this study.

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Can graphene take part in the fight against COVID-19?

Efaverinz and nano-gold-loaded mannosylated niosomes: a host cell-targeted topical HIV-1 prophylaxis via thermogel system

Synthesis, characterization and biocompatibility of a multifunctional gold nanoparticle system for the delivery of single-stranded RNA to lymphocytes

Green synthesis of nanometal impregnated biomass -antiviral potential

Antiviral activity of algae biosynthesized silver and gold nanoparticles against Herps Simplex (HSV-1) virus in vitro using cell-line culture technique

Nanoparticles as antiviral agents against adenoviruses

Green synthesis of silver nanoparticles from medicinal plants and evaluation of their antiviral potential against chikungunya virus

Development and Evaluation of Peptide-Functionalized Gold Nanoparticles for HIV Integrase Inhibition

Evaluation of Multitudinous Potentials of Photosynthetic Microalga, Neochloris aquatica RDS02 Derived Silver Nanoparticles

Gold nanoparticles for preparation of antibodies and vaccines against infectious diseases

Size-dependent neutralizing activity of gold nanoparticle-based subunit vaccine against dengue virus

Golden-star nanoparticles as adjuvant effectively promotes immune response to foot-and-mouth disease virus-like particles vaccine

Immunohistochemical and histological changes in the spleen induced by gold nanoparticles as alternative adjuvant against rift valley fever virus

Negatively charged glyconanoparticles modulate and stabilize the secondary structures of a gp120 V3 loop peptide: Toward fully synthetic HIV vaccine candidates

Gold nanorod vaccine for respiratory syncytial virus

How can nanotechnology help to combat COVID-19? Opportunities and urgent need

Toward Nanotechnology-Enabled Approaches against the COVID-19 Pandemic

Nanoparticle-Based Strategies to Combat COVID-19

Advances in nanomaterials and their applications in point of care (POC) devices for the diagnosis of infectious diseases

Nanotechnology-based disinfectants and sensors for SARS-CoV-2

Gold Nanoparticles Crossing Blood-Brain Barrier Prevent HSV-1 Infection and Reduce Herpes Associated Amyloid-βsecretion

Diversity of Bacterial Synthesis of Silver Nanoparticles

Current Development of Silver Nanoparticle Preparation , Investigation , and Application in the Field of Medicine

Metal Nanoparticles: a Promising Treatment for Viral and Arboviral Infections

Silver nanoparticles as potential antiviral agents

Nanoparticles as a novel and promising antiviral platform in veterinary medicine

Biomaterials-based formulations and surfaces to combat viral infectious diseases

Nano-based approaches in the development of antiviral agents and vaccines

Gold nanoparticles show potential in vitro antiviral and anticancer activity

Fungi-assisted silver nanoparticle synthesis and their applications

Detail review on chemical, physical and green synthesis, classification, characterizations and applications of nanoparticles

In vitro antiviral activity of Cinnamomum cassia and its nanoparticles against H7N3 influenza a virus

Virucidal activity of gold nanoparticles synthesized by green chemistry using garlic extract

Physicochemical properties and in vitro stability studies of green synthesized gold nanoparticles using pelargonium sidoides

Biosynthesis, characterization, and biological activities of procyanidin capped silver nanoparticles

Green synthesis of gold nanoparticles capped with procyanidins from leucosidea sericea as potential antidiabetic and antioxidant agents

Recent Advances in the Development of Antimicrobial Nanoparticles for Combating Resistant Pathogens

Biological synthesis of metallic nanoparticles ( MNPs ) by plants and microbes : their cellular uptake , biocompatibility , and biomedical applications

New Approaches in Breast Cancer Therapy Through Green Nanotechnology and Nano-Ayurvedic Medicine -Pre-Clinical and Pilot Human Clinical Investigations

Saudi Journal of Biological Sciences Influence of gold and silver nanoparticles on the germination and growth of Mimusops laurifolia seeds in the South-Western regions in Saudi Arabia

Optimization for biogenic microbial synthesis of silver nanoparticles through response surface methodology , characterization , their antimicrobial , antioxidant , and catalytic potential

Impact of Particle Size and Polydispersity Index on the Clinical Applications of Lipidic Nanocarrier Systems

Antimicrobial and catalytic activities of biosynthesized gold, silver and palladium nanoparticles from Solanum nigurum leaves

Characterization, antibacterial, antioxidant, antidiabetic, anti-inflammatory and antityrosinase activity of green synthesized silver nanoparticles using Calophyllum tomentosum leaves extract

Antiviral activity of Ribavirin nano-particles against measles virus

Acyclovir-loaded sulfobutyl ether-β-cyclodextrin decorated chitosan nanodroplets for the local treatment of HSV-2 infections

Self-assembled gold nanoparticles for in-vitro inhibition of bovine viral diarrhea virus as surrogate model for HCV

Delivery of antisense peptide nucleic acid by gold nanoparticles for the inhibition of virus replication

Theoretical Design of Functionalized Gold Nanoparticles as Antiviral Agents against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)

Gold Nanocarriers for Macrophage-Targeted Therapy of Human Immunodeficiency Virus

Consensus M2e peptide conjugated to gold nanoparticles confers protection against H1N1, H3N2 and H5N1 influenza A viruses

Enhanced inhibition of influenza virus infection by peptide-noble-metal nanoparticle conjugates

Biosynthesis of Silver and Gold Nanoparticles Using Aqueous Extract from Crinum latifolium Leaf and Their Applications Forward Antibacterial Effect and Wastewater Treatment

N -( 3-hydroxymethyl-βcarboline-1-yl-ethyl-2-yl ) -l -Phe : development toward a nanoscaled antitumor drug capable of treating complicated thrombosis and inflammation

Metal complexes of β-carboline: Advances in anticancer therapeutics

Neuropharmacological potentials of β-carboline alkaloids for neuropsychiatric disorders

Synthesis and evaluation of antiviral activities of novel sonochemical silver nanorods against HIV and HSV viruses

Cytotoxicity and antiviral activity of electrochemical -synthesized silver nanoparticles against poliovirus

Silver nanoparticles as potential antiviral agents against African swine fever virus

Antiviral Activity of Silver Nanoparticles Immobilized onto Textile Fabrics Synthesized by Radiochemical Process

Antiviral activity of graphene-silver nanocomposites against non-enveloped and enveloped viruses

In vitro assessment of activity of graphene silver composite sheets against multidrug-resistant bacteria and Tomato Bushy Stunt Virus

Evaluation of Ag nanoparticle coated air filter against aerosolized virus: Anti-viral efficiency with dust loading

Antibacterial and Antiviral Properties of Silver Nanoparticles Synthesized By Marine Actinomycetes

Silver nanoparticle treatment ameliorates biliary atresia syndrome in rhesus rotavirus inoculated mice

Evaluations of potential antiviral effects of green zinc oxide and silver nanoparticles against bovine herpesvirus-1

Multi-bioactive silver nanoparticles synthesized using mosquitocidal Bacilli and their characterization

Biosynthesis of silver nanoparticles using isolated Bacillus subtilis: characterization, antimicrobial activity, cytotoxicity, and their performance as antimicrobial agent for textile materials

Silver nanoparticles synthesis mediated by new isolates of Bacillus spp., nanoparticle characterization and their activity against Bean Yellow Mosaic Virus and human pathogens

Green-synthesized silver nanoparticles as a novel control tool against dengue virus (DEN-2) and its primary vector Aedes aegypti

Ultra-sonication-assisted silver nanoparticles using Panax ginseng root extract and their anti-cancer and antiviral activities

Water treatment with exceptional virus inactivation using activated carbon modified with silver (Ag) and copper oxide (CuO) nanoparticles

Nanoparticles in the fight against mosquito-borne diseases: bioactivity of Bruguiera cylindrica-synthesized nanoparticles against dengue virus DEN-2 (in vitro) and its mosquito vector Aedes aegypti (Diptera: Culicidae)

Biological activity of green-synthesized silver nanoparticles depends on the applied natural extracts: A comprehensive study

Immunomodulatory activities of curcumin-stabilized silver nanoparticles: Efficacy as an antiretroviral therapeutic

Antiviral potential of green synthesized silver nanoparticles of lampranthus coccineus and malephora lutea

Anti-chikungunya activity of green synthesized silver nanoparticles using Carica Papaya leaves in animal cell culture model

Hepatitis c virus ns3 protease and helicase inhibitors from red sea sponge (Amphimedon) species in green synthesized silver nanoparticles assisted by in silico modeling and metabolic profiling

Reversal of H1N1 influenza virusinduced apoptosis by silver nanoparticles functionalized with amantadine

Silver Nanoparticle Based Codelivery of Oseltamivir to Inhibit the Activity of the H1N1 Influenza Virus through ROS-Mediated Signaling Pathways

Delivery of VP1 siRNA to inhibit the EV71 virus using functionalized silver nanoparticles through ROS-mediated signaling pathways

Antiviral and immunomodulatory activity of silver nanoparticles in experimental rsv infection

Potent antiviral effect of silver nanoparticles on SARS-CoV-2

Promising antimicrobial activities of oil and silver nanoparticles obtained from Melaleuca alternifolia leaves against selected skin-infecting pathogens

Antiviral activity of tannic acid modified silver nanoparticles: Potential to activate immune response in herpes genitalis

Introduction to DNA Viruses

Introduction to RNA Viruses

Novel Gold Nanorod-Based HR1 Peptide Inhibitor for Middle East Respiratory Syndrome Coronavirus

Gold nanoparticle-adjuvanted S protein induces a strong antigen-specific IgG response against severe acute respiratory syndrome-related coronavirus infection, but fails to induce protective antibodies and limit eosinophilic infiltration in lungs

Disinfection of waterborne viruses using silver nanoparticle-decorated silica hybrid composites in water environments

Determination of Air Filter Anti-Viral Efficiency against an Airborne Infectious Virus

Anti-chikungunya activity of green synthesized silver nanoparticles using Carica Papaya leaves in animal cell culture model

Highly Active Antiretroviral Therapy (HAART)

Herpes simplex virus: Global infection prevalence and incidence estimates

Discovery reveals mechanism that turns herpes virus on and off

Potential application of silver nanoparticles to control the infectivity of Rift Valley fever virus in vitro and in vivo

Nanobiosensors for the Detection of Novel Coronavirus 2019-nCoV and Other Pandemic/Epidemic Respiratory Viruses: A Review

Nanobiosensors as new diagnostic tools for SARS, MERS and COVID-19: from past to perspectives

Development of Label-Free Colorimetric Assay for MERS-CoV Using Gold Nanoparticles