key: cord-1012950-2ms4hs9p
authors: Ranjbar, Sheyda; Fatahi, Yousef; Atyabi, Fatemeh
title: The quest for a better fight: How can nanomaterials address the current therapeutic and diagnostic obstacles in the fight against COVID-19?
date: 2021-10-04
journal: J Drug Deliv Sci Technol
DOI: 10.1016/j.jddst.2021.102899
sha: 2ec5a7c9dd48dff26830331526ee298b1b96d1f2
doc_id: 1012950
cord_uid: 2ms4hs9p

The inexorable coronavirus disease 2019 (COVID-19) pandemic with around 226 million people diagnosed and approximately 4.6 million deaths, is still moving toward more frightening statistics, calling for the urgent need to explore solutions for the current challenges in therapeutic and diagnostic approaches. The challenges associated with existing therapeutics in COVID-19 include lack of in vivo stability, efficacy, and safety. Nanoparticles (NPs) can offer a handful of tools to tackle these problems by enabling efficacious and safe delivery of both virus- and host-directed therapeutics. Furthermore, they can enable maximized clinical outcome while eliminating the chance of resistance to therapy by tissue-targeting and concomitant delivery of multiple therapeutics. The promising application of NPs as vaccine platforms is reflected by the major advances in developing novel COVID-19 vaccines. Two of the most critical COVID-19 vaccines are mRNA-based vaccines delivered via NPs, making them the first FDA-approved mRNA vaccines. Besides, NPs have been deployed as simple, rapid, and precise tools for point of care disease diagnosis. Not enough said NPs can also be exploited in novel ways to expedite the drug discovery process. In light of the above, this review discusses how NPs can overcome the hurdles associated with therapeutic and diagnostic approaches against COVID-19.

In addition to what has been mentioned, the other important target for developing antivirals against 13 SARS-CoV-2 is S protein due to its essential role in virus attachment to host ACE2 receptors. 14 Neutralizing antibodies (nAbs) against S protein or its receptor-binding domain (RBD) are being 15 designed and evaluated [7] ; also, recently, the first Ab against S protein entered phase I clinical 16

trial [48] . Besides, peptide inhibitors against SARS-CoV-2 are being designed by the aid of 17 molecular dynamics (MD) simulations [49] . These molecules inhibit the priming of S protein by 18 transmembrane protease serine 2 (TMPRSS2), an essential step for the fusion of viral and host cell 19 membranes. In this context, nanomaterials can provide a unique characteristic of multivalent 20 binding to the virus receptors. These nAbs or peptide inhibitors can be conjugated on the surface 21 of NPs not only to be protected, but also to increase the chance of interaction with virus receptors 22 to further inhibit the viral attachment and fusion to host cells ( Figure 2 ). In an interesting study, a 23 nAb-conjugated photothermal NP was designed to capture and inactivate SARS-CoV-2 [50] . This 1 NP takes advantage of surface nAbs, which enable targeting, capturing, and inhibition of SARS-2

CoV-2 entry to ACE2-expressing host cells and a semiconductive polymer, which shows excellent 3 photothermal effects upon light emitting diode (LED) light excitation. This study highlights the 4 multi-functional approach of utilization of NPs for complete inactivation of SARS-CoV-2. 5

The second mode of therapeutics is host-directed drugs. These therapeutics are used to dampen the 7 harmful exaggerated host response, which can lead to ARDS. In this phase infiltration of immune 8 cells and the cytokine release syndrome (CRS) lead to dysfunctional immune response and 9 production of non-neutralizing Abs [51] . Host-directed therapeutics are generally 10 immunosuppressive agents such as glucocorticoids (GCs), monoclonal antibodies (mAbs) against 11 interleukin (IL)-6 (tocilizumab), IL-1 receptor blocker (anakinra), tumor necrosis factor (TNF)-α 12 inhibitor (etanercept), and JAK inhibitors (baricitinib) [52, 53] . Since the heightened inflammation 13 in the lung is one of the major causes of ARDS, the delivery of the immunosuppressive drugs to 14 the inflammatory lung can be one of the most effective strategies. A large body of evidence shows 15 that inflammatory tissues release the mediators that induce the EPR effect [54] . It is widely known 16 that NPs can passively accumulate in the EPR-enhanced target sites as they do in the TME. 17

However, the inflammatory tissue differs with TME in the presence of a functional lymphatic 18 drainage system, in this case, macrophage uptake can enable the retention of NPs in inflammatory 19 tissues [54] . Many of the host-directed therapeutics are similar to those used against rheumatoid 20 arthritis (RA). Since NPMDD had shown promising results in RA [55, 56] , exploiting NPs for this 21 purpose can also provide benefits in the COVID-19 emergency. For instance, long term delivery 22 of etanercept in RA was achieved via temperature modulated electrostatic interaction between the 23 positively charged etanercept and the negatively charged amphiphilic co-polymer, succinylated 1 pullulan-g-oligo(L-lactide) (SPL) [57] . The nanocomplex showed the increased stability of 2 etanercept as well as enhanced pharmacokinetic profile. Also, the successful delivery of 3 Tocilizumab was achieved by the Hyaluronate-Au NP/tocilizumab complex [58] . Since mAbs and 4 proteins need protection from degradation in the systemic circulation, mAb-conjugated NPs or 5 protein/mAb-loaded NPs can be excellent candidates for safe delivery of these therapeutics. 6

Furthermore, the safety issues regarding the immunogenicity or toxicity of these agents can be 7 addressed via NP-based approaches. 8

Another group of medications in this category is Janus Kinase (JAK) inhibitors. The intracellular 9 delivery of JAK inhibitors, and enhancing their bioavailability can be achieved via NPMDD. For 10 instance, co-polymer-based NPs were used for the simultaneous delivery of two JAK inhibitors in 11 non-small cell lung cancer (NSCLC) to overcome the resistance to therapy [59] . And also other 12 co-polymer based NPs were used to improve the bioavailability of baricitinib [60] . 13 NPs also have been used for the delivery of corticosteroids in different diseases such as cancer, 14 RA, and neuroinflammatory diseases [61] . Different NPs have been employed for such purposes 15

including PEGylated liposomes, polymers (micelles and drug conjugates), inorganic scaffolds, and 16 hybrid NPs. NPs passive accumulation in the inflammatory tissues also enables the significant 17 reduction in the needed-dose of GCs, leading to improved efficacy, specificity, and tolerability of 18 these therapeutics. Besides, NPs can enhance the physicochemical characteristics and also the half-19 life of GCs [61] . Furthermore, they can also provide a depot of GCs in the body by controlled 20 delivery platforms. 21

Mesenchymal stem cells (MSCs) therapy also was proved to be efficacious treatment modality in 22 COVID-19 pneumonia patients [62] . This effect is attributed to the immunomodulatory roles 23 associated with MSCs, which attenuate the ARDS. However, lack of in vivo stability of MSCs and 1 their tendency to aggregate hinders their application. On the other hand, it has been reported that 2 MSC-derived exosomes as cell-free therapeutics can provide the therapeutic efficacy of MSCs 3 without having the mentioned problem. The biocompatibility and cell targeting ability of these 4 exosomes also makes them ideal candidates for drug delivery in COVID-19 [63] . 5

In the past, monotherapy with antiviral agents like ribavirin against SARS-CoV and MERS-CoV 7 showed limited efficacy in patients and also provoked safety concerns regarding hemolysis 8 collateral effects [64] . In this sense, combinational therapies based on the administration of 9 ribavirin with ritonavir and lopinavir were evaluated and showed promise in SARS patients [65] . 10 Furthermore, different combinations of interferons (IFNs) with ribavirin or lopinavir/ritonavir 11 were evaluated in SARS and MERS patients [66] [67] [68] . Besides, combinations of virus-directed 12 therapies with host-directed therapies have also been investigated including combinations of IFNs 13 with immunosuppressive agents such as corticosteroids and mycophenolate mofetil in MERS 14 patients [69, 70] . 15 Different combinations of therapeutics were also evaluated in COVID-19 patients, which yielded 16 promising results. For instance, a triple combination of IFN beta-1b, lopinavir/ritonavir, and 17 ribavirin was compared with lopinavir/ritonavir therapy in COVID-19 patients with mild to 18 moderate symptoms [71] . The result revealed that the combination therapy was more effective in 19 alleviating the symptoms and shortening the hospitalization duration. Other combinations such as 20 darunavir/cobicistat [72] and emtricitabine/tenofovir (NCT04334928) were also investigated in 21 COVID-19. In this context, NPs can offer an exclusive advantage of concomitant delivery of drugs. 22

Concomitant delivery of therapeutics has several benefits such as reducing the drug administration 23 J o u r n a l P r e -p r o o f frequencies, which helps to improve the compliance of patients and lowers the risk of resistance 1 to treatment regimen while increases the efficacy and safety of the therapy. 2 Nanomaterials are excellent candidates for such purpose and there are plenty of strategies that 3 enable simultaneous delivery of drugs by a single nanocarrier [73] . Different therapeutics can also 4 be loaded in different compartments of NPs so that even non-compatible molecules can be co 5 loaded in an NP and also by tailoring the physicochemical characteristics of each compartment or 6 layer, the release profile of drugs can be controlled so that the therapeutic concentration of each 7 medicine remains adequate during a long time. Best examples of concomitant delivery of antivirals 8 via NPs can be found in attempts being made in combinational therapies against HIV. For instance, 9

PLGA NPs were used for delivery of efavirenz, lopinavir, and ritonavir, with entrapment 10 efficiency of around 80% for each drug [74] . Besides, lactoferrin NPs were used for the delivery 11 of zidovudine, efavirenz, and lamivudine. Another study in primates revealed that LNPs 12 simultaneously carrying lopinavir, ritonavir, and tenofovir significantly enhanced intracellular 13 concentrations in lymph nodes and blood and were able to sustain the drug concentrations in 14 plasma for up to7 days [75] . These studies emphasize the great potential of NPS to be deployed in 15 combinational regimens in COVID-19. 16

NPs 18

The major and primary target of SARS-CoV-2 is the respiratory system, where there is a high 19 expression of ACE2 receptors [76] . The abundant ACE2 receptors existing in lung and bronchial 20 branches cells provide the binding site for SARS-CoV-2, which can lead to the clinical 21 manifestations of the disease such as pneumonia and in more advanced cases, ARDS. By 22 considering this, pulmonary delivery of therapeutic agents against SARS-CoV-2 can be a great 23 option for a successful treatment. In this sense, NPs can be exploited as promising tools for such 1 a purpose. Pulmonary delivery of drugs by NPs can increase the concentration of drugs in the lung 2 and reduce their side effects. Furthermore, the sustained release of drugs from NPs in the lungs 3

can provide a depot of therapeutics, which results in enhanced patient compliance by reducing the 4 dose frequency. For instance, administration of amikacin-loaded SLNs by micro sprayer in rats 5 increased the drug concentration in the lungs, highlighting the potential of pulmonary delivery of 6 amikacin loaded SLNs in cystic fibrosis patients [77] . Also, the amikacin liposome inhalation 7 suspension Arikayce (®) (Insmed, NJ, USA) got FDA approval in 2018 for the treatment of 8 mycobacterium avium complex (MAC) lung disease [78] . Many other antibiotics including 9

itraconazole, voriconazole, ciprofloxacin, anti-tuberculosis drugs, etc., have been formulated for 10 pulmonary delivery by different NPs [79] . 11

Recently, an inhalable liposomal drug delivery system was utilized to enhance the efficacy and 12 safety of HQC in COVID-19 in a pre-clinical study [34] . Another study, evaluated the intra-13 pulmonary delivery of remdesivir by nanostructured aggregates using thin film freezing [80] . Also, 14 there are hypotheses about intra-pulmonary delivery of salinomycin and NO-releasing 15 nanomaterials in COVID-19 [36] [41] . 16 Although the respiratory system is the primary target of SARS-CoV-2, the virus can spread to 17 other organs with a high density of ACE2 receptors in severe cases. For instance, the 18 cardiovascular system including heart and endothelial cells also express high amounts of ACE2 19 receptor and can be potential targets for the invasion of SARS-CoV-2 [81] . Besides, ACE2 and 20 TMPRSS2 are also found abundantly in the gastrointestinal tract (GIT) including the duodenum, 21 small intestine, pancreas, and liver, which makes these organs susceptible to SARS-CoV-2 [76] . 22

Furthermore, the central nervous system (CNS) is also not immune to the attack of SARS-CoV-2 23 [82] . The blood brain barrier (BBB), which protects CNS from the invasion of pathogens, can get 1 harmed as a result of the CRS triggered in response to SARS-CoV-2, leading to its increased 2 permeability to the virus. Furthermore, sensory or motor nerve endings can provide a pathway for 3 the migration of the virus to CNS. In particular, olfactory nerves can make a direct passage from 4 the nasal cavity to CNS, enabling the direct invasion of SARS-CoV-2 to CNS [82] . In each of the 5 mentioned cases, NPMDD approaches can also be helpful. Since NPs have been successfully used 6 for targeting the cardiovascular system [83] , liver [84] , GIT [85] , and CNS [86] . 7

The reproductive system also expresses high amounts of ACE2 receptors particularly in the 8 placenta, uterus, and fetal interface of pregnant women [87] . There is evidence regarding the 9 increased susceptibility of pregnant women to SARS-CoV-2 as a result of the changes in the 10 anatomical structure of the respiratory system, hormones, immune system, and also upregulation 11 in ACE2 receptors during pregnancy [88] . In this condition, adverse effects associated with anti-12 COVID-19 therapies on fetus becomes of great concern. NPs can be implemented to improve the 13 efficacy and safety of drugs in pregnant women. In addition to the general benefits that NPs can 14 provide by the delivery of antivirals, NPs can have additional benefits as fetus-safe delivery 15 systems. NPs characteristics including size and charge can be tailored so that their affinity to 16 maternal target organs be increased while the possibility of their interaction with the placenta is 17 minimized [88] . 18

There has been great endeavor in designing prophylactic and therapeutic vaccines for COVID- 19. 20 According to WHO COVID-19-Landscape of novel coronavirus candidate vaccine development 21

worldwide, there are currently 105 candidate vaccines in clinical evaluation against SARS-CoV- 2 22 and 184 vaccines in the preclinical stage. 84 percent of current COVID-19 vaccines in clinical 23 phase are administered via injection (84%), mostly intra muscular, and 65% of them require 2 1 doses to obtain the desirable immunity, while 14% require one dose and only 1% require 3 doses. 2

One of the most important areas of implementing NPs for prophylaxis of COVID-19 is developing 3 mRNA-loaded LNPs since the two FDA-approved vaccines used for mass vaccination belong to 4 this category, which will be discussed in section 3.3. Among other vaccines, there is a non-5 replicating viral vector named Ad26.COV2.S with EUA, developed by the Janssen Pharmaceutical 6

Companies (Johnson & Johnson group), that has shown good safety, immunogenicity, and efficacy 7 after a single dose [89] .There are two non-replicating viral vectors being used for mass vaccination 8 in countries other than the U.S. The Vaxzeveria is developed by University of Oxford/AstraZeneca 9 and Gam-COVID-Vac/Sputnik V vaccine, is produced in Russia by the Gamaleya Research 10 Institute [90] . Vaxzeveria, is an adenovirus-based non-replicating vector, which showed an 11 efficacy of 62-90% in phase 3 clinical trials [91] , and Gam-COVID-Vac/Sputnik V vaccine is 12 based on the combination of the two replication-deficient adenoviruses type 26 (rAd26) and rAd5, 13 with genetic information for expression of the full-length glycoprotein S of SARS-CoV-2 [92] . 14 There are also several other vaccines in different stages of clinical trials that have been 15 comprehensively reviewed elsewhere [90] . 16 In the following, the beneficial role of NPs in developing each kind of vaccine against SARS-17

CoV-2, which fall into different categories as inactive or live-attenuated viruses, virus-like 18 particles (VLPs), RNA and DNA-based vaccines, and protein subunit vaccines, is discussed. 19

Subunit vaccines consist of protein or glycoprotein molecules of a pathogen, that can induce a 21 protective immune response, and account for the 31% of current COVID-19 candidate vaccines in 22 clinical phase. The S, E, M, and N proteins of SARS-CoV-2 are potential antigens that are being 1 used in subunit vaccines of COVID-19 [7] . However, these antigens are prone to degradation and 2 loss of activity in the biological environment. Furthermore, without an appropriate delivery 3 system, these antigens are not likely to accumulate in their site of action, which is lymph nodes. 4

Moreover, the chance of the uptake of particulate antigens by antigen-presenting cells (APCs) is 5 much higher than that of soluble antigens [93] . In this line of thought, NPs are the best candidates 6 for the delivery of subunit vaccines due to their exclusive characteristics that can guaranty 7 successful antigen delivery. NPs have been widely used for this purpose in various infectious 8 diseases and cancers [18, 94] . NPs are excellent vehicles for the delivery of antigens since not only 9 they can enhance the in vivo stability of antigens, but also can deliver antigens effectively to lymph 10 nodes, where their particulate structure will further facilitate the internalization of antigens by 11

APCs. Followed by the uptake of antigen laden NPs, APCs will mature and cross-present the 12 antigen via MHC1 complex on their surface, a signal which can activate CD8 + cells to activate 13

Ag-specific cytotoxic T cell-mediated immunity [18] . In addition to the role of NPs in carrying the 14 viral antigen, the antigen itself can be assembled to a nanoparticulate structure. For instance, a 15 self-assembling polypeptide NP vaccine based on the repetition of the heptad repeat region (HRC) 16 of SARS-CoV S protein was designed. The self-assembly vaccine could successfully trigger anti-17 SARS antibodies even in the absence of adjuvants. The potent immunogenic effect of the system 18 was due to the repetitive display of the epitope and size of the particle, which ensured its successful 19 uptake and presentation by APCs [95] . Another study evaluated the role of RNA as a molecular 20 chaperon to enable the folding of monomeric antigens of MERS-CoV RBD to high order and more 21 immunologically relevant conformations to form a potent self-assembly NP vaccine [96] . Even an 22

NP-base vaccine without any viral antigens was found to exert an immuno-prophylactic effect on 23 mouse-adapted SARS-CoV via the prior development of inducible bronchus-associated lymphoid 1 tissue (iBALT) in the lung. The reported NP was protein cage NP (PCN) derived from the small 2 heat-shock protein (sHsp 16.5) of the hyper-thermophilic archaeon Methanococcus jannaschii that 3 effectively cleared respiratory viruses and also succeeded to avoid the host exaggerated immune 4 response and further lung damage [97] . 5

Another important moiety in vaccines is adjuvant, which can trigger a more potent immune 6 response and lower the needed antigen dose [98] . Some NPs intrinsically can act as adjuvants via 7 triggering the immune response, however, the efficacy of NPs as adjuvants should be meticulously 8 evaluated. For instance, in a recent study [99] , a candidate vaccine based on the recombinant S 9 protein of SARS-CoV was designed. The subunit vaccine was used in combination with two 10 adjuvants separately since the adjuvant-free formulations could not induce a potent immune 11 response and caused lung eosinophilic immunopathology (LEI). Accordingly, the first system was 12

Au NPs conjugated with the S protein in which Au NPs were used because of their intrinsic 13 immuno-stimulatory properties, and the other adjuvant was a Toll-like receptor (TLR) agonist. 14 Results showed that although Au NP based vaccine was able to induce a strong Ab response, it 15 failed to prevent the LEI. On the other hand, the TLR agonist-adjuvanted vaccine could both 16 induce a strong immune response and successfully abate the LEI. This study reveals that relying 17 on the intrinsic immuno-stimulatory role of NPs is not always promising. Yet, another major 18 benefit of NP-based antigen delivery is the possibility of concomitant delivery of adjuvants along 19 with antigens, which has proved to be a promising strategy in previous attempts in other infections. NPs that act as adjuvants and can be used in conjunction with antigen-loaded NPs. Matrix M 2 adjuvant is the Novavax patent, which is more tolerable than the primary formulation and can 3 recruit APCs to the injection site and facilitate antigen presentation in local lymph nodes. In 2017, 4

Novavax reported a MERS-CoV S NP vaccine, which was used with Matrix M1 adjuvant in mice 5 [100] . The combination was able to produce an effective immune response by producing anti-S 6 Table 1 . 19

Virus-like particles (sVLPs) account for the 5% of the current COVID-19 candidate vaccines in 21 clinical phase. NP-based sVLPS are generally like antigen-laden NPs and the difference is in the 22 antigen position in NP. In antigen-based NPs, the virus antigen is loaded into the NPs, while in 23 sVLPs antigen is placed on the surface of NPs. Incubation of NPs with specific viral proteins can 1 maintain sVLPs, which resemble the natural viral particles. One of the most important features of 2 NPs is that their size can be tailored to resemble the virus while they have viral antigens on their 3 surface. These sVLPs will be able to stimulate the immune response in the body, while they are 4 generally harmless because they lack the virus replication system. Coronavirus structural proteins, 5 especially the spike protein can be a potential model antigen for designing vaccines. For instance, 6

Au NPs (100 nm) with a protein corona of avian coronavirus spike protein was used for vaccination 7 in an avian model of coronavirus infection [103] . These sVLPs showed superiority over free 8 proteins in antigen delivery and subsequent immune response of antibody secretion and T-cell 9 response leading to the overall better therapeutic outcome in vivo. The VLPs even outperformed 10 the inactivated virus in antiviral protection. 11

Alike antigen-based vaccines, sVLPs can also co-deliver adjuvants to impose a more potent 12 immunity (Figure 3 ). Based on this approach, Lin et al.,2019, designed a viromimetic vaccine 13 against MERS-CoV; in their platform, stimulator of interferon genes (STING) agonist as adjuvants 14 was loaded in hollow polymeric NPs whose surface was coated with the MERS-CoV RBD 15 antigens [104] . Consequently, the morphology of RBD-coated STING agonist loaded polymeric 16 hollow NPs resembled the original virus. Altogether, the NPs could deliver antigens alongside 17 adjuvants to lymph nodes where they managed to release the latter in a pH-dependent manner. 18

Thus, they enabled significant local immune activation and lowered systemic reactogenicity. This 19 safe and efficient vaccine was able to trigger potent humoral and cellular immune response without 20 the occurrence of LEI. SARS-CoV mostly encode the full-length S, S1, S2 protein, or RBD. Other mRNAs also encode 4 other structural proteins of the virus such as E, M, and N [7] . These mRNAs followed by cellular 5 uptake and triggering the cellular machinery, are translated to the functional viral proteins that can 6 trigger immunity. To protect these highly sensitive molecules from degradation by extracellular 7

RNases and also to enable their effective intracellular delivery, NPs can be used as appropriate 8 tools ( Figure 4) . Also, to stimulate a more potent response, the idea of combining multiple mRNAs 9 into a single vaccine exists. In this case, concomitant delivery of mRNAs via a single carrier can 10 be promising. Different NPs have been used for the delivery of mRNAs such as dendrimers, 11 cationic polymers including PEI and chitosan, nano-emulsions, liposomes, and lipid NPs. lipid 12 nanoparticles (LNPs) are the most used NPs as mRNA delivery vehicles that consist of ionizable 13 lipid, phospholipid, PEG-lipid as the half-life increasing moiety, and cholesterol as the stability-14 enhancing component [105] . The structure of LNPs including their multilamerallity, which can 15 be tailored by using cholesterol derivatives, plays a pivotal role in enhanced gene delivery of these 16

NPs [106] . CoV-2, which composes of cationic LNPs as carriers of mRNA and shows an efficacy of around 23 94% among 30k participants [107] . Moderna/NIAID vaccine has been approved for adults ages 18 1 or older in the U.S. The BNT162b2, developed by the BioNTech/Pfizer/ Fosun Pharma group, is 2 also an mRNA-based LNP vaccine, which showed an efficacy of 95% among more than 43k 3 participants enrolled in its phase 3 clinical trial [108] . Pfizer vaccine is approved for adults ages 4 16 and older in the U.S. with EUA for ages 12-15. 5 Also, a thermostable LNP-encapsulated mRNA vaccine named ARCoV that encodes RBD of 

In addition to the great need for developing therapeutic approaches against the ongoing COVID-2 19, developing reliable laboratory diagnostic tools are also among the primary concerns. Different 3 laboratory approaches have been developed for the diagnosis of COVID-19 the most routine of 4 which is RT-PCR. This approach, however, has its hurdles; for instance, it is only done by 5 professional people in laboratories and is also very time-consuming. Furthermore, despite the 6 reliability of this approach, it is not error-free since there has been a report of some false-7 positive/negative cases, particularly in the early stages of the disease [12] . In this sense, developing 8 novel approaches, which can diagnose the COVID-19 rapidly, easily, and accurately remains a 9 priority. A great effort is being invested in designing NP-based approaches that can help in the 10 diagnosis of the virus via colorimetric, electrochemical, and lateral flow immunoassays. Gold 11 nanoparticles are especially appropriate in this sense due to their exclusive characteristics such as 12 localized surface plasmon resonance (LSPR) shift and thermoplasmonic heat generation ability. In 13 the following the NP-based diagnostic tools used for COVID-19 and other closely-related diseases 14 such as MERS and SARS, are discussed. 15

One of the important diagnostic approaches is the detection of a specific target of viral antigens, 17 proteins, or genome, and different studies are reporting the application of NPs for this purpose. In 18 a study, a colorimetric assay was designed for the detection of MERS-CoV via colorimetric 19 changes of Au NPs [112] . The assay was based on the changes in the Au NPs LSPR shift, which 20 was detectable in ultraviolet-visible (UV-vis) spectrophotometry. For this purpose, a thiol-21 modified probe was designed that matched with the complementary base pairs in the upstream of 22 the E protein gene (upE) and open reading frames (ORF) 1a on MERS-CoV. In the presence of 23 the virus, dsDNA was formed via hybridization of probe and target, which turned into a disulfide 24 induced self-assembly that could prevent Au NPs aggregation after salt addition. The color and 1 UV-Vis spectral changes after LSPR shift due to the NPs aggregation were then interpreted. 2

Another NP-based platform for the detection of MERS-CoV along with two other viruses was 3 designed [113] . In this sensor, pyrrolidinyl peptide nucleic acid (acpcPNA) probes with the 4 complementary sequence with that of the MERS-CoV genome were used. These probes also had 5 a positive charge to be able to aggregate the citrate-stabilized Ag NPs. In the presence of the 6 complementary nucleic acid, hybridization of acpcPNA and target prevented Ag NPs aggregation. 7

Yet in the absence of the target or the mismatching nucleotides, the acpcPNA-induced Ag NPs 8 aggregation led to a detectable color change. The proposed sensor enabled the rapid, sensitive, and 9 specific detection of the viral genome. Apart from colorimetric assays, Au NPs were used in an 10 electrochemical immunosensor for the detection of HCoV and MERS-CoV [114] . In this 11 biosensor, carbon electrodes were modified with Au NPs, which were immobilized with HCoV 12 and MERS-CoV S protein antigens. Followed by the addition of varying concentrations of viral 13 antigens with a constant concentration of specific Ab, the voltammetric response was detected. 14 The peak current was associated with free antigen concentration since, in the absence of free 15 antigen, binding of Ab to immobilized antigen could lower the electron transfer efficiency leading 16 to a decrease in the current. Recently, a dual functionalized biosensor was designed based on the 17 LSPR and plasmonic photothermal effect (PPT) of Au nanoislands (NIs) chips [115] . The AuNIs 18

were functionalized with complementary DNA receptors of specific regions in the SARS-CoV- 2 19 genome including RdRp-COVID, ORF1ab-COVID, and E genes. In the presence of the virus, the 20 hybridization of target and receptors were detectable via LSPR response. The important feature of 21 this biosensor was the thermoplasmonic enhancement, which took advantage of the PPT effect of 22

AuNIs to increase the precision of the biosensor. The plasmonic heat generated by excitation of 23

AuNIs at the specific wavelength, increased the kinetics of hybridization of fully-matched 1 sequences, while disabled the hybridization of closely related sequences with some mismatch 2 points. This PPT effect enables the discrimination of similar genes from the specific target with a 3 limit of detection (LOD) concentration of 0.22 pM. Another recent study developed a rapid 4 selective naked-eye method that enabled the detection of the SARS-CoV-2 with LOD of 0. 18 5 ng/μL of RNA [116] . In this method, Au NPs were capped with thiol-modified antisense 6 oligonucleotides (ASOs) specific for the N gene of SARS-CoV-2. Agglomeration of Au NPs in 7 the presence of the target RNA led to their LSPR change. At this stage, the addition of RNaseH 8 by detaching the RNA strand from the hybrid facilitated further agglomeration of Au NPs enabling 9 the visual detection of the precipitation ( Figure 5 ). The mentioned NP-based detection tools with 10 their promising results accentuate the great potential of NPs to be deployed in diagnostic 11 approaches. 12

Serologic detection methods for identification of immune response to SARS-CoV-2 are not the 14 gold standard in disease detection because antibody responses vary based on the patient's 15 condition, age, and immune system. Besides, immunoglobulin M (IgM) and immunoglobulin 16 (IgG) antibodies reach the detectable threshold over days to weeks after the onset of the disease, 17 so early tests might lead to false-negative results [117] . Moreover, these tests also might yield 18 false-positive results in analogous infections [117] . Yet the research in this field is dynamic for 19 exploring innovative diagnostic tools that can easily and rapidly detect antibodies. There have been 20 recent advances in NP-based lateral-flow assays for the detection of IgG and IgM antibodies 21 against SARS-CoV-2. Chen et al., 2020, developed a lateral flow immunoassay (LFIA) that used 22

lanthanide-doped polystyrene nanoparticles (LaNPs) to detect IgG against SARV-CoV-2 in human 23 serum [118] . This method can be used as an alternative to the chest computed tomography (CT) 1 method for confirmatory diagnosis of suspicious samples whose RT-PCR was reported negative. 2

In this assay LaNPs that served as a fluorescent reporter were functionalized with mouse anti-3 human IgG. Also, recombinant nucleocapsid phosphoprotein (rNCp) was dispensed onto the test 4 line to capture IgG. As the diluted sample migrated through the LFIA strip, in the presence of anti-5 SARS-CoV-2 IgG, the complex of mouse-anti human IgG and sample IgG formed in the test line 6 (with rNCP), which could be detected after 10 min via the fluorescence reader. This assay could 7 successfully detect a suspicious negative RT-PCR sample as IgG positive. In another recent study, 8

an LFIA based on Au NPs was designed for rapid and on-site detection of anti-SARS-CoV-2 IgM 9

antibodies [12] . For this purpose, antihuman IgG-conjugated Au NPs were used as detecting probe 10 and SARS-CoV-2 N protein was coated in the test line ( Figure 6 ). When the sample was added on 11 the strip, the antihuman IgM-conjugated Au NPs could capture the antibody and the complex 12 

Different role of NPs as viral antigens or antibody detecting tools was discussed so far. However, 19

NPs can also be used in other applications such as drug discovery platforms. In an interesting 20 study, NPs were used innovatively as a high-throughput screening platform for SARS-CoV N 21 protein inhibitor [119] . N protein plays a pivotal role in SARS-CoV replication and is a potential 22 target for anti-SARS therapeutics. In this study, the anti-SARS-CoV N protein activity of 23 polyphenolic compounds was analyzed via the optical NP-based RNA oligonucleotide(RO) 1 biochip system. For this purpose, SARS-CoV N protein was immobilized on a glass chip and then 2 was treated with quantum dots (QDs), which were conjugated with RO sensitive to SARS-CoV N 3 protein to enable the binding of RO and N protein. Then the inhibitor was spotted on the chip and 4 followed by washing and unspecific binding removal the detection was performed via image 5 analysis (Figure 7 ). By this low-cost method, two potent inhibitors of SARS-CoV N protein were 6 detected. This study highlights the fact that NPs can be innovatively exploited in novel 7 applications, which can expedite the process of drug discovery for diseases including COVID-19. 8

In this review, the potential ways that NPs can be deployed to provide a solution for current 10 shortcomings in the therapeutic and diagnostic approaches in COVID-19 were discussed. Besides, 11 very recent advances in the field of NP-based vaccines and diagnostic tools were covered. 12 NPMDD can be a powerful tool to address the existing challenges in treatment of COVID-19. NPs 13 can enhance the in vivo stability of protein/nucleic acid -based therapeutics in COVID-19. Also, 14

NPs conjugation with anti-S nAbs, can enhance viral entry inhibition both by protecting nABs 15 from degradation and enabling the multivalent binding of the virus to NPs. The therapeutic benefits 16 of NPMDD also include enhancing the efficacy and safety of host-directed therapeutics to stop 17 CRS. The passive targeting of NPs to the inflammatory tissue due to the EPR effect is one 18 promising strategy to enable effective delivery of drugs to the infected lung. The other important 19 feature of NPs is the ability of concomitant delivery of therapeutics, which seems to add a 20 significant benefit to COVID-19 combinational regimens. The pulmonary delivery of therapeutics 21 by nanomaterials is another solution to decrease the safety issues caused by high concentration 22

and frequency intake of therapeutics. 23

It is noteworthy that all of the mentioned applications of NPMDD need prior meticulous 1 investigations to find the optimal characteristics and best material needed for each purpose and 2 also by considering the potential adverse effects associated with NPs administration. For instance, 3 the stability and bioavailability of NPs, their interactions with biologic tissue, and also SARS-4

CoV-2 should be thoroughly investigated, for some NPs might lack the required stability and 5 bioavailability, particularly following oral administration, some have unintended interactions with 6 biological tissues and environment, some have intrinsic toxicities and also off-target effects [120] . 7

Besides, the mentioned scavenger effect of NPs also should be evaluated regarding the biological 8 fate of the virus-NP complex. 9

The essential role of NPs in designing vaccines against SARS-CoV-2 is conspicuously reflected 10 by the recent achievements in vaccine discovery of COVID-19 (table 1). In this application LNP-11 based platforms for delivery of mRNAs are the most effective strategy as two of the most 12 efficacious vaccines worldwide belong to this category. 13

NPs can also offer great advantages in diagnostic approaches. In the condition when rapid and 14 precise detection of disease is of great importance, NPs can be used as tools to enable the detection 15 of the virus in simple yet accurate ways. In particular, Au NPs can be great candidates due to their 16 LSPR and also PPT effect, where the former can enable naked-eye detection of viruses and the 17 latter can enhance the selectivity of diagnostic platforms. NPs can also be used in serologic 18 detection of Abs in LFIA platforms, which can be used as a point of care diagnostic materials. In 19 addition to the mentioned applications of NPs in fighting against COVID-19, their novel 20

applications are yet to be discovered. For instance, NPs have been used as antiviral agents 21 screening biochip to find the inhibitor of SARS-CoV N protein [119] . 22

To sum up, NPs can play a pivotal role in addressing the current gaps in the therapeutic and 1 diagnostic approaches in COVI-19, yet their efficacy and safety should be meticulously evaluated 2 in clinical studies. 3

Funding. This research did not receive any specific grant from funding agencies in the public, 5 commercial, or not-for-profit sectors. [116] . Copyright 2020 ACS. 

WHO Director-General's statement on IHR Emergency Committee on Novel Coronavirus (2019-nCoV)

Coronavirus Disease (COVID-19) Dashboard, in

Emerging coronaviruses: Genome structure, replication, and pathogenesis

Genomic characterization of the 2019 novel human-pathogenic coronavirus isolated from a patient with atypical pneumonia after visiting Wuhan, Emerging microbes & infections

Features, Evaluation, and Treatment of Coronavirus (COVID-19)

Cryo-EM structure of the SARS coronavirus spike glycoprotein in complex with its host cell receptor ACE2

Research and Development on Therapeutic Agents and Vaccines for COVID-19 and Related Human Coronavirus Diseases

COVID-19) Update: FDA Issues Emergency Use Authorization for Potential COVID-19 Treatment

COVID-19) Update: FDA Authorizes Drug for Treatment of COVID-19

Assay Techniques and Test Development for COVID-19 Diagnosis

Rapid Detection of IgM Antibodies against the SARS-CoV-2 Virus via Colloidal Gold Nanoparticle-Based Lateral-Flow Assay

The unique role of nanoparticles in nanomedicine: imaging, drug delivery and therapy

Nanoparticles in the clinic: An update

Doxil® -The first FDA-approved nano-drug: Lessons learned

Progress in Nanomedicine: Approved and Investigational Nanodrugs

Nanoparticle-Mediated Drug Delivery and Gene Therapy

Nanoparticle Vaccines Against Infectious Diseases

Anisotropic plasmonic nanostructures for colorimetric sensing

Nanomaterials Designed for Antiviral Drug Delivery Transport across Biological Barriers

Can Nanotechnology and Materials Science Help the Fight against SARS-CoV-2?

Potential Antiviral Drugs for SARS-Cov-2 Treatment: Preclinical Findings and Ongoing Clinical Research

COVID-19: consider cytokine storm syndromes and immunosuppression

Reducing mortality from 2019-nCoV: host-directed therapies should be an option

Structural basis for inhibition of the RNAdependent RNA polymerase from SARS-CoV-2 by remdesivir

Peptides: Prospects for Use in the Treatment of COVID-19

Short peptides derived from the interaction domain of SARS coronavirus nonstructural protein nsp10 can suppress the 2'-O-methyltransferase activity of nsp10/nsp16 complex

Evidence of Protein Binding by a Nucleopeptide Based on a Thyminedecorated L-Diaminopropanoic Acid through CD and In Silico Studies

Nanosuspension of efavirenz for improved oral bioavailability: formulation optimization, in vitro, in situ and in vivo evaluation

Design of antiretroviral drugpolymeric nanoparticles laden buccal films for chronic HIV therapy in paediatrics

Inhibition of H1N1 influenza virus-induced apoptosis by functionalized selenium nanoparticles with amantadine through ROS-mediated AKT signaling pathways

Inhibitory activity of selenium nanoparticles functionalized with oseltamivir on H1N1 influenza virus

Antiviral efficacy of nanoparticulate vacuolar ATPase inhibitors against influenza virus infection

A Strategy to Treat COVID-19 Disease With Targeted Delivery of Inhalable Liposomal Hydroxychloroquine: A Preclinical Pharmacokinetic Study

Production and characterization of biocompatible nano-carrier based on Fe3O4 for magnetically hydroxychloroquine drug delivery

Pulmonary delivery of nanostructured lipid carriers for effective repurposing of salinomycin as an antiviral agent

Ivermectin, a new candidate therapeutic against SARS-CoV-2/COVID-19

Safety and efficacy of favipiravir versus hydroxychloroquine in management of COVID-19: A randomised controlled trial

Respiratory delivery of favipiravir-tocilizumab combination through mucoadhesive protein-lipidic nanovesicles: prospective therapeutics against COVID-19

Theoretical investigation of favipiravir antiviral drug based on fullerene and boron nitride nanocages

Nitric oxide (NO) and nanoparticles -Potential small tools for the war against COVID-19 and other human coronavirus infections

siRNA could be a potential therapy for COVID-19

Nanoparticle-mediated systemic delivery of siRNA for treatment of cancers and viral infections

Lipid Nanoparticle Technology for Clinical Translation of siRNA Therapeutics

Nonviral siRNA delivery to the lung: investigation of PEG-PEI polyplexes and their in vivo performance

Selective organ targeting (SORT) nanoparticles for tissue-specific mRNA delivery and CRISPR-Cas gene editing

A SARS-CoV-2 targeted siRNA-nanoparticle therapy for COVID-19

First antibody against COVID-19 spike protein enters phase I

Computational Design of ACE2-Based Peptide Inhibitors of SARS-CoV-2

A Neutralizing Antibody-Conjugated Photothermal Nanoparticle Captures and Inactivates SARS-CoV-2, bioRxiv

The trinity of COVID-19: immunity, inflammation and intervention

COVID-19 and immunosuppression: a review of current clinical experiences and implications for ophthalmology patients taking immunosuppressive drugs

Use of anakinra in severe COVID-19: A case report

Nanomedicine for drug targeting: strategies beyond the enhanced permeability and retention effect

Nanomedicine delivers promising treatments for rheumatoid arthritis

Lipid-Based Nanoparticles as a Potential Delivery Approach in the Treatment of Rheumatoid Arthritis

Temperature-modulated noncovalent interaction controllable complex for the long-term delivery of etanercept to treat rheumatoid arthritis

Hyaluronate-Gold Nanoparticle/Tocilizumab Complex for the Treatment of Rheumatoid Arthritis

Biodegradable Nanoparticles Mediated Co-delivery of Erlotinib (ELTN) and Fedratinib (FDTN) Toward the Treatment of ELTN-Resistant Non-small Cell Lung Cancer (NSCLC) via Suppression of the JAK2/STAT3 Signaling Pathway

Nano-encapsulation and characterization of baricitinib using poly-lactic-glycolic acid co-polymer

Novel Drug Delivery Systems Tailored for Improved Administration of Glucocorticoids

Transplantation of ACE2(-) Mesenchymal Stem Cells Improves the Outcome of Patients with COVID-19 Pneumonia

Mesenchymal Stem Cell Derived Exosomes: a Nano Platform for Therapeutics and Drug Delivery in Combating COVID-19

Severe Acute Respiratory Syndrome: Historical, Epidemiologic, and Clinical Features

Proteases and protease inhibitors in infectious diseases

Ribavirin and Interferon Therapy for Critically Ill Patients With Middle East Respiratory Syndrome: A Multicenter Observational Study

Combination therapy with lopinavir/ritonavir, ribavirin and interferon-α for Middle East respiratory syndrome

Treatment With Lopinavir/Ritonavir or Interferon-β1b Improves Outcome of MERS-CoV Infection in a Nonhuman Primate Model of Common Marmoset

Treatment outcomes for patients with Middle Eastern Respiratory Syndrome Coronavirus (MERS CoV) infection at a coronavirus referral center in the Kingdom of Saudi Arabia

Triple combination of interferon beta-1b, lopinavir–ritonavir, and ribavirin in the treatment of patients admitted to hospital with COVID-19: an open-label, randomised, phase 2 trial

Antiviral Activity and Safety of Darunavir/Cobicistat for the Treatment of COVID-19, Open Forum Infectious Diseases

Chapter 16 -Layer-by-Layer coated drug-core nanoparticles as versatile delivery platforms

Polymeric nanoparticles containing combination antiretroviral drugs for HIV type 1 treatment

Anti-HIV Drug-Combination Nanoparticles Enhance Plasma Drug Exposure Duration as Well as Triple-Drug Combination Levels in Cells Within Lymph Nodes and Blood in Primates, AIDS research and human retroviruses

Tissue distribution of ACE2 protein, the functional receptor for SARS coronavirus. A first step in understanding SARS pathogenesis

Biodistribution of amikacin solid lipid nanoparticles after pulmonary delivery

FDA approves a new antibacterial drug to treat a serious lung disease using a novel pathway to spur innovation

Nanoparticle-mediated pulmonary drug delivery: a review

Development of Remdesivir as a Dry Powder for Inhalation by Thin Film Freezing

The role of ACE2 in cardiovascular physiology

Nervous system involvement after infection with COVID-19 and other coronaviruses

Application of the Nano-Drug Delivery System in Treatment of Cardiovascular Diseases

Therapeutic targeting of liver inflammation and fibrosis by nanomedicine

Nanoparticles for oral delivery: Design, evaluation and state-of-the-art

Nanomaterials for Drug Delivery to the Central Nervous System

The SARS-CoV-2 receptor ACE2 expression of maternal-fetal interface and fetal organs by single-cell transcriptome study

Analysis of the susceptibility to COVID-19 in pregnancy and recommendations on potential drug screening, European journal of clinical microbiology & infectious diseases : official publication of the

Safety and Efficacy of Single-Dose Ad26.COV2.S Vaccine against Covid-19

Anti-Coronavirus Vaccines: Past Investigations on SARS-CoV-1 and MERS-CoV, the Approved Vaccines from BioNTech/Pfizer, Moderna, Oxford/AstraZeneca and others under Development Against SARS-CoV-2 Infection

Safety and efficacy of an rAd26 and rAd5 vector-based heterologous prime-boost COVID-19 vaccine: an interim analysis of a randomised

Distinct Immunologic Properties of Soluble Versus Particulate Antigens

Nanoparticle systems for cancer vaccine

Peptide nanoparticles as novel immunogens: design and analysis of a prototypic severe acute respiratory syndrome vaccine

Chaperna-Mediated Assembly of Ferritin-Based Middle East Respiratory Syndrome-Coronavirus Nanoparticles

Inducible bronchusassociated lymphoid tissue elicited by a protein cage nanoparticle enhances protection in mice against diverse respiratory viruses

Working together: interactions between vaccine antigens and adjuvants

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

MERS-CoV spike nanoparticles protect mice from MERS-CoV infection

Structural analysis of full-length SARS-CoV-2 spike protein from an advanced vaccine candidate

ISCOM technologybased Matrix M™ adjuvant: success in future vaccines relies on formulation

Synthetic virus-like particles prepared via protein corona formation enable effective vaccination in an avian model of coronavirus infection

Viromimetic STING Agonist-Loaded Hollow Polymeric Nanoparticles for Safe and Effective Vaccination against Middle East Respiratory Syndrome Coronavirus

Expression kinetics of nucleoside-modified mRNA delivered in lipid nanoparticles to mice by various routes

Deconvoluting Lipid Nanoparticle Structure for Messenger RNA Delivery

Efficacy and Safety of the mRNA-1273 SARS-CoV-2 Vaccine

Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine

A Thermostable mRNA Vaccine against COVID-19

A Comparison of Plasmid DNA and mRNA as Vaccine Technologies

DNA Nanoparticles and Development of DNA Delivery Vehicles for Gene Therapy

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

Multiplex Paper-Based Colorimetric DNA Sensor Using Pyrrolidinyl Peptide Nucleic Acid-Induced AgNPs Aggregation for Detecting MERS-CoV, MTB, and HPV Oligonucleotides

An electrochemical immunosensor for the corona virus associated with the Middle East respiratory syndrome using an array of gold nanoparticle-modified carbon electrodes

Dual-Functional Plasmonic Photothermal Biosensors for Highly Accurate Severe Acute Respiratory Syndrome Coronavirus 2 Detection

Selective Naked-Eye Detection of SARS-CoV-2 Mediated by N Gene Targeted Antisense Oligonucleotide Capped Plasmonic Nanoparticles

Understanding Antibody Testing for COVID-19

Rapid and Sensitive Detection of anti-SARS-CoV-2 IgG, Using Lanthanide-Doped Nanoparticles-Based Lateral Flow Immunoassay

A facile inhibitor screening of SARS coronavirus N protein using nanoparticle-based RNA oligonucleotide

Drug delivery and nanoparticles:applications and hazards