Silica-coated Gd(DOTA)-loaded protein nanoparticles enable magnetic resonance imaging of macrophages

Plant Virus Nanoparticles Combat Cancer

Plant virus nanoparticles (PVNPs) have garnered considerable interest as a promising nanotechnology approach to combat cancer. Owing to their biocompatibility, stability, and adjustable surface functionality, PVNPs hold tremendous potential for both therapeutic and imaging applications. The versatility of PVNPs is evident from their ability to be tailored to transport a range of therapeutic agents, including chemotherapy drugs, siRNA, and immunomodulators, thereby facilitating targeted delivery to the tumor microenvironment (TME). Furthermore, PVNPs may be customized with targeting ligands to selectively bind to cancer cell receptors, reducing off-target effects. Additionally, PVNPs possess immunogenic properties and can be engineered to exhibit tumor-associated antigens, thereby stimulating anti-tumor immune responses. In conclusion, the potential of PVNPs as a versatile platform for fighting cancer is immense, and further research is required to fully explore their potential and translate them into clinical applications.

Convenient site-selective protein coupling from bacterial raw lysates to coenzyme A-modified tobacco mosaic virus (TMV) by Bacillus subtilis Sfp phosphopantetheinyl transferase

A facile enzyme-mediated strategy enables site-specific covalent one-step coupling of genetically tagged luciferase molecules to coenzyme A-modified tobacco mosaic virus (TMV-CoA) both in solution and on solid supports. Bacillus subtilis surfactin phosphopantetheinyl transferase Sfp produced in E. coli mediated the conjugation of firefly luciferase N-terminally extended by eleven amino acids forming a 'ybbR tag' as Sfp-selective substrate, which even worked in bacterial raw lysates. The enzymes displayed on the protein coat of the TMV nanocarriers exhibited high activity. As TMV has proven a beneficial high surface-area adapter template stabilizing enzymes in different biosensing layouts in recent years, the use of TMV-CoA for fishing ybbR-tagged proteins from complex mixtures might become an advantageous concept for the versatile equipment of miniaturized devices with biologically active proteins. It comes along with new opportunities for immobilizing multiple functionalities on TMV adapter coatings, as desired, e.g., in handheld systems for point-of-care detection.

Photothermal immunotherapy of melanoma using TLR-7 agonist laden tobacco mosaic virus with polydopamine coat

Photothermal therapy (PTT) is a promising cancer treatment that debulks tumors locally while priming immune responses. However, PTT as a standalone treatment approach often has limited systemic efficacy, motivating the development of synergistic combination approaches. Toward this goal, herein, the tobacco mosaic virus (TMV) was loaded with a small molecule immunomodulator, toll-like receptor 7 agonist (1V209), and its surface was coated with photothermal biopolymer polydopamine (PDA). The resulting 1V209-laden and PDA-coated TMV was used to treat B16F10 dermal melanoma in C57BL/6 mice. 1V209-TMV-PDA was intratumorally injected and irradiated using an 808-nm near infrared laser. 60 % of the mice receiving PTT with intratumoral 1V209-TMV-PDA + laser remained alive at the end point - in contrast to only 20 % survivors were observed in the control group. Immunological analysis indicates systemic anti-tumor immunity being induced by the combination therapy with a greater number of tumor-specific T cells (as determined by a splenocyte assay). This study highlights the potential of TMV versatility as a multifunctional nano-platform for combined PTT-immunotherapy.

Structurally Modified Plant Viruses and Bacteriophages with Helical Structure. Properties and Applications

Structurally modified virus particles can be obtained from the rod-shaped or filamentous virions of plant viruses and bacteriophages by thermal or chemical treatment. They have recently attracted attention of the researchers as promising biogenic platforms for the development of new biotechnologies. This review presents data on preparation, structure, and properties of the structurally modified virus particles. In addition, their biosafety for animals is considered, as well as the areas of application of such particles in biomedicine. A separate section is devoted to one of the most relevant and promising areas for the use of structurally modified plant viruses – design of vaccine candidates based on them.

Synthesis, modification and bioapplications of nanoscale copper chalcogenides

Copper chalcogenides have a simple general formula, variable atomic ratios, and complicated crystal structures, which lead to their wealth of optical, electrical, and magnetic properties with great potential for wide applications ranging from energy conversion to the biomedical field. Herein, we summarize the recent advances in (1) the synthesis of size- and morphology tunable nanostructures by different methods; (2) surface modification and functionalization for different purposes; and (3) bioapplications for diagnosis and treatment of tumors by different imaging and therapy methods, as well as antibacterial applications. We also briefly discuss the future directions and challenges of copper chalcogenide nanoparticles in the biomedical field.

The pharmacology of plant virus nanoparticles

The application of nanoparticles for medical purposes has made enormous strides in providing new solutions to health problems. The observation that plant virus-based nanoparticles (VNPs) can be repurposed and engineered as smart bio-vehicles for targeted drug delivery and imaging has launched extensive research for improving the therapeutic and diagnostic management of various diseases. There is evidence that VNPs are promising high value nanocarriers with potential for translational development. This is mainly due to their unique features, encompassing structural uniformity, ease of manufacture and functionalization by means of expression, chemical biology and self-assembly. While the development pipeline is moving rapidly, with many reports focusing on engineering and manufacturing aspects to tailor the properties and efficacy of VNPs, fewer studies have focused on gaining insights into the nanotoxicity of this novel platform nanotechnology. Herein, we discuss the pharmacology of VNPs as a function of formulation and route of administration. VNPs are reviewed in the context of their application as therapeutic adjuvants or nanocarrier excipients to initiate, enhance, attenuate or impede the formulation's toxicity. The summary of the data however also underlines the need for meticulous VNP structure-nanotoxicity studies to improve our understanding of their in vivo fates and pharmacological profiles to pave the way for translation of VNP-based formulations into the clinical setting.

Immunoelectron Microscopy of Viral Antigens

Immunoelectron microscopy is a powerful technique for identifying viral antigens and determining their structural localization and organization within vaccines and viruses. While traditional negative staining transmission electron microscopy provides structural information, identity of components within a sample may be confounding. Immunoelectron microscopy allows for identification and visualization of antigens and their relative positions within a particulate sample. This allows for simple qualitative analysis of samples including whole virus, viral components, and viral‐like particles. This article describes methods for immunogold labeling of viral antigens in a liquid suspension, with examples of immunogold‐labeled influenza virus glycoproteins, and also discusses the important considerations for sample preparation and determination of morphologies. Together, these methods allow for understanding the antigenic makeup of viral particulate samples, which have important implications for molecular virology and vaccine development. © 2019 The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Supramolecular and biomacromolecular enhancement of metal-free magnetic resonance imaging contrast agents

Many contrast agents for magnetic resonance imaging are based on gadolinium, however side effects limit their use in some patients. Organic radical contrast agents (ORCAs) are potential alternatives, but are reduced rapidly in physiological conditions and have low relaxivities as single molecule contrast agents. Herein, we use a supramolecular strategy where cucurbit[8]uril binds with nanomolar affinities to ORCAs and protects them against biological reductants to create a stable radical in vivo. We further overcame the weak contrast by conjugating this complex on the surface of a self-assembled biomacromolecule derived from the tobacco mosaic virus.

Delivery of siRNA therapeutics using cowpea chlorotic mottle virus-like particles

While highly promising in medicine, gene therapy requires delivery agents to protect and target nucleic acid therapeutics. We developed a plant viral siRNA delivery platform making use of self-assembling cowpea chlorotic mottle virus (CCMV). CCMV was loaded with siRNAs targeting GFP or FOXA1; to further enhance cell uptake and intracellular trafficking, resulting in more efficient gene knockdown, we appended CCMV with a cell penetrating peptide (CPP), specifically M-lycotoxin peptide L17E.

Polydopamine-decorated tobacco mosaic virus for photoacoustic/magnetic resonance bimodal imaging and photothermal cancer therapy

Nanotheranostic reagents that integrate magnetic resonance imaging (MRI) and photothermal therapy (PTT) offer a promising strategy for the treatment of human disease. However, classic gadolinium (Gd)-based T1-MRI contrast agents are limited by their low relaxivity. To address this, we produced Gd-loaded Tobacco mosaic virus (TMV) particles coated with the mussel-inspired biopolymer polydopamine (PDA). Such biocompatible nanotheranostic reagents can be used to facilitate PTT, guided by multimodal magnetic resonance/photoacoustic imaging. The r1-relaxivity of the Gd-TMV-PDA particles at 60 MHz was ∼80 mM-1 s-1, compared to 13.63 mM-1 s-1 for the uncoated Gd-TMV particles. The Gd-TMV-PDA particles also promoted strong near-infrared absorption with high photothermal conversion efficiency (28.9%) and demonstrated excellent photoacoustic contrast. Multimodal imaging and PTT resulted in the effective killing of PC-3 prostate cancer cells. Gd-TMV-PDA nanoparticles therefore offer a promising theranostic approach that can now be tested in vivo in cancer models.

Nanoparticle-Based Paramagnetic Contrast Agents for Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is a noninvasive medical imaging modality that is routinely used in clinics, providing anatomical information with micron resolution, soft tissue contrast, and deep penetration. Exogenous contrast agents increase image contrast by shortening longitudinal (T 1) and transversal (T 2) relaxation times. Most of the T 1 agents used in clinical MRI are based on paramagnetic lanthanide complexes (largely Gd-based). In moving to translatable formats of reduced toxicity, greater chemical stability, longer circulation times, higher contrast, more controlled functionalisation and additional imaging modalities, considerable effort has been applied to the development of nanoparticles bearing paramagnetic ions. This review summarises the most relevant examples in the synthesis and biomedical applications of paramagnetic nanoparticles as contrast agents for MRI and multimodal imaging. It includes the most recent developments in the field of production of agents with high relaxivities, which are key for effective contrast enhancement, exemplified through clinically relevant examples.

Plant virus-based materials for biomedical applications: Trends and prospects

Nanomaterials composed of plant viral components are finding their way into medical technology and health care, as they offer singular properties. Precisely shaped, tailored virus nanoparticles (VNPs) with multivalent protein surfaces are efficiently loaded with functional compounds such as contrast agents and drugs, and serve as carrier templates and targeting vehicles displaying e.g. peptides and synthetic molecules. Multiple modifications enable uses including vaccination, biosensing, tissue engineering, intravital delivery and theranostics. Novel concepts exploit self-organization capacities of viral building blocks into hierarchical 2D and 3D structures, and their conversion into biocompatible, biodegradable units. High yields of VNPs and proteins can be harvested from plants after a few days so that various products have reached or are close to commercialization. The article delineates potentials and limitations of biomedical plant VNP uses, integrating perspectives of chemistry, biomaterials sciences, molecular plant virology and process engineering.

Application of Plant Viruses as a Biotemplate for Nanomaterial Fabrication

Viruses are widely used to fabricate nanomaterials in the field of nanotechnology. Plant viruses are of great interest to the nanotechnology field because of their symmetry, polyvalency, homogeneous size distribution, and ability to self-assemble. This homogeneity can be used to obtain the high uniformity of the templated material and its related properties. In this paper, the variety of nanomaterials generated in rod-like and spherical plant viruses is highlighted for the cowpea chlorotic mottle virus (CCMV), cowpea mosaic virus (CPMV), brome mosaic virus (BMV), and tobacco mosaic virus (TMV). Their recent studies on developing nanomaterials in a wide range of applications from biomedicine and catalysts to biosensors are reviewed.

Nitroxyl Modified Tobacco Mosaic Virus as a Metal-Free High-Relaxivity MRI and EPR Active Superoxide Sensor

Superoxide overproduction is known to occur in multiple disease states requiring critical care; yet, noninvasive detection of superoxide in deep tissue remains a challenge. Herein, we report a metal-free magnetic resonance imaging (MRI) and electron paramagnetic resonance (EPR) active contrast agent prepared by "click conjugating" paramagnetic organic radical contrast agents (ORCAs) to the surface of tobacco mosaic virus (TMV). While ORCAs are known to be reduced in vivo to an MRI/EPR silent state, their oxidation is facilitated specifically by reactive oxygen species-in particular, superoxide-and are largely unaffected by peroxides and molecular oxygen. Unfortunately, single molecule ORCAs typically offer weak MRI contrast. In contrast, our data confirm that the macromolecular ORCA-TMV conjugates show marked enhancement for T1 contrast at low field (<3.0 T) and T2 contrast at high field (9.4 T). Additionally, we demonstrated that the unique topology of TMV allows for a "quenchless fluorescent" bimodal probe for concurrent fluorescence and MRI/EPR imaging, which was made possible by exploiting the unique inner and outer surface of the TMV nanoparticle. Finally, we show TMV-ORCAs do not respond to normal cellular respiration, minimizing the likelihood for background, yet still respond to enzymatically produced superoxide in complicated biological fluids like serum.

The in vivo fates of plant viral nanoparticles camouflaged using self-proteins: overcoming immune recognition

Nanoparticles offer a promising avenue for targeted delivery of therapies. To slow clearance, nanoparticles are frequently stealth-coated to prevent opsonization and immune recognition. Serum albumin (SA) has been used as a bio-inspired stealth coating. To develop this shielding strategy for clinical applications, it is critical to understand the interactions between the immune system and SA-camouflaged nanoparticles. This work investigates the in vivo processing of SA-coated nanoparticles using tobacco mosaic virus (TMV) as a model system. In comparing four different SA-formulations, the particles with high SA coverage conjugated to TMV via a short linker performed the best at preventing antibody recognition. Irrelevant of the coating chemistry, all formulations led to similar levels of TMV-specific antibodies after repeat administration in mice; importantly though, SA-specific antibodies were not detected and the TMV-specific antibodies were unable to recognize shielded SA-coated TMV. Upon uptake in macrophages, the shielding agent and nanoparticle separate, where TMV trafficked to the lysosome and SA appears to recycle. The distinct intracellular fates of the TMV carrier and SA shielding agent explain why anti-TMV but not SA-specific antibodies are generated. This work characterizes the outcomes of SA-camouflaged TMV after immune recognition, and highlights the effectiveness of SA as a nanoparticle shielding agent.

Bioinspired Silica Mineralization on Viral Templates

Plant virus capsids are attractive entities for nanotechnological applications because of their variation in shape and natural assembly ability. This chapter describes the production and modification of three differently shaped plant virus capsids for silica mineralization purposes. The chosen plant viruses exhibit either an icosahedral (cowpea mosaic virus, CPMV), or a flexuous rod-like structure (potato virus X, PVX), or a rigid rod-like shape (tobacco mosaic virus, TMV), and are well-known and frequently used plant viruses for biotechnological applications. We describe the production (including genetic or chemical modification) and purification of the plant viruses or of empty virus-like particles in the case of CPMV, as well as the characterization of these harvested templates. The mineralization procedures and differences in the protocols specific to the distinct viruses are described, and the analyses of the mineralization results are explained.

Dual Functionalization of Rod-Shaped Viruses on Single Coat Protein Subunits

Plant viruses are emerging as versatile tools for nanotechnology applications since it is possible to modify their multivalent protein surfaces and thereby introduce and display new functionalities. In this chapter, we describe a tobacco mosaic virus (TMV) variant that exposes two selectively addressable amino acid moieties on each of its 2130 coat protein (CP) subunits. A lysine as well as a cysteine introduced at accessible sites of every CP can be modified with amino- and/or thiol-reactive chemistry such as N-hydroxysuccinimide esters (NHS ester) and maleimide containing reagents alone or simultaneously. This enables the pairwise immobilization of distinct molecules in close vicinity to each other on the TMV surface by simple standard conjugation protocols. We describe the generation of the mutations, the virus propagation and isolation as well as the dual functionalization of the TMV variant with two fluorescent dyes. The labeling is evaluated by SDS-PAGE and spectrophotometry and the degree of labeling (DOL) calculated.

Nanomanufacture of Free-Standing, Porous, Janus-Type Films of Polymer-Plant Virus Nanoparticle Arrays

We present a facile method for preparing hierarchical assemblies of cowpea mosaic virus (CPMV) nanoparticles adsorbed onto patterned polypyrrole copolymer arrays, which can be released as a freely standing and microporous polymer-protein membrane with a Janus-type structure. The patterning protocol is based on colloidal sphere lithography wherein a sacrificial honeycomb pattern composed of colloidal polystyrene (PS) microspheres is assembled on an electrode. A thin layer of polypyrrole film is electropolymerized within the interstices of the template and monitored using an electrochemical quartz crystal microbalance with dissipation (EC-QCM-D) and microscopy. Dissolving the PS template reveals an inverse opaline pattern capable of electrostatically capturing the CPMV particles. Through an electrochemical trigger, the polypyrrole-CPMV delaminates from the surface producing a self-sustaining polymer-protein membrane that can potentially be used for sensing and nanocargo applications.

Lithium-containing biomaterials inhibit osteoclastogenesis of macrophagesin vitroand osteolysisin vivo

Li-containing bioceramics were promising biomaterials for inhibiting osteoclastogenesis of macrophages and osteolysisin vivo, potentially using for treating osteoporosis.

Synthesis of Metal-Organic Frameworks on Tobacco Mosaic Virus Templates

Tobacco mosaic virus (TMV) has long been exploited as a robust biological scaffold for organic/inorganic modification owing to its anisotropic structure and chemically addressable amino acid residues on both the exterior and interior. We present the fabrication of a crystalline microporous metal-organic framework (MOF) shell on the exterior of TMV, which retains its rod-like morphology, and produces uniformly formed core-shell structures with high accessible surface area and pore volume. We also describe an exfoliation method that can recover the intact viral particle from the core-shell composite.

Glycyrrhetinic acid-functionalized mesoporous silica nanoparticles as hepatocellular carcinoma-targeted drug carrier

In this study, a glycyrrhetinic acid-functionalized mesoporous silica nanoparticle (MSN-GA) was prepared for active tumor targeting. MSN-GA exhibited satisfactory loading capacity for insoluble drugs, uniform size distribution, and specific tumor cell targeting. Glycyrrhetinic acid, a hepatocellular carcinoma-targeting group, was covalently decorated on the surface of MSN via an amido bond. The successful synthesis of MSN-GA was validated by the results of Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), and zeta potential measurement. TEM images revealed the spherical morphology and uniform size distribution of the naked MSN and MSN-GA. Curcumin (CUR), an insoluble model drug, was loaded into MSN-GA (denoted as MSN-GA-CUR) with a high-loading capacity (8.78%±1.24%). The results of the in vitro cellular experiment demonstrated that MSN-GA-CUR significantly enhanced cytotoxicity and cellular uptake toward hepatocellular carcinoma (HepG2) cells via a specific GA receptor-mediated endocytosis mechanism. The results of this study provide a promising nanoplatform for the targeting of hepatocellular carcinoma.

Gadolinium-Loaded Poly(N-vinylcaprolactam) Nanogels: Synthesis, Characterization, and Application for Enhanced Tumor MR Imaging

We report the synthesis of poly(N-vinylcaprolactam) nanogels (PVCL NGs) loaded with gadolinium (Gd) for tumor MR imaging applications. The PVCL NGs were synthesized via precipitation polymerization using the monomer N-vinylcaprolactam (VCL), the comonomer acrylic acid (AAc), and the degradable cross-linker 3,9-divinyl-2,4,8,10-tetraoxaspiro-[5,5]-undecane (VOU) in aqueous solution, followed by covalently binding with 2,2',2″-(10-(4-((2-aminoethyl)amino)-1-carboxy-4-oxobutyl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl) triacetic acid (NH₂-DOTA-GA)/Gd complexes. We show that the formed Gd-loaded PVCL NGs (PVCL-Gd NGs) having a size of 180.67 ± 11.04 nm are water dispersible, colloidally stable, uniform in size distribution, and noncytotoxic in a range of the studied concentrations. The PVCL-Gd NGs also display a r₁ relaxivity (6.38-7.10 mM^-1 s^-1), which is much higher than the clinically used Gd chelates. These properties afforded the use of the PVCL-Gd NGs as an effective positive contrast agent for enhanced MR imaging of cancer cells in vitro as well as a subcutaneous tumor model in vivo. Our study suggests that the developed PVCL-Gd NGs could be applied as a promising contrast agent for T₁-weighted MR imaging of diverse biosystems.

Template-Directed Synthesis of Porous and Protective Core-Shell Bionanoparticles

Metal-organic frameworks (MOFs) are promising high surface area coordination polymers with tunable pore structures and functionality; however, a lack of good size and morphological control over the as-prepared MOFs has persisted as an issue in their application. Herein, we show how a robust protein template, tobacco mosaic virus (TMV), can be used to regulate the size and shape of as-fabricated MOF materials. We were able to obtain discrete rod-shaped TMV@MOF core-shell hybrids with good uniformity, and their diameters could be tuned by adjusting the synthetic conditions, which can also significantly impact the stability of the core-shell composite. More interestingly, the virus particle underneath the MOF shell can be chemically modified using a standard bioconjugation reaction, showing mass transportation within the MOF shell.

Design of virus-based nanomaterials for medicine, biotechnology, and energy

This review provides an overview of recent developments in "chemical virology." Viruses, as materials, provide unique nanoscale scaffolds that have relevance in chemical biology and nanotechnology, with diverse areas of applications. Some fundamental advantages of viruses, compared to synthetically programmed materials, include the highly precise spatial arrangement of their subunits into a diverse array of shapes and sizes and many available avenues for easy and reproducible modification. Here, we will first survey the broad distribution of viruses and various methods for producing virus-based nanoparticles, as well as engineering principles used to impart new functionalities. We will then examine the broad range of applications and implications of virus-based materials, focusing on the medical, biotechnology, and energy sectors. We anticipate that this field will continue to evolve and grow, with exciting new possibilities stemming from advancements in the rational design of virus-based nanomaterials.

Multiple Administrations of Viral Nanoparticles Alter in Vivo Behavior-Insights from Intravital Microscopy

Multiple administrations of nanoparticle-based formulations are often a clinical requirement for drug delivery and diagnostic imaging applications. Steady pharmacokinetics of nanoparticles is desirable to achieve efficient therapeutic or diagnostic outcomes over such repeat administrations. While clearance through mononuclear phagocytic system is a key determinant of nanoparticle persistence in vivo, multiple administrations could potentially result in altered pharmacokinetics by evoking innate or adaptive immune responses. Plant viral nanoparticles (VNPs) represent an emerging class of programmable nanoparticle platform technologies that offer a highly organized proteinaceous architecture and multivalency for delivery of large payloads of drugs and molecular contrast agents. These very structural features also render them susceptible to immune recognition and subsequent accelerated systemic clearance that could potentially affect overall efficiency. While the biodistribution and pharmacokinetics of VNPs have been reported, the biological response following repeat administrations remains an understudied area of investigation. Here, we demonstrate that weekly administration of filamentous plant viruses results in the generation of increasing levels of circulating, carrier-specific IgM and IgG antibodies. Furthermore, PVX specific immunoglobulins from the serum of immunized animals quickly form aggregates when incubated with PVX in vitro. Such aggregates of VNP-immune complexes are also observed in the mouse vasculature in vivo following repeat injections when imaged in real time using intravital two-photon laser scanning microscopy (2P-LSM). The size of aggregates diminishes at later time points, coinciding with antibody class switching from IgM to IgG. Together, our results highlight the need for careful in vivo assessment of (viral) nanoparticle-based platform technologies, especially in studying their performance after repeat administration. We also demonstrate the utility of intravital microscopy to aid in this evaluation.

Serum albumin 'camouflage' of plant virus based nanoparticles prevents their antibody recognition and enhances pharmacokinetics

Plant virus-based nanoparticles (VNPs) are a novel class of nanocarriers with unique potential for biomedical applications. VNPs have many advantageous properties such as ease of manufacture and high degree of quality control. Their biocompatibility and biodegradability make them an attractive alternative to synthetic nanoparticles (NPs). Nevertheless, as with synthetic NPs, to be successful in drug delivery or imaging, the carriers need to overcome several biological barriers including innate immune recognition. Plasma opsonization can tag (V)NPs for clearance by the mononuclear phagocyte system (MPS), resulting in shortened circulation half lives and non-specific sequestration in non-targeted organs. PEG coatings have been traditionally used to 'shield' nanocarriers from immune surveillance. However, due to broad use of PEG in cosmetics and other industries, the prevalence of anti-PEG antibodies has been reported, which may limit the utility of PEGylation in nanomedicine. Alternative strategies are needed to tailor the in vivo properties of (plant virus-based) nanocarriers. We demonstrate the use of serum albumin (SA) as a viable alternative. SA conjugation to tobacco mosaic virus (TMV)-based nanocarriers results in a 'camouflage' effect more effective than PEG coatings. SA-'camouflaged' TMV particles exhibit decreased antibody recognition, as well as enhanced pharmacokinetics in a Balb/C mouse model. Therefore, SA-coatings may provide an alternative and improved coating technique to yield (plant virus-based) NPs with improved in vivo properties enhancing drug delivery and molecular imaging.

Novel roles for well-known players: from tobacco mosaic virus pests to enzymatically active assemblies

The rod-shaped nanoparticles of the widespread plant pathogen tobacco mosaic virus (TMV) have been a matter of intense debates and cutting-edge research for more than a hundred years. During the late 19th century, their behavior in filtration tests applied to the agent causing the 'plant mosaic disease' eventually led to the discrimination of viruses from bacteria. Thereafter, they promoted the development of biophysical cornerstone techniques such as electron microscopy and ultracentrifugation. Since the 1950s, the robust, helically arranged nucleoprotein complexes consisting of a single RNA and more than 2100 identical coat protein subunits have enabled molecular studies which have pioneered the understanding of viral replication and self-assembly, and elucidated major aspects of virus-host interplay, which can lead to agronomically relevant diseases. However, during the last decades, TMV has acquired a new reputation as a well-defined high-yield nanotemplate with multivalent protein surfaces, allowing for an ordered high-density presentation of multiple active molecules or synthetic compounds. Amino acid side chains exposed on the viral coat may be tailored genetically or biochemically to meet the demands for selective conjugation reactions, or to directly engineer novel functionality on TMV-derived nanosticks. The natural TMV size (length: 300 nm) in combination with functional ligands such as peptides, enzymes, dyes, drugs or inorganic materials is advantageous for applications ranging from biomedical imaging and therapy approaches over surface enlargement of battery electrodes to the immobilization of enzymes. TMV building blocks are also amenable to external control of in vitro assembly and re-organization into technically expedient new shapes or arrays, which bears a unique potential for the development of 'smart' functional 3D structures. Among those, materials designed for enzyme-based biodetection layouts, which are routinely applied, e.g., for monitoring blood sugar concentrations, might profit particularly from the presence of TMV rods: Their surfaces were recently shown to stabilize enzymatic activities upon repeated consecutive uses and over several weeks. This review gives the reader a ride through strikingly diverse achievements obtained with TMV-based particles, compares them to the progress with related viruses, and focuses on latest results revealing special advantages for enzyme-based biosensing formats, which might be of high interest for diagnostics employing 'systems-on-a-chip'.

Modified TMV Particles as Beneficial Scaffolds to Present Sensor Enzymes

Tobacco mosaic virus (TMV) is a robust nanotubular nucleoprotein scaffold increasingly employed for the high density presentation of functional molecules such as peptides, fluorescent dyes, and antibodies. We report on its use as advantageous carrier for sensor enzymes. A TMV mutant with a cysteine residue exposed on every coat protein (CP) subunit (TMVCys) enabled the coupling of bifunctional maleimide-polyethylene glycol (PEG)-biotin linkers (TMVCys/Bio). Its surface was equipped with two streptavidin [SA]-conjugated enzymes: glucose oxidase ([SA]-GOx) and horseradish peroxidase ([SA]-HRP). At least 50% of the CPs were decorated with a linker molecule, and all thereof with active enzymes. Upon use as adapter scaffolds in conventional "high-binding" microtiter plates, TMV sticks allowed the immobilization of up to 45-fold higher catalytic activities than control samples with the same input of enzymes. Moreover, they increased storage stability and reusability in relation to enzymes applied directly to microtiter plate wells. The functionalized TMV adsorbed to solid supports showed a homogeneous distribution of the conjugated enzymes and structural integrity of the nanorods upon transmission electron and atomic force microscopy. The high surface-increase and steric accessibility of the viral scaffolds in combination with the biochemical environment provided by the plant viral coat may explain the beneficial effects. TMV can, thus, serve as a favorable multivalent nanoscale platform for the ordered presentation of bioactive proteins.