Coronavirus disease 2019 (COVID-19) is the worst pandemic disease of the current millennium. This disease is caused by the highly contagious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which first exhibited human-to-human transmission in December 2019 and has infected millions of people within months across 213 different countries. Its ability to be transmitted by asymptomatic carriers has put a massive strain on the currently available testing resources. Currently, there are no clinically proven therapeutic methods that clearly inhibit the effects of this virus, and COVID-19 vaccines are still in the development phase. Strategies need to be explored to expand testing capacities, to develop effective therapeutics, and to develop safe vaccines that provide lasting immunity. Nanoparticles (NPs) have been widely used in many medical applications, such as biosensing, drug delivery, imaging, and antimicrobial treatment. SARS-CoV-2 is an enveloped virus with particle-like characteristics and a diameter of 60–140 nm. Synthetic NPs can closely mimic the virus and interact strongly with its proteins due to their morphological similarities. Hence, NP-based strategies for tackling this virus have immense potential. NPs have been previously found to be effective tools against many viruses, especially against those from the Coronaviridae family. This Review outlines the role of NPs in diagnostics, therapeutics, and vaccination for the other two epidemic coronaviruses, the 2003 severe acute respiratory syndrome (SARS) virus and the 2012 Middle East respiratory syndrome (MERS) virus. We also highlight nanomaterial-based approaches to address other coronaviruses, such as human coronaviruses (HCoVs); feline coronavirus (FCoV); avian coronavirus infectious bronchitis virus (IBV); coronavirus models, such as porcine epidemic diarrhea virus (PEDV), porcine reproductive and respiratory syndrome virus (PRRSV), and transmissible gastroenteritis virus (TGEV); and other viruses that share similarities with SARS-CoV-2. This Review combines the salient principles from previous antiviral studies with recent research conducted on SARS-CoV-2 to outline NP-based strategies that can be used to combat COVID-19 and similar pandemics in the future.

Metal oxide semiconductors with a bandgap between 2 and 4 eV are an important class of compounds in the electronics industry and for photocatalysis. With the demand for these materials expanding rapidly, especially in the field of photocatalysis, the fabrication of nanoscale metal oxide particles, which increases the surface-to-volume ratio and thereby reduces the materials costs, is an emphasis of current research. For the purpose of photocatalysis, another important quality is the ability to absorb light efficiently. However, due to the wide bandgap of metal oxide semiconductors, the absorptions are limited to the UV region. Conveniently, a wider range of wavelengths and physical properties can be enabled by doping these metal oxide nanoparticles. Furthermore, the synthesis of doped metal oxides in nanoparticle form offers utility in an expansive array of systems, substrates, and dispersion media. However, the reliable synthesis of nanosized colloidal particles of doped metal oxides remains an ongoing challenge for materials researchers. This manuscript gives a concise overview of research conducted regarding the synthesis of visible-light-active doped metal oxide nanoparticles (NPs) and analyzes how doping impacts the optical properties, making them active in the visible to near-infrared regions. The effects of doping on applications are also summarized. Given that the most commonly doped metal oxide materials are TiO 2 and ZnO, this review highlights both anion-and cation-doped TiO 2 and ZnO nanoparticles. In addition, doped perovskite nanoparticles (e.g., BaTiO 3 and SrTiO 3 ) as well as some of the lesser studied doped metal oxide nanoparticle systems are covered. This work is intended to provide not only a broad overview of existing doped metal oxide nanoparticles but also a foundation for the development of semiconducting nanoparticle architectures for next-generation applications.

Doping is an effective way to tune the band gap of metal oxide semiconductor materials. Doped tin oxide nanoparticles have proven to be effective materials for various electro-optical applications, particularly when deposited in thin-film architectures. However, doping in metal oxide nanoparticles generally leads to distorted shapes and a lack of uniformity, making the ready preparation of spherical, monodisperse doped tin oxide stand-alone nanoparticles an elusive task. This report describes a facile, solution-based method for the synthesis of stable, monodisperse antimony- and zinc-doped tin oxide nanoparticles, which opens the door to disperse these materials in a variety of media and expand their range of applications. The band gap of the tin oxide nanoparticles was successfully tuned upon doping with antimony and zinc. The tin-oxide-based nanomaterials were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Separately, the optical properties of the nanoparticles were evaluated by UV–vis diffuse reflectance spectroscopy (DRS) and photoluminescence spectroscopy (PL). These nanoparticles can be very effective in creating well-controlled systems for photocatalysis, solar cells, optoelectronics, multilayered devices, and for the treatment of air and water pollutants.

Due to their good magnetic properties, excellent biocompatibility, and low price, magnetic iron oxide nanoparticles (IONPs) are the most commonly used magnetic nanomaterials and have been extensively explored in biomedical applications. Although magnetic IONPs can be used for a variety of applications in biomedicine, most practical applications require IONP-based platforms that can perform several tasks in parallel. Thus, appropriate engineering and integration of magnetic IONPs with different classes of organic and inorganic materials can produce multifunctional nanoplatforms that can perform several functions simultaneously, allowing their application in a broad spectrum of biomedical fields. This review article summarizes the fabrication of current composite nanoplatforms based on integration of magnetic IONPs with organic dyes, biomolecules (e.g., lipids, DNAs, aptamers, and antibodies), quantum dots, noble metal NPs, and stimuli-responsive polymers. We also highlight the recent technological advances achieved from such integrated multifunctional platforms and their potential use in biomedical applications, including dual-mode imaging for biomolecule detection, targeted drug delivery, photodynamic therapy, chemotherapy, and magnetic hyperthermia therapy.

This paper reports the synthesis and study of doped metal oxides as the shell in core−shell nanoparticle architectures. Specifically, the paper describes the synthesis of gold nanoparticles (Au NPs) and gold−silver nanoshells (GS-NSs) coated with antimony-and zinc-doped tin oxide (SnO 2 ) shells (i.e., Au@ATO, Au@ZTO, GS-NS@ATO, and GS-NS@ZTO) with a comparison to the undoped SnO 2 -coated analogues Au@SnO 2 and GS-NS@ SnO 2 . The doped tin oxide core−shell nanoparticles prepared here were thoroughly characterized using scanning electron microscopy, transmission electron microscopy, dynamic light scattering, energydispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Separately, their optical properties were evaluated by UV−vis and photoluminescence spectroscopy. The results demonstrate that noble-metal nanoparticles such as Au NPs and GS-NSs, which exhibit strong surface plasmon resonances at visible-to-near-IR wavelengths, can be activated across a broader region of the solar spectrum when used in conjunction with wideband-gap semiconductors. In particular, utilization of a GS-NS core induces near-complete suppression in the electron−hole recombination processes in the tin oxide materials. Potential impacts on sensing and photonic applications are highlighted.