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.

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.

The emergence of plasmonic nanostars with their attractive properties and unique versatility has enabled a wide range of advanced technologies critical to human health, safety, energy, and environmental remediation with vast potential for further exploration. In addition to their superior surface-to-volume ratios compared to those of other plasmonic nanostructures, plasmonic nanostars arguably possess the largest numbers of hotspots with intensely amplified electric fields when they are subjected to suitable electromagnetic waves to trigger localized surface plasmon resonance (LSPR). These outstanding characteristics make plasmonic nanostars ideal for many applications that benefit from the plasmonic enhancement effect of LSPR and/or the large surface area. Over the past decade, an increasing number of research endeavors has been reported on the synthesis and application of plasmonic nanostars to advance the state-of-the-art for various existing technologies. These contributions are pertinent to real-time image-guided multifunctional anticancer theranostics, the ultrasensitive on-site detection of the devastating virus SARS-CoV-2, multimodal multiplexed brain imaging, greatly enhanced catalysts for energy and environmental processes, or more efficient and stable solar cells. In addition to the enhancement of important but familiar technologies, plasmonic nanostars have also been employed to push the technological frontiers in multiple fields to enable applications such as maskless write-on lithography, nanosized field electron emitters, coherent random lasers, neural activity modulation, and optically controlled electrical currents. Despite great performance in various fields since their introduction, the nascency of this unique class of plasmonic nanostructures and the rise of unique types of plasmonic nanostars, in addition to the dominance of gold nanostars in recent years, indicate that there are still many opportunities for study, exploration, and development. This Review outlines a comprehensive picture of the current state of plasmonic nanostar research with a focus on their technological and scientific applications. We hope this Review will enlighten future collective endeavors to develop more effective plasmonic nanostars and incorporate them into mainstream technologies so that these stars can truly shine.

This paper reports the fabrication of highly stable semi-hollow gold-silver nanostars (hAuAgNSts). Galvanic replacement between silver nanostars (AgNSts) and chloroauric acid afforded optically tunable hAuAgNSts with plasmonic resonances ranging from UV to visible to near-infrared wavelengths. Moreover, the compositionally unique bimetallic hAuAgNSts exhibited strong extinction maxima in the UV−vis range, which contrasts AgNSts (centered in the UV) and the more common gold nanostars (AuNSts; centered largely in the near infrared). Notably, the hAuAgNSts exhibited enhanced thermal and colloidal stability without the need for surface modification when compared to AgNSts and AuNSts. This latter feature offers additional opportunities in the fields of photocatalysis and photovoltaics as well as alternative strategies for post-synthetic modification that enable applications in biosensing and theranostics.

Titanium dioxide (TiO2) and tin oxide (SnO2) are two popular wide band-gap semiconductors for photocatalytic and electronic applications such as solar cells, optoelectronic devices, and lithium-ion batteries. Nanosized TiO2 structures have strong absorption in the UV region while SnO2 is a powerful transparent conducting oxide. Composites of TiO2 and SnO2 are especially attractive since they form a type-II heterojunction extending the lifetime of charge carriers and enhancing photoconversion efficiency. In this study, the synthesis of TiO2 nanoparticles as well as their uniform and controlled coating with SnO2 shells are described, providing the first utilization of sodium stannate to grow SnO2 shells on a metal-oxide core. The step-growth method utilized here shows the ability to vary the shell thickness between 5-40 nm while maintaining uniformity of the shell. As such, the complete synthesis route involves facile and reproducible surfactant-free solution-based methods at moderate temperatures. The nanoparticles 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). Overall, this paper represents reliable nanoscale fabrication techniques offering key advancements in photovoltaic and optoelectronic applications. Keywords: TiO2, SnO2, Heterojunction, Core-shell, Nanoparticles, Wide Band-gap Semiconductor