The development of technology enables the reduction of material size in science. The use of particle reduction in size from micro to nanoscale not only provides benefits to diverse scientific fields but also poses potential risks to humans and the environment. For the successful application of nanomaterials in bioscience, it is essential to understand the biological fate and potential toxicity of nanoparticles. The aim of this study was to evaluate the biological distribution as well as the potential toxicity of magnetic nanoparticles to enable their diverse applications in life science, such as drug development, protein detection, and gene delivery. We recently synthesized biocompatible silica-overcoated magnetic nanoparticles containing rhodamine B isothiocyanate (RITC) within a silica shell of controllable thickness [MNPs@SiO₂(RITC)]. In this study, the MNPs@SiO₂(RITC) with 50-nm thickness were used as a model nanomaterial. After intraperitoneal administration of MNPs@SiO₂(RITC) for 4 weeks into mice, the nanoparticles were detected in the brain, indicating that such nanosized materials can penetrate blood–brain barrier (BBB) without disturbing its function or producing apparent toxicity. After a 4-week observation, MNPs@SiO₂(RITC) was still present in various organs without causing apparent toxicity. Taken together, our results demonstrated that magnetic nanoparticles of 50-nm size did not cause apparent toxicity under the experimental conditions of this study.

A novel and universal procedure has been developed for producing nanosized stable silver particles on cotton fabrics in a simple and cost-effective manner with complete control of the silver loading level on the fabrics; the antibacterial effect of Ag-nanocoated fabrics on various bacteria was evaluated by growth inhibition; for biomedical applications, skin irritation tests on guinea pigs were performed and no side effects were observed.

In the search for new therapeutic agents for currently incurable diseases, attention has turned to traditionally “undruggable” targets, and collections of drug-like small molecules with high diversity and quality have become a prerequisite for new breakthroughs. To generate such collections, the diversity-oriented synthesis (DOS) strategy was developed, which aims to populate new chemical space with drug-like compounds containing a high degree of molecular diversity. The resulting DOS-derived libraries have been of great value for the discovery of various bioactive small molecules and therapeutic agents, and thus DOS has emerged as an essential tool in chemical biology and drug discovery. However, the key challenge has become how to design and synthesize drug-like small-molecule libraries with improved biological relevancy as well as maximum molecular diversity. This Perspective presents the development of privileged substructure-based DOS (pDOS), an efficient strategy for the construction of polyheterocyclic compound libraries with high biological relevancy. We envisioned the specific interaction of drug-like small molecules with certain biopolymers via the incorporation of privileged substructures into polyheterocyclic core skeletons. The importance of privileged substructures such as benzopyran, pyrimidine, and oxopiperazine in rigid skeletons was clearly demonstrated through the discovery of bioactive small molecules and the subsequent identification of appropriate target biomolecule using a method called “fluorescence difference in two-dimensional gel electrophoresis”. Focusing on examples of pDOS-derived bioactive compounds with exceptional specificity, we discuss the capability of privileged structures to serve as chemical “navigators” toward biologically relevant chemical spaces. We also provide an outlook on chemical biology research and drug discovery using biologically relevant compound libraries constructed by pDOS, biology-oriented synthesis, or natural product-inspired DOS.

Owing to its high sensitivity and great applicability, the fluorescence phenomenon has been considered as an inevitable research tool in the modern scientific fields of chemistry, biology, materials science, biomedical science, and their interfaces. Many strategies have been pursued to understand and manipulate the photophysical properties of fluorescent materials, but the scientific community has been focused on the repeated application of existing organic fluorophores or the identification of unique fluorescence properties in a trial-and-error basis without systematic studies. Moreover, recent studies are emphasizing the necessity of deeper understanding about the structure–photophysical property relationship of organic fluorophores for the development of better fluorescent probes. Herein, we provide an overview of a novel fluorescent molecular framework, Seoul-Fluor, which can be rationally engineered to furnish a wide variety of fluorophores in terms of the photophysical properties. Seoul-Fluor is built on an indolizine-based fluorescent platform with three different positions to introduce various substituents: R¹ and R² substituents for electronic perturbation; R³ substituent as a functional handle for bioconjugation. Over the past decade, we have demonstrated that the Seoul-Fluor system has (i) tunable and predictable emission wavelength covering a full visible-color range; (ii) controllable quantum yield via photoinduced electron transfer phenomenon; and (iii) environment-sensitive fluorogenic properties that can be modified through intramolecular charge transfer processes. We convincingly demonstrated the prediction of photophysical properties, that is, emission wavelength and quantum yield, through the construction of a systematic set of analogues and the subsequent analysis of their photophysical properties without the highly sophisticated theoretical support. Guided by quantifiable parameters such as the Hammett substituent constants or energy levels of the molecular orbitals, this unique organic fluorophore can serve as a versatile molecular platform for the development of novel fluorescent switchable biosensors and fluorogenic bioprobes. In this Account, we will discuss the discovery and recent progress made on Seoul-Fluor, the rational design of Seoul-Fluor-based bioprobes, and their practical applications to specific biological processes that are facilitated by systematic studies of the structure–photophysical property relationships.