Editorial: Recent Advances in Responsive Optical Nanomaterials

Abstract

Responsive optical nanoparticles comprise nanostructured materials with tunable optical properties in response to external stimuli. Due to these unique features, they are often referred to as smart optical nanomaterials (Blum et al., 2015; Li and Yin, 2019). One compelling feature of these remarkable nanostructures is their optical property changes in response to a diverse set of stimuli, including both local environmental changes (temperature, pH, vapors, ionic strength, depletant, humidity, solvent, etc.) and remote stimuli (electric field, ultrasound, magnetic field, mechanical force, gravity force, light, X-ray, etc.). A few famous materials in this regard include photonic crystals (He et al., 2012; Fenzl et al., 2014), plasmonic nanostructures (Jiang et al., 2017; Zeng et al., 2020), and photo-catalysts (Teixeira et al., 2018). Because of their broad applications in sensing, color display, anticounterfeiting, catalysis, and biomedicine, chemists have developed many working principles and strategies for synthesizing smart nanostructured materials and exploiting their unique optical properties. With these exciting developments, this invited Research Topic covers the synthesis, assembly of smart optical nanomaterials and their emerging applications in biomedicine, sensing, and photocatalysis, which includes one minireview, one review, and five original research articles contributed from 38 researchers. In developing these attractive optical nanomaterials, synthesizing responsive nanostructures, and assembling them into more complex secondary structures (including both photonic crystals and plasmonic superstructures) are important. The chemical components, shapes, sizes of nanoparticles and periodicity, order, and orientation of superstructure determine the material performances and smart responses upon external stimuli. To this end, plasmonic nanomaterials, particularly noblemetal Au and Ag, have gained great success because of their unique localized surface plasmon resonance (LSPR), which produces sharp extinction peaks and exhibits bright color complementary to the peak position. Previous extensive studies have demonstrated that the plasmonic properties of metal nanostructures are very sensitive to their chemical components, sizes, and shapes. For example, core/shell nanostructures with metal shells have demonstrated superior plasmonic properties, such as widely tunable LSPR peaks and enhanced scattering properties (Li et al., 2020). In this research topic, FePt–Au core-shell nanoparticles are reported by reducing Au precursors at high temperature (Wei et al.). This method produces Au nanoshells with tunable shell thicknesses and optical properties. In addition to these intrinsic particle properties, plasmonic nanostructures can exhibit dynamic color-switching when being assembled into superstructures due to the plasmon coupling between neighboring particles. Their optical properties can be further tuned by controlling interparticle separation upon external stimuli. To this end, Liu et al. created a pH-responsive assembly and disassembly of Au nanoparticles in colloidal dispersions (Liu et al.). In this work, they introduced 3-aminopropyltriethoxysilane (APTES) as the capping ligand and pH-responsive agent Edited and reviewed by: Andreas Rosenkranz, University of Chile, Chile