Synthesis and Applications of Optical Materials

As optical materials have shown outstanding physical and chemical characteristics in the bio, medical, electronics, energy and related fields of studies, the potential benefits of using these materials have been widely recognized [...].

magnetic beads [14], a microfluidic platform that performs an immunoassay of viral antigens in a simple, automated, yet highly sensitive manner. The automated device achieves a highly sensitive magnetic bead-based sandwich immunoassay for the influenza A H1N1 virus within 32.5 min. The detection limit of the method is 5.1 × 10 −4 hemagglutination units, which is 2 × 10 3 times more sensitive than that of the conventional hemagglutination method and is comparable to PCR.
Carbon materials have been a great candidate as optical materials [15][16][17][18]. Limosani et al. reported successfully synthesized N-doped carbon quantum dots (N-CQDs) using a hydroxyl radical opening of fullerene with hydrogen peroxide [19]. The N-CQDs were probed for metal ion detection in aqueous solutions and during bioimaging and displayed a Cr 3+ and Cu 2+ selectivity shift at a higher degree of -NH 2 functionalization, as well as HEK-293 cell nuclei marking. W.-H. Park reviewed the various characterization methods of chemical vapor deposition of monolayer graphene electrodes (CVD-MG), which are devised and developed for achieving a largescale, highly flexible, and transparent electrode [20].
The optical properties of metal nanoparticles have long been of interest in material science and applications [21][22][23][24]. The development of high efficiency dye-sensitized solar cells (DSSCs) has received tremendous attention [25][26][27]. Lee et al. studied an effect of Au NPs and scattering layer in dye-sensitized solar cells (DSSCs). Based on freestanding TiO 2 nanotube arrays [28], they introduced Au nanoparticles (Au NPs) and a scattering layer to change the power conversion efficiency (PCE) of DSSCs. The Au NPs layer could act as a better source of electron generation because the plasmonic absorption band of Au NPs is 530 nm, which matches the dye absorbance, and a scattering layer had better light harvesting by scattering.
Surface-enhanced Raman spectroscopy (SERS) has become an essential analytical tool for various target molecules detection [29][30][31][32][33][34][35][36]. However, the direct detection of H 2 O 2 by SERS is not possible because of its low Raman cross-section. Pham et al. reported nonenzymatic hydrogen peroxide detection using SiO 2 @Ag@Au alloy SERS NPs [37]. The peroxidase-mimicking activity of SiO 2 @Au@Ag alloy NPs in the presence of TMB was investigated using SERS for detecting H 2 O 2 . Briefly, in the presence of H 2 O 2 , the SiO 2 @Au@Ag alloy catalyzed the conversion of TMB to oxidized TMB, which was absorbed onto the surface of the SiO 2 @Au@Ag alloy. The evaluation of the SERS band to determine the H 2 O 2 level utilized the SERS intensity of oxidized TMB bands.
The reproducible, reliable fabrication for large area SERS substrates in a low-cost remains a challenge. Luo et al. reported large area patterning of highly reproducible and sensitive SERS sensors based on 10 nm annular gap arrays using a patterning method based on nanosphere lithography and adhesion lithography technics [38].
Various composites and shapes of optical materials are introduced [39,40]. The high optical absorption and emission of bidimensional MoS 2 are fundamental properties for optoelectronic and biodetection applications. Cortijo-Campos et al. reported size effects in single-and few-layer MoS 2 nanoflakes on Raman phonons and photoluminescence [41]. Hossain et al. reported recent studies of NIR (near infrared)-light responsive materials for photothermal cell treatments [42]. In their review, various nanomaterials such as metal and carbon-based nanomaterials are compared systematically.  Acknowledgments: This work was supported by Konkuk University in 2020 (2020-A019-0224).

Conflicts of Interest:
The authors declare no conflict of interest.