_applied sciences_  
_Editorial_  
Special Issue on New Frontiers in Diatom Nanotechnology  
**[PERSON] \({}^{\star}\)\({}^{\copyright}\) and [PERSON] \({}^{\copyright}\)**  
Institute of Applied Sciences and Intelligent Systems (ISASI), National Research Council, 80131 Napoli, Italy  
\({}^{\star}\) Correspondence: [EMAIL_ADDRESS]  
Diatoms are unicellular algae that live in aquatic environments. The diatom cell is enclosed in a porous biosilica microshell, called a frustule, which is characterized by a nanostructured morphology showing pores of tens of nanometers and a large specific surface area up to 200 m\({}^{2}\)/g. The [impressive similarities between the morphology of frustules and that of artificially-produced porous silica, the low cost, and the availability all around the world make the nanostructured silica of diatoms an attractive source of material for several technological applications. Other peculiar properties of the diatom biosilica include biocompatibility, tailored surface chemistry, chemical inertness, and thermal stability. The Special Issue \"New Frontiers in Diatom Nanotechnology\" focused on, but was not limited to, some recent technological applications of nanostructured biosilica in the fields of nanoengineering, photonics, biosensing, drug delivery, and tissue engineering. The Special Issue of _Applied Sciences_ entitled \"New Frontiers in Diatom Nanotechnology\" collects three original papers [1, 2, 3] and two reviews [4, 5], providing new insights into the applications of diatom nanotechnology. [PERSON] et al. [1] investigated the in vivo incorporation of iridium, ruthenium, aluminum, and zinc luminescent organometallic complexes into _Phaeodactylum tricornutum_ diatom microalgae. This biotechnological protocol is a simple method for preparing biosilica doped by luminescent organometallic complexes, with the benefit of easily achieving silica nanostructures that combine the photoluminescence of organometallic complexes with the structural properties of diatoms, optimized by nature over a billion years. Moreover, the film-forming properties of the semibentonic diatom can be exploited for the self-assembly of in vivo luminescent biosilica films, which offer interesting potential applications in photonics. [PERSON] et al. [2] investigated the use of natural diatoms as drug scaffolds for carbon monoxide releasing molecules (CORMs). To this aim, they functionalized the _Cosicndiscus_ frustules with the drug cis-[Re(CO)\({}_{2}\)Br\({}_{4}\)]\({}^{2}\) complex (ReCCORM-2) and its vitamin B12 derivative (B\({}_{12}\)-ReCCORM-2) via standard chemisorption techniques. The effects of the drugs on the neovascularization were studied in vivo in the zebrafish (_Danio rerio_) model. Applying doses \(\geq\)25 uM, the molecules significantly reduced the development of intersegmental and subintesinal vessels in zebrafish, revealing a high anti-angiogenic potential. In addition, the diatom frustules did not induce any toxic in vivo response in the zebrafish embryos, including inflammation. [PERSON] et al. [3] demonstrated the application of diatoms and diatomaceous earth (DE) in removing toxic dyes such as Congo Red (CR), which was used as a model compound, from water. In this work, DE was modified by Mg-Al-layered double hydroxide (DE-LDH) using a simple co-precipitation method. LDHs are ideal candidates for the removal of organic and inorganic pollutants from water; they also have some advantages such as low cost, non-toxicity, higher adsorption capacity, and high thermal stability. In order to study the DE-LDH adsorbents, isotherms were used in the batch adsorption, and kinetic studies were carried out for CR removal. The study suggested the promising application of DE-LDH as an effective material for application in the removal of CR from aqueous solutions for the purpose of industrial wastewater treatment.