Direct Optical Fabrication of Fluorescent, Multilevel 3D Nanostructures for Highly Efficient Chemosensing Platforms

Abstract

Development of fast and intuitive detection techniques for explosive vapors is highly desired for security applications. Among those techniques, fluorescence quenching has advantages in terms of portability and maintenance cost compared to electrically driven platforms. One of the challenging issues is the restricted sensitivity (i.e., low initial quenching and quenching saturation) caused by hindered diffusion of gaseous analytes inside a dense, solid film, and resulting limited surface area, where the target molecules are reacting. Here, multilevel 3D porous nanostructures are introduced, which possess strong fluorescence and enhanced sensing abilities, produced by a rapid and scalable lithographic technique. The cyanostilbene fluorophore with low‐absorption around patterning wavelengths (≈355 nm) is newly designed to be incorporated into transparent photopolymer. The emission color and intensity of the composite films under excitation can be precisely controlled by adjusting the concentration of fluorophore based on intermolecular effects. The patterned, monolithic film with low‐volume fraction (<40%) offers efficient diffusion paths inside a film and a large number of reaction sites for detecting gaseous analytes, enabling fast fluorescence quenching at an early stage (≈7.5 times higher than the solid film at 30 s) and fully suppressed fluorescence without quenching saturation, which cannot be achieved by conventional solid films.

Fabrication of Nanoshell-Based 3D Periodic Structures by Templating Process using Solution-derived ZnO

“…After UV irradiation (wavelength 355 nm) through the phase shift mask using an Nd:YAG laser (Awave355-300mW40K, Advanced Optowave) with a beam expander and a collimator, the sample was post-exposure-baked (65 °C for 7 min) on a hot plate. The unexposed regions were then removed using propylene glycol methyl ether acetate (PGMEA) (SU-8 developer, MicroChem) followed by rinsing with ethanol so that a 3D polymeric template was obtained [ 32 – 36 ].…”

“…In this paper, we demonstrate a combination of a proximity field nanopatterning (PnP) process [ 32 – 36 ] and infiltration process with solution-derived ZnO, in order to create a nanoshell-based 3D periodic structure. PnP is a method to form 3D polymeric periodic structures utilizing a 3D intensity distribution of light into a photopolymer, generated by the passage of light through a phase shift mask with periodic relief patterns.…”

Atomic Layer Deposition of Inorganic Thin Films on 3D Polymer Nanonetworks

“…To evolve into more industrial processes, Jeon et al developed PMIL, also known as proximity-field nanopatterning (PnP), in which all complex interference optics are integrated into a single conformal phase-mask (Figure 2e) [23,37,48,[53][54][55][56][57][58]. The principle of this technique is to imprint the Talbot interference, caused by the interference of diffractions arising from the phase mask with the surface relief structure, onto the photopolymer.…”

Fundamental principles and development of proximity-field nanopatterning toward advanced 3D nanofabrication

“…For the convenient removal of 3D polymeric structures with a liquid process, novolak-based (AZ5124, 9260) and phenolic-based (NR5) photoresists are applied as 3D templates for material conversion [40,53]. Another approach is development of functional photoresists: biocompatible hydrogels such as poly(hydroxyethyl) methacrylate (PHEMA) [54] and poly(ethylene glycol) diacrylate (PEGDA) [55], organic-inorganic hybrid photoresist such as polyhedral oligomeric silsesquioxane (POSS) [56] and poly(methyl silsesquioxane) (PMSSQ) [57], and functional molecule-doped SU-8 [58].…”