Engineering of Solid-State Nanoporous Laser through Dendrimer-Encapsulated Fluorophores.

Dendrimers─nanosized macromolecules that can function as hosts for encapsulation of guest molecules─provide new avenues to engineer gain media for lasing systems. In this context, this study investigates the interplay between the geometric features of a model porous scattering medium, nanoporous anodic alumina (NAA), and the chemical features of a model fluorophore-dendrimer encapsulation system to maximize random lasing. The inner surface of the NAA platforms is functionalized with fluorophore molecules encapsulated within dendrimers via an electrostatic interaction. The resulting solid-state composite structures emit well-resolved, intense random lasing when subjected to optical pumping. By engineering fluorophore-dendrimer and geometric features of scattering medium, we can precisely tune the characteristics of random lasing emissions. It is found that lasing structures with low porosity and thickness functionalized with fluorophore molecules encapsulated in second-generation dendrimers provide the best platforms for lasing generation, resulting in a strongly polarized laser at ∼594 nm that has a high quality-gain product of ∼1588 au, a polarization quality of ∼0.86, and a lasing threshold of ∼0.05 mJ pulse-1. Comparative analysis indicates that dendrimers achieve 2.5 times better random lasing than conventional surfactants due to improved encapsulation and minimization of photobleaching. Our results reveal the importance of the fluorophore encapsulation method and design of scattering media in the engineering of random lasing platforms for applications in optical and optoelectrical systems.

Tailoring Tamm Plasmon Resonances in Dielectric Nanoporous Photonic Crystals.

The fields of plasmonics and photonic crystals (PCs) have been combined to generate model light-confining Tamm plasmon (TMM) cavities. This approach effectively overcomes the intrinsic limit of diffraction faced by dielectric cavities and mitigates losses associated with the inherent properties of plasmonic materials. In this study, nanoporous anodic alumina PCs, produced by two-step sinusoidal pulse anodization, are used as a model dielectric platform to establish the methodology for tailoring light confinement through TMM resonances. These model dielectric mirrors feature highly organized nanopores and narrow bandwidth photonic stopbands (PSBs) across different positions of the spectrum. Different types of metallic films (gold, silver, and aluminum) were coated on the top of these model dielectric mirrors. By structuring the features of the plasmonic and photonic components of these hybrid structures, the characteristics of TMM resonances were studied to elucidate effective approaches to optimize the light-confining capability of this hybrid TMM model system. Our findings indicate that the coupling of photonic and plasmonic modes is maximized when the PSB of the model dielectric mirror is broad and located within the midvisible region. It was also found that thicker metal films enhance the quality of the confined light. Gas sensing experiments were performed on optimized TMM systems, and their sensitivity was assessed in real time to demonstrate their applicability. Ag films provide superior performance in achieving the highest sensitivity (S = 0.038 ± 0.001 nm ppm-1) based on specific binding interactions between thiol-containing molecules and metal films.

Understanding the Intrinsic Rectification Properties of Nanoporous Anodic Alumina by Selective Chemical Etching.

The distribution of oxygen and aluminum vacancies across the hemispherical barrier oxide layer (BOL) of nanoporous anodic alumina (NAA) relies intrinsically on the electric field-driven flow of electrolytic species and the incorporation of electrolyte impurities during the growth of anodic oxide through anodization. This phenomenon provides new opportunities to engineer BOL's inherited ionic current rectification (ICR) fingerprints. NAA's characteristic ICR signals are associated with the space charge density gradient across BOL and electric field-induced ion migration through hopping from vacancy to vacancy. In this study, we engineer the intrinsic space charge density gradient of the BOL of NAA under a range of anodizing potentials in hard and mild anodization regimes. Real-time characterization of the ICR fingerprints of NAA during selective etching of the BOL makes it possible to unravel the distribution pattern of vacancies through rectification signals as a function of etching direction and time. Our analysis demonstrates that the space charge density gradient varies across the BOL of NAA, where the magnitude and distribution of the space charge density gradient are revealed to be critically determined by anodizing the electrolyte, regime, and potential. This study provides a comprehensive understanding of the engineering of ion transport behavior across blind-hole NAA membranes by tuning the distribution of defects across BOL through anodization conditions. This method has the potential to be harnessed for developing nanofluidic devices with tailored ionic rectification properties for energy generation and storage and sensing applications.

Structural Engineering of the Barrier Oxide Layer of Nanoporous Anodic Alumina for Iontronic Sensing.

The hemispherical barrier oxide layer (BOL) closing the bottom tips of hexagonally distributed arrays of cylindrical nanochannels in nanoporous anodic alumina (NAA) membranes is structurally engineered by anodizing aluminum substrates in three distinct acid electrolytes at their corresponding self-ordering anodizing potentials. These nanochannels display a characteristic ionic current rectification (ICR) signal between high and low ionic conduction states, which is determined by the thickness and chemical composition of the BOL and the pH of the ionic electrolyte solution. The rectification efficiency of the ionic current associated with the flow of ions across the anodic BOL increases with its thickness, under optimal pH conditions. The inner surface of the nanopores in NAA membranes was chemically modified with thiol-terminated functional molecules. The resultant NAA-based iontronic system provides a model platform to selectively detect gold metal ions (Au3+) by harnessing dynamic ICR signal shifts as the core sensing principle. The sensitivity of the system is proportional to the thickness of the barrier oxide layer, where NAA membranes produced in phosphoric acid at 195 V with a BOL thickness of 232 ± 6 nm achieve the highest sensitivity and low limit of detection in the sub-picomolar range. This study provides exciting opportunities to engineer NAA structures with tailorable ICR signals for specific applications across iontronic sensing and other nanofluidic disciplines.

Facile preparation of tissue engineering scaffolds with pore size gradients using the muesli effect and their application to cell spheroid encapsulation.

Porous biodegradable scaffolds have many applications in bioengineering, ranging from cell culture and transplantation, to support structures, to induce blood vessel and tissue formation in vivo. While numerous strategies have been developed for the manufacture of porous scaffolds, it remains challenging to control the spatial organization of the pores. In this study, we introduce the use of the granular convection effect, also known as the muesli or brazil nut effect, to rapidly engineer particulate templates with a vertical size gradient. These templates can then be used to prepare scaffolds with pore size gradients. To demonstrate this approach, we prepared templates with particle size gradients, which were then infused with a prepolymer solution consisting of the pentaerythritol ethoxylate (polyol), sebacoyl chloride (acid chloride), and poly(caprolactone). Following curing, the template was dissolved to yield biodegradable polyester-ether scaffolds with pore size gradients that could be tuned depending on the size range of the particulates used. The application of these scaffolds was demonstrated using pancreatic islets, which were loaded via centrifugation and retained within the scaffold's pores without a decrease in viability. The proposed strategy provides a facile approach to prepare templates with spatially organized pores that could potentially be used for cell transplantation, or guided tissue formation.