Functional nanoarrays for investigating stem cell fate and function

Stem cells show excellent potential in the field of tissue engineering and regenerative medicine based on their excellent capability to not only self-renew but also differentiate into a specialized cell type of interest. However, the lack of a non-destructive monitoring system makes it challenging to identify and characterize differentiated cells before their transplantation without compromising cell viability. Thus, the development of a non-destructive monitoring method for analyzing cell function is highly desired and can significantly benefit stem cell-based therapies. Recently, nanomaterial-based scaffolds (e.g., nanoarrays) have made possible considerable advances in controlling the differentiation of stem cells and characterization of the differentiation status sensitively in real time. This review provides a selective overview of the recent progress in the synthesis methods of nanoarrays and their applications in controlling stem cell fate and monitoring live cell functions electrochemically. We believe that the topics discussed in this review can provide brief and concise guidelines for the development of novel nanoarrays and promote the interest in live cell study applications. A method which can not only control but also monitor stem cell fate and function will be a promising technology that can accelerate stem cell therapies.

Ion-Exchange Loading Promoted Stability of Platinum Catalysts Supported on Layered Protonated Titanate-Derived Titania Nanoarrays

Supported metal catalysts are one of the major classes of heterogeneous catalysts, which demand good stability in both the supports and catalysts. Herein, layered protonated titanate-derived TiO₂ (LPT-TiO₂) nanowire arrays were synthesized to support platinum catalysts using different loading processes. The Pt ion-exchange loading on pristine LPTs followed by thermal annealing resulted in superior Pt catalysts supported on the LPT-TiO₂ nanoarrays with excellent hydrothermal stability and catalytic performance toward CO and NO oxidations as compared to the Pt catalysts through wet-impregnation on the anatase TiO₂ (ANT-TiO₂) nanoarrays resulted from thermal annealing of LPT nanoarrays. Both loading processes resulted in highly dispersed Pt nanoparticles (NPs) with average sizes smaller than 1 nm at their pristine states. However, after hydrothermal aging at 800 °C for 50 h, highly dispersed Pt NPs were only retained on the ion-exchanged LPT-TiO₂ nanoarrays with the support structure consisting of a mixture of 74% anatase and 26% rutile TiO₂. For the wet-impregnation loading directly on anatase TiO₂ nanoarrays derived from LPT, the Pt catalysts experienced severe agglomeration after hydrothermal aging, with the nanoarray supports consisting of 86% anatase and 14% rutile TiO₂. Spectroscopy analysis suggested that Pt²⁺ cations intercalated into the interlayers of the titanate frameworks through ion-exchange impregnation procedure, which altered the chemical and electronic structures of the catalysts, resulting in the shifts of the electronic binding energy, Raman bands, and optical energy bandgap. The ion-exchangeable nature of LPT nanoarrays clearly provides a structural modification in Pt-doped LPT that has resulted in a strong interaction between the Pt catalysts and LPT-TiO₂ nanoarray supports, leading to the enhanced hydrothermal stability of the catalysts. Considering the wide applications of the LPT and TiO₂ nanomaterials as supports for catalysts, this finding provides a new pathway to design highly stable supported metal catalysts for different reactions.

Direct Synthesis of Conformal Layered Protonated Titanate Nanoarray Coatings on Various Substrate Surfaces Boosted by Low-Temperature Microwave-Assisted Hydrothermal Synthesis

Layered protonated titanates (LPTs) are promising support materials for catalytic applications because their high surface area and cation exchange capacity provide the possibility of achieving a high metal dispersion. However, the reported LPT nanomaterials are mainly limited to free-standing nanoparticles (NPs) and usually require high temperature and pressure conditions with extended reaction time. In this work, a high-throughput microwave-assisted hydrothermal method was developed for the direct synthesis of conformal LPT nanoarray coatings onto the three-dimensional honeycomb monoliths as well as other substrate surfaces at low temperature (75-95 °C) and pressure (1 atm). Using TiCl₃ as the titanium source, H₂O₂ as the oxidant, and hydrochloric acid as the pH controller, a peroxotitanium complex (PTC) was formed and identified to play an essential role for the formation of LPT nanoarrays. The gaseous O₂ released during the decomposition of PTC promotes the mass transfer of the precursors, making this method applicable to substrates with complex geometries. With the optimized conditions, a growth rate of 42 nm/min was achieved on cordierite monolith substrates. When loaded with Pt NPs, the LPT nanoarray-based monolithic catalysts showed excellent low-temperature catalytic activity for CO and hydrocarbon oxidation as well as satisfactory hydrothermal stability and mechanical robustness. The low temperature and pressure requirements of this facile hydrothermal method overcome the size- and pressure-seal restrictions of the reactors, making it feasible for scaled production of LPT nanoarray-based devices for various applications.

Dimensional tailoring of hydrothermally grown zinc oxide nanostructures in a continuous flow micro reactor

Dynamic deposition of ZnO nanostructures with varying morphologies (nanorods, nanocones, nanopencils, nanosheets, etc.), diameters, lengths and aerial densities on ITO-PET substrates has been achieved using a continuous flow microreactor in which we maintained a homeostatic zinc concentration and varied the other reactants’ concentrations.

Facet-selective interface design of a BiOI(110)/Br-Bi2O2CO3(110) p–n heterojunction photocatalyst

A BiOI₍₁₁₀₎/Br-BOC₍₁₁₀₎ p–n heterostructure photocatalyst with a high interface quality was designed and synthesized by facet-dependent selective adsorption.