Thin-walled SnO₂nanotubes functionalized with Pt and Au catalysts via the protein templating route and their selective detection of acetone and hydrogen sulfide molecules

Abstract

Bio-inspired Pt (∼2 nm) and Au (∼2.7 nm) catalysts encapsulated by a protein shell, i.e., Pt-apoferritin (Pt@AF) and Au-apoferriten (Au@AF), were synthesized via the hollow protein nanocage (apoferritin) templating route and directly functionalized on the interior and exterior walls of electrospun SnO2 nanotubes (NTs) during controlled single-nozzle electrospinning followed by high temperature calcination with heating rate control. Fast crystallization of the exterior shell and outward diffusion of the interior Sn precursors and crystallites result in the continued growth of a tubular wall, which is related to rapid heating driven Ostwald-ripening behavior. Very importantly, the Pt and Au nanoparticles (NPs) were immobilized onto thin-walled SnO2 NTs with a diameter of ∼350 nm and a shell thickness of ∼40 nm without any aggregation of catalysts due to high dispersibility, which originated from repulsive electrostatic (Coulombic) forces acting on the surface charged protein shells, leading to an enhanced catalytic effect and outstanding gas sensing properties. Pt-loaded SnO2 NTs exhibited superior acetone response (R(air)/R(gas) = 92 at 5 ppm) compared to pure SnO2 NFs (R(air)/R(gas) = 4.8 at 5 ppm) and SnO2 NTs (Rair/Rgas = 11 at 5 ppm) while Au-loaded SnO2 NTs showed a high response when exposed to hydrogen sulfide (R(air)/R(gas) = 34 at 5 ppm), offering selective gas detection with minimal cross-sensitivity against other interfering gases such as NH3, CO, NO, C6H5CH3, and C5H12. Our results provide a new insight into facile, cost-effective, and highly dispersible catalyst loading on the interior and exterior walls of hollow metal oxide NTs via simple electrospinning as a potential breath analyzer.

WO3 Nanofiber-Based Biomarker Detectors Enabled by Protein-Encapsulated Catalyst Self-Assembled on Polystyrene Colloid Templates

“…Apoferritin is a 24-subunit protein complex that exhibits a hollow spherical structure with outer diameter in the range of 12-13 nm and an inner cavity diameter in the range of 7-8 nm ( Figure 1 a). [ 32,33 ] Apoferritin can contain different types of ionic molecules inside the empty cavity by controlling the pH of the apoferritin in solution. The ionic molecules can be attracted to negatively charged channels and diffused into apoferritin through the narrow negatively charged hydrophilic channels along the threefold symmetry axes.…”

Electrospun one-dimensional nanostructures: a new horizon for gas sensing materials

“…SnO 2 NTs have also been functionalized by bio-inspired Pt particles (2 nm diameter) at 0.16 wt % and Au particles (2.7 nm diameter) at 0.08 wt % using a protein nanocage by single-nozzle electrospinning [183] as shown schematically in Fig. 8.…”

“…In comparison, dense SnO 2 NFs show a response of 2.6 at 5 ppm H 2 S and pristine SnO 2 NTs show a response of 4.7 at 5 ppm H 2 S, respectively (Fig. 8,l) [183]. …”

“…(j) EDX elemental mapping of Au-loaded SnO 2 NTs; (k) dynamic acetone sensing transition in a concentration range of 1–5 ppm at 350 °C and (l) dynamic H 2 S sensing transition in a concentration range of 1–5 ppm at 300 °C. Reproduced with permission from [183], copyright 2015 Royal Society of Chemistry.…”

Dual-color plasmonic enzyme-linked immunosorbent assay based on enzyme-mediated etching of Au nanoparticles

“…However, in some cases, the use of a costly and bulky readout is not applicable. For example, portable and affordable devices are greatly welcome for in-home personal healthcare111213141516. Therefore, the development of colorimetric ELISA with improved accuracy for naked-eye inspection could be greatly desired.…”