A Practical Guide to Analyzing and Reporting the Movement of Nanoscale Swimmers

The recent invention of nanoswimmerssynthetic, powered objects with characteristic lengths in the range of 10–500 nmhas sparked widespread interest among scientists and the general public. As more researchers from different backgrounds enter the field, the study of nanoswimmers offers new opportunities but also significant experimental and theoretical challenges. In particular, the accurate characterization of nanoswimmers is often hindered by strong Brownian motion, convective effects, and the lack of a clear way to visualize them. When coupled with improper experimental designs and imprecise practices in data analysis, these issues can translate to results and conclusions that are inconsistent and poorly reproducible. This Perspective follows the course of a typical nanoswimmer investigation from synthesis through to applications and offers suggestions for best practices in reporting experimental details, recording videos, plotting trajectories, calculating and analyzing mobility, eliminating drift, and performing control experiments, in order to improve the reliability of the reported results

A Practical Guide to Analyzing and Reporting the Movement of Nanoscale Swimmers

The recent invention of nanoswimmerssynthetic, powered objects with characteristic lengths in the range of 10–500 nmhas sparked widespread interest among scientists and the general public. As more researchers from different backgrounds enter the field, the study of nanoswimmers offers new opportunities but also significant experimental and theoretical challenges. In particular, the accurate characterization of nanoswimmers is often hindered by strong Brownian motion, convective effects, and the lack of a clear way to visualize them. When coupled with improper experimental designs and imprecise practices in data analysis, these issues can translate to results and conclusions that are inconsistent and poorly reproducible. This Perspective follows the course of a typical nanoswimmer investigation from synthesis through to applications and offers suggestions for best practices in reporting experimental details, recording videos, plotting trajectories, calculating and analyzing mobility, eliminating drift, and performing control experiments, in order to improve the reliability of the reported results

A Practical Guide to Analyzing and Reporting the Movement of Nanoscale Swimmers

The recent invention of nanoswimmerssynthetic, powered objects with characteristic lengths in the range of 10–500 nmhas sparked widespread interest among scientists and the general public. As more researchers from different backgrounds enter the field, the study of nanoswimmers offers new opportunities but also significant experimental and theoretical challenges. In particular, the accurate characterization of nanoswimmers is often hindered by strong Brownian motion, convective effects, and the lack of a clear way to visualize them. When coupled with improper experimental designs and imprecise practices in data analysis, these issues can translate to results and conclusions that are inconsistent and poorly reproducible. This Perspective follows the course of a typical nanoswimmer investigation from synthesis through to applications and offers suggestions for best practices in reporting experimental details, recording videos, plotting trajectories, calculating and analyzing mobility, eliminating drift, and performing control experiments, in order to improve the reliability of the reported results

Color Tuning of an Acidic Blue Dye by Intercalation into the Basic Interlayer Galleries of a Poly(allylamine)/Synthetic Fluoromica Nanocomposite

The intercalation of an acidic blue dye, Brilliant Blue FCF, into poly(allylamine) (PAA)/synthetic fluoromica (Na-TSM) was investigated as a function of the reaction pH (1.5−12.0) and the loading of the polyelectrolyte and acidic dye. Surprisingly, the colored solids so obtained show a variety of colors from the original blue to yellow through green with only a slight increase in the reaction pH. At low and neutral pH (1.5−9.5), the acidic blue dye molecules were adsorbed/intercalated on/in PAA/Na-TSM mainly through electrostatic interactions between protonated amine groups on the PAA chains and sulfonate groups of the dye, resulting in the original blue color. UV−visible spectroscopic data hint that the adsorbed/intercalated dye molecules were aggregated. The color shifted to blue-green at pH 10.0 and finally to yellow at pH 12.0. At high pH, the PAA layers have lower charge density and the dye is well-dispersed within the interlayer galleries. The fraction of neutral primary amine groups increases with increasing reaction pH, and interaction of the neutral amine groups to the dye becomes the dominant driving force for intercalation. On the basis of these intercalation results at different pH and some control experiments, the pH-dependent color change of the intercalated dye appears to be caused by inhibition of the intramolecular interaction between N+ in the dye conjugated system and a free sulfonate group

Encapsulation of Anionic Dye Molecules by a Swelling Fluoromica through Intercalation of Cationic Polyelectrolytes

To develop a novel layered host material with the ability to encapsulate anionic substances, the intercalation of three cationic polyelectrolytes into synthetic sodium fluortetrasilisic mica (Na-TSM) was investigated. With polyethylenimine (PEI) and poly(allylamine hydrochloride) (PAH), the conformation of the intercalated polycation and its ability to accommodate anionic guests depended on its state of protonation. The quaternary ammonium polycation poly(diallyldimethylammonium) (PDDA), which had the lowest charge density of the three polymers studied, adopted a coiled conformation within the anionic host at both high and low pH, resulting in an excess of cationic sites within the interlayer of the polysilicate. Powder X-ray diffraction patterns and adsorption isotherms showed two different stages of PDDA intercalation with different adsorption free energies. Atomic force microscopy images showed that the PDDA−clay nanocomposites maintained the shape of the original nanosheets, indicating the successful conversion of the lamellar host into a 2D material with anion exchange capacity. The anion-accepting ability of these nanocomposites was quantified by studying the encapsulation of a bulky anionic blue dye as a function of the loading of PDDA. From dehydration and X-ray powder diffraction experiments, it was concluded that the dye−polyelectrolyte−clay nanocomposites possessed two kinds of interlayer galleries, and the anionic dye was site-selectively intercalated into hydrated galleries in which PDDA strands were coiled

Layer-by-Layer Assembly of Thin Film Zener Diodes from Conducting Polymers and CdSe Nanoparticles

Ultrathin films have been prepared by self-assembling trioctylphosphine oxide, TOPO, capped n-type 20−40 Å diameter CdSe nanoparticles and 1,6-hexadecanethiol, HDT, onto p-doped semiconducting polymers, chemically deposited poly(3-methylthiophene), PMeT (for Device A), and electrochemically deposited poly(pyrrole), Ppy (for Device B). The semiconducting polymers have, in turn, been electrochemically layered (for Device A) or layer-by-layer chemically assembled (for Device B) onto derivatized conducting substrates. The ultrathin films have been characterized by absorption and emission spectroscopy, transmission electron microscopy, scanning force microscopy, X-ray photoelectron spectroscopy, and by electrochemical measurements. By controlling the level of doping into the p-type junction, it was possible to prepare dissymmetrical junctions and observe a rectifying behavior in the forward direction and a Zener breakdown in the reverse direction for Au/PMeT/(HDT/CdSe)3, Device A, and for Au/MEA/Ppy/(HDT/CdSe)3, Device B. Additionally, Au/MeA/PAH/CdSe (PAH = poly(allylamine hydrochloride)), Au/MEA/Ppy/PSS/CdSe (PSS = polystyrene sulfonate), and Au/MEA/Ppy/α-ZrP/CdSe (α-ZrP = α zirconium phosphate) films have been prepared and characterized

Dynamics of Electron Recombination and Transport in Water-Splitting Dye-Sensitized Photoanodes

Water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) use visible light to split water using molecular sensitizers and water oxidation catalysts codeposited onto mesoporous TiO₂ electrodes. Despite a high quantum yield of charge injection and low requirement for the catalytic turnover rate, the quantum yield of water splitting in WS-DSPECs is typically low (<1%). Here we examine the charge separation and recombination processes in WS-DSPECs photoanodes functionalized with varying amounts of IrO₂ nanoparticle catalyst. Charge extraction and transient open-circuit voltage decay measurements provide insight into the relationship between light intensity, conduction band electron density, open-circuit photovoltage, and recombination time scale. We correlate these results with electrochemical impedance spectroscopy and present the first complete equivalent circuit model for a WS-DSPEC. The data show quantitatively that recombination of photoinjected electrons with oxidized sensitizer molecules and scavenging by the water oxidation catalyst limit the concentration of conduction band electrons and by extension the photocurrent of WS-DSPECs

Coaxially Gated In-Wire Thin-Film Transistors Made by Template Assembly

Nanowire field effect transistors were prepared by a wet chemical template replication method using anodic aluminum oxide membranes. The membrane pores were first lined with a thin SiO2 layer by the surface sol−gel method. Au, CdS (or CdSe), and Au wire segments were then sequentially electrodeposited within the pores, and the resulting nanowires were released by dissolution of the membrane. Electrofluidic alignment of these nanowires between source and drain leads and evaporation of gold over the central CdS (CdSe) stripe affords a “wrap-around gate” structure. At VDS = −2 V, the Au/CdS/Au devices had an ON/OFF current ratio of 103, a threshold voltage of 2.4 V, and a subthreshold slope of 2.2 V/decade. A 3-fold decrease in the subthreshold slope relative to that of planar nanocrystalline CdSe devices can be attributed to coaxial gating. The control of dimensions afforded by template synthesis should make it possible to reduce the gate dielectric thickness, channel length, and diameter of the semiconductor segment to sublithographic dimensions while retaining the simplicity of the wet chemical synthetic method

Template Electrodeposition of Single-Phase p- and n-Type Copper Indium Diselenide (CuInSe₂) Nanowire Arrays

CuInSe2 nanowire arrays were fabricated by electrodeposition from aqueous solutions of copper sulfate, indium sulfate, selenium dioxide, and citric acid, using anodic alumina membranes as templates. X-ray diffraction patterns showed that the wires were single phase (chalcopyrite structure) but polycrystalline, and a band gap of ∼1 eV was obtained from optical measurements. TEM and SEM confirmed that the grain size in nanowires annealed at 400 °C was in the range of 40 nm. The composition of the nanowires was uniform along the length of the wires and could be tuned by varying the electrodeposition potential. Analysis by ICP-MS showed that naowires grown at −700 mV were slightly Cu-rich, whereas those grown at −750 mV were slightly In-rich. Mott−Schottky plots were employed to determine the doping type and flat band potential, verifying that the Cu- and In-rich wires were p- and n-type, respectively. Single-wire electrical transport measurements were also performed and showed that both types of wires had resistivities in the range 10−1−10−3 Ω·cm, consistent with carrier concentrations in the range 1018−1020 cm−3