Jonathan Howse

The current state of the art in nanopropulsion devices was recently reviewed by Ebbens and Howse in an article last Friday.^[SoftMatter] A short summary of the nano- systems is presented below with video action shots when I could find them.

The Whitesides

Catalyst: Pt
Fuel: H₂O₂
Propulsion: Bubble propulsion
Terrain: Aqueous meniscus
Max Speed: 2 cm/s
Mitch’s Name: The Karl Benz (since it was the first)
Article: Autonomous Movement and Self-Assembly

The Sen-Mallouk-Crespi

Catalyst: Pt
Fuel: H₂O₂
Propulsion: Self electrophoresis/Interfacial tension
Terrain: Settled near boundary in aqueous solution
Max Speed: 6.6 um/s
Mitch’s Names: The Ford Mustang of nanopropulsion. (It is a hot rod, get it?)
Article: Catalytic Nanomotors: Autonomous Movement of Striped Nanorods

The Jones-Golestanian

Catalyst: Pt
Fuel: H₂O₂
Propulsion: Pure self diffusiophoresis
Terrain: Free aqueous solution
Max Speed: 3um/s
Mitch’s Name: The Volkswagen Beetle
Article: Self-Motile Colloidal Particles: From Directed Propulsion to Random Walk

The Mano-Heller

Catalyst: Glucose oxidase and Biliruben oxidase
Fuel: Glucose
Propulsion: Self electrophoresis
Terrain: Aqueous meniscus
Max Speed: 1 cm/s
Mitch’s Name: The Komatsu Truck (because it is huge)
Article: Bioelectrochemical Propulsion

The Feringa

Catalyst: Synthetic catalse
Fuel: H₂O₂
Propulsion: Bubble/interfacial
Terrain: Acetonitrile solution
Max Speed: 35 um/s
Mitch’s Name: The F150 (has some exhaust issues)
Article: Catalytic molecular motors: fuelling autonomous movement by a surface bound synthetic manganese catalase

The Sen-Mallouk

Catalyst: Pt (CNT) (+cathodic reactions at Au)
Fuel: H2O2/N2H4
Propulsion: Self electrophoresis
Terrain: Settled near boundary in aqueous solution
Max Speed: 200 um/s
Mitch’s Names: The Ford Mustang GT (has more kick than the regular version)
Article: Bipolar Electrochemical Mechanism for the Propulsion of Catalytic Nanomotors in Hydrogen Peroxide Solutions

The Feringa v2

Catalyst: Glucose oxidase and catalse
Fuel: Glucose
Propulsion: Local oxygen bubble formation
Terrain: Free aqueous buffer solution
Max Speed: 0.2–0.8 um/s
Mitch’s Name: The Chevrolet Nova (more hot rod action)
Article: Autonomous propulsion of carbon nanotubes powered by a multienzyme ensemble

The Gibbs-Zhao

Catalyst: Pt
Fuel: H₂O₂
Propulsion: Bubble release mechanism
Terrain: Aqueous solution
Max Speed: 6 um/s
Mitch’s Name: The Rover
Article: Autonomously motile catalytic nanomotors by bubble propulsion

The Bibette

Engine: External magnetic field
Propulsion: Flagella
Terrain: Aqueous solution
Max Speed: unknown
Mitch’s name: The BMW Mini E (because there is no such thing as a magnetic car)
Article: Microscopic artificial swimmers

The Sagués

Engine: External magnetic field
Propulsion: Doublet rotation coupling with boundary interactions
Terrain: Settled near boundary in aqueous solution
Max Speed: 3.2 um/s
Mitch’s Name: The Smart ED
Article: Magnetically Actuated Colloidal Microswimmers

The Fischer

Engine: External magnetic field
Propulsion: Propeller drive
Terrain: Aqueous solution
Max Speed: 40 um/s
Mitch’s Name:
Article: Controlled Propulsion of Artificial Magnetic Nanostructured Propellers

The Najafi-Golestanian

Engine: Conformation changes in linking units
Propulsion: Time irreversible translations
Terrain: Free solution
Max Speed: ?
Mitch’s Name: The Eternal Concept Car
Article: Propulsion at low Reynolds number

Some devices that were not included by the authors of the review article, but should definitely be included in any list like this are below:

The Gracias

Engine: External magnetic field
Propulsion: Brute Force
Terrain: Aqueous solution
Max Speed: ?
Mitch’s Name: The Truck Cranes
Article: Tetherless thermobiochemically actuated microgrippers

Tetherless Microgrippers Grabs Tissue Sample – Watch today’s top amazing videos here

The Nelson

Engine: External electromagnetic fields
Propulsion: Flagella
Terrain: ?
Max Speed: 18 um/s
Mitch’s Name: The Tesla Roadster (simply awesome)
Article: Characterizing the Swimming Properties of Artificial Bacterial Flagella

Artificial Sperm – Watch more funny videos here

Link to Review Article: In pursuit of propulsion at the nanoscale

Mitch

That is the highly controversial claim made by Kate Ovchinnikova and Gerald Pollack in Langmuir earlier this year.^[Langmuir] Electroneutrality is a guiding principal in electrochemistry and is a method to understanding electrolytic cells (Pt electrodes in dilute aqueous NaCl solutions). It stipulates that any charge imbalance across an electrochemical system is quickly (~ns) balanced by the salt present in the water being driven by the electric field in such a way to neutralize that charge imbalance. Thus the need for salt bridges and all that wonderful G-chem stuff we have learned. There is even a cool little applet you can play with electroneutrality by the Harvey Project. When I tried to sit down with electrochemists to discuss the claims by O&P they quickly dismissed them out of hand after reading the beginning of their paper. So the big question is, did O&P stumble across something amazing or did they spectacularly overstate the results of their experiment.

I can summarize their paper succinctly:

1. Insert electrodes into electrolytic cell
2. Turn on power supply
3. Disconnect the electrodes from the circuit
4. Remove the bridge between beakers
5. Reconnect electrodes to measure residual charge in the two beakers.

The design seems thoughtful enough, but before I get into the merits of their results I need to take time to mention a few gems in their paper. Here is a quote from them.

Bubble formation occurred in all experiments (n > 20), although position and growth rate were inconsistent. In most cases, formation began during the charging phase and continued through discharge. Characteristics of bubble formation were not pursued in any detail, but may warrant future study.

But it doesn’t warrant further study,  all chemists know where their bubbles came from.

An other eye catcher is that they didn’t use a standard electrochemical setup. They used my trusty NI USB-6009, I know that product well as a chunk of my thesis was acquired with it. It doesn’t make the experiment invalid, but why use crap when you are trying to disprove such a time honored concept as electroneutrality. Maz and I know from experience that the USB-6009 floats if their isn’t a sufficient load on it or if their isn’t an appreciable external voltage.

Here is a quote from them contemplating that HCl solutions have an overall positive charge.

One might speculate, for example, whether ordinary acidic solutions, which have low pH, might contain net positive charge, while ordinary basic solutions might contain net negative charge.

So far everything has been “quirky”, it isn’t until the end when you perceive something really odd.

Water appears able to adopt two structural networks that have mirror symmetry to one another. The fact that these networks are macro phenomena deserves further study.

A second and related issue is the potential for disturbance of these structural networks. It is now established that when water is left standing for long periods, it develops thixotropic properties, implying macrostructure.7 Such macrostructure is expected to be fragile. The fact that removing and inserting electrodes did not apparently ruin the charge-containing structure implies that, once formed, the structural network can re-form rather readily. This is an additional subject requiring further study.

7:Vybiral, B. Water and the Cell; Pollack, G. H., Cameron, I., Wheatley, D., Eds.; Springer: New York, 2006; pp 299-314.

It is with that last statement you say to yourself, “Oh, I get it. This is a homeopathy paper.” Water being able to adopt structures of the solutes that were dissolved in it is a hallmark of the quackery that is homeopathy. O&P’s claim isn’t that bold, but it has hints of the same idea. Claiming macrostructures (~mm) of water that extend past the picosecond domain is absurd.

Although I haven’t discussed the results of their paper, would you really trust it anyways?

Horacio Corti and Agustin Colussi have done an excellent job dissecting the technical irregularities of the paper and I encourage you to read their comments on the article (link below). If you come to a different conclusion or find me in error, please leave a comment and join the discussion.

Links

• Can Water Store Charge? (Ovchinnikova and Pollack)
• Do Concentration Cells Store Charge in Water? Comment on Can Water Store Charge? (Corti and Colussi)
• Reply to Comment on Can Water Store Charge? (Ovchinnikova and Pollack)
• Response to Reply to Comment on Can Water Store Charge (Corti and Colussi)

Mitch

Graphic abstract from: Stabilization of Superparamagnetic Iron Oxide Core−Gold Shell Nanoparticles in High Ionic Strength Media

Pun From: Play on the famous quote by Friedrich Nietzsche

Mitch

1. I need a way to analyze the RGB of every pixel in an image.
2. I need to develop a simple algorithm to manipulate the RGB for every pixel.
3. Apply the algorithm and generate the colored picture.

RGB is the value for Red, Green, and Blue coded for each pixel. They run from 0 to 255. So, I wrote a script that will analyze this pixel information using php. My canvas was Yow et al.’s recent image of colloidosomes, shown below.

A gray scale picture will have the same value for RGB. The simplest manipulations will be to hold either R, G, or B to zero and let the others retain their original value. This yields teal for R=0, violet for G=0, and yellow for B=0.

To generate blue (R=0, G=0), green (R=0, B=0), and red (G=0, B=0) you’ll need to set two values to zero.

Primary colors are nice, but if you want to have softer gentler colors you’ll need to apply an algorithm to your RGBs. For a light blue, I use the following R=(0.2 * B), G=(0.6 * B), B=B.

An orange I like is R=R, G= (0.5 * R), B=0.

If someone knows a simpler way of SEM color manipulation please share. Also, if someone would like me to make a script where you can upload your SEM image and apply a single color filter let me know.

Mitch