Quantum Dot Nanosensors for Visual Sensing

As we advance into artificial sensing technology, it is pertinent that use of such technology be made to advance the interests of humans in general and improve the quality of life. Such motives have mostly been the driving force of technologies. For what is invented for space exploration helps fight diseases on earth and other examples include what was designed for war later supplementing great engineering technologies. The end result is usually the driving force or as a side motive at minimum. The advancement of nanotechnology means much more components in the same space and hence much smaller equipments. Sensors, were they small enough, could be used to replace the complicated biological and natural sensors in humans or animals and even be given to computers and robots.

Usage of Quantum Dots explore such a use of a nanosensor and design it so as to restore the vision of visually impaired humans or give eyesight to computers; not using something as crude and huge in size as a camera or a lens rather targeting the core of sensing itself. Inherently, this research targets the retina itself. An artificial replacement for retina would enable humans to benefit from a restored vision without invasive brain surgeries. Computers, at the same time, will be able to detect photons with a much much greater sensitivity than a normal digital camera based optical detection method. Photo-detection needs a complicated device or materials engineered to the extent that the sensor would not be a physical obstruction in terms of its size when placed in the human eye or as an attachment to it as well as be biocompatible. To keep up with both these de facto requirements and many others implications of them, extensive study of the mechanism and biocompatibility has been done in research work for the selection of the materials and the literature shows an in-depth detail on why the materials chosen would make graphene and graphite based quantum dots a great candidate combination for such sensors. They can be used with two routes in the basic design; the generation of photocurrent via quantum dots on detection of photons or polarization of human nerves to fire neurons via quantum dots whenever photons are detected.

Works on the topic:

Cheng, Shih-Hao et al. All Carbon-Based Photodetectors: An eminent integration of graphite quantum dots and two dimensional graphene. Scientific Reports 3, Article number: 2694. Published: 18 September 2013.

Tang, L. et al. Deep ultraviolet photoluminescence of water-soluble self passivated graphene quantum dots. ACS Nano 6, 5102–5110 (2012).

Li, Y. et al. An Electrochemical Avenue to Green-Luminescent Graphene Quantum Dots as Potential Electron-Acceptors for Photovoltaics. Adv. Mater. 23, 776–780 (2011).

Li, X. et al. Large-area synthesis of high-quality and uniform graphene films on copper foils. Science 324, 1312–1314 (2009).

Katherine Lugo et al. . Remote switching of cellular activity and cell signaling using light in conjunction with quantum dots. Vol 3.(2012)

Quantum Dots – A Definition, How They Work, Manufacturing, Applications and Their Use In Fighting Cancer Printable Document. Online Document: Accessed on: 27 May 2014.

Lin, Rieke and Research groups. Quantum Dots and Cells. Website: Accessed on 27 May 2014.

K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V. Dubonos, I. V. Grigorieva, and A. A. Firsov, Electric field effect in atomically thin carbon films, Science 306, 666 (2004)

K. Novoselov, D. Jiang, F. Schedin, T. Booth, V. Khotkevich, S.Morozov, and A. Geim, Two-dimensional atomic crystals, Proc. Natl. Acad. Sci. USA 102,10451 (2005).

Carion O., Mahler B., Pons T., Dubertret B., “Synthesis, encapsulation, purification and coupling of single quantum dots in phospholipid micelles for their use in cellular and in vivo imaging,” Nat. Protoc. 2(10), 2383–2390 (2007).10.1038/nprot.2007.351

Chaoxu Li, J. A.. “Biodegradable nanocomposites of amyloid fibrils and graphene with shape-memory and enzyme-sensing properties”, Nature Nanotechnology, 421–427 (2012)

Kian, P. L., Qiaoliang, B., Goki, E. & Manish, C. Graphene oxide as a chemically tunable platform for optical applications. Nat. Chem. 2, 1015–1024 (2010).

Galande, C. et al. Quasi-molecular fluorescence from graphene oxide. Sci. Rep. 1, 85 (2011).

Jingzhi, S. et al. The Origin of Fluorescence from Graphene Oxide. Sci. Rep. 2, 972 (2012).

Sargent, E. H. Photodetectors: A sensitive pair. Nat. Nanotech. 7, 349–350 (2012).

Konstantatos, G. & Sargent, E. H. PbS colloidal quantum dot photoconductive photodetectors: Transport, traps, and gain. Appl. Phys. Lett. 91, 173505–173508 (2007).

Zhang, D., Gan, L., Cao, Y., Wang, Q. & Guo, X. Understanding Charge Transfer at PbS-Decorated Graphene Surfaces toward a Tunable Photosensor. Adv Mater. 24, 2715–2720 (2012).

Konstantatos, G. & Sargent, E. H. Nanostructured materials for photon detection. Nat. Nanotech. 5, 391–400 (2010).

Shen, J., Zhu, Y., Chen, C., Yang, X. & Li, C. Facile preparation and upconversion luminescence of graphene quantum dots. Chem. Commun. 47, 2580–2582 (2011)

Furnace simulation

 

As the research of Highbrows Engineering on furnace development specifically for Pakistani industry progresses, we would like to share it with every one else to keep it open sourced.

On the course of furnace simulation development, we have been reviewing and testing furnace simulators online and any options that might be there in the form of desktop applications so as to develop FurnoSim, the Pakistani bred industrial furnace simulator. The aim is to benefit both the industry as a commercial product as well as an academic product for students and professionals and it is on our to do list of products that are coming up.

Steeluniversity.org shares a free online furnace simulator which can calculate some basic cycles for some preset processes such as alloying. Although these do not cater the professional needs but they can be very exciting for fresh professionals or students to learn the processes without actually wasting energy and material. Go ahead and test their online electric arc furnace training simulator, for example. On the main page they also have other metallurgy and testing related simulation links that may come in handy for atleast learning and academic presentations.

On the side, keeping our promise of sharing the research with the world, our physics and electronics research side has been making progress and will be coming up with products soon. As a treat, a theoretical moving particle simulation is shared below with explanation:

This moving charge simulator shows for how +ive / -ive acceleration of electron emits light / radiation - fields point radially towards the charge and when the charge accelerates, the difference of where the charge should have been with previous velocity and where the charge is now with the change is a perpendicular shift of the field lines. This shift travels away form the charge at the speed of light as radiations. This can also be taken as a mathematical version of light where the light is considered as mathematical correction of the difference being updated through out the universe at the maximum speed possible (which is the speed of light). This changes with respect to relativity when you accelerate the electron to the speed of light and is also shown in the simulation (if you accelerate it to that point in the settings).

Nanotechnology for engineering applications

If you wish to deign alienware, you would be better off asking a science fiction author to suggest an approach for science. Which is why, yesterday's science fiction is today's technology.

A number of reasons have contributed to the fact that we are now looking towards the applications of smaller and smaller equipment. Nanotechnology can be used to compliment almost any other technology as it allows for 'more' literally. In some cases, nanotechnology is needed simply because only a component that small could fit in there without much disturbance or due to physical dimensions. Nanometer scale sensors make the possibilities of even the craziest ideas look real.

The idea of nano robots is one of the factors that drives nano scientists' motivation. It might be extremely useful to create a nano robot that is equipped with a nano scale sensor to measure localized real time stresses in structures. Structural integrity of a engineering equipment, constructions and large sized installations is vital in most cases. Materials engineers usually have to perform non destructive and destructive tests time and again to make sure that the structure will hold. This results in a lot of man hours and expenses. Furthermore, it is mostly mixed qualitative and quantitative decision by the engineer about when the structure needs to be reinforced, totally replaced or retested for cracks or failures again. An engineer might be wrong (human error) and might delay the test above a duration before which the structure might fail or the engineer might wrongly predict the duration period itself. This can result in catastrophic structural failures and result in either the equipment being shut down / totally replaced or even accidents.

To avoid such errors and to further add continuous monitoring, nano sensors can be placed within the structure itself which can then monitor the structure for local stresses. The combination of local stresses at different point can then give the overall view of stresses in the structure. When nano sensors are placed within the structure itself and are able to send the data to a monitoring computer, it would be able to not only monitor the real time stresses of the structure, but it would also give statistics for how the structure is used, what tasks put the most amount of stresses (and hence fatigue) on the structure. A higher fatigue would mean a higher degradation and early failure of the structure. Such statistics from actual real time monitoring rather than by timed testing can be of more use. As compared to the timed and scheduled testing, real time monitoring will give usage data of each second, enabling the computer to plot a graph of the statistics. This data will help engineers decide how to best use their equipment so that its structure gets minimum fatigue. In short, this will result in optimization and minimum wastage.

This can be easily done by using nano sensors that detect stresses. Piezoelectric materials would be a good category to start looking for the possible implementation materials and designs as they convert compression and tension into electricity (that can be used as the signal for computer to interpret).

R&D around the world

How R&D scores up for different countries.

Smell of new electronic equipment

A question I was asked a few years ago; what is the familiar smell in all electronic stores and in new electronic equipment. I asked some electronic engineers, they didn't know anything specific and had different theories about it. Then I came across a few concepts of electronic materials which I compiled to suggest the most precise reasons possible.

Smell of new electronic equipment (almost similar or atleast recognizable) depends on these major factors:

• Capacitor compounds.
• Lead vapors in small amounts from soldered points.
• Silicone (which is used in coating silicon wafers or protecting/damping circuits) "Cures" itself by reacting with moisture in the air to for acetic acid (smells a bit pungent like car hydraulics).
• Ozone in small amounts (in case they are ON).

(In old and running equipment it might be burning dust.)

...a mixture of above smells in variable quantities attributes to the smell of new electronic equipment. Smell might vary to some extent as the quantity of each factor changes.

Different compounds used in the manufacturing contribute in both old and new equipment. Adding ozone if its on and dust in old or stored new one. It's ozone that makes the rodents afraid to dwell behind the 'ON' electronic equipment. Ozone is toxic for humans too so sleeping while there's something sparking in a circuit board is dangerous.

I think present analyzers have the capacity to check which type of vapours are present in any air sample and this could further be verified.

Why do tubelights make noise?

If you ever wondered why does your tube light or other fluorescent lights make noise (often noticeable in a quiet room and sometimes even in normal background noise in case of old lights). The reason magnetostriction. When current moves through coils or wires, magnetic field is produced with it. This magnetic field causes the material to magnetic and demagnetize (and in case of alternating current (AC) at the frequency of ~50Hz). During the process of magnetization and its reversal, the magnetic domains change their orientation and hence the material changes dimensions to some extent.

This change due to rotation of magnetic domains to align with the magnetic field causes the material to vibrate at hence causing the noise. This is generally the noise that we hear from the tube lights, but one man's limitation is another man's sensor. This effect can be used to create magnetostrictive materials that act as sensors or actuators.

Note (from Wikipedia under creative commons share alike license): Most magnetic materials are polycrystalline, composed of microscopic crystalline grains. These grains are not the same as domains. Each grain is a little crystal, with the crystal lattices of separate grains oriented in random directions. In most materials, each grain is big enough to contain several domains. Each crystal has an "easy" axis of magnetization, and is divided into domains with the axis of magnetization parallel to this axis, in alternate directions.

Why do two parts of a broken magnet repel each other?

When you break a magnet, it often seems that the polarities have flipped.

This doesn't actually happen.

No polarity reversal occurs when you think the poles have flipped

- you are dealing with a magnet that has an axial field 

(pointing out through the flat face.) When you break 
it, each half has similar field, pointing in the same direction, which 
is unstable. One piece will want to flip so that the fields line up 
anti-parallel (lower energy situation).  

Whether the broken magnet attracts or repels each other depends

on how the poles were previously present.

If the original magnet looked like
  +-----------------------------+
N |                             | S
  +-----------------------------+ 

After it's broken, it becomes
  +-----------+     +---------------+
N |           |S   N|               | S
  +-----------+     +---------------+ 

The two broken parts will attract each other.

However, if the original magnet looked like:

(poles on the flat faces of the magnet)

                N
  +--------------------------------+
  |                                |
  +--------------------------------+
                S

After it is broken, it becomes


         N                    N
  +---------------+   +-----------------+
  |               |   |                 |
  +---------------+   +-----------------+
         S                    S

Therefore the two parts will repel each other and will try to invert.

These are only two simple cases. In reality, the poles
of a magnet can be more complicated. This just illustrates how the poles
affect behavior of magnets.