Nanotechnology Quantum Computing Global Communications Network


id28229Published on Jul 28, 2013

A fascinating applied Nanotechnology engineering documentary where current research for a quantum computer based global communications network is described. Just another example of how the applications derived from advances in quantum physics and the understanding of quantum mechanics will very soon be changing our everyday lives!

 

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When fluid dynamics mimic quantum mechanics


MIT researchers expand the range of quantum behaviors that can be replicated in fluidic systems, offering a new perspective on wave-particle duality.

Larry Hardesty, MIT News Office     July 29, 2013

When fluid dynamics mimic quantum mechanics

                            Image: Dan Harris  
When the waves are confined to a circular corral, they reflect back on themselves, producing complex patterns (grey ripples) that steer the droplet in an apparently random trajectory (white line). But in fact, the droplet’s motion follows statistical patterns determined by the wavelength of the waves.
In the early days of quantum physics, in an attempt to explain the wavelike behavior of quantum particles, the French physicist Louis de Broglie proposed what he called a “pilot wave” theory. According to de Broglie, moving particles — such as electrons, or the photons in a beam of light — are borne along on waves of some type, like driftwood on a tide.
Physicists’ inability to detect de Broglie’s posited waves led them, for the most part, to abandon pilot-wave theory. Recently, however, a real pilot-wave system has been discovered, in which a drop of fluid bounces across a vibrating fluid bath, propelled by waves produced by its own collisions.
In 2006, Yves Couder and Emmanuel Fort, physicists at Université Paris Diderot, used this system to reproduce one of the most famous experiments in quantum physics: the so-called “double-slit” experiment, in which particles are fired at a screen through a barrier with two holes in it.
In the latest issue of the journal Physical Review E (PRE), a team of MIT researchers, in collaboration with Couder and his colleagues, report that they have produced the fluidic analogue of another classic quantum experiment, in which electrons are confined to a circular “corral” by a ring of ions. In the new experiments, bouncing drops of fluid mimicked the electrons’ statistical behavior with remarkable accuracy.
“This hydrodynamic system is subtle, and extraordinarily rich in terms of mathematical modeling,” says John Bush, a professor of applied mathematics at MIT and corresponding author on the new paper. “It’s the first pilot-wave system discovered and gives insight into how rational quantum dynamics might work, were such a thing to exist.”
Joining Bush on the PRE paper are lead author Daniel Harris, a graduate student in mathematics at MIT; Couder and Fort; and Julien Moukhtar, also of Université Paris Diderot. In a separate pair of papers, appearing this month in the Journal of Fluid Mechanics, Bush and Jan Molacek, another MIT graduate student in mathematics, explain the fluid mechanics that underlie the system’s behavior.
Interference inference
The double-slit experiment is seminal because it offers the clearest demonstration of wave-particle duality: As the theoretical physicist Richard Feynman once put it, “Any other situation in quantum mechanics, it turns out, can always be explained by saying, ‘You remember the case of the experiment with the two holes? It’s the same thing.’”If a wave traveling on the surface of water strikes a barrier with two slits in it, two waves will emerge on the other side. Where the crests of those waves intersect, they form a larger wave; where a crest intersects with a trough, the fluid is still. A bank of pressure sensors struck by the waves would register an “interference pattern” — a series of alternating light and dark bands indicating where the waves reinforced or canceled each other.

Photons fired through a screen with two holes in it produce a similar interference pattern — even when they’re fired one at a time. That’s wave-particle duality: the mathematics of wave mechanics explains the statistical behavior of moving particles.
In the experiments reported in PRE, the researchers mounted a shallow tray with a circular depression in it on a vibrating stand. They filled the tray with a silicone oil and began vibrating it at a rate just below that required to produce surface waves.
They then dropped a single droplet of the same oil into the bath. The droplet bounced up and down, producing waves that pushed it along the surface.
The waves generated by the bouncing droplet reflected off the corral walls, confining the droplet within the circle and interfering with each other to create complicated patterns. As the droplet bounced off the waves, its motion appeared to be entirely random, but over time, it proved to favor certain regions of the bath over others.
It was found most frequently near the center of the circle, then, with slowly diminishing frequency, in concentric rings whose distance from each other was determined by the wavelength of the pilot wave.
The statistical description of the droplet’s location is analogous to that of an electron confined to a circular quantum corral and has a similar, wavelike form.
“It’s a great result,” says Paul Milewski, a math professor at the University of Bath, in England, who specializes in fluid mechanics. “Given the number of quantum-mechanical analogues of this mechanical system already shown, it’s not an enormous surprise that the corral experiment also behaves like quantum mechanics. But they’ve done an amazingly careful job, because it takes very accurate measurements over a very long time of this droplet bouncing to get this probability distribution.”
“If you have a system that is deterministic and is what we call in the business ‘chaotic,’ or sensitive to initial conditions, sensitive to perturbations, then it can behave probabilistically,” Milewski continues. “Experiments like this weren’t available to the giants of quantum mechanics. They also didn’t know anything about chaos.
Suppose these guys — who were puzzled by why the world behaves in this strange probabilistic way — actually had access to experiments like this and had the knowledge of chaos, would they have come up with an equivalent, deterministic theory of quantum mechanics, which is not the current one? That’s what I find exciting from the quantum perspective.”

Nanotechnology – Producing the Quantum computer


Published on May 25, 2013

http://youtu.be/To55y5wPsdU

 

201306047919620

Nanotechnology. The production of the quantum computer based on the quantum spin of electrons and its application to calculation, computing and technology!

Watch here; Nanotechnology Documentary – Quantum Computing, what it is, how it works!

 

New qubit control bodes well for future of quantum computing


QDOTS imagesCAKXSY1K 8January  11, 2013

Yale University scientists have found a way to observe quantum information while preserving its integrity, an achievement that offers researchers greater control in the volatile realm of quantum mechanics and greatly improves the prospects of quantum computing.

Quantum computers would be exponentially faster than the most powerful computers of today.

“Our experiment is a dress rehearsal for a type of process essential for quantum computing,” said Michel Devoret, the Frederick William Beinecke Professor of Applied Physics & Physics at Yale and principal investigator of research published Jan. 11 in the journal Science. “What this experiment really allows is an active understanding of quantum mechanics. It’s one thing to stare at a theoretical formula and it’s another thing to be able to control a real quantum object.”

In quantum systems, microscopic units called qubits represent information. Qubits can assume either of two states — “0” or “1” — or both simultaneously. Correctly recognizing, interpreting, and tracking their state is necessary for quantum computing. However, the act of monitoring them usually damages their information content.

The Yale physicists successfully devised a new, non-destructive measurement system for observing, tracking and documenting all changes in a qubit’s state, thus preserving the qubit’s informational value. In principle, the scientists said, this should allow them to monitor the qubit’s state in order to correct for random errors.

“As long as you know what error process has occurred, you can correct,” Devoret said. “And then everything’s fine. You can basically undo the errors.”

qubits_0An innovation by Yale University physicists offers scientists greater control in the volatile realm of quantum mechanics and greatly improves the prospects of quantum computing. Quantum computers would be exponentially faster than the most powerful computers oftoday.

“That’s the key,” said Michael Hatridge, a postdoctoral associate in physics at Yale and lead author of the Science paper, “the ability to talk to the qubit and hear what it’s telling you.”

 

He continued: “A major problem with quantum computing is the finite lifetime of information stored in the qubits, which steadily decays and which must be corrected. We now know that it is possible to do this correction by feedback involving a continuous measurement. Our work advances the prospects of large-scale quantum computers by opening the door to continuous measurement-based quantum feedback.”

The Yale physicists successfully measured one qubit. The challenge ahead is to measure and control many at once, and the team is developing ultra-fast digital electronics for this purpose.

“We are on the threshold between the ability to measure and control one or two qubits, and many,” Hatridge said.

Other authors of the paper are S. Shankar, M. Mirrahimi, F. Schackert, K. Geerlings, T. Brecht, K.M. Sliwa, B. Abdo, L. Frunzio, S.M. Girvin, and R.J. Schoelkopf.

Support for the research was provided by the National Science Foundation, the United States Army Research Office, the Intelligence Advanced Research Projects Activity, the Agence National de Recherche, and the College de France.

Photoluminescent SiC tetrapods


qdot-imagescaf658qe-4.jpgAndrew P. Magyar, Igor Aharonovich, Mor Baram, Evelyn L. Hu

(Submitted on 29 Nov 2012)

Photoluminescent SiC tetrapods

Abstract: Recently, significant research efforts have been made to develop complex nanostructures to provide more sophisticated control over the optical and electronic properties of nanomaterials. However, there are only a handful of semiconductors which allow control over their geometry via simple chemical processes. Here, we present a molecularly seeded synthesis of a complex nanostructure, SiC tetrapods, and report on their structural and optical properties. The SiC tetrapods exhibit narrow linewidth photoluminescence at wavelengths spanning the visible to near infrared spectral range. Synthesized from low-toxicity, earth abundant elements, these tetrapods are a compelling replacement for technologically important quantum optical materials that frequently require toxic metals such as Cd and Se. This new, previously unknown geometry of SiC nanostructures is a compelling platform for biolabeling, sensing, spintronics and optoelectronics.

Comments: 14 pages, 4 figures
Subjects: Materials Science (cond-mat.mtrl-sci)
Cite as: arXiv:1211.6801 [cond-mat.mtrl-sci]
(or arXiv:1211.6801v1 [cond-mat.mtrl-sci] for this version)

Submission history

From: Andrew Magyar [view email] [v1] Thu, 29 Nov 2012 02:50:49 GMT  (1877kb,D)

Tetrapod Quantum Dots: The Future is Now


Mr Stephen Squires, CEO
Quantum Materials Corporation
United States
This presentation will be given at Printed Electronics USA 2012 on Dec 05, 2012.

Presentation Summary

A software controlled flow chemistry process for mass synthesis of high quantum yield inorganic Group II-VI Tetrapod Quantum Dots (TQD) is being developed that will scale to produce Kilogram quantities per day. These TQD are notable for their 90+% conversion for full tetrapod shape, equally high uniformity and selectivity of arm length and width (vital for electron transport). Tetrapod Quantum Dots are recognized as having superior characteristics among quantum dot shapes.
In addition, QMC has the exclusive worldwide license to quantum dot printing technologies developed by our CSO, Dr. Ghassan Jabbour, that have wide applications in R2R printed electronics and thin-film solar cell production.
We will discuss how the timeline for Quantum Dot applications is moving from the future to the present.

Speaker Biography (Stephen Squires)

Mr. Squires is the Chief Executive Officer for both Quantum Materials Corporation and it’s subsidiary, Solterra Renewable Technologies, Inc. He has over 25 years’ experience in advanced materials, nanotechnology and other emerging technologies. Prior to QMC/SRT, Stephen consulted on these fields with emphasis on applications engineering, strategic planning, commercialization and marketing.
From 1983 to 2001, Mr. Squires was Founder and CEO of Aviation Composite Technologies Inc., which he grew to have over 200 employees. ACT was merged with USDR Aerospace in 2001. He subsequently founded what is now Quantum Materials Corporation because of his lifelong interest in advanced materials, nanoparticles and Quantum Dots, with a vision to realize the potential of their unique quantum features.
Quantum Materials Corporations goal is to help Companies provide better technology at lower price points that are affordable in a mass marketplace. At the same time, he formed Solterra Renewable Technologies to create mass produced thin-film quantum dot solar cells using patented R2R printing technologies.

Nanoparticles for Molecular Imaging


by Professor Andrew Tsourkas

Professor Andrew Tsourkas, Cellular and Molecular Imaging LabDepartment of BioengineeringUniversity of Pennsylvania
Corresponding author: atsourk@seas.upenn.edu

Over the past decade there has been an explosion in the number of nanotechnology-based agents that have been applied to biological and medical applications. It is generally believed that these agents will revolutionize how medicine is practiced. One particularly promising direction that has garnered a great deal of interest is molecular imaging.

The development of nanotechnology-based imaging probes offers to substantially improve the specificity and sensitivity of diagnostic imaging by allowing for the non-invasive and quantitative detection of specific biomolecules in living subjects.

In general, molecular imaging probes consist of a nanoparticle that has been functionalized with a targeting agent. The targeting agent is typically selected to recognize a disease biomarker located on the cell surface;1-4 however, probes have also been developed that strictly bind healthy tissue, thus leaving malignancies within target tissues unlabeled.5-7 In either case, the nanoparticles serve to enhance the contrast between malignant and benign tissue.

Interest in the use of nanoparticles stems from their ability to provide improved contrast compared with more traditional contrast agents and the ability to control their pharmacokinetics through variations of their size, surface properties, and shape.8 The strong contrast enhancing capabilities of nanoparticles can typically be attributed to atomic constraints that occur at the nanometer size-scale and/or the cumulative effect that results from packing many contrast agents into nanometer-sized particles.

For example, when iron oxide particles are synthesized at the nanometer-size scale they exhibit “superparamagnetic” properties because they can exist as single-domain crystals. In contrast, larger iron oxide particles generally consist of multiple magnetic domains that are aligned in the short range, but at longer distances the domains are anti-aligned and thus exhibit a reduced net magnetic effect per iron ion.

As a result, on a per iron ion basis, nano-sized iron oxide particles are generally able to generate more contrast on magnetic resonance images than larger micron-sized nanoparticles. Of course, the total iron content cannot be ignored. Since, micron-sized iron oxide particles are composed of significantly more iron ions than nanoparticles, they exhibit much stronger MR contrast on a per particle basis. This has allowed single micron-sized particles to be imaged via MR.9

To date, most nanoparticles that have been developed for magnetic resonance imaging applications have been characterized in terms of their relaxivity per ion (e.g. Fe, Gd, etc). Although this is certainly of great value, it can be argued that for molecular imaging applications it is even more important to calculate relaxivity on a per particle basis. For example, if a tumor cell has ten receptors on its surface, the binding of ten micron-sized particles of iron oxide would certainly provide more contrast than ten nanoparticles, even though the smaller nanoparticles would likely have a higher relaxivity per iron ion than the micron-sized particle.

This argument is, of course, not limited to iron oxide particles. A recent comparison that we made between Gd-labeled dendrimers and Gd-labeled dendrimer nanoclusters (DNCs) also highlights the importance of calculating the relaxivity per nanoparticle.1 In this study, Gd-labeled DNCs were formed by simply cross-linking Gd-labeled dendrimers into a higher-order structure, with a mean hydrodynamic diameter of ~150nm. While both the dendrimers and DNCs exhibited a similar relaxivity per Gd ion, the DNCs possessed >1,000-times more Gd per particle. As a result of this higher payload, the tumor-targeted Gd-labeled DNCs provided a dramatic improvement in contrast compared with Gd-labeled dendrimers, in tumor-bearing mice.

Aside from the contrast-enhancing capabilities of molecular imaging agents, it is also of critical importance to characterize the pharmacokinetics of new nanoparticle formulations. Particle size, shape, and charge are all known to be major driving forces responsible for dictating the blood half-life and biodistribution.

In general, nanoparticles at the length scale of ~10-100nm have generally exhibited longer circulations times and improved tissue penetration than micron-sized particles. These pharmacokinetic properties can lead to improved targeting and in many cases can be used to overcome the lower contrast-enhancing capabilities of smaller particles – hence the growing interest in using nanoparticles as opposed to micron-sized particle for molecular imaging applications.

In applications where long circulation times and additional contrast is not necessary, there has even been a movement to make molecular imaging probes that are <5.5nm in diameter to encourage renal filtration.10 This would allow for more rapid imaging, since unbound nanoparticles would be cleared much faster, and reduced toxicity for the same reasons.

In addition to the physical-chemical properties of the nanoparticle itself, the targeting agent also plays an instrumental role in the utility of nanoparticle-based contrast agents. For the most part, targeting agents that have been evaluated for molecular imaging applications have mirrored those used for targeted therapeutics (e.g. folic acid, transferrin, anti-HER2/neu antibodies, etc.).

For cancer imaging, these agents have shown a great deal of promise when used to assess the availability of therapeutic targets and monitor the efficacy of treatment; however, tumor cell receptors are unlikely to be adopted for diagnostic imaging due to the lack of any single receptor that is highly up-regulated across most tumors.

For diagnostic imaging, a biomarker that is universally present would have to be identified for clinical utility. Borrowing from FDG-PET imaging, one option that is being explored involves taking advantage of the increased metabolic rate of cancer cells and the resultant acidic microenvironment. Accordingly, various agents are being developed that specifically bind to cells that exist in subphysiologic pH.11 Since, an acidic microenvironment is common to most tumors, it is expected that tumor pH could serve as a more universal target. Ligands that target angiogeneisis or hypoxia could also potentially be utilized to expand the versatility of targeted molecular imaging probes. Of course, when biomarkers with increased universality are selected, it often comes at the cost of reduced specificity – a criticism that has often plagued FDG-PET.

In conclusion, nanoparticles have shown great promise as molecular imaging probes. However, as the number of nanoparticle formulations continues to expand it will be increasingly important to establish proper indices by which they can be compared. It will also be important to develop creative targeting strategies that can be used to identify disease with high sensitivity and high predictive value.


References

1. Cheng Z, Thorek DL, Tsourkas A. Gadolinium-conjugated dendrimer nanoclusters as a tumor-targeted T1 magnetic resonance imaging contrast agent. Angew Chem Int Ed Engl. 2010;49(2):346-50.
2. Thorek DL, Chen AK, Czupryna J, Tsourkas A. Superparamagnetic iron oxide nanoparticle probes for molecular imaging. Ann Biomed Eng. 2006 Jan;34(1):23-38.
3. Tsourkas A, Shinde-Patil VR, Kelly KA, Patel P, Wolley A, Allport JR, Weissleder R. In vivo imaging of activated endothelium using an anti-VCAM-1 magnetooptical probe. Bioconjug Chem. 2005 May-Jun;16(3):576-81.
4. Zhang CY, Lu J, Tsourkas A. Iron chelator-based amplification strategy for improved targeting of transferrin receptor with SPIO. Cancer Biol Ther. 2008 Jun;7(6):889-95.
5. Montet X, Weissleder R, Josephson L. Imaging pancreatic cancer with a peptide-nanoparticle conjugate targeted to normal pancreas. Bioconjug Chem. 2006 Jul-Aug;17(4):905-11.
6. Reimer P, Weissleder R, Shen T, Knoefel WT, Brady TJ. Pancreatic receptors: initial feasibility studies with a targeted contrast agent for MR imaging. Radiology. 1994 Nov;193(2):527-31.
7. Tanimoto A, Kuribayashi S. Hepatocyte-targeted MR contrast agents: contrast enhanced detection of liver cancer in diffusely damaged liver. Magn Reson Med Sci. 2005;4(2):53-60.
8. Moghimi SM, Hamad I. Factors Controlling Pharmacokinetics of Intravenously Injected Nanoparticulate Systems. In: de Villiers MM, Aramwit P, Kwon GS, editors. Nanotechnology in Drug Delivery. New York: Springer; 2009. p. 267-82.
9. Shapiro EM, Skrtic S, Sharer K, Hill JM, Dunbar CE, Koretsky AP. MRI detection of single particles for cellular imaging. Proc Natl Acad Sci U S A. 2004 Jul 27;101(30):10901-6.
10. Choi HS, Liu W, Misra P, Tanaka E, Zimmer JP, Itty Ipe B, Bawendi MG, Frangioni JV. Renal clearance of quantum dots. Nat Biotechnol. 2007 Oct;25(10):1165-70.
11. Reshetnyak YK, Andreev OA, Lehnert U, Engelman DM. Translocation of molecules into cells by pH-dependent insertion of a transmembrane helix. Proc Natl Acad Sci U S A. 2006 Apr 25;103(17):6460-5.

Copyright AZoNano.com, Professor Andrew Tsourkas (University of Pennsylvania)

Nanotechnology and MRI imaging


October 17, 2012 by tildabarliya

Author: Tilda Barliya PhD via Pharmaceutical Intelligence: http://pharmaceuticalintelligence.com/2012/10/17/nanotechnology-and-mri-imaging/

The recent advances of “molecular and medical imaging” as an integrated discipline in academic medical centers has set the stage for an evolutionary leap in diagnostic imaging and therapy. Molecular imaging is not a substitute for the traditional process of image formation and interpretation, but is intended to improve diagnostic accuracy and sensitivity.

Medical imaging technologies allow for the rapid diagnosis and evaluation of a wide range of pathologies. In order to increase their sensitivity and utility, many imaging technologies such as CT and MRI rely on intravenously administered contrast agents. While the current generation of contrast agents has enabled rapid diagnosis, they still suffer from many undesirable drawbacks including a lack of tissue specificity and systemic toxicity issues. Through advances made in nanotechnology and materials science, researchers are now creating a new generation of contrast agents that overcome many of these challenges, and are capable of providing more sensitive and specific information (1)

Magnetic resonance imaging (MRI) contrast enhancement for molecular imaging takes advantage of superb and tunable magnetic properties of engineered magnetic nanoparticles, while a range of surface chemistry offered by nanoparticles provides multifunctional capabilities for image-directed drug delivery. In parallel with the fast growing research in nanotechnology and nanomedicine, the continuous advance of MRI technology and the rapid expansion of MRI applications in the clinical environment further promote the research in this area.

It is well known that magnetic nanoparticles, distributed in a magnetic field, create extremely large microscopic field gradients. These microscopic field gradients cause substantial diphase and shortening of longitudinal relaxation time (T1) and transverse relaxation time (T2 and T2*) of nearby nuclei, e.g., proton in the case of most MRI applications. The magnitudes of MRI contrast enhancement over clinically approved conventional gadolinium chelate contrast agents combined with functionalities of biomarker specific targeting enable the early detection of diseases at the molecular and cellular levels with engineered magnetic nanoparticles. While the effort in developing new engineered magnetic nanoparticles and constructs with new chemistry, synthesis, and functionalization approaches continues to grow, the importance of specific material designs and proper selection of imaging methods have been increasingly recognized (2)

Earlier investigations have shown that the MRI contrast enhancement by magnetic nanoparticles is highly related to their composition, size, surface properties, and the degree of aggregation in the biological environment.

Therefore, understanding the relationships between these intrinsic parameters and relaxivities of nuclei under influence of magnetic nanoparticles can provide critical information for predicting the properties of engineered magnetic nanoparticles and enhancing their performance in the MRI based theranostic applications. On the other hand, new contrast mechanisms and imaging strategies can be applied based on the novel properties of engineered magnetic nanoparticles. The most common MRI sequences, such as the spin echo (SE) or fast spin echo (FSE) imaging and gradient echo (GRE), have been widely used for imaging of magnetic nanoparticles due to their common availabilities on commercial MRI scanners. In order to minimize the artificial effect of contrast agents and provide a promising tool to quantify the amount of imaging probe and drug delivery vehicles in specific sites, some special MRI methods, such as  have been developed recently to take maximum advantage of engineered magnetic NPs

  • off-resonance saturation (ORS) imaging
  • ultrashort echo time (UTE) imaging

Because one of the major limitations of MRI is its relative low sensitivity, the strategies of combining MRI with other highly sensitive, but less anatomically informative imaging modalities such as positron emission tomography (PET) and NIRF imaging, are extensively investigated. The complementary strengths from different imaging methods can be realized by using engineered magnetic nanoparticles via surface modifications and functionalizations. In order to combine optical or nuclear with MR for multimodal imaging, optical dyes and radio-isotope labeled tracer molecules are conjugated onto the moiety of magnetic nanoparticles

Since most functionalities assembled by magnetic nanoparticles are accomplished by the surface modifications, the chemical and physical properties of nanoparticle surface as well as surface coating materials have considerable effects on the function and ability of MRI contrast enhancement of the nanoparticle core.

The longitudinal and transverse relaxivities, Ri (i=1, 2), defined as the relaxation rate per unit concentration (e.g., millimole per liter) of magnetic ions, reflects the efficiency of contrast enhancement by the magnetic nanoparticles as MRI contrast agents. In general, the relaxivities are determined, but not limited, by three key aspects of the magnetic nanoparticles:

  1. Chemical composition,
  2. Size of the particle or construct and the degree of their aggregation
  3. Surface properties that can be manipulated by the modification and functionalization.

(It is also recognized that the shape of the nanoparticles can affect the relaxivities and contrast enhancement. However these shaped particles typically have increased sizes, which may limit their in vivo applications. Nevertheless, these novel magnetic nanomaterials are increasingly attractive and currently under investigation for their applications in MRI and image-directed drug delivery).

Composition Effect: The composition of magnetic nanoparticles can significantly affect the contrast enhancing capability of nanoparticles because it dominates the magnetic moment at the atomic level. For instance, the magnetic moments of the iron oxide nanoparticles, mostly used nanoparticulate T2 weighted MRI contrast agents, can be changed by incorporating other metal ions into the iron oxide.  The composition of magnetic nanoparticles can significantly affect the contrast enhancing capability of nanoparticles because it dominates the magnetic moment at the atomic level. For instance, the magnetic moments of the iron oxide nanoparticles, mostly used nanoparticulate T2 weighted MRI contrast agents, can be changed by incorporating other metal ions into the iron oxide.

Size Effect: The dependence of relaxation rates on the particle size has been widely studied both theoretically and experimentally. Generally the accelerated diphase, often described by the R2* in magnetically inhomogeneous environment induced by magnetic nanoparticles, is predicted into two different regimes. For the relatively small nanoparticles, proton diffusion between particles is much faster than the resonance frequency shift. This resulted in the relative independence of T2 on echo time. The values for R2 and R2*are predicted to be identical. This process is called “motional averaging regime” (MAR). It has been well demonstrated that the saturation magnetization Ms increases with the particle size. A linear relationship is predicted between Ms1/3 and d-1. Therefore, the capability of MRI signal enhancement by nanoparticles correlates directly with the particle size. 

Surface Effect: MRI contrast comes from the signal difference between water molecules residing in different environments that are under the effect of magnetic nanoparticles. Because the interactions between water and the magnetic nanoparticles occur primarily on the surface of the nanoparticles, surface properties of magnetic nanoparticles play important roles in their magnetic properties and the efficiency of MRI contrast enhancement. As most biocompatible magnetic nanoparticles developed for in vivo applications need to be stabilized and functionalized with coating materials, the coating moieties can affect the relaxation of water molecules in various forms, such as diffusion, hydration and hydrogen binding.

The early investigation carried at by Duan et al suggested that hydrophilic surface coating contributes greatly to the resulted MRI contrast effect. Their study examined the proton relaxivities of iron oxide nanocrystals coated by copolymers with different levels of hydrophilicity including: poly(maleic acid) and octadecene (PMO), poly(ethylene glycol) grated polyethylenimine (PEG-g-PEI), and hyperbranched polyethylenimine (PEI). It was found that proton relaxivities of those IONPs depend on the surface hydrophilicity and coating thickness in addition to the coordination chemistry of inner capping ligands and the particle size.

The thickness of surface coating materials also contributed to the relaxivity and contrast effect of the magnetic nanoparticles. Generally, the measured T2 relaxation time increases as molecular weight of PEG increases.

In Summary

Much progress has taken place in the theranostic applications of engineered magnetic nanoparticles, especially in MR imaging technologies and nanomaterials development. As the feasibilities of magnetic nanoparticles for molecular imaging and drug delivery have been demonstrated by a great number of studies in the past decade, MRI guiding and monitoring techniques are desired to improve the disease specific diagnosis and efficacy of therapeutics. Continuous effort and development are expected to be focused on further improvement of the sensitivity and quantifications of magnetic nanoparticles in vivo for theranostics in future.

The new design and preparation of magnetic nanoparticles need to carefully consider the parameters determining the relaxivities of the nanoconstructs. Sensitive and reliable MRI methods have to be established for the quantitative detection of magnetic nanoparticles. The new generations of magnetic nanoparticles will be made not only based on the new chemistry and biological applications, but also with combined knowledge of contrast mechanisms and MRI technologies and capabilities. As new magnetic nanoparticles are available for theranostic applications, it is anticipated that new contrast mechanism and MR imaging strategies can be developed based on the novel properties of engineered magnetic nanoparticles.

References:

1http://www.omicsonline.org/2157-7439/2157-7439-2-115.php

2http://www.clinical-mri.com/pdf/CMRI/8036XXP14Ap454-472.PDF

3http://www.thno.org/v02p0086.htm

4http://www.omicsonline.org/2157-7439/2157-7439-2-115.pdf

5http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3017480/

6http://www.nature.com/nmeth/journal/v7/n12/full/nmeth1210-957.html

7http://endomagnetics.com/wp-content/uploads/2011/01/TargOncol_Review_2009.pdf

8http://www.nature.com/nnano/journal/v2/n5/abs/nnano.2007.105.html

9http://www.azonano.com/article.aspx?ArticleID=2680

Towards Quantum Dot Lasers with Temperature Independent Threshold


October 9, 2012 By 

Towards Quantum Dot Lasers with Temperature Independent Threshold

October 9, 2012 By  Leave a Comment

Quantum Dots-in-Rods

 

 

 

 

 

 

Among the numerous applications envisioned for semiconductor nanocrystals, quantum dot lasers are one of the most interesting. In contrast to bulk materials, the delta-like density of quantum dot electronic states predicts a low, temperature-independent lasing threshold. This gives enhanced device performance compared to other gain media, especially at elevated temperatures. Quantum dots grown by epitaxial techniques have proven to be suitable candidates for potential commercialization of quantum dot lasers. However, colloidal quantum dots offer an interesting low-cost alternative, being synthesized through wet chemistry at low temperature and standard pressure.

Now, Iwan Moreels, Gabriele Rainò (IBM Research – Zurich), and co-workers have successfully produced colloidal CdSe/CdS quantum dot-in-rods with an almost constant amplified stimulated emission threshold over a temperature interval from 5–325 K. This feature is unique to quantum dots and highlights their potential as a gain material, suitable for lasing at elevated temperatures. These results will pave the way towards low cost, solution processable quantum dot lasers.

The research was reported in Advanced Optical Materials, a new section in Advanced Materialsdedicated to breakthrough discoveries and fundamental research in photonics, plasmonics, metamaterials, and more, covering all aspects of light-matter interactions. To get Advanced Optical Materials email alerts click here.