For example human nasal passages are lined with cilia small hairs that sway back and forth to remove dust and other foreign particles.
Others have designed such magnetically actuated materials by infusing polymers with magnetic particles. However Wang says it s difficult to control the distribution and therefore the movement of particles through a polymer.
MIT engineers show their magnetic microhairs in action. Video: Melanie Gonick/MIT Instead she and Zhu chose to manufacture an array of microscopic pillars that uniformly tilt in response to a magnetic field.
or particles move across them. The work might enable new kinds of biomedical or microfluidic devices or solar panels that could automatically clean themselves of dust and grit.
or other forces to move fluids or particles. Varanasi s team decided to use external fields such as magnetic fields to make surfaces active exerting precise control over the behavior of particles
or droplets moving over them. The system makes use of a microtextured surface with bumps
or ridges just a few micrometers across that is then impregnated with a fluid that can be manipulated for example an oil infused with tiny magnetic particles or ferrofluid
When droplets of water or tiny particles are placed on the surface a thin coating of the fluid covers them forming a magnetic cloak.
or particle along as the layer itself is drawn magnetically across the surface. Tiny ferromagnetic particles approximately 10 nanometers in diameter in the ferrofluid could allow precision control
when it s needed such as in a microfluidic device used to test biological or chemical samples by mixing them with a variety of reagents.
While other researchers have developed systems that use magnetism to move particles or fluids these require the material being moved to be magnetic and very strong magnetic fields to move them around.
and particles slide around with virtually no friction needs much less force to move these materials.
The researchers found that by controlling the concentration of electrons in a graphene sheet they could change the way the material responds to a short but intense light pulse.
If the graphene sheet starts out with low electron concentration the pulse increases the material s electrical conductivity.
But if the graphene starts out with high electron concentration the pulse decreases its conductivity the same way that a metal usually behaves.
Therefore by modulating graphene's electron concentration the researchers found that they could effectively alter graphene's photoconductive properties from semiconductorlike to metallike.
The finding also explains the photoresponse of graphene reported previously by different research groups which studied graphene samples with differing concentration of electrons.
We were able to tune the number of electrons in graphene and get either response,
and the bottom electrode the electron concentration of graphene could be tuned. The researchers then illuminated graphene with a strong light pulse and measured the change of electrical conduction by assessing the transmission of a second low-frequency light pulse.
In a surprising finding the team discovered that part of the conductivity reduction at high electron concentration stems from a unique characteristic of graphene:
its electrons travel at a constant speed similar to photons which causes the conductivity to decrease when the electron temperature increases under the illumination of the laser pulse.
Our experiment reveals that the cause of photoconductivity in graphene is very different from that in a normal metal or semiconductors,
when electrically charged cause electrons to create photons of the same wavelength or color traveling in the same direction.
Hepatocytes grab onto these particles because they resemble the fatty droplets that circulate in the blood after a high-fat meal is consumed. he liver is a natural destination for nanoparticles,
The new MIT particles consist of three or more concentric spheres made of short chains of a chemically modified polymer.
and released once the particles enter a target cell. Gene silencing A key feature of the MIT system is that the scientists were able to create a ibraryof many different materials
400 variants of their particles in cervical cancer cells by measuring whether they could turn off a gene coding for a fluorescent protein that had been added to the cells.
With the best-performing particles, the researchers reduced gene expression by more than 50 percent, for a dose of only 0. 20 milligrams per kilogram of solution about one-hundredth of the amount required with existing endothelial
but the particles also successfully delivered RNA to the kidneys and heart, among other organs.
Although the particles did penetrate endothelial cells in the liver, they did not enter liver hepatocytes. hat interesting is that by changing the chemistry of the nanoparticle you can affect delivery to different parts of the body,
The researchers plan to test additional potential targets in hopes that these particles could eventually be deployed to treat cancer, atherosclerosis,
For this project, Hammond and her graduate student, Stephen Morton, devised dozens of candidate particles. The most effective were a type of particle called liposomes spherical droplets surrounded by a fatty outer shell.
The MIT team designed their liposomes to carry doxorubicin inside the particle core, with erlotinib embedded in the outer layer.
The particles are coated with a polymer called PEG, which protects them from being broken down in the body
or filtered out by the liver and kidneys. Another tag folate, helps direct the particles to tumor cells,
which express high quantities of folate receptors. Once the particles reach a tumor and are taken up by cells, the particles start to break down.
Erlotinib, carried in the outer shell, is released first, but doxorubicin release is delayed and takes more time to seep into cells,
giving erlotinib time to weaken the cellsdefenses. here a lag of somewhere between four and 24 hours between
The researchers tested the particles in mice implanted with two types of human tumors: triple-negative breast tumors and non-small-cell lung tumors.
even when those drugs were given in a time-staggered order. his particle delivery system not only provides a platform for time-staggered treatment strategies in cancer,
As a next step before possible clinical trials in human patients, the researchers are now testing the particles in mice that are programmed genetically to develop tumors on their own,
however, extra energy produces extra electrons behavior that could significantly increase solar-cell efficiency. An MIT team has identified now the mechanism by
In most photovoltaic (PV) materials, a photon (a packet of sunlight) delivers energy that excites a molecule,
causing it to release one electron. But when high-energy photons provide more than enough energy,
the molecule still releases just one electron plus waste heat. A few organic molecules don follow that rule.
Instead, they generate more than one electron per high-energy photon. That phenomenon known as singlet exciton fission was identified first in the 1960s.
However, achieving it in a functioning solar cell has proved difficult and the exact mechanism involved has become the subject of intense controversy in the field.
In 2013, they reported making the first solar cell that gives off extra electrons from high-energy visible light,
and devices that take advantage of exciton fission until we understand the fundamental mechanism at work until we know what the electrons are actually doing,
To support his theoretical study of electron behavior within PVS, Van Voorhis used experimental data gathered in samples specially synthesized by Baldo and Timothy Swager, MIT John D. Macarthur Professor of Chemistry.
an electron in an excited molecule swaps places with an electron in an unexcited molecule nearby.
The excited electron brings some energy along and leaves some behind, so that both molecules give off electrons.
The result: one photon in, two electrons out. he simple theory proposed decades ago turns out to explain the behavior,
Van Voorhis says. he controversial, or xotic, mechanisms proposed more recently aren required to explain what being observed here.
the electrons move so quickly that the molecules giving and receiving them don have time to adjust.
and each atom has six to 10 electrons. hese are complicated systems to calculate, Van Voorhis says. hat the reason that 50 years ago they couldn compute these things
Long-term MRIMRI uses magnetic fields and radio waves that interact with protons in the body to produce detailed images of the body s interior.
they also created smaller particles (tens of microns long) that can be injected through a needle.
After injection these particles clump together to form a solid sensor. DDMPS absorbs molecular oxygen
which alters the proton spins inside the silicone a phenomenon that can be detected with MRI.
The knee now used by thousands of patients worldwide utilizes iron particles suspended in oil between steel plates
#Excitons observed in action for the first time A quasiparticle called an exciton responsible for the transfer of energy within devices such as solar cells LEDS
The particles determine how energy moves at the nanoscale. The efficiency of devices such as photovoltaics and LEDS depends on how well excitons move within the material he adds.
An exciton which travels through matter as though it were a particle pairs an electron
which carries a negative charge with a place where an electron has been removed known as a hole. Overall it has a neutral charge
For example in a solar cell an incoming photon may strike an electron kicking it to a higher energy level.
The particles themselves don t move but the boosted energy gets passed along from one to another.
Plants absorb energy from photons and this energy is transferred by excitons to areas where it can be stored in chemical form for later use in supporting the plant s metabolism.
#Tiny particles could help verify goods Some 2 to 5 percent of all international trade involves counterfeit goods, according to a 2013 United nations report.
smartphone-readable particle that they believe could be deployed to help authenticate currency, electronic parts, and luxury goods, among other products.
The particles, which are invisible to the naked eye, contain colored stripes of nanocrystals that glow brightly
These particles can easily be manufactured and integrated into a variety of materials, and can withstand extreme temperatures, sun exposure,
the senior author of a paper describing the particles in the April 13 issue of Nature Materials.
'A massive encoding capacity'The new particles are about 200 microns long and include several stripes of different colored nanocrystals,
To manufacture the particles, the researchers used stop-flow lithography, a technique developed previously by Doyle.
a reaction is set off that forms a solid polymeric particle. In this case, each polymer stream contains nanocrystals that emit different colors,
allowing the researchers to form striped particles. So far, the researchers have created nanocrystals in nine different colors,
With particles that contain six stripes, there are 1 million different possible color combinations; this capacity can be enhanced exponentially by tagging products with more than one particle.
For example, if the researchers created a set of 1, 000 unique particles and then tagged products with any 10 of those particles,
there would be 1030 possible combinations far more than enough to tag every grain of sand On earth. t really a massive encoding capacity,
while on the technical staff at Lincoln Lab. ou can apply different combinations of 10 particles to products from now until long past our time
Versatile particles The microparticles could be dispersed within electronic parts or drug packaging during the manufacturing process,
The researchers demonstrated the versatility of their approach by using two polymers with radically different material properties one hydrophobic and one hydrophilic o make their particles.
suggesting that the process could easily be adapted to many types of products that companies might want to tag with these particles,
Another advantage to these particles is that they can be read without an expensive decoder like those required by most other anti-counterfeiting technologies.
anyone could image the particles after shining near-infrared light on them with a laser pointer. The researchers are also working on a smartphone app that would further process the images
and reveal the exact composition of the particles. The research was funded by the U s. Air force, the Office of the Assistant Secretary of defense for Research and Engineering, the Singapore-MIT Alliance, the National Science Foundation, the U s army Research Office,
Based on Lu graduate school research at MIT, the assay uses biological particles called bacteriophages, or phages,
and for other means across other industries. hages are the most abundant biological particle On earth.
which excites electrons that flow through the thylakoid membranes of the chloroplast. The plant captures this electrical energy
These particles are very strong antioxidants that scavenge oxygen radicals and other highly reactive molecules produced by light
Wrapping the particles in polyacrylic acid a highly charged molecule, allows the particles to penetrate the fatty, hydrophobic membranes that surrounds chloroplasts.
In these chloroplasts, levels of damaging molecules dropped dramatically. Using the same delivery technique, the researchers also embedded semiconducting carbon nanotubes,
photosynthetic activity measured by the rate of electron flow through the thylakoid membranes was 49 percent greater than that in isolated chloroplasts without embedded nanotubes.
and boosted photosynthetic electron flow by about 30 percent. Yet to be discovered is how that extra electron flow influences the plantssugar production. his is a question that we are still trying to answer in the lab:
What is the impact of nanoparticles on the production of chemical fuels like glucose? Giraldo says.
it alters the tube fluorescence. e could someday use these carbon nanotubes to make sensors that detect in real time, at the single-particle level,
and Institute for Medical Engineering and Science is the senior author of a paper describing the particles in the Proceedings of the National Academy of Sciences the week of Feb 24.
These particles congregate at tumor sites where MMPS cleave hundreds of peptides which accumulate in the kidneys
However these instruments are not readily available in the developing world so the researchers adapted the particles
Nonliving particles of similar size and shape show no such effect the team found nor do nonmotile bacteria that are swept along passively by the water.
Previous studies have revealed that when foreign particles such as the dye bind to albumin immune cells in the lymph nodes efficiently capture the albumin. e realized that might be an approach that you could try to copy in a vaccine design a vaccine molecule that binds to albumin
#3-D images with only one photon per pixel Lidar rangefinders which are common tools in surveying
and measuring the time it takes for reflected photons to arrive back and be detected. In this week s issue of the journal Science researchers from MIT s Research Laboratory of Electronics (RLE) describe a new lidar-like system that can gauge depth
when only a single photon is detected from each location. Since a conventional lidar system would require about 100 times as many photons to make depth estimates of similar accuracy under comparable conditions the new system could yield substantial savings in energy and time
which are at a premium in autonomous vehicles trying to avoid collisions. The system can also use the same reflected photons to produce images of a quality that a conventional imaging system would require 900 times as much light to match
and it works much more reliably than lidar in bright sunlight when ambient light can yield misleading readings.
and Computer science and lead author on the new paper explains the very idea of forming an image with only a single photon detected at each pixel location is counterintuitive.
The way a camera senses images is through different numbers of detected photons at different pixels Kirmani says.
Darker regions would have fewer photons and therefore accumulate less charge in the detector while brighter regions would reflect more light
and lead to more detected photons and more charge accumulation. In a conventional lidar system the laser fires pulses of light toward a sequence of discrete positions
and reflected photons are detected that it can rule out the misleading signals produced by stray photons.
The MIT researchers system by contrast fires repeated bursts of light from each position in the grid only until it detects a single reflected photon;
A highly reflective surface one that would show up as light rather than dark in a conventional image should yield a detected photon after fewer bursts than a less-reflective surface would.
So the MIT researchers system produces an initial provisional map of the scene based simply on the number of times the laser has to fire to get a photon back.
Filtering out noisethe photon registered by the detector could however be a stray photodetection generated by background light.
They ve used a very clever set of information-theoretic techniques to extract a lot of information out of just a few photons
Another thing that s really fascinating is that they re also getting intensity information out of a single photon
and then coat it with particles about 100 times smaller. Using that approach, they produced textured surfaces that could be heated to temperatures at least 100 degrees Celsius higher than smooth ones before droplets bounced.
To decouple those two effects, the researchers coated the surface featuring spaced-out microscale posts with nanoscale particles.
This icro-nanosurface texture provides both the extensive surface area of the tiny particles and the wide spacing of the posts to let the vapor flow.
#Self-steering particles go with the flow MIT chemical engineers have designed tiny particles that can teerthemselves along preprogrammed trajectories
Such particles could make it more feasible to design lab-on-a-chip devices, which hold potential as portable diagnostic devices for cancer and other diseases.
Much of that extra instrumentation is needed to keep the particles flowing single file through the center of the channel,
or by flowing two streams of liquid along the outer edges of the channel, forcing the particles to stay in the center.
and takes advantage of hydrodynamic principles that can be exploited simply by altering the shapes of the particles.
when a particle is confined in a narrow channel, it has strong hydrodynamic interactions with both the confining walls and any neighboring particles.
These interactions, which originate from how particles perturb the surrounding fluid, are powerful enough that they can be used to control the particlestrajectory as they flow through the channel.
The MIT researchers realized that they could manipulate these interactions by altering the particlessymmetry. Each of their particles is shaped like a dumbbell
but with a different-size disc at each end. When these asymmetrical particles flow through a narrow channel, the larger disc encounters more resistance,
or drag, forcing the particle to rotate until the larger disc is lagging behind. The asymmetrical particles stay in this slanted orientation as they flow.
Because of this slanted orientation, the particles not only move forward, in the direction of the flow, they also drift toward one side of the channel.
As a particle approaches the wall, the perturbation it creates in the fluid is reflected back by the wall,
just as waves in a pool reflect from its wall. This reflection forces the particle to flip its orientation and move toward the center of the channel.
Slightly asymmetrical particles will overshoot the center and move toward the other wall, then come back toward the center again until they gradually achieve a straight path.
Very asymmetrical particles will approach the center without crossing it, but very slowly. But with just the right amount of asymmetry, a particle will move directly to the centerline in the shortest possible time. ow that we understand how the asymmetry plays a role,
we can tune it to what we want. If you want to focus particles in a given position,
you can achieve that by a fundamental understanding of these hydrodynamic interactions, Eral says. he paper convincingly shown that shape matters,
and swarms can be redirected provided that shapes are designed well, says Patrick Tabeling, a professor at the École Supérieure de Physique et de Chimie Industrielles in Paris,
who was not part of the research team. he new and quite sophisticated mechanism may open new routes for manipulating particles and cells in an elegant manner.
In 2006, Doyle lab developed a way to create huge batches of identical particles made of hydrogel, a spongy polymer.
To create these particles, each thinner than a human hair, the researchers shine ultraviolet light through a mask onto a stream of flowing building blocks,
or oligomers. Wherever the light strikes, solid polymeric particles are formed in the shape of the mask, in a process called photopolymerization.
During this process, the researchers can also load a fluorescent probe such as an antibody at one end of the dumbbell.
The other end is stamped with a barcode a pattern of dots that reveals the particle target molecule.
This type of particle can be useful for diagnosing cancer and other diseases, following customization to detect proteins
scientists can read the fluorescent signal as the particles flow by in single file. elf-steering particles could lead to simplified flow scanners for point-of-care devices,
and measuring a coupling of photons and electrons on the surface of an unusual type of material called a topological insulator.
This type of coupling had been predicted by theorists, but never observed. The researchers suggest that this finding could lead to the creation of materials
Their method involves shooting femtosecond (millionths of a billionth of a second) pulses of mid-infrared light at a sample of material and observing the results with an electron spectrometer, a specialized high-speed camera the team developed.
They demonstrated the existence of a quantum-mechanical mixture of electrons and photons, known as a Floquet-Bloch state, in a crystalline solid.
electrons move in a crystal in a regular, repeating pattern dictated by the periodic structure of the crystal lattice.
Photons are electromagnetic waves that have a distinct, regular frequency; their interaction with matter leads to Floquet states, named after The french mathematician Gaston Floquet. ntanglingelectrons with photons in a coherent manner generates the Floquet-Bloch state,
which is periodic both in time and space. Victor Galitski, a professor of physics at the University of Maryland who was involved not in this research,
The researchers mixed the photons from an intense laser pulse with the exotic surface electrons on a topological insulator.
They also found there were different kinds of mixed states when the polarization of the photons changed.
That actually modifies how electrons move in this system. And when we do this the light does not even get absorbed. g
When the particles encounter thrombin the thrombin cleaves the peptides at a specific location releasing fragments that are excreted then in the animals urine.
Light interaction with graphene produces particles called plasmons while light interacting with hbn produces phonons.
In this so-called low battery, the electrodes are suspensions of tiny particles carried by a liquid
it is composed of a similar semisolid, colloidal suspension of particles. Chiang and Carter refer to this as a emisolid battery. impler manufacturing processthis approach greatly simplifies manufacturing,
Having the electrode in the form of tiny suspended particles instead of consolidated slabs greatly reduces the path length for charged particles as they move through the material a property known as ortuosity.
maybe they could use our particles as well, Brandl says. hen we came up with the idea to use our particles to remove toxic chemicals, pollutants,
or hormones from water, because we saw that the particles aggregate once you irradiate them with UV LIGHT. trap for ater-fearingpollutionthe researchers synthesized polymers from polyethylene glycol,
a widely used compound found in laxatives, toothpaste, and eye drops and approved by the Food and Drug Administration as a food additive,
the stabilizing outer shell of the particles is shed, and now nrichedby the pollutants they form larger aggregates that can then be removed through filtration, sedimentation,
The unmatched speed at which it can move electrons plus its essentially two-dimensional form factor make it an attractive alternative
By demonstrating a new way to change the amount of electrons that reside in a given region within a piece of graphene they have a proof-of-principle in making the fundamental building blocks of semiconductor devices using the 2-D material.
because its charge-carrier density the number of free electrons it contains can be increased easily
or gain electrons to cancel out those charges but we've come up with a third way.
or gaining electrons the graphene says'I can hold the electrons for you and they'll be right nearby.'
and the possibility of waveguiding lensing and periodically manipulating electrons confined in an atomically thin material.
but semiconductors allow a measure of control over those electrons. Since modern electronics are all about control,
The researchers have used the technique to determine that materials with a highly organized structure at the nanoscale are not more efficient at creating free electrons than poorly organized structures#a finding
First the cell absorbs sunlight which excites electrons in the active layer of the cell.
Each excited electron leaves behind a hole in the active layer. The electron and hole is called collectively an exciton.
In the second step called diffusion the exciton hops around until it encounters an interface with another organic material in the active layer.
During dissociation the exciton breaks apart freeing the electron and respective hole. In step four called charge collection the free electron makes its way through the active layer to a point where it can be harvested.
In previous organic solar cell research there was ambiguity about whether differences in efficiency were due to dissociation or charge collection#because there was no clear method for distinguishing between the two.
Was a material inefficient at dissociating excitons into free electrons? Or was the material just making it hard for free electrons to find their way out?
To address these questions the researchers developed a method that takes advantage of a particular characteristic of light:
and it tells us that we don't need highly ordered nanostructures for efficient free electron generation.
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