NANOPARTIKEL FOR BRAIN.pdf

8/12/2019 NANOPARTIKEL FOR BRAIN.pdf

1/5

MAY 2006 | VOLUME 1 | NUMBER 2

RESEARCH NEW

Using nanoparticles (NPs) for drug delivery of

anticancer agents has significant advantagessuch as the ability to target specific locations in

the body, the reduction of the overall quantity

of drug used, and the potential to reduce the

concentration of the drug at nontarget sites

resulting in fewer unpleasant side effects.

For intravenously injected particles,

biocompatibility is the first issue. The second is

to promote specific carrier-target interactions

or devise specific carrier physicochemical

properties to enable selective targeting. Recent

research has made advances on both fronts.

Researchers from Harvard Medical School,

Massachusetts Institute of Technology (MIT),

MIT-Harvard Center for Cancer NanotechnologyExcellence, and Gwangju Institute of Science

and Technology in Korea have reported the

successful use of targeted NP-aptamer

bioconjugates for in vivochemotherapy

[Farokhzad et al., Proc. Natl. Acad. Sci. USA

(2006) 103, 6315]. The aim of the joint effort of

Omid C. Farokhzad and Robert Langers groups

was to design a system able to target cancer

cells specifically, introduce chemotherapy drugs

directly into the cells and release them over

time, and avoid uptake by noncancerous cells.

To achieve this, the researchers devised a NP-based system using biodegradable and

biocompatible poly(D,L-lactic-co-glycolic acid).

An anticancer drug, in this case docetaxel (Dtxl),

is encapsulated in the 150 nm NPs. The surface

of the NPs is then functionalized with aptamers

(Apt) nucleic acid ligands that promote cell-

specific uptake by binding to target antigens,

analogous to antibodies. In this case, the RNA

aptamers that recognize the prostate-specific

membrane antigen (PSMA), which is expressed

by prostate cancer cells, are used. The NPs are

also functionalized with poly(ethylene glycol)

(PEG) to reduce uptake by tissue macrophagesand nontargeted cells. The polymeric NPs

dissolve slowly once inside the cancerous cell,

releasing the Dtxl. The rate of dissolution can be

designed into the system so that drugs are

released over a predetermined time.

After a single administration of the Dtxl-NP-Apt

bioconjugates into mice, which had been

implanted with human prostate cancer cell

lines, five out of seven animals showed

complete tumor reduction and all survived the

109-day study. The ability to treat tumors in

one go is particularly attractive. Early diagnosis

of cancer creates the opportunity for localized

treatment options, explains Farokhzad.Since all of the components of the NP-based

system, except the RNA aptamers, are already

approved by the Food and Drug Administration

for clinical use, Farokhzad is confident that such

NP-based treatment systems could be feasible

in the near future, not only for cancer but other

diseases as well. As Langer explains, [we] can

put different things inside or on the outside of

the NPs. This technology can be applied to

almost any disease.

Cordelia Sealy

Nanoparticles target cancer cells in vivoNANOPARTICLES

Nanoparticles turn up the heatNANOPARTICLES

Researchers from Ohio University have developed a

novel way of studying the heat generated by metal

nanoparticles (NPs), especially Au, under optical

illumination. [Richardson et al., Nano Lett. (2006) 6,

783].

We wanted to understand how much heat can be

generated locally by nanoscale metal NPs when

illuminated with light, explains Alexander O. Govorov.

By using an ice matrix and observing the melting

effect, Hugh H. Richardson and coworkers were able to

characterize the heat generated by Au NPs.This heat can be so intense that the melting of the

ice matrix looks like a nano-explosion, says Govorov.

The researchers found a strong dependence of the

melting effect on position, which they believe is the

result of the NPs with different geometries forming

complexes. Since each geometry has a unique thermal

response, this leads to an overall mesoscopic character

for the heat generation. The heat generation is also

enhanced in a collection of NPs.

The heat generation capabilities of NPs have been

suggested for several applications, including protein

labeling for all-optical imaging, fabricating composites

with novel thermal and optical properties, remote

release of drugs when excited by light, and

photothermal therapy for cancer treatment. This last

application has been the focus of much research in the

medical field. Recently, researchers from Georgia

Institute of Technology and the University of

California at San Francisco have found that Au

nanoparticles can be made to absorb and scatter much

more strongly in the near-infrared region if they are

rod-shaped [Huang et al.,J. Am. Chem. Soc. (2006)

128, 2115]. The Au nanorods are synthesized and

conjugated to anti-epidermal growth factor receptor

monoclonal antibodies so that they bind onto thesurface of malignant cancer cells. The bound nanorods

make the malignant cells clearly visible when observed

in dark field, using a laboratory microscope. The

malignant cells also require only about half the laser

energy required to destroy nonmalignant cells

photothermally. The use of Au nanorods allows both

effective cancer cell diagnosis and photothermal

therapy, say the researchers.

Cordelia Sealy

A model of Au NPs excited with laser light andresults of calculated temperature increase for acomplex of 16 NPs (left). A surface map of the iceusing Raman spectroscopy. A crater on the surfaceof the ice after massive heat generation from AuNPs is visible (right). (Courtesy of Alexander O.Govorov.)

Prostate cancer cells that have taken upfluorescently labeled NPs (red) and can releasechemotherapy drugs. The cells nuclei andcytoskeletons are stained blue and green.(Courtesy of Benjamin A. Teply.)


2/5


RESEARCH NEWS

Itamar Willner and colleagues at the Hebrew

University of Jersusalem, Israel have devised an

alternative to the polymerase chain reaction (PCR) for

the amplified detection of DNA [Weizmann et al.,

Angew. Chem. Int. Ed. (2006) 45, 2238].

PCR is the standard method for amplifying nucleic

acids for analysis, diagnosis, and manipulation. It is thekey that has advanced genome research, genetic

engineering, and DNA analysis. However, the PCR

process suffers from basic limitations, as it is error

prone, requires long analysis time intervals, and the

quantification of the analyzed DNA is limited,

explains Willner.

This led the researchers to design and demonstrate

another method based on a DNA/enzyme machine

that, on detection of a specific target sequence, is

activated to devour a supply of DNA fuel, giving a

fluorescent waste product and a further machine. The

formation of more DNA-cutting machines accelerates

further cleavage of the fuel, amplifying the fluorescent

signal that is produced, so it is large enough to be

detected.

The researchers demonstrate the potential of theirsystem by detecting one of the genetic mutations

characteristic of Tay-Sachs disease. The disease is fatal

in early childhood and the defective gene is thought to

be carried by 1 in 30 Ashkenazi Jews. The system was

able to detect the mutation with a sensitivity limit of

10 fM. The normal sequence gives a much smaller

signal even at micromolar levels, and other DNA

sequences give no detectable signal at all.

Despite this ultrahigh sensitivity, the researchers note

a saturation in fluorescent signal. Changes of orders of

magnitude in the concentration of the mutated

sequence are observed as only relatively small changes

in the evolved fluorescence.

The practical applications of such systems are

enormous, says Willner. DNA machines may be used

for the rapid analysis of pathogens or geneticdisorders. We believe that the development... is a

general, new scientific paradigm.

The group is already developing simpler and more

effective machines. Furthermore, the method is not

limited to DNA sensing. The machines can be

conjugated to protein antigen/antibody complexes to

provide a whole new sensing area for bioanalytics,

Willner told Nano Today.

Jonathan Wood

Biomolecular machine provides alternative to PCRNANOBIOTECHNOLOGY

Technique images proteins in living cell membranesCHARACTERIZATION

A scanning probe microscopy technique has been

adapted by a group of UK and US researchers to

allow the imaging of individual protein complexeson the surfaces of live cells [Shevchuk et al.,

Angew. Chem. Int. Ed. (2006) 45, 2212]. The

advance should open up new areas of membrane

biology, say the researchers from the University

of Cambridge, Imperial College London, The

Babraham Institute, Ionscope, and the University

of Kentucky.

There has been a great deal effort to use

scanning probe microscopies to image proteins

and structures on live cells directly, but without

much success since the cell surface is both soft

and responsive, explains David Klenerman of the

University of Cambridge.

The team adapted a technique called scanning ionconductance microscopy (SICM) developed by

Paul Hansma and colleagues, improving the

resolution by an order of magnitude.

We believe [this] to be a major breakthrough,

says Klenerman. While such experiments have

been proposed ever since scanning probe

microscopy was developed 25 years ago, this is

the first time that they have been achieved. This

is not an iterative improvement in resolution but

a quantum step, since it allows individual protein

complexes to be imaged directly on the

membrane of live cells and their dynamics to be

followed.

A nanoscale pipette is used as the scanning probein SICM, and the ion current between an

electrode in the pipette and an electrode in the

sample chamber is used as the feedback control.

The probe senses a reduction in ion current when

a surface is encountered within a hemisphereextending from the pipette tip with the same

radius as the pipettes inner radius. This means

that sensing is both vertical and lateral under the

tip, helping to prevent the pipette walls from

touching the cell surface.

Quartz pipettes with an inner diameter of 13 nm

were used in a SICM system with enhanced

mechanical stability and custom-designed

software. The resolution of the instrument was

tested by imaging a monolayer of bacterial

proteins arranged in a square lattice with a

spacing of 13.1 nm. The individual protein

molecules are clearly identifiable, and a fast

Fourier transform of the image indicates that thelateral resolution is ~3-6 nm.

Having determined the capabilities of their SICM

setup, the group imaged the plasma membranes

of sperm cells. Under certain conditions, these

cells exhibit protrusions that are generallythought to be transmembrane proteins or protein

complexes. SICM could visualize these

protrusions, showing two populations with

diameters of ~14 nm and ~30 nm in size. The

researchers observations reveal that a small

number of these proteins diffuse, disappear, or

appear over time in the cell surface, showing the

SICM technique can also follow changes in

membrane structure.

The next steps are to continue to improve the

instrument both hardware and software and

exploit the new capabilities to follow biological

processes on live cells down to the level of single

molecules, says Klenerman.Jonathan Wood

SICM images of protein complexes in the surface of a sperm cell membrane. The images in (a) are taken10 min apart. Areas where the position and shape of the proteins change over time are circled. By coloringthe two images red and green, then overlapping them (b), the changes are immediately apparent.( 2006 Wiley-VCH.)

(a) (b)


3/5


RESEARCH NEW

Researchers from the University of

Chicago and Argonne National

Laboratory believe that they have

revealed the mechanism for the self

assembly of large areas of nanocrystal

monolayers [Bigioni et al., Nat. Mater.

(2006) 5, 265].

A lacy coffee-stain-like ring of material

with clumps of particles is usually left

behind when a drop of a colloidal

solution of nanoparticles (NPs) dries

on a surface. However, an alternative

drying behavior that produces highly

uniform, long-range-orderednanocrystal monolayers is possible. In

this regime, the morphology of a NP

film is controlled by evaporation

kinetics and particle interactions with

the liquid-air interface. At the start of

the process, a saturated two-

dimensional solution of NPs forms at

the liquid-air interface. Monolayer

islands of nanocrystals form on the top

surface of the drop, which grow and

merge to form a continuous

monolayer over the entire liquid-air

interface. Unlike ordinary two-dimensional growth, the islands show

exponential and linear growth

behaviors. This creates monolayers

with exceptional long-range order and

an extraordinary degree of perfection

(of up to 108 particles), say the

researchers. The monolayer shows no

lace- or ring-like patterns and no

clumps of particles. The researchers

suggest two requirements for such

highly ordered self-assembly: (1) rapid

evaporation (to segregate particles

near the liquid-air interface); and

(2) an attractive interaction between

the particles and liquid-air interface

(to localize them on the interface).

This drop-dry self-assembly method is

simple, robust, scalable, and insensitive

to substrate material or topography,

making it an excellent candidate for

the fabrication of ultrathin films.

Cordelia Sealy

Self-assembly

leaves no stainNANOPARTICLES

Blood compatibility is a vital

property for biomedical devices

intended for use in vivo.

Researchers from Rensselaer

Polytechnic Institute (RPI) and

Albany College of Pharmacy

have developed blood-

compatible carbon nanotubes

that could form the basis of

new generations of nanodevicesfor medical applications

[Murugesan et al., Langmuir

(2006) 22, 3461].

The design of blood-compatible devices primarily relies on

the immobilization of the glycosaminoglycan (GAG) heparin

on their surfaces. Proteoglycans (PGs), consisting of a core

protein to which multiple GAG chains are linked, have

essential physiological, biochemical, and structural functions

within the body. Consequently, the researchers combined

these structures with carbon

nanotubes. We applied some

activation-coupling chemistry,

which we had previously

developed for the preparation of

blood-compatible plastics, to

carbon nanotubes, explains

Robert J. Linhardt of RPI. The

researchers replaced the core

protein of PGs with multiwalledcarbon nanotubes (MWNTs) and

heparinized the material in a

three-stage process.

We believe this represents a new enabling technology in the

field of nanomedicine, says Linhardt. It could be useful for

artificial or reconstruction of blood vessels, blood-compatible

dialyzers, and drug delivery systems. The researchers are now

undertaking in vivoanimal studies.

Cordelia Sealy

Designing in blood compatibilityCARBON NANOTUBES

Nanorice combines best of both worlds

NANOPARTICLES

The plasmonic properties of metallic

nanostructures, where light interacts

with free electrons giving rise to

collective oscillations of charge density,

are attracting interest for a range of

applications. However, the rational

design and control of nanostructures

with structurally tunable plasmon

resonances and large, well-defined

optical fields is needed for real devices.

There are two current approaches,

both of which produce structures with

two tunable plasmon resonances:

cylindrical nanoparticles, or nanorods,

and dielectric core-metal shell

nanoparticles, or nanoshells.Researchers from Rice University

have devised a hybrid nanoparticle

geometry that combines the plasmonic

properties of both nanorods and

nanoshells [Wang et al., Nano Lett.

(2006) 6, 827].

The rice-shaped nanoparticle consists

of a hematite dielectric core with a

nanometer-thick Au shell. We [grew] a

thin, homogeneous Au shell around a hematite particle

to create a layered nanostructure with a shape known

as a prolate spheroid, explains Naomi J. Halas. The

strong resemblance of the resulting

particles to grains of rice earned them

their moniker. Nanorice are special

particles because they truly are

hybrids, combining the tunable

plasmon properties of nanoshells with

the high field focusing shape of

nanorods in a single particle, says

Halas. The results indicate that

plasmon tunability arising from

variation in the shell thickness is far

more geometrically sensitive than

that arising from variation of the

length of the nanorice. Furthermore,

the plasmon modes of nanorice can be

tuned across a broader spectral rangethan either nanorods or nanoshells.

The strong, tunable local fields make

nanorice suitable for surface-

enhanced spectroscopy sensing

substrates. The optical properties of

these nanoparticles are ideal for

sensing applications, says Halas.

Nanorice has advantages for

spectroscopic sensing and

characterization of large biomolecules, like proteins and

DNA, or biological samples.

Cordelia Sealy

Schematic of Au-coated hematitenanostructure (top). Transmissionelectron micrograph of nanorice(middle). Calculated localelectromagnetic field for nanoriceilluminated at its plasmon resonantfrequency by light polarized in thelongitudinal axis of the structure(bottom). [Credit: Hui Wang andFei Lee, Rice University.]

(Image courtesy of Robert J. Linhardt.)


4/5


RESEARCH NEW

Both the size and shape of Au nanoparticles (NPs)

affects their uptake by mammalian cells, according

to research from the University of Toronto,

Canada [Chithrani et al., Nano Lett. (2006) 6,

662]. The findings could influence the design of

more complex NPs being developed for biomedical

applications.

Fine-tuning the properties of NPs generally

involves altering their size and shape. However,

little is known about how such structural

reengineering can alter the nanostructures

interactions with cells. But measures that promote or

impede cellular uptake could have importantimplications for the efficacy of biomedical applications.

This information could also help inform toxicity

studies.

Previously, researchers just looked at targeting

molecules on the surface of the nanostructures to

dictate uptake, says Warren C. W. Chan. It was

speculated that size and shape may influence how

nanostructures go into cells. However, no one

conducted a full study.

Chan and colleagues performed their investigations on

spherical and rod-shaped colloidal Au NPs 14-100 nm

in diameter. The nanostructures were incubated for6 hours with HeLa cells in solution containing growth

medium and 10% serum. Cellular uptake of the NPs

can be observed using transmission electron

microscopy (TEM). Concentrations of Au within the

cells were measured using inductively coupled plasma

atomic emission spectroscopy.

A comparison of differently sized nanostructures

reveals that the HeLa cells accept more 50 nm

particles than any other. The greatest number of

50 nm NPs entering a cell was over 6000, whereas

maximum uptake for 14 nm and

74 nm sized NPs was only around 3000. The team

also observed significant variations in uptake

concentration for differently-shaped particles. For

instance, HeLa cells ingested 500% more 74 nm

spherical NPs and 375% more 14 nm spherical

NPs compared with the same size rod-shaped

particles.

Chan acknowledges that alternative nanostructure-

cell combinations could yield quite different results.

Uptake mechanisms could hinge on the number of

receptors that certain cells have and how thosereceptors are clustered. The nature of molecules bound

to different NPs could also influence uptake processes.

All these variables need to be investigated.

This is the first study, Chan told Nano Today. We

really have to develop a full understanding of the

interface between nanostructures and biological

systems to develop knowledge of how to design these

nanostructures for biology.

Paula Gould

Size matters to cell uptake but so does shapeNANOPARTICLES

Nanofiber scaffold repairs brain tissue

BIOMATERIALS

Researchers from Massachusetts Institute of

Technology, University of Hong Kong, and the

Fourth Military Medical University, Xian, China,have used a self-assembling peptide scaffold to

repair severed brain structures in blind rodents

and restore their sight [Ellis-Behnke et al., Proc.

Natl. Acad. Sci. USA (2006) 103, 5054].

The findings indicate that similar scaffolds could

be used to restore some critical functionality in

human victims of traumatic brain injury.

Restoring functionality, such as speech or sight,

following damage to the central nervous system

involves promoting the regrowth of branch-like

axons. Broken neuronal connections, which carry

out vital communications, can then be reinstated.

However, this is typically hampered by the

formation of scar tissue, the emergence of gaps in

nervous tissue, and the failure of many adult

neurons to initiate axonal extension.

The researchers opted to use a highly hydrated

nanofiber scaffold, formed spontaneously from

peptides, to create an environment conducive to

axon regeneration. They severed the optic nerve

of immature and adult hamsters, then injected

1% peptide scaffold solution directly into the

injury site. Subsequent follow-up revealed that

the gaps in the brain tissue had closed up and

axons had regrown across the lesion sites.

Behavioral studies on the treated adult rodents

indicated that six out of eight could respond to

visual cues. The two nonresponders had suffered

vascular injury during surgery. The treated groups

vision improved as testing progressed, indicating

the value of long-term rehabilitation.

The peptide scaffold has several advantages that

make it particularly suited to brain repair,

according to Rutledge G. Ellis-Behnke. The self-

assembling material can fill the voids of anirregular cut, brain cells migrate into the scaffold,

it is biodegradable (disappearing from the brain

within about four weeks), and does not appear to

provoke a significant immune response.

While the material has considerable clinical

potential, research is needed to optimize the

scaffold formulation and understand how it might

be administered to patients with severe traumatic

brain injuries, says Ellis-Behnke. The team is taking

a two-pronged approach. A study of chronic injury

will assess the scaffolds performance in healing

optic nerves that have been severed and left for

up to a month. A second series of experiments will

look more specifically at stroke.

If we can reconnect parts of the brain that were

disconnected by a stroke, then we may be able to

restore speech to an individual who is able to

understand what is said, but has lost the ability to

speak, says Ellis-Behnke. This is not about

restoring 100% of damaged brain cells, but 20%

or even less may be enough to restore function,

and that is our goal.

Paula Gould

Photo of a section from the brain of an 8-month-old hamster treated with a self-assembling peptidenanofiber scaffold at the time of surgery. Theaxons, shown by green fluorescence, have regrownthrough the cut and have formed functionalconnections at approximately 82% of normal

density. (Courtesy of Rutledge G. Ellis-Behnke.)

TEM images of Au nanoparticles with diameters of (a) 14 nm and(b) 50 nm in cells. (Courtesy of B. Devika Chithrani.)

(a) (b)


5/5


RESEARCH NEW

Researchers from the University of

Zaragoza in Spain suggest that

inorganic materials, such as silica, can

offer the properties needed for

nanoparticle (NP)-based drug delivery,

namely nontoxicity, biocompatibility,

high stability, and a hydrophilic and

porous structure useful for tailoring

the encapsulation of drugs [Arruebo

et al., Chem. Mater. (2006), 18, 1911].

We have developed silica particles

belonging to the MCM family, as well

as hollow silica microcapsules,

explains Jesus Santamara. Fe is

deposited inside the porous structure

of the particles and microcapsules in

order to obtain magnetic drug-delivery

vectors. This enables the particles and

capsules to be targeted to specific

locations, such as a diseased organ, by

a magnetic field.

Both types of silica structure are small

enough to be transported through the

vascular system. The release rate from

the silica structures could be

controlled by adjusting their size and

porous structure, suggests Santamara.The magnetic material is embedded

inside the silica matrix, which has

advantages in minimizing potential

side effects.

The researchers are undertaking in vivo

animal studies and drug diffusion

studies in simulated body fluids.

Cordelia Sealy

Silica key to

drug deliveryNANOPARTICLES

ZnO nanoparticles damage E. coli

TOXICOLOGY

Many concerns have been raised

about the impact ofnanoengineered materials on

the environment, so a study

showing that ZnO nanoparticles

can damage Escherichia colicells

is likely to be the center of

considerable scrutiny [Brayner

et al., Nano Lett. (2006) 6, 866].

The ZnO nanoparticles (NPs)

used in the study are very similar to a semiconducting,

crystalline form of TiO2 that is approved for use in

sunscreens. TiO2 anatase has a band gap of 3.23 eV,

while the gap for ZnO is 3.3 eV. Both materials can

reflect and scatter ultraviolet (UV) A and B light. In

addition, ZnO is of interest for a variety ofapplications in the microelectronics industry,

including sensors, photocatalysis, solar cells,

transparent electrodes, electroluminescent devices,

and laser diodes.

Researchers from the University of Paris 7 and the

Museum of Natural History, Paris synthesized ZnO

NPs in di(ethylene glycol) medium by forced hydrolysis

of Zn2+ salts. Small molecules and macromolecules

were added to control the size and shape of NPs. Their

size, shape, and morphology were characterized by

transmission electron microscopy (TEM) and X-ray

diffraction. Then the team

incubated E. coliovernight insolutions of ZnO NPs with

differing concentrations

(10-2 M to 10-4 M).

Subsequent TEM analysis

shows that lower

concentrations of ZnO NPs

induce no damage in E. coli

cells. However, internalization

of NPs within E. colicells and some cell leakage was

observed at concentrations higher than 1.3 x 10-3 M.

Internalization of ZnO NPs may be influenced by the

attached molecules and macromolecules that were

added to control size, says Roberta Brayner. The

majority of NPs used by industry are stabilized bymolecules such as phosphines or surfactants such as

sodium decylsulfate. These molecules can be toxic to

living cells and the environment, she says. Very few

studies have been done on the toxicological impact of

these new hybrid nanomaterials.

The researchers are also carrying out conductometric

studies of cell content release, examining the effect of

varying particulate size, shape, and concentration on

bacterial growth, and looking at the mechanism of

cellular internalization.

Paula Gould

E. coli cells seen before (a) and after (b) contactwith ZnO NPs. (Courtesy of Roberta Brayner.)

(a) (b)

The increased production of nanoparticles (NPs) is making it

more likely that such materials will end up in watercourses,

either as medical or industrial waste, or when used as

ecological tools, with unknown consequences for aquatic life.

Now, research has shown that both TiO2 and fullerene NPS

can be harmful to the freshwater zooplankton Daphnia magna

[Lovern and Klaper, Environ. Toxicol. Chem. (2006) 25, 1132].

The researchers from the University of Wisconsin-Milwaukee

used two alternative methods to prepare C60 and TiO2 NPs:

filtration in tetrahydrofuran and sonication. The average

diameter of the TiO2 particles is 10-20 nm, while that of C60is 0.72 nm. Groups of young D. magnawere then exposed to

four test solutions with varying concentrations of NPs. The

number of D. magnastill alive in each solution after 1 hour,

24 hours, and 48 hours was assessed.

Exposure to both filtered C60 and TiO2 caused mortality in the

zooplankton. Filtered C60 proved to be lethal at much lower

concentrations than TiO2, confirming suspicions that smaller

particles could be more harmful. The method of NP

preparation also appeared to affect toxicity. Solutions of

unfiltered, sonicated TiO2 had little observable effect, even at

high concentrations. Mortality rates for sonicated C60fluctuated considerably, rather than increasing steadily with

concentration. The findings can be explained by the greater

spread of particle size in unfiltered solutions and the tendency

for particulate clumping, the researchers suggest.

The results should be useful to those seeking to establish

guidelines for nanoparticle handling and disposal, says Sarah B.

Lovern. Daphniaare a great species to study because they

have been used in toxicity tests for many other chemicals. So

the results of this study can be compared to other studies ofpotentially harmful compounds, she says. The researchers are

now focusing on other, nonlethal effects that fullerene and

TiO2 NPs may have on aquatic organisms, as well as

investigating other materials.

Mortality is important, but Daphniachange their behavior

when a contaminant is present in a body of water. These

changes in behavior may make them more likely to be preyed

upon by fish and could affect the food web, she says.

Paula Gould

Zooplankton suffer under nanoparticle exposureTOXICOLOGY

Correction

In the February issue of NanoToday, we mistakenly stated

that the half-life of 18F is 11 min

[Nano Today(2006) 1 (1), 13] ,

as the result of a typographical

error. The correct half-life is

110 min. We thank Douglas

Smyth of the Royal Adelaide

Hospital in Australia for bringing

this to our attention.

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NANOPARTIKEL FOR BRAIN.pdf