optoelectronic world

 

Delivered through another SMP-based interventional de- REFERENCE a catheter vice, they believe that human trials could 1. W. Small et al., Optics Express 13( 20) (Oct. 3, The researchers deliver the SMP micro- begin 12 to 18 months after reaching a li- ^2005). actuator in its straight rod form through censing agreement, according to Small.

^{ILENE SCHNEIDER is a freelance writer living in} a catheter near the vascular occlusion, Ilene Schneider Irvine, CA; e-mail: ischnei440@aol.com. located by fluoroscopy that is routinely used in stroke treatment. The polyure-thane-based SMP device is connected to PHOTOVOLTAICS a diode laser that emits 4. 89 W at 810 nm.

Immersed in water at body temperature, Nanocrystal solar cells combine the polymer changes shape when irradi- organic and inorganic qualities ated, from a straight rod into a 10-mm- long spiral structure with a maximum In hopes of eventually generating power from photovoltaic materials that are both diameter of 3 mm in just three seconds . environmentally stable and low cost, researchers at Lawrence Berkeley National The device is then retracted and the blood Laboratory and the University of California at Berkeley have combined desirable clot removed from the body. characteristics of organic and inorganic solar cells using inorganic nanocrystals

The corkscrew shape was chosen to in colloidal solution. maintain the waveguiding ability of the Nanometer-size crystals of cadmium selenide (CdSe) and cadmium telluride SMP microactuator while providing a (Cd Te) were synthesized and spin cast in separate layers from filtered pyridine means for capturing a blood clot (see solutions to create ultrathin flexible films of the semiconductor nanocrystals figure). The researchers estimate that on a substrate of indium tin oxide (ITO) glass coated with 2 Å of alumina. laser heating of the SMP polymer would Donor-acceptor, type-II heterojunctions, typical of organic materials (as op- raise the temperature of the surround- posed to conventional p-n junctions of inorganic materials) were created by ing blood by approximately 12°C, to alternately juxtaposing Cd Te and CdSe layers on the substrate. Annealing the 49°C, which can be sustained for about Cd Te layer for 15 minutes at

SMP microactuator. ers achieved photovoltaic
The work was performed under the conversion efficiency in the
auspices of the U.S. Department of prototype device of almost 3%, which is good for organic materials but an order
Energy by LLNL and supported by the of magnitude below efficiencies achievable with conventional inorganic photo-
National Institutes of Health/National voltaic materials. While hoping to eventually improve efficiency, however, the re-
Institute of Biomedical Imaging and searchers view the current demonstration as an important first step.
Bioengineering. Currently, the group is “Our colloidal inorganic nanocrystals share all of the primary advantages
discussing its technology with medical of organics—scalable and controlled synthesis, an ability to be processed in
device manufacturers and plans to con- solution, and a decreased sensitivity to substitutional doping—while retaining
duct animal studies to further evaluate the broadband absorption and superior transport properties of traditional
the technique. photovoltaic semiconductors,” said Ilan Gur, lead author of a paper in Science
The researchers expect to make modi- on the work and a doctoral candidate in the research group of Paul Alivisatos,
fications including a sheath around the who directs the Materials Science Division at Lawrence Berkeley National
optical fiber for easier manipulation, Laboratory (LBNL; Berkeley, CA). ¹
radio-opacity for visualization under flu- Hassaun A. Jones-Bey
oroscopic guidance, and a method of se-
curing the captured clot after retraction
for withdrawal from the body. Based on
the researchers’ previous experience with

15 minutes without causing permanent 200°C prior to deposition of tissue damage. the CdSe layer, minimized

The scientists have tested the device mixing at the interface. with an in vitro feasibility study using Both nanocrystal layers an artificial blood clot made of an acryl- (CdSe and Cd Te) are electri- amide hydrogel inserted into an experi- cal insulators in the absence mental water-filled model of a carotid ar- of light, whereas full-sun il- tery with a 60° bifurcation. The polymer lumination decreased re- microactuator device was pushed into sistance in each layer by at the artificial clot, activated, and used to least an order of magnitude pull back the occlusion against the flow. and increased conductivity

The scientists used thermal imaging and in the bilayered device by computer simulation to characterize the more than three orders of optical and photothermal behavior of the magnitude. The research-

 

REFERENCE

11. I. Gur, N.A. Fromer, M.L. Geier, A.P. Alivisatos, Science 310, 462 (Oct. 21, 2005).