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to the surface and appear dark. When theresearchers expose the sensor to an aque-ous stream containing a protein that bindsto lipids, the liquid crystal moleculesrespond within seconds by switching to aplanar orientation. Viewed under a micro-scope, the crystals then transmit polarizedlight and appear bright.

“This is a beautiful example of how onecan use novel materials to create a signal,”says Chad Mirkin, a chemist at North-western University in Evanston, Ill.

By adding different receptors to thelipids, researchers can tune the sensor todetect specific molecules. For instance,when Abbott and his colleagues attached areceptor called biotin to the lipids, the sen-sor detected a bacterial protein that bindsto biotin. The researchers describe theirresults in the Dec. 19 Science.

Abbott’s team has made sensors out ofliquid crystals before (SN: 8/18/01, p. 103),but those sensors didn’t include membranecomponents. When attached to fluid lipidmolecules, receptors can move about freelyinstead of being fixed in one place.

“That becomes important for bindingthings like viruses,” which attach to severalreceptors at once on cell surfaces, saysAbbott. Mobile receptors in the artificialsensors can reorganize to bind specific tar-gets just as receptors in a cell do.

Because the sensors don’t require elec-tric power, Abbott envisions deploying net-works of coin-size devices for long-termmonitoring in the field. Researchers couldshine a laser on the sensors to determine theorientation of the liquid crystals. SaysAbbott: “You could interrogate the sensorsfrom 1,000 feet away on the ground or froma helicopter.”

Although the sensitivity of the new sen-sor is not yet as high as that of others indevelopment, the device is part of a newgeneration of inexpensive, sophisticated

sensors, says Mirkin. Existing sensors arenot sufficient in this new era of homelandsecurity, he adds.

The Wisconsin group is currentlyincreasing the sensitivity of its device andfocusing on detecting dangerous molecules,such as cholera toxins and chemical andbiowarfare agents. —A. GOHO

Bones of InventionGerman cave yields Stone Age figurines

Excavations in caves in southwesternGermany are carving out a new chapter inart prehistory. Most recently, researcherssifting through dirt that had been dug outof the Hohle Fels cave uncovered three tinyfigurines that were sculpted from mam-moth ivory between 35,000 and 30,000years ago.

The figurines, each nearlyas long as athumb,depict ahorse’s head, aduck or someother waterbird,and a half-lion,half-human crea-ture.

Along with themore than a dozen ivory figurines andother artifacts discovered decades ago atthree nearby Stone Age cave sites, the newspecimens belong to one of the oldestknown art traditions in the world, saysproject director Nicholas J. Conard of theUniversity of Tübingen in Germany.

“Southwestern Germany was probablyone of several centers of ancient figurativeart,” Conard says. The new German findscome from a time when artwork began toflourish in Europe. Conard’s report on thefigurines appears in the Dec. 18/25 Nature.

Three different laboratories producedradiocarbon dates for animal bones andcharcoal at the four caves. Although no fos-sils of Homo sapiens or Neandertals haveturned up at these locations, Conard sus-pects that people entered the region around40,000 years ago and subsequently pro-duced the figurines. Animal remains andivory-working debris in Hohle Fels and theother German caves indicate that they wereoccupied repeatedly in the winter and spring.

According to Conard, the new figurinessupport the controversial theory that a siz-able portion of prehistoric artwork reflectsshamans’ supernatural rituals (SN: 10/5/96,p. 216). The half-man, half-lion figure—thesecond such sculpture found in southwest-ern Germany—fits with the belief that

shamans can transform into certain ani-mals, he notes. Also, traditional societiesoften regard water birds as spirits that ushershamans into supernatural worlds.

There are several sites in Europe andAfrica harboring roughly 30,000-year-oldrock and cave art, although some research-ers now contend that a couple of the Euro-pean locations may be only 15,000 to20,000 years old.

Even so, the newly found figurines chal-lenge the view that ancient art in Europegradually evolved from simple origins,archaeologist Anthony Sinclair of the Uni-versity of Liverpool in England remarks ina commentary accompanying Conard’sreport. “The first modern humans inEurope were, in fact, astonishingly preco-cious artists,” he writes.

The German finds suggest that Stone Ageart began with realistic depictions of theworld and evolved toward other modes ofexpression, such as the use of geometricdesigns, remarks archaeologist Steven Kuhnof the University of Arizona in Tucson.

The motiva-tions of Stone

Age people forcreating the Hohle Fels

figurines remain hazy, Kuhn adds.To detect the objects’ purposes,

researchers must unearth more sculpturesalong with evidence about how the arti-facts were used, he says.

It’s intriguing that at least some peopleliving 30,000 years ago spent a lot of timecreating figurines, says anthropologist

Mark Collard of Washington State Univer-sity in Pullman. Only large groups withsecure food supplies could have supportedsuch activity, he theorizes. —B. BOWER

Gel Bots?Vibrated goo mimicsslithery motions

A physicist’s hunch about snail locomotionis inspiring a new way to make robots—fromgoop. Experiments show that matchstick-size slivers of hydrogel, the type of materialused for soft contact lenses, can ooze alonglike snails, slither like snakes, and creepahead like inchworms.

Greatly miniaturized robots made ofhydrogel might someday shimmy across thesurfaces of microchips, acting as tiny deliv-ery carts or movable barriers. Some incar-nations might glide through a person’sintestines or other internal cavities collect-ing medical data or dispensing medication,the experimenters say.

Biomechanics specialists have longknown that snails and other limbless crea-tures locomote by sending waves of mus-cular contractions down their bodies. To

LIQUID SWIRL Inside this gold grid, each tinysquare of liquid crystal measures 280 micronsacross and is topped with lipid membranes.The crystals polarize light and change fromdark (left) to a colorful soap-bubble appearance(right) when exposed to a target molecule.

FLIGHTY FIND AGerman cave yieldedthree 30,000-year-oldivory figurines, includingthis water bird.

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