New sensor derived from frogs may help fight bacteria and save wildlife

Oct 19, 2010
An electronic chip developed by the Princeton engineers is coated with antimicrobial peptides from the skin of an African frog. When the peptides come in contact with bacterial contaminates the chip generates an electric signal as a warning. Credit: Photo: Frank Wojciechowski

Princeton engineers have developed a sensor that may revolutionize how drugs and medical devices are tested for contamination, and in the process also help ensure the survival of two species of threatened animals.

To be fair, some of the credit goes to an African frog.

In the wild, the African clawed frog produces antibacterial peptides -- small chains of -- on its skin to protect it from infection. Princeton researchers have found a way to attach these peptides, which can be synthesized in the laboratory, to a small electronic chip that emits an electrical signal when exposed to harmful bacteria, including pathogenic E. coli and salmonella.

"It's a robust, simple platform," said Michael McAlpine, an assistant professor of mechanical and aerospace engineering and the lead researcher on the project. "We think these chips could replace the current method of testing medical devices and drugs."

A paper outlining their development of the sensor was published online October 18 in the Proceedings of the National Academy of Science. The research was funded by the American Asthma Foundation and by the Air Force Office of Scientific Research.

The current testing method has a major drawback: It relies on the blood of the horseshoe crab, a species that is roughly 450 million years old. The horseshoe crab population has declined in recent years, and as a result, so too has the population of a bird that feasts on the crab.

The crab became desirable for testing because its immune system has evolved to cope with the constant threat of invasion from its bacteria-rich environment. Its blood contains antimicrobial cells, known as amebocytes, that defend the crab against bacteria -- similar to the way the peptides protect the African frog's skin.

For almost 40 years, an aqueous extract made from horseshoe crab blood cells, called Limulus amebocyte lysate (LAL), has been used for testing drugs and medical devices for contamination.

In the era before the use of these animal extracts for testing, although drugs and were sterilized, they would sometimes cause patients to develop fevers due to an immune reaction to endotoxins, which are remnants of bacteria destroyed by the sterilization process. When a sample from a drug or device is added to LAL and the solution hardens into a gel, it indicates the sample is contaminated and not safe for human use.

New approach could help save animal populations

To produce LAL, the crabs are captured and roughly 30 percent of their blood drained before they are returned to the ocean. There is disagreement on how many crabs die as a result of the procedure, but their estimated mortality rate can be as high as 30 percent, according to the United States Geological Survey.

A conservative estimate puts the number of horseshoe crabs on the Atlantic Coast between New Jersey and Virginia at between 2.3 to 4.5 million, according to the Ecological Research & Development Group. In recent years, the populations of the horseshoe crab and shore birds that rely on them for food both have been in decline, with the red knot, a rust-colored species of shore bird, of particular concern.

Princeton engineers, assistant professor Micheal McAlpine and graduate student Manu Mannoor, have developed an electronic chip that may replace horseshoe crab blood for testing drugs and medical devices for contamination and could relieve pressure on two threatened species of animals. Credit: Photo: Frank Wojciechowski

Each spring the bird migrates 20,000 miles from the islands of Tierra del Fuego, off the southern tip of South America, to the Delaware Bay on the east coast of the United States. From April to May, the bird feasts on horseshoe crab eggs found on beaches, nearly doubling its body weight to sustain its health for the long flight south.

Studies have discovered a precipitous decline in the red knot population. One study by researchers at the University of Toronto found that the Tierra del Fuego population of red knots declined from 53,000 birds to 27,000 birds between 2000 and 2002. The decline has been linked to the reduction in the number of horseshoe crabs, as a result of harvesting their blood for medical testing and their use as fishing bait for eel and conch.

In response, Delaware, Maryland and New York have limited the number of crabs that can be harvested each year to less than 150,000, and New Jersey has implemented a moratorium on harvesting the crabs.

In 2009, since implementing the measures, the number of red knots visiting Delaware Bay was estimated at 24,000, up from 18,000 the year before, but still far lower than the population of 100,000 to 150,000 of two decades ago.

McAlpine and Manu Mannoor, a Princeton graduate student who worked on the project, hope that technology based on their electronic chip will eventually replace LAL as the standard for contamination testing, obviating the need for horseshoe crab blood and helping both the crabs and the red knots rebound.

At the same time, producing this new sensory device would not put pressure on the frog species. "No frogs were harmed in the making of this sensor," he said.

Explore further: Study solves the bluetongue disease 'overwintering' mystery

Related Stories

Regulators allow horseshoe crab harvest

Feb 12, 2008

The New Jersey Marine Fisheries Council has declined to extend a moratorium on horseshoe crab harvesting aimed at protecting migrating shore birds.

Red knot birds threatened by crab decline

Feb 21, 2006

Virginia Tech and New Jersey scientists say a reduction in the number of red knot shorebirds is linked with a decline in Delaware Bay's horseshoe crabs.

Climate change affects horseshoe crab numbers

Oct 04, 2010

Having survived for more than 400 million years, the horseshoe crab is now under threat – primarily due to overharvest and habitat destruction. However, climatic changes may also play a role. Researchers ...

Climate change implicated in decline of horseshoe crabs

Aug 30, 2010

A distinct decline in horseshoe crab numbers has occurred that parallels climate change associated with the end of the last Ice Age, according to a study that used genomics to assess historical trends in population sizes.

Recommended for you

Study solves the bluetongue disease 'overwintering' mystery

Sep 12, 2014

The bluetongue virus, which causes a serious disease that costs the cattle and sheep industries in the United States an estimated $125 million annually, manages to survive the winter by reproducing in the insect that transmits ...

Taking the 'sting' out of reproduction

Sep 12, 2014

(Phys.org) —Female parasitic wasps have more reproductive success when working together with other females, which can also explain sex biased reproduction, according to new research.

Golden retriever study sniffs for cancer clues

Sep 11, 2014

(HealthDay)—Michael Court is a scientist and a dog lover, so he jumped at the chance to enroll his golden retriever in a nationwide study aimed at fighting cancer and other ills in canines.

User comments : 0