WEST LAFAYETTE, Ind. — Researchers have created the tiniest laser since its invention nearly 50 years ago, paving the way for a host of innovations, including superfast computers that use light instead of electrons to process information, advanced sensors and imaging.

Researchers have created the tiniest laser since its invention nearly 50 years ago. Because the new device, called a 'spaser', is the first of its kind to emit visible light, it represents a critical component for possible future technologies based on 'nanophotonic' circuitry. The color diagram (a) shows the nanolaser's design: a gold core surrounded by a glasslike shell filled with green dye. Scanning electron microscope images (b and c) show that the gold core and the thickness of the silica shell were about 14 nanometers and 15 nanometers, respectively. A simulation of the SPASER (d) shows the device emitting visible light with a wavelength of 525 nanometers. (Birck Nanotechnology Center, Purdue University)

Because the new device, called a “spaser,” is the first of its kind to emit visible light, it represents a critical component for possible future technologies based on “nanophotonic” circuitry, said Vladimir Shalaev, the Robert and Anne Burnett Professor of Electrical and Computer Engineering at Purdue University.

Such circuits will require a laser-light source, but current lasers can’t be made small enough to integrate them into electronic chips. Now researchers have overcome this obstacle, harnessing clouds of electrons called “surface plasmons,” instead of the photons that make up light, to create the tiny spasers.

Findings are detailed in a paper appearing online in the journal Nature that reports on work conducted by researchers at Purdue, Norfolk State University and Cornell University.

Nanophotonics may usher in a host of radical advances, including powerful “hyperlenses” resulting in sensors and microscopes 10 times more powerful than today’s and able to see objects as small as DNA; computers and consumer electronics that use light instead of electronic signals to process information; and more efficient solar collectors.

“Here, we have demonstrated the feasibility of the most critical component – the nanolaser – essential for nanophotonics to become a practical technology,” Shalaev said.

The “spaser-based nanolasers” created in the research were spheres 44 nanometers, or billionths of a meter, in diameter – more than 1 million could fit inside a red blood cell. The spheres were fabricated at Cornell, with Norfolk State and Purdue performing the optical characterization needed to determine whether the devices behave as lasers.

The findings confirm work by physicists David Bergman at Tel Aviv University and Mark Stockman at Georgia State University, who first proposed the spaser concept in 2003.

“This work represents an important milestone that may prove to be the start of a revolution in nanophotonics, with applications in imaging and sensing at a scale that is much smaller than the wavelength of visible light,” said Timothy D. Sands, the Mary Jo and Robert L. Kirk Director of the Birck Nanotechnology Center in Purdue’s Discovery Park.

The spasers contain a gold core surrounded by a glasslike shell filled with green dye. When a light was shined on the spheres, plasmons generated by the gold core were amplified by the dye. The plasmons were then converted to photons of visible light, which was emitted as a laser.

Spaser stands for surface plasmon amplification by stimulated emission of radiation. To act like lasers, they require a “feedback system” that causes the surface plasmons to oscillate back and forth so that they gain power and can be emitted as light. Conventional lasers are limited in how small they can be made because this feedback component for photons, called an optical resonator, must be at least half the size of the wavelength of laser light.

The researchers, however, have overcome this hurdle by using not photons but surface plasmons, which enabled them to create a resonator 44 nanometers in diameter, or less than one-tenth the size of the 530-nanometer wavelength emitted by the spaser.

“It’s fitting that we have realized a breakthrough in laser technology as we are getting ready to celebrate the 50th anniversary of the invention of the laser,” Shalaev said.

The first working laser was demonstrated in 1960.

The research was conducted by Norfolk State researchers Mikhail A. Noginov, Guohua Zhu and Akeisha M. Belgrave; Purdue researchers Reuben M. Bakker, Shalaev and Evgenii E. Narimanov; and Cornell researchers Samantha Stout, Erik Herz, Teeraporn Suteewong and Ulrich B. Wiesner.

Future work may involve creating a spaser-based nanolaser that uses an electrical source instead of a light source, which would make them more practical for computer and electronics applications.

The work was funded by the National Science Foundation and U.S. Army Research Office and is affiliated with the Birck Nanotechnology Center, the Center for Materials Research at Norfolk State, and Cornell’s Materials Science and Engineering Department.

WEST LAFAYETTE, Ind. — A new prostate cancer “homing device” could improve detection and allow for the first targeted treatment of the disease.

A team of Purdue University researchers has synthesized a molecule that finds and penetrates prostate cancer cells and has created imaging agents and therapeutic drugs that can link to the molecule and be carried with it as cargo.

A radioimaging application used for body scans is expected to enter clinical trials this fall, and an optical imaging application used to measure prostate cancer cells in blood samples is already in clinical trials.

Philip Low, the Ralph C. Corley Distinguished Professor of Biochemistry who led the team, said a targeted treatment could be much more effective in treating cancer and would greatly reduce the harmful side effects associated with current treatments.

This image depicts transporter molecules carrying therapeutic drugs to PSMA targets on a prostate cancer cell. A Purdue research team designed a molecule that finds and penetrates prostate cancer cells and can transport drugs or imaging agents into the cell. (Image courtesy of Low laboratory)

“Currently none of the drugs available to treat prostate cancer are targeted, which means they go everywhere in the body as opposed to only the tumor, and so are quite toxic for the patient,” said Low, who is a member of the Purdue Cancer Center. “By being able to target only the cancer cells, we could eliminate toxic side effects of treatments. In addition, the ability to target only the cancer cells can greatly improve imaging of the cancer to diagnose the disease, determine if it has spread or is responding to treatment.”

Prostate cancer is the most common cancer, other than skin cancers, and is the second leading cause of cancer death in American men, according to the American Cancer Society. It is estimated that about 192,280 new cases will be diagnosed and 27,360 men will die of prostate cancer in the United States this year.

The molecule Low’s team created attaches to prostate-specific membrane antigen, or PSMA, a protein that is found on the membrane of more than 90 percent of all prostate cancers. It also is found on the blood vessels of most solid tumors and could provide a way to cut off the tumor blood supply, Low said.

“A lot of new drugs are being designed to destroy the vasculature of solid tumors, and, if they could be linked to this new targeting molecule, we could have a two-pronged attack for prostate cancer,” he said. “We could not only kill the prostate cancer cells directly, we could also destroy the vasculature that feeds the tumors.”

There also is potential for the targeting molecule to be used to attack the vasculature of solid tumors of other types of cancers, Low said.

Two papers detailing the work of the Purdue team were published in the June 1 issue of Molecular Pharmaceutics. Endocyte Inc. funded the work.

The team’s animal study data shows an ability to eliminate human prostate cancer cells in mice with no evidence of collateral toxicity in normal tissue.

Sumith Kularatne, a graduate student in Purdue’s chemistry department and first author of both papers, compared the targeting molecule to a homing device.

“The molecule acts like a homing device for prostate cancer,” he said. “PSMA, which is found only on prostate cancer cells and tumor blood vessels, acts as the homing signal that the molecule targets. The molecule and its cargo go only to cancerous tissue, leaving healthy tissue unharmed.”

Once the molecule reaches the PSMA protein, it binds to it. The molecule is designed with a specific shape that fits with the protein like a key to a lock, Kularatne said. The molecule and its cargo are then carried inside the cell with the protein as it goes through its normal cycle.

In 1995 Low developed a similar method to infiltrate cancer cells by attaching treatments to the vitamin folate, which many cancers rapidly consume. This method provided a “Trojan Horse” entry of large treatment molecules that otherwise would not be able to enter cancer cells.

Low was inspired to find a similar way to target prostate cancer, which does not have the same appetite for folate, he said.

A clinical trial of the radioimaging application is expected to begin at the Indiana University Medical Center in the fall through a collaboration between the Purdue Cancer Center and the Indiana University Cancer Center with additional support from Endocyte Inc.

A radioimaging agent linked to the targeting molecule will be injected into prostate cancer patients and pictures will be taken using a special camera that detects radioactivity. The pictures show where the cancer is present to help doctors determine if it has metastasized, or spread, to any other areas of the body. It also will help doctors decide on the best course of treatment, Low said.

There is currently only one radioimaging agent for prostate cancer approved by the Food and Drug Administration.

“The current imaging capabilities available for prostate cancer are very poor,” Low said. “The existing imaging agent is limited because of its large size, which is difficult to get into a solid tumor. Also it seeks out a target located inside the cancer cell and is only able to mark injured cells that are falling apart as opposed to actively growing cancer cells.”

The targeting molecule and radioimaging agent combination designed by Low’s group is more than 150 times smaller than the existing agent and has much easier penetration through a solid tumor to reach all of the cells inside, he said. It also has the advantage of targeting an area of PSMA exposed on the outside of cancer cells.

Already in clinical trials is an optical imaging application that involves attaching a fluorescent dye to the targeting molecule and mixing it with a patient’s blood sample. Circulating prostate cancer cells in the sample fluoresce and are easily measured to help in diagnosing patients with prostate cancer. Researchers also are investigating whether this could be used to evaluate a patient’s response to therapy, Low said.

Low’s research group modeled the targeting molecule after a naturally occurring molecule that strongly binds to PSMA, called DUPA. Several alterations were necessary to create a molecule that fit the needs of a homing device and delivery vehicle, Kularatne said. The team created an area on the molecule that would link to various imaging or therapeutic agents to bring them along as cargo and created a spacer that would stretch the molecule so that its cargo would not keep it from properly fitting into the binding site. The spacer also was designed to improve binding of the targeting molecule to PSMA.

In addition to Low and Kularatne, co-authors of the papers include Endocyte researchers Kevin Wang and Hari-Krishna R. Santhapuram, graduate student in medicinal chemistry Zhigang Zhou, graduate student in chemistry Jun Yang, and professor of medicinal chemistry and molecular pharmacology Carol B. Post.

Low is the chief science officer for Endocyte, a Purdue Research Park-based company that develops receptor-targeted therapeutics for the treatment of cancer and autoimmune diseases. Endocyte holds the license to many of Low’s drug-targeting technologies.

WEST LAFAYETTE, Ind. — Girls ages 10-12 are being recruited to participate in a mini-Camp Calcium at Purdue University.

The camp will include three clinical campus visits, six weeks apart. For three weeks before each campus visit, participants will consume a fiber product in a yogurt-like drink.

During a previous Camp Calcium, Technician Leslie Ann Hawrysz, clinical research coordinator in foods and nutrition at Purdue, conducted a bone density scan on a student participating in Camp Calcium. The study ultimately concluded too much salt in the diet reduces bone density in both African-American and Caucasian adolescent girls. (Purdue file photo/Richard Myers-Walls.)

Participants will then stay on campus for two days to complete a calcium absorption test, blood collections, physical fitness tests and bone density measurements.

A minimum three-week “wash-out” period will follow the campus visit before beginning the next study treatment phase.

The girls will be paid for each study phase completed.

Eligibility requirements include a healthy weight, pre-menarche status, no broken bones in the last six months and no medications that influence calcium absorption.

Registration deadline is June 6. For more information about the study or schedule, or to receive an application packet, contact Berdine Martin at 1-800-830-0175, 765-494-6559 or fnbone@purdue.edu

Researchers will study the effect of added fiber on the absorption of calcium in dairy products in preteen girls.

During adolescence, maximum bone growth occurs and a high percentage of calcium is taken into the bone. Purdue’s Department of Foods and Nutrition is studying dietary factors that influence calcium absorption and bone health. Previous studies in adults have shown a positive effect of a particular kind of fiber called galacto-oligosaccharide on calcium absorption. Since maximum bone strength is achieved in adolescence, this short study will be studying preteens.

WEST LAFAYETTE, Ind. — A Purdue University researcher is looking for adults to participate in a speech perception study in the Department of Speech, Language and Hearing Sciences.

Participants will participate in a listening session that is one to three hours, and the compensation is $10 per hour. People interested in participating must be 18 years or older, be native speakers of American English, have normal hearing and normal or corrected-to-normal vision.

Karen Iler Kirk, professor of speech, language and hearing sciences, is leading the study. To participate, or for more information on the study, contact Lindsay Prusick, a graduate research assistant, at (765) 494-0948 or lprusick@purdue.edu

The study is funded by the National Institutes of Health. The Department of Speech, Languages and Hearing Sciences is housed in the College of Liberal Arts.

WEST LAFAYETTE, Ind. — A Purdue University researcher is seeking adults to participate in a listening study in the Department of Speech, Language and Hearing Sciences.

Karen Iler Kirk, professor of speech, language and hearing sciences, is leading the study. Participants will participate in four sessions, with each session lasting 60-90 minutes. Hearing and vision screenings will be completed during the first visit. Those who pass the screenings will be asked to identify voices while listening to sentences spoken by several different talkers.

People interested in participating must be ages 18-65, have no reported speech or hearing difficulties, have normal or corrected-to-normal vision, and be a native speaker of general American English. Compensation is $40 upon completion of four sessions.

To participate, or for more information on the study, contact Vidya Krull, a research assistant, at vganesh@purdue.edu .