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Duke, UCLA Developing Inkjet POC Tests to Rival Lab-Based Immunoassays


NEW YORK (360Dx) – A team led by researchers at Duke University and the University of California, Los Angeles has developed an inkjet-printed proof-of-concept platform that they said could enable the use of point-of-care tests for the broad range of medical conditions already served by sandwich antibody immunoassays, or ELISAs.

The test is not only easy to manufacture in high volumes through inkjet printing but it also could enable testing at the point of care for an exceptionally broad range of applications, Ashutosh Chilkoti, one of the test's developers and a biomedical engineering researcher at Duke University, said in an interview.

"Wherever one uses a sandwich immunoassay, which is a mainstay in clinical medicine for diagnosis, we can convert it to this format," Chilkoti said. "The format is very simple. The brightness of [analyte-based] spots in the immunoassay correlates with the concentration of the analyte in blood, serum, plasma, urine, or saliva."

The test uses a nanoscale film, or polymer brushes, 30 to 100 nanometers thick, that the researchers grow on a glass slide.

"The film has a unique property," Chilkoti said. "When it is wet, in blood or water, for example, the film prevents binding of molecules or proteins to the surface. So it is a non-fouling surface. But when it's dry, you can inkjet-print reagents or antibodies to it."

The anti-fouling surface eliminates nonspecific binding, or the binding of analytes that are not the targets of testing but could hamper the test's sensitivity. In traditional antibody immunoassays, blocking and washing steps are required to prevent unwanted binding by nonspecific proteins, which takes up time and entails training.

To manufacture their test, the Duke and UCLA researchers print reagents, or capture antibodies, onto dry brushes in a central zone — creating spots that are 100 microns, or so, in diameter. The capture antibodies are physically trapped so that they remain in place in the presence of blood, water, or another aqueous solution, Chilkoti said.

The team also inkjet prints detection antibodies onto the dry brushes, but these antibodies are designed so that they dissolve from the brushes and diffuse in the presence of blood or another liquid sample. They then bind to the capture antibodies, carrying with them the analytes of interest when they are present in the sample. Fluorescent chemical labels attached to the detection antibodies emit light upon excitation, and the system is then able to calculate the concentration of the analyte, Chilkoti said.

The inkjet printing manufacturing process may be the key to enabling point-of-care applications, he said, adding that the method could be used to inexpensively manufacture a broad range of assays and diagnostic targets.

A large part of the manufacturing cost of ELISAs is generally associated with reagent antibodies, but with the Duke test, each inkjet-printed spot is a picoliter in size, so "vanishingly small amounts of reagents are needed to create the assay," Chilkoti said.

"Inkjet printing is very fast and completely automated, and at the same time it's among the simplest manufacturing technologies you can think of," he said. "Using industrial strength printers, you can crank out a high volume of tests, very quickly and very cheaply."  

The technology enables high-performance diagnostic testing that could be applied at the point of care in low-resource settings that are far from central laboratories and that don't have trained test personnel or other routine lab-testing infrastructure, the researchers said.

The test's versatility also enables its use in clinics and laboratories, Chilkoti added.

The technology can be applied to testing for cancers and infectious diseases, including sexually transmitted diseases, Chilkoti noted. "It can be adapted to test for anything for which there is a known marker that diagnoses a disease and for which you can make an antibody sandwich, or ELISA," he added. "There are literally thousands of tests that fit this category."

In a small pilot study published earlier this month in Proceedings of the National Academy of Sciences, the developers described their use of a proof-of-concept platform to demonstrate its clinical utility.

They tested for leptin, a protein in fat cells that circulates in the bloodstream and supports energy regulation in the body. Recent research by investigators at Duke University determined that a low serum leptin level, below 50 pg/mL, is a major biochemical risk factor in predicting infant mortality due to malnutrition. The researchers in found that leptin measurements could be used to identify and provide targeted treatment to malnourished children at highest risk of death.

That provided the motivation to use leptin as part of the Duke-UCLA proof-of-concept demonstration.     

The Duke-UCLA team conducted its pilot study at Duke University Medical Center where they compared serum leptin levels detected by the inkjet-printed assay to the levels detected by a clinical ELISA, from three lean and 10 obese pediatric patients. The pilot studies demonstrated high concordance between the inkjet assay and the clinical ELISA, which were performed in parallel in a central laboratory at the medical center on all 13 patients, the researchers said.

The proof-of-concept study demonstrates the feasibility of merging the inkjet-printed assay technology with compact, field-portable, cost-effective, and easy-to-use mobile phone-based detection platforms, the researchers said.

Measurements from the assay were obtained using a tabletop fluorescence scanner. While this approach would allow for POC testing in a peripheral laboratory near or attached to a clinic in limited resource settings, a tabletop scanner is too burdensome for use in the field, the researchers said. To address this issue, they investigated the feasibility of portable fluorescence imaging using a mobile phone-based fluorescence microscope.

Transitioning to the mobile phone-based detection platform reduced detection sensitivity and inter-assay consistency, the researchers said. However, they noted that they expect that the fluorescence collection efficiency and sensitivity of portable, low-cost detectors will rival table-top fluorescence scanners, as mobile phone detector technology, computational imaging, and sensing approaches continue to evolve.

One company, Immucor, is already using the inkjet-printing platform developed by the Duke-UCLA team to develop blood typing and other blood testing applications. After licensing the technology from Duke in 2014, Immucor began developing its own blood tests, Chilkoti said.

The Duke-UCLA team is continuing to develop and validate the platform in POC applications with the knowledge that any advances will benefit Immucor, Chilkoti said.

"We continue to push the boundaries of use at the point of care," he noted. "We are scientists so we want to see how far we can push this technology."