Medical diagnostic laboratories often test a single sample for several proteins to detect patterns that indicate disease. But current methods limit the number they can detect at one time. Now, researchers at the Massachusetts Institute of Technology have created tiny, easy-to-build, jelly-like particles that each contain tests for multiple proteins (Anal. Chem., DOI: 10.1021/ac1022343). Using multiple particles in combination could help doctors efficiently detect practically limitless numbers of proteins to diagnose disease, the researchers say.
Doctors want to measure many different proteins because complex diseases such as multiple sclerosis and cancer are not caused by single proteins. Laboratories can screen a sample for up to 100 different proteins at once using color-coded beads, each covered with a unique antibody that captures a specific target. Other methods increase the number of coded tests but cannot detect proteins at low concentrations.
MIT's Patrick Doyle and colleagues thought a better route to multiple protein detection would use gelatinous particles, which they had previously designed to detect RNA strands (Anal. Chem., DOI: 10.1021/ac9005292). For use with proteins, the particle's gel network would contain many antibodies, which the researchers thought would increase the signal and equal the test sensitivity of the colored bead method.
The scientists made each particle in a microfluidic channel three times the diameter of a human hair. Several water-based solutions containing a material called polyethylene glycol flowed side-by-side in this tiny channel without mixing to create the particles' two halves. One half contained three streams of unique capture antibodies. The other half had only one stream of a fluorescent dye. The scientists then used ultraviolet light to link the polyethylene glycol strands, turning the stratified stream into a gel. By blocking the light with a patterned mask, they formed unique patterns on the fluorescent dye half of the particle to serve as a barcode for the antibodies present on the other half.
To screen for proteins, the scientists covered the stripes with a solution containing a second antibody and applied the same fluorescent dye to determine which ones had captured proteins. Then they read out those particles' fluorescent barcodes to identify the targets.
With their barcoded particles, Doyle's group detected three cytokines, proteins that signal an immune response, at concentrations from 1 to 8 pg/mL. The sensitivity is comparable to enzyme-linked immunosorbent assays, or ELISA, the "gold standard" for detecting single proteins, Doyle says.
Amy Herr, a researcher who develops microanalytical systems for medical diagnostics at the University of California, Berkeley, says that Doyle's streamlined approach to producing antibody-functionalized particles could allow doctors to rapidly adjust combinations of tests while they search for a diagnosis.
Larry Kricka, co-director of the Center for Biomedical Micro and Nanotechnology at the University of Pennsylvania, agrees that the technique to synthesize the particles is "very inventive, clever, and quite compelling." But he wonders if the particle's analytical abilities will ever prove advantageous enough for clinical laboratories to justify changing their equipment and revalidating their tests.