At the heart of Rice University’s Programmable Bio-Nano-Chip is a grid that contains microsponges, tiny agarose beads programmed to capture biomarkers. The biomarkers help clinicians detect signs of disease in patients. (Credit: Jeff Fitlow/Rice Univ.) |
Microsponges derived from seaweed may help diagnose heart disease, cancers,
HIV and other diseases quickly and at far lower cost than current clinical
methods. The microsponges are an essential component of Rice Univ.’s
Programmable Bio-Nano-Chip (PBNC) and the focus of a new paper in the journal Small.
The paper by John McDevitt, the Brown-Wiess Professor in Bioengineering and
Chemistry, and his colleagues at Rice’s BioScience Research Collaborative views
the inner workings of PBNCs, which McDevitt envisions as a mainstream medical
diagnostic tool.
PBNCs to diagnose a variety of diseases are currently the focus of six human
clinical trials.
PBNCs capture biomarkers found in blood, saliva, and other bodily fluids. The
biomarkers are sequestered in tiny sponges set into an array of inverted
pyramid-shaped funnels in the microprocessor heart of the credit card-sized
PBNC.
When a fluid sample is put into the disposable device, microfluidic channels
direct it to the sponges, which are infused with antibodies that detect and
capture specific biomarkers. Once captured, they can be analyzed within minutes
with a sophisticated microscope and computer built into a portable,
toaster-sized reader.
The biomarker capture process is the subject of the Small paper. The microsponges are 280-micrometer beads of agarose,
a cheap, common, lab-friendly material derived from seaweed and often used as a
matrix for growing live cells or capturing proteins.
The beauty of agarose is its ability to capture a wide range of targets from
relatively huge protein biomarkers to tiny drug metabolites. In the lab,
agarose starts as a powder, like Jell-O. When mixed with hot water, it can be
formed into gels or solids of any size. The size of the pores and channels in
agarose can be tuned down to the nanoscale.
The challenge, McDevitt said, was defining a new concept to quickly and
efficiently capture and detect biomarkers within a microfluidic circuit. The
solution developed at Rice is a network of microsponges with tailored pore
sizes and nano-nets of agarose fibers. The sponge-like quality allows a lot of
fluid to be processed quickly, while the nano-net provides a huge surface area
that can be used to generate optical signals 1,000 times greater than
conventional refrigerator-sized devices. The mini-sensor ensembles, he said,
pack maximum punch.
The team found that agarose beads with a diameter of about 280 micrometers
are ideal for real-world applications and can be mass-produced in a
cost-effective way. These agarose beads retain their efficiency at capturing
biomarkers, are easy to handle and don’t require specialized optics to see.
McDevitt and his colleagues tested beads with pores up to 620 nm and down to
45 nm wide. Pores near 140 nm proved best at letting proteins infuse the beads’
internal nano-nets quickly, a characteristic that enables PBNCs to test for disease
in less than 15 minutes.
The team reported on experiments using two biomarkers, carcinoembryonic
antigens and Interleukin-1 beta proteins (and matching antibodies for both),
purchased by the lab. After soaking the beads in the antibody solutions, the
researchers tested their ability to recognize and capture their matching
biomarkers. In the best cases, they showed near-total efficiency (99.5%) in the
detection of bead-bound biomarkers.
McDevitt has expected for some time that a three-dimensional bead had
greater potential to capture and hold biomarkers than the standard for such
tests, the enzyme-linked immunosorbent assay (ELISA) technique. ELISA analyses
fluids placed in an array of 6.5-mm wells that have a layer of biomarker
capture material spread out at the bottom. Getting results through ELISA
requires a lab full of equipment, he said.
“The amount of optical signal you get usually depends on the thickness
of a sample,” McDevitt said. “Water, for example, looks clear in a
small glass, but is blue in an ocean or a lake. Most modern clinical devices
read signals from samples in flat or curved surfaces, which is like trying to
see the blue color of water in a glass. It’s very difficult.”
By comparison, PBNCs give the researchers an ocean of information. “We
create an ultrahigh-surface-area microsponge that collects a large amount of
material,” he said. “The sponge is like a jellyfish with tentacles
that capture the biomarkers.”
The agarose bead is engineered to become invisible in water. “That
makes it an ideal environment to capture biomarkers, because the matrix doesn’t
get in the way of visualizing the contents. This is a nice use of novel
biomaterials that are cheap as dirt, yet yield powerful performance,”
McDevitt said.
According to previous studies, only a fraction—less than 10%—of capture
antibodies in the “gold standard” ELISA arrays are still active by
the time a test begins. By comparison, nearly all of the antibodies in the
agarose beads retain their ability to detect and capture biomarkers, McDevitt
said.
Ultimately, he said, PBNCs will enable rapid, cost-effective diagnostic
tests for patients who are ailing, whether they’re in an emergency room, in an
ambulance or even while being treated in their own homes. Even better, the
chips may someday allow for quick and easy testing of the healthy to look for
early warning signs of disease.
Co-authors of the paper included first author Jesse Jokerst, a National
Institutes of Health postdoctoral fellow at Stanford University; postdoctoral
students James Camp, Jorge Wong, Alexis Lennart, Amanda Pollard and Yanjie
Zhou, all of the departments of Chemistry and Biochemistry at the University of
Texas at Austin; Mehnaaz Ali, an assistant professor of chemistry at Xavier
University; and from the McDevitt Lab at Rice, Pierre Floriano, director of
microfluidics and image and data analysis; Nicolaos Christodoulides, director
of assay development; research scientist Glennon Simmons and graduate student
Jie Chou.
The National Institutes of Health, through the National Institute of Dental
and Craniofacial Research, funded the research.
