Physicians often test the levels of a few telltale blood
proteins in seriously injured or ill patients to detect organ failure and other
problems. Now Vista Therapeutics,
a startup based in Santa Fe,
NM, hopes to improve the care of
these patients with sensitive devices for continuous bedside monitoring of such
blood biomarkers. Instead of taking daily snapshots of the patient’s levels of
blood proteins, the company’s nanosensors should allow for continuous
monitoring of changes that occur over periods of only a few hours.
Spencer Farr, CEO of Vista Therapeutics, says that the first
application of the technology will be for careful monitoring of patients whose
status can change rapidly–such as those in the ICU after suffering a heart
attack or traumatic injuries from a car accident. “We envision having a branch
in the patient’s IV that tests continuously or every five to ten minutes,” says
Farr. The nanowires are sensitive enough that they should be able to detect
trace biomarkers that diffuse into the IV line from the blood. After a car
wreck, for example, patients could be closely monitored for molecular warning
signs of impending kidney and other organ failure.
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To make the detectors, Vista Therapeutics has licensed
nanowire sensing technologies developed by Harvard University
chemist Charles Lieber.
Silicon nanowires, semiconducting wires as thin as two nanometers, have what
Lieber calls the “ultimate sensitivity,” even with completely unprocessed
samples such as blood. When a single protein binds to an antibody along the
wire, the current flowing through the wire changes. Arrays of hundreds of
nanowires, each designed to detect a different molecule in the same sample, can
be arranged on tiny, inexpensive chips. The changes can be monitored
continuously as molecules bind and unbind, making it possible to detect subtle
trends over time, without requiring multiple blood draws.
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The standard protein-detection technique, ELISA, is very
sensitive but, Farr says, takes 90 minutes to perform. It starts with a blood
draw that must be extensively processed–first to purify the proteins, then to
label them with fluorescent dyes–and then tested with expensive imaging
equipment in a hospital lab. “ELISA is a powerful technology for one-time
measurements,” says Farr, “but there’s no existing technology for continuous
biomarker measurement.”
The sensitivity of nanowire detectors should also open up
the possibility of finding new biomarkers.
The blood biomarkers that doctors routinely test for–including
prostate-specific antigen for cancer screening and c-reactive protein, a sign
of heart failure–can be monitored with ELISA because their levels change over
days or weeks. Because nanowire sensors allow for extremely sensitive, continuous
monitoring, they should allow doctors to monitor the levels of blood proteins
and other molecules whose concentration changes over a much shorter timescale.
Changes in these biomarkers are currently undetectable. “We expect we’ll be
able to include those that change rapidly, peaking within a matter of a few
hours,” says Farr. Because it hasn’t been practical to make such measurements
before, it’s not clear just what these biomarkers will be, but Farr hopes that Vista will uncover them.
Initially, Vista will
market clinical devices for monitoring known biomarkers in IV lines. In the
future, the company might develop implantable chips for patients with chronic
diseases such as diabetes. A nanowire chip in an artery in the wrist might
continuously monitor blood glucose and proteins indicative of early liver
damage and other diabetic complications. The device could send alerts to a
wristwatch. Because nanowires are so sensitive and inexpensive, they could also
find their way into home
tests for cancer, where early detection is key, says Farr.