Fluorescence technique detects diseases in blood
Doctors can screen for infectious agents or diseases by looking for
the presence of marker proteins. Immunological assays are often used for this, but
they cannot detect a marker protein unless a certain amount of it is present in
a blood sample. This means that sometimes the disease must already have progressed
substantially to be detected. Researchers from the University of Pennsylvania in
Philadelphia have devised a technique that analyzes low-abundance proteins in blood.
As reported in the April issue of Nature Medicine,
the researchers created a method they call fluorescent amplification catalyzed by
T7 polymerase technique (FACTT). It uses RiboGreen, a fluorescent dye that detects
RNA, to sense subfemtomolar levels of protein. Once a double-stranded DNA template
has bound to the targeted infection-related protein molecules, RNA polymerase amplifies
the molecules, and the resulting molecules are highlighted by RiboGreen.
The researchers compared the detection
of the Her2 breast cancer marker with ELISA (enzyme-linked immunosorbent assay)
and FACTT in mouse blood. FACTT detected the cancer marker in three out of seven
mice after two days and in all seven after 11 days. The ELISA technique could not
detect any Her2, even after 11 days.
They also compared the detection of
Her2 in human blood between the two techniques. Using FACTT, nine out of 10 patients
who tested positive for Her2 were identified, and using ELISA, only two showed elevated
levels of Her2.
The investigators believe that the
results show promise for the use of the technology for monitoring infection and
disease at early stages.
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