  We propose for the first time an E. coli bacteria sensor based on the
evanescent field of the fundamental mode of a suspended-core terahertz fiber.
The sensor is capable of E. coli detection at concentrations in the range of
104-109 cfu/ml. The polyethylene fiber features a 150 {\mu}m core suspended by
three deeply sub-wavelength bridges in the center of a 5.1 mm-diameter cladding
tube. The fiber core is biofunctionalized with T4 bacteriophages which bind and
eventually destroy (lyse) their bacterial target. Using environmental SEM we
demonstrate that E. coli is first captured by the phages on the fiber surface.
After 25 minutes, most of the bacteria is infected by phages and then destroyed
with ~1{\mu}m-size fragments remaining bound to the fiber surface. The
bacteria-binding and subsequent lysis unambiguously correlate with a strong
increase of the fiber absorption. This signal allows the detection and
quantification of bacteria concentration. Presented bacteria detection method
is label-free and it does not rely on the presence of any bacterial
"fingerprint" features in the THz spectrum.
