Chemical sensors have
been developed based on amplified fluorescence quenching of solid-state conjugated
polymer films (AFP). These sensors consists of a glass capillary tube whose
interior is coated with a polymer film comprised of a conjugated backbone with
pentiptycene groups. In operation, the AFP polymer is excited to a fluorescent
state using a light source external to the capillary tube. An air pump is then
used to draw the sample through the capillary; compounds containing
nitroaromatic groups (TNT, RDX, etc.) bind to the polymer, causing fluorescence
to be quenched. The change in fluorescence is read as a change in response at a
photometer positioned axially to the capillary. In conventional fluorescent-based
sensors, the signal arises due to 1:1 analyte to chromophore binding. In AFP, because the polymer chains are
electronically conjugated, binding at any point along the polymer chain results
in complete quenching of all sites on the polymer. The result is that a single analyte
molecule activates multiple chromophores.
The effective amplification in response by this technique over monomeric
quenching is estimated to be from 100X to 1000X. It is primarily used in vapor
sensing applications such as detection landmines and other explosive
devices. AFP technology is relatively new.
As such, it is employed in a limited number of sensor devices, nearly
all handheld in configuration.