Fiber optic probes (FO) were manufactured
according to a previously reported procedure.44 (link) Briefly, TECS-clad step-index multimode fibers (Thorlabs Inc.),
with a numerical aperture of 0.39 and a core diameter of 1000 μm,
were cut to a length of 6.5 cm. At one end, a surface plasmon resonance
(SPR)-sensitive zone (1 cm long) was fabricated by removing the jacket
layer with a stripping tool and the cladding layer by dissolution
in acetone. The SPR zone of the tip was subsequently cleaned with
Milli-Q water and isopropanol and blow-dried under N2.
As-prepared tips were sputter-coated with 50 nm of gold and stored
under argon until further use.
FO-SPR measurements were performed
by optically connecting the tips to a Y-optical splitter via a commercially
available bare fiber terminator (Thorlabs Inc.). Polychromatic light
from a halogen light source (12 V, HL-2000-LL, Ocean Insight) was
coupled into the input arm of the Y-optical splitter, guided to the
fiber tip, back-reflected at the gold-coated cross section of the
tip, and guided through the output arm of the splitter to a spectrometer
(HR4000, Ocean Insight). The reflected light spectrum was normalized
by the spectrum of the fiber in air before surface modification and
processed by dedicated LabView software.
For the electropolymerization
on the FO, the upper gold-coated
part of the fiber was connected using a conductive copper tape (Reichelt
Elektronik GmbH & Co. KG). To ensure electrical connection across
the transition from the SPR zone to the upper gold-coated part of
the fiber as well as a constant electrode area, a layer of conductive
silver paint (RS Components Ltd) was applied and subsequently coated
with a layer of liquid heat shrink tubing (Performix Liquid Tape,
Plastidip, Plasti Dip Europe GmbH).
according to a previously reported procedure.44 (link) Briefly, TECS-clad step-index multimode fibers (Thorlabs Inc.),
with a numerical aperture of 0.39 and a core diameter of 1000 μm,
were cut to a length of 6.5 cm. At one end, a surface plasmon resonance
(SPR)-sensitive zone (1 cm long) was fabricated by removing the jacket
layer with a stripping tool and the cladding layer by dissolution
in acetone. The SPR zone of the tip was subsequently cleaned with
Milli-Q water and isopropanol and blow-dried under N2.
As-prepared tips were sputter-coated with 50 nm of gold and stored
under argon until further use.
FO-SPR measurements were performed
by optically connecting the tips to a Y-optical splitter via a commercially
available bare fiber terminator (Thorlabs Inc.). Polychromatic light
from a halogen light source (12 V, HL-2000-LL, Ocean Insight) was
coupled into the input arm of the Y-optical splitter, guided to the
fiber tip, back-reflected at the gold-coated cross section of the
tip, and guided through the output arm of the splitter to a spectrometer
(HR4000, Ocean Insight). The reflected light spectrum was normalized
by the spectrum of the fiber in air before surface modification and
processed by dedicated LabView software.
For the electropolymerization
on the FO, the upper gold-coated
part of the fiber was connected using a conductive copper tape (Reichelt
Elektronik GmbH & Co. KG). To ensure electrical connection across
the transition from the SPR zone to the upper gold-coated part of
the fiber as well as a constant electrode area, a layer of conductive
silver paint (RS Components Ltd) was applied and subsequently coated
with a layer of liquid heat shrink tubing (Performix Liquid Tape,
Plastidip, Plasti Dip Europe GmbH).
