The Au NPs
were prepared by using a previous research method that was modified
slightly.24 (link) Briefly, in a conical flask,
50 mL of HAuCl4·4H2O solution was heated
to 130 °C by magnetic stirring for 20 min. Following that, 0.2
M sodium citrate solution (2 mL) was mixed to the above solution while
it was continuously boiling and stirring. After 20 min, the solution’s
color changed from yellow to wine red, confirming the formation of
Au NPs. To remove excess sodium citrate, the prepared Au NPs were
centrifuged at 2000 rpm for 20 min before use. Each centrifuge tube
was filled with 1.5 mL of Au colloid, and 1.4 mL of supernatant was
removed after centrifugation. The remaining part of each extractor
tube was transferred into a centrifuge tube for the flowing experiment.
The formulation of the SERS swab is based on some modifications
from previous literature.23 (link) First, the
cotton swab was washed with deionized water and then immersed in a
NaCl solution for 20 min; it was later removed from the NaCl solution
and desiccated in an oven at 60 °C for 3 min to activate the
SERS cotton fiber. After that, a swab was treated with pure Au colloid
solution to prepare the CS-Au NP substrate.
were prepared by using a previous research method that was modified
slightly.24 (link) Briefly, in a conical flask,
50 mL of HAuCl4·4H2O solution was heated
to 130 °C by magnetic stirring for 20 min. Following that, 0.2
M sodium citrate solution (2 mL) was mixed to the above solution while
it was continuously boiling and stirring. After 20 min, the solution’s
color changed from yellow to wine red, confirming the formation of
Au NPs. To remove excess sodium citrate, the prepared Au NPs were
centrifuged at 2000 rpm for 20 min before use. Each centrifuge tube
was filled with 1.5 mL of Au colloid, and 1.4 mL of supernatant was
removed after centrifugation. The remaining part of each extractor
tube was transferred into a centrifuge tube for the flowing experiment.
The formulation of the SERS swab is based on some modifications
from previous literature.23 (link) First, the
cotton swab was washed with deionized water and then immersed in a
NaCl solution for 20 min; it was later removed from the NaCl solution
and desiccated in an oven at 60 °C for 3 min to activate the
SERS cotton fiber. After that, a swab was treated with pure Au colloid
solution to prepare the CS-Au NP substrate.
