posted on 2024-03-07, 17:34authored byKwangrok
R. Choi, Madeline L. Honig, Philippe Bühlmann
The
physical delamination of the sensing membrane from underlying
electrode bodies and electron conductors limits sensor lifetimes and
long-term monitoring with ion-selective electrodes (ISEs). To address
this problem, we developed two plasma-initiated graft polymerization
methods that attach ionophore-doped polymethacrylate sensing membranes
covalently to high-surface-area carbons that serve as the conducting
solid contact as well as to polypropylene, poly(ethylene-co-tetrafluoroethylene), and polyurethane as the inert polymeric electrode
body materials. The first strategy consists of depositing the precursor
solution for the preparation of the sensing membranes onto the platform
substrates with the solid contact carbon, followed by exposure to
an argon plasma, which results in surface-grafting of the in situ
polymerized sensing membrane. Using the second strategy, the polymeric
platform substrate is pretreated with argon plasma and subsequently
exposed to ambient oxygen, forming hydroperoxide groups on the surface.
Those functionalities are then used for the initiation of photoinitiated
graft polymerization of the sensing membrane. Attenuated total reflection-Fourier
transform infrared spectroscopy, water contact angle measurements,
and delamination tests confirm the covalent attachment of the in situ
polymerized sensing membranes onto the polymeric substrates. Using
membrane precursor solutions comprising, in addition to decyl methacrylate
and a cross-linker, also 2-(diisopropylamino)ethyl methacrylate as
a covalently attachable H+ ionophore and tetrakis(pentafluorophenyl)borate
as ionic sites, both plasma-based fabrication methods produced electrodes
that responded to pH in a Nernstian fashion, with the high selectivity
expected for ionophore-based ISEs.