8 research outputs found
Solid Contact Thin-Film Ion-Selective Membranes for Ion Transfer Voltammetry: Fundamental Studies and Applications
Water is the source of life, and its rich electrolytes play a pivotal role in all life on Earth. Back to human beings, the electrolyte concentration and distribution in the body are closely associated with health, thus solid-state ion-selective electrode (ISE) meet this need just perfectly to be made into a wearable sensor to monitor the concentration of various ions in the human body at any time. Although the best available ionophore-assisted ion-selective membrane (ISM) based ion-selective electrode has been developed for over a century, all-solid-contact ion-selective electrode still faces the problem of lack of stability. Many researchers have found that the electrochemical signal disruption is due to the condensation of water molecules forming a so-called water layer between the solid support of the electrode and ion-selective membrane. The addition of the lipophilic transducing material behind the membrane has indeed suppressed the water layer formation for a certain period of time.
Additionally, conventional ion-selective membrane potentiometry is a passive method for ion detection. However, the new alternative approach attracts a lot of attention, thin-film cyclic voltammetry can provide multi-ions detection, lower detection, and responding time manipulation. The fundamental theory of the ion-to-electron transfer was well understood, but in practical use, the transducing layer, commonly made of poly(3-octylthiophene) (POT) or the other derivatives (PEDOT-C14), is not reproducible for the ion-selective electrode from batch to batch, as well as the voltammetric current is the contribution of electron-transfer coupled with the ion-transfer, where it is hard to analyze the deviation of ion sensing coming from the transducing layer or ionophore selectivity effect on the ion-transfer. This thesis shows the approach to separate the two transduction events at each interface (electrode/membrane and membrane/sample) with their phase boundary potentials and then we further developed the thin-film cyclic voltammetry technique in analytical chemistry. A promising practical use for solid contact thin-film ion-selective electrodes is present and pushes forward the development of this field.</p
Surfactants for Optode Emulsion Stabilization without Sacrificing Selectivity or Binding Constants
Separating boundary potential changes at thin solid contact ion transfer voltammetric membrane electrodes
Thin ion-selective membrane films deposited on solid electrode substrate are useful tools to study ion transfer processes. This is because the experimental conditions may be chosen such that diffusion processes within the membrane and contacting aqueous solution are not rate limiting. In an ideal case, therefore, equilibrium considerations may be used to describe the resulting ion transfer voltammograms. For example, the electrochemical oxidation of an electrically neutral redox molecule in the membrane results in a cationic oxidized form. To preserve electroneutrality, a cation is transferred out of the membrane into solution, freeing the cation-exchanger of the membrane to become the counterion of the oxidized redox molecule. This work describes a model system that agrees well with thermodynamic theory, using the lipophilic (1-dodecyl-1H-1,2,3-triazol-4-yl)ferrocene as redox molecule and a monovalent reference cation for ion transfer. The full peak width at half maximum was found as 0.110 V, in agreement with theory, and with peak current proportional to scan rate supporting thin layer behavior. The charge passed during the voltammetric scan was related to ion-exchanger concentration available for ion extraction as a function of potential. Subtraction of the ion transfer potential using the reference ion from the experimental one for each charge increment gave the potential change for the electrochemical ion-to-electron transducer. In one application, the potential change of the polymeric transducing layer poly(3-octylthiophene) (POT) film upon electrochemical oxidation within the membrane was characterized. A non-linear potential–charge curve was observed, in contrast to earlier assumptions
Mass Transfer from Ion-Sensing Component-Loaded Nanoemulsions into Ion-Selective Membranes: An Electrochemical Quartz Crystal Microbalance and Thin-Film Coulometry Study
Recent work has shown
that ion-selective components may be transferred
from nanoemulsions (NEs) to endow polymeric membranes with ion-selective
sensing properties. This approach has also been used for nanopipette
electrodes to achieve single-entity electrochemistry, thereby sensing
the ion-selective response of single adhered nanospheres. To this
date, however, the mechanism and rate of component transfer remain
unclear. We study here the transfer of lipophilic ionic compounds
from nanoemulsions into thin plasticized poly(vinyl chloride) (PVC-DOS)
films by chronoamperometry and quartz crystal microbalance. Thin-film
cyclic coulovoltammetry measurements serve to quantify the uptake
of lipophilic species into blank PVC-DOS membranes. Electrochemical
quartz crystal microbalance data indicate that the transfer of the
emulsion components is insignificant, ruling out simple coalescence
with the membrane film. Ionophores and ion-exchangers are shown to
transfer into the membrane at rates that correlate with their lipophilicity
if mass transport is not rate-limiting, which is the case with more
lipophilic compounds (calcium and sodium ionophores). On the other
hand, with less lipophilic compounds (valinomycin and cation-exchanger
salts), transfer rates are limited by mass transport. This is confirmed
with rotating disk electrode experiments in which a linear relationship
between the diffusion layer thickness and current is observed. The
data suggests that once the nanoemulsion container approaches the
membrane surface, transfer of components occur by a three-phase partition
mechanism where the aqueous phase serves as a kinetic barrier. The
results help better understand and quantify the interaction between
nanoemulsions and ion-selective membranes and predict membrane doping
rates for a range of components
Ink-Jet Printing-Assisted Modification on Polyethersulfone Membranes Using a UV-Reactive Antimicrobial Peptide for Fouling-Resistant Surfaces
Ink-Jet Printing-Assisted Modification on Polyethersulfone Membranes Using a UV-Reactive Antimicrobial Peptide for Fouling-Resistant Surfaces
Antimicrobial
peptides (AMPs) are promising candidates for surface
coatings to control biofilm growth on water treatment membranes because
of their broad activity and the low tendency of bacteria to develop
resistance to AMPs. However, general and convenient surface modification
methods are limited, and a deeper understanding of the antimicrobial
mechanism of action is needed for surface-attached AMPs. Here, we
show a method for covalently attaching AMPs on porous ultrafiltration
membranes using ink-jet printing and provide insight into the mode
of action for the covalently tethered peptide RWRWRWA-(Bpa) (Bpa,
4-benzophenylalanine) against Pseudomonas aeruginosa. AMP-coated ultrafiltration membranes showed surface antibacterial
activity and reduced biofilm growth. Fluorescence microscopy analysis
revealed that the modified surfaces could cause cell membrane disruption,
which was seen by live uptake of propidium iodide stain, and scanning
electron microscopy images showed compromised cell membranes of attached
bacteria. This study indicated that the mode of action of covalently
tethered AMPs was similar to that of freely soluble AMPs. The deeper
understanding of the mode of action of AMPs covalently attached to
surfaces could lead to a more rational approach for designing surfaces
with antibacterial activity
Ink-Jet Printing-Assisted Modification on Polyethersulfone Membranes Using a UV-Reactive Antimicrobial Peptide for Fouling-Resistant Surfaces
Antimicrobial
peptides (AMPs) are promising candidates for surface
coatings to control biofilm growth on water treatment membranes because
of their broad activity and the low tendency of bacteria to develop
resistance to AMPs. However, general and convenient surface modification
methods are limited, and a deeper understanding of the antimicrobial
mechanism of action is needed for surface-attached AMPs. Here, we
show a method for covalently attaching AMPs on porous ultrafiltration
membranes using ink-jet printing and provide insight into the mode
of action for the covalently tethered peptide RWRWRWA-(Bpa) (Bpa,
4-benzophenylalanine) against Pseudomonas aeruginosa. AMP-coated ultrafiltration membranes showed surface antibacterial
activity and reduced biofilm growth. Fluorescence microscopy analysis
revealed that the modified surfaces could cause cell membrane disruption,
which was seen by live uptake of propidium iodide stain, and scanning
electron microscopy images showed compromised cell membranes of attached
bacteria. This study indicated that the mode of action of covalently
tethered AMPs was similar to that of freely soluble AMPs. The deeper
understanding of the mode of action of AMPs covalently attached to
surfaces could lead to a more rational approach for designing surfaces
with antibacterial activity