Oil-Membrane Protection of Electrochemical Sensors for Fouling- and pH-Insensitive Detection of Lipophilic Analytes

Abstract

To take full advantage of the reagent- and label-free sensing capabilities of electrochemical sensors, a frequent and remaining challenge is interference and degradation of the sensors due to uncontrolled pH or salinity in the sample solution or foulants from the sample solution. Here, we present an oil-membrane sensor protection technique that allows for the permeation of hydrophobic (lipophilic) analytes into a sealed sensor compartment containing ideal salinity and pH conditions while simultaneously blocking common hydrophilic interferents (proteins, acids, bases, etc.) In this paper, we validate the oil-membrane sensor protection technique by demonstrating continuous cortisol detection via electrochemical aptamer-based (EAB) sensors. The encapsulated EAB cortisol sensor exhibits a 5 min concentration-on rise time and maintains a measurement signal of at least 7 h even in the extreme condition of an acidic solution of pH 3.

Week-long operation of electrochemical aptamer sensors: New insights into self-assembled monolayer degradation mechanisms and solutions for stability in biofluid at body temperature

“…26 We initially sought to test this phosphatidylcholine-terminated monolayer with the vancomycin aptamer used throughout this work but were unable to generate sensors with appreciable response to vancomycin. We therefore utilized previously reported aptamer sequences targeting cortisol 46 and L-phenylalanine, 47 with which the phosphatidylcholine-terminated passivation layer resulted in significant improvement in maintaining sensor response with repeated scanning in serum at 37 °C as compared to MCH (Figure S7). The hydrogel protection and anti-fouling monolayer strategies utilized here are unoptimized and are reported to simply demonstrate that fouling-induced loss in sensor response can be prevented over multi-day time scales, and therefore we expect can perform for at least one week or more under optimized conditions.…”

A Dual Approach of an Oil–Membrane Composite and Boron-Doped Diamond Electrode to Mitigate Biofluid Interferences

“…Generalizing the problematic solutes as hydrophilic theoretically presents a significant opportunity for filtering out these species by implementing a hydrophobic protective barrier for sensors systems. Here we implement an oil-impregnated polycarbonate track-etch (PCTE) membrane as a semipermeable hydrophobic filter to mitigate the diffusion of hydrophilic interfering species [ 35 ]. The oil–membrane conditions used during this study include no-oil as a control and castor oil as a robust hydrophobic barrier.…”

“…The oil–membrane conditions used during this study include no-oil as a control and castor oil as a robust hydrophobic barrier. Castor oil has been shown to maintain buffer conditions over a 12-h timespan, likely due to its high viscosity and high water-octanol partition coefficient that considerably slow the passage of hydrophilic species [ 35 ]. Other oil–membrane composites were not investigated as our goal was to simply demonstrate the ability of the oil–membrane in maintaining sensor performance in biological fluids.…”

Electrochemical Aptamer-Based Sensors with Tunable Detection Range

“…Thus, a variety of methods have also been developed to enhance the pH tolerance of E-AB sensors. For example, an oil membrane sensor could protect the E-AB sensors from salinity and pH . Besides, the impact of pH is closely related to the redox probe used in the E-AB sensors.…”