A Dual Approach of an Oil–Membrane Composite and Boron-Doped Diamond Electrode to Mitigate Biofluid Interferences
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2021-12-02 |
| Journal | Sensors |
| Authors | Madeleine DeBrosse, Yuchan Yuan, Michael Brothers, Aleksandar Karajić, Jeroen van Duren |
| Institutions | United States Air Force Research Laboratory, University of Cincinnati |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”This research presents a novel dual-approach system combining a Boron-Doped Diamond (BDD) electrode with an oil-membrane composite to achieve significantly lower detection limits (LODs) for electrochemical biosensors operating in raw biofluids.
- Core Value Proposition: Mitigation of two primary sensor failure modes in biofluids: background current interference (solvent/solute effects) and electrode fouling (protein adsorption).
- BDD Functionality: The BDD electrode material suppresses background current from water electrolysis, providing a wider potential window and inherently lower baseline noise compared to traditional gold electrodes.
- Oil-Membrane Functionality: A hydrophobic barrier (castor oil impregnated in a track-etch membrane) blocks the diffusion of hydrophilic interferents (e.g., proteins, salts, NADH) while permitting the passage of target hydrophobic analytes (e.g., hormones, drugs).
- Detection Limit Achievement: In an ideal buffer environment (1x PBS), BDD achieved an average 140-fold (up to 365-fold maximum) reduction in LOD compared to gold (1.03 µM vs. 116 µM for hexacyanoferrate).
- Biofluid Protection Success: The oil-membrane protection scheme maintained BDD performance in human serum, achieving an 84-fold average improvement in LOD (1.8 ± 1.3 µM) compared to unprotected BDD directly exposed to serum (83 ± 47 µM).
- Generalizability: This approach is highly generalizable, enabling existing enzymatic or electrochemical sensors to function effectively in complex matrices and potentially reach nanomolar (nM) detection limits for hydrophobic analytes.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| BDD Material Type | Conductive O-terminated polycrystalline diamond | N/A | Films grown on conductive silicon substrate. |
| BDD Sheet Resistivity | 3 to 8 | Ω-cm | Confirmed semiconductive property. |
| BDD Potential Window (in PBS) | > 2.0 | V | Significantly wider than gold (Figure 2a). |
| Gold LOD (in 1x PBS) | 116 ± 63 | µM | Hexacyanoferrate (II/III) probe. |
| BDD LOD (in 1x PBS) | 1.03 ± 0.43 | µM | Hexacyanoferrate (II/III) probe. |
| LOD Reduction (BDD vs. Gold, High) | 365 | Fold | Maximum reduction achieved in buffer. |
| BDD Sensitivity (in 1x PBS) | 22.7 ± 2.6 | ΔCharge (µC)/mM | Lower than gold (50.8 ± 0.6 ΔCharge (µC)/mM). |
| BDD LOD (in Human Serum, Unprotected) | 83 ± 47 | µM | Performance severely degraded by fouling/interferents. |
| BDD LOD (in Human Serum, Oil-Protected) | 1.8 ± 1.3 | µM | Using Castor Oil membrane. |
| LOD Improvement (Oil Protection) | 84 (Average) / 247 (High) | Fold | Improvement over unprotected BDD in serum. |
| Membrane Material | Polycarbonate Track-Etch (PCTE) | N/A | PVP-free, used as substrate for oil. |
| Membrane Pore Size | 1 | µm | Used for oil impregnation. |
| Incubation Time (U-boat Setup) | 18 | h | Time allowed for diffusion and equilibrium. |
| Electrochemical Method | Chronocoulometry (CC) | N/A | Two-step, 30-s step duration. |
Key Methodologies
Section titled “Key Methodologies”- BDD Electrode Fabrication: Conductive O-terminated polycrystalline BDD films on conductive silicon were sourced. A 2-mm diameter active area was defined using Kapton® polyimide tape, and the electrode was secured to an acrylic backing using marine epoxy.
- BDD Electrochemical Cleaning: Due to the delicate thin-film structure, BDD electrodes were cleaned exclusively in 0.5 M H2SO4 via cyclic voltammetry (CV) over an extended potential range (0 to 2.2 V) for 120 scans.
- Oil-Membrane Setup: A 3D-printed U-boat setup, coated with FluoroPel 1601 V fluoropolymer to minimize non-specific adsorption, was used to separate fluid compartments.
- Membrane Preparation: Polycarbonate Track-Etch (PCTE) membranes (1 µm pore size) were soaked in Castor Oil (hydrophobic barrier) or used dry (no-oil control).
- Biofluid Testing: The oil-impregnated membrane was placed between two chambers: one containing 1x PBS (buffer side) and the other containing human serum (biofluid side). The setup was incubated for 18 hours.
- Electrochemical Measurement: Two-step chronocoulometry (CC) was performed on the BDD electrode placed in the buffer side. Redox-active probes (hexacyanoferrate (II/III) and hexaammineruthenium (II/III)) were titrated into the buffer side.
- Data Analysis: The signal (ΔCharge) was calculated as the change in charge between 0 and 30 seconds of the oxidation step. The Limit of Detection (LOD) was defined as 3 * σ / m (where σ is the standard deviation of the blank and m is the slope of the linear trendline).
Commercial Applications
Section titled “Commercial Applications”The dual BDD and oil-membrane approach is critical for advancing electrochemical sensing in complex biological environments, particularly for analytes that are typically difficult to detect due to low concentration or high background noise.
- Wearable and Continuous Monitoring: Enables continuous, long-term monitoring of hydrophobic biomarkers (e.g., steroid hormones like cortisol, testosterone) and small-molecule drugs in raw biofluids (sweat, interstitial fluid) by preventing fouling and maintaining low LODs over extended periods (demonstrated 18 h stability in serum).
- Therapeutic Drug Monitoring (TDM): Provides a platform for highly sensitive, real-time measurement of orally administered hydrophobic drugs in blood or serum, crucial for personalized medicine and ensuring therapeutic windows.
- High-Sensitivity Enzymatic Biosensors: The oil-membrane can be leveraged to trap hydrophilic redox reporters generated by enzymatic reactions within the sensor compartment, significantly enhancing the sensitivity of enzymatic sensors to achieve nM detection limits for low-concentration metabolites.
- Advanced Electrochemical Materials: Utilizes Boron-Doped Diamond (BDD) (supplied by Diamond Foundry Inc.) as a chemically inert, highly stable electrode material suitable for harsh biological environments and applications requiring broad electrochemical windows.
- Point-of-Care (POC) Diagnostics: Facilitates the development of robust POC devices that can analyze raw, unprocessed biofluids (blood, serum) without requiring complex sample preparation steps, reducing time and cost.
View Original Abstract
Electrochemical biosensors promise a simple method to measure analytes for both point-of-care diagnostics and continuous, wearable biomarker monitors. In a liquid environment, detecting the analyte of interest must compete with other solutes that impact the background current, such as redox-active molecules, conductivity changes in the biofluid, water electrolysis, and electrode fouling. Multiple methods exist to overcome a few of these challenges, but not a comprehensive solution. Presented here is a combined boron-doped diamond electrode and oil-membrane protection approach that broadly mitigates the impact of biofluid interferents without a biorecognition element. The oil-membrane blocks the majority of interferents in biofluids that are hydrophilic while permitting passage of important hydrophobic analytes such as hormones and drugs. The boron-doped diamond then suppresses water electrolysis current and maintains peak electrochemical performance due to the foulant-mitigation benefits of the oil-membrane protection. Results show up to a 365-fold reduction in detection limits using the boron-doped diamond electrode material alone compared with traditional gold in the buffer. Combining the boron-doped diamond material with the oil-membrane protection scheme maintained these detection limits while exposed to human serum for 18 h.
Tech Support
Section titled “Tech Support”Original Source
Section titled “Original Source”References
Section titled “References”- 2019 - Accessing analytes in biofluids for peripheral biochemical monitoring [Crossref]
- 2017 - What Are Clinically Relevant Levels of Cellular and Biomolecular Analytes? [Crossref]
- 2019 - Achievements and Challenges for Real-Time Sensing of Analytes in Sweat within Wearable Platforms [Crossref]
- 2020 - From the beaker to the body: Translational challenges for electrochemical, aptamer-based sensors [Crossref]
- 2020 - Consideration of Sample Matrix Effects and “biological” Noise in Optimizing the Limit of Detection of Biosensors [Crossref]
- 1986 - Permeability of small nonelectrolytes through lipid bilayer membranes [Crossref]
- 2019 - Intrinsic Membrane Permeability to Small Molecules [Crossref]
- 2018 - Drug permeability profiling using cell-free permeation tools: Overview and applications [Crossref]