Common Substrate Materials for Precious Metal Bioelectrodes and Their Applicable Detection Scenarios

| Author: Huili Biotech Technical Team

I. Overview

Precious metal bioelectrodes are core sensing components in fields such as electrochemical sensing, biomarker detection and breath gas analysis. Their performance depends not only on the surface precious metal active layer, but also directly on the mechanical properties, chemical stability and electrical characteristics of the substrate material. The substrate determines the electrode's flexibility, upper operating temperature limit, corrosion resistance and biocompatibility, making it a core decision factor in product selection and solution design.

Notably, the preparation process imposes decisive constraints on substrate selection: the screen printing process requires high-temperature sintering for curing, and is only applicable to high-temperature-resistant substrate materials. In contrast, the magnetron sputtering process can deposit precious metal thin films at room temperature or low temperatures, with no strict high-temperature requirements for substrates. It enables customized electrode processing on a wide range of heat-labile biocompatible materials, greatly expanding the substrate selection range and application scenarios of bioelectrodes.

II. Classification of Common Substrate Materials

By material properties, mainstream substrates fall into three categories, adapted to different application forms and detection scenarios:

  1. Flexible polymer substrates
    This is the most mainstream substrate type for portable and wearable bioelectrodes, and can be divided into two tiers based on temperature resistance and process compatibility:
    • High-temperature resistant type (PI, polyimide): It features excellent temperature resistance (withstanding process temperatures above 200°C) and stable dielectric properties. It is compatible with both high-temperature sintering in screen printing and magnetron sputtering coating processes, and has high mechanical strength, serving as the standard substrate material for high-performance flexible bioelectrodes.
    • Low-temperature compatible type (PET, PEN, medical-grade PU, etc.): Materials such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and medical-grade polyurethane (PU) have lower cost, better flexibility and good skin compatibility, but their long-term temperature resistance is mostly below 120°C, making them unable to withstand the high-temperature sintering process of screen printing pastes. Benefiting from the low-temperature deposition characteristic of magnetron sputtering, these heat-labile biocompatible materials can be processed into customized precious metal electrodes, and are widely used in affordable biomedical scenarios such as disposable skin biochemical sensing, non-invasive breath detection and home health monitoring.
  2. Rigid inorganic substrates
    Mainly glass, monocrystalline silicon wafers and alumina ceramics, with ultra-high surface flatness and uniform film adhesion. They are suitable for laboratory R&D, high-precision reference electrodes and chip-level integrated electrodes, but have the drawbacks of fragility, high cost and incompatibility with flexible wearable scenarios. Such substrates are compatible with both screen printing and magnetron sputtering processes.
  3. Metal substrates
    Represented by titanium, titanium-tungsten alloy and stainless steel, they combine electrical conductivity and structural strength, can serve directly as both the electrode conductive layer and support substrate, and have strong electrochemical corrosion resistance. They are mostly used in industrial environmental detection, implantable sensing and high-current operation scenarios. Such substrates have high temperature resistance and are compatible with both preparation processes.

III. Characteristics of Core Precious Metal Electrode Materials and Scenario Adaptation

Gold (Au), platinum (Pt), titanium (Ti) and titanium-tungsten (TiW) are the four most widely used precious/active metal materials in bioelectrodes, with distinct electrochemical properties adapted to different detection principles and application scenarios:

1. Gold (Au)-based Electrodes

Core material properties: Extremely strong chemical stability, resistance to oxidation at room temperature, excellent biocompatibility, moderate electrochemical window, easy surface modification such as thiol self-assembled monolayer (SAM) and antibody immobilization, and superior electrical conductivity.

  • Electrochemical detection: Highly suitable for conventional electrochemical analysis including cyclic voltammetry (CV), differential pulse voltammetry (DPV) and amperometry. It is the standard material for electrodes detecting metabolites like glucose and lactic acid.
  • Biosensing: Gold electrodes are the preferred substrate for enzyme biosensors, immunosensors and DNA sensors. They enable immobilization of biorecognition molecules via surface modification, with low non-specific adsorption and high detection signal-to-noise ratio.
  • Breath detection: Suitable for electrochemical catalytic detection of organic volatiles such as acetone and ethanol in breath. It works especially well in portable room-temperature breath analyzers, with no oxidation drift during long-term use and better stability than ordinary metal electrodes. When paired with low-temperature flexible substrates (PET/PU), gold electrodes can be fabricated into disposable home-use gold electrode biosensors via sputtering, balancing cost and application safety.

2. Platinum (Pt)-based Electrodes

Core material properties: Extremely high catalytic activity, wide electrochemical window, high temperature resistance, strong resistance to strong acid and alkali corrosion, and excellent long-term working stability. It is a classic catalytic electrode material for gas sensing and electrochemical reactions.

  • Electrochemical detection: Suitable for detection requiring high overpotential, such as heavy metal ion detection and reactive oxygen species (ROS) detection. It can function as working electrode, counter electrode and reference electrode simultaneously, adapting to harsh electrolyte environments.
  • Biosensing: Mostly used as signal amplification electrodes for enzyme-catalyzed reactions, as well as implantable in vivo biosensors. It has sound biocompatibility and withstands long-term corrosion in complex body fluid environments.
  • Breath detection: It is the core electrode material for detecting breath gas molecules such as carbon monoxide (CO), hydrogen and methane. Platinum's catalytic effect enables efficient redox of gas molecules, with low detection limit and fast response, making it the mainstream solution for breath analyzer gas sensors.

3. Titanium (Ti)-based Electrodes

Core material properties: High cost-effectiveness, high mechanical strength, strong corrosion resistance, and easy formation of a dense oxide layer on the surface. It is usually used as a bottom adhesion layer or directly as a substrate electrode, with excellent biocompatibility.

  • Electrochemical detection: Mostly serves as a transition adhesion layer substrate for precious metal thin films, improving the adhesion between gold/platinum coatings and polymer substrates. Pure titanium electrodes can be used for electrochemical detection in conventional aqueous environments at significantly lower cost than precious metal electrodes.
  • Biosensing: Titanium substrate meets implantable-grade biocompatibility requirements, and is mostly used for implantable physiological signal detection electrodes and as the conductive base for mass-produced disposable biosensing electrodes.
  • Breath detection: Generally not used as a direct catalytic layer, but mainly as the bottom conductive and support structure of breath electrodes, paired with surface-sputtered platinum/gold active layers to effectively reduce overall material cost.

4. Titanium-Tungsten (TiW)-based Electrodes

Core material properties: Titanium-tungsten alloy combines the corrosion resistance of titanium and the high hardness/high melting point of tungsten. It forms dense films with strong diffusion barrier capability, and is a classic adhesion and barrier layer material for high-performance thin film electrodes.

  • Electrochemical detection: Mainly used as an intermediate barrier layer for gold and platinum thin film electrodes, preventing precious metal atoms from diffusing into the substrate and improving long-term working stability. It is suitable for electrochemical equipment for long-term continuous monitoring.
  • Biosensing: Adapted to high-precision thin film biosensors, effectively inhibiting substrate ion migration, avoiding signal drift and improving batch consistency. It is mostly used in medical-grade quantitative detection biosensors.
  • Breath detection: Applied in high-temperature, high-humidity breath detection environments, improving film adhesion and anti-aging performance and extending the service life of breath sensors. It is a common substrate solution for industrial and vehicle-mounted breath detectors.

IV. Selection Summary

  • For convenient biological modification and room-temperature detection of breath organics, gold-based electrodes are preferred;
  • For gas catalytic detection and high-stability CO/hydrogen breath analysis, platinum-based electrodes are preferred;
  • For cost control and structural support as the bottom conductive layer, titanium-based electrodes are preferred;
  • For high stability, anti-diffusion performance and long-life continuous monitoring, titanium-tungsten alloy substrate electrodes are preferred;
  • For disposable, skin-contact bioelectrodes made of flexible low-temperature substrates (PET/PU, etc.), customized processing can only be achieved via magnetron sputtering process, and screen printing process is not applicable.
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