Introduction
Protein quantification methods are often built on similar biological principles, but differ in how the signal is generated and measured.
Many established assays, such as ELISA, rely on optical detection. In contrast, Redox Electrochemical Detection (RED) uses an electrochemical readout to quantify proteins.
Understanding how RED works—from binding to signal—helps explain how electrochemical approaches can support protein quantification across a range of workflows.
From Binding to Signal: The Core Assay Principle
At its core, RED-based quantification follows a familiar structure:
- Affinity capture
→ the target protein binds to a specific capture molecule on the sensor surface - Enzymatic labelling
→ a detection reagent labelled with an enzyme (typically HRP) binds to the captured complex - Signal generation
→ the enzyme catalyses a reaction that produces an electrochemically active species
This combination of specific binding + enzymatic amplification underpins many quantitative assays, including RED-based approaches.
What Is RED?
RED (Redox Electrochemical Detection) uses a well-established enzymatic system—HRP with TMB substrate—but measures the reaction differently.
Instead of detecting a colour change, RED measures electron transfer at an electrode.
- HRP catalyses the oxidation of TMB
- This produces an electroactive species
- A small electrical potential is applied
- Electron transfer occurs at the electrode
- The resulting current is measured
This electrical current is directly related to:
- the amount of enzyme present
- and therefore the amount of target protein
This allows RED to translate a familiar assay chemistry into an electrical signal that can be used for quantitative protein measurement.
From Enzyme Activity to Quantitative Signal
The key difference in RED is how the signal is captured.
In optical assays:
- signal builds over time
- measurement depends on colour development
In RED:
- electron transfer is measured directly
- signal is generated as the reaction occurs
This allows the system to translate molecular binding into a quantitative electrical readout, without relying on optical detection.
How the Assay Is Performed in Practice
In RED-based systems such as Amperia™, the assay is carried out using sensor strips with integrated electrodes.
- Sensors are functionalised with capture molecules
- The sensor moves through a sequence of wells:
- sample
- wash
- detection reagent
- substrate
- Each step is controlled within a guided workflow
- The final signal is measured electrochemically at the sensor tip
This structured process supports consistent timing and exposure across samples.
Why Detection Method Matters
While the assay format remains affinity-based, the detection method can influence performance in practice.
Electrochemical detection:
- does not rely on light transmission
- is less affected by sample turbidity or colour
- measures signal directly at the sensor surface
This can be particularly relevant when working with:
- crude lysates
- cell culture media
- process intermediates
where optical interference may affect traditional readouts.
Supporting Different Assay Formats
RED-based detection can be applied across multiple assay formats, depending on the target:
- Sandwich assays
→ signal increases with analyte concentration (e.g. AAV capsids) - Inverse occupancy assays
→ signal decreases with analyte concentration (e.g. antibodies) - Competitive assays
→ signal reflects competition for binding sites (e.g. tagged proteins)
This flexibility allows a single detection principle to be used across different biologic targets.
Conclusion
Redox Electrochemical Detection (RED) combines established biochemical principles with a different approach to signal measurement.
By translating enzymatic activity into an electrical signal, RED provides an alternative way to quantify proteins—particularly in workflows where consistency, speed, and sample complexity are important considerations.
Understanding how RED works—from affinity capture to electrochemical readout—helps place it within the broader landscape of protein quantification methods.