# Polypyrrole-Coated Microneedle Platform for Offline Electrochemical Detection of Interferon-Alpha in Interstitial Fluid

## TL;DR

A new microneedle biosensor coated with polypyrrole can detect interferon-alpha in interstitial fluid with minimal invasiveness and without complex equipment.

## Contribution

A minimally invasive, offline electrochemical biosensor using polypyrrole-coated microneedles for detecting interferon-alpha in interstitial fluid is developed.

## Key findings

- PPy-coated microneedles achieved a detection limit of 8.6 pg/mL for IFN-α.
- Intermediate PPy concentration (50 mmol·L–1) provided optimal surface properties and biocompatibility.
- The biosensor demonstrated robust selectivity and safety in gelatin matrices and cytotoxicity assays.

## Abstract

Monitoring cytokines, such as interferon-alpha (IFN-α),
is
essential for assessing immune responses during viral infections and
in immunotherapies. Here, we report the development of a microneedle-based
electrochemical biosensor for detecting IFN-α in interstitial
fluid (ISF), which combines minimally invasive sampling with label-free,
offline analysis. The device comprises polycaprolactone (PCL) microneedles
fabricated via 3D-printed molds and thermocompression, coated with
polypyrrole (PPy) to enable conductivity and biomolecule immobilization.
A range of PPy concentrations (10–200 mmol·L–1) was evaluated to optimize performance. Structural and physicochemical
analyses revealed that intermediate PPy content (50 mmol·L–1) ensured optimal surface roughness, porosity (29.7%),
and electroactive area, while preserving mechanical integrity and
biocompatibility. Electrochemical impedance spectroscopy and cyclic
voltammetry demonstrated a sensitive and specific response to IFN-α,
with a limit of detection of 8.6 pg/mL and a linear range of up to
1000 pg/mL. Selectivity studies in gelatin matrices and cytotoxicity
assays confirmed the robust performance and safety of the system.
The biosensor operates via skin insertion, immunocapture, and analyte
quantification after removal, enabling offline detection without complex
instrumentation. These results demonstrate the potential of PPy-coated
microneedles as cost-effective, scalable, and minimally invasive platforms
for cytokine monitoring in point-of-care diagnostics.