# Caffeic Acid-Driven Green Synthesis of Rhenium Nanoparticles Embedded in Self-Templating Double-Shelled ZnMn2O4 Hollow Microspheres for Ultrasensitive Epinephrine Detection in Biofluids

## TL;DR

A new electrochemical sensor using rhenium nanoparticles in a ZnMn2O4 structure detects epinephrine in biofluids with high sensitivity and accuracy.

## Contribution

A novel green synthesis method creates Re@ZnMn2O4 for ultrasensitive epinephrine detection in biofluids.

## Key findings

- The sensor has a broad detection range (0.5–1951.3 μM) and low detection limit (0.21 μM).
- It shows excellent reproducibility, stability, and resistance to interferents.
- Accurate epinephrine quantification was achieved in human serum and urine.

## Abstract

In the present work, we report an electrochemical sensor
based
on rhenium (Re) nanoparticles embedded within a double-shelled ZnMn2O4 hollow microsphere (Re@ZnMn2O4) for ultrasensitive detection of epinephrine (EP) in biofluids.
The Re@ZnMn2O4 material was synthesized via
a coprecipitation and annealing route, followed by a green, caffeic
acid (CA)-assisted chemical reduction. Structural and morphological
analyses, including spectrophotometry, confirmed the high purity,
crystallinity, and integrity of the material. Electrochemical performance
was evaluated using voltammetry and impedance spectroscopy. The Re@ZnMn2O4-modified electrode exhibited superior electrochemical
activity attributed to its high conductivity, large surface area,
abundant active sites, and efficient charge transfer enabled by the
hollow architecture. EP oxidation followed a diffusion-controlled
2e–/2H+ transfer mechanism. The sensor
demonstrated a broad linear detection range (0.5–1951.3 μM),
a low detection limit (0.21 μM), and good sensitivity (0.282
μA μM–1 cm–2). Furthermore,
it showed remarkable reproducibility, long-term stability, and strong
resistance to common interferents. Its practical potential was validated
by accurate EP quantification in human serum and urine, highlighting
its applicability in clinical diagnostics and biomedical monitoring.