# Sulfate‐Directed Silver Dendrites with Enhanced Stability for Ultrasensitive SERS‐Based Therapeutic Drug Monitoring

## TL;DR

This paper introduces a new type of silver-based sensor that is more stable and sensitive, making it suitable for monitoring drug levels in patients at the point of care.

## Contribution

The novel use of sulfate ions to create oxidation-resistant silver dendrites with long-term stability and high sensitivity for SERS-based drug monitoring.

## Key findings

- Sulfate-directed silver dendrites (s-AgDs) show robust SERS performance for seven months under ambient conditions.
- s-AgDs detect five clinically relevant drugs in blood plasma with minimal pretreatment and high reproducibility.
- The dendrites have sub-picomolar sensitivity and high hot-spot density due to sulfate-induced anisotropic growth.

## Abstract

Silver‐based surface‐enhanced Raman spectroscopy (SERS) substrates offer exceptional signal enhancement but suffer from poor long‐term stability due to oxidative degradation, limiting their utility for real‐world applications. Here, we introduce sulfate‐directed silver dendrites (s‐AgDs) as oxidation‐resistant SERS substrates with extended shelf life, reproducible signal performance, and sub‐picomolar sensitivity. Sulfate ions promote anisotropic growth and form a surface‐associated sulfate layer, resulting in dendritic morphologies with high hot‐spot density and suppressed surface oxidation. The AgDs demonstrate robust SERS performance over seven months under ambient conditions. We demonstrate translational utility by detecting five clinically relevant drugs in aqueous and blood plasma matrices with minimal pretreatment and excellent reproducibility. These results establish s‐AgDs as a stable, reproducible, and application‐ready SERS platform for point‐of‐care therapeutic drug monitoring.

This study presents sulfate‐directed silver dendrites (s‐AgDs) as oxidation‐resistant SERS substrates with long‐term stability, reproducibility, and sub‐picomolar sensitivity. Sulfate ions guide anisotropic growth and protect the surface, enabling improved performance over 7 months under ambient conditions. The s‐AgDs detect multiple therapeutic drugs in blood plasma, enabling them as a robust platform for point‐of‐care drug monitoring.