# One-Shot SERRS Detection of Iron and Acidity in Aqueous Systems

## TL;DR

A new optical sensor detects iron and acidity in water, overcoming pH-related interference for accurate results.

## Contribution

A dual-probe SERRS platform is introduced for simultaneous and pH-independent detection of Fe(II) and pH in aqueous systems.

## Key findings

- Fe(II) detection reaches 30 ppb with high selectivity against other metal ions.
- The MBA probe provides a reliable pH readout independent of Fe(II) quantification.
- The sensor avoids false results at alkaline pH by decoupling pH effects from iron detection.

## Abstract

Optical strategies
for ion sensing hold promise for portable and
in situ analysis, yet their reliability is frequently limited by pH-dependent
interferences that alter metal–ligand interactions. Herein,
we present a multiprobe surface-enhanced resonance Raman scattering
(SERRS) platform that enables simultaneous quantification of Fe­(II)
and direct in situ pH readout in aqueous media. The sensor is constructed
from polystyrene beads (PS) densely coated with silver nanoparticles
and functionalized with two probes: phenanthroline (Phen), a metal-selective
dye, hydrophobically entrapped within a cetrimonium bromide (CTAB)
bilayer to retain its Fe­(II) binding activity, and 4-mercaptobenzoic
acid (MBA), covalently anchored to the silver surface to provide a
reliable pH response. Resonant excitation at 532 nm maximizes SERRS
sensitivity, yielding Fe­(II) detection down to 30 ppb with strong
selectivity against competing metal ions. Crucially, the MBA readout
decouples pH effects from Fe­(II) quantification, avoiding false results
at alkaline pH where iron hydroxide precipitates dominate. This dual-sensing
strategy provides a robust concept to overcome pH interference in
optical ion sensing and paves the way for portable, time-resolved
monitoring of metal ions in biological and environmental systems.