# A Review of Aggregation-Based Colorimetric and SERS Sensing of Metal Ions Utilizing Au/Ag Nanoparticles

## TL;DR

This paper reviews colorimetric and SERS sensing methods using Au/Ag nanoparticles for detecting metal ions, highlighting their complementary roles and recent advancements.

## Contribution

The paper provides a comprehensive review of aggregation-based sensing technologies for metal ions, emphasizing their integration and recent methodological improvements.

## Key findings

- Colorimetric assays enable rapid, visual detection of metal ions suitable for point-of-care testing.
- SERS offers high sensitivity and structural information for precise quantification in complex samples.
- Dual-mode platforms combining both methods improve reliability through signal verification.

## Abstract

The accurate monitoring and dynamic analysis of metal ions are of considerable practical significance in environmental toxicology and life sciences. Colorimetric analysis and surface-enhanced Raman scattering (SERS) sensing technologies, utilizing the aggregation effect of gold and silver nanoparticles (Au/Ag NPs), have emerged as prominent methods for rapid metal ion detection. While sharing a common plasmonic basis, these two techniques serve distinct yet complementary analytical roles: colorimetric assays offer rapid, instrument-free visual screening ideal for point-of-care testing (POCT), whereas SERS provides superior sensitivity and structural fingerprinting for precise quantification in complex matrices. Furthermore, the synergistic integration of these modalities facilitates the development of dual-mode sensing platforms, enabling mutual signal verification for enhanced reliability. This article evaluates contemporary optical sensing methodologies utilizing aggregation effects and their advancements in the detection of diverse metal ions. It comprehensively outlines methodological advancements from nanomaterial fabrication to signal transduction, encompassing approaches such as biomass-mediated green synthesis and functionalization, targeted surface ligand engineering, digital readout systems utilizing intelligent algorithms, and multimodal synergistic sensing. Recent studies demonstrate that these techniques have attained trace-level identification of target ions regarding analytical efficacy, with detection limits generally conforming to or beyond applicable environmental and health safety regulations. Moreover, pertinent research has enhanced detection linear ranges, anti-interference properties, and adaptability for POCT, validating the usefulness and developmental prospects of this technology for analysis in complicated matrices.