Trace Detection of Malachite Green in Stream Water

Importance of the Topic

Malachite green (MG) has been widely used as a textile dye and aquaculture fungicide despite its known toxicity to fish and mammals. Residual MG and its metabolites accumulate in edible tissues, posing significant risks to human health. Even trace amounts above regulatory limits (2 µg/kg) are considered hazardous, and illegal applications continue to threaten seafood safety worldwide.

Objectives and Study Overview

The primary goal of this study is to demonstrate a simple, rapid assay for on-site detection of MG in stream water associated with aquaculture. By leveraging Metrohm’s portable SERS platform, the work aims to validate sensitivity down to low-ng/mL levels and outline a streamlined field protocol for routine screening.

Methodology and Instrumentation

A series of stream water samples was spiked with MG at concentrations ranging from 1 ng/mL to 10 µg/mL. Each 0.1 mL sample (pH 7.0) was mixed with 0.8 mL of gold nanoparticle (Au NP) colloid and 0.1 mL of 500 mM NaCl to enhance SERS signal. Spectra were acquired using Metrohm Instant SERS Analyzer (MISA Advanced) equipped with Orbital-Raster-Scan technology. Key acquisition parameters included a 1 s integration time, 10 averages, and laser power set to Class 1 safety levels.

Instrumentation

• MISA Advanced (Metrohm Instant SERS Analyzer) with vial and P-SERS attachments
• ID Kit – Au NP containing gold colloid, disposable spatula, droppers, and sample vials
• MISA Cal software (version 1.0.15) and firmware 0.9.33

Key Results and Discussion

Distinct SERS spectra of MG were obtained across the tested concentration range. Clear, baseline-subtracted signals were detectable down to 1 ng/mL. The intensity profile demonstrated a reliable concentration-dependent response, confirming the method’s suitability for trace analysis in complex water matrices without extensive sample preparation.

Benefits and Practical Applications

• On-site testing capability reduces sample transport delays.
• Minimal user training required thanks to a straightforward assay format.
• Rapid throughput with results in minutes supports routine monitoring.
• Detection limits exceed regulatory requirements for food safety.

Future Trends and Opportunities

Advances in nanoparticle substrates and SERS data analysis will further improve sensitivity and specificity. Integrating portable SERS devices with cloud-based analytics can enable real-time surveillance of multiple contaminants. Expansion of field-deployable assays to other banned or emerging aquaculture agents will strengthen food safety enforcement globally.

Conclusion

The combination of MISA Advanced and gold nanoparticle-enhanced SERS offers a robust, user-friendly solution for rapid MG detection in stream water. With detection limits well below permissible levels, this method facilitates proactive monitoring of illegal fungicidal use in aquaculture, contributing to consumer protection and regulatory compliance.