Etching-based plasmonic sensing mechanisms in metallic nanostructures: advances and applications in food safety and environmental monitoring

The health of humans is closely linked to the quality of food and the environment. Various pollutants including heavy metals, pathogens, antibiotic residues, and toxins can adversely affect food safety and environmental sustainability, posing significant risks to human well-being. Therefore, continuous monitoring of food and environmental safety is essential. Traditional methods for monitoring these factors include culture-based techniques for pathogens, immunological assays, and chromatography. Although effective, these methods often suffer from drawbacks such as complexity, time consumption, and the need for skilled operators. However, emerging sensing technologies present a promising alternative to address these challenges. A diverse array of sensing approaches utilizing nanomaterials have emerged, offering versatility across various analytes. The unique optical properties of nanomaterials have particularly advanced the field of optical sensing. The localized surface plasmon resonance (LSPR) characteristics of nanomaterials, dependent on their size, morphology, and structure, make them valuable tools for fabricating optical sensors. Optical sensing can be executed through several methods including etching processes that oxidize metal atoms in nanostructures into soluble ions. This oxidation correlates with changes in the LSPR spectra and is often accompanied by observable color changes in samples. Given the critical need for food and environmental monitoring and the intriguing optical properties of analytes detectable through etching-based approaches, this review aims to comprehensively discuss the recent advancements in etching-based detection methods for significant analytes in food technology and environmental analysis and the mechanisms of nanomaterial etching; additionally, it provides insights into various metallic nanomaterials with distinct morphologies. Unlike previous reviews that have primarily focused on gold nanoparticles or nanorods, this work offers a broader and more comparative perspective by integrating gold, silver, and hybrid nanostructures with diverse morphologies, extending beyond the narrower focus of earlier studies. The review further highlights that anisotropic nanostructures such as nanorods, nanostars, and nanoplates exhibit superior LSPR tunability and sensitivity in etching-based biosensing, while core-shell and hybrid architectures offer greater versatility for controlled etching. By summarizing these relationships and the most effective etching mechanisms for specific analyte categories, this review provides a concise reference for designing high-performance plasmonic sensors for food and environmental monitoring.