Detecting and quantifying micro- and nanoplastics (MNPs) in the environment is a crucial task that needs to be addressed as soon as possible by the scientific community. Many analytical techniques have been proposed, but a common agreement on analytical protocols and regulations still has to be reached. Nanomaterial-based techniques have shown promising results in this field. In this review, we focus on the recent results published on the use of plasmonic noble metal materials for the detection of MNPs. Plasmonic materials can be exploited in different ways due to their peculiar optical end electronic properties. Surface plasmon resonance, plasmon enhanced fluorescence, UV–Vis spectroscopy, and surface enhanced Raman scattering (SERS) will be considered in this review, examining the advantages and drawbacks of each approach.

Surface-enhanced Raman scattering (SERS) is becoming widely used as an analytical tool, and the search for stable and highly responsive SERS substrates able to give ultralow detection of pollutants is a current challenge. In this paper we boosted the SERS response of Gold nanostars (GNS) demonstrating that their coating with a layer of silver having a proper thickness produces a 7-fold increase in SERS signals. Glass supported monolayers of these GNS@Ag were then prepared using simple alcoxyliane chemistry, yielding efficient and reproducible SERS chips, which were tested for the detection of molecules representative of different classes of pollutants. Among them, norfloxacin was detected down to 3 ppb, which is one of the lowest limits of detection obtained with this technique for the analyte.

The dramatic increase of environmental pollution leads to the demand of new sampling strategies that could perform in-situ monitoring and rapid identification. In this regard, Surface Enhanced Raman Spectroscopy is a good candidate among the possible analytical techniques. Thus, enormous efforts are in course to select best nanoplatforms able to maximize the SERS effect and in turn to reach the lowest limit of pollutant detection. In this work, we investigated the SERS response of colloidal gold nanostars (GNS) coated with a layer of silver with increasing thickness. In particular, we observed a maximum in the SERS signal at a precise silver thickness. The so-optimized GNS@Ag were used to prepare glass supported SERS substrates, displaying good enhancement factor and high homogeneity intra sample. We also evaluate the reproducibility on large-scale production, demonstrating again a good homogeneity of the response and the overall goodness of the substrates. Our glassy SERS-active chips were fruitfully used to detect norfloxacin and thiram, as representative of harmful and toxic pollutants.

Convenient, rapid, highly sensitive and on-site iron determination is important for environmental safety and human health. We developed a sensing system for the detection of Fe(III) in water based on 7-mercapto-4-methylcoumarine (MMC)-stabilized silver-coated gold nanostars (GNS@Ag@MMC), exploiting a redox reaction between the Fe(III) cation and the silver shell of the nanoparticles, which causes a severe transformation of the nanomaterial structure, reverting it to pristine GNSs. This system works by simultaneously monitoring changes in the Localized Surface Plasmon Resonance (LSPR) and Surface-Enhanced Raman Spectroscopy (SERS) spectra as a function of added Fe(III). The proposed sensing system is able to detect the Fe(III) cation in the 1.0 × 10⁻⁵–1.5 × 10⁻⁴ M range, and its selectivity of the GNS@Ag@MMC sensor toward iron has been verified monitoring the LSPR and the SERS response to other cations with a clear selectivity toward Fe(III).