Dendrimer-based magneto-plasmonic nanosorbents for water quality monitoring using surface-enhanced Raman spectroscopy

In this work, we report the synthesis of magneto-plasmonic dendrimer-based nanosorbents containing Au nanostars and we demonstrate that they can be used as versatile optical sensors for the detection of pesticides in spiked water samples. The magnetic hybrid nanoparticles were obtained by conjugating silica-functionalized G5-NH₂ PAMAM dendrimers to silica-coated magnetite cores. The resulting magnetic-PAMAM conjugates were then used to reduce and sequester Au seeds for the subsequent in situ growth of Au nanostars. The dendrimer-based magneto-plasmonic substrates containing the Au anisotropic nanophases were then investigated regarding their ability to monitor water quality through surface-enhanced Raman scattering (SERS) spectroscopy. As a proof-of-concept, the ensuing multifunctional materials were investigated as SERS probing systems to detect dithiocarbamate pesticides (ziram and thiram) dissolved in water samples. It was observed that the magneto-plasmonic hybrid materials enhance the Raman signal of these pesticides under variable operational conditions, suggesting the versatility of these systems for water quality monitoring. Moreover, a detailed analysis of the SERS data was accomplished to predict the adsorption profile of the dithiocarbamate pesticides to the Au surface.

Colloidal nanomaterials for water quality improvement and monitoring

Water is the most important resource for all kind forms of live. It is a vital resource distributed unequally across different regions of the globe, with populations already living with water scarcity, a situation that is spreading due to the impact of climate change. The reversal of this tendency and the mitigation of its disastrous consequences is a global challenge posed to Humanity, with the scientific community assuming a major obligation for providing solutions based on scientific knowledge. This article reviews literature concerning the development of nanomaterials for water purification technologies, including collaborative scientific research carried out in our laboratory (nanoLAB@UA) framed by the general activities carried out at the CICECO-Aveiro Institute of Materials. Our research carried out in this specific context has been mainly focused on the synthesis and surface chemical modification of nanomaterials, typically of a colloidal nature, as well as on the evaluation of the relevant properties that arise from the envisaged applications of the materials. As such, the research reviewed here has been guided along three thematic lines: 1) magnetic nanosorbents for water treatment technologies, namely by using biocomposites and graphite-like nanoplatelets; 2) nanocomposites for photocatalysis (e.g., TiO2/Fe3O4 and POM supported graphene oxide photocatalysts; photoactive membranes) and 3) nanostructured substrates for contaminant detection using surface enhanced Raman scattering (SERS), namely polymers loaded with Ag/Au colloids and magneto-plasmonic nanostructures. This research is motivated by the firm believe that these nanomaterials have potential for contributing to the solution of environmental problems and, conversely, will not be part of the problem. Therefore, assessment of the impact of nanoengineered materials on eco-systems is important and research in this area has also been developed by collaborative projects involving experts in nanotoxicity. The above topics are reviewed here by presenting a brief conceptual framework together with illustrative case studies, in some cases with original research results, mainly focusing on the chemistry of the nanomaterials investigated for target applications. Finally, near-future developments in this research area are put in perspective, forecasting realistic solutions for the application of colloidal nanoparticles in water cleaning technologies.

Dual functional PDMS sponge SERS substrate for the on-site detection of pesticides both on fruit surfaces and in juice

A versatile dual-functional polydimethylsiloxane (PDMS) sponge Surface Enhanced Raman Scattering (SERS) substrate has been fabricated for the on-site detection of pesticide residues both on the surface and in solution with minimum or no sample pretreatment.

Hybrid nanostructures for SERS: materials development and chemical detection

This review focuses on recent developments in hybrid and nanostructured substrates for SERS (surface-enhanced Raman scattering) studies. Thus substrates composed of at least two distinct types of materials, in which one is a SERS active metal, are considered here aiming at their use as platforms for chemical detection in a variety of contexts. Fundamental aspects related to the SERS effect and plasmonic behaviour of nanometals are briefly introduced. The materials described include polymer nanocomposites containing metal nanoparticles and coupled inorganic nanophases. Chemical approaches to tailor the morphological features of these substrates in order to get high SERS activity are reviewed. Finally, some perspectives for practical applications in the context of chemical detection of analytes using such hybrid platforms are presented.