Surface-enhanced Raman scattering detection of thiram and ciprofloxacin using chitosan-silver coated paper substrates.

Fast detection of contaminants of emerging concern (CECs) in water resources is of great environmental interest. Ideally, sustainable materials should be used in water quality monitoring technologies implemented for such purposes. In this regard, the application of bio-based materials aimed at the fabrication of analytical platforms has become of great importance. This research merges both endeavors by exploring the application of chitosan-coated paper, decorated with silver nanoparticles (AgNPs), on surface-enhanced Raman scattering (SERS) spectroscopy studies of two distinct types of CECs dissolved in aqueous samples: an antibiotic (ciprofloxacin) and a pesticide (thiram). Our results indicate the superior SERS performance of biocoated substrates compared to their non-coated paper counterparts. The detection limits achieved for thiram and ciprofloxacin using the biocoated substrates were 0.024 ppm and 7.7 ppm, respectively. The efficient detection of both analytes is interpreted in terms of the role of the biopolymer in promoting AgNPs assemblies that result in local regions of enhanced SERS activity. Taking advantage of these observations, we use confocal Raman microscopy to obtain Raman images of the substrates using ciprofloxacin and thiram as molecular probes. We also demonstrate that these biobased substrates can be promising for on-site analysis when used in conjunction with portable Raman instruments.

Corrigendum: Colloidal nanomaterials for water quality improvement and monitoring.

[This corrects the article DOI: 10.3389/fchem.2022.1011186.].

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.

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.

Dendrimer stabilized nanoalloys for inkjet printing of surface-enhanced Raman scattering substrates.

Research on paper substrates prepared by inkjet deposition of metal nanoparticles for sensing applications has become a hot topic in recent years; however, the design of such substrates based on the deposition of alloy nanoparticles remains less explored. Herein, we report for the first time the inkjet printing of dendrimer-stabilized colloidal metal nanoalloys for the preparation of paper substrates for surface-enhanced Raman scattering (SERS) spectroscopy. To this end, nanoassemblies containing variable molar ratios of Au:Ag were prepared in the presence of poly(amidoamine) dendrimer (PAMAM), resulting in plasmonic properties that depend on the chemical composition of the final materials. The dendrimer-stabilized Au:Ag:PAMAM colloids exhibit high colloidal stability, making them suitable for the preparation of inks for long-term use in inkjet printing of paper substrates. Moreover, the pre-treatment of paper with a polystyrene (PS) aqueous emulsion resulted in hydrophobic substrates with improved SERS sensitivity, as illustrated in the analytical detection of tetramethylthiuram disulfide (thiram pesticide) dissolved in aqueous solutions. We suggest that the interactions established between the two polymers (PAMAM and PS) in an interface region over the cellulosic fibres, resulted in more exposed metallic surfaces for the adsorption of the analyte molecules. The resulting hydrophobic substrates show long-term plasmonic stability with high SERS signal retention for at least ninety days.

Electrocatalytic reduction of organohalides mediated by the dihalo-molybdenum phosphinic complexes trans-[MoX(2)(Ph(2)PCH(2)CH(2)PPh(2))(2)] (X = I, Br)-A mechanistic study by cyclic voltammetry digital simulation.

trans-[MoX(2)(dppe)(2)] (X = I, Br) act as inner-sphere electron-transfer mediators for the electrocatalytic reduction of organohalides RX to R + X(-), at both Mo(II)--> Mo(I) and Mo(I)--> Mo(0) reduction processes, each of them involving a cathodically induced heterolytic metal-halide bond cleavage with liberation of X(-) that is followed by addition of RX to the metal. Digital simulation of cyclic voltammetry at a wide range of scan rates allowed to estimate the rate constants of the various chemical steps for both electrocatalytic cycles, which were compared in terms of Mo-X bond dissociation energies, electronic and stereochemical effects.