4 research outputs found
Surface-Enhanced Raman Scattering Spectral Imaging for the Attomolar Range Detection of Crystal Violet in Contaminated Water
A series
of nanocomposites based on polyamide (NL16, PA) filter
membranes containing metal nanoparticles (NPs) have been prepared
by filtration under reduced pressure of the metal colloids. The ensuing
materials were then investigated as substrates for surface-enhanced
Raman scattering (SERS) imaging studies envisaging the spectroscopic
detection of vestigial organic pollutants dissolved in contaminated
water. The organic dye crystal violet (CV) was used here as a model
pollutant because it is a hazardous compound present in certain effluent
waters. Moreover this compound is well-known for its strong SERS activity,
which is clearly advantageous in the context of material development
for SERS. Indeed, several preparative strategies were employed to
prepare PA-based composites, and the impact on SERS detection was
investigated. These include the use of chemical and morphological
distinct plasmonic NPs (Ag, Au), a variable metal load and changing
the order of addition of the analytical specimens. These studies demonstrate
that the parameters employed in the fabrication of the SERS substrates
have a strong impact on the Raman signal enhancement. The use of Raman
imaging during the fabrication process allows establishing improvements
that translate to better performances of the substrates in the analyte
detection. The results have been interpreted by considering an integrated
set of operational parameters that include the affinity of CV molecules
to the substrate, amount and dispersion of NPs in the PA membranes,
and the detection method. Â Noteworthy the use of SERS analysis
assisted with Raman imaging allowed achieving a detection limit for
CV as low as 100 aM in ultrapure water and 10 fM in real samples
Raman Signal Enhancement Dependence on the Gel Strength of Ag/Hydrogels Used as SERS Substrates
A series
of hydrogel samples composed of Ag nanoparticles dispersed
in carrageenan gels have been prepared and used in SERS studies. These
studies demonstrate the dependence of the enhancement of the SERS
signal on the strength of the Ag/polysaccharide hydrogel. 2,2âČ-Dithiodipyridine
was used as the analyte probe. Several strategies were employed in
order to vary the gel strength. These include the increase of the
polysaccharide content in the gel, the addition of KCl as cross-linker,
and the variation of the type of carrageenan (Îș, Îč, λ)
network. An increase in the gel strength originates an increase in
the SERS enhancement observed. The results have been interpreted considering
hot spots increase due to the formation of Ag particles nanojunctions
as the biopolymer matrix tends to rearrange into stronger gels. This
is the first report showing that there is a direct correlation between
the gel strength of a hydrogel composite used as substrate and its
analytical SERS sensitivity
High-throughput tool to discriminate effects of NMs (Cu-NPs, Cu-nanowires, CuNO<sub>3</sub>, and Cu salt aged): transcriptomics in <i>Enchytraeus crypticus</i>
<p>The current testing of nanomaterials (NMs) via standard toxicity tests does not cover many of the NMs specificities. One of the recommendations lays on understanding the mechanisms of action, as these can help predicting long-term effects and safe-by-design production. In the present study, we used the high-throughput gene expression tool, developed for <i>Enchytraeus crypticus</i> (4âĂâ44k Agilent microarray), to study the effects of exposure to several copper (Cu) forms. The Cu treatments included two NMs (spherical and wires) and two copper-salt treatments (CuNO<sub>3</sub> spiked and Cu salt field historical contamination). To relate gene expression with higher effect level, testing was done with reproduction effect concentrations (EC<sub>20</sub>, EC<sub>50</sub>), using 3 and 7âdays as exposure periods. Results showed that time plays a major role in the transcriptomic response, most of it occurring after 3âdays. Analysis of gene expression profiles showed that Cu-salt-aged and Cu-nanowires (Nwires) differed from CuNO<sub>3</sub> and Cu-nanoparticles (NPs). Functional analysis revealed specific mechanisms: Cu-NPs uniquely affected senescence and cuticle pattern formation, which can result from the contact of the NPs with the wormsâ tegument. Cu-Nwires affected reproduction via male gamete generation and hermaphrodite genitalia development. CuNO<sub>3</sub> affected neurotransmission and locomotory behavior, both of which can be related with avoidance response. Cu salt-aged uniquely affected phagocytosis and reproductive system development (via different mechanisms than Cu-Nwires). For the first time for Cu (nano)materials, the adverse outcome pathways (AOPs) drafted here provide an overview for common and unique effects per material and linkage with apical effects.</p
Fluorescent Bioactive Corrole Grafted-Chitosan Films
Transparent
corrole grafted-chitosan films were prepared by chemical
modification of chitosan with a corrole macrocycle, namely, 5,10,15-trisÂ(pentafluorophenyl)Âcorrole
(TPFC), followed by solvent casting. The obtained films were characterized
in terms of absorption spectra (UVâvis), FLIM (fluorescence
lifetime imaging microscopy), structure (FTIR, XPS), thermal stability
(TGA), thermomechanical properties (DMA), and antibacterial activity.
The results showed that the chemical grafting of chitosan with corrole
units did not affect its film-forming ability and that the grafting
yield increased with the reaction time. The obtained transparent films
presented fluorescence which increases with the amount of grafted
corrole units. Additionally, all films showed bacteriostatic effect
against S. aureus, as well as good
thermomechanical properties and thermal stability. Considering these
features, promising applications may be envisaged for these corrole-chitosan
films, such as biosensors, bioimaging agents, and bioactive optical
devices