Sara Fateixa

Sara Fateixa, Helena I. S. Nogueira and Tito Trindade
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.

B. Barrocas, M. C. Oliveira, H. I.S. Nogueira, S. Fateixa, O. C. Monteiro
Several methods have been used to tailor nanomaterials structure and properties. Some- times, slight changes in the structure outcomes expressive improvements in the optical and photocatalytic properties of semiconductor nanoparticles. In this context, the influ- ence of the metal doping and the morphology on a catalyst performance was studied in this work. Here, ruthenium doped titanate nanotubes (RuTNT) were synthesised for the first time using an amorphous Ru-containing precursor. Afterwards, the photocatalytic performance of this sample was compared to the one obtained for ruthenium titanate nanowires (RuTNW), recently reported. Two samples, RuTNW and RuTNT, were produced using the same Ru-containing precursor but distinct hydrothermal methodologies. The powders were structural, morphological and optical characterized by X-ray diffraction and fluorescence, transmission electron microscopy, Raman, X-ray photoelectron and photo- luminescence spectroscopies. Distinct variations on the structural and optical properties of the RuTNT and RuTNW nanoparticles, due to ruthenium incorporation were observed. Their potential use as photocatalysts was evaluated on the hydroxyl radical photo-assisted production. Both samples were catalytic for this reaction, presenting better performances than the pristine counterparts, being RuTNT the best photocatalyst. Subsequently, the degradation of two emergent pollutants, caffeine and sulfamethazine, was studied. RuTNT demonstrated to be better photocatalyst than RuTNW for caffeine but identical perfor- mances were obtained for sulfamethazine. For both catalysts, the degradation mechanism of the pollutants was explored through the identification and quantification of the inter- mediate compounds produced and several differences were found. This indicates the importance of the structural and morphological aspects of a material on its catalytic performance.

J. L. Lopes, A. C. Estrada, S. Fateixa, M. Ferro, T, Trindade
Graphene-based materials are elective materials for a number of technologies due to their unique properties. Also, semiconductor nanocrystals have been extensively explored due to their size-dependent properties that make them useful for several applications. By coupling both types of materials, new applications are envisaged that explore the synergistic properties in such hybrid nanostructures. This research reports a general wet chemistry method to prepare graphene oxide (GO) sheets decorated with nanophases of semiconductor metal sulfides. This method allows the in situ growth of metal sulfides onto GO by using metal dialkyldithiocarbamate complexes as single-molecule precursors. In particular, the role of GO as heterogeneous substrate for the growth of semiconductor nanocrystals was investigated by using Raman spectroscopic and imaging methods. The method was further extended to other graphene-based materials, which are easily prepared in a larger scale, such as exfoliated graphite oxide (EGO).

S. Fateixa, M. Raposo, H.I.S. Nogueira, T. Trindade
An important feature in the fabrication of surface-enhanced Raman scattering (SERS) platforms is, together with the high efficiency, to allow the rapid collection and analysis of a vestigial analyte. Conventional substrates based on rigid solid materials or metal hydrosols are not suitable for sample extraction, limiting their application in areas such as water quality monitoring. Herein, we have developed a strategy to fabricate SERS active sub- strates (Ag/LCP) based on liquid-crystal polymer (LCP) textile fibers decorated with Ag nanoparticles (NPs). Two distinct methods for substrate preparation envisaging the SERS detection of the pesticide thiram have been explored in this research. In a first stage, we have investigated the usefulness of both approaches using ethanolic solutions of the pesticide thiram, and after real samples spiked with thiram were used to explore the analysis in real environment. The SERS analysis of thiram dissolved in Aveiro Estuary water and in fruit juices have pro- vided enhancement factors of 1.67 × 107 and 3.86 × 105, respectively, using the Ag/LCP composites. Noteworthy, in the latter case, the detection limit (0.024 ppm) achieved is lower than the maximal residue limit (MRL) of 5 ppm in fruit, as prescribed by European regulations (EU) 2016/1. Moreover, the selectivity of the SERS substrates for different pesticides was also evaluated, analyzing distinct pesticides such as paraquat and sodium diethyldithiocarbamate. SERS active Ag/LCP/PA filter membranes were also prepared using Ag/LCP composites supported by a polyamide (PA) filter, which can be an easy alternative to prepare simple, highly efficient and low-cost SERS active filter membranes for water analysis.

P. C. Pinheiro, S. Fateixa, Ana L. Daniel-da-Silva, tito trindade
Resistance of pathogenic micro-organisms to conventional antibiotics is an essential issue for public health. the presence of such pharmaceuticals in aquatic ecosystems has been of major concern for which remediation and ultra-sensitive monitoring methods have been proposed. A less explored strategy involves the application of multifunctional nanosorbents for the uptake and subsequent detection of vestigial contaminants. in this study, colloidal nanoparticles (nps) of iron oxide and gold were encapsulated in multi-layers of a charged polyelectrolyte (pei: polyethyleneimine), envisaging the effective capture of tetracycline (TC) and its subsequent detection by Surface Enhanced Raman Scattering (SeRS). Adsorption studies were performed by varying operational parameters, such as the solution pH and contact time, in order to evaluate the performance of the nanosorbents for the uptake of tc from water. While the magnetic nanosorbents with an external pei layer (fe3o4@pei and fe3o4@ PEI-Au@PEI particles) have shown better uptake efficiency for TC, these materials showed less SERS sensitivity than the fe3o4@pei- Au nanosorbents, whose SeRS sensitivity for tc in water has reached the limit of detection of 10 nM. Thus, this study highlights the potential of such magneto-plasmonic nanosorbents as multi-functional platforms for targeting specific contaminants in water, by taking into consideration both functionalities investigated: the removal by adsorption and the SeRS detection across the nanosorbents’ surfaces.

S. Fateixa, M. C. Neves, A. Almeida, J. Oliveira, T. Trindade
Submicron particles of amorphous SiO2 have been used to grow Ag2S nanophases at their surfaces. SEM and TEM analysis showed morphological well-defined nanocomposite particles consisting of Ag2S nanocrystals dispersed over the silica surfaces. These SiO2/Ag2S nanocomposites were investigated as anti-fungal agents against Aspergillus niger in different experimental conditions, including as nanofillers in cellulosic fibres. The anti-fungal activity in these composite systems is suggested to result from a syn- ergistic effect due to Ag2S anti-fungal centres and the SiO2 surfaces in promoting the adsorption of the fungus.

A. L Daniel-da-Silva, S. Fateixa, A. J. Guiomar, B. F. O. Costa, N. J. O. Silva, T. Trindade, B. J. Goodfellow, A. M Gil
Magnetic hydrogel κ-carrageenan nanospheres were successfully prepared via water-in-oil (w/o) microemulsions combined with thermally induced gelation of the polysaccharide. The size of the nanospheres (an average diameter (????) of about 50 and 75 nm) was modulated by varying the concentration of surfactant. The nanospheres contained superparamagnetic magnetite nanoparticles (????8 nm), previously prepared by co-precipitation within the biopolymer. Carboxyl groups, at a concentration of about 4 mmol g−1, were successfully grafted at the surface of these magnetic nanospheres via carboxymethylation of the κ-carrageenan. The carboxylated nanospheres were shown to be thermo-sensitive in the
37–45 ◦C temperature range, indicating their potential as thermally controlled delivery systems for drugs and/or magnetic particles at physiological temperatures. Finally, preliminary results have been obtained for IgG antibody conjugation of the carboxylated nanospheres and the potential of these systems for bio-applications is discussed.

A. Semitela, S. Carvalho, C. Fernandes, S. Pinto, S.Fateixa, H. I. S. Nogueira, I. Bdikin, A. Completo, P. A. A. P. Marques, G. Gonçalves
Biomimetics offers excellent prospects for design a novel generation of improved biomaterials. Here the controlled integration of graphene oxide (GO) derivatives with a 3D marine spongin (MS) network is explored to nanoengineer novel smart bio-based constructs for bone tissue engineering. The results point out that 3D MS surfaces can be homogeneously coated by layer-by-layer (LbL) assembly of oppositely charged polyethyleneimine (PEI) and GO. Notably, the GOPEI@MS bionanocomposites present a high structural and mechanical stability under compression tests in wet conditions (shape memory). Dynamic mechanically (2 h of sinusoidal compression cyclic interval (0.5 Hz, 0–10% strain)/14 d) stimulates GOPEI@MS seeded with osteoblast (MC3T3-E1), shows a significant improvement in bioactivity, with cell proliferation being two times higher than under static conditions. Besides, the dynamic assays show that GOPEI@MS bionanocomposites are able to act as mechanical stimulus-responsive scaffolds able to resemble physiological bone extracellular matrix (ECM) requirements by strongly triggering mineralization of the bone matrix. These results prove that the environment created by the system cell-GOPEI@MS is suitable for controlling the mechanisms regulating mechanical stimulation-induced cell proliferation for potential in vivo experimentation.

E. L. Afonso, L. Carvalho, S. Fateixa, C. O. Amorim, V. S. Amaral, C. Valed, E. Pereira, C. M. Silva, T. Trindade, C. B. Lopes
Technology critical elements (TCE) are considered the vitamins of nowadays technology. Factors such as high demand, limited sources and geopolitical pressures, mining exploitation and its negative impact, point these elements as new emerging contaminants and highlight the importance for removal and recycling TCE from contaminated waters. This paper reports the synthesis, characterization and application of hybrid nanostructures to remove and recover lanthanides from water, promoting the recycling of these high value elements. The nanocomposite combines the interesting properties of graphite nanoplatelets, with the magnetic properties of magnetite, and exhibits good sorption properties towards La(III), Eu(III) and Tb(III). The sorption process was very sensitive to solution pH, evidencing that electrostatic interactions are the main binding mechanism in- volved. Removal efficiencies up to 80% were achieved at pH 8, using only 50 mg/L of nanocomposite. In ternary solution, occurred a preferential removal of Eu(III) and Tb(III). The equilibrium evidenced a rare but interesting behaviour, and as a proof-of-concept the recoveries and reutilization rates, at consecutive cycles, highlight the recyclability of the composite without loss of efficiency. This study evidences that surface charge and the number of active sites of the composite controls the removal process, providing new insights on the interactions between lanthanoids and magnetic-graphite-nanoplatelets.

T. Fernandes, S. Fateixa, M. Ferro, H. I.S. Nogueira, A. L. Daniel-da-Silva, T. Trindade
Surface-Enhanced Raman Scattering (SERS) using colloidal metal (Ag, Au) nanoparticles has been regarded as a powerful method for detecting organic pollutants at vestigial levels. Although less investi- gated, the controlled synthesis of binary nanostructures comprising two metals provides an alternative route to SERS platforms with tuned surface plasmon resonances. Here, we demonstrate that the use of dendrimers allows the formation of distinct combinations of Ag:Au nanostructures that are composed of smaller metal nanocrystals. Our research highlights the role of the dendrimer macromolecules as a multipurpose ligand in the generation of such hybrid nanostructure, including as a reducing agent, an effective long-term colloidal stabilizer and as a molecular glue for interconnecting the primary metal nanocrystals. Noteworthy, the dendrimer-based Ag:Au hybrid nanostructures are more SERS sensitive as compared to the corresponding colloidal blends or to the single-phase metals, as revealed by using molecular pesticides as analytes in spiked water samples. We suggest that the high SERS sensitivity of the hybrid nanostructures is due to interparticle plasmonic coupling occurring between the primary metal nanoparticle aggregates, whose arrangement is templated by the presence of the dendrimer macromolecules.

S.Fateixa, P. C. Pinheiro, H. I.S. Nogueira, T. Trindade
Polymer based composites containing metal nanoparticles are shown to provide new substrates for SERS detection and simultaneously enable the development of new tools for molecular sensing. A very impor- tant aspect on the use of hybrid materials relates to the observation of synergistic effects that result from the use of distinct components such as a polymer and metal nanoparticles. We report here the prepara- tion of new SERS substrates made from blends of colloidal Au (nanospheres and nanorods) and PtBA (poly(t-butylacrylate)). The observed SERS enhancement depends on the characteristics of the obtained hybrid material. When compared to the starting Au colloids, the Au/PtBA nanocomposites led to SERS spectra with more intense bands, using 2,20-dithiodipyridine as molecular probe. The origin of the stron- ger Raman signal in this case, is possibly due to a combination of events related to the nanocomposite characteristics, including the formation of Au assemblies at the polymer surface due to particle clustering, and the absorption increase in a spectral region closer to the laser excitation wavelength. The strategy described here is a low-cost process with potential for the up-scale fabrication of SERS substrates, namely by using other types of nanocomposites.

D. K. Sharma, S. Fateixa, M.J. Hortigüela R. Vidyasagar, G. Otero-Irurueta, H. I.S. Nogueira, M. K. Singh, A. Kholkin
Tuning the band-gap of graphene is a current need for real device applications. Copper (Cu) as a substrate plays
a crucial role in graphene deposition. Here we report the fabrication of in-situ nitrogen (N) doped graphene via chemical vapor deposition (CVD) technique and the effect of Cu substrate thickness on the growth mechanism. The ratio of intensities of G and D peaks was used to evaluate the defect concentration based on local activation model associated with the distortion of the crystal lattice due to incorporation of nitrogen atoms into graphene lattice. The results suggest that Cu substrate of 20μm in thickness exhibits higher defect density (1.86×1012 cm−2) as compared to both 10 and 25 μm thick substrates (1.23×1012 cm−2 and 3.09×1011 cm−2, respectively). Furthermore, High Resolution -X-ray Photoelectron Spectroscopy (HR-XPS) precisely affirms ~0.4 at% of nitrogen intercalations in graphene. Our results show that the substitutional type of nitrogen doping dominates over the pyridinic configuration. In addition, X-ray diffraction (XRD) shows all the XRD peaks associated with carbon. However, the peak at ~24° is suppressed by the substrate peaks (Cu). These results suggest that nitrogen atoms can be efficiently incorporated into the graphene using thinner copper substrates, rather than the standard 25 μm ones. This is important for tailoring the properties by graphene required for microelectronic applications.

T. Fernandes, S. Fateixa, H. I. S. Nogueira, A. L. Daniel-da-Silva, T. Trindade
Dendrimers are polymers with well-defined architec- tures and tunable chemistry, which make them useful in a num- ber of applications. Herein, the chemistry of poly(amido)amine (PAMAM) dendrimers with different functional groups was ex- plored to produce a variety of plasmonic systems based on Au colloidal nanoparticles. The resulting systems present long-term colloidal stability and were investigated as sensitive platforms for surface-enhanced Raman scattering (SERS). The application of these SERS platforms for the detection of water trace pollu- tants, was explored through the analysis of selected pesticides. Noteworthy, dendrimer coated Au nanoparticles with tunable properties such as size, shape and surface chemistry, were ob- tained by varying the dendrimer chemical properties. The sur- face chemistry of PAMAM capped Au colloids was explored in order to produce target selective SERS substrates for pesticide detection, that allowed to reach detection limits down to 10 nM.

S. Fateixa, A. L. Daniel-da-Silva, N. Jordão, A. Barros-Timmons, T. Trindade
Although many polymer nanocomposites have been described, the impact of colloidal nanoparticles (NPs) used as fillers on the thermal behavior of the matrix has been described only in a few cases. Here we apply thermal methods to inquire the effect of organically capped Ag and Au particles on poly(tert-butyl acry- late) (PtBA) based composites. The nanocomposites have been prepared by ex situ and in situ methods; in the former method the metal NPs were isolated from the respective colloids and then blended into cast films obtained from tetrahydrofuran solutions of the polymer; while in the latter the in situ poly- merization of tert-butyl acrylate using miniemulsions was carried out in the presence of homogeneously dispersed colloidal NPs. The nanocomposite materials were then characterized by differential scanning calorimetry (DSC) to assess the effect of colloidal metal NPs on the glass transition temperature of the polymer (Tg ) namely by considering their chemical nature, average particle size, and metal load. Although similar effects have been observed when Au or Ag NPs were employed as nanofillers, it was also found that the Tg depends on the NPs morphological characteristics and on the preparative method employed to obtain the nanocomposite. This research also highlights the relevance of the surface chemistry of colloidal nanofillers on the thermal behavior of the respective composites.

S. Fateixa, P. C. Pinheiro, H. I.S. Nogueira, T. Trindade
Spectroscopic methods based on surface-enhanced Raman scattering (SERS) are among the analytical tools most exploited in recent years for the detection of vestigial amounts of compounds with envi- ronmental and health relevance. In the last decades, SERS methods have been largely improved with the unprecedented progress in instrumentation and materials development in the scope of nanoscale sci- ence. The current developments in Raman instruments, in particular for Raman imaging, brought a new look on composites and its applications. The use of confocal microscopes allows high resolution Raman mapping with short measurement times, creating strongly improved Raman images in two and three dimensions. In this manuscript, we will present an overview of our own research on the development of malleable and easy-handled SERS substrates based on textile fibres for analytical detection. The strate- gies employed for the coating of the textile fibres with gold nanoparticles (NPs) will be described in detail. A final section will focus on the combination of Raman imaging and SERS for the development of substrates based on textile fibres and their application on the detection of water pollutants and bio- molecules. A case study on the development of cotton swab fibres coated with Au NPs for SERS detection of L-lactate will be illustrated in more detail.

L. Menilli, A. R. Monteiro, S. Lazzarotto, F. M. P. Morais , A. T. P. C. Gomes, N. M. M. Moura, S. Fateixa, M. A. F. Faustino, M. G. P. M. S. Neves, T. Trindade, Giorgia Miolo
The development of new photodynamic therapy (PDT) agents designed for bladder cancer (BC) treatments is of utmost importance to prevent its recurrence and progression towards more invasive forms. Here, three different porphyrinic photosensitizers (PS) (TMPyP, Zn-TMPyP, and P1-C5) were non-covalently loaded onto graphene oxide (GO) or graphene quantum dots (GQDs) in a one-step process. The cytotoxic effects of the free PS and of the corresponding hybrids were compared upon blue (BL) and red-light (RL) exposure on T24 human BC cells. In addition, intracellular reactive oxygen species (ROS) and singlet oxygen generation were measured. TMPyP and Zn-TMPyP showed higher efficiency under BL (IC50: 0.42 and 0.22 μm, respectively), while P1-C5 was more active under RL (IC50: 0.14 μm). In general, these PS could induce apoptotic cell death through lysosomes damage. The in vitro photosensitizing activity of the PS was not compromised after their immobilization onto graphene-based nanomaterials, with Zn-TMPyP@GQDs being the most promising hybrid system under RL (IC50: 0.37 μg/mL). Overall, our data confirm that GO and GQDs may represent valid platforms for PS delivery, without altering their performance for PDT on BC cells.

A. R. Monteiro, C. I. V. Ramos, S. Fateixa, N. M. M. Moura, M. G. P. M. S. Neves, T. Trindade
Telomerase inhibition has been an important
strategy in cancer therapies, but for which effective drugs are
still required. Here, noncovalent hybrid nanoplatforms
containing the tetracationic 5,10,15,20-tetrakis(1-methyl-
pyridinium-4-yl)porphyrin (TMPyP) and graphene oxide
(GO) were prepared for promoting telomerase inhibition
through the selective detection and stabilization of DNA
guanine-quadruplex (G-Q) structures. Upon binding TMPyP to the GO sheets, the typical absorption bands of porphyrin have been red-shifted and the fluorescence emission was quenched. Raman mapping was used for the first time to provide new insights into the role of the electrostatic and π−π stacking interactions in the formation of such hybrids. The selective recovery of fluorescence observed during the titration of TMPyP@GO with G-Q, resembles a selective “turn-off−on” fluorescence sensor for the detection of G-Q, paving the way for a new class of antitumor drugs.

N.C.T. Martins, S. Fateixa, T. Fernandes, H. I.S. Nogueira, Tito Trindade
Hydrophobic substrates for surface-enhanced
Raman scattering (SERS) of adsorbate species are of great interest
in chemical analysis because they can concentrate the analyte
molecules in a small area of the surface, thereby improving the
SERS sensitivity. Here, we propose a general strategy to fabricate
hydrophobic paper-based substrates for SERS applications. The
paper substrates have been manufactured by inkjet printing of
aqueous emulsions containing Ag and polystyrene (PS) colloidal
nanoparticles. In a first stage, the SERS performance of the
substrates was optimized by varying the relative amounts of polymer/metal colloidal nanoparticles, the number of printing layers, and the degree of hydrophobicity of the substrates, using crystal violet as a molecular probe, which is well known for its strong SERS activity. In these conditions, the strongest surface Raman enhancement was observed for the highest water contact angle (146°) achieved. The selected Ag/PS-coated paper substrates showed wide applicability for several analytes, but in this study, a detailed analysis is provided for the pesticide thiram as a proof of concept. Several samples spiked with thiram have been analyzed by SERS, giving a detection limit of 0.024 ppm thiram in mineral water and apple juice, while in apple peel, the detection limit achieved for the same pesticide was 600 ng/cm2. We suggest that this one-step fabrication method produces a hydrophobic coating whose nanoscale features improve the SERS performance of the paper substrates.

A. M. Salgueiro, A. L. Daniel-da-Silva, S. Fateixa, T. Trindade
In this work we investigate the effect of spherical and rod-shaped Au nanoparticles (NPs) in the microstructure, thermomechanical and release properties of thermosensitive ????-carrageenan hydrogels. Thermal and mechanical analyses of the composites revealed that the Au NPs reinforce the structure of the hydrogel and the mechanism of gel reinforcement is discussed. The effect of the NPs on the microstructure and strength of the hydrogel had implications in the mechanism of controlled release as demonstrated by in vitro release studies using a drug model (methylene blue: MB). Noteworthy, the mechanism of MB release followed either a diffusion or polymer relaxation mechanism, depending on the morphology of the Au NPs incorporated in the hydrogel. Consequently, ????-carrageenan hydrogels containing Au NPs exhibited not only optical features modulated by the fillers morphology, but also showed a behavior as drug carriers that can be also adjusted by Au NPs characteristics.

S. Fateixa, R. S. Carvalho, A. L. Daniel-da-Silva, H. I. S. Nogueira, T. Trindade
In this research, we investigated the use of lanthano- polyoxometalates {LnPOM, K9[Ln(W5O18)2], Ln = Eu, Tb} as luminophores in thermosensitive polysaccharides such as carra- geenan hydrogels. We demonstrate that the LnPOM species still show the characteristic photoluminescence bands of the LnIII ion when incorporated in the gel matrix. Moreover, the strength of the carrageenan hydrogels increases by increasing the amount of LnPOM added because of the effect of K+ ions as cross-linkers, but without compromising the photoluminescent behaviour. Nanoscale homogeneity is crucial regarding applica- tions of hydrogels responsive to external stimuli. This research shows that the final LnPOM-loaded hydrogels are homogene- ous as a consequence of the diffusion behaviour of the lumino- phore species within the gel network. Therefore, we anticipate that the association of carrageenan hydrogels to luminescent lanthanopolyoxometalates might be of great relevance for opti- cal devices and in particular for bioimaging techniques.

P. C. Pinheiro, S.Fateixa, H. I. S. Nogueira, T. Trindade
Magnetite nanoparticles (MNPs) decorated with gold nanostars (AuNSs) have been prepared by using a seed growth method without the addition of surfactants or colloidal stabilizers. The hybrid nanomaterials were investigated as adsorbents for the uptake of tetracycline (TC) from aqueous solutions and subsequent detection using surface-enhanced Raman scattering (SERS). Several parameters were investigated in order to optimize the performance of these hybrid platforms on the uptake and SERS detection of TC, including variable pH values and the effect of contact time on the removal of TC. The spatial distribution of TC and AuNS on the hybrid composites was accomplished by coupling SERS analysis with Raman imaging studies, allowing also for the determination of the detection limit for TC when dissolved in ultrapure water (10 nM) and in more complex aqueous matrices (1 μM). Attempts were also made to investigate the adsorption modes of the TC molecules at the surface of the metal NPs by taking into account the enhancement of the Raman bands in these different matrices.

F. L. Sousa, A. Almeida, A. V. Girão, S. Fateixa, T. Trindade
Silver nanoparticles (NPs) encapsulated in amorphous silica shells are syn- thesized and evaluated for their antibacterial action using the Gram-negative Escherichia coli bacterium. These inorganic capsules are synthesized using a new approach that comprises the use of oil-in-water-in-oil (O/W/O) multiple emulsions to fabricate SiO2 capsules incorporating organically capped Ag NPs. This strategy is explored as a mean to promote the bioadhesion of the microorganisms to the silica rough surfaces while still keeping the system with a high surface area for the active metal. The results have shown that
the hybrid capsules enable a slow release of cationic silver from the interior of the silica microsphere to the external medium probably through the pore channels in the shell. The antibacterial activity against E. coli is mainly deter- mined by the Ag+ ion release rate, suggesting that these particulates can be employed as a robust system for prolonged used as an antimicrobial material.

C. F. Marques, S. M. Olhero, P. M.C. Torres, J.C.C. Abrantes, S Fateixa, H. I.S. Nogueira, I.A.C. Ribeiro, A. Bettencourt, A. Sousa, P. L. Granja, J.M.F. Ferreira
Advances on the fabrication of sintering-free biphasic calcium phosphate (BCP)/natural polymer composite scaffolds using robocasting as additive manufacturing technique are presented in the present work. Inks with high amounts of BCP powders (45vol%) containing different HA/β-TCP ratios, in presence of crosslinked polymer, were successfully fine-tuned for extrusion by robocasting. The non-existence of sintering step opened the possibility to obtain drug loaded scaffolds by adding levofloxacin to the extrudable inks. The drug presence induced slightly changes on the rheological behaviour of the inks, more emphasized for the BCP compositions with higher amounts of β-TCP, and consequently, on the microstructure and on the mechanical properties of the final scaffolds. The strong interaction of β-TCP with chitosan difficult the preparation of suitable rheological inks for printing. Drug delivery studies revealed a fast release of levofloxacin with a high burst of drug within the first 30 min. Levofloxacin loaded samples also presented bacteria growth inhibition ability, proving that antibiotic was not degraded during the fabrication process and its bactericidal efficacy was preserved. From the results obtained, the composite scaffolds containing higher amounts of HA (around 80% HA/20% β-TCP) constitute a promising bi-functional synthetic bone substitute for simultaneous local bone regeneration and infection treatments.

S.Fateixa, A. V. Girão, H. I. S. Nogueira, T. Trindade
Nanocomposites containing Ag nanoparticles (average diameter $11 nm) dispersed in poly(tert- butylacrylate) were prepared by in situ polymerization via miniemulsions and constitute active and versatile SERS substrates. The use of this synthetic strategy enables the dual use of the final composites as SERS substrates, both as aqueous emulsions and as cast films, shown here by several measurements using thiosalicylic acid as the testing analyte. The main advantage of these types of materials is related to the potential to scale up and the widespread use of handy substrates, using technology already available. This requires homogeneous composite substrates with SERS activity and this was demonstrated here by means of confocal Raman microscopy. Finally, a series of experiments were carried out on Ag/polymer nanocomposites submitted to temperature variations below and above the polymer glass transition temperature (Tg) in order to conclude about the effect of temperature processing conditions on the composites’ SERS activity.

J.Nogueira, M. António, S. M. Mikhalev, S. Fateixa, T. Trindade, A. L. Daniel-da-Silva
Porous carbon materials derived from biopolymers are attractive sorbents for the removal of emerging pollutants from water, due to their high specific surface area, high porosity, tunable surface chemistry, and reasonable cost. However, carrageenan biopolymers were scarcely investigated as a carbon source to prepare porous carbon materials. Herein, hydrochars (HCs) and porous activated carbons (ACs) derived from natural occurring polysaccharides with variable sulfate content (κ-, ι- and λ-carrageenan) were prepared and investigated in the uptake of ciprofloxacin, which is an antibiotic detected in water sources and that poses serious hazards to public health. The materials were prepared using hydrothermal carbonization and subsequent chemical activation with KOH to increase the available surface area. The activated carbons were markedly microporous, presenting high specific surface area, up to 2800 m2/g. Activated carbons derived from κ- and λ-carrageenan showed high adsorption capacity (422 and 459 mg/g, respectively) for ciprofloxacin and fast adsorption kinetics, reaching the sorption equilibrium in approximately 5 min. These features place the ACs investigated here among the best systems reported in the literature for the removal of ciprofloxacin from water.

D. K. Sharma, E. V. Ramana, S. Fateixa, M. J. Hortigüela, G. Otero-Irurueta, H. I.S. Nogueira, A. Kholkin
Molybdenum disulfide (MoS2) is a transition metal dichalcogenide, which along with graphene, has a great potential to become a material of choice for the next generation of nanoelectronics. We report the synthesis of a large-area MoS2 obtained by sulfurization of MoO3 using chemical vapor deposition (CVD) at different Ar base pressures. The optimal pressure for the growth was found to be ∼50 mbar (millibar). The evolution of MoS2 phase as a function of Ar gas pressure was monitored by confocal Raman spectroscopy. As synthesized MoS2 shows direct bandgap of 1.6 eV evaluated by UV–vis spectroscopy. We report for the first time the valence band spectra and the work function of MoS2 on SiO2/Si calculated by ultraviolet photoemission spectroscopy, which was found to be 4.67 eV. In-situ electrical measurements demonstrated expected semiconducting behavior of the grown triangular crystals. These studies show MoS2 crystallites growth by controlling the parameters in CVD process

H. I. S. Nogueira, C. Bornes, S. Fateixa, T. Trindade
omposite agarose films were prepared with EuIII containing polyoxometalates, in particular the organic-inor- ganic hybrid [Eu(W5O18)2(pic)4]13– (Hpic = 3-hydroxypicolinic acid) and a Mo blue EuIII derivative. The latter compound shows interesting EuIII based photoluminescence properties, described for a molybdenum blue compound for the first time. Imaging of optical properties and morphology of the films was explored by Raman and fluorescence measurements in a confocal mi- croscopy system, together with the AFM profile. Raman and fluorescence imaging are powerful tools for the characterization of the films, in particular their chemical composition and homo- geneity at the micrometric scale.

S. Fateixa, M. Wilhelm, A. M. Jorge, H. I. S. Nogueira, T. Trindade
We demonstrate in this research that surface-enhanced resonance Raman scattering combined with Raman imaging can be effectively used for analysis of distinct forms of organic dyes in antimicrobial Ag-loaded textile fibers. The potential of this approach, as a non-destructive characterization method of fabrics, was evaluated with Raman studies performed on the molecular forms of methylene blue (MB), used here as the organic dye model. On the basis of the surface-enhanced Raman scattering spectra of MB monomers and dimers, the Raman imaging of Ag-loaded linen fibers previously treated with MB solution was performed and then used for identification of the adsorbate species in distinct regions of the substrates. A semi-quantitative analysis is then performed by considering the area of the Raman bands ascribed to the MB molecular forms and image analysis applied to Raman images.

S. Fateixa, A. L. Daniel-da-Silva, H. I. S. Nogueira, T. Trindade
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. 2,2′-Dithiodipyr-
idine 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 (κ, ι, 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.

S. Fateixa, M. R. Correia, T. Trindade
We demonstrate that surface-enhanced Raman scattering (SERS) spectroscopy can be used to monitor variations in the aspect ratio (AR) of colloidal gold nanorods (NRs) during a chemical etching process. The AR of colloidal Au NRs prepared by a seed method was deliberately decreased by addition of aqueous K2S2O8. SERS studies using a 1064 nm laser line revealed a decrease on the detection sensitivity as the nanorods became shorter and using the anion diethyldithiocarbamate (DTC) as the analytical probe. The morphological changes observed for distinct reaction times have also been confirmed by TEM and optical measurements. The dependence of the SERS sensitivity observed for Au NRs of variable AR has been investigated either by using colloids submitted to etching at distinct reaction temperatures or by using a distinct excitation laser line. Therefore, this spectroscopic method offers the possibility to probe in situ changes on the AR of colloidal Au NRs in analytical contexts in which other techniques cannot be easily implemented.

B. T. Barrocas, M. C. Oliveira, H. I. S. Nogueira, S. Fateixa, O. C. Monteiro
Titanate elongated nanomaterials have been studied as promising catalysts for photoassisted oxidation processes, and various methods have been used to tailor their properties. In this context, the synthesis and photocatalytic evaluation of novel ruthenium-modified titanate nanowires is described. In this work, pristine (TNW) and modified nanowires (RuTNW) were obtained through the hydrothermal treatment of an amorphous precursor, and they were characterized by XRD, Raman, XRF, XPS, TEM, DRS, and PL. The results indicate some alterations on the structure and on the optical properties of these semiconductor nanoparticles, owing to ruthenium incorporation. Regarding the structure, several possible Ru positions can be anticipated: in the TiO6 octahedra, substituting Ti4+, or localized in interstitial sites, or in the interlayers, replacing some Na+. Anticipating their potential use for oxidation photocatalysis, namely, for pollutants removal, the samples were evaluated for hydroxyl radical production, using the probe molecule terephthalic acid. Both samples were catalytic for this photoactivated process, with RuTNW being the best photocatalyst. Afterward, the degradation of caffeine, used as a model pollutant, was evaluated under UV−vis and visible radiation. Regardless of the radiation type in use, a clear improvement on TNW photocatalytic performance was observed after Ru incorporation. In fact, RuTNW was the best catalyst for caffeine photodegradation (20 ppm; 0.13 g/L), with a complete pollutant removal after 60 min, using UV−vis radiation. Through the identification and quantification of the intermediates produced during irradiation, a longer time (more than 120 min) is however required to complete the degradation process. A proposal for the photogenerated charge-transfer mechanism in these photoactivated processes is also given and discussed.

S.Fateixa, M. Wilhelm, H. I. S. Nogueira, T. Trindade
Textile fibres containing Ag nanoparticles have been widely explored for a number of antimicrobial fabrics. Moreover, it is well-known that textile dyeing is a critical stage in the manufacture thereof. This research shows that surface enhanced Raman scattering (SERS) and Raman imaging can be used with advantage in the monitoring of this process. Using Ag containing linen fibres stained with methylene blue (MB), it was possible to map the local distribution of the MB dye in the fibres by Raman imag- ing. MB was selected as the SERS molecular probe and as a model dye. Composites of linen fibres and Ag nanoparticles were pre- pared by distinct methods and used as SERS substrates in order to evaluate the effect of the preparative method on the Raman images. Our results demonstrate that by using Raman imaging associated to the presence of Ag nanoparticles, it is possible to dis- tinguish the local distribution of the dye on the textile surface. This investigation allows to foreseeing the use of this technique in terms of quality control of Ag containing fabrics, which is a market in great expansion.

P. C. Pinheiro, S. Fateixa, T. Trindade
Sensitive and reliable procedures for detecting vestigial antibiotics are of great relevance for water quality monitoring due to the occurrence of such emergent pollutants in the aquatic environment. As such, we describe here research concerning the use of multifunctional nanomaterials combining magnetic and plasmonic components. These nanomaterials have been prepared by decorating magnetite nanoparticles (MNP) with colloidal gold nanoparticles (Au NPs) of distinct particle size distributions. Several analytical conditions were investigated in order to optimize the surface enhanced Raman scattering (SERS) detection of penicillin G (PG) dissolved in water. In particular, the dependence of the SERS signal by using distinct sized Au NPs adsorbed at the MNP was investigated. Additionally, microscopic methods, including Raman confocal microscopy, were employed to characterize the SERS substrates and then to qualitatively detect penicillin G using such substrates. For example, magnetic–plasmonic nanocomposites can be employed for magnetically concentrate analyte molecules and their removal from solution. As a proof of concept, we applied magneto-plasmonic nanosorbents in the removal of aqueous penicillin G and demonstrate the possibility of SERS sensing this antibiotic.

S. Fateixa, H. I. S. Nogueira, T. Trindade
Polymer based nanocomposites containing metal nanoparticles (e.g. Au, Ag) have gained increased atention as a new class of SERS (Surface Enhanced Raman Scatering) sub- strates for analytical platforms. On the other hand, the application of SERS using such platforms can also provide new insights on the properties of composite materials. In this chapter, we review recent research on the development of SERS substrates based on poly- mer nanocomposites and their applications in diferent ields. The fundamentals of SERS are briely approached and subsequently there is a reference to the strategies of prepara- tion of polymer based nanocomposites. Here the main focus is on SERS studies that have used a diversity of polymer based nanocomposites, highlighting certain properties of the materials that are relevant for the envisaged functionalities. A inal section is devoted to the joint use of Raman imaging and SERS in nanocomposites development, a topic that presents a great potential still to be explored as shown by the recent research in this ield.

P. C. Pinheiro, S. Fateixa, H. I. S. Nogueira, Tito Trindade
The implementation of polymer-based composites provides a plausible alternative to develop efficient, handy and scalable sub- strates for surface-enhanced Raman spectroscopy (SERS) aiming the widespread use of this technique for chemical analysis and molecular sensing. In this research, new poly(methylmethacrylate) based nanocomposites for SERS were prepared by in situ miniemulsion polymerization in the presence of organically capped metal silver nanoparticles. The ensuing composites have been investigated as analytical platforms for SERS detection of DNA constituents for variable analytical conditions. Finally, we show that in special cases, selective detection of DNA bases by SERS can be possible by varying the pH of the solution under analysis.

P. C. Pinheiro, S. Fateixa, H. I. S. Nogueira, T. Trindade
Enhancement of Raman signals of the nucleobase adenine on an Ag based composite was studied using the 1064 nm laser line. The composite comprise emulsions of Ag nanoparticles encapsulated in poly(t- butylacrylate) (PtBA) beads that act as substrate for the Surface-Enhanced Raman Scattering (SERS) of adenine. For this system, Raman enhancement was observed for the ring-stretching vibrational mode of adenine after aggregation of the Ag/poly(t-butylacrylate) emulsion and isolation of the solid compos- ite. This is a convenient and alternative analytical approach to SERS monitoring of solutions of adenine over the more common use of pure Ag colloids. As a consequence, this research contributes to develop innovative studies on DNA fragments using polymeric platforms that can act as highly sensitive SERS substrates.

M. A. Martins, S. Fateixa, A. V. Girão, S. S. Pereira, T. Trindade
We report the synthesis of morphological uniform composites using miniemulsions of poly(tert-butyl acrylate) or poly(styrene) containing organically capped gold nanocrystals (NCs). The optical features of such hybrid structures are dominated by plasmonic effects and depend critically on the morphology of the resulting nanocomposite. In particular, we demonstrate the ability to tune the overall optical response in the visible spectral region by varying the Au NCs arrangement within the polymer matrix, and therefore the interparticle plasmon coupling, using Au NCs resulting from the same batch of synthesis. This is a consequence of two well-known effects on the optical properties of Au particles: the variation of the surrounding dielectric refractive index and interparticle plasmonic coupling. The research reported here shows a general strategy to produce optical responsive nanocomposites via control of the morphology of submicro- metric polymer particles containing metal nanocrystals and thus is an alternative to the more common strategy of size tuning metal nanoparticles used as nanofillers.

S. Fateixa, S. F. Soares, A. L. Daniel-da-Silva, H. I. S. Nogueira, T. Trindade
The controlled release of pesticides using hydrogel vehicles is an important procedure to limit the amount of these compounds in the environment, providing an effective way for crop protection. A key- step in the formulation of new materials for these purposes encompasses the monitoring of available pesticides in the gel matrix under variable working conditions. In this work, we report a series of bionano- composites made of Ag nanoparticles (NPs) and gelatine A for the surface enhanced Raman scattering (SERS) detection of sodium diethyldithiocarbamate (EtDTC) as a pesticide model. These studies demon- strate the effectiveness of these substrates for the detection of EtDTC in aqueous solutions in a concen- tration as low as 10−5 M. We have monitored the Raman signal enhancement of this analyte in bionanocomposites having an increasing amount of gelatine due to their relevance in formulating hydro- gels of variable gel strengths. Under these conditions, the bionanocomposites have shown an effective SERS activity using EtDTC, demonstrating their effectiveness in the qualitative detection of this analyte. Finally, experiments involving the release of EtDTC from Ag/gelatine samples have been monitored by SERS, which attest the potential of this spectroscopic method in the laboratorial monitoring of hydrogels for pesticide release.

E. Soto, F. Vaquero, N. Mota, S. Fateixa, T. Trindade, R.M. Navarro, J. L. G. Fierro
This work studies the variation in the photocatalytic properties of CdS derived from the insertion of In, Ga, Ag-In and Ag-Ga in the CdS lattice through solvothermal methodology. Solvothermal synthesis of
3þ 3þ 3þ þ 3þ þ CdS-M photocatalysts has been succesful for the insertion of Ga , In , Ga /Ag and In /Ag
into the
hexagonal crystal lattice of one-dimensional CdS. The insertion of In, Ga, Ag-In and Ag-Ga modifies the
band gap and the relative position of EVB. CdS modified with In3þ or Ga3þ shows an increase in the band
gap and upshift in the relative position of the valence band energy which leads to a low efficiency þ 3þ þ 3þ þ
hydrogen production. The co-addition of Ag -In or Ag -Ga favours the insertion of Ag ions into the CdS lattice with narrower band gap. Of all the co-substituted photocatalysts, the CdS-AgGa was the only one that showed a higher photoactivity with respect to the CdS. The increase in the photoactivity of the CdS-AgGa photocatalyst is related to the band gap narrowing and downshift in the relative position of the valence band energy which enhance their visible light absorption and potential for oxidation. The CdS-AgGa photocatalyst shows small segregation of metallic Ag nanoparticles at the surface which also assist in the photoactivity of the sample.

J. L. Lopes, S.Fateixa, A. C. Estrada, J. D. Gouveia, J. R. B. Gomes, T. Trindade
Graphene oxide (GO) has been widely explored as a platform
for producing hybrid materials exhibiting synergistic properties of interest in
heterogeneous (photo)catalysis. However, there has been less emphasis in
demonstrating that such properties are intrinsic to the nature of the hybrid
material, which to some extent can be attributed to the lack of straightforward
screening techniques. In this work, we demonstrate that surface-enhanced
Raman scattering can be easily explored to probe certain regions of GO
sheets decorated with a semiconductor (ZnS). In particular, our studies reveal
an enhancement of the Raman signal of 4-mercaptopyridine (4-MPy), which
was used as a molecular probe, upon adsorption on ZnS@GO materials when
compared to adsorption on the separated parent ZnS powders or GO flakes.
The GO sheets in the composite play an important role in the enhancement of the Raman signal observed for this molecular probe because they create energy levels within the ZnS energy gap. This hypothesis was further confirmed by electronic density functional theory calculations employed to investigate the adsorption mechanism of 4-MPy on both ZnS and ZnS@GO substrates. The calculated results are in accordance with the experimental data, predicting the adsorption mode on both S and Zn surface sites, with preference toward the sulfur atom due to the influence of GO.

S. Fateixa, H.I. S. Nogueira, T. Trindade
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 spectro-
scopic 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. 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.

A. L. Daniel-da-Silva, A. M. Salgueiro, S. Fateixa, J. Moreira, A. C. Estrada, A. M. Gil, T. Trindade
Today polysaccharide based hydrogel nanocomposites are receiving high importance as biomaterials for drug delivery. Inorganic nanoparticles (NPs) are incorporated into the polymer matrix to provide novel functionalities to the hydrogels. However, the effect of nanofillers on the release properties has not been totally understood. In this work, we investigate the influence of inorganic functional nanofillers (Fe3O4 and Au NPs) with variable size and shape on the structure of κ-carrageenan hydrogels and on the kinetics and release mechanism of methylene blue (MB) as model drug. It was shown that, depending on the nature of the nanofiller incorporated, and for equivalent nanofiller content, the mechanism of MB release can be adjusted either to by diffusion or polymer relaxation mechanism. The mechanism of the MB release was found to be determined by the strength and microstructure of the gel network and extent of gel swelling, which are affected by the extent of incorporation of the nanofillers.

L. S. Rocha, J. Nogueira, A. L. Daniel-da-Silva, P. Marques, S. Fateixa, E. Pereira, T. Trindade
There is a growing interest in developing more environmentally friendly softeners for hardness reduction of water supplied for domestic consumption. This work focuses on exploring biopolymer-based softeners, through the surface modification of graphene oxide (GO) with the anionic biopolymer κ-carrageenan (GO-Si(κ)CRG). The performance of the modified GO to decrease the hardness of natural waters containing high levels of Ca2+ was assessed. The sorption efficiency was dependent on the initial Ca2+ concentration and on the sorbent dose, with 8–34% removal for GO and 21–100% for GO-Si(κ)CRG. The surface modification considerably improved the adsorptive efficiency and under certain experimental conditions, it was possible to convert very hard water (300 mg L− 1 CaCO3) to soft water. Importantly, the performance was not affected by the presence of other ions typically found in natural bottled waters. The kinetics was well described by pseudo-first-order and diffusion models. The multi-linear nature observed in Boyd’s and Webber’s plots suggested that both film diffusion and pore diffusion controlled the sorption rate. The maximum Ca2+ sorption capacity at monolayer coverage of GO-Si (κ)CRG was 47.6 ± 3.2 mg g− 1. The electrostatic attraction between sulfonate groups and calcium cations is likely to be the main mechanism involved in the sorption process of Ca2+ by GO-Si(κ)CRG. Overall, the results indicate good prospects for the development of a new class of softeners based on the GO modification described.