Aim: Enhance the colloidal stability and photothermal capacity of graphene oxide (GO) by functionalizing it with sulfobetaine methacrylate (SBMA)-grafted bovine serum albumin (BSA; i.e., SBMA-g-BSA) and by loading IR780, respectively. Materials & methods: SBMA-g-BSA coating and IR780 loading into GO was achieved through a simple sonication process. Results: SBMA-g-BSA-functionalized GO (SBMA-BSA/GO) presented an adequate size distribution and cytocompatibility. When in contact with biologically relevant media, the size of the SBMA-BSA/GO only increased by 8%. By loading IR780 into SBMA-BSA/GO, its photothermal capacity increased by twofold. The combination of near infrared light with SBMA-BSA/GO did not induce photocytotoxicity on breast cancer cells. In contrast, the interaction of IR780-loaded SBMA-BSA/GO with near infrared light caused the ablation of cancer cells. Conclusion: IR780-loaded SBMA-BSA/GO displayed an improved colloidal stability and phototherapeutic capacity.

Reduced graphene oxide (rGO) nanomaterials display promising properties for application in cancer photothermal therapy (PTT). rGO is usually obtained by treating graphene oxide (GO) with hydrazine hydrate. However, this reducing agent contributes for the low cytocompatibility exhibited by rGO. Furthermore, rGO has a low water stability and does not show selectivity towards cancer cells. Herein, rGO attained using an environmentally-friendly method was functionalized with a novel hyaluronic acid (HA)-based amphiphilic polymer to be used in targeted cancer PTT. Initially, the green-reduction of GO with L-Ascorbic acid was optimized considering the near infrared absorption and the size distribution of the nanomaterials. Then, rGO was functionalized with the HA-based amphiphile. The functionalization of rGO improved its stability, cytocompatibility and internalization by CD44 overexpressing cells, which indicates the targeting capacity of this nanoformulation. Furthermore, the on-demand PTT mediated by HA-functionalized rGO induced cancer cells’ ablation, thereby confirming its potential for targeted cancer therapy.

Density functional theory is used to investigate the origins of the excellent catalytic activity of the Mo2CTx MXene for the water gas shift reaction. By considering different possibilities for the MXene surface termination (Tx = none, O, F, or a mixture of O and F), we conclude that its ideal composition should contain both F and O adatoms, essential for controlling the exothermicity of the reaction and avoiding saturation by oxygenated species. More precisely, while Mo2CO2 and Mo2CF2 are too inert towards water adsorption and dissociation and the bare Mo2C MXene is inactivated upon coverage by oxygenated species, our calculations predict that regions near one or two O adatoms in the midst of F surface terminations should be the active catalytic sites. Indeed, in the vicinity of the O adatoms, water adsorbs with moderate strength, dissociates with a very low energy barrier (0.14–0.20 eV), and the dissociation is moderately exothermic.

Biomarkers are molecules that are present in tissues or body fluids of an individual and allow the monitorization of the state of health by their presence, absence, or concentration, within given values, in tissues or biological fluids. Often, the analysis of biomarkers is difficult and invasive and so it is necessary the development of new technologies that allow their detection. Raman spectroscopy is a vibrational technique based on the interaction of light with materials and allows the production of characteristic spectra of determined substances. In particular, surface-enhanced Raman spectroscopy (SERS) is a method of Raman spectroscopy in which an enhancement in the Raman signals is visible, namely because of the addition of metallic particles to the sample that is going to be analysed. Two-dimensional (2D) materials like molybdenum disulfide have been gaining attention because of their excellent SERS performance. This thesis presents a study based on molybdenum disulfide combined with metallic nanoparticles, of silver and gold, for the detection of bioanalytes through SERS. Initially, it is presented a literature review about SERS technique, 2D materials and biomarkers to contextualize this work. The experimental work initiates with the synthesis of MoS2 by an hydrothermal process and its characterization through several techniques (TEM, SEM, XRD, UV/VIS and Raman). Then, different deposition techniques of the material with the metallic nanoparticles prepared by the citrate method, were developed allowing the formation of hybrid materials deposited in silica and gold wafers. Raman spectroscopy was used to detect different analytes: glucose, lactate, adenine and rhodamine B. Only rhodamine B was effectively detected using these substrates. This led to preliminary tests of enzymatic immobilization of lactate dehydrogenase in gold wafers for the detection of lactate. The studies have shown to be promising for this detection. In a second phase of the work, in situ development of hybrids (containing MoS₂ and gold nanoparticles) by an exfoliation method were tested. For that, the exfoliation of MoS₂ was carried directly using the gold colloids. This exfoliation was tested using gold nanoparticles with different sizes (15 and 50 nm) and after that, particles functionalized with 4-mercaptobenzoic acid to monitor their presence during the exfoliation. These processes were characterized by UV/VIS, TEM, SEM and Raman and allow to conclude that the developed method allow the production of hybrids with sandwich-like structure where the particles are intercalated between the layers of MoS₂. In terms of Raman analysis, the same analytes were tested as before, rhodamine B, glucose, lactate and adenine. The utilization of this hybrids revealed promising for the detection of rhodamine B, glucose and adenine only being unable to detect lactate.

In this study, we employed density functional theory calculations to investigate the adsorption behavior of α and β isomers of d-glucopyranose, d-galactopyranose, d-fructopyranose, and d-mannopyranose on the Ti2CO2 MXene surface, in order to understand the potential of this material for sensing sugars. The adsorption process was found to occur via strong noncovalent interactions, primarily through hydrogen bonding and with the hexoses oriented parallel to the surface. The calculated adsorption energies vary between −0.78 (α-d-fructopyranose) and −1.00 eV (β-d-glucopyranose). Importantly, while the charge transfer was found to be negligible, the work function of the material was found to change by up to 0.3 eV in the case of the compound that adsorbs most strongly, β-d-glucopyranose, while less important changes were found for the other studied hexoses. We also explored the influence of defects in the MXene structure on the adsorption of β-d-glucopyranose and observed that oxygen or titanium vacancies enhance the adsorption strength. These findings indicate that the Ti2CO2 MXene is a promising candidate for selective glucopyranose sensing, which can be interesting for glucose detection applications.

Sulfurization of molybdenum layers is a promising route for obtaining large-scale and high-quality transition metal dichalcogenides. Here we describe the synthesis of continuous and homogeneous MoS2 in the centimeter scale by the thermal vapor sulfurization of pre-deposited molybdenum precursors on SiO2. Metallic molybdenum as well as MoO3 were used as precursors while the sulfurization was performed by chemical vapor deposition. A multi-technique characterization was employed to fully describe the deposition of molybdenum as well as its sulfurization. Thus, Raman spectroscopy, X-ray and ultra-violet photoelectron spectroscopies as well as scanning electron and atomic force microscopies indicated that the molybdenum layers were completely transformed in MoS2. The samples were homogeneous in the centimeter scale and quite flat with a root mean square roughness of 1.4 Å. Furthermore, its work function was 4.1 eV.

In the past decade, nanotechnology’s rapid developments have created quite a lot of prospects for researchers and engineers to check up on. And nanofluids are important consequences of this progression. Nanofluids are created by suspending nanoparticles with average diameters below 100 nm in conventional heat transfer carriers such as water, oil, ethylene glycol, etc. Nanofluids are considered to offer substantial advantages over usual heat transfer fluids. When dispersed in a uniform way and suspended stably in the base fluids, a minimal amount of nanoparticles can significantly improve the thermal properties of host fluids. Present work attempts to address this challenge considering state-of-the-art advances in understanding, discussing, and mitigating problems about nanofluids’ stability. Stable and highly conductive nanofluids are produced by generally, one-step and two-step production methods. Both approaches suffer from problems with the nanoparticles’ agglomeration to be an important one. Thus, numerous numerical models and the principal physical phenomena affecting the stability (fundamental physical principles that govern the interparticle interactions, clustering and deposition kinetics, and colloidal stability theories) have been analyzed. Concerning the particles’ dynamic motion, the significance of different forces in nanofluid in particulate flows such as drag, lift (Magnus and Saffman), Brownian, thermophoretic, Van der Waals, electrostatic double-layer forces are investigated. Furthermore, an overview of nanofluids’ thermophysical properties, physical models, and heat transfer models is​ included in this work. In order to realize the unexpected discoveries and overcome classical models’ limitations, several researchers have suggested new physical concepts and mechanisms, and they have created new models to enhance the transport properties. This review study includes numerous aspects of the nanofluids’ science by investigating applications, thermal properties and giving critical chronological milestones about the nanofluids’ evolution. Also, the present review discusses in detail various modeling and slip mechanisms for the heat transfer of nanofluids. Potential novel 2D materials as nanofluids have also been discussed and reported. A brief overview of the potential applications utilizing nanofluids has been reviewed, and future research gaps have been reported. Furthermore, recommendations were extracted regarding current scientific gaps and future research directions to cover the physical phenomenon, stability, thermophysical properties, overview of some applications, and the limitations hindering these nanofluids’ deployment. The review is presumed to be valuable for scholars and researchers working in the area of numerical simulations of nanofluids and experimental aspects and help them understand the fundamental physical phenomena taking place during these numerical simulations and experiments and explore the potential of nanofluids both in academia and industry.

Two-dimensional few-layered transition-metal nitrides and carbides, called MXenes, have attracted a great interest given their large surface areas and their unique physicochemical properties. Motivated by the known reactivity of surfaces of bulk transition metal carbides on the mechanism behind the water-gas shift (WGS) reaction, density functional theory (DFT) calculations were employed to investigate the bonding of water and its dissociation on a set of eighteen M2X MXene (M = Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W, while X = C or N) surfaces. Here it is shown that all the studied MXenes exothermically adsorb water, with adsorption energies ranging from -1.43 to -2.94 eV, and greatly facilitate its dissociation, with energy barriers below 0.44 eV. These results reinforce the role of MXenes in promoting water dissociation, effectively suggesting their potential as catalysts for industrially relevant processes such as the WGS reaction.

Due to their vast range of promising biomedical and electronic applications, there is a growing interest in bioinorganic lamellar nanomaterials. MXenes are one such class of materials, which stand out by virtue of their demonstrated biocompatibility, pharmacological applicability, energy storage performance, and feasibility as single-molecule sensors. Here, we report on first-principles predictions, based on density functional theory, of the binding energies and ground-state configurations of six selected amino acids (AAs) adsorbed on O-terminated two-dimensional titanium carbide, Ti2CO2. We find that most AAs (aspartic acid, cysteine, glycine, and phenylalanine) prefer to adsorb via their nitrogen atom, which forms a weak bond with a surface Ti atom, with bond lengths of around 2.35 Å. In contrast, histidine and serine tend to adsorb parallel to the MXene surface, with their α carbon about 3 Å away from it. In both adsorption configurations, the adsorption energies are on the order of the tenths of an electronvolt. In addition, we find a positive, nearly linear correlation between the binding energy of each studied AA and its van der Waals volume, which suggests an adsorption dominated by van der Waals forces. This relationship allowed us to predict the adsorption energies for all of the proteinogenic AAs on the same Ti2CO2 MXene. Our analysis additionally shows that in the parallel adsorption mode there is a negligible transfer of charge density from the AA to the surface but noticeable in the N-bonded adsorption mode. In the latter, the isosurfaces of charge density differences show accumulation of shared electrons in the region between N and Ti, confirming the predicted N–Ti bond. The moderate adsorption energy values calculated, as well as the preservation of the integrity of both the AAs and the surface upon adsorption, reinforce the capability of Ti2CO2 as a promising reusable biosensor for amino acids.

MXenes are a recently discovered class of two-dimensional materials, which have been attracting much interest by virtue of their promising biomedical and electronic applications. Here, we report on the results of first-principles calculations, based on density functional theory (DFT) including dispersion, of the adsorption energies and configurations of the five nucleobases, molecules conforming nucleotides in nucleic acids, such as DNA and RNA, on the oxygen-terminated titanium carbide MXene surface (Ti2CO2), chosen as a prototype MXene due to titanium being the most biocompatible transition metal. We find that physisorption is the most likely mechanism of adsorption on the Ti2CO2 (0001) basal surface, with the molecules sitting parallel to the MXene, about 2.5 Å away. The calculated adsorption energies and Bader charge transfer values are moderate, as desired for sensing applications. We find a fair correlation between the adsorption energies and the van der Waals volumes of the nucleobases, hinting towards an adsorption dominated by van der Waals interactions. No structural deformation is observed on the molecules or on the surface. Thus, all of our conclusions support the potential applicability of the Ti2CO2 MXene as a suitable nucleobase sensor.