Platinum Nanoparticles Supported by Carbon Nanotubes: Improvement in electrochemical sensor performance for caffeine determination.

Platinum nanoparticles supported by carbon nanotubes were obtained by a simple chemical route and used for preparation of electrochemical sensor towards caffeine determination. Carbon nanotubes were used before and after an acid treatment, yielding two different materials. Morphological and structural characterization of these materials showed platinum nanoparticles (size around 12 nm) distributed randomly along carbon nanotubes. Modified electrodes were directly prepared through a dispersion of these materials. Voltammetric studies in the presence of caffeine revealed an electrocatalytic effect of platinum oxides, electrochemically produced from the chemical oxidation of the platinum nanoparticles. This behavior was explored in the development a selective method for caffeine determination based on platinum oxide reduction at a lower potential value (+0.45 V vs. Ag/AgCl). Using the best set of experimental conditions, it was shown a linear relationship for the caffeine concentration ranging from 5.0 to 25 µmol L-1 with a sensitivity of 449 nA L µmol-1. Limits of detection and quantification of 0.54 and 1.80 µmol L-1 were calculated, respectively. Recovery values for real samples of caffeine pharmaceutical formulations between 98.6% and 101.0% (n = 3) were obtained using the proposed procedure. Statistical calculations showed good concordance (95% confidence level) between the added and recovery values.

Influence of Defects and Charges on the Colloidal Stabilization of Graphene in Water.

Mastering graphene preparation is an essential step to its integration into practical applications. For large-scale purposes, full graphite exfoliation appears as a suitable route for graphene production. However, it requires overpowering attractive van der Waals forces demanding large energy input, with the risk of introducing defects in the material. This difficulty can be overcome by using graphite intercalation compounds (GICs) as starting material. The greater inter-sheet separation in GICs (compared with graphite) allows the gentler exfoliation of soluble graphenide (reduced graphene) flakes. A solvent exchange strategy, accompanied by the oxidation of graphenide to graphene, can be implemented to produce stable aqueous graphene dispersions (Eau de graphene, EdG), which can be readily incorporated into many processes or materials. In this work, we prove that electrostatic forces are responsible for the stability of fully exfoliated graphene in water, and explore the influence of the oxidation and solvent exchange procedures on the quality and stability of EdG. We show that the amount of defects in graphene is limited if graphenide oxidation is carried out before exposing the material to water, and that gas removal of water before the incorporation of pre-oxidized graphene is advantageous for the long-term stability of EdG.

Probing the Electronic Structure of Prussian Blue and Analog Films by Photoemission and Electron Energy Loss Spectroscopies.

X-ray photoelectron spectroscopy (XPS) and reflection electron energy loss spectroscopy (REELS) were employed to characterize the electronic properties of Prussian blue (PB) and its analogs when electrodeposited over metal-decorated carbon nanotubes (CNTs). Through an investigation of the influence of carbon nanotubes (CNTs) and preparation conditions on the electronic structure, valuable insights were obtained regarding their effects on electrochemical properties. XPS analysis enabled the probing of the chemical composition and oxidation states of the film materials, unveiling synthesis-driven variations in their electronic properties. REELS provided information on energy loss and electronic transitions, enabling further characterization of the changes in the electronic structure induced by different preparation methods. Such findings emphasize the importance of surface characterization to understand how the unique electronic properties of such materials can be harnessed to enhance their performance and functionality.

Nanoarchitected graphene/copper oxide nanoparticles/MoS2 ternary thin films as highly efficient electrodes for aqueous sodium-ion batteries.

Sodium-ion batteries (SIBs) operating in aqueous electrolyte are an emerging technology that promises to be safer, cheaper, more sustainable and more efficient than their lithium-based counterparts. One of the great challenges associated with this technology is the development of advanced materials with high specific capacity to be used as electrodes. Herein, we describe an ingenious strategy to prepare unprecedented tri-component nanoarchitected thin films with superior performance when applied as anodes in aqueous SIBs. Taking advantage of the broadness and versatility of the liquid-liquid interfacial route, three transparent nanocomposite films comprising graphene, molybdenum sulphide and copper oxide nanoparticles have been prepared. The samples were characterized using several techniques, and the results demonstrated that depending on the specific experimental strategy, different nanoarchitectures are achieved, resulting in different and improved properties. An astonishing capacity of 1377 mA h g-1 at 0.1 A g-1 and a degree of recovery of 100% were observed for the film in which the interactions among the components were optimized. This is among the highest capacity values reported in the literature and demonstrates the potential of these tri-component materials to be used as anodes in aqueous sodium-ion batteries.

One-step selective layer assemble: A versatile approach for the development of a SARS-CoV-2 electrochemical immunosensor.

The appearance of new viruses and diseases has made the development of rapid and reliable diagnostic tests crucial. In light of it, we proposed a new method for assembling an electrochemical immunosensor, based on a one-step approach for selective layer formation. For this purpose, a mixture containing the immobilizing agent (polyxydroxybutyrate, PHB) and the recognition element (antibodies against SARS-CoV-2 nucleocapsid protein) was prepared and used to modify a screen-printed carbon electrode with electrodeposited graphene oxide, for the detection of SARS-CoV-2 nucleocapsid protein (N-protein). Under optimum conditions, N-protein was successfully detected in three different matrixes - saliva, serum, and nasal swab, with the lowest detectable values of 50 pg mL-1, 1.0 ng mL-1, and 50 pg mL-1, respectively. Selectivity was assessed against SARS-CoV-2 receptor-binding domain protein (RBD) and antibodies against yellow fever (YF), and no significant response was observed in presence of interferents, reinforcing the suitability of the proposed one-step approach for selective layer formation. The proposed biosensor was stable for up to 14 days, and the mixture was suitable for immunosensor preparation even after 60 days of preparation. The proposed assembly strategy reduces the cost, analysis time, and waste generation. This reduction is achieved through miniaturization, which results in the decreased use of reagents and sample volumes. Additionally, this approach enables healthcare diagnostics to be conducted in developing regions with limited resources. Therefore, the proposed one-step approach for selective layer formation is a suitable, simpler, and a reliable alternative for electrochemical immunosensing.

A versatile 3D printed multi-electrode cell for determination of three COVID-19 biomarkers.

3D-printing has shown an outstanding performance for the production of versatile electrochemical devices. However, there is a lack of studies in the field of 3D-printed miniaturized settings for multiplex biosensing. In this work, we propose a fully 3D-printed micro-volume cell containing six working electrodes (WEs) that operates with 250 µL of sample. A polylactic acid/carbon black conductive filament (PLA/CB) was used to print the WEs and subsequently modified with graphene oxide (GO), to support protein binding. Cyclic voltammetry was employed to investigate the electrochemical behaviour of the novel multi-electrode cell. In the presence of K3[Fe(CN)6], PLA/CB/GO showed adequate peak resolution for subsequent label-free immunosensing. The innovative 3D-printed cell was applied for multiplex voltammetric detection of three COVID-19 biomarkers as a proof-of-concept. The multiple sensors showed a wide linear range with detection limits of 5, 1 and 1 pg mL-1 for N-protein, SRBD-protein, and anti-SRBD, respectively. The sensor performance enabled the selective sequential detection of N protein, SRBD protein, and anti-SRBD at biological levels in saliva and serum. In summary, the miniaturized six-electrode cell presents an alternative for the low-cost and fast production of customizable devices for multi-target sensing with promising application in the development of point-of-care sensors.

Graphene-Binding Peptide in Fusion with SARS-CoV-2 Antigen for Electrochemical Immunosensor Construction.

The development of immunosensors to detect antibodies or antigens has stood out in the face of traditional methods for diagnosing emerging diseases such as the one caused by the SARS-CoV-2 virus. The present study reports the construction of a simplified electrochemical immunosensor using a graphene-binding peptide applied as a recognition site to detect SARS-CoV-2 antibodies. A screen-printed electrode was used for sensor preparation by adding a solution of peptide and reduced graphene oxide (rGO). The peptide-rGO suspension was characterized by scanning electron microscopy (SEM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). The electrochemical characterization (electrochemical impedance spectroscopy-EIS, cyclic voltammetry-CV and differential pulse voltammetry-DPV) was performed on the modified electrode. The immunosensor response is based on the decrease in the faradaic signal of an electrochemical probe resulting from immunocomplex formation. Using the best set of experimental conditions, the analytic curve obtained showed a good linear regression (r2 = 0.913) and a limit of detection (LOD) of 0.77 µg mL-1 for antibody detection. The CV and EIS results proved the efficiency of device assembly. The high selectivity of the platform, which can be attributed to the peptide, was demonstrated by the decrease in the current percentage for samples with antibody against the SARS-CoV-2 S protein and the increase in the other antibodies tested. Additionally, the DPV measurements showed a clearly distinguishable response in assays against human serum samples, with sera with a response above 95% being considered negative, whereas responses below this value were considered positive. The diagnostic platform developed with specific peptides is promising and has the potential for application in the diagnosis of other infections that lead to high antibody titers.

Liquid-liquid interfaces: a unique and advantageous environment to prepare and process thin films of complex materials.

Thin film technology is pervasive for many fields with high impact in our daily lives, which makes processing materials such as thin films a very important subject in materials science and technology. However, several paramount materials cannot be prepared as thin films through the well-known and consolidated deposition routes, which strongly limits their applicability. This is particularly noticeable for multi-component and complex nanocomposites, which present unique properties due to the synergic effect between the components, but have several limitations to be obtained as thin films, mainly if homogeneity and transparence are required. This review highlights the main advances of a novel approach to both process and synthesize different classes of materials as thin films, based on liquid/liquid interfaces. The so-called liquid/liquid interfacial route (LLIR) allows the deposition of thin films of single- or multi-component materials, easily transferable over any kind of substrate (plastics and flexible substrates included) with precise control of the thickness, homogeneity and transparence. More interesting, it allows the in situ synthesis of multi-component materials directly as thin films stabilized at the liquid/liquid interface, in which problems related to both the synthesis and processing are solved together in a single step. This review presents the basis of the LLIR and several examples of thin films obtained from different classes of materials, such as carbon nanostructures, metal and oxide nanoparticles, two-dimensional materials, organic and organometallic frameworks, and polymer-based nanocomposites, among others. Moreover, specific applications of those films in different technological fields are shown, taking advantage of the specific properties emerging from the unique preparation route.

Introduction to celebrating Latin American talent in chemistry.

In celebration of the excellence and breadth of Latin American research achievements across the chemical sciences, we are delighted to present an introduction to the themed collection, Celebrating Latin American talent in chemistry.

A simple enzymeless approach for Paraoxon determination using imidazole-functionalized carbon nanotubes.

This work describes the application of a glassy carbon electrode (GCE) modified with imidazole functionalized carbon nanotubes (CNT-H-IMZ) for Paraoxon (PX) determination in samples of commercial, fresh and 100% orange juice. Homemade multi-walled CNTs were treated according to the Hummers procedure to oxidize graphite and later chemically functionalized with imidazole groups. Modified electrodes with CNT-H-IMZ presented a high peak current of PX reduction and an electrocatalytic effect in comparison to the other electrodes. This behavior was associated with the synergistic contribution of IMZ and CNT that increases the electrochemical activity of PX. Repeatability and reproducibility studies showed that the relative peak current values did not show significant differences between them, less than 10%, and it was possible to define that the diffusional process is the mechanism that limits the electrode mass transport. After the optimization of parameters inherent to the methodology and the voltammetric technique, the proposed device presented a linear region of 1.0 to 16.0 µM-1 (R2 = 0.99), presenting LOD and LOQ as 120 and 400 nM-1, respectively. The method proposed was successfully applied to PX determination in spiked samples.

A black phosphorus-based cathode for aqueous Na-ion batteries operating under ambient conditions.

We present the unprecedented application of a black phosphorus-based nanocomposite as an electrode for aqueous Na-ion batteries under ambient conditions. An impressive specific capacity of up to 200 mA h g-1 was reached after 50 cycles in a NaCl aqueous solution used as a supporting electrolyte. Post-characterization indicated the integrity of the black phosphorus.

Molybdenum-based two-dimensional materials: Synthesis, dispersion, exfoliation and thin film deposition.

We report a simple and effective route to synthesize, disperse, exfoliate and process different molybdenum-based 2-dimensional (2D) materials. Starting from a reaction between ammonium molybdate and ammonium sulfide solutions, a powder consisting of a mixture between amorphous molybdenum oxide and sulfide is obtained. By tuning the atmosphere and the temperature, different compositions can be prepared by thermal treatment of this sample: heat treatments in ambient atmosphere produce MoO3 with different morphologies, controllable according to the chosen temperature. On the other hand, heat treatments in inert atmosphere produce mixtures between crystalline 2D MoS2 and MoO3. Further handling of these mixtures with acetonitrile separates the components due to the different solvent/solid affinities, with the layered MoS2 becoming homogeneously dispersed, and the MoO3 agglomerating as a solid easily removed by centrifugation. The resulting sulfide dispersions in acetonitrile present high stability, and they are constituted by exfoliated MoS2, which means that acetonitrile is a tri-functional agent, separating the sulfide/oxide mixture, exfoliating the sulfide and stabilizing the dispersion. The MoS2 dispersions were used to produce homogeneous, freestanding and transparent thin films through the liquid-liquid interfacial route, which were easily deposited over different substrates and characterized by different techniques.

A new approach for the achievement of stable aqueous dispersions of carbon nanotubes.

A novel methodology to prepare stable aqueous dispersions of raw single- and multi-walled carbon nanotubes is reported, based on dispersions previously prepared in tetrahydrofuran containing a phenol that donates electrons to nanotubes and provides colloidal stability through electrostatic repulsion. A proposed mechanism for the stabilization of the dispersions is presented. Conductive and transparent thin films are prepared through a liquid/liquid interfacial route starting from these dispersions.

Molecular orientation and femtosecond charge transfer dynamics in transparent and conductive electrodes based on graphene oxide and PEDOT:PSS composites.

The conducting polymer, poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid (PEDOT:PSS), is certainly one of the most important substitute materials for indium tin oxide in organic devices. Its metallic conductivity and transmittance bring favorable perspectives for organic photovoltaic applications. Although graphene oxide (GO) is not a good conductor, it can form high-quality thin films and can be transparent, and additionally, GO is an inexpensive material and can be easily synthesized. This study investigated how the conductivity of a composite film of graphene oxide (GO) and different amounts of PEDOT:PSS can be modified. The effects of GO:PEDOT:PSS composites with several PEDOT:PSS proportions were analyzed in regards to the composite molecular structure and ordering, charge transfer dynamics (in the femtosecond range), electrical properties and morphology. For the best conductivity ratio GO found with 5% PEDOT:PSS, a solvent treatment was also performed, comparing the resistivity of the film when treated with dimethyl sulfoxide (DMSO) and with ethylene glycol.

Facile room temperature synthesis of large graphene sheets from simple molecules.

The largest graphene sample obtained through a chemical reaction under ambient conditions (temperature and pressure), using simple molecules such as benzene or n-hexane as precursors, is reported. Starting from a heterogeneous reaction between solid iron chloride and the molecular precursor (benzene and n-hexane) at a water/oil interface, graphene sheets with micrometric lateral size are obtained as a film deposited at the liquid/liquid (L/L) interface. The pathway involving the cyclization and aromatization of n-hexane to benzene at the L/L interface, and the sequence of conversion of benzene to biphenyl and biphenyl to condensed rings (which originates the graphene structures) was followed by different characterization techniques and a mechanistic proposal is presented. Finally, we demonstrate that this route can be extended for the synthesis of N-doped graphene, using pyridine as the molecular precursor.

Electrostatic stabilization of multi-walled carbon nanotubes dispersed in nonaqueous media.

Dispersing carbon nanotubes is an easy and low-cost way to manipulate these solids and allows the preparation of more complex materials or devices, so it is fundamental for further uses that these dispersions have controlled properties and high colloidal stability. In this work we report the spontaneous electrical charge build-up in pristine multi-walled carbon nanotubes dispersed in common organic solvents such as chloroform and tetrahydrofuran and the achievement of dispersions stable for long periods without adding passivant agents or functional groups on nanotubes surface. Results from electrokinetics, homo- and heterocoagulation provided macroscopic evidences that carbon nanotubes acquire electric charges after dispersion in some organic liquids and we confirmed this process by measuring in situ Raman spectra of the nanotubes dispersions with higher surface electric potentials. We also show that the signal of electric potential of the dispersions can be predicted by the acid-base behaviour of the dispersing medium, corroborating previously reports for other dispersions of carbon nanomaterials.

Nonenzymatic electrochemical sensor based on imidazole-functionalized graphene oxide for progesterone detection.

The modification of electrode surfaces has been the target of study for many researchers in order to improve the analytical performance of electrochemical sensors. Herein, the use of an imidazole-functionalized graphene oxide (GO-IMZ) as an artificial enzymatic active site for voltammetric determination of progesterone (P4) is described for the first time. The morphology and electrochemical performance of electrode modified with GO-IMZ were characterized by scanning electron microscopy and cyclic voltammetry, respectively. Under optimized conditions, the proposed sensor showed a synergistic effect of the GO sheets and the imidazole groups anchored on its backbone, which promoted a significant enhancement on electrochemical reduction of P4. Figures of merits such as linear dynamic response for P4 concentration ranging from 0.22 to 14.0 µmol L-1, limit of detection of 68 nmol L-1 and limit of quantification and 210 nmol L-1 were found. In addition, presented a higher sensitivity, 426 nA L µmol-1, when compared to the unmodified electrode. Overall, the proposed device showed to be a promising platform for a simple, rapid, and direct analysis of progesterone.

Photoanode for Aqueous Dye-Sensitized Solar Cells based on a Novel Multicomponent Thin Film.

Most of the dye-sensitized solar cells (DSSCs) developed so far use organic electrolytes and water-sensible sensitizers. The search for aqueous DSSCs, a promising technology for solar-energy conversion, implies finding materials that are stable in aqueous solution. In this study, Prussian blue (PB) was utilized as an innovative sensitizer in a photoanode for DSSCs and a novel synthetic approach to a carbon nanotubes/TiO2 /PB nanocomposite thin film was developed. The photoresponse was evaluated in a total aqueous electrolyte, and photocurrents of 600 µA cm-2 were achieved.

Highly Conducting, Sustainable, Nanographitic Rubber Composites.

Environmentally friendly multifunctional rubber composites are reported. Graphitic nanocarbon (NC) deriving from cracking of biogas (methane/carbon dioxide) and natural rubber extracted directly from the Hevea brasiliensis tree are the two components of these composites produced via latex technology. While maintaining and enhancing the intrinsic thermal and mechanical characteristics of rubber, the presence of NC shows a significant improvement on the electrical response. For a 10 wt % NC content, a 1010-fold increase in conductivity has been achieved with a conductivity value of 7.5 S·m-1, placing these composites among the best obtained using other carbon fillers. In addition, the piezoresistive behavior has also been verified. These promising green composites have a potential use in a variety of applications such as sealing of electronic devices and sensors.

Ultrafast interface charge transfer dynamics on P3HT/MWCNT nanocomposites probed by resonant Auger spectroscopy.

The interfacial electronic structure and charge transfer dynamics of poly-3-hexylthiophene (P3HT) and multi-walled carbon nanotube (Fe-MWCNT) nanocomposites were investigated by near-edge X-ray absorption fine structure (NEXAFS) and resonant Auger (RAS) spectroscopies around the sulfur K-edge. Nanocomposites with 5 wt% (P3HT/Fe-MWCNT-5%) and 10 wt% (P3HT/Fe-MWCNT-10%) of Fe-MWCNT species were prepared and compared with pristine P3HT film. The quantitative NEXAFS analysis shows a strong π-π interchain interaction of the pristine P3HT polymer film, which is reduced by the presence of the Fe-MWCNT. S-KL2,3L2,3 RAS spectra were measured at photon energies corresponding to the main electronic transitions appearing in the S-K edge NEXAFS spectrum. Ultrafast charge transfer times were estimated from the RAS spectra using the core-hole clock approach with the S 1s core-hole lifetime as an internal clock. The π-π interchain charge transfer time increases from 4.7 fs on pristine P3HT polymer to 6.5 fs on the P3HT/Fe-MWCNT-5% nanocomposite. The electronic coupling between P3HT and Fe-MWCNT species occurs mainly through the P3HT π* molecular orbital. The increase of Fe-MWCNT concentration from 5 to 10 wt% reduces the charge transfer rate at the resonance maximum due probably to Fe-MWCNT aggregation, reducing the P3HT and Fe-MWCNT electronic coupling.