A miniaturized additive-manufactured carbon black/PLA electrochemical sensor for pharmaceuticals detection.

Additive manufacturing is a technique that allows the construction of prototypes and has evolved a lot in the last 20 years, innovating industrial fabrication processes in several areas. In chemistry, additive manufacturing has been used in several functionalities, such as microfluidic analytical devices, energy storage devices, and electrochemical sensors. Theophylline and paracetamol are important pharmaceutical drugs where overdosing can cause adverse effects, such as tachycardia, seizures, and even renal failure. Therefore, this paper aims at the development of miniaturized electrochemical sensors using 3D printing and polylactic acid-based conductive carbon black commercial filament for theophylline and paracetamol detection. Electrochemical characterizations of the proposed sensor were performed to prove the functionality of the device. Morphological characterizations were carried out, in which chemical treatment could change the surface structure, causing the improvement of the analytical signal. Thus, the detection of theophylline at a linear range of 5.00-150 µmol L-1 with a limit of detection of 1.2 µmol L-1 was attained, and the detection of paracetamol at a linear range of 1.00-200 µmol L-1 with a limit of detection of 0.370 µmol L-1 was obtained, demonstrating the proposed sensor effectively detected pharmaceutical drugs.

Circular Economy Electrochemistry: Recycling Old Mixed Material Additively Manufactured Sensors into New Electroanalytical Sensing Platforms.

Recycling used mixed material additively manufactured electroanalytical sensors into new 3D-printing filaments (both conductive and non-conductive) for the production of new sensors is reported herein. Additively manufactured (3D-printed) sensing platforms were transformed into a non-conductive filament for fused filament fabrication through four different methodologies (granulation, ball-milling, solvent mixing, and thermal mixing) with thermal mixing producing the best quality filament, as evidenced by the improved dispersion of fillers throughout the composite. Utilizing this thermal mixing methodology, and without supplementation with the virgin polymer, the filament was able to be cycled twice before failure. This was then used to process old sensors into an electrically conductive filament through the addition of carbon black into the thermal mixing process. Both recycled filaments (conductive and non-conductive) were utilized to produce a new electroanalytical sensing platform, which was tested for the cell's original application of acetaminophen determination. The fully recycled cell matched the electrochemical and electroanalytical performance of the original sensing platform, achieving a sensitivity of 22.4 ± 0.2 µA µM-1, a limit of detection of 3.2 ± 0.8 µM, and a recovery value of 95 ± 5% when tested using a real pharmaceutical sample. This study represents a paradigm shift in how sustainability and recycling can be utilized within additively manufactured electrochemistry toward promoting circular economy electrochemistry.

Sensing performances of spinel ferrites MFe2O4 (M = Mg, Ni, Co, Mn, Cu and Zn) based electrochemical sensors: A review.

The history of ferrites comes from many centuries and was fundamental in many fields. Initially, ferrites were extracted directly from nature, but in the last century, scientists learned to produce ferrites with different properties that gave origin to many advances in industrial and instrumental applications. More recently, the designed preparation of ferrites with nanometric size revealed remarkable characteristics. In the last years, different spinel ferrites were used as electroactive layers to build high-performance modified electrodes. In this review, it is presented a critical overview of the utilization of spinel ferrites (with a general formula MFe2O4, where M2+ = Mg2+, Ni2+, Co2+, Cu2+, Mn2+ and Zn2+) to create differentiated voltammetric sensors. The association of these materials with graphene, glassy carbon, carbon nitride, ionic liquids, nanoparticles of noble metals, oxides of transition metals and other materials can produce notable synergic responses towards electrochemical activity. Some of these sensors can produce very sensitive signals and ample concentration ranges for compounds such hydrogen peroxide, glucose and bisphenol A, and present potential for many other applications. Along this review, all these aspects will be discussed and the main results are organized in tables, using as a base the metal associated with the ferrite.

Electrocatalytic water oxidation reaction promoted by cobalt-Prussian blue and its thermal decomposition product under mild conditions.

Cobalt-Prussian blue analogues are remarkable catalysts for the oxygen evolution reaction (water oxidation) under mild conditions such as neutral pH. Although there are extensive reports in the literature about the application of these catalysts in water oxidation (the limiting step for hydrogen evolution), some limitations must be overcome in terms of improving the turnover frequency, oxygen production, long term stability, and elucidation of the mechanism. Another important feature to consider is the industrial processability of electrolytic cells for water splitting. For these reasons, we have reported herein a comparison of the electrochemical and chemical properties of three catalysts produced from cobalt-Prussian blue. Co-Co PBA 60 refers to cobalt-Prussian blue heated up to 60 °C with a high content of water. Co-Co PBA 200 is the same starting material but heated up to 200 °C with a low water content. Finally, Co3O4 is a thermal decomposition product obtained from heating cobalt-Prussian blue up to 400 °C. Although Co-Co PBA 60 has a higher overpotential for water oxidation than Co-Co PBA 200, this catalyst is kinetically faster than Co PBA 200. It is suggested that the water coordinated to Co2+ in Co-Co PBA 60 can accelerate the reaction and that there is a balance between the thermodynamic and kinetic characteristics for determining the final properties of the catalyst at pH = 7. Another important observation is that the Co3O4 catalyst has the best performance among the considered catalysts with the highest TON and TOF. This suggests that the different mechanisms and surface effects demonstrated by the Co3O4 catalyst are more conducive to efficient water oxidation than those of Prussian blue. Further studies concerning the effect of water and surface on these catalysts under mild conditions are essential to gain a better understanding of the mechanism of water oxidation and to advance the development of new catalysts.

3D-printed reduced graphene oxide/polylactic acid electrodes: A new prototyped platform for sensing and biosensing applications.

This work presents a novel procedure involving the sequential chemical treatment to generate reduced graphene oxide (rGO) within 3D-printed polylactic acid (PLA) electrodes and their potential applications for sensing and biosensing. A new configuration of a compact all-3D-printed electrochemical device containing the three electrodes is presented, in which the working electrode was treated to generate rGO within PLA (rGO-PLA) after treatment within NaBH4. The rGO-PLA electrodes presented a notable current increase for the redox probe ferrocene-methanol in comparison with the same surface treated by dimethylformamide immersion. Also, the electrochemical impedance spectroscopic data that presented the lowest resistance to electron transfer for the proposed electrode. The electrochemical experiments were in accordance with Raman spectra and surface roughness obtained by atomic force microscopy images. As proofs-of-concept, the rGO-PLA electrode was applied for serotonin determination in synthetic urine using differential-pulse voltammetry with a limit of detection of 0.032 µmol L-1. Also, the second application involved the fabrication of a tyrosinase-based biosensor capable of determining catechol in natural water samples with a limit of detection of 0.26 µmol L-1. Based on both applications, the 3D-printed rGO-PLA showed to be an excellent platform for sensing and biosensing purposes.

Production of 3D-printed disposable electrochemical sensors for glucose detection using a conductive filament modified with nickel microparticles.

Three-dimensional printing techniques have been widely used in the fabrication of new materials applied to energy, sensing and electronics due to unique advantages, such as fast prototyping, reduced waste generation, and multiple fabrication designs. In this paper, the production of a conductive 3D-printing filament composed of Ni(OH)2 microparticles and graphene within a polylactic acid matrix (Ni-G-PLA) is reported. The nanocomposite was characterized by thermogravimetric, energy-dispersive X-ray spectroscopic, scanning electronic microscopic, Raman spectroscopic and electrochemical techniques. Characteristics such as printability (using fused deposition modelling), electrical conductivity and mechanical stability of the polymer nanocomposite were evaluated before and after 3D printing. The novel 3D-printed disposable electrode was applied for selective detection of glucose (enzyme-less sensor) with a detection limit of 2.4 µmol L-1, free from the interference of ascorbic acid, urea and uric acid, compounds typically found in biological samples. The sensor was assembled in a portable electrochemical system that enables fast (160 injection h-1), precise (RSD < 5%) and selective determination of glucose without the need of enzymes (electrocatalytic properties of the Ni-G-PLA nanocomposite). The obtained results showed that Ni-G-PLA is a promising material for the production of disposable sensors for selective detection of glucose using a simple and low-cost 3D-printer.

Electrochemical synthesis of Prussian blue from iron impurities in 3D-printed graphene electrodes: Amperometric sensing platform for hydrogen peroxide.

This communication shows the electrochemical synthesis of Prussian blue (PB) films on additive manufactured (3D-printed) electrodes from iron impurities found at the graphene-polylactic acid (G/PLA) substrate and its application as a highly selective sensor for H2O2. The 3D-printed G/PLA electrode was immersed in dimethylformamide for 30 min to exposure the iron impurities within the PLA matrix. Next, cyclic voltammograms (200 cycles) in the presence of potassium ferricyanide in 0.1 mol L-1 KCl + 0.01 mol L-1 HCl were performed to grow the PB films. The sensing properties of this novel PB/G/PLA platform were evaluated for the amperometric detection of H2O2 using batch-injection analysis, with a limit of detection of 0.56 µmol L-1 under the application of 0.0 V (vs Ag/AgCl/KClsat.). The applicability of the sensor was demonstrated for the analysis of milk samples (10-fold diluted in the supporting electrolyte), resulting in proper recovery values (94-101%).

Additive-manufactured (3D-printed) electrochemical sensors: A critical review.

Additive manufacturing or three-dimensional (3D)-printing is an emerging technology that has been applied in the development of novel materials and devices for a wide range of applications, including Electrochemistry and Analytical Chemistry areas. This review article focuses on the contributions of 3D-printing technology to the development of electrochemical sensors and complete electrochemical sensing devices. Due to the recent contributions of 3D-printing within this scenario, the aim of this review is to present a guide for new users of 3D-printing technology considering the required features for improved electrochemical sensing using 3D-printed sensors. At the same time, this is a comprehensive review that includes most 3D-printed electrochemical sensors and devices already reported using selective laser melting (SLM) and fused deposition modeling (FDM) 3D-printers. The latter is the most affordable 3D-printing technique and for this reason has been more often applied for the fabrication of electrochemical sensors, also due to commercially-available conductive and non-conductive filaments. Special attention is given to critically discuss the need for the surface treatment of FDM 3D-printed platforms to improve their electrochemical performance. The insertion of biochemical and chemical catalysts on the 3D-printed surfaces are highlighted as well as novel strategies to fabricate filaments containing chemical modifiers within the polymeric matrix. Some examples of complete electrochemical sensing systems obtained by 3D-printing have successfully demonstrated the enormous potential to develop portable devices for on-site applications. The freedom of design enabled by 3D-printing opens many possibilities of forthcoming investigations in the area of analytical electrochemistry.

Waterproof paper as a new substrate to construct a disposable sensor for the electrochemical determination of paracetamol and melatonin.

Disposable electrochemical sensors using sustainable and cheap materials are an exciting alternative to produce new kinds of sensing platforms. Waterproof paper (WP) is a biodegradable and biocompatible material that allows dropped of the sample on its surface without absorption by fibers. Also, WP can be used for miniaturized sensors construction. In this work, a conductive ink was produced with nail polish and graphite powder, using the WP as the sensor substrate for paracetamol (PAR) and melatonin (MEL) voltammetric determination. PAR is a pharmaceutical commonly used in high doses for the relief of pain and fever, and MEL is a hormone related to several diseases besides a direct relation to sleep quality. Using differential pulse voltammetry for PAR determination, the WP sensor showed a linear response in the concentration ranging from 0.50 µmol L-1 to 100 µmol L-1 with a limit of detection (LOD) of 53.6 nmol L-1. Square wave voltammetry was applied for MEL determination, and the proposed electrode presented linear response ranging from 0.80 µmol L-1 to 100 µmol L-1 and LOD of 32.5 nmol L-1. The sensor showed excellent repeatability and reproducibility for consecutive measurements. Then, the disposable WP sensor was successfully applied in the determination of PAR and MEL in pharmaceutical and biological samples, with recovery values, above 91.1%. The described architecture allowed the manufacture of a disposable, simple, and low-cost electroanalytical device that can be used for electrochemical sensing.

Analysis of solvent-accessible voids and proton-coupled electron transfer of 2,6-bis(1H-imidazol-2-yl)pyridine and its hydrochloride.

The crystal structures of the solid form of solvated 2,6-bis(1H-imidazol-2-yl)pyridine (H2dimpy) trihydrate, C11H9N5·3H2O·[+solvent], I, and its hydrate hydrochloride salt 2-[6-(1H-imidazol-2-yl)pyridin-2-yl]-1H-imidazol-3-ium chloride trihydrate, C11H10N5+·Cl-·3H2O, II, are reported and analysed in detail, along with potentiometric and spectrophotometric titrations for evaluation of the acid-base equilibria and proton-coupled electron-transfer reactions. Compound I crystallizes in the high-symmetry trigonal space group P3221 with an atypical formation of solvent-accessible voids, as a consequence of the 32 screw axis in the crystallographic c-axis direction, which are probably occupied by uncharacterized disordered solvent molecules. Additionally, the trihydrated chloride salt crystallizes in the conventional monoclinic space group P21/c without the formation of solvent-accessible voids. The acid-base equilibria of H2dimpy were studied by potentiometric and spectrophotometric titrations, and the results suggest the formation of H3dimpy+ (pKa1 = 5.40) and H4dimpy2+ (pKa2 = 3.98), with the electrochemical behaviour of these species showing two consecutive irreversible proton-coupled electron-transfer reactions. Density functional theory (DFT) calculations corroborate the interpretation of the experimental results and support the assignment of the electrochemical behaviour.

3D Printed Graphene Electrodes Modified with Prussian Blue: Emerging Electrochemical Sensing Platform for Peroxide Detection.

3D printing technologies have been considered an important technology due to the ease manufacturing of objects, freedom of design, waste minimization, and fast prototyping. In chemistry, this technology potentializes the fabrication of conductive electrodes in large scale for sensing applications. Herein, we reported the modification of a 3D printed graphene electrode with Prussian blue. The modified electrode (3DGrE/PB) was characterized by microscopy (SEM and AFM) and spectroscopic techniques, and its electrochemical properties were compared to the traditional electrodes: glassy carbon, gold, and platinum. The 3DGrE/PB was used in the sensing of hydrogen peroxide in real-world samples of milk and mouthwash, and the results obtained according to the technique of batch-injection analysis were satisfactory for the concentration range typically found in such samples. Thus, 3DGrE/PB can be used as a new platform for sensing of molecular targets.

3D-Printed Low-Cost Spectroelectrochemical Cell for In Situ Raman Measurements.

Raman spectroelectrochemistry is a powerful technique for characterizing structural changes of materials during electrochemical reactions and investigating the mechanism of film deposition and adsorption processes on the surfaces of electrodes. Moreover, in situ measurements enable identification of catalytic sites and reaction intermediates, which facilitates the comprehension of reaction mechanisms. The limitations of this technique include the high-cost and the complexity of the experimental arrangement required by commercial spectroelectrochemical cells (SEC). Thus, 3D-printing technology emerges as an excellent alternative for the production of SEC, with desirable shape, low-cost, and robustness in a short period of time. In this work, an SEC and a 3D-printed working electrode were fabricated from acrylonitrile-butadiene-styrene (ABS) and conductive graphene polylactic acid (PLA) filaments, respectively. The proposed SEC and the 3D-printed electrode were printed within 3.5 h with an estimated cost of materials of less than US $2. Then, the 3D-printed SEC and the electrode were used in a study of structural changes of Prussian blue according to different voltage bias.

Electrochemical water oxidation by cobalt-Prussian blue coordination polymer and theoretical studies of the electronic structure of the active species.

The search for earth-abundant metal-based catalysts for the oxygen evolution reaction (OER) that operates under neutral conditions is a challenge in the field of sustainable energy. Many strategies have been used, and coordination polymers with structures similar to Prussian blue appear to be interesting electrocatalysts due to their efficiency, stability and tunable properties. In this paper, a novel catalyst produced from a cobalt-pentacyanidoferrate precursor is presented and applied in studies of the OER. This material showed a high surface active area and electrocatalytic activity comparable to traditional cobalt hexacyanidoferrate. According to the theoretical calculations, the improvement of these properties is an effect of the framework arrangement and it is not caused by changes of the electronic structure. Further experimental evidence is necessary to determine the active species. However, our results of spin densities obtained from DFT calculations suggest that the active species for water oxidation is the radical Fe(iii)-CN-Co(iii)-O˙.

Visible-Light-Driven Epoxyacylation and Hydroacylation of Olefins Using Methylene Blue/Persulfate System in Water.

A visible-light-driven strategy for hydroacylation and epoxyacylation of olefins in water using methylene blue as photoredox catalyst and persulfate as oxidant is reported. In this unprecedented unified approach, two different transformations are accomplished using only one set of reagents. The method has a broad scope spanning a range of aromatic and aliphatic aldehydes as well as conjugated and nonconjugated olefins to deliver ketones and epoxyketones from abundant and inexpensive chemical feedstocks.

Graphite Screen-Printed Electrodes Applied for the Accurate and Reagentless Sensing of pH.

A reagentless pH sensor based upon disposable and economical graphite screen-printed electrodes (GSPEs) is demonstrated for the first time. The voltammetric pH sensor utilizes GSPEs which are chemically pretreated to form surface immobilized oxygenated species that, when their redox behavior is monitored, give a Nernstian response over a large pH range (1-13). An excellent experimental correlation is observed between the voltammetric potential and pH over the entire pH range of 1-13 providing a simple approach with which to monitor solution pH. Such a linear response over this dynamic pH range is not usually expected but rather deviation from linearity is encountered at alkaline pH values; absence of this has previously been attributed to a change in the pKa value of surface immobilized groups from that of solution phase species. This non-deviation, which is observed here in the case of our facile produced reagentless pH sensor and also reported in the literature for pH sensitive compounds immobilized upon carbon electrodes/surfaces, where a linear response is observed over the entire pH range, is explained alternatively for the first time. The performance of the GSPE pH sensor is also directly compared with a glass pH probe and applied to the measurement of pH in "real" unbuffered samples where an excellent correlation between the two protocols is observed validating the proposed GSPE pH sensor.

Unravelling the chemical morphology of a mesoporous titanium dioxide interface by confocal Raman microscopy: new clues for improving the efficiency of dye solar cells and photocatalysts.

The presence of anatase and rutile domains on nanocrystalline films of P25 TiO2, as well as the distinct coordination modes of carboxylates on those phases, were revealed by confocal Raman microscopy, a technique that showed to be suitable for imaging the chemical morphology down to submicrometric size.

Probing the binding of tetraplatinum(pyridyl)porphyrin complexes to DNA by means of surface plasmon resonance.

Tetrapyridylporphyrins containing four chloro(2,2'-bipyridine)platinum(II) complexes attached at the meta (3-H(2)TPtPyP) and para (4-H(2)TPtPyP) positions of the peripheral pyridine ligands were synthesized and their interaction with DNA investigated. The compounds were isolated in the solid state and characterized by means of spectroscopic and analytical techniques. According to molecular simulations, the two isomers exhibit contrasting structural characteristics, consistent with a saddle shape configuration for 3-H(2)TPtPyP and a planar geometry for 4-H(2)TPtPyP. Surface plasmon resonance studies were carried out on the interaction of the complexes with calf thymus DNA, revealing a preferential binding of 3-H(2)TPtPyP, presumably at the DNA major grooves.

Spectroscopic and electrochemical properties of iron(II) complexes of polydentate Schiff bases containing pyrazine, pyridine and imidazole groups.

We report the synthesis and spectroscopic/electrochemical properties of iron(II) complexes of polydentate Schiff bases generated from 2-acetylpyridine and 1,3-diaminopropane, acetylpyrazine and 1,3-diaminopropane, and from 2-acetylpyridine and L-histidine. The complexes exhibit bis(diimine)-iron(II) chromophores in association with pyrazine, pyridine or imidazole groups displaying contrasting pi-acceptor properties. In spite of their open geometry, their properties are much closer to those of macrocyclic tetraimineiron(II) complexes. An electrochemical/spectroscopic correlation between E degrees (FeIII/II) and the energies of the lowest MLCT band has been observed, reflecting the stabilization of the HOMO levels as a consequence of the increasing backbonding effects in the series of compounds. Mössbauer data have also confirmed the similarities in their electronic structure, as deduced from the spectroscopic and theoretical data.