Solution-based printing approaches permit digital designs to be converted into physical objects by depositing materials in a layer-by-layer additive fashion from microscale to nanoscale resolution. The extraordinary adaptability of this technology to different inks and substrates has received substantial interest in the recent literature. In such a context, this review specifically focuses on the realization of inks for the deposition of ZnO, a well-known wide bandgap semiconductor inorganic material showing an impressive number of applications in electronic, optoelectronic, and piezoelectric devices. Herein, we present an updated review of the latest advancements on the ink formulations and printing techniques for ZnO-based nanocrystalline inks, as well as of the major applications which have been demonstrated. The most relevant ink-processing conditions so far explored will be correlated with the resulting film morphologies, showing the possibility to tune the ZnO ink composition to achieve facile, versatile, and scalable fabrication of devices of different natures.
A new catalase amperometric biosensor for hydroperoxides detection has been built as part of research aimed at the development of biosensors based on layered double hydroxides (LDH) used as support for enzyme immobilization. The fabricated device differs from those developed so far, usually based on an LDH enzyme nanocomposite adsorbed on a glassy carbon (GC) electrode and cross-linked by glutaraldehyde, since it is based on an amperometric gas diffusion electrode (Clark type) instead of a GC electrode. The new biosensor, which still uses LDH synthesized by us and catalase enzyme, is robust and compact, shows a lower LOD (limit of detection) value and a linearity range shifted at lower concentrations than direct amperometric GC biosensor, but above all, it is not affected by turbidity or emulsions, or by the presence of possible soluble species, which are reduced to the cathode at the same redox potential. This made it possible to carry out accurate and efficient determination of H2O2 even in complex or cloudy real matrices, also containing very low concentrations of hydrogen peroxide, such as milk and cosmetic products, i.e., matrices that would have been impossible to analyze otherwise, using conventional biosensors based on a GC–LDH enzyme. An inaccuracy ≤7.7% for cosmetic samples and ≤8.0% for milk samples and a precision between 0.7 and 1.5 (as RSD%), according to cosmetic or milk samples analyzed, were achieved.
Layered Double Hydroxides (LDHs) are a relevant class of inorganic lamellar nanomaterials that have attracted significant interest in life science-related applications, due to their highly controllable synthesis and high biocompatibility. Under a general point of view, this class of materials might have played an important role for the origin of life on planet Earth, given their ability to adsorb and concentrate life-relevant molecules in sea environments. It has been speculated that the organic–mineral interactions could have permitted to organize the adsorbed molecules, leading to an increase in their local concentration and finally to the emergence of life. Inspired by nature, material scientists, engineers and chemists have started to leverage the ability of LDHs to absorb and concentrate molecules and biomolecules within life-like compartments, allowing to realize highly-efficient bioinspired platforms, usable for bioanalysis, therapeutics, sensors and bioremediation. This review aims at summarizing the latest evolution of LDHs in this research field under an unprecedented perspective, finally providing possible challenges and directions for future research.
In this paper, a novel non-enzymatic modified glassy carbon (GC) sensor, of the (GC-Agpaste)-catalytic proline-assisted LDH type, for H2O2 determination was fabricated, studied, characterized and employed to determine the hydrogen peroxide content in healthy and diabetic human urine. LDH (whose composition can be schematized as [ZnIIAlIII (OH)2]+ NO3−·nH2O) is glued to glassy carbon by means of silver paste, while proline, which increases the catalytic properties of LDH, is used free in solution in the phosphate buffer. A voltametric survey was first conducted to ascertain the positive effect induced by the presence of proline, i.e., the increase of sensor sensitivity. Then a deep study of the new three-electrode amperometric proline-assisted LDH sensor, whose working electrode was of the same type as the one used to perform the cyclic voltammetry, was carried out, working at first in static air, then in a nitrogen atmosphere. Possible interferences from various substances, both oxidants and antioxidants, were also investigated. Lastly, the new amperometric sensor was successfully used to determine the H2O2 level in human urine from both healthy and diabetic subjects. The effect of proline in enhancing the properties of the sensor system was also investigated. The limit of detection (LOD) of the new catalytic sensor was of the order of 0.15 mmol L−1, working in air, and of 0.05 µmol L−1, working in nitrogen atmosphere.
Aims: A new basic research was conducted concerning the possibility of using a flow DCFC (Direct Catalytic Fuel Cell) for analytical purposes, checking ethanol and glucose. Also making considerations on the energy conversion aspect of these fuels. Background: There are a large number of studies concerning catalytic or microbial fuel cells, which allow to obtain electricity, both using liquid fuels, such as ethanol and methanol, or solid fuels, such as carbohydrates, biomass and so on. These systems are frequently characterized by high conversion efficiency but also high complexity and considerable costs. Objective: In the present research we investigated the possibility of using a very simple flow system to carry out measurement of ethanol concentration, or glucose analysis, using the same flow system associated with a small reactor containing yeast (Saccharomyces Cerevisiae). Methods: The main operating conditions have been optimized and the concentration range where the flow system response shows a linear correlation with the fuel concentration was also identified. Result: The current delivered by the catalytic system operating in flow was determined and the calibration sensitivity values are higher than the sensitivity found when operating in batch mode. It has also been shown that it is possible to realize a very simple system, which can be used to study and evaluate the conversion of chemical energy into electrical energy, using ethanol or glucose as fuel and the theoretical importance and analytical advantages have been emphasized, so that the use of carbohydrates, such as solid fuels, could represent. Conclusion: Present research has shown how, by operating in flow mode, rather than in batch, it is possible to have advantages from an analytical point of view, since a considerable increase in the sensitivity of the method can be obtained, probably attributable to a reduction in the effects of poisoning. Moreover, how it is possible to study and optimize the energy conversion conditions by means of a simple and inexpensive apparatus.
Taking inspiration from our recent work in which a new sensor for hydrogen peroxide was proposed, our research group has now developed a simple, fast, and inexpensive voltametric system for determining proline concentration both in standard solutions and in real samples (red and white wines). This system uses a non-enzymatic sensor based on a working electrode of glassy carbon (GC) modified with a layered double hydroxide (LDH) compound, of the type GC-Ag(paste)-LDH-H2O2, with hydrogen peroxide in solution at fixed concentration, in a three electrode cyclic voltammetry setup. Using an increasing concentration of standard solutions of L-proline, the method shows a linearity range, in semilogarithmic coordinates, between 125 μmol L−1 and 3200 μmol L−1 of proline, with a limit of detection (LOD) value of 85.0 μmol L−1 and a limit of quantitation (LOQ) value of 95.0 μmol L−1. The developed method is applied to the determination of proline in several samples of commercial Italian wines. The results are compared with those obtained by applying the classic spectrophotometric method of ninhydrin, obtaining a good correlation of the results.
Poly(dimethylsiloxane) (PDMS) devices must often be so thin (e.g., <100 μm) and, therefore, so fragile that their mechanical release becomes challenging. As a simple solution, PDMS devices are frequently released by dissolving an underlying sacrificial resist. However, there may be several other issues, including temperature gradients during fabrication, electrical characterization, handling, co-integration with electronics, fabrication time, and cost. Here, we show that conventional printed circuit boards (PCBs) can be ideal sacrificial carriers, which can also perform useful functions during fabrication. The thick (e.g., 35 μm) and thermally conductive PCB copper layer behaves as an excellent heat spreading plate during temperature-sensitive process steps (e.g., PDMS curing and sintering of conductive inks) and enables pre-release electrical stimulations and characterizations of PDMS, which may help during process development. Experiments and finite element method (FEM) simulations confirm that the PCB copper layer can improve temperature uniformity. The UV-protecting film attached to the PCB can be cut to constitute a frame for easy handling. The PCB photoresist enables the straightforward release of PDMS by acetone, which is among the most environmentally friendly chemicals. Contacts can be opened by a simple bump-cut-peel strategy. As proofs of concept, we demonstrate pre-release capacitive characterization of PDMS for evaluating the ability to fabricate thin, but uniform and robust devices and post-release resistive characterization of stretchable strain sensor or interconnects encapsulated in PDMS. The proposed approach is simple, cheap, and environmentally friendly, can improve temperature uniformity throughout the pre-release process steps, enables pre-release electrical characterizations, can simplify co-integration with electronics and can be generalized to other elastomers.
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