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The design of multifunctional nanostructured materials is the key to the development of smart wearable devices. For instance, nanostructures endowed with both piezoelectric and photocatalytic activities could well be the workhorse for solar-light-driven self-cleaning wearable sensors. In this work, a simple strategy for the assembly of a flexible, semitransparent piezophotocatalytic system is demonstrated by leveraging rational wet chemistry synthesis of ZnO-based nanosheets/nanoflowers (NSs/NFs) under basic pH conditions onto flexible ITO/PET supports. A KMnO4 pretreatment before the ZnO synthesis (seeded ZnO) allows for the control of the density, size, and orientation of the NSs/NFs systems compared to the systems produced in the absence of seeding (seedless ZnO). The electrical response of the sensors is extracted at a 1 V bias as a function of bending in the interval between 0 and 90°, being the responsivity toward bending significantly enhanced by the KMnO4 treatment effect. The photocatalytic activity of the sensors is analyzed in aqueous solution (methylene blue, 25 μM) by a solar simulator, resulting in similar values between seedless and seeded ZnO. Upon bending the sensor, the photocatalytic activity of seedless ZnO is almost unaffected, whereas that of seeded ZnO is improved by about 25%. The sensor’s reusability and repeatability are tested in up to three different cycles. These results open up the way toward the seamless integration of bending sensitivity and photocatalysis into a single device.

The synthesis of crystals with a high surface-to-volume ratio is essential for innovative, high-performance electronic devices and sensors. The easiest way to achieve this in integrated devices with electronic circuits is through the synthesis of high-aspect-ratio nanowires aligned vertically to the substrate surface. Such surface structuring is widely employed for the fabrication of photoanodes for solar cells, either combined with semiconducting quantum dots or metal halide perovskites. In this review, we focus on wet chemistry recipes for the growth of vertically aligned nanowires and technologies for their surface functionalization with quantum dots, highlighting the procedures that yield the best results in photoconversion efficiencies on rigid and flexible substrates. We also discuss the effectiveness of their implementation. Among the three main materials used for the fabrication of nanowire-quantum dot solar cells, ZnO is the most promising, particularly due to its piezo-phototronic effects. Techniques for functionalizing the surfaces of nanowires with quantum dots still need to be refined to be effective in covering the surface and practical to implement. The best results have been obtained from slow multi-step local drop casting. It is promising that good efficiencies have been achieved with both environmentally toxic lead-containing quantum dots and environmentally friendly zinc selenide.

The design of multifunctional materials is of pivotal importance for developing wearable biosensors. In particular, the advancement in self-cleaning materials suitable for bending sensors, i.e. devices able to track human body movements for healthcare monitoring [1], has raised much interest in recent pandemic times. Such technology can be facilitated by leveraging piezo-photocatalytic cleaning effects under visible light [2]. Herein, we show a new class of ZnO-based nanosheets (NSs) synthesized in aqueous solution (85 °C, 24 hours) onto seeded or seedless ITO/PET surfaces that couple sensing to photocatalysis. UV-vis and FT-IR spectroscopies show the typical absorption peaks of ZnO. A nano-squared pattern is observed on ITO, likely resulting from mixed SnO2:ZnO nanocubic photocatalytic composites [3]. In the absence of the MnOOH seed layer film (seedless ZnO), NSs show flower-like morphology showing a significantly lower density (about twenty times) with respect to the seeded version. The electrical response of the sensors is extracted at a 1 V bias as a function of bending in the interval between 0° and 90°. The sensing response is dependent on the density of the ZnO NSs. Upon bending from 0° to 90°, the seedless ZnO sensors show 50-70 μA decrease, whereas the seeded ZnO sensors show a 180-200 μA decrease, which is about two times higher than the currently reported ZnO based bending sensors [4]. As a control, the bare ITO supports only show few μA decrease upon bending. The photocatalytic activity of the sensors is analysed in aqueous solution (methylene blue, 25 μM) at 1 Sun illumination. The seeded ZnO sensors show the best photocatalytic performances with respect to seedless ZnO and bare ITO. Upon bending the sensor inside the cuvette, the photocatalytic activities of bare ITO and seeded ZnO are improved (about 30%), whereas seedless ZnO is unaffected. After washing with deionized water, the sensors retain most of their photocatalytic activity. References [1] C. Chiappara, V. Campisciano, G. Arrabito, V. Errico, G. Saggio, G. Buscarino, M. Scopelliti, M. Gruttadauria, F. Giacalone, B. Pignataro, Bending Sensors Based on Thin Films of Semitransparent Bithiophene- Fulleropyrrolidine Bisadducts, ChemPlusChem 2020, 85, 2455. [2] S. C.Tu, Y.X. Guo, Y. H. Zhang, C. Hu, T. R. Zhang, T. Y. Ma, H. W. Huang, Piezocatalysis and Piezo- Photocatalysis: Catalysts Classification and Modification Strategy, Reaction Mechanism, and Practical Application. Adv. Funct. Mater. 2020, 30, 2005158. [3] R. Kumar, Ahmad Umar, Rajesh Kumar, M.S. Chauhan, Yas Al-Hadeethi, ZnO–SnO2 nanocubes for fluorescence sensing and dye degradation applications, Ceramics International, 2021, 47, 6201–6210. [4] M. Panth, B. Cook, M. Alamri, D. Ewing, A. Wilson, and J. Z. Wu, Flexible Zinc Oxide Nanowire Array/Graphene Nanohybrid for High-Sensitivity Strain Detection, ACS Omega 2020 5 (42), 27359-27367.

Fine control of nanoparticle clustering within polymeric matrices can be tuned to enhance the physicochemical properties of the resulting composites, which are governed by the interplay of nanoparticle surface segregation and bulk clustering. To this aim, out-of-equilibrium strategies can be leveraged to program the multiscale organization of such systems. Here, we present experimental results indicating that bulk assembly of highly photoactive clusters of titanium dioxide nanoparticles within an in situ synthesized polysiloxane matrix can be thermally tuned. Remarkably, the controlled nanoparticle clustering results in improved degradation photocatalytic performances of the material under 1 sun toward methylene blue. The resulting coatings, in particular the 35 wt % TiO2-loaded composites, show a photocatalytic degradation of about 80%, which was comparable to the equivalent amount of bare TiO2 and two-fold higher with respect to the corresponding composites not subjected to thermal treatment. These findings highlight the role of thermally induced bulk clustering in enhancing photoactive nanoparticle/polymer composite properties.

The design of wearable sensors coupling versatile analytical detection to self-cleaning is a highly desired combination, tackling the need of smart devices in response to the recent virus pandemics. To this aim, this work shows ZnO nanostructures obtained by a mild wet-chemistry approach onto ITO/PET flexible supports, resulting in wearable piezoelectric sensors exhibiting photocatalytic activity. ITO surfaces are treated with 0.5 mM KMnO4 aqueous solution (20 minutes, 90°C); ZnO growth is subsequently carried out by a previously shown wet-chemistry method [1]. SEM analysis shows the presence of a good surface coverage of ZnO nanosheets (NSs) (about 1.5 NSs/μm2) in the case of treated ITO, whereas low-density larger flower-like ZnO NSs (about 0.25 NSs/μm2) are observed on the control ITO surface – i.e. not treated by the KMnO4 solution. XPS analysis highlights the presence of zinc and oxygen, whereas manganese traces are detected by depth profile analysis. Chronoamperometric measurements show current reduction upon 1V bias towards bending, in full accordance with previous reports [2]. Electrical impedance spectroscopy (PBS buffer, pH = 7.4) shows that ZnO reduces impedance with respect to the bare ITO electrode at low sampling frequencies (0.1 -1 Hz), being ZnO NSs on treated ITO the system which provides the lowest values. In full accordance to the electrochemical data, piezophotocatalytic tests show that high-density ZnO NSs provide the best results towards photodegradation of methylene blue (25 μM, solar light simulator).

We designed, fabricated, and validated a piezoresistive bending sensor, a fundamental component of wearable electronic devices for monitoring human motion. The most diffused opaque carbon-based resistance flex sensors suffer from low detection for small bending angles. The sensor we here present is based on a semi-transparent active material (fulleropyrrolidine bisadducts polymer) and has the remarkable advantage of good electrical properties for low bending angles. The fabrication steps are effective since a pre-patterned ITO/PET surface is functionalized by chronoamperometric deposition, and the silver electrical contacts are inkjet printed. We propose a fitting function of the measured thin film resistance curve vs. the bending angle, showing promising properties as a complimentary bending sensor to the most diffused flex sensors. The results pave the way to new applications and more performant wearables.

Over the past decade, halide perovskite systems have captured widespread attention among researchers since their exceptional photovoltaic (PV) performance was disclosed. The unique combination of optoelectronic properties and solution processability shown by these materials has enabled perovskite solar cells (PSCs) to reach efficiencies higher than 25% at low fabrication costs. Moreover, PSCs display enormous potential for modern unconventional PV applications, since they can be made lightweight, semitransparent (ST), and/or flexible by means of appropriate design strategies. In particular, by enabling transparency and high efficiency simultaneously, ST-PSCs hold great promise for future versatile utilization in the context of building-integrated PVs (BIPVs) or as top cells to be coupled with conventional lower-bandgap bottom cells in tandem PV devices. The present Review wants to provide a detailed overview of latest research about ST-PSCs for BIPVs and tandems, by critically reporting on the most updated and effective design strategies in view of these two possible future applications. The differences and similarities between the available approaches are punctually highlighted, emphasizing the importance of a rigorous application-orientated ST-PSC design. Last but not least, the main challenges and issues about device design, operation, and stability that need to be addressed before commercialization are thoroughly scanned.

Naturally occurring extracellular vesicles and artificially made vesicles represent important tools in nanomedicine for the efficient delivery of biomolecules and drugs. Since its first appearance in the literature 50 years ago, the research on vesicles is progressing at a fast pace, with the main goal of developing carriers able to protect cargoes from degradation, as well as to deliver them in a time- and space-controlled fashion. While natural occurring vesicles have the advantage of being fully compatible with their host, artificial vesicles can be easily synthetized and functionalized according to the target to reach. Research is striving to merge the advantages of natural and artificial vesicles, in order to provide a new generation of highly performing vesicles, which would improve the therapeutic index of transported molecules. This progress report summarizes current manufacturing techniques used to produce both natural and artificial vesicles, exploring the promises and pitfalls of the different production processes. Finally, pros and cons of natural versus artificial vesicles are discussed and compared, with special regard toward the current applications of both kinds of vesicles in the healthcare field.

The impact of layered double hydroxides (LDHs) within the multidisciplinary fields of materials sciences, physics, chemistry, and biology is rapidly growing, given their easiness of synthesis, flexibility in composition, tunable biocompatibility and morphology. LDHs constitute a versatile platform for the realization of new classes of functional systems, showing unique enhanced surface effects and unprecedented properties for application in very different fields, namely, surface chemistry and catalysis, storage and triggered release of functional anions, flame retardants, drug delivery and nanomedicine, remediation, energy storage and conversion. These systems can be synthesized as self-assembled hierarchical nanosheet thin films by means of low temperature solution-based approaches, which are accessible by many laboratories and have the advantages of low cost, mild conditions, and environmental friendliness. In addition, the possibility of LDHs to be exfoliated into 2D nanosheets has been demonstrated to further improve their performance in many applications, as well as to be an attractive route to achieve building blocks for fabricating a wide plethora of hybrid functional architectures. LDHs are therefore a playground for exciting new research covering all of the most intriguing features of 2D materials and more. This Special Issue on “Layered Double Hydroxides” gathers a multidisciplinary collection of original contributions and review articles from authors with diverse scientific backgrounds and who employ LDHs for very different applications, permitting the demonstration of their versatility. Along with LDH-focused papers, this Special Issue also includes some research in which materials different to LDHs resulted in a convenient choice for selected purposes.

Fine control of nanoparticle clustering within polymeric matrices can be tuned to enhance the physicochemical properties of the resulting composites, which are governed by the interplay of nanoparticle surface segregation and bulk clustering. To this aim, out-of-equilibrium strategies can be leveraged to program the multiscale organization of such systems. Here, we present experimental results indicating that bulk assembly of highly photoactive clusters of titanium dioxide nanoparticles within an in situ synthesized polysiloxane matrix can be thermally tuned. Remarkably, the controlled nanoparticle clustering results in improved degradation photocatalytic performances of the material under 1 sun toward methylene blue. The resulting coatings, in particular the 35 wt % TiO2-loaded composites, show a photocatalytic degradation of about 80%, which was comparable to the equivalent amount of bare TiO2 and two-fold higher with respect to the corresponding composites not subjected to thermal treatment. These findings highlight the role of thermally induced bulk clustering in enhancing photoactive nanoparticle/polymer composite properties.

Natural evolution has chosen the localization of biomolecular processes into crowded sub-cellular femtoliter (fL) scale compartments for organizing complex biological processes. [1] Many synthetic biology platforms with life-like activities have been able to mimic these systems under different compartment sizes regimes. [2] However, the fabrication of crowded compartments down to sub-cellular scales is challenging, mainly because of high surface-volume ratio of these systems, finally compromising the stability of the encapsulated biomolecules. In this regard, we here bridge this gap by showing the possibility to produce femtoliter-scale aqueous droplets using a novel inkjet printing approach reproducing a theoretical model from Eggers et al. [3] The fL-scale droplets are spiked with non-ionic surfactants to stabilize the water/oil interface whilst not compromising ink viscosity and surface tension. [4] When injected into nL-scale mineral oil droplets, the fL-droplets form an almost-regular circular pattern at the border of mineral oil drops due to Marangoni flows (see Figure). Remarkably, downscaling at the fL-size induces the spontaneous formation of molecularly crowded shell structures at the water/oil interface, as observed by fluorescence microscopy, showing typical thickness in order of hundreds of nanometers, in accordance with previously reported models. [5] Molecular crowding effects are tested by using fluorescence lifetime imaging under the convenient phasor plot approach, [6] revealing different characteristic lifetimes of specific probe molecules in the confined volumes with respect to macroscopic solutions. The fL-scale compartments autonomously trigger the formation of unique features (e.g., spatial heterogeneity, up-concentration, molecular proximity) that are mediated by the intermolecular interactions in these novel environments. Remarkably, the crowding conditions are observed not to affect the conformation variation of a model DNA hairpin in presence of molecular triggers and of a CYP2E1-catalyzed enzymatic reaction. Our results can be a first step towards the fabrication of lab-on-a-chip compartments for molecularly crowded confinement mimicking sub-cellular environments. Bibliography 1. S. F. Banani et al., Nat. Rev. Mol. Cell Biol. 2017, 18, 285. 2. B. C. Buddingh’, J. C. M. Van Hest, Acc. Chem. Res. 2017, 50, 769. 3. G. Arrabito, F. Cavaleri et al. Adv. Biosys. 2019, 1900023 4. J. Eggers, Phys. Rev. Lett. 1993, 71, 3458. 5. M. Staszak, J. Surfactants Deterg. 2016, 19, 297. 6. C. Stringari et al. Proc. Natl. Acad. Sci. USA 2011, 108, 13582.

Printing technologies represent a powerful tool for the direct micro- and nano- fabrication of biomolecular structures at the interface between life and materials sciences (Arrabito et al., 2012). Their continuous development over the last years has permitted the onset of man-made biosystems with customizable dimensions (from the micron-scale down to the nanometer scale), composition (organic molecules, DNA, proteins, phospholipids), and relevant functions (molecular interactions, drug screening, cellular biointerfaces, cell-like compartments). In this work, we show the possibility to leverage the fabrication of a wide class of solid-supported or liquid-liquid based synthetic compartments by printing tools at different scales. Scanning probe lithography methodologies will be shown for sub- cellular scale manipulation of living cells or for studies of molecular interactions onto porous surfaces. In particular, DNA-based protein immobilization coupled with dip-pen or polymer pens lithography permits the scalable fabrication of single-cell biochips (Arrabito et al., 2013; Arrabito et al., 2014). Inkjet printing will be shown for the fabrication of size scalable aqueous or oil-based synthetic compartments leading to molecular interaction studies at solid-liquid or liquid-liquid interfaces. The effect of droplet downsizing down to the femtoliter scale will be shown to affect the molecular interactions within aqueous compartments, mimicking the behaviour observed in cellular organells, in terms of molecular confinement and molecular crowding effects (Arrabito et al., 2019). In the case of oil-based compartments, fragmentation phenomena at surfactant-laden water-based interfaces bring to the formation of femtoliter- scale oil compartments detected by a microfluidic platform (Arrabito et al., 2019).

This work presents a novel mechanism for the spontaneous fragmentation of picoliter-scale oil droplets at the interface with an immiscible water phase, and the electrical characterization of the resulting immersed “daughter” droplets by an electrical impedance chip (see Figure). [1] In particular, picoliter-scale fluorinated oil droplets are produced by inkjet printing at velocity higher than 5 m/s. Upon impact on the surfactant laden water phase at moderately high Weber number , i.e. around 10, the oil droplet is subjected to spreading and capillary instabilities at the water/air interface. These ultimately lead to its rupture in smaller sized droplets, according to the reported models for macroscale droplets, [2] for which fragmentation results in “daughter” droplets with volumes reduced of about 10-30 %. Remarkably, the picoliter scale downscaling leads to a novel surfactant-driven fragmentation due to the low Bond number - around 10^(-4) -10^(-5), the droplet immersion mainly depending on surface tension forces. Indeed, the non-ionic Polyoxyethylene (20) sorbitan monolaurate was observed to permit the droplet immersion in the water phase only if spiked in the water phase at concentrations equal or higher than its critical micellar concentration. The emerging “daughter” droplets are characterized by a microfluidic chip with integrated microelectrodes, permitting to extract number, velocities and diameter distribution (about 3 μm) by means of electrical impedance measurements. The electrical characterizations show that the droplets have volumes in the femtoliter scale and are not subjected to inertial focusing, owing to their small size. [3] This work can be considered an important advancement for understanding the effects of downscaling on fragmentation phenomena at immiscible interfaces, leading to a knowledge platform for a tailored oil droplets fabrication applicable for drug encapsulation, pharmaceutic preparations, and thin-film wrapping around droplets.[4] Bibliography 1. D. Spencer, F. Caselli, P. Bisegna and H. Morgan., Lab Chip, 2016, 16, 2467. 2. H. Lhuissier, C. Sun, A. Prosperetti, and D. Lohse, Phys. Rev. Lett., 2013, 110, 3. G. Arrabito, V. Errico, A. De Ninno, F. Cavaleri, V. Ferrara, B. Pignataro, and F.Caselli, Langmuir, 2019, 35, 4936. 4. D. Kumar, J. D. Paulsen, T. P. Russell, N. Menon, Science, 2018, 359, 775.

This work presents the fabrication of femtoliter-scale oil droplets by inkjet printing based on a novel mechanism for the spontaneous fragmentation at the interface with an immiscible water phase and the electrical characterization of the resulting immersed “daughter” droplets. [1] In particular, picoliter-scale fluorinated oil droplets impact on surfactant laden water phase at moderately high Weber number (101), and are subjected to spreading and capillary instabilities at the water/air interface which ultimately lead to rupture in smaller sized droplets, according to reported models for macroscale droplets systems - [2] the emerging fragmentation results in “daughter” droplets having volumes of about 10-30 % with respect to the initial droplet volume. Remarkably, the picoliter scale downscaling leads to a novel surfactant-driven fragmentation due to the low Bond number (around 10-4-10-5), meaning that droplet immersion is dependent on surface tension forces and not on gravitational forces. In fact, the non-ionic Polyoxyethylene (20) sorbitan monolaurate was observed to permit the droplet immersion in the water phase only if spiked in the water phase at concentrations equal or higher than its critical micellar concentration (i.e. around 0.003% v/v). The resulting oil “daughter” droplets are characterized by a chip with integrated microelectrodes, permitting to extract number, velocities and diameter distribution (peaked at about 3 m) employing electrical impedance measurements. In accordance with reported models, the electrical characterizations show that the droplets have volumes in the femtoliter scale and are subjected to inertial focusing. [3] This work can be considered an important advancement for understanding the effects of downscaling on fragmentation phenomena at immiscible interfaces, leading to a knowledge platform for a tailored oil droplets fabrication applicable for drug encapsulation, pharmaceutic preparations, and thin-film wrapping around droplets. [4] Bibliography 1. D. Spencer, F. Caselli, P. Bisegna and H. Morgan., Lab Chip, 2016, 16, 2467. 2. H. Lhuissier, C. Sun, A. Prosperetti, and D. Lohse, Phys. Rev. Lett., 2013, 110, 3. G. Arrabito, V. Errico, A. De Ninno, F. Cavaleri, V. Ferrara, B. Pignataro, and F.Caselli, Langmuir, 2019, 35, 4936. 4. D. Kumar, J. D. Paulsen, T. P. Russell, N. Menon, Science, 2018, 359, 775.

Single-cell microarrays are emerging tools to unravel intrinsic diversity within complex cell populations, opening up new approaches for the in-depth understanding of highly relevant diseases. However, most of the current methods for their fabrication are based on cumbersome patterning approaches, employing organic solvents and/or expensive materials. Here, we demonstrate an unprecedented green-chemistry strategy to produce single-cell capture biochips onto glass surfaces by all-aqueous inkjet printing. At first, a chitosan film is easily inkjet printed and immobilized onto hydroxyl-rich glass surfaces by electrostatic immobilization. In turn, poly(ethylene glycol) diglycidyl ether is grafted on the chitosan film to expose reactive epoxy groups and induce antifouling properties. Subsequently, microscale collagen spots are printed onto the above surface to define the attachment area for single adherent human cancer cells harvesting with high yield. The reported inkjet printing approach enables one to modulate the collagen area available for cell attachment in order to control the number of captured cells per spot, from single-cells up to double- and multiple-cell arrays. Proof-of-principle of the approach includes pharmacological treatment of single-cells by the model drug doxorubicin. The herein presented strategy for single-cell array fabrication can constitute a first step toward an innovative and environmentally friendly generation of aqueous-based inkjet-printed cellular devices.

In this study, a novel bithiophene‐fulleropyrrolidine bisadducts system (bis‐Th2PC 60 ) was synthesized and electropolymerized by chronoamperometry onto flexible ITO/PET substrates. The resulting semitransparent thin film was characterized by XPS, FT‐IR, cyclic voltammetry and optical techniques, confirming the good outcome of the electropolymerization process. AFM investigations permitted to highlight an inherent disordered granular morphology, in which the grain‐to‐grain separation depends upon the application of bending. The electrical resistance of the thin film was characterized as function of bending (in the range 0°‐90°), showing promising responsivity to low bending angles (10°‐30°). The ΔR/R0 variations turn out to be 8%,16% and 20% for bending angles equal to 10°, 20° and 30°, respectively. This study represents a first step towards the understanding of piezoresistive properties in electropolymerized fullerenes‐based thin films, opening up applications as bending sensor.

Organic Photovoltaics (OPVs) based on Bulk Heterojunction (BHJ) blends are a mature technology. Having started their intensive development two decades ago, their low cost, processability and flexibility rapidly funneled the interest of the scientific community, searching for new solutions to expand solar photovoltaics market and promote sustainable development. However, their robust implementation is hampered by some issues, concerning the choice of the donor/acceptor materials, the device thermal/photo-stability, and, last but not least, their morphology. Indeed, the morphological profile of BHJs has a strong impact over charge generation, collection, and recombination processes; control over nano/microstructural morphology would be desirable, aiming at finely tuning the device performance and overcoming those previously mentioned critical issues. The employ of compatibilizers has emerged as a promising, economically sustainable, and widely applicable approach for the donor/acceptor interface (D/A-I) optimization. Thus, improvements in the global performance of the devices can be achieved without making use of more complex architectures. Even though several materials have been deeply documented and reported as effective compatibilizing agents, scientific reports are quite fragmentary. Here we would like to offer a panoramic overview of the literature on compatibilizers, focusing on the progression documented in the last decade.

The continuous progress of printing technologies over the past 20 years has fueled the development of a plethora of applications in materials sciences, flexible electronics, and biotechnologies. More recently, printing methodologies have started up to explore the world of Artificial Biology, offering new paradigms in the direct assembly of Artificial Biosystems (small condensates, compartments, networks, tissues, and organs) by mimicking the result of the evolution of living systems and also by redesigning natural biological systems, taking inspiration from them. This recent progress is reported in terms of a new field here defined as Printing Biology, resulting from the intersection between the field of printing and the bottom up Synthetic Biology. Printing Biology explores new approaches for the reconfigurable assembly of designed life-like or life-inspired structures. This work presents this emerging field, highlighting its main features, i.e., printing methodologies (from 2D to 3D), molecular ink properties, deposition mechanisms, and finally the applications and future challenges. Printing Biology is expected to show a growing impact on the development of biotechnology and life-inspired fabrication.

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.

This work presents the first reported imbibition mechanism of femtoliter (fL)-scale droplets produced by microchannel cantilever spotting (μCS) of DNA molecular inks into porous substrates (hydrophilic nylon). Differently from macroscopic or picoliter droplets, the downscaling to the fL-size leads to an imbibition process controlled by the subtle interplay of evaporation, spreading, viscosity, and capillarity, with gravitational forces being quasi-negligible. In particular, the minimization of droplet evaporation, surface tension, and viscosity allows for a reproducible droplet imbibition process. The dwell time on the nylon surface permits further tuning of the droplet lateral size, in accord with liquid ink diffusion mechanisms. The functionality of the printed DNA molecules is demonstrated at different imbibed oligonucleotide concentrations by hybridization with a fluorolabeled complementary sequence, resulting in a homogeneous coverage of DNA within the imbibed droplet. This study represents a first step toward the μCS-enabled fabrication of DNA-based biosensors and microarrays into porous substrates.

Layered double hydroxides show intriguing physical and chemical properties arising by their intrinsic self-assembled stacking of molecular-thick 2D nanosheets, enhanced active surface area, hosting of guest species by intercalation and anion exchanging capabilities. Here, we report on the unprecedented emerging intense ultraviolet photoluminescence in Zn/Al layered double hydroxide high-aspect-ratio nanoplatelets, which we discovered to be fully activated by drying under vacuum condition and thermal desorption as well. Photoluminescence and its quenching were reproducibly switched by a dehydration–hydration process. Photoluminescence properties were comprehensively evaluated, such as temperature dependence of photoluminescence features and lifetime measurements. The role of 2D morphology and arrangement of hydroxide layers was demonstrated by evaluating the photoluminescence before and after exfoliation of a bulk phase synthetized by a coprecipitation method.

Layered double hydroxides (LDHs) are an emergent class of biocompatible inorganic lamellar nanomaterials that have attracted significant research interest owing to their high surface-to-volume ratio, the capability to accumulate specific molecules, and the timely release to targets. Their unique properties have been employed for applications in organic catalysis, photocatalysis, sensors, drug delivery, and cell biology. Given the widespread contemporary interest in these topics, time-to-time it urges to review the recent progresses. This review aims to summarize the most recent cutting-edge reports appearing in the last years. It firstly focuses on the application of LDHs as catalysts in relevant chemical reactions and as photocatalysts for organic molecule degradation, water splitting reaction, CO2 conversion, and reduction. Subsequently, the emerging role of these materials in biological applications is discussed, specifically focusing on their use as biosensors, DNA, RNA, and drug delivery, finally elucidating their suitability as contrast agents and for cellular differentiation. Concluding remarks and future prospects deal with future applications of LDHs, encouraging researches in better understanding the fundamental mechanisms involved in catalytic and photocatalytic processes, and the molecular pathways that are activated by the interaction of LDHs with cells in terms of both uptake mechanisms and nanotoxicology effects.

Dip-pen lithography (DPL) technique has been employed to develop a new flexible biosensor realized on nylon with the aim to detect the activity of human topoisomerase. The sensor is constituted by an ordered array of a DNA substrate on flexible nylon supports that can be exploited as a drug screening platform for anticancer molecules. Here, we demonstrate a rapid protocol that permits to immobilize minute quantities of DNA oligonucleotides by DPL on nylon surfaces. Theoretical and experimental aspects have been investigated to successfully print DNA oligonucleotides by DPL on such a porous and irregular substrate.

Inkjet printing is here employed for the first time as a method to produce femtoliter-scale oil droplets dispersed in water. In particular, picoliter-scale fluorinated oil (FC40) droplets are printed in the presence of perfluoro-1-octanol surfactant at a velocity higher than 5 m/s. Femtoliter-scale oil droplets in water are spontaneously formed through a fragmentation process at the water/air interface using minute amounts of nonionic surfactant (down to 0.003% v/v of Tween 80). This fragmentation occurs by a Plateau-Rayleigh mechanism at a moderately high Weber number (10(1)). A microfluidic chip with integrated microelectrodes allows droplets characterization in terms of number and diameter distribution (peaked at about 3 mu m) by means of electrical impedance measurements. These results show an unprecedented possibility to scale oil droplets down to the femtoliter scale, which opens up several perspectives for a tailored oil-in-water emulsion preparations, and cellular biology. fabrication for drug encapsulation, pharmaceutic preparations, and cellular biology.

The assembly of scalable liquid compartments for binding assays in array formats constitutes a topic of fundamental importance in life sciences. This challenge can be addressed by mimicking the structure of cellular compartments with biological native conditions. Here, inkjet printing is employed to develop up to hundreds of picoliter aqueous droplet arrays stabilized by oil-confinement with mild surfactants (Tween-20). The aqueous environments constitute specialized compartments in which biomolecules may exploit their function and a wide range of molecular interactions can be quantitatively investigated. Raster Image Correlation Spectroscopy (RICS) is employed to monitor in each compartment a restricted range of dynamic intermolecular events demonstrated through protein-binding assays involving the biotin/streptavidin model system.

Nanotransducers can offer crucial advantages in comparison with conventional sensors and actuators. However, interfacing and packaging nanostructures into complete electronic systems is very complex. Here we describe a wet chemical method for cointegrating arrays of ZnO nanowires into systems on printed circuit boards (PCBs). First, we deposit on the PCB a MnOOH layer for reproducibly increasing the nanowires density. Afterwards, we numerically demonstrate that the ligand ethylenediamine, at the isoelectric point of the ZnO nanowires tips, can effectively control, at very low concentrations, both zinc speciation and supersaturation in the nutrient solution. Accordingly, we combine potassium chloride and ethylenediamine, produced in situ from a safer precursor (ethanolamine), for concurrently thinning the nanowires (top width around 60 nm) and stabilizing their top faces. Our synergic approach enables the solution growth of ZnO nanowires which are untapered and have high densities (> 8/μm2) and record length (> 15 µm) and aspect ratio (> 200) for plastic substrates which may not withstand high temperatures. These characteristics permit to simultaneously add the top electrode, package the nanowires, improve their mechanical robustness and connect to the electronic interface by a simple flip chip adhesive bonding procedure. As proofs of concept we describe flexible PCB heaters (electrical to thermal energy conversion) with power densities comparable with state of the art flexible heaters and a wearable piezotronic heartbeat detector comprising both ZnO nanowires (mechanical to electric energy conversion) and electronics on a single flexible PCB. Our results open the way to the cointegration of nanotransducers and electronics on conventional PCBs.

Mesoangioblasts are outstanding candidates for stem-cell therapy and are already being explored in clinical trials. However, a crucial challenge in regenerative medicine is the limited availability of undifferentiated myogenic progenitor cells because growth is typically accompanied by differentiation. Here reversible myogenic-differentiation switching during proliferation is achieved by functionalizing the glass substrate with high-density ZnO nanowires (NWs). Specifically, mesoangioblasts grown on ZnO NWs present a spherical viable undifferentiated cell state without lamellopodia formation during the entire observation time (8 days). Consistently, the myosin heavy chain, typically expressed in skeletal muscle tissue and differentiated myogenic progenitors, is completely absent. Remarkably, NWs do not induce any damage while they reversibly block differentiation, so that the differentiation capabilities are completely recovered upon cell removal from the NW-functionalized substrate and replating on standard culture glass. This is the first evidence of a reversible myogenic-differentiation switch that does not affect the viability. These results can be the first step toward for the in vitro growth of a large number of undifferentiated stem/progenitor cells and therefore can represent a breakthrough for cell-based therapy and tissue engineering.

We herein aim to report on the fabrication of DNA nano-heterostructures usable as a robust multi-functional analytical system to obtain multiple and complex data in parallel format from a single sample with unprecedented analytical performances. The ability of chemical information contained in the sequences of programmed DNA structures to organize matter made DNA become a unique material in “the nanoworld”. Such carefully designed DNA nanostructures can then be functionalized/templated with different biomolecules/nanomaterials as different as nanoparticles, nanowires, organic molecules, peptides, and proteins with controlled spacing on the nanometer scale (

This book is intended for non-specialists and students, presenting a unique introduction to the field of DNA nanotechnology. The primary focus is on the extraordinary advantages of specificity and sensitivity obtained by integrating DNA nanostructures in bioanalytical devices. DNA Nanotechnology for Bioanalysis provides a concise and rigorous description for the fabrication of various types of functional nanostructures by optimized software-aided high-yield synthesis. Following this is the explanation of methods to decorate these nanostructures with molecules such as proteins, metal nanoparticles or bioorganic moieties covalently bonded onto DNA via self-assemblage processes. Also provided is a concise review on non-canonical DNA structures (such as G-quadruplexes) and their targeting by small molecules for applications in pharmacology. Finally, it describes the exciting applications of DNA nanostructures in life sciences and nanomedicine, including ultraspecific molecular delivery, control of cell behavior, analysis of cell lysate and DNA-based nano-tools for super-resolution sub-cellular imaging.

Molecular confinement is known to lead to acceleration of molecular dynamics along with surface interaction. Nature employs confinement in molecularly crowded, heterogeneous and, specialized femtoliter (fL) compartments inside living cells for spontaneously achieving higher reaction efficiency and spatial-programming of composite, multi-step biochemical processes. We here show the facile production of aqueous fL droplets for studying molecular confinement on a biochip. We prepare fL aqueous droplets in oil drops on solid substrates by a “field-free”- no external electric fields and electrolytes - piezoelectric inkjet printing in which a novel actuating waveform is employed by picoliter sized nozzles (Fig 1.a). The droplets form an almost-regular circular pattern at the border of mineral oil drops, (Fig 1.b) and Alexa 647 molecules, at 10-0.01 µM concentrations, form ring patterns at the surfactant/oil interface (Fig.1c) as predicted by numerical adsorption general models. At the single droplet level, we show that molecular confinement leads to modify solute-solvent and solvent driven solute-solute interactions. Confinement effects are tested by using Fluorescence lifetime imaging which reveals different characteristic lifetimes of specific molecules in confined volumes with respect to macroscopic solutions. The same method using the signal of a molecular rotor- i.e. 9-(2-Carboxy-2-cyanovinyl)julolidine - did not reveal changes in solution viscosity due to confinement. We exploit the possibility of analyzing molecules “in action” in fL volume solutions to study the behavior of molecular machines in confined environments. At these volume scales, by employing a model DNA beacon machine, we highlight that DNA-machines/ target interaction is favored in confined conditions with respect to microliter/macroscopic volumes.