"Writing biochips": high-resolution droplet-to-droplet manufacturing of analytical platforms.

The development of high-resolution molecular printing allows the engineering of analytical platforms enabling applications at the interface between chemistry and biology, i.e. in biosensing, electronics, single-cell biology, and point-of-care diagnostics. Their successful implementation stems from the combination of large area printing at resolutions from sub-100 nm up to macroscale, whilst controlling the composition and volume of the ink, and reconfiguring the deposition features in due course. Similar to handwriting pens, the engineering of continuous writing systems tackles the issue of the tedious ink replenishment between different printing steps. To this aim, this review article provides an unprecedented analysis of the latest continuous printing methods for bioanalytical chemistry, focusing on ink deposition systems based on specific sets of technologies that have been developed to this aim, namely nanofountain probes, microcantilever spotting, capillary-based polymer pens and continuous 3D printing. Each approach will be discussed revealing the most important applications in the fields of biosensors, lab-on-chips and diagnostics.

Improved Photocatalytic Activity of Polysiloxane TiO2 Composites by Thermally Induced Nanoparticle Bulk Clustering and Dye Adsorption.

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.

Artificial Biosystems by Printing Biology.

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.

Tackling Performance Challenges in Organic Photovoltaics: An Overview about Compatibilizers.

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.

Oil-in-Water fL Droplets by Interfacial Spontaneous Fragmentation and Their Electrical Characterization.

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 (101). A microfluidic chip with integrated microelectrodes allows droplets characterization in terms of number and diameter distribution (peaked at about 3 µm) 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 fabrication for drug encapsulation, pharmaceutic preparations, and cellular biology.

Configurable low-cost plotter device for fabrication of multi-color sub-cellular scale microarrays.

The construction and operation of a low-cost plotter for fabrication of microarrays for multiplexed single-cell analyses is reported. The printing head consists of polymeric pyramidal pens mounted on a rotation stage installed on an aluminium frame. This construction enables printing of microarrays onto glass substrates mounted on a tilt stage, controlled by a Lab-View operated user interface. The plotter can be assembled by typical academic workshops from components of less than 15,000 Euro. The functionality of the instrument is demonstrated by printing DNA microarrays on the area of 0.5 cm2 using up to three different oligonucleotides. Typical feature sizes are 5 µm diameter with a pitch of 15 µm, leading to densities of up to 10(4)-10(5) spots/mm2. The fabricated DNA microarrays are used to produce sub-cellular scale arrays of bioactive epidermal growth factor peptides by means of DNA-directed immobilization. The suitability of these biochips for cell biological studies is demonstrated by specific recruitment, concentration, and activation of EGF receptors within the plasma membrane of adherent living cells. This work illustrates that the presented plotter gives access to bio-functionalized arrays usable for fundamental research in cell biology, such as the manipulation of signal pathways in living cells at subcellular resolution.

Label-free impedimetric analysis of microplastics dispersed in aqueous media polluted by Pb2+ ions.

The rapid differentiation between polluted and unpolluted microplastics (MPs) is critical for tracking their presence in the environment and underpinning their potential risks to humans. However, the quantitative analysis of polluted microplastics on the field is limited by the lack of rapid methods that do not need optical analysis nor their capture onto sophisticated electrochemical sensor platforms. Herein, a simple analytical approach for MPs dispersed in aqueous media leveraging electrochemical impedance spectroscopy (EIS) analysis on screen-printed sensors is presented. This method is demonstrated by the EIS-based analysis of two standards of microplastics beads (MPs), one of polystyrene (PS) and one of polystyrene carboxylated (PS-COOH), when exposed to aqueous solutions containing Pb2+ ions. The adsorption of Pb2+ ions on the MPs was quantitatively determined by voltammetric analysis. EIS permitted to rapidly (about 2 minutes) differentiate clean MPs from the Pb2+ polluted ones. These results could constitute a first-step towards the realization of a portable impedimetric sensor for the quantification of microplastics polluted by metal ions in aqueous solutions.

Red-Light-Photosensitized Tyrosine 10 Nitration of ß-Amyloid1-42 Diverts the Protein from Forming Toxic Aggregates.

Several studies have highlighted the presence of nitration damage following neuroinflammation in Alzheimer's disease (AD). Accordingly, post-transcriptional modifications of ß-amyloid (Aß), including peptide nitration, have been explored as a marker of the disease. However, the implications of Aß nitration in terms of aggregation propensity and neurotoxicity are still debated. Here, we show new data obtained using a photoactivatable peroxynitrite generator (BPT-NO) to overcome the limitations associated with chemical nitration methods. We found that the photoactivation of BPT-NO with the highly biocompatible red light selectively induces the nitration of tyrosine 10 of freshly solubilized full-length Aß1-42. Photonitrated Aß1-42 was, therefore, investigated for aggregation states and functions. It resulted that photonitrated Aß1-42 did not aggregate into small oligomers but rather self-assembled into large amorphous aggregates. When tested on neuronal-like SH-SY5Y cells and microglial C57BL/6 BV2 cells, photonitrated Aß1-42 showed to be free of neurotoxicity and able to induce phagocytic microglia cells. We propose that light-controlled nitration of the multiple forms in which Aß occurs (i.e., monomers, oligomers, fibrils) could be a tool to assess in real-time the impact of tyrosine nitration on the amyloidogenic and toxic properties of Aß1-42.

Biochips for cell biology by combined dip-pen nanolithography and DNA-directed protein immobilization.

A general methodology for patterning of multiple protein ligands with lateral dimensions below those of single cells is described. It employs dip pen nanolithography (DPN) patterning of DNA oligonucleotides which are then used as capture strands for DNA-directed immobilization (DDI) of oligonucleotide-tagged proteins. This study reports the development and optimization of PEG-based liquid ink, used as carrier for the immobilization of alkylamino-labeled DNA oligomers on chemically activated glass surfaces. The resulting DNA arrays have typical spot sizes of 4-5 µm with a pitch of 12 µm micrometer. It is demonstrated that the arrays can be further functionalized with covalent DNA-streptavidin (DNA-STV) conjugates bearing ligands recognized by cells. To this end, biotinylated epidermal growth factor (EGF) is coupled to the DNA-STV conjugates, the resulting constructs are hybridized with the DNA arrays and the resulting surfaces used for the culturing of MCF-7 (human breast adenocarcinoma) cells. Owing to the lateral diffusion of transmembrane proteins in the cell's plasma membrane, specific recruitment and concentration of EGF receptor can be induced specifically at the sites where the ligands are bound on the solid substrate. This is a clear demonstration that this method is suitable for precise functional manipulations of subcellular areas within living cells.

Label-free approaches for extracellular vesicle detection.

Extracellular vesicles (EVs) represent pivotal mediators in cell-to-cell communication. They are lipid-membranous carriers of several biomolecules, which can be produced by almost all cells. In the current Era of precision medicine, EVs gained growing attention thanks to their potential in both biomarker discovery and nanotherapeutics applications. However, current technical limitations in isolating and/or detecting EVs restrain their standard use in clinics. This review explores all the state-of-the-art analytical technologies which are currently overcoming these issues. On one end, several innovative optical-, electrical-, and spectroscopy-based detection methods represent advantageous label-free methodologies for faster EV detection. On the other end, microfluidics-based lab-on-a-chip tools support EV purification from low-concentrated samples. Altogether, these technologies will strengthen the routine application of EVs in clinics.

Vertically Aligned Nanowires and Quantum Dots: Promises and Results in Light Energy Harvesting.

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.

Self-Cleaning Bending Sensors Based on Semitransparent ZnO Nanostructured Films.

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.

Solution processed micro- and nano-bioarrays for multiplexed biosensing.

This Feature article reports on solution dispensing methodologies which enable the realization of multiplexed arrays at the micro- and nanoscale for relevant biosensing applications such as drug screening or cellular chips.

Inkjet printing methodologies for drug screening.

We show for the first time a contactless, low-cost, and rapid drug screening methodology by employing inkjet printing for molecular dispensing in a microarray format. Picoliter drops containing a model substrate (d-glucose)/inhibitor (d-glucal) couple were accurately dispensed on a single layer consisting of the enzymatic target (glucose oxidase) covalently linked to a functionalized silicon oxide support. A simple colorimetric detection method allowed one to prove the screening capability of the microarray with the possibility to assay with high reproducibility at the single spot level. Measurements of the optical signal as a function of concentration and of time verified the occurrence at the solid-liquid interface of the competitive enzymatic inhibition with a similar behavior occurring for this system in a solution phase along with overcoming competition effects. We propose this methodology as a general application for drug screening purposes, since it may be extended to any kind of enzyme-substrate/inhibitor or ligand-target biochemical system.

On the Interaction between 1D Materials and Living Cells.

One-dimensional (1D) materials allow for cutting-edge applications in biology, such as single-cell bioelectronics investigations, stimulation of the cellular membrane or the cytosol, cellular capture, tissue regeneration, antibacterial action, traction force investigation, and cellular lysis among others. The extraordinary development of this research field in the last ten years has been promoted by the possibility to engineer new classes of biointerfaces that integrate 1D materials as tools to trigger reconfigurable stimuli/probes at the sub-cellular resolution, mimicking the in vivo protein fibres organization of the extracellular matrix. After a brief overview of the theoretical models relevant for a quantitative description of the 1D material/cell interface, this work offers an unprecedented review of 1D nano- and microscale materials (inorganic, organic, biomolecular) explored so far in this vibrant research field, highlighting their emerging biological applications. The correlation between each 1D material chemistry and the resulting biological response is investigated, allowing to emphasize the advantages and the issues that each class presents. Finally, current challenges and future perspectives are discussed.

Aqueous Processed Biopolymer Interfaces for Single-Cell Microarrays.

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.

Bending Sensors Based on Thin Films of Semitransparent Bithiophene-Fulleropyrrolidine Bisadducts.

A novel bithiophene-fulleropyrrolidine bisadducts system (bis-Th2PC60 ) 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 a 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.

Mastering the Tools: Natural versus Artificial Vesicles in Nanomedicine.

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.

Printing Life-Inspired Subcellular Scale Compartments with Autonomous Molecularly Crowded Confinement.

A simple, rapid, and highly controlled platform to prepare life-inspired subcellular scale compartments by inkjet printing has been developed. These compartments consist of fL-scale aqueous droplets (few µm in diameter) incorporating biologically relevant molecular entities with programmed composition and concentration. These droplets are ink-jetted in nL mineral oil drop arrays allowing for lab-on-chip studies by fluorescence microscopy and fluorescence life time imaging. Once formed, fL-droplets are stable for several hours, thus giving the possibility of readily analyze molecular reactions and their kinetics and to verify molecular behavior and intermolecular interactions. Here, this platform is exploited to unravel the behavior of different molecular probes and biomolecular systems (DNA hairpins, enzymatic cascades, protein-ligand couples) within the compartments. The fL-scale size induces the formation of molecularly crowded confined shell structures (hundreds of nanometers in thickness) at the droplet surface, allowing discovery of specific features (e.g., heterogeneity, responsivity to molecular triggers) that are mediated by the intermolecular interactions in these peculiar environments. The presented results indicate the possibility of using this platform for designing nature-inspired confined reactors allowing for a deepened understanding of molecular confinement effects in living subcellular compartments.