All-Optical Electrochemiluminescence.

Electrochemiluminescence (ECL) is widely employed for medical diagnosis and imaging. Despite its remarkable analytical performances, the technique remains intrinsically limited by the essential need for an external power supply and electrical wires for electrode connections. Here, we report an electrically autonomous solution leading to a paradigm change by designing a fully integrated all-optical wireless monolithic photoelectrochemical device based on a nanostructured Si photovoltaic junction modified with catalytic coatings. Under illumination with light ranging from visible to near-infrared, photogenerated holes induce the oxidation of the ECL reagents and thus the emission of visible ECL photons. The blue ECL emission is easily viewed with naked eyes and recorded with a smartphone. A new light emission scheme is thus introduced where the ECL emission energy (2.82 eV) is higher than the excitation energy (1.18 eV) via an intermediate electrochemical process. In addition, the mapping of the photoelectrochemical activity by optical microscopy reveals the minority carrier interfacial transfer mechanism at the nanoscale. This breakthrough provides an all-optical strategy for generalizing ECL without the need for electrochemical setups, electrodes, wiring constraints, and specific electrochemical knowledge. This simplest ECL configuration reported so far opens new opportunities to develop imaging and wireless bioanalytical systems such as portable point-of-care sensing devices.

Non-linear nanoscale piezoresponse of single ZnO nanowires affected by piezotronic effect.

Zinc oxide (ZnO) nanowires (NWs) as semiconductor piezoelectric nanostructures have emerged as material of interest for applications in energy harvesting, photonics, sensing, biomedical science, actuators or spintronics. The expression for the piezoelectric properties in semiconductor materials is concealed by the screening effect of the available carriers and the piezotronic effect, leading to complex nanoscale piezoresponse signals. Here, we have developed a metal-semiconductor-metal model to simulate the piezoresponse of single ZnO NWs, demonstrating that the apparent non-linearity in the piezoelectric coefficient arises from the asymmetry created by the forward and reversed biased Schottky barriers at the semiconductor-metal junctions. By directly measuring the experimental I-V characteristics of ZnO NWs with conductive atomic force microscope together with the piezoelectric vertical coefficient by piezoresponse force microscopy, and comparing them with the numerical calculations for our model, effective piezoelectric coefficients in the range d 33eff ∼ 8.6 pm V-1-12.3 pm V-1 have been extracted for ZnO NWs. We have further demonstrated via simulations the dependence between the effective piezoelectric coefficient d 33eff and the geometry and physical dimensions of the NW (radius to length ratio), revealing that the higher d 33eff is obtained for thin and long NWs due to the tensor nature proportionality between electric fields and deformation in NW geometries. Moreover, the non-linearity of the piezoresponse also leads to multiharmonic electromechanical response observed at the second and higher harmonics that indeed is not restricted to piezoelectric semiconductor materials but can be generalized to any type of asymmetric voltage drops on a piezoelectric structure as well as leaky wide band-gap semiconductor ferroelectrics.

Biocompatibility and Electrical Stimulation of Skeletal and Smooth Muscle Cells Cultured on Piezoelectric Nanogenerators.

Nanogenerators are interesting for biomedical applications, with a great potential for electrical stimulation of excitable cells. Piezoelectric ZnO nanosheets present unique properties for tissue engineering. In this study, nanogenerator arrays based on ZnO nanosheets are fabricated on transparent coverslips to analyse the biocompatibility and the electromechanical interaction with two types of muscle cells, smooth and skeletal. Both cell types adhere, proliferate and differentiate on the ZnO nanogenerators. Interestingly, the amount of Zn ions released over time from the nanogenerators does not interfere with cell viability and does not trigger the associated inflammatory response, which is not triggered by the nanogenerators themselves either. The local electric field generated by the electromechanical nanogenerator-cell interaction stimulates smooth muscle cells by increasing cytosolic calcium ions, whereas no stimulation effect is observed on skeletal muscle cells. The random orientation of the ZnO nanogenerators, avoiding an overall action potential aligned along the muscle fibre, is hypothesised to be the cause of the cell-type dependent response. This demonstrates the need of optimizing the nanogenerator morphology, orientation and distribution according to the potential biomedical use. Thus, this study demonstrates the cell-scale stimulation triggered by biocompatible piezoelectric nanogenerators without using an external source on smooth muscle cells, although it remarks the cell type-dependent response.

Optimization of a Piezoelectric Energy Harvester and Design of a Charge Pump Converter for CMOS-MEMS Monolithic Integration.

The increasing interest in the Internet of Things (IoT) has led to the rapid development of low-power sensors and wireless networks. However, there are still several barriers that make a global deployment of the IoT difficult. One of these issues is the energy dependence, normally limited by the capacitance of the batteries. A promising solution to provide energy autonomy to the IoT nodes is to harvest residual energy from ambient sources, such as motion, vibrations, light, or heat. Mechanical energy can be converted into electrical energy by using piezoelectric transducers. The piezoelectric generators provide an alternating electrical signal that must be rectified and, therefore, needs a power management circuit to adapt the output to the operating voltage of the IoT devices. The bonding and packaging of the different components constitute a large part of the cost of the manufacturing process of microelectromechanical systems (MEMS) and integrated circuits. This could be reduced by using a monolithic integration of the generator together with the circuitry in a single chip. In this work, we report the optimization, fabrication, and characterization of a vibration-driven piezoelectric MEMS energy harvester, and the design and simulation of a charge-pump converter based on a standard complementary metal-oxide-semiconductor (CMOS) technology. Finally, we propose combining MEMS and CMOS technologies to obtain a fully integrated system that includes the piezoelectric generator device and the charge-pump converter circuit without the need of external components. This solution opens new doors to the development of low-cost autonomous smart dust devices.

Suspended Silicon Microphotodiodes for Electrochemical and Biological Applications.

Local electric stimulation of tissues and cells has gained importance as therapeutic alternative in the treatment of many diseases. These alternatives aim to deliver a less invasively stimuli in liquid media, making imperative the development of versatile micro- and nanoscale solutions for wireless actuation. Here, a simple microfabrication process to produce suspended silicon microphotodiodes that can be activated by visible light to generate local photocurrents in their surrounding medium is presented. Electrical characterization using electrical probes confirms their diode behavior. To demonstrate their electrochemical performance, an indirect test is implemented in solution through photoelectrochemical reactions controlled by a white-LED lamp. Furthermore, their effects on biological systems are observed in vitro using mouse primary neurons in which the suspended microphotodiodes are activated periodically with white-LED lamp, bringing out observable morphological changes in neuronal processes. The results demonstrate a simplified and cost-effective wireless tool for photovoltaic current generation in liquid media at the microscale.

Heat-controlled micropillar array device for microsystems technology.

A new temperature-controlled smart soft material micropillar array has been fabricated via in situ integration of the liquid-crystalline elastomer-based component into the hybrid microdevice. Such design allows for developing pushing elements with fast lifetime values of ca. 5 s, and opens huge opportunities for the use of hybrid smart microdevices with total control on the actuation time/response, repeatability, stability and energy saving.

Barcode tagging of human oocytes and embryos to prevent mix-ups in assisted reproduction technologies.

STUDY QUESTION: Is the attachment of biofunctionalized polysilicon barcodes to the outer surface of the zona pellucida an effective approach for the direct tagging and identification of human oocytes and embryos during assisted reproduction technologies (ARTs)? SUMMARY ANSWER: The direct tagging system based on lectin-biofunctionalized polysilicon barcodes of micrometric dimensions is simple, safe and highly efficient, allowing the identification of human oocytes and embryos during the various procedures typically conducted during an assisted reproduction cycle. WHAT IS KNOWN ALREADY: Measures to prevent mismatching errors (mix-ups) of the reproductive samples are currently in place in fertility clinics, but none of them are totally effective and several mix-up cases have been reported worldwide. Using a mouse model, our group has previously developed an effective direct embryo tagging system which does not interfere with the in vitro and in vivo development of the tagged embryos. This system has now been tested in human oocytes and embryos. STUDY DESIGN, SIZE, DURATION: Fresh immature and mature fertilization-failed oocytes (n = 21) and cryopreserved day 1 embryos produced by in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) (n = 205) were donated by patients (n = 76) undergoing ARTs. In vitro development rates, embryo quality and post-vitrification survival were compared between tagged (n = 106) and non-tagged (control) embryos (n = 99). Barcode retention and identification rates were also calculated, both for embryos and for oocytes subjected to a simulated ICSI and parthenogenetic activation. Experiments were conducted from January 2012 to January 2013. PARTICIPANTS/MATERIALS, SETTING, METHODS: Barcodes were fabricated in polysilicon and biofunctionalizated with wheat germ agglutinin lectin. Embryos were tagged with 10 barcodes and cultured in vitro until the blastocyst stage, when they were either differentially stained with propidium iodide and Hoechst or vitrified using the Cryotop method. Embryo quality was also analyzed by embryo grading and time-lapse monitoring. Injected oocytes were parthenogenetically activated using ionomycin and 6-dimethylaminopurine. MAIN RESULTS AND THE ROLE OF CHANCE: Blastocyst development rates of tagged (27/58) and non-tagged embryos (24/51) were equivalent, and no significant differences in the timing of key morphokinetic parameters and the number of inner cell mass cells were detected between the two groups (tagged: 24.7 ± 2.5; non-tagged: 22.3 ± 1.9), indicating that preimplantation embryo potential and quality are not affected by the barcodes. Similarly, re-expansion rates of vitrified-warmed tagged (19/21) and non-tagged (16/19) blastocysts were similar. Global identification rates of 96.9 and 89.5% were obtained in fresh (mean barcode retention: 9.22 ± 0.13) and vitrified-warmed (mean barcode retention: 7.79 ± 0.35) tagged embryos, respectively, when simulating an automatic barcode reading process, though these rates were increased to 100% just by rotating the embryos during barcode reading. Only one of the oocytes lost one barcode during intracytoplasmic injection (100% identification rate) and all oocytes retained all the barcodes after parthenogenetic activation. LIMITATIONS, REASONS FOR CAUTION: Although the direct embryo tagging system developed is effective, it only allows the identification and traceability of oocytes destined for ICSI and embryos. Thus, the traceability of all reproductive samples (oocytes destined for IVF and sperm) is not yet ensured. WIDER IMPLICATIONS OF THE FINDINGS: The direct embryo tagging system developed here provides fertility clinics with a novel tool to reduce the risk of mix-ups in human ARTs. The system can also be useful in research studies that require the individual identification of oocytes or embryos and their individual tracking. STUDY FUNDING/COMPETING INTEREST(S): This study was supported by the Sociedad Española de Fertilidad, the Spanish Ministry of Education and Science (TEC2011-29140-C03) and the Generalitat de Catalunya (2009SGR-00282 and 2009SGR-00158). The authors do not have any competing interests.

Fe/Au galvanic nanocells to generate self-sustained Fenton reactions without additives at neutral pH.

The generation of reactive oxygen species (ROS) via the Fenton reaction has received significant attention for widespread applications. This reaction can be triggered by zero-valent metal nanoparticles by converting externally added H2O2 into hydroxyl radicals (˙OH) in acidic media. To avoid the addition of external additives or energy supply, developing self-sustained catalytic systems enabling onsite production of H2O2 at a neutral pH is crucial. Here, we present novel galvanic nanocells (GNCs) based on metallic Fe/Au bilayers on arrays of nanoporous silica nanostructures for the generation of self-sustained Fenton reactions. These GNCs exploit the large electrochemical potential difference between the Fe and Au layers to enable direct H2O2 production and efficient release of Fe2+ in water at neutral pH, thereby triggering the Fenton reaction. Additionally, the GNCs promote Fe2+/Fe3+ circulation and minimize side reactions that passivate the iron surface to enhance their reactivity. The capability to directly trigger the Fenton reaction in water at pH 7 is demonstrated by the fast degradation and mineralization of organic pollutants, by using tiny amounts of catalyst. The self-generated H2O2 and its transformation into ˙OH in a neutral environment provide a promising route not only in environmental remediation but also to produce therapeutic ROS and address the limitations of Fenton catalytic nanostructures.

Near-IR Photoinduced Electrochemiluminescence Imaging with Structured Silicon Photoanodes.

Infrared (IR) imaging devices that convert IR irradiation (invisible to the human eye) to a visible signal are based on solid-state components. Here, we introduce an alternative concept based on light-addressable electrochemistry (i.e., electrochemistry spatially confined under the action of a light stimulus) that involves the use of a liquid electrolyte. In this method, the projection of a near-IR image (λexc = 850 or 840 nm) onto a photoactive Si-based photoanode, immersed into a liquid phase, triggers locally the photoinduced electrochemiluminescence (PECL) of the efficient [Ru(bpy)3]2+-TPrA system. This leads to the local conversion of near-IR light to visible (λPECL = 632 nm) light. We demonstrate that compared to planar Si photoanodes, the use of a micropillar Si array leads to a large enhancement of local light generation and considerably improves the resolution of the PECL image by preventing photogenerated minority carriers from diffusing laterally. These results are important for the design of original light conversion devices and can lead to important applications in photothermal imaging and analytical chemistry.

A novel embryo identification system by direct tagging of mouse embryos using silicon-based barcodes.

BACKGROUND: Measures to prevent assisted reproductive technologies (ART) mix-ups, such as labeling of all labware and double-witnessing protocols, are currently in place in fertility clinics worldwide. Technological solutions for electronic witnessing are also being developed. However, none of these solutions eliminate the risk of identification errors, because gametes and embryos must be transferred between containers several times during an ART cycle. Thus, the objective of this study was to provide a proof of concept for a direct embryo labeling system using silicon-based barcodes. METHODS: Three different types of silicon-based barcodes (A, B and C) were designed and manufactured, and microinjected into the perivitelline space of mouse pronuclear embryos (one to four barcodes per embryo). Embryos were cultured in vitro until the blastocyst stage, and rates of embryo development, retention of the barcodes in the perivitelline space and embryo identification were assessed every 24 h. Release of the barcodes after embryo hatching was also determined. Finally, embryos microinjected with barcodes were frozen and thawed at the 2-cell stage to test the validity of the system after cryopreservation. RESULTS: Barcodes present in the perivitelline space, independently of their type and number, did not affect embryo development rates. The majority of embryos (>90%) retained at least one of the microinjected barcodes in their perivitelline space up to the blastocyst stage. Increasing the number of barcodes per embryo resulted in a significant increase in embryo identification rates, but a significant decrease in the barcode release rates after embryo hatching. The highest rates of successful embryo identification (97%) were achieved with the microinjection of four type C barcodes, and were not affected by cryopreservation. CONCLUSIONS: Our results demonstrate the feasibility of a direct embryo labeling system and constitute the starting point in the development of such systems.

Localised actuation in composites containing carbon nanotubes and liquid crystalline elastomers.

A liquid crystalline elastomer-carbon nanotube (LCE-CNT) composite displays a reversible shape change property in response to light. The development of some systems such as tactile devices requires localised actuation of this material. A method is reported that combines mechanical stretching and thermal crosslinking of an LCE-CNT for creating sufficiently well-aligned liquid crystal units to produce localised actuation. The method demonstrates that it is feasible to optically drive a LCE-CNT film within a localised area, since only the walls of the stretched parts of the film contain aligned LC domains.

ZnO Nanosheet-Coated TiZrPdSiNb Alloy as a Piezoelectric Hybrid Material for Self-Stimulating Orthopedic Implants.

A Ti-based alloy (Ti45Zr15Pd30Si5Nb5) with already proven excellent mechanical and biocompatibility features has been coated with piezoelectric zinc oxide (ZnO) to induce the electrical self-stimulation of cells. ZnO was grown onto the pristine alloy in two different morphologies: a flat dense film and an array of nanosheets. The effect of the combined material on osteoblasts (electrically stimulable cells) was analyzed in terms of proliferation, cell adhesion, expression of differentiation markers and induction of calcium transients. Although both ZnO structures were biocompatible and did not induce inflammatory response, only the array of ZnO nanosheets was able to induce calcium transients, which improved the proliferation of Saos-2 cells and enhanced the expression of some early differentiation expression genes. The usual motion of the cells imposes strain to the ZnO nanosheets, which, in turn, create local electric fields owing to their piezoelectric character. These electric fields cause the opening of calcium voltage gates and boost cell proliferation and early differentiation. Thus, the modification of the Ti45Zr15Pd30Si5Nb5 surface with an array of ZnO nanosheets endows the alloy with smart characteristics, making it capable of electric self-stimulation.

Focus ion beam micromachined glass pipettes for cell microinjection.

Cell handling is currently hindered by rudimentary-manufactured manipulators. Restrictive designs of glass pipettes and other micromanipulators limit functionality and often damage cells, ultimately resulting in lysis. We present a novel technique to design and mill conventional glass pipettes at specifically chosen angles and geometries. Focus ion beam milling by Ga+ ions yields extremely polished edges. Results from mouse embryo piercing correlate increased penetration rates with decreased pipette angle. Milled pipettes maintain structural integrity after repeated piercing. For the first time, the effects of unintentionally implanted Ga+ on embryo development are addressed. Optimum embryo development up to blastocyst stage after manipulation reveal little impact of residual implanted Ga+, suggesting biocompatibility and paving the way to introducing ion milling techniques in the biomedical device arena. The milling technique can be adequately tailored to specific applications and allows for mass production, presenting a promising avenue for future, increasingly demanding, cell handling.

Internalization and cytotoxicity analysis of silicon-based microparticles in macrophages and embryos.

Microchips can be fabricated, using semiconductor technologies, at microscopic level to be introduced into living cells for monitoring of intracellular parameters at a single cell level. As a first step towards intracellular chips development, silicon and polysilicon microparticles of controlled shape and dimensions were fabricated and introduced into human macrophages and mouse embryos by phagocytosis and microinjection, respectively. Microparticles showed to be non-cytotoxic for macrophages and were found to be localized mainly inside early endosomes, in tight association with endosomal membrane, and more rarely in acidic compartments. Embryos with microinjected microparticles developed normally to the blastocyst stage, confirming the non-cytotoxic effect of the particles. In view of these results silicon and polysilicon microparticles can serve as the frame for future intracellular chips development and this technology opens the possibility of real complex devices to be used as sensors or actuators inside living cells.

Internalization and Viability Studies of Suspended Nanowire Silicon Chips in HeLa Cells.

Micrometer-sized silicon chips have been demonstrated to be cell-internalizable, offering the possibility of introducing in cells even smaller nanoelements for intracellular applications. On the other hand, silicon nanowires on extracellular devices have been widely studied as biosensors or drug delivery systems. Here, we propose the integration of silicon nanowires on cell-internalizable chips in order to combine the functional features of both approaches for advanced intracellular applications. As an initial fundamental study, the cellular uptake in HeLa cells of silicon 3 µm × 3 µm nanowire-based chips with two different morphologies was investigated, and the results were compared with those of non-nanostructured silicon chips. Chip internalization without affecting cell viability was achieved in all cases; however, important cell behavior differences were observed. In particular, the first stage of cell internalization was favored by silicon nanowire interfaces with respect to bulk silicon. In addition, chips were found inside membrane vesicles, and some nanowires seemed to penetrate the cytosol, which opens the door to the development of silicon nanowire chips as future intracellular sensors and drug delivery systems.

Intracellular polysilicon barcodes for cell tracking.

During the past decade, diverse types of barcode have been designed in order to track living cells in vivo or in vitro, but none of them offer the possibility to follow an individual cell up to ten or more days. Using silicon microtechnologies a barcode sufficiently small to be introduced into a cell, yet visible and readily identifiable under an optical microscope, is designed. Cultured human macrophages are able to engulf the barcodes due to their phagocytic ability and their viability is not affected. The utility of the barcodes for cell tracking is demonstrated by following individual cells for up to ten days in culture and recording their locomotion. Interestingly, silicon microtechnology allows the mass production of reproducible codes at low cost with small features (bits) in the micrometer range that are additionally biocompatible.

Permanently hydrophilic, piezoelectric PVDF nanofibrous scaffolds promoting unaided electromechanical stimulation on osteoblasts.

Biomimetic functional scaffolds for tissue engineering should fulfil specific requirements concerning structural, bio-chemical and electro-mechanical characteristics, depending on the tissue that they are designed to resemble. In bone tissue engineering, piezoelectric materials based on poly(vinylidene fluoride) (PVDF) are on the forefront, due to their inherent ability to generate surface charges under minor mechanical deformations. Nevertheless, PVDF's high hydrophobicity hinders sufficient cell attachment and expansion, which are essential in building biomimetic scaffolds. In this study, PVDF nanofibrous scaffolds were fabricated by electrospinning to achieve high piezoelectricity, which was compared with drop-cast membranes, as it was confirmed by XRD and FTIR measurements. Oxygen plasma treatment of the PVDF surface rendered it hydrophilic, and surface characterization revealed a long-term stability. XPS analysis and contact angle measurements confirmed an unparalleled two-year stability of hydrophilicity. Osteoblast cell culture on the permanently hydrophilic PVDF scaffolds demonstrated better cell spreading over the non-treated ones, as well as integration into the scaffold as indicated by SEM cross-sections. Intracellular calcium imaging confirmed a higher cell activation on the piezoelectric electrospun nanofibrous scaffolds. Combining these findings, and taking advantage of the self-stimulation of the cells due to their attachment on the piezoelectric PVDF nanofibers, a 3D tissue-like functional self-sustainable scaffold for bone tissue engineering was fabricated.

Improving Morphological Quality and Uniformity of Hydrothermally Grown ZnO Nanowires by Surface Activation of Catalyst Layer.

This paper presents a study about the dependence of the hydrothermal growth of ZnO nanowires (NWs) with the passivation level of the active surface of the Au catalyst layer. The hydrothermal method has many potential applications because of its low processing temperature, feasibility, and low cost. However, when a gold thin film is utilized as the seed material, the grown NWs often lack morphological homogeneity; their distribution is not uniform and the reproducibility of the growth is low. We hypothesize that the state or condition of the active surface of the Au catalyst layer has a critical effect on the uniformity of the NWs. Inspired by traditional electrochemistry experiments, in which Au electrodes are typically activated before the measurements, we demonstrate that such activation is a simple way to effectively assist and enhance NW growth. In addition, several cleaning processes are examined to find one that yields NWs with optimal quality, density, and vertical alignment. We find cyclic voltammetry measurements to be a reliable indicator of the seed-layer quality for subsequent NW growth. Therefore, we propose the use of this technique as a standard procedure prior to the hydrothermal synthesis of ZnO NWs to control the growth reproducibility and to allow high-yield wafer-level processing.

Electromechanical Nanogenerator-Cell Interaction Modulates Cell Activity.

Noninvasive methods for in situ electrical stimulation of human cells open new frontiers to future bioelectronic therapies, where controlled electrical impulses could replace the use of chemical drugs for disease treatment. Here, this study demonstrates that the interaction of living cells with piezoelectric nanogenerators (NGs) induces a local electric field that self-stimulates and modulates their cell activity, without applying an additional chemical or physical external stimulation. When cells are cultured on top of the NGs, based on 2D ZnO nanosheets, the electromechanical NG-cell interactions stimulate the motility of macrophages and trigger the opening of ion channels present in the plasma membrane of osteoblast-like cells (Saos-2) inducing intracellular calcium transients. In addition, excellent cell viability, proliferation, and differentiation are validated. This in situ cell-scale electrical stimulation of osteoblast-like cells can be extrapolated to other excitable cells such as neurons or muscle cells, paving the way for future bioelectronic medicines based on cell-targeted electrical impulses.

Study of Galfenol direct cytotoxicity and remote microactuation in cells.

Remote microactuators are of great interest in biology and medicine as minimally-invasive tools for cellular stimulation. Remote actuation can be achieved by active magnetostrictive transducers which are capable of changing shape in response to external magnetic fields thereby creating controlled displacements. Among the magnetostrictive materials, Galfenol, the multifaceted iron-based smart material, offers high magnetostriction with robust mechanical properties. In order to explore these capabilities for biomedical applications, it is necessary to study the feasibility of material miniaturization in standard fabrication processes as well as evaluate the biocompatibility. Here we develop a technology to fabricate, release, and suspend Galfenol-based microparticles, without affecting the integrity of the material. The morphology, composition and magnetic properties of the material itself are characterized. The direct cytotoxicity of Galfenol is evaluated in vitro using human macrophages, osteoblast and osteosarcoma cells. In addition, cytotoxicity and actuation of Galfenol microparticles in suspension are evaluated using human macrophages. The biological parameters analyzed indicate that Galfenol is not cytotoxic, even after internalization of some of the particles by macrophages. The microparticles were remotely actuated forming intra- and extracellular chains that did not impact the integrity of the cells. The results propose Galfenol as a suitable material to develop remote microactuators for cell biology studies and intracellular applications.