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Disinfection of water is essential to prevent the growth of pathogens, but at high levels, it can cause harm to human health. Therefore, accurate monitoring of disinfectant concentrations in water is essential to ensure safe drinking water. The use of multiple disinfectants at different stages in water treatment plants makes it necessary to also identify the type and concentrations of all of the disinfectant species present. Here, we demonstrate an effective approach to identify and quantify multiple disinfectants (using the example of free chlorine and potassium permanganate) in water using single-walled carbon nanotube (SWCNT)-based reagent-free chemiresistive sensing arrays. Facile fabrication of chemiresistive devices makes them a popular choice for the implementation of sensor arrays. Our sensing array consists of functionalized and unfunctionalized (blank) SWCNT sensors to distinguish the disinfectants. The distinct responses from the different sensors at varying concentrations and pH can be fitted to the mathematical model of a Langmuir adsorption isotherm separately for each sensor. Blank and functionalized sensors respond through different mechanisms that result in varying responses that are concentration- and pH-dependent. Chemometric techniques such as principal component analysis (PCA) and partial least-squares-discriminant analysis (PLS-DA) were used to analyze the sensor data. PCA showed an excellent separation of the analytes over five different pHs (5.5, 6.5, 7.5, 8.5, and 9.5). PLS-DA provided excellent separability as well as good predictability with a Q2of 94.26% and an R2of 95.67% for the five pH regions of the two analytes. This proof-of-concept solid-state chemiresistive sensing array can be developed for specific disinfectants that are commonly used in water treatment plants and can be deployed in water distribution and monitoring facilities. We have demonstrated the applicability of chemiresistive devices in a sensor array format for the first time for aqueous disinfectant monitoring.

Graphene-based pH sensors are a robust, durable, sensitive, and scalable approach for the sensitive detection of pH in various environments. However, the mechanisms through which graphene responds to pH variations are not well-understood yet. This study provides a new look into the surface science of graphene-based pH sensors to address the existing gaps and inconsistencies among the literature concerning sensing response, the role of defects, and surface/solution interactions. Herein, we demonstrate the dependence of the sensing response on the defect density level of graphene, measured by Raman spectroscopy. At the crossover point (ID/IG= 0.35), two countervailing mechanisms balance each other out, separating two regions where either a surface defect induced (negative slope) or a double layer induced (positive slope) response dominates. For ratios above 0.35, the pH-dependent induction of charges at surface functional groups (both pH-sensitive and nonsensitive groups) dominates the device response. Below a ratio of 0.35, the response is dominated by the modulation of charge carriers in the graphene due to the electric double layer formed from the interaction between the graphene surface and the electrolyte solution. Selective functionalization of the surface was utilized to uncover the dominant acid–base interactions of carboxyl and amine groups at low pH while hydroxyl groups control the high pH range sensitivity. The overall pH-sensing characteristics of the graphene will be determined by the balance of these two mechanisms.

Humans continuously interact with physical, chemical, and biological environments that influence their health, safety, and quality of life. Sensing devices, such as electrochemical sensors that translate environmental qualities into electrical signals, are crucial for detecting biomarker concentrations in various biofluids. However, the understanding of electrochemical sensing is often incomplete, necessitating further study of chemical reactions and sensor‐electrode interactions for healthcare applications. This review analyzes crucial topics in chemical reactions in electrochemical sensing environments. First, the dynamics of chemical energy, the roles of acidic and alkaline fluids, chemical reaction tendencies, thermodynamic equilibria, Gibbs free energy, water dissociation, and the pH scale are discussed. Sensor materials or biomarkers undergo oxidation and reduction reactions in electrochemical sensing. Oxygen‐derived radicals and nonradical reactive species significantly influence biochemical reactions, cellular responses, and clinical outcomes. Then, the review delves into the impact of oxidation reduction reactions on human pathophysiology, redox reactions in hemoglobin, redox environments in human serum albumin and cells/tissues, and thermodynamics of biological redox reactions. Finally, recent advances in electrochemical techniques are presented and research challenges and future perspectives in electrochemical sensing for health applications are addressed. Numerous fields of application and tremendous research potential of electrochemical sensing techniques have made them an enormous area of resource, as evidenced by the number of published scientific journal papers. This work analyzes the fundamentals, applicability, and advancements of electrochemical sensing techniques in the field of human health monitoring.

Electrochemical Biosensing Electrochemical biosensing is a rapidly growing field within global healthcare research. In article 2300100, Matiar M. R. Howlader and co‐workers provide a comprehensive review of the underlying principles and technological advancements in electrochemical sensing for health monitoring applications.

The ability to form tissue-like constructs that have high cell density with proper cell–cell and cell–ECM interactions is critical for many applications including tissue models for drug discovery and tissue regeneration. Newly emerging bioprinting methods sometimes lack the high cellular density needed to provide biophysical cues to orchestrate cellular behavior to recreate tissue architecture and function. Alternate methods using self-assembly can be used to create tissue-like constructs with high cellular density and well-defined microstructure in the form of spheroids, organoids, or cell sheets. Cell sheets have a particularly interesting architecture in the context of tissue regeneration and repair as they can be applied as patches to integrate with surrounding tissues. Until now, the preparation of these sheets has involved culturing on specialized substrates that can be triggered by temperature or phase change (hydrophobic to hydrophilic) to release cells growing on them and form sheets. Here a new technique is proposed that allows delamination of cells and secreted ECM and rapid self-assembly into a cell sheet using a simple pH trigger and without the need to use responsive surfaces or applying external stimuli such as electrical and magnetic fields, only with routine tissue culture plates. This technique can be used with cells that are capable of syncytialization and fusion such as skeletal muscle cells and placenta cells. Using C2C12 myoblast cells we show that the pH trigger induces a rapid delamination of the cells as a continuous layer that self-assembles into a thick dense sheet. The delamination process has little effect on cell viability and maturation and preserves the ECM components that allow sheets to adhere to each other within a short incubation time enabling formation of thicker constructs when multiple sheets are stacked (double- and quadruple-layer constructs are formed here). These thick grafts can be used for regeneration purposes or as in vitro models.

Premature neonates with underdeveloped lungs experience respiratory issues and need respiratory support, such as mechanical ventilation or extracorporeal membrane oxygenation (ECMO). The “artificial placenta” (AP) is a noninvasive approach that supports their lungs and reduces respiratory distress, using a pumpless oxygenator connected to the systemic circulation, and can address some of the morbidity issues associated with ECMO. Over the past decade, microfluidic blood oxygenators have garnered significant interest for their ability to mimic physiological conditions and incorporate innovative biomimetic designs. Achieving sufficient gas transfer at a low enough pressure drop for a pumpless operation without requiring a large volume of blood to prime such an oxygenator has been the main challenge with microfluidic lung assist devices (LAD). In this study, we improved the gas exchange capacity of our microfluidic-based artificial placenta-type LAD while reducing its priming volume by using a modified fabrication process that can accommodate large-area thin film microfluidic blood oxygenator (MBO) fabrication with a very high gas exchange surface. Additionally, we demonstrate the effectiveness of a LAD assembled by using these scaled-up MBOs. The LAD based on our artificial placenta concept effectively increases oxygen saturation levels by 30% at a flow rate of 40 mL/min and a pressure drop of 23 mmHg in room air, which is sufficient to support partial oxygenation for 1 kg preterm neonates in respiratory distress. When the gas ambient environment was changed to pure oxygen at atmospheric pressure, the LAD would be able to support premature neonates weighing up to 2 kg. Furthermore, our experiments reveal that the LAD can handle high blood flow rates of up to 150 mL/min and increase oxygen saturation levels by ∼20%, which is equal to an oxygen transfer of 7.48 mL/min in an enriched oxygen environment and among the highest for microfluidic AP type devices. Such performance makes this LAD suitable for providing essential support to 1–2 kg neonates in respiratory distress.

We report a simple method of preparing autonomous and rapid self-adhesive hydrogels and their use as building blocks for additive manufacturing of functional tissue scaffolds. Dynamic cross-linking between 2-aminophenylboronic acid-functionalized hyaluronic acid and poly(vinyl alcohol) yields hydrogels that recover their mechanical integrity within 1 min after cutting or shear under both neutral and acidic pH conditions. Incorporation of this hydrogel in an interpenetrating calcium-alginate network results in an interfacially stiffer but still rapidly self-adhesive hydrogel that can be assembled into hollow perfusion channels by simple contact additive manufacturing within minutes. Such channels withstand fluid perfusion while retaining their dimensions and support endothelial cell growth and proliferation, providing a simple and modular route to produce customized cell scaffolds.

The development of power generators that can function in harsh snowy environments and in contact with snow can be beneficial but challenging to accomplish. Herein, we introduce the first snow-based triboelectric nanogenerator (snow-TENG) that can be used as an energy harvester and a multifunctional sensor based on the principle of snow-triboelectrification. In this work, we used a 3D printing technique for the precise design and deposition of the electrode and triboelectric layer, leading to flexible, stretchable and metal-free triboelectric generators. Based on the single electrode mode, the device can generate an instantaneous output power density as high as 0.2 mW/m2, an open circuit voltage up to 8 V, and a current density of 40 μA/m2. In addition, the snow-TENG can function as a miniaturized weather station to monitor the weather in real time to provide accurate information about the snowfall rate, snow accumulation depth, wind direction, and speed in snowy and/or icy environments. In addition, the snow-TENG can be used as a wearable power source and biomechanical sensor to detect human body motions, which may prove useful for snow-related sports. Unlike conventional sensor platforms, our design works without the need for batteries or image processing systems. We envision these devices could potentially be integrated into solar panels to ensure continuous power supply during snowy weather conditions.

The development of highly sensitive sensors and power generators that could function efficiently in extreme temperatures and contact with fire can be lifesaving but challenging to accomplish. Herein, we report, for the first time, a fire-retardant and self-extinguishing triboelectric nanogenerator (FRTENG), which can be utilized as a motion sensor and/or power generator in occupations such as oil drilling, firefighting or working in extreme temperature environments with flammable and combustible materials. The device takes advantage of the excellent thermal properties of carbon derived from resorcinol-formaldehyde aerogel whose electrical, mechanical and triboelectric properties have been improved via the introduction of Polyacrylonitrile nanofibers and graphene oxide nanosheets. This FRTENG is not flammable even after 90 s of trying, whereas conventional triboelectric materials were entirely consumed by fire under the same conditions. The developed device shows exceptional charge transfer characteristics, leading to a potential difference up to 80 V and a current density up to 25 µA/m2. When integrated into firefighter's shoes, the FRTENG is able to discern the movements of a firefighter in hazardous situations, while providing the high thermal stability missing in conventional TENGs. The fire-retardant and self-extinguishing characteristics offered by the FRTENG makes it a path-breaking device for lifesaving wearable applications.

Colorimetric methods are commonly used to quantify free chlorine in drinking water. However, these methods are not suitable for reagent-free, continuous, and autonomous applications. Here, we demonstrate how functionalization of a pencil-drawn film with phenyl-capped aniline tetramer (PCAT) can be used for quantitative electric readout of free chlorine concentrations. The functionalized film can be implemented in a simple fluidic device for continuous sensing of aqueous free chlorine concentrations. The sensor is selective to free chlorine and can undergo a reagent-free reset for further measurements. Our sensor is superior to electrochemical methods in that it does not require a reference electrode. It is capable of quantification of free chlorine in the range of 0.1–12 ppm with higher precision than colorimetric (absorptivity) methods. The interactions of PCAT with the pencil-drawn film upon exposure to hypochlorite were characterized spectroscopically. A previously reported detection mechanism relied on the measurement of a baseline shift to quantify free chlorine concentrations. The new method demonstrated here measures initial spike size upon exposure to free chlorine. It relies on a fast charge built up on the sensor film due to intermittent PCAT salt formation. It has the advantage of being significantly faster than the measurement of baseline shift, but it cannot be used to detect gradual changes in free chlorine concentration without the use of frequent reset pulses. The stability of PCAT was examined in the presence of free chlorine as a function of pH. While most ions commonly present in drinking water do not interfere with the free chlorine detection, other oxidants may contribute to the signal. Our sensor is easy to fabricate and robust, operates reagent-free, and has very low power requirements and is thus suitable for remote deployment.

The dynamics of blood flow in the smallest vessels and passages of the human body, where the cellular character of blood becomes prominent, plays a dominant role in the transport and exchange of solutes. Recent studies have revealed that the microhaemodynamics of a vascular network is underpinned by its interconnected structure, and certain structural alterations such as capillary dilation and blockage can substantially change blood flow patterns. However, for extravascular media with disordered microstructure (e.g. the porous intervillous space in the placenta), it remains unclear how the medium’s structure affects the haemodynamics. Here, we simulate cellular blood flow in simple models of canonical porous media representative of extravascular biological tissue, with corroborative microfluidic experiments performed for validation purposes. For the media considered here, we observe three main effects: first, the relative apparent viscosity of blood increases with the structural disorder of the medium; second, the presence of red blood cells (RBCs) dynamically alters the flow distribution in the medium; third, symmetry breaking introduced by moderate structural disorder can promote more homogeneous distribution of RBCs. Our findings contribute to a better understanding of the cell-scale haemodynamics that mediates the relationship linking the function of certain biological tissues to their microstructure.

Phosphorus is required for plants and humans to survive because it is needed for cell signaling, skeletal integrity, energy storage and metabolism. Phosphorus measurements are performed using colorimetric and electrochemical methods. Colorimetry is the most accepted method for commercial devices for phosphorus monitoring while electrochemical systems are still in the research phase. Here we provide the first comprehensive review of solid-state sensors for phosphate monitoring. The review focuses on solid state reagent storage for colorimetric sensors and different materials used in solid state electrochemical sensors. The electrochemical sensors are further classified into three groups: potentiometric, amperometric and voltammetric. All sensors are evaluated based on parameters such as measurement range, limit of detection (LOD), working pH and response time. Finally, we discuss limitations of the current sensors and future directions for the development of these sensors.

The placenta is a vital interface between the mother and her developing fetus. Micro-haemodynamics of the placenta, where the particulate nature of blood flow cannot be ignored, mediates the relationship between the organ's structure and its function. However, the placenta's complex architecture and its relation to pregnancy pathologies remain poorly understood. This review covers current challenges in characterising placental micro-haemodynamics. Recent progress in three-dimensional multiscale imaging has stimulated the development of image-based theoretical models, but existing approaches do not fully harness the available data, and new tools are needed for the assimilation of complex imaging datasets. Although the placenta at term is available for in vivoimaging or ex vivoexperimentation, insight into placental micro-rheology is limited, necessitating the use of biomimetic models. Microfluidic approaches offer opportunities for well-controlled characterisation of micro-rheology in complex geometries, but challenges remain in the robust fabrication of these systems. Recent advances in high-performance simulations for suspension flows enable parametrisation of key physical processes at the micro-scale. Future progress can be made by optimising computational architecture and integrating micro-haemodynamics with solute transport. Both experimental and computational approaches require translation to the organ scale. New upscaling approaches will need to accommodate non-local interactions in microvascular network flows and address the lack of clear scale separation across the placental architecture. Together, recent advances in cross-disciplinary imaging and modelling over the last ten years have opened a pathway for an in silicohuman placenta, accelerating the development of precision obstetrics medicine in the next decade.

Extrusion-based 3D printing is often performed using a single ink or switching between two or more inks. The ability to create compositional variation in-situ by rapid mixing of two different inks inside the printhead with dynamically changing ratios can produce a broad palette of material composition that is useful in making functionally graded materials for applications in soft robotics or integrated sensors. However, rapid mixing of high viscosity polymer inks in low Reynolds number flows has been a challenge. Here, we demonstrate a multimaterial microfluidic printhead mixer (MM-PHM) that is capable of mixing dynamically controllable ratios of different silicone inks to print graded materials. The MM-PHM uses a pulsatile injection of multiple inks, pneumatically inside a mixing junction, combined with a free-floating static mixer to produce various compositions from up to four different base inks. The performance of the MM-PHM when dissimilar inks are used has been assessed using both experimental and computational (fluids dynamics) methods. To illustrate the versatility of this method, a 2D colored gradient map, and 3D Rubix cube have been fabricated using four-color inks to produce nine different material combinations. This scalable method expands the palette of multimaterial 3D printing materials that can be fabricated and constructed in complex shapes and varying properties.

In this paper, reactive ion etch process of silicone materials, specifically polydimethylsiloxane (PDMS), was characterised using Plackett-Burman fractional factorial and Box-Behnken response surface designs. These design of experiment techniques allow for efficient analysis of input parameters and their effects on response parameters. The Plackett-Burman design was used in screening for critical factors in eight experiments. RF power, pressure and flow rate of sulphur hexafluoride were determined as critical parameters. Oxygen and nitrogen gas composition in plasma had little positive effect on etch rate. The three-critical parameter, three-level Box-Behnken design produced 15 experiments. Based on the data obtained, the effects of critical parameters on the etch rate and surface roughness were studied. Response surface plots along with a second order polynomial were derived using statistical analysis software yielding an approximated model with R² = 99.53%.

Molybdenum disulfide (MoS2) is a promising material for applications in sensors, energy storage, energy conversion devices, solar cells, and fuel cells. Because many of those applications require conductive materials, we recently developed a method for preparing a conductive form of MoS2(c-MoS2) using dilute aqueous hydrogen peroxide in a simple and safe way. Here, we investigate modulating the chemical and mechanical surface properties of c-MoS2thin films using diazonium chemistry. In addition to a direct passivation strategy of c-MoS2with diazonium salts for electron-withdrawing groups, we also propose a novel in situsynthetic pathway for modification with electron-donating groups. The obtained results are examined by Raman spectroscopy and X-ray photoelectron spectroscopy. The degree of surface passivation of pristine and functionalized c-MoS2films was tested by exposing them to aqueous solutions of different metal cations (Fe2+, Zn2+, Cu2+, and Co2+) and detecting the chemiresistive response. While pristine films were found to interact with several of the cations, modified films did not. We propose that a surface charge transfer mechanism is responsible for the chemiresistive response of the pristine films, while both modification routes succeeded at complete surface passivation. Functionalization was also found to lower the coefficient of friction for semiconducting 2H-MoS2, while all conductive materials (modified or not) also had lower coefficients of friction. This opens up a pathway to a palette of dry lubricant materials with improved chemical stability and tunable conductivity. Thus, both in situand direct diazonium chemistries are powerful tools for tuning chemical and mechanical properties of conductive MoS2for new devices and lubricants based on conductive MoS2.

This work describes a versatile and cost-effective cell culture method for micropatterning and growing adherent cells on porous membranes using pressure-sensitive double-sided adhesives. This technique also allows cell culture using conventional methods and their easy integration into microfluidic chip devices. Adhesives can be used to form different patterns of cultured cells, which can be used for cell proliferation and wound-healing models. To demonstrate the viability of our system, we evaluate the toxicity effect of five different adhesives on two distinct airway epithelial cell lines and show functional applications for cell patterning and microfluidic cell culture chip fabrication. We developed a sandwiched microfluidic device that enabled us to culture cells in a submerged condition and transformed it into a dynamic platform when required. The viability of cells and their inflammatory responses to IL-1β stimulation were investigated. Our technique is applicable for conventional culturing of cells, widely available in biomedical research labs, while enabling the introduction of perfusion for an advanced dynamic cell culture model when needed.

Additive manufacturing and 3D printing technology using thermoplastics and metals have found mainstream use and acceptance. Nevertheless, these methods are not suitable for several industrially important materials, such as silicones and epoxies that are formed by mixing two or more reactive components and chemically inducing crosslinking. The reaction increases the viscosity of the material significantly, which greatly affects the printing process. Here, we develop an inkjet-based printing method that generates droplets of the reactive components simultaneously, merges and mixes them in free space and deposits these curing droplets so that 3D structures can be formed. It uses low viscosity, highly reactive silicone inks that cannot be printed using conventional methods of additive manufacturing and expands the range of 3D printable materials. The method enables stable and uninterrupted printing and allows for multi and rapid start-stop cycles. The high reactivity of the ink used allows printing of high aspect ratio features, as well as structures that do not require supporting scaffolds. The capabilities of the new printing method, such as non-contact printing, on-demand printing, and the ability to handle highly reactive materials make it suitable for a wide range of industrial and home use of 3D printing technology for non-thermoplastic polymeric materials.

Phenanthrolines are a class of ligands known to bind with many different metal cations to form complexes. The aromatic backbone of phenanthroline also allows for preferential adsorption on few-layer graphene (FLG) films via π–π stacking. Here we investigate the effects of adsorption and the resulting steric restrictions on the binding ability of four different phenanthroline derivatives: phenanthroline, neocuproine, bathophenanthroline, and bathocuproine. In solution, a wide range of metal cations tested formed complexes with these ligands, but only Cu2+and Ag+showed evidence of binding to ligands adsorbed onto FLG, as measured by the chemiresistive response of the films. The substituents present on each ligand affected the magnitude of the response in different ways. Raman and X-ray photoelectron spectroscopy (XPS) were used to study two different systems in more detail: iron with phenanthroline, which shows a response in solution (ferroin) but not on the FLG surface (purported monoligand complex), and copper with neocuproine, which responds both in solution (bis[neocuproine]copper(I)) and on the FLG surface (monoligand complex). Raman and XPS data indicate complexing of copper by surface-bound ligands. Theoretical calculations show that the copper–neocuproine monocomplex has a higher adsorption energy and binding energy to a graphene surface than the iron–phenanthroline monocomplex. The reduction of copper(II) to copper(I) by the surface-bound neocuproine further results in a stronger charge transfer response from the sensor. The results of this study provide insights into the mechanisms of solid-state sensing of metal cations for water quality detection based on steric and electrochemical restrictions induced by surface adsorption.

Smart skin-like electronics are urgently crucial for artificial muscles, while the development of self-powered two-dimensional-like multifunctional material systems remains significant challenges. Here, we demonstrate a new class of printed smart electronic skin (SES) with multi-sensing properties and energy conversion capability using simple and cost-effective printing techniques. The resulting all-organic self-powering SES functioning as a human-monitoring device where it can detect a variety of external stimuli and works as an ultra-flexible biomechanical energy harvester. Remarkably, our SES exhibits excellent antibacterial properties in addition to self-adaptive performance under various conditions, such as being bent, cut, sewed, hammered, punctured, and washed. The proposed SES devices here have the promise for broad applications in future functional-wearables for human-machine interface, soft robotics, and skin prosthetics.

In article number 1701385, Ponnambalam Ravi Selvaganapathy and co‐workers use a lamination‐based planar processing strategy enabled by nanoparticle adhesives to address one of the prominent technical challenges found in the tissue engineering field – the incorporation of perfusable hollow networks for nutrient and waste transport within artificial 3D tissue constructs. Without these vascular‐like networks, the cells embedded within the constructs would quickly become necrotic. Silicon Carbide, used as a nanoadhesive, has been shown to be very effective in adhering microstructured layers of biologically important extracellular matrices containing collagen to form perfusable 3D netoworks suitable for growing cells.

Additive manufacturing via layer‐by‐layer adhesive bonding holds much promise for scalable manufacturing of tissue‐like constructs, specifically scaffolds with integrated vascular networks for tissue engineering applications. However, there remains a lack of effective adhesives capable of composite layer fusion without affecting the integrity of patterned features. Here, the use of silicon carbide is introduced as an effective adhesive to achieve strong bonding (0.39 ± 0.03 kPa) between hybrid hydrogel films composed of alginate and collagen. The techniques have allowed us to fabricate multilayered, heterogeneous constructs with embedded high‐resolution microchannels (150 µm–1 mm) that are precisely interspaced (500–600 µm). Hydrogel layers are effectively bonded with silicon carbide nanoparticles without blocking the hollow microchannels and high cell viability (90.61 ± 3.28%) is maintained within the scaffold. Nanosilica is also tested and found to cause clogging of smaller microchannels when used for interlayer bonding, but is successfully used to attach synthetic polymers (e.g., Tygon) to the hydrogels (32.5 ± 2.12 mN bond strength). This allows us to form inlet and outlet interconnections to the gel constructs. This ability to integrate hollow channel networks into bulk soft material structures for perfusion can be useful in 3D tissue engineering applications. Composite hydrogel lamination for biofabrication of 3D hollow channel constructs. The novel use of adhesive nanoparticles for the creation of thick, multilayered hydrogel structures with embedded, perfusable hollow channel networks is demonstrated. These mechanically robust and cytocompatible scaffolding materials can serve as vascular substitutes in tissue engineering applications.

Palladium nanomaterials have shown great promise for use in sensing and energy storage devices, and developing simple and inexpensive top-down and bottom-up methods for creating such materials has attracted much attention. In spite of tremendous progress in recent years, creating hierarchical multiscale materials which are dually optimized at the nanoscale for addressing various functional demands and are amenable for micro/macroscale integration into practical devices, remains a challenge. Here we demonstrate a rapid and simple approach based on kinetically-controlled electrochemical deposition and photolithography for creating programmable hierarchical multiscale palladium structures. Through electrochemical methods, we are able to structurally and functionally program palladium materials based on their deposition kinetics. Structures ranging from 2D thin films into 3D globules decorated with nano-needles are created with a tunable hydrogen storage capacity, Raman signal magnitude, and analytical sensitivity. Furthermore, lithography-based methods are used to pattern these programmable structures into highly organized and periodic configurations.

The accuracy of many biological and chemical sensors is critically dependent on the stability of the potential imposed or sensed through a reference electrode. As these sensors are miniaturized, the reference electrode has to be miniaturized simultaneously without any loss to its stability. In this paper, we describe a new microfluidic miniaturized silver/silver chloride reference electrode that demonstrates significantly better stability and lifetime than conventional designs. In our new design, we have miniaturized the existing format of the macroscale reference electrode and added the capability to replenish the internal solution by integrating it with a microfluidic channel. The replenishment of the internal solution significantly improves the performance of these electrodes over other miniaturized designs. We demonstrate reference electrodes that are very stable (potential variation of <0.1 mV), with minimal drift (∼1 mV) and lifetimes longer than 100 hours. We have also characterized the behavior of these electrodes to changes in pH and chlorine concentration of the external solution. The results indicate insensitivity of the microfluidic reference electrode potential to the presence of any analyte in the test solution.