Micropillar Electrodes Research Articles

A numerical study of geometric and flow factors influencing the performance of micropillar electrode biosensors

Micropillar array electrodes have piqued the interest of researchers as a promising new technology. With their enhanced surface area characteristics, such electrodes result in improved microfluidic biosensor performance. While the efficiency of biosensors has been found to diminish due to certain fundamental phenomena, current knowledge of such underlying phenomena within the micropillar electrode array context, is rather limited. Consequently, further study is required to reduce them, so as to understand and evaluate their effects on biosensor performance. This work seeks to address this gap in the literature. In particular, we seek to highlight phenomenological factors apart from diffusion boundary layer effects. The study is done by employing a finite-element based software, COMSOL Multiphysics. This is done to numerically investigate the effects of geometry and flow conditions on micropillar electrode biosensor performance. Two configurations—staggered and inline—are analyzed. The results demonstrate that due to enhanced mixing induced within the flow, the staggered arrangement has a 25% improvement in response time compared to the inline arrangement. Additional parametric tests also indicate that relative factors due to geometry and flow play a significant role in controlling concentration rates. Overall, it is shown that biosensor response times are most effectively controlled when the ratio of the flow’s inertia and viscous forces is less than 0.1.

Roles of Wettability and Wickability on Enhanced Hydrogen Evolution Reactions.

Bubble dynamics significantly impact mass transfer and energy conversion in electrochemical gas evolution reactions. Micro-/nanostructured surfaces with extreme wettability have been employed as gas-evolving electrodes to promote bubble departure and decrease the bubble-induced overpotential. However, effects of the electrodes' wickability on the electrochemical reaction performances remain elusive. In this work, hydrogen evolution reaction (HER) performances are experimentally investigated using micropillar array electrodes with varying interpillar spacings, and effects of the electrodes' wettability, wickability as well as bubble adhesion are discussed. A deep learning-based object detection model was used to obtain bubble counts and bubble departure size distributions. We show that microstructures on the electrode have little effect on the total bubble counts and bubble size distribution characteristics at low current densities. At high current densities, however, micropillar array electrodes have much higher total bubble counts and smaller bubble departure sizes compared with the flat electrode. We also demonstrate that surface wettability is a critical factor influencing HER performances under low current densities, where bubbles exist in an isolated regime. Under high current densities, where bubbles are in an interacting regime, the wickability of the micropillar array electrodes emerges as a determining factor. This work elucidates the roles of surface wettability and wickability on enhancing electrochemical performances, providing guidelines for the optimal design of micro-/nanostructured electrodes in various gas evolution reactions.

CTAB-Modulated Electroplating of Copper Micropillar Arrays for Non-Enzymatic Glucose Sensing with Improved Sensitivity.

Micropillar array electrodes represent a promising avenue for enhancing detection sensitivity and response current. However, existing methods for depositing electrode materials on micropillar arrays often result in uneven distribution, with the thin sidewall layer being less conductive and prone to corrosion. In addressing this issue, this study introduces electroplating to enhance the copper layer on the sidewall of micropillar array electrodes. These electrodes, fabricated through standard microelectronics processes and electroplating, are proposed for non-enzymatic glucose detection, with the copper layer deposited via electroplating significantly enhancing sensitivity. Initially, the impact of cetyltrimethylammonium bromide (CTAB) concentration as an inhibitor on the surface morphology and sensitivity of the plated layer was investigated. It was discovered that CTAB could decrease surface roughness, hinder the development of large and coarse grains, generate small particles, and boost sensitivity. Compared to the uncoated electrode and plating without CTAB, sensitivity was elevated by a factor of 1.66 and 1.62, respectively. Subsequently, the alterations in plating morphology and detection performance within a range of 0.3 ASD to 3 ASD were examined. Sensitivity demonstrated a tendency to increase initially and then decrease. The electrode plated at 0.75 ASD achieved a maximum sensitivity of 3314 μA·mM-1·cm-2 and a detection limit of 15.9 μM. Furthermore, a potential mechanism explaining the impact of different morphology on detection performance due to CTAB and current density was discussed. It was believed that the presented effective strategy to enhance the sensitivity of micropillar array electrodes for glucose detection would promote the related biomedical detection applications.

Supercapacitive MnO2/PEDOT: PSS Modified 3D-Printed Polymeric Micro-Pillar Electrode for Extraction of Photosynthetic Electrons

Photosynthetic bio-electrochemical cells (PBECs) have been reported as having promising potential for the renewable energy field. When photosynthesis occurs, photosynthetic electrons (PEs) were generated and excited in photosystem II by sunlight. These PEs were transferred via photosynthetic apparatuses in thylakoid membranes (TMs) and finally consumed to reduce NADP. So far, several attempts have been made to maximize the extraction of PEs from the TMs. Firstly, a micro-pillar electrode was demonstrated to enhance PEs extraction by maximizing the contact area with TMs [1]. As another study, for effective electrical connections with TMs, carbon nanotubes (CNTs) [2], or graphene oxide (GO) [3] were utilized to enhance PEs harvesting. Furthermore, supercapative materials were exploited to improve the performance of TM-based PBECs. For instance, PEs harvesting was enhanced in Au electrode modified with ruthenium dioxide (RuO2) nanosheets compared to a pristine Au electrode [4]. In another study, a dual-feature electrode of Au and PEDOT was introduced to collect and store PEs [5]. Although there were various attempts to harvest PEs effectively, their electrodes were still limited to the two-dimension. Thus, it is required that a three-dimensional electrode with supercapacitance to achieve more efficient PEs harvesting for practical application.In this work, we propose a supercapacitive MnO2/PEDOT:PSS-modified 3D-printed polymeric micro-pillar electrode to efficiently collect and spontaneously store the PEs. For the maximization of PE harvesting, diameter, pitches (center to center), and aspect ratio (A/R) of the micro-pillars were controlled. To fabricate the current collection layer, Au was sputtered on the 4-aminothiophenol coated stereolithographically (SLA) printed micro-pillar substrate. PEDOT:PSS was electrodeposited as secondary current collect and adhesion layer between Au and MnO2. Then, MnO2 was electrochemically deposited on PEDOT:PSS layer for efficient attachment with TMs and storage of PEs. Finally, TMs were carefully dip-coated on MnO2/PEDOT:PSS micro-pillar electrode. The morphology of each step in the electrode fabrication was analyzed by optical microscopy and scanning electron microscopy (SEM). The enhanced electrochemical surface area (ECSA) of 3D-printed MnO2/PEDOT:PSS micro-pillar electrode was compared to flat electrode using cyclic voltammetry (CV). The capacitive performance of 3D-printed TM/MnO2/PEDOT:PSS micro-pillar electrode was carefully analyzed using CV and Galvano charge-discharge measurements. Measured ECSA of MnO2/PEDOT:PSS micro-pillar electrode was 5 folds increase than that of flat electrode. MnO2/PEDOT:PSS micro-pillar electrode was achieved 4 folds and 180 folds larger than PEDOT:PSS and Au micro-pillar electrode, respectively. 212 F/g of gravimetric and 257 mF/cm2 of areal capacitance were measured in 3D-printed MnO2/PEDOT:PSS micro-pillar electrode. It was confirmed that PEs can be electrochemically extracted from TM deposited 3D-printed MnO2/PEDOT:PSS micro-pillar electrode using CV. To measure a light-triggered PE current, a standard three electrode system was configured with a 3D-printed TM/MnO2/PEDOT:PSS micro-pillar electrode. The light-driven PE current of 27 μA/cm2 was measured in a 3D-printed MnO2/PEDOT:PSS micro-pillar electrode under 100 mW/cm2 of illumination with a bias potential of 0.5 V versus Ag/AgCl.

Flexible 3D printed microwires and 3D microelectrodes for heart-on-a-chip engineering

We developed a heart-on-a-chip platform that integrates highly flexible, vertical, 3D micropillar electrodes for electrophysiological recording and elastic microwires for the tissue’s contractile force assessment. The high aspect ratio microelectrodes were 3D-printed into the device using a conductive polymer, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). A pair of flexible, quantum dots/thermoplastic elastomer nanocomposite microwires were 3D printed to anchor the tissue and enable continuous contractile force assessment. The 3D microelectrodes and flexible microwires enabled unobstructed human iPSC-based cardiac tissue formation and contraction, suspended above the device surface, under both spontaneous beating and upon pacing with a separate set of integrated carbon electrodes. Recording of extracellular field potentials using the PEDOT:PSS micropillars was demonstrated with and without epinephrine as a model drug, non-invasively, along with in situ monitoring of tissue contractile properties and calcium transients. Uniquely, the platform provides integrated profiling of electrical and contractile tissue properties, which is critical for proper evaluation of complex, mechanically and electrically active tissues, such as the heart muscle under both physiological and pathological conditions.

Multiplexed detection of biomarkers using a microfluidic chip integrated with mass-producible micropillar array electrodes

Quantifying multiple biomarkers with high sensitivity in tiny biological samples is essential to meet the growing demand for point-of-care testing. This paper reports the development of a novel microfluidic device integrated with mass-producible micropillar array electrodes (μAEs) for multiple biomarker detections. The μAE are mass-fabricated by soft lithography and hot embossing technique. Pt–Pd bimetallic nanoclusters (BNC) are modified on the surface of μAEs by constant potential (CP)/multi-potential step (MPS) electrodeposition strategies to improve the electroanalytical performance. The experimental result displays that Pt–Pd BNC/μAEs have good sensitivity enhancement compared with bare planar electrodes and bare μAEs, the enhancement being 56.5 and 9.5 times respectively, from the results of the H2O2 detection. Furthermore, glucose, uric acid and sarcosine were used as model biomarkers to show the biosensing capability with high sensitivity. The linear range and LOD of the glucose, uric acid and sarcosine detection are 0.1 mM–12 mM, 10 μM–800 μM and 2.5 μM–100 μM, 58.5, 3.4 and 0.4 μM, respectively. In particular, biosensing chips show wide linear ranges covering required detection ranges of glucose, uric acid and sarcosine in human serum, indicating the developed device has great potential in self-health management and clinical requirements.

Photolithographic Structuring of Ordered Silicon Micropillar Electrodes for Lithium-Ion Batteries and Electrochemical Performance

Ordered and vertically oriented silicon (Si) micropillar structures, when optimally designed, can accommodate the lithiation-induced volumetric expansion that is limiting the implementation of Si as negative electrodes in Li-ion batteries. As there is not much work in this area, this study is focused on evaluating systematically the potential of Si micropillar electrodes prepared by photolithographic structuring of Si. The specific objective is to determine the effect of micropillar length and the free space around the pillars on the electrochemical performance of the electrode. The Si micropillar electrode with the pillar length of 14 μm showed a high specific capacity (2600 mAh/g) and a high areal capacity (3 mAh/cm2), which were stable for over 100 cycles. However, there was significant capacity degradation in 32 and 48 μm-long Si pillar electrodes due to cracking and electrode damage during cycling. In the 32 μm Si micropillar electrode, a small change in porosity from 69 to 86% caused a substantial increase in specific capacity from 1400 to 2000 mAh/g over 100 cycles, with the areal capacity decreasing from 3 to 2 mAh/cm2. The findings also show the directions for further work for the optimization of Si micropillar electrodes.

Out-of-Plane Electronics on Flexible Substrates Using Inorganic Nanowires Grown on High-Aspect-Ratio Printed Gold Micropillars.

Out-of-plane or3Delectronics on flexible substrates are an interesting direction that can enable novel solutions such as efficient bioelectricity generation and artificial retina. However, the development of devices with such architectures is limited by the lack of suitable fabrication techniques. Additive manufacturing (AM) can but often fail to provide high-resolution, sub-micrometer 3D architectures. Herein, the optimization of a drop-on-demand (DoD), high-resolution electrohydrodynamic (EHD)-based jet printing method for generating 3D gold (Au) micropillars is reported. Libraries of Au micropillar electrode arrays (MEAs) reaching a maximum height of 196µm and a maximum aspect ratio of 52 are printed. Further, by combining AM with the hydrothermal growth method, a seedless synthesis of zinc oxide (ZnO) nanowires (NWs) on the printed Au MEAs is demonstrated. The developed hybrid approach leads to hierarchical light-sensitive NW-connected networks exhibiting favorable ultraviolet (UV) sensing as demonstrated via fabricating flexible photodetectors (PDs). The 3D PDs exhibit an excellent omnidirectional light-absorption ability and thus, maintain high photocurrents over wide light incidence angles (±90°). Lastly, the PDs are tested under both concave and convex bending at 40mm, showing excellent mechanical flexibility.

Oxygen Plasma-Mediated Microstructured Hydrocarbon Membrane for Improving Interface Adhesion and Mass Transport in Polymer Electrolyte Fuel Cells.

Developing a method for fabricating high-efficient and low-cost fuel cells is imperative for commercializing polymer electrolyte membrane (PEM) fuel cells (FCs). This study introduces a mechanical and chemical modification technique using the oxygen plasma irradiation process for hydrocarbon-based (HC) PEM. The oxygen functional groups were introduced on the HC-PEM surface through the plasma process in the controlled area, and microsized structures were formed. The modified membrane was incorporated with plasma-treated electrodes, improving the adhesive force between the HC-PEM and the electrode. The decal transfer was enabled at low temperatures and pressures, and the interfacial resistance in the membrane-electrode assembly (MEA) was reduced. Furthermore, the micropillar structured electrode configuration significantly reduced the oxygen transport resistance in the MEA. Various diagnostic techniques were conducted to find out the effects of the membrane surface modification, interface adhesion, and mass transport, such as physical characterizations, mechanical stress tests, and diverse electrochemical measurements.

Numerical Study on a Bio-Inspired Micropillar Array Electrode in a Microfluidic Device.

The micropillar array electrode (µAE) has been widely applied in microchip-based electrochemical detection systems due to a large current response. However, it was found that amplifying the current through further adjusting geometrical parameters is generally hindered by the shielding effect. To solve this problem, a bio-inspired micropillar array electrode (bµAE) based on the microfluidic device has been proposed in this study. The inspiration is drawn from the structure of leatherback sea turtles’ mouths. By deforming a μAE to rearrange the micropillars on bilateral sides of the microchannel, the contact area between micropillars and analytes increases, and thus the current is substantially improved. A numerical simulation was then used to characterize the electrochemical performance of bµAEs. The effects of geometrical and hydrodynamic parameters on the current of bµAEs were investigated. Moreover, a prototypical microchip integrated with bµAE was fabricated for detailed electrochemical measurement. The chronoamperometry measurements were conducted to verify the theoretical performance of bµAEs, and the results suggest that the experimental data are in good agreement with those of the simulation model. This work presents a novel bµAE with great potential for highly sensitive electrochemical detection and provides a new perspective on the efficient configuration of the µAE.

Development of a novel microfluidic biosensing platform integrating micropillar array electrode and acoustic microstreaming techniques

Quantifying biomarkers at the early stage of the disease is challenging due to the low abundance of biomarkers in the sample and the lack of sensitive techniques. This article reports the development of a novel microfluidic electrochemical biosensing platform to address this challenge. The electrochemical sensing is achieved by utilizing a micropillar array electrode (μAE) coated with 3D bimetallic Pt–Pd nanotrees to enhance the sensitivity. A bubble-based acoustic microstreaming technique is integrated with the device to increase the contact of analyte molecules with the surface of electrodes to further enhance the electrochemical performance. The current density of Pt–Pd NTs/μAE with acoustic microstreaming is nearly 22 times that of the bare planar electrode in potassium ferrocyanide solution. The developed biosensor has demonstrated excellent sensing performance. For hydrogen peroxide detection, both the Pt–Pd NTs/μAE and acoustic microstreaming contribute to the sensitivity enhancement. The current density of the Pt–Pd NTs/μAE is approximatively 28 times that of the bare μAE. With acoustic microstreaming, this enhancement is further increased by nearly 1.6 times. The platform has a linear detection range of 5–1000 μM with a LOD of 1.8 μM toward hydrogen peroxide detection, while for sarcosine detection, the linear range is between 5 and 100 μM and LOD is 2.2 μM, respectively. Furthermore, the sarcosine biosensing shows a high sensitivity of 667 μA mM−1∙cm−2. Such a sensing platform has the potential as a portable device for high sensitivity detection of biomarkers.

Ultrarapid and ultrasensitive detection of SARS-CoV-2 antibodies in COVID-19 patients via a 3D-printed nanomaterial-based biosensing platform.

Rapid detection of antibodies during infection and after vaccination is critical for the control of infectious outbreaks, understanding immune response, and evaluating vaccine efficacy. In this manuscript, we evaluate a simple ultrarapid test for SARS‐CoV‐2 antibodies in COVID‐19 patients, which gives quantitative results (i.e., antibody concentration) in 10–12 s using a previously reported nanomaterial‐based three‐dimensional (3D)‐printed biosensing platform. This platform consists of a micropillar array electrode fabricated via 3D printing of aerosolized gold nanoparticles and coated with nanoflakes of graphene and specific SARS‐CoV‐2 antigens, including spike S1, S1 receptor‐binding domain (RBD) and nucleocapsid (N). The sensor works on the principle of electrochemical transduction, where the change of sensor impedance is realized by the interactions between the viral proteins attached to the sensor electrode surface and the antibodies. The three sensors were used to test samples from 17 COVID‐19 patients and 3 patients without COVID‐19. Unlike other serological tests, the 3D sensors quantitatively detected antibodies at a concentration as low as picomole within 10–12 s in human plasma samples. We found that the studied COVID‐19 patients had higher concentrations of antibodies to spike proteins (RBD and S1) than to the N protein. These results demonstrate the enormous potential of the rapid antibody test platform for understanding patients' immunity, disease epidemiology and vaccine efficacy, and facilitating the control and prevention of infectious epidemics.

MnO2-Modified 3D-Printed Lattice Photo-Bioelectrode for Photosynthetic Energy Conversion from Spinach Thylakoids

Photosynthetic bio-solar energy conversion has been widely investigated as a promising potential in the field of renewable energy due to its high internal quantum efficiency. Thylakoid membranes (TMs) are organelles in chloroplasts where photosynthesis occurs. Once photosynthesis begins photosynthetic electrons (PEs) were generated, and they were transferred via proteins embedded in TMs by sequential redox reactions. To efficiently collect PEs, several approaches were reported to improve electrical connections such as carbon nanotube modified electrode [1], graphene oxide (GO)/TMs composites [2], or ruthenium oxide (RuO2) modified electrode [3]. As another approach, TM-alginate films were electrosprayed on SU-8 micro-pillar electrode to enlarge the electrochemical surface area between TMs and electrode [4]. However, the previous works were still limited in using two-dimensional electrodes with a marginal increase of electrode surface area.In this study, we aimed to maximize the electrochemically-active surface of TM-decorated bioelectrodes using 3D-printed polymeric lattices. We designed an octet-truss lattice structure with a high specific surface area. For the large surface area of the electrode with a high volume fraction, a strut diameter of the lattice was set to be 0.4 mm in the unit cell of an octet-truss lattice with a total length of 2.5 mm. To maximize light transmission, the octet-truss lattice was 3D-printed with a clear resin using stereolithography (SLA). To grant electrical conductivity on the hydrophobic nature of poly(urethane dimethacrylate) resin, poly(dopamine) (PDA) was polymerized as a binder on SLA-printed lattices followed by immersion in the 1.3 wt% of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solution for 30 min. After immersion in PEDOT:PSS solution, PEDOT:PSS coated lattice was gently dried to remove the remaining solution with N2 gun and annealed in a vacuum oven at 120 ℃ for 15 min. On the other hand, the intrinsic electrical conductivity of PEDOT:PSS is lower than 1 S/cm. Therefore, to enhance the conductivity of annealed PEDOT:PSS layer, PEDOT:PSS coated lattice was immersed 5 wt% of ethylene glycol (EG) solution. Then, EG-treated PEDOT:PSS coated lattice was annealed in a vacuum oven as above described. Due to the removal of surplus insulating PSS chains and reorientation of PEDOT chains, the resistance of EG-treated PEDOT:PSS coated lattice was measured thousands of times lower than no treated lattice. A manganese oxide (MnO2) was electrochemically deposited for improved attachment to TMs at 0.5 V vs Ag/AgCl for 2 min. Then, TMs of 1 mg chl/ml were drop-cast on MnO2/PEDOT:PSS/PDA octet-truss lattice electrode. Each intermediate product was carefully analyzed using SEM, optical microscopy, and fluorescence spectroscopy. The PE currents from TM/MnO2/PEDOT:PSS/PDA octet-truss lattice electrode were measured and compared to a flat electrode and with different layers of lattice structures. With 2 layers of TM/MnO2/PEDOT:PSS/PDA octet-truss lattice electrode, the PE currents were increased 4 times compared to PE currents of the flat electrode. Acknowledgement This work was supported by the National Research Foundation of Korea(NRF) Grant funded by the Korean Government(MSIT) (No. 2020R1A2C3013158), and the Human Resources Development program (No.20204030200110) of the Korea Institute of Energy Technology Evaluation and Planning(KETEP) grant funded by the Korea government Ministry of Trade, Industry and Energy.

Enhancing Electrochemical Performance of Stretchable/Flexible Li‐Ion Microbatteries by Tuning Microstructured Electrode Dimensions

AbstractIncreasing surface area between electrodes and electrolytes drastically has proven to improve electrochemical performances of microbatteries. 3D surface enhancement owing to the design of micropillar electrodes has permitted to fulfill this need while maintaining the same footprint area. Lithium nickel manganese oxide (cathode) and Lithium titanate (anode) micropillars with different sizes are successfully fabricated on aluminum foils by laser ablation technique and are then separated by a polymer electrolyte to form stretchable lithium‐ion microbatteries. The electrochemical performance of full batteries composed of different micropillar sizes is studied in detail. The importance of controlling the width of micropillars is demonstrated and correlated with a simple theoretical model to optimize the battery properties. It is also shown that areal capacity values can be enhanced by improving the electrode/electrolyte interfaces using a simple treatment under vacuum.

3D-printed hierarchical pillar array electrodes for high-performance semi-artificial photosynthesis.

The rewiring of photosynthetic biomachineries to electrodes is a forward-looking semi-artificial route for sustainable bio-electricity and fuel generation. Currently, it is unclear how the electrode and biomaterial interface can be designed to meet the complex requirements for high biophotoelectrochemical performance. Here we developed an aerosol jet printing method for generating hierarchical electrode structures using indium tin oxide nanoparticles. We printed libraries of micropillar array electrodes varying in height and submicrometre surface features, and studied the energy/electron transfer processes across the bio-electrode interfaces. When wired to the cyanobacterium Synechocystis sp. PCC 6803, micropillar array electrodes with microbranches exhibited favourable biocatalyst loading, light utilization and electron flux output, ultimately almost doubling the photocurrent of state-of-the-art porous structures of the same height. When the micropillars' heights were increased to 600 µm, milestone mediated photocurrent densities of 245 µA cm-2 (the closest thus far to theoretical predictions) and external quantum efficiencies of up to 29% could be reached. This study demonstrates how bio-energy from photosynthesis could be more efficiently harnessed in the future and provide new tools for three-dimensional electrode design.

Stable and efficient seawater splitting on a porous phosphate-intercalated NiFe (oxy)hydroxide@NiMoO4 core-shell micropillar electrode

Seawater splitting powered by solar or wind sources is a significant renewable energy storage technology for the production of green hydrogen energy. However, both the chlorine evolution reaction and chloride corrosion are intractable issues in seawater splitting. Here, a porous electrode based on a phosphate-intercalated NiFe (oxy)hydroxide shell coated on a nickel molybdate (NiMoO4) micropillar core (denoted as P-NiFe@NiMoO4) is synthesized through an electrochemical oxidation strategy. During the electrochemical oxidation process, the etching of MoO2 promotes the reconstruction of NiFe (oxy)hydroxide and the formation of porous structures in an alkaline solution. The optimized P-NiFe@NiMoO4 electrocatalysts afford a low overpotential of 258 mV at a current density of 100 mA/cm2 in alkaline seawater. By pairing the anode with a cathode of as-synthesized P-NiMoO, the electrolyzer presents a low voltage of 1.63 V at 100 mA/cm2 in alkaline seawater with excellent stability. Moreover, the remarkable stability of the anode seems to be attributed to the in-situ phosphate formed during the electrochemical oxidation process to passivate chloride corrosion.

Scalable two-tier protruding micro-/nano-optoelectrode arrays with hybrid optical-electrical modalities by hierarchical modular design

In situ spatiotemporal characterization of correlated bioelectrical and biochemical processes in living multicellular systems remains a formidable challenge but can offer crucial opportunities in biology and medicine. A promising approach is to develop bio-interfaced multifunctional micro-/nano-sensor arrays with complementary biophotonic-bioelectronic modalities and biomimetic topology to achieve combined bioelectrical and biochemical detection and tight device-cell coupling. However, a system-level engineering strategy is still missing to create multifunctional micro-/nano-sensor arrays that meet the multifaceted design requirements for in situ spatiotemporal characterizations of living systems. Here, we demonstrate a hierarchical modular design and fabrication approach to develop scalable two-tier protruding micro-/nano-optoelectrode arrays that extend the design space of biomimetic micro-/nano-pillar topology, plasmonic nanoantenna-based biophotonic function in surface-enhanced Raman spectroscopy (SERS), and micro-/nano-electrode-based bioelectronics function in electrochemical impedance spectroscopy (EIS). Notably, two-tier protruding micro-/nano-optoelectrode arrays composed of nanolaminate nanoantenna arrays on top of micropillar electrode arrays can support plasmonic nanocavity modes with high SERS enhancement factors (≈106) and large surface-to-volume ratio with significantly reduced interfacial impedance in EIS measurements. We envision that scalable two-tier protruding micro-/nano-optoelectrode arrays can potentially serve as bio-interfaced multifunctional micro-/nano-sensor arrays for in situ correlated spatiotemporal bioelectrical-biochemical measurements of living multicellular systems such as neuronal network cultures, cancerous organoids, and microbial biofilms.

Heterogeneous Effects on Chemo-Mechanical Coupling Behaviors at the Single-Particle Level

Understanding and alleviating the chemo-mechanical degradation of silicon anodes is a formidable challenge due to the large volume change during operations. Here, for a comprehensive understanding of heterogeneous effects on chemo-mechanical behaviors at the single-particle level, in situ observation of single-crystalline silicon micropillar electrodes under the inhomogeneous extrinsic conditions, taken as an example, was made. The observation shows that the anisotropic deformation patterns and fracture starting sites are reshaped with the combination of the inhomogeneous electrochemical driving force for charge transfer at the interface between the silicon micropillar and the electrolyte, and crystal orientation-dependent lithiation dynamics. Also, the numerical simulation unravels the underlying mechanisms of deformation and fracture behaviors, and well predicts the relative depth of lithiation at the time of crack initiation under heterogeneous conditions. The results show that heterogeneities arising from extrinsic conditions may induce inhomogeneous mechanical damage and tailor lithiation degree at an active particle level, offering insights into designing large-volume-change battery particles with good mechanical integrity and electrochemical performance under heterogeneous impacts.

Antibody Tests: Sensing of COVID‐19 Antibodies in Seconds via Aerosol Jet Nanoprinted Reduced‐Graphene‐Oxide‐Coated 3D Electrodes (Adv. Mater. 7/2021)

In article number 2006647, Rahul Panat and co-workers report the development of a 10-second COVID-19 antibody test that represents the fastest detection of this pathogen biomarker. The test uses an electrochemical cell consisting of aerosol jet nanoprinted 3D micropillar electrodes coated with reduced graphene oxide and viral antigens. This generic platform could be a game-changer in controlling the spread of infectious diseases during pandemics.

Dopamine sensing with robust carbon nanotube implanted polymer micropillar array electrodes fabricated by coupling micromolding and infiltration coating processes

Flexible electrochemical sensors are preferred to monitor the levels of neurotransmitters which are important to understand human central nervous system and diagnose/treat many brain-related diseases. Robust conductive coating is essential for these neural sensors to promote their sensitivity and selectivity. By coupling micropattern molding and infiltration coating processes, we successfully fabricated composite electrodes with part of carbon nanotubes (CNT) exposed to the sample while the rest of it embedded in polymer micropillars and the sensor base. Together with the micropillar array pattern, the partial implantation configuration provides the electrodes a stable coating with minimal conductivity loss in a 7-day impedance test. Cyclic voltammetric studies indicate a quasi-reversible behavior of dopamine and a retention of 93% signal after a two-hour fouling experiment. When detecting dopamine via differential pulse voltammetry (DPV), it exhibits a detection limit of 0.77 nM, quantification limit of 2.34 nM, and sensitivity of 0.453 nA/nM. Well separated DPV peaks were observed when sensing dopamine without and with excess uric acid, ascorbic acid, and glucose, common interfering bioactive compounds. Given successful demonstration on both rigid and soft substrate surfaces, this new fabrication method and its sensor products could help advance important in vivo neurotransmitter sensing and other electrochemical applications.