Alexander Eden

Conventional strategies for achieving electromechanical stability in MEMS zipping actuators often rely on complex assemblies, feedback controllers, or multilayer structures. Here, we demonstrate a fundamentally different design paradigm: programmable multistability achieved solely through engineered shaping of the fixedelectrode profile. By fabricating microprofiled silicon cavities with tailored curvature sequences, we realize actuators that exhibit two, three, or more discrete, voltage-addressable stable states, with activation thresholds on the order of 100 V. An energy-minimization framework accurately predicts these responses, with experiments matching model predictions within 5% of total displacement. We further highlight two application opportunities: (i) amplitude-programmable actuators capable of micrometer-precision positioning, and (ii) threshold-sensitive mechanical switches operating with sub-microwatt power consumption. Together, these results establish "profile engineering" as a powerful and general strategy for encoding mechanical logic directly into surface geometryshifting system complexity from active electronics into passive structure-and enabling compact, low-power adaptive microsystems.

Three-dimensional (3D) localization and single-particle tracking (SPT) are powerful techniques for characterizing shape, motion, and deformation of materials. However, these methods often require complex optical setups that demand expert use, limiting their accessibility to the wider scientific community. This paper presents a new technique called individualized defocusing particle tracking (IDPT), which uses intrinsic aberrations in ordinary lab microscopes to perform 3D surface measurements at camera frame rates. The IDPT technique comprises a simple in-situ calibration procedure and 3D localization algorithm that leverages particles’ unique defocusing patterns to enhance measurement sensitivity while compensating for optics-induced bias errors. Our empirical approach implicitly transforms systematic optical effects—including those caused by misalignment or defects of optical elements—into valuable sources of positional information, allowing our method to work with common lab microscopes. We validate the IDPT technique through synthetic and benchtop experiments involving rigid body motion of a planar substrate and the dynamic deformation of elastic discs, demonstrating that our algorithm surpasses comparable SPT algorithms in accuracy and resolution. The IDPT technique is simple yet robust, offering broad applicability for dynamic surface profilometry and deformation analysis.

Due to the surface‐dominant nature of electrokinetic ion transport in confined geometries, ionic currents in nanofluidic channels are fundamentally governed by the interfacial chemistry of the constituent substrates. In this work, the intrinsic coupling between charge‐regulated oxide surfaces and local changes in concentration and pH induced during the operation of bipolar nanofluidic diodes is numerically explored. Using a heterogeneous SiO₂‐Al₂O₃ nanochannel as a representative example, field‐dependent ion accumulation and depletion effects are shown to have a marked effect on the local surface chemistry and resulting charge density of the amphoteric Al₂O₃ surface in particular. While the SiO₂ surface tends to remain relatively indifferent to the presence of an applied potential due to its low point of zero charge (PZC), the comparatively high PZC of Al₂O₃ renders it much more susceptible to the extent of ion accumulation and depletion events which drive localized concentration and pH changes. Including this surface coupling in models can be necessary to capture the true behavior of real‐world devices; comparison with a fixed‐charge model demonstrates that only a fully coupled model can quantitatively reproduce reported experimental current measurements in heterogeneous SiO₂‐Al₂O₃ nanochannels, the limiting behavior of which is revealed to stem from this surface‐to‐bulk coupling.

Nanofluidic channels with a bio-inspired polydopamine and poly-l-lysine coating exhibit significant diodicity and are capable of exceeding 1000-fold current rectification under certain conditions.

We report on the investigation of electropreconcentration phenomena in micro‐/nanofluidic devices integrating 100 μm long nanochannels using 2D COMSOL simulations based on the coupled Poisson–Nernst–Planck and Navier–Stokes system of equations. Our numerical model is used to demonstrate the influence of key governing parameters such as electrolyte concentration, surface charge density, and applied axial electric field on ion concentration polarization (ICP) dynamics in our system. Under sufficiently extreme surface‐charge‐governed transport conditions, ICP propagation is shown to enable various transient and stationary stacking and counter‐flow gradient focusing mechanisms of anionic analytes. We resolve these spatiotemporal dynamics of analytes and electrolyte ICP over disparate time and length scales, and confirm previous findings that the greatest enhancement is observed when a system is tuned for analyte focusing at the charge, excluding microchannel, nanochannel electrical double layer (EDL) interface. Moreover, we demonstrate that such tuning can readily be achieved by including additional nanochannels oriented parallel to the electric field between two microchannels, effectively increasing the overall perm‐selectivity and leading to enhanced focusing at the EDL interfaces. This approach shows promise in providing added control over the extent of ICP in electrokinetic systems, particularly under circumstances in which relatively weak ICP effects are observed using only a single channel.

Surface coatings are extensively used in capillary electrophoresis to increase separation efficiency and resolution. The stability of these coatings across a wide pH range is desirable to achieve repeatable migration times; therefore, a comprehensive understanding of coating degradation timescales is needed. We present a novel platform for automated zeta potential analysis based upon current monitoring that delivers improved time resolution over the existing methods. Using our platform, we measure the zeta potential continuously during aminosilane coating reactions and infer changes in the surface composition. We found that the change in the zeta potential after coating depended on the monomer type and solvent, while its stability was influenced by the coating solvent and exposure pH. Our versatile platform provides an elegant approach for evaluating the molecular composition, reactivity, and stability of surfaces in real time.

Bipolar electrodes (BPEs) are conductors that, when exposed to an electric field, polarize and promote the accumulation of counter-ionic charge near their poles. The rich physics of electrokinetic behavior near BPEs have not yet been rigorously studied, with our current understanding of such bipolar effects being restricted to steady-state conditions (under constant applied fields). Here, we reveal the dynamic electrokinetic and electrochemical phenomena that occur near nanoconfined BPEs throughout all stages of a reaction. Specifically, we demonstrate, both experimentally and through numerical modeling, that the removal of an electric field produces solution-phase charge imbalances in the vicinity of the BPE poles. These imbalances induce intense and short-lived nonequilibrium electric fields that drive the rapid transport of ions towards specific BPE locations. To determine the origin of these electrokinetic effects, we monitored the movement and fluorescent behavior (enhancement or quenching) of charged fluorophores within well-defined nanofluidic architectures via real-time optical detection. By systematically varying the nature of the fluorophore, the concentration of the electrolyte, the strength of the applied field, and oxide growth on the BPE surface, we dissect the ion transport events that occur in the aftermath of field-induced polarization. The results contained in this work provide new insights into transient bipolar electrokinetics that improve our understanding of current analytical platforms and can drive the development of new micro- and nano-electrochemical systems.