The photoelectrochemical (PEC) activity of microstructured electrodes remains low despite the highly enlarged surface area and enhanced light harvesting. To obtain a deeper understanding of the effect of 3D geometry on the PEC performance, well-defined WO₃/n-Si and WO₃/pn-Si micropillar arrays are fabricated and subjected to a quantitative analysis of the relationship between the geometry of the micropillars (length, pitch) and their PEC activity. For WO₃/n-Si micropillars, it is found that the photocurrent increases for WO₃/n-Si pillars, but not in proportion to the increase in surface area that results from increased pillar length or reduced pillar pitch. Optical simulations show that a reduced pillar pitch results in areas of low light intensity due to a shadowing effect. For WO₃/pn-Si micropillar photoelectrodes, the p–n junction enhances the photocurrent density up to a factor of 4 at low applied bias potential (0.8 V vs RHE) compared to the WO₃/n-Si. However, the enhancement in photocurrent density increases first and then decreases with reduced pillar pitch, which scales with the photovoltage generated by the p–n junction. This is related to an increased dead layer of the p–n junction Si surface, which results in a decreased photovoltage even though the total surface area increases.

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A microfluidic protein aggregation device (microPAD) that allows the user to perform a series of protein incubations with various concentrations of two reagents is demonstrated. The microfluidic device consists of 64 incubation chambers to perform individual incubations of the protein at 64 specific conditions. Parallel processes of metering reagents, stepwise concentration gradient generation, and mixing are achieved simultaneously by pneumatic valves. Fibrillation of bovine insulin was selected to test the device. The effect of insulin and sodium chloride (NaCl) concentration on the formation of fibrillar structures was studied by observing the growth rate of partially folded protein, using the fluorescent marker Thioflavin-T. Moreover, dual gradients of different NaCl and hydrochloric acid (HCl) concentrations were formed, to investigate their interactive roles in the formation of insulin fibrils and spherulites. The chip-system provides a bird’s eye view on protein aggregation, including an overview of the factors that affect the process and their interactions. This microfluidic platform is potentially useful for rapid analysis of the fibrillation of proteins associated with many misfolding-based diseases, such as quantitative and qualitative studies on amyloid growth.

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Wireless photoelectrochemical (PEC) devices promise easy device fabrication as well as reduced losses. Here, the design and fabrication of a stand-alone ion exchange material-embedded, Si membrane-based, photoelectrochemical cell architecture with micron-sized pores is shown, to overcome the i) pH gradient formation due to long-distance ion transport, ii) product crossover, and iii) parasitic light absorption by application of a patterned catalyst. The membrane-embedded PEC cell with micropores utilizes a triple Si junction cell as the light absorber, and Pt and IrO _x as electrocatalysts for the hydrogen evolution reactions and oxygen evolution reactions, respectively. The solar-to-hydrogen efficiency of 7% at steady-state operation, as compared to an unpatterned η _PV of 10.8%, is mainly attributed to absorption losses by the incorporation of the micropores and catalyst microdots. The introduction of the Nafion ion exchange material ensures an intrinsically safe PEC cell, by reducing the total gas crossover to <0.1%, while without a cation exchange membrane, a crossover of >6% is observed. Only in a pure electrolyte of 1 m H ₂ SO ₄ , a pH gradient-free system is observed thus completely avoiding the build-up of a counteracting potential.

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A microfluidic platform or "microfluidic batch adsorption device" is presented, which performs two sets of 9 parallel protein incubations with/without adsorbent particles to achieve an adsorption isotherm of a protein in a single experiment. The stepwise concentration gradient of a target protein was created by the integration of microvalves into the device. The nanoliter-scale reactor (41 nl) allows about 5000 times reduction of sample consumption and fast analysis compared with a conventional 96 well plate. The integration of two sets of parallel reactors as reference reactors and adsorption reactors, respectively, in a single microfluidic format has many advantages, such as the exclusion of the influence of undesired experimental fluctuations, and the possibility of real-time tracing of adsorption processes. We performed batch adsorption of albumin-fluorescein isothiocyanate conjugate (FITC-BSA) on polymeric particles (Source 15Q) to obtain an adsorption isotherm. The obtained on-chip parameters maximum adsorption amount (Q_max) and adsorption constant (K_eq) were 0.33 ± 0.03 ng per particle and 0.97 ± 0.22 L g^-1, respectively, which are in good agreement with off-chip values (Q_max = 0.34 ± 0.01 ng per particle and K_eq = 0.81 ± 0.10 L g^-1). On-chip adsorption isotherms of FITC-BSA at various concentrations of sodium chloride (NaCl) were measured to evaluate the effect of this salt on the adsorption capability of Source 15Q. The microfluidic device serves as a new analytical tool, useful in biotechnological and industrial applications, where the adsorption behavior of (bio)molecules on commercial adsorbent particles plays critical roles, such as protein separation and purification, detection of analytes and biomarkers, and solid-phase immunoassays.

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A microfluidic platform or "microfluidic mapper" is demonstrated, which in a single experiment performs 36 parallel biochemical reactions with 36 different combinations of two reagents in stepwise concentration gradients. The volume used in each individual reaction was 36 nl. With the microfluidic mapper, we obtained a 3D enzyme reaction plot of horseradish peroxidase (HRP) with Amplex Red (AR) and hydrogen peroxide (H2O2), for concentration ranges of 11.7 μM to 100.0 μM and 11.1 μM to 66.7 μM for AR and H2O2, respectively. This system and methodology could be used as a fast analytical tool to evaluate various chemical and biochemical reactions especially where two or more reagents interact with each other. The generation of dual concentration gradients in the present format has many advantages such as parallelization of reactions in a nanoliter-scale volume and the real-time monitoring of processes leading to quick concentration gradients. The microfluidic mapper could be applied to various problems in analytical chemistry such as revealing of binding kinetics, and optimization of reaction kinetics.

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We present a novel microfluidic system for the pH-gradient focusing of proteins with the integration of 16 parallel micro-mixers, a micro-column, and a multiplexer. In this work we successfully achieved the creation of 16 non-linear gradients and the generation of a solid-phase micro-column for the realization of anion exchange chromatography on a single chip. With the device we demonstrated the separation of a protein mixture of R-phycoerythrin and FITC-BSA based on pH-gradient chromatofocusing.@en