Practical Insights into the Impedance Response of Interdigitated Electrodes: Extraction of Relative Static Permittivity and Electrolytic Conductivity

This work aims to provide a detailed understanding of the challenges related to the computation of the relative static permittivity and electrolytic conductivity of a sample medium from its impedance response recorded with interdigitated electrode (IDE) geometries. Within the scope of the study, impedance data has been measured and evaluated for a total of nine sample media using two distinct IDE geometries. Particular emphasis is laid upon the compensation of parasitic influences affecting the impedance response. With the raw data supporting this study fully disclosed, the reader is offered the opportunity to comprehensively retrace the evaluation procedure proposed in the text

Simulation-based evaluation of single pass continuous diafiltration with alternating permeate flow direction

In the framework of modern bioprocessing continuous ultrafiltration/diafiltration (UF/DF) is getting increasingly popular. However, while continuous UF can be easily implemented using a so-called single pass tangential flow filtration (SPTFF) module, continuous DF requires a more complicated setup including several SPTFF modules and intermittent dilution steps. Recently, we introduced a novel module design for continuous DF allowing simultaneous delivery of fresh buffer while withdrawing the permeate, thus achieving high degrees of buffer exchange within a single unit. In addition, the system allows to cyclically switch the flow direction of DF buffer through the membranes. Those uncommon features, however, also make it more difficult to determine an operation optimum experimentally by means of trial and error. Therefore, here a detailed finite element model of the physical processes within the module is presented, predicting key figures such as the obtained diafiltration efficiency and the resulting pressures. Because within the module all flow channels are filled by a 3D-printed porous grid supporting the membranes from both sides, the modified Brinkman equation was used to simulate the hydrodynamics, while common mass balance differential equations including accumulation, convection, and an anisotropic dispersion term were used for the simulation of concentration profiles of dissolved species. The predicted key figures are in good agreement with experimental results, obtained for feed solutions including up to 50 g/L of protein and being operated with and without switching the flow direction of the diafiltration buffer. A thorough parameter study reveals that the module shows the best performance for unidirectional flow of the diafiltration buffer, reaching diafiltration efficiencies independence to the applied diavolumes which are comparable to the ones of a conventional multi-stage setup using three SPTFF modules. Therefore, the simulation-based evaluation of optimum operation conditions reveals that the new module design has the potential to realize truly continuous diafiltration setups with high efficiency, requiring only one unit and no extra external piping for returning diafiltration in counterflow. Such simplified setups should be especially useful in small, flexible processing plants as they are increasingly demanded in the biopharmaceutical industry

Configurable 3D Printed Microfluidic Multiport Valves with Axial Compression

In the last decade, the fabrication of microfluidic chips was revolutionized by 3D printing. It is not only used for rapid prototyping of molds, but also for manufacturing of complex chips and even integrated active parts like pumps and valves, which are essential for many microfluidic applications. The manufacturing of multiport injection valves is of special interest for analytical microfluidic systems, as they can reduce the injection to detection dead volume and thus enhance the resolution and decrease the detection limit. Designs reported so far use radial compression of rotor and stator. However, commercially available nonprinted valves usually feature axial compression, as this allows for adjustable compression and the possibility to integrate additional sealing elements. In this paper, we transfer the axial approach to 3D-printed valves and compare two different printing techniques, as well as six different sealing configurations. The tightness of the system is evaluated with optical examination, weighing, and flow measurements. The developed system shows similar performance to commercial or other 3D-printed valves with no measurable leakage for the static case and leakages below 0.5% in the dynamic case, can be turned automatically with a stepper motor, is easy to scale up, and is transferable to other printing methods and materials without design changes

Predicting the potential of capacitive deionization for the separation of pH‐dependent organic molecules

One of the main steps in the biotechnological production of chemical building blocks, such as, e.g. bio-based succinic acid which is used for lubricants, cosmetics, food, and pharmaceuticals, is the isolation and purification of the target molecule. A new approach to isolate charged, bio-based chemicals is by electrosorption onto carbon surfaces. In contrast to ion exchange, electrosorption does not require additional chemicals for elution and regeneration. However, while the electrosorption of inorganic salts is well understood and in commercial use, the knowledge about electrosorption of weak organic acids including the strong implications of the pH-dependent dissociation and their affinity towards physical adsorption must be expanded. Here, we show a detailed discussion of the main pH-dependent effects determining the achievable charge efficiencies and capacities. An explicit set of equations allows the fast prediction of the named key figures for constant voltage and constant current operation. The calculated and experimental results obtained for the electrosorption of maleic acid show that the potential-free adsorption of differently protonated forms of the organic acid play a dominating role in the process. At pH 8 and a voltage threshold of 1.3 V, charge efficiencies of 25% and capacities around 40 mmol/kg could be reached for a constant current experiment. While this capacity is clearly below that of ion exchange resins, the required carbon materials are inexpensive and energy costs are only about 0.013 €/mol. Therefore, we anticipate that electrosorption has the potential to become an interesting alternative to conventional unit operations for the isolation of charged target molecules

On the Integration of Dielectrometry into Electrochemical Impedance Spectroscopy to Obtain Characteristic Properties of a Dielectric Thin Film

We demonstrate a novel impedimetric approach providing unprecedented insight into characteristic properties of dielectric thin films covering electrode surfaces. The concept is based on the joint interpretation of electrochemical impedance spectroscopy (EIS) together with dielectrometry (DEM) whose informative value is mutually interconnected. The advantage lies in the synergistic compensation of individual shortcomings adversely affecting conventional impedimetric analysis strategies relying exclusively on either DEM or the traditional EIS approach, which in turn allows a reliable determination of thickness and permittivity values. The versatility of the method proposed is showcased by an in-situ growth-monitoring of a nanoporous, crystalline thin film (HKUST-1) on an interdigitated electrode geometry

New Approach for Investigating Diffusion Kinetics Within Capacitive Deionization Electrodes Using Electrochemical Impedance Spectroscopy

Capacitive deionization (CDI) has become an important research topic in terms of water purification as it is a cost- and energy efficient approach for the desalination of brackish water. Carbon- based materials are often used as electrodes in this process due to a variety of morphologies and their suitable performance in this field. In recent studies it has been already shown that a conscientiously chosen set of electrode properties has an enormous effect on the performance behavior of CDI cells. However, most of the studies focus on the optimization of the electrosorption capacity, while the question on how material properties influence the kinetic behavior of a CDI setup has been less intensively studied so far. Here we show that the kinetic effects of electrode materials can be studied in great detail by using electrochemical impedance spectroscopy (EIS). EIS studies of CDI electrodes have been reported before, however, in contrast to these we introduce a method of presenting and analyzing EIS results. This is especially suitable for extracting the frequency ranges in which different rate limiting mechanisms dominate. The new Nyquist Incline Frequency plot (NIF) shows the local slope of the Nyquist plot in dependency of the applied frequency. By this, electron transfer and mass transfer mechanisms which show a characteristic slope in the classical Nyquist plot can be directly visualized together with the information in which time domain they occur. The data derived from the new EIS plot show a clear correlation to pore size distributions from BET measurements, as well as effective capacities and electrosorption kinetics, extracted from CDI experiments. Therefore, we think that by using the NIF plot electrode materials for CDI processes can be conveniently characterized and compared within a single diagram, helping to standardize CDI material development

Magnetism and Afterglow United: Synthesis of Novel Double Core‐Shell Eu2+^{2+}‐doped Bifunctional Nanoparticles

Afterglow–magnetic nanoparticles (NPs) offer enormous potential for bioimaging applications, as they can be manipulated by a magnetic field, as well as emitting light after irradiation with an excitation source, thus distinguishing themselves from fluorescent living cells. In this work, a novel double core–shell strategy is presented, uniting co‐precipitation with combustion synthesis routes to combine an Fe$_{3}$O$_{4}$ magnetic core (≈15 nm) with an afterglow SrAl$_{2}$O$_{4}$:Eu$^{2+}$,Dy$^{3+}$ outer coat (≈10 nm), and applying a SiO$_{2}$ protective middle layer (≈16 nm) to reduce the luminescence quenching caused by the Fe core ions. The resulting Fe$_{3}$O$_{4}$@SiO$_{2}$@SrAl$_{2}$O$_{4}$:Eu$^{2+}$,Dy$^{3+}$ NPs emit green light attributed to the 4f$^{6}$5d$^{1}$→4f$^{7}$ ($^{8}$S$_{7/2}$) transition of Eu$^{2+}$ under UV radiation and for a few seconds afterwards. This bifunctional nanocomposite can potentially be applied for the detection and separation of cells or diagnostically relevant molecules

Continuous single pass diafiltration with alternating permeate flow direction for high efficiency buffer exchange

Looking at current trends within downstream processing (DSP) of high value bioproducts, it shows that there are ongoing efforts in replacing batch processes by continuous variants. However, a unit procedure which still lacks a simple and compact continuous variant is diafiltration. Here, we present such a single piece of diafiltration equipment achieving continuous buffer exchange of up to 99.90%. The device is composed of a 3D-printed single pass diafiltration (SPDF) module containing two commercial ultrafiltration membranes. While the retentate is flowing through a narrow channel between the two membranes, the channels above and below can supply diafiltration buffer or remove permeate solution. The obtained results illustrate systematically the vulnerability of the device to the effect of concentration polarization at the membrane surface, and that this problem can be strongly reduced using an alternating direction of diafiltration buffer perfusion through the membranes as process inherent backflush. By this, a quasi-stationary operation could be obtained during continuous diafiltration, making the device an interesting option for in-process buffer exchange