Ferenc Ender

Phenylalanine Ammonia-Lyase-Catalyzed Deamination of an Acyclic Amino Acid: Enzyme Mechanistic Studies Aided by a Novel Microreactor Filled with Magnetic Nanoparticles

Phenylalanine ammonia‐lyase (PAL), found in many organisms, catalyzes the deamination of l‐phenylalanine (Phe) to (E)‐cinnamate by the aid of its MIO prosthetic group. By using PAL immobilized on magnetic nanoparticles and fixed in a microfluidic reactor with an in‐line UV detector, we demonstrated that PAL can catalyze ammonia elimination from the acyclic propargylglycine (PG) to yield (E)‐pent‐2‐ene‐4‐ynoate. This highlights new opportunities to extend MIO enzymes towards acyclic substrates. As PG is acyclic, its deamination cannot involve a Friedel–Crafts‐type attack at an aromatic ring. The reversibility of the PAL reaction, demonstrated by the ammonia addition to (E)‐pent‐2‐ene‐4‐ynoate yielding enantiopure l‐PG, contradicts the proposed highly exothermic single‐step mechanism. Computations with the QM/MM models of the N‐MIO intermediates from l‐PG and l‐Phe in PAL show similar arrangements within the active site, thus supporting a mechanism via the N‐MIO intermediate.

Microfluidic multiple cell chip reactor filled with enzyme-coated magnetic nanoparticles — An efficient and flexible novel tool for enzyme catalyzed biotransformations

Biotransformation of L-phenylalanine (L-1a) and five unnatural substrates (rac-1b–f) by phenylalanine ammonia-lyase (PAL) was investigated in a novel microfluidic device (Magne-Chip) that comprises microliter volume reaction cells filled with PAL-coated magnetic nanoparticles (MNPs). Experiments proved the excellent reproducibility of enzymecatalyzed biotransformation in the chip and the excellent reusability of the enzyme layer during 14 h continuous measurement (>98% over 7 repetitive measurements with L-1a). The platform also enabled fully automatic multiparameter measurements with a single biocatalyst loading of about 1 mg PAL-MNP. Computational fluid dynamics (CFD) calculations were used to study the flow field in the chambers and the effect of unintended bubble formation. Optimal flow rate for L-1a reaction and specific activities for rac-1b–f under these conditions were determined.

Thermal transient characterization of semiconductor devices with multiple heat sources-Fundamentals for a new thermal standard

The thermal performance of semiconductor devices is most often specified according to JEDEC standards JESD51 1-14 which describe precisely how various steady-state thermal metrics are to be measured. Most of these metrics represent a thermal resistance between the junction of a semiconductor and some reference; e.g. Rth-JA (Junction-to-ambient), Rth-JB (Junction-to-board), or Rth-JC (Junction-to-case). However all of the above thermal metrics characterize the steady-state behaviour and have been designed for semiconductors with a single heat source only. While the extension of a stationary thermal resistance Rth-JX to the corresponding transient thermal impedance Zth-JX is straightforward the adaptation of existing standards for the characterization of devices with multiple heat sources is far less obvious. This publication gives an overview on the theoretical framework which allows extending the existing thermal metrics in a compliant way.

Thermal compact modeling approach of droplet microreactor based Lab-on-a-Chip devices

The paper presents a novel compact model which enables the thermal analysis of microchannels consisting of continuously moving microdroplets with biologically active content inside. The compact model utilizes the switched capacitor approach to describe the convective heat transfer and as a behavioral model, it can be easily integrated into an IC-MEMS design flow. With this novel approach the temperature profile of the channel can be calculated in minutes compared to conventional numerical techniques that requires days or weeks. The model was validated by a standard CFD solver and a good match was achieved. HighlightsA novel compact model for thermal aware design of droplet reactor based LoC devices is presented.Model is applicable for various boundary conditions e.g. volumetric enzyme reaction.The compact model was validated by conventional CFD solver and resulted in good match.The compact model provided a 450 fold reduction in execution time.As a behavioral model it can be easily integrated into the IC-MEMS design flow.

Thermal characterization of multichip structures

The advances in electronic packaging made it possible to encapsulate several independent semiconductor dice into a single package. In the last decade many packaging configurations are realized which range from the multichip modules to the 3D stack-die structures. Thermal aware design of such structures become complex, though. To understand the thermal behavior of multichip structure containing multiple dissipating elements placed on different dice, the couplings between individual dice have to be characterized. To determine their thermal transfer impedance matrix (TTIM) is a practical way to describe the thermal relations. In this paper we demonstrate the method utilized for TTIM measurements and also show how thermal surroundings (e.g. the PCB the chip is mounted on) affect the thermal relations inside the package. In addition, the temperature dependent non-linearity of the TTIMs is also described.

Optimization of microfluidic flow sensors for different flow ranges by FEM simulation

Finite element simulation and post-processing results of calorimetric type microfluidic mass flow sensors are presented. The output characteristics of a calorimetric flow sensor are functions of the geometrical position of the temperature sensor elements. A given flow sensor (with a given technology on a given substrate) can be optimized for different flow ranges by determining the position of the temperature sensor elements. The simplified mathematical model of the steady-state thermal profile along the microfluidic channel is presented. It is also shown how the output characteristics depend on the position of the temperature sensors and the ratio of the convective and conductive heat transfer. The optimal parameters of a silicon substrate based microfluidic flow sensor for low and for high flow ranges were calculated by FEM simulation. Based on the simulation results the silicon substrate based microfluidic flow sensor could be optimized for different flow ranges.

Heat and mass transfer reduced order modeling approach of droplet microreactor based Lab-on-a-Chip devices

The paper presents a novel reduced order model, which enables the heat and mass transfer analysis of microchannels consisting of continuously moving microdroplets with enzymatic reactions inside. Due to the low Reynolds number, which is typical in microfluidic applications, the hydrodynamics can be described as Taylor-flow. The reduced order model contains the main features of Taylor-flow such as microcirculation and back flow. These are needed to achieve an accurate model of the convective heat and mass transfer. The model has been validated by a standard CFD simulation for two cases: firstly, for a purely thermal problem with constant heat flux through the wall; secondly, for an enzymatic reaction with multi-component diffusion. The results show that in the first case the model yields results with around 5% error. In the second case the error is less than 10%. The accuracy was tested for a wide range of Reynolds numbers. With this novel approach the temperature profile on the channel wall can be calculated in a few hours compared to conventional numerical techniques which would require weeks.

Flow sensor for microfluidic applications — Based on standard PWB technology

In this paper the design and implementation of a microfluidic flow sensor constructed on standard PWB (printed wiring board) and PDMS (Polydimethylsiloxane) technology is presented. The measurement principle is based on convective heat transfer. Calculations and computer aided simulations were performed to find optimal working conditions. A pressure-driven measurement system was built to characterize the device. The measurements confirmed that the flow sensor is able to work from 1.6 ml/min up to 10 ml/min range.

Microfluidic flow-through chambers for higher performance

This paper presents a study on the effect of the different geometries on the velocity distributions in flow-through microchambers. The chambers are filled with magnetic nanopar-ticles and continuous flow is applied in them. Our goal was to find a good and simple geometry to ensure that the flow-through times, therefore the reaction times at most of the laminar flow lines are similar in the chamber. The homogeneity of the velocity field is also desired. For the investigations we performed CFD simulations. A simple method for the reaction time calculation is presented. New geometries are simulated and compared with the original chamber shape used in our previous experiments. The results are promising, in the new geometries the reaction time distribution in the middle of the chamber as well as the velocity field is more homogeneous than in the original case. The simulations were done with the help of the open source CFD software OpenFOAM. Based on the simulation results new microfluidic structures were designed for the further experiments with the magnetic nanoparticles.

Optimal thermal design of CMOS for direct integration of carbon nanotubes

Carbon nanotubes (CNTs) exhibit many remarkable mechanical, electrical and thermal properties, which can be exploited in various smart sensing applications by integrating them in a standard CMOS process. However, such integration process is challenging since CMOS process is not suitable for high temperature application required for local CNT synthesis. This work involves designing power efficient CMOS compatible micro-heaters that can generate CNT growth temperature while maintaining CMOS compatible temperature in the microsystem. One metal interconnect layer and a polysilicon layer available in AMS 0.18 μm CMOS technology have been used to design the micro-heaters. This paper proposes and compares four optimal micro-heater designs alongside their thermal & thermomechanical analysis using ANSYS. The promising results are expected to lead the way for successful implementation of carbon nanotube based sensors in a commercial CMOS process.