Franz Keplinger

Miniaturized multi-enzyme biosensors integrated with pH sensors on flexible polymer carriers for in vivo applications

Abstract An electrochemical glucose sensor has been integrated, together with a pH sensor, on a flexible polyimide substrate for in vivo applications. The glucose sensor is based on the measurement of H 2 O 2 produced by the membrane-entrapped enzyme glucose oxidase (GOD). To minimize electrochemical interference, an electrode configuration was designed to perform differential measurements. The solid-state pH sensor employs a PVC-based neutral carrier membrane. The enzymes GOD and catalase were immobilized into two layers of photolithographically patterned hydrogels. The intended use of this device is the short-term monitoring of glucose and pH in intensive care units and operating theatres, especially for neurosurgical applications. The developed immobilization technique can also be used to create integrated multi-sensor chips for clinical analysers. The glucose and pH sensor exhibited excellent performance during tests in buffer solutions, serum and whole blood.

Miniaturized sensors for the viscosity and density of liquids-performance and issues

This paper reviews our recent work on vibrating sensors for the physical properties of fluids, particularly viscosity and density. Several device designs and the associated properties, specifically with respect to the sensed rheological domain and the onset of non-Newtonian behavior, are discussed.

Characterizing Vibrating Cantilevers for Liquid Viscosity and Density Sensing

Miniaturized liquid sensors are essential devices in online process or condition monitoring. In case of viscosity and density sensing, microacoustic sensors such as quartz crystal resonators or SAW devices have proved particularly useful. However, these devices basically measure a thin-film viscosity, which is often not comparable to the macroscopic parameters probed by conventional viscometers. Miniaturized cantilever-based devices are interesting alternatives for such applications, but here the interaction between the liquid and the oscillating beam is more involved. In our contribution, we describe a measurement setup, which allows the investigation of this interaction for different beam cross-sections. We present an analytical model based on an approximation of the immersed cantilever as an oscillating sphere comprising the effective mass and the intrinsic damping of the cantilever and additional mass and damping due to the liquid loading. The model parameters are obtained from measurements with well-known sample liquids by a curve fitting procedure. Finally, we present the measurement of viscosity and density of an unknown sample liquid, demonstrating the feasibility of the model.

Development of miniaturized semiconductor flow sensors

Abstract Miniaturized flow sensors based on thin film germanium thermistors were developed offering high flow sensitivities and short response times. The thermistors are placed on a silicon nitride diaphragm carried by a silicon frame. Using the controlled overtemperature scheme the measurable airflow rate ranges from 0.6 to 150 000 cm 3 /h. In this paper we mainly report on the dynamic properties of the sensor. The response of the sensor to step changes of the heater power will be compared with its response to shock waves for both the constant power mode and the constant overtemperature operating mode. A simple arrangement for the generation of acoustic shock waves will be presented.

A suspended plate viscosity sensor featuring in-plane vibration and piezoresistive readout

Miniaturized viscosity sensors are often characterized by high-resonance frequencies and low-vibration amplitudes. The viscosity parameter obtained by such devices is therefore not always comparable to those probed by conventional laboratory equipment. We present a novel micromachined viscosity sensor with relatively low operating frequencies in the kHz range. The sensor utilizes Lorentz force excitation and piezoresistive readout. The resonating part consists of a rectangular plate suspended by four beam springs. The first mode of vibration is an in-plane mode. Thus, the contribution of the moving plate to the device damping is low, whereas the overall mass is high. This principle improves the quality factor and gives additional freedom to the device designer. This paper presents the device concept, the fabrication process and a prototype of the viscosity sensor. Measurement results demonstrate the feasibility of the device and show that the damping of the device is an appropriate measure for the viscosity.

A micromachined doubly-clamped beam rheometer for the measurement of viscosity and concentration of silicon-dioxide-in-water suspensions

In this contribution we demonstrate the feasibility of a sensor system for viscosity and concentration measurement of complex liquids, in particular suspensions of silicon dioxide particles in water. The sensor system is based on a doubly clamped micromachined beam vibrating in the sample liquid, and an optical readout utilizing a DVD player pickup head. The vibrating beam features resonance frequencies in the range of several 10 kHz, and higher mechanical amplitudes than microacoustic sensors, e.g., quartz thickness shear mode (TSM) resonators or surface acoustic wave (SAW) devices. We show that the damping of the beam is dominated by the viscosity of the liquid, and that this relation also holds for the considered complex liquids, whereas a TSM resonator sensor fails to detect the steady state shear viscosity of the suspensions.

Microfluidic Biosensing Systems Using Magnetic Nanoparticles

In recent years, there has been rapidly growing interest in developing hand held, sensitive and cost-effective on-chip biosensing systems that directly translate the presence of certain bioanalytes (e.g., biomolecules, cells and viruses) into an electronic signal. The impressive and rapid progress in micro- and nanotechnology as well as in biotechnology enables the integration of a variety of analytical functions in a single chip. All necessary sample handling and analysis steps are then performed within the chip. Microfluidic systems for biomedical analysis usually consist of a set of units, which guarantees the manipulation, detection and recognition of bioanalytes in a reliable and flexible manner. Additionally, the use of magnetic fields for performing the aforementioned tasks has been steadily gaining interest. This is because magnetic fields can be well tuned and applied either externally or from a directly integrated solution in the biosensing system. In combination with these applied magnetic fields, magnetic nanoparticles are utilized. Some of the merits of magnetic nanoparticles are the possibility of manipulating them inside microfluidic channels by utilizing high gradient magnetic fields, their detection by integrated magnetic microsensors, and their flexibility due to functionalization by means of surface modification and specific binding. Their multi-functionality is what makes them ideal candidates as the active component in miniaturized on-chip biosensing systems. In this review, focus will be given to the type of biosening systems that use microfluidics in combination with magnetoresistive sensors and detect the presence of bioanalyte tagged with magnetic nanoparticles.

Resonant pressure wave setup for simultaneous sensing of longitudinal viscosity and sound velocity of liquids

Increasing demands for online monitoring of liquids have not only resuted in many new devices relying on well-established sensing parameters like shear viscosity but also initiated research on alternative parameters. Recently, the longitudinal viscosity has been evaluated as a promising candidate because the devices arising enable the bulk of the liquid to be probed rather than a thin surface layer. We report on a multi-purpose sensor which allows simultaneous measurement of the sound velocity and longitudinal viscosity of liquids. The device embodiment features a cube-shaped chamber containing the sample liquid, where one boundary surface carries a flush-mounted PZT transducer. In operation, the transducer induces standing, resonant pressure waves in the liquid under test. We studied the influences of sound velocity and longitudinal viscosity on the generated pressure waves by means of the Navier–Stokes equation for adiabatic compressible liquids and exploited both parameters as the basic sensing mechanism. Furthermore, a three-port network model describing the interaction of the transducer and sample liquid was developed in order to be applied for extracting the parameters of interest from the raw measurement data. Finally, we demonstrate the device and method by carrying out and discussing test measurements on glycerol–water solutions.

Robust Precision Position Detection With an Optical MEMS Hybrid Device

For vibration and displacement sensors, robustness is one of the key requirements. Optical measurement concepts are among the most promising possibilities to achieve it. The presented microoptoelectromechanical system sensor modulates a light flux by means of two congruently placed aperture gratings: one etched into a seismic mass and the other fixed to the sensor package. Commercially available LED and photodetector components at the top and bottom of the sandwich structure generate and detect this modulated light flux and allow for a cost-effective implementation. The prototype used for experimental verification is actuated by inertial forces and exhibits a high sensitivity of 0.85 mV/nm for displacements of the seismic mass and a corresponding noise level of about 14 pm/√Hz. This sensitivity and noise level can be further improved, paving the way for small, lightweight, robust, and high-precision displacement sensors for a large variety of applications.

A Novel Sensor System for Liquid Properties Based on a Micromachined Beam and a Low-Cost Optical Readout

For the measurement of liquid parameters like viscosity and density vibrating micromachined structures offer useful alternatives to bulky conventional measurement equipment. Evaluating the shift of the resonance frequency and the change of the damping factor of such devices allows the simultaneous determination of viscosity and density. Furthermore, these sensors can even be used for complex liquids like emulsions where other microacoustic sensors like TSM quartz resonators, in comparison to conventional laboratory viscometers, measure in a different rheological domain. In our contribution we present a novel implementation of a viscosity and density sensor system utilizing a doubly-clamped vibrating micromachined beam. The beam deflection is determined by means of a laser pickup head as it is used, e.g., in DVD drives, yielding high sensitivity and a low-cost setup at the same time. The measured damping factor correlates well with the viscosity of the respective liquid, whereas the resonance frequency is also influenced by the liquids density.