Heiko Schäfer

A programmable planar electroosmotic micropump for lab-on-a-chip applications

A programmable planar micropump for lab-on-a-chip applications has been developed. The device consists of an electroosmotic micropump combined with a mass flow sensor in a closed control loop. The micropump design with a vertical arrangement of multiple narrow polymer pumping microchannels reduces the pump area to 1/10 compared to planar micropumps with widened shallow pumping channels. This design allows the fabrication of the channel system in only one process step and is compatible with post-CMOS processing. An analytical model is presented to estimate the flow rate in a field-free pressure-driven section of the channel. It is shown that the micropump with optimized dimensions of rib structures allows high pressure low voltage pumping. The electroosmotic micropump with a suggested design using microchannels of SU-8 and polyacrylamide gel electrodes has been fabricated and tested. The pumping rate is bidirectionally linear and reaches 10 nl min−1 in a 1 cm long pressure-driven channel at an applied voltage of 40 V, which corresponds to a zero-flow pressure of 65 Pa. The micropump has been operated successfully in a closed control loop together with an on-chip mass flow sensor and external control circuitry for flow rates between 0 and 30 nl min−1.

Monolithical integration of polymer-based microfluidic structures on application-specific integrated circuits

In this paper, a concept for a monolithically integrated chemical lab on microchip is presented. It contains an ASIC (Application Specific Integrated Circuit), an interface to the polymer based microfluidic layer and a Pyrex glass cap. The top metal layer of the ASIC is etched off and replaced by a double layer metallization, more suitable to microfluidic and electrophoresis systems. The metallization consists of an approximately 50 nm gold layer and a 10 nm chromium layer, acting as adhesion promoter. A necessary prerequisite is a planarized ASIC topography. SU-8 is used to serve as microfluidic structure because of its excellent aspect ratio. This polymer layer contains reservoirs, channels, mixers and electrokinetic micro pumps. The typical channel cross section is 10μm•10μm. First experimental results on a microfluidic pump, consisting of pairs of interdigitated electrodes on the bottom of the channel and without any moving parts show a flow of up to 50μm per second for low AC-voltages in the range of 5 V for aqueous fluids. The microfluidic system is irreversibly sealed with a 150μm thick Pyrex glass plate bonded to the SU-8-layer, supported by oxygen plasma. Due to capillary forces and surfaces properties of the walls the system is self-priming. The technologies for the fabrication of the microfluidic system and the preparation of the interface between the lab layer and the ASIC are presented.

Microfluidics meets thin-film electronics: a new approach towards an integrated intelligent lab-on-a-chip

A novel architecture for a lab-on-a-chip is presented. The architecture consists of a microfluidic system including integrated optical sensors and thin film transistors. The concept is based on the TFA (Thin Film on ASIC) technology that was developed at University of Siegen. The device consists of two substrate plates that are sandwiched together using oxygen plasma bonding. The thicker bottom plate contains the contacts to the microfluidic channels, while the thinner top plate contains the microfluidic system. The top plate is bonded face down onto the bottom substrate, and, on its reverse side, hydrogenated amorphous silicon (a-Si:H) based pin-diodes and thin film transistors (TFTs) are deposited for optical detection and data transfer. The pin-diodes and the TFTs are manufactured by PECVD (Plasma Enhanced Chemical Vapor Deposition) from silane, ammonia and dopant gases at temperatures around 200°C. Sputtered ZnO:Al is used as semitransparent front contact for the diodes, while Al and Cr are used as contacts to the transistors. The TFTs are used as switches to read out an array of pin-diodes. Experimental results for an electrokinetic microfluidic pump and the a-Si:H devices are reported. Further developments and potential applications for microanalysis are outlined.

Monolithic Integrated a-Si:H based pin-Diodes with Orthogonal Liquid Light Guidance Structures for Lab-on-Microchip Applications

We report the fabrication of an amorphous silicon based fluorescence sensor for miniaturized total analysis systems along with experimental results on optical excitation and detection elements. The pin-photodiode exhibits a dynamic range of 110dB and a room temperature dark current of less than 3000 charge carriers per ms according to a detector area of 0.1256mm 2 . The spectral response is ranging from 320nm to 780nm with a maximum at 600nm @ 80% quantum efficiency. To provide high sensitivity, the excitation light irradiates the fluid orthogonally to the active sensor detection direction by means of specifically designed microfluidic capillaries filled with e.g. methylene iodide or 1,2-o-dibrombenzene. The liquid core, which is enclosed by solid cladding materials, has been calculated to dimensions of a width of 16.75µm or 59.67µm with a height from 15µm to 50µm according to a number of propagating modes inside of 16 or 57, respectively.

Characterization of a Micro Capillary Zone Electrophoresis System With Integrated Amorphous Silicon Based Optical Detectors

A pplication specific L ab-on- M icrochips (ALMs) making use of the combination of complex microfluidic networks with microelectronic circuits and micro optical components allow the realization of miniaturized application specific biological and chemical processing and analysis devices. Fluorescence sensing is one of the most widely used detection technologies, e.g. for DNA fluorescence labelling in M icro C apillary E lectrophoresis (µCE) due to its superior sensitivity and specificity. Unfortunately, commercially available fluorescence sensing systems are physically very large, non portable, expensive and constrain the analysis in portable diagnostic and medical care. Integrated semiconductor optoelectronic devices can provide a portable, parallel and inexpensive solution for on chip fluorescence sensing. Most µCE applications working in the spectral range of visible light. For the integration of optical detection components a photon energy range of 1.6 eV - 3.1 eV is of interest. The a-Si:H technology accomplished due to the low dark current and high absorption coefficient against to crystalline silicon the requirements in that spectral range. In this paper we combine a:Si-H photo sensors with a fluidic micro system to detect the fluorescence of a rhodamine analyte mixture. The analyte mixture was excited by light with a wavelength in the range of λ Ex = 450 - 490 nm. The a-Si:H detector reveals a low dark current density on the order of 10 -10 A/cm 2 and a sufficient dynamic range of ∼100 dB under illumination of ∼1000 lx as a function of bias voltage. The measurement shows that the movement of the rhodamine plug in the microchannel causes a significant rise in the pin-diode photo current, which correlates to the evaluated signal of a microscope image detector. The photo current difference for excitation and additional fluorescence amounts to 2.4 µA.

A Planar Electroosmotic Micropump for Lab-on-Microchip Applications

The scope of the paper is to provide a theoretical and experimental treatment allowing to optimize critical design parameters for planar electroosmotic micropumps. The suggested design with a vertical arrangement of multiple narrow polymer pumping microchannels reduces the pump area to 1/10 compared to planar micropumps with widened shallow pumping channels. This design allows the fabrication of the channel system in only one process step, compatible with post-CMOS processing and suitable for monolithical integration on labchips. A simple analytical model has been developed to characterize the flow rate in a field free pressure-driven section of the channel. It is shown that the micropump with optimized dimensions of rib structures makes possible high pressure low voltage pumping. For high pressure capacity the distance between the ribs must be on the order of 0.5-1 µm with an aspect ratio of 10-20. The electroosmotic micropump with microchannels of SU-8 and polyacrylamide gel electrodes has been fabricated and tested. The pumping rate is bidirectionally linear and reached 10 nl/min at applied voltage of 40 V in 1 cm long pressure-driven channel, which corresponds to zero-flow pressure of 65 Pa.