Ulrik Hanke

Recent Developments in Optical Detection Technologies in Lab-on-a-Chip Devices for Biosensing Applications

The field of microfluidics has yet to develop practical devices that provide real clinical value. One of the main reasons for this is the difficulty in realizing low-cost, sensitive, reproducible, and portable analyte detection microfluidic systems. Previous research has addressed two main approaches for the detection technologies in lab-on-a-chip devices: (a) study of the compatibility of conventional instrumentation with microfluidic structures, and (b) integration of innovative sensors contained within the microfluidic system. Despite the recent advances in electrochemical and mechanical based sensors, their drawbacks pose important challenges to their application in disposable microfluidic devices. Instead, optical detection remains an attractive solution for lab-on-a-chip devices, because of the ubiquity of the optical methods in the laboratory. Besides, robust and cost-effective devices for use in the field can be realized by integrating proper optical detection technologies on chips. This review examines the recent developments in detection technologies applied to microfluidic biosensors, especially addressing several optical methods, including fluorescence, chemiluminescence, absorbance and surface plasmon resonance.

Integrated optical microfluidic biosensor using a polycarbazole photodetector for point-of-care detection of hormonal compounds

Abstract. A picogram-sensitive optical microfluidic biosensor using an integrated polycarbazole photodiode is developed. The photodetector is mainly composed of the blend heterojunction of poly [N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C71-butyric acid methyl ester (PC70BM) and the poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) as the hole transport layer. Analyte detection is accomplished via a chemiluminescent immunoassay performed in a poly(dimethylsiloxane)-gold-glass hybrid microchip, on which antibodies were immobilized and chemiluminescent horseradish peroxidase-luminol-peroxide reactions were generated. Enhanced sensor response to the chemiluminescent light is achieved by optimizing the thickness of PCDTBT:  PC70BM and PEDOT:PSS. Using the optimized polycarbazole photodiode for detecting the human thyroid-stimulating hormone as the model target, the integrated biosensor demonstrates an excellent linearity in the range of 0.03 to 10  ng/ml with an analytical sensitivity of 68  pg/ml. The sensor response shows high specificity and reproducibility. Hormone detection in clinical samples is further demonstrated and compared with a commercial enzyme-linked immunosorbent assay. The integrated device reported here has potential to detect other hormonal compounds or protein targets. Moreover, the presented concept enables the development of miniaturized, low-cost but highly sensitive optical microfluidic biosensors based on integrated polymer photodetectors with high potential for point-of-care diagnostics.

Modeling of Spring Constant and Pull-down Voltage of Non uniform RF MEMS Cantilever

In this paper, we are going to present a model of spring constant and pull down voltage for non uniform RF MEMS cantilever. In order to reduce the pull down voltage, it is usual to use a beam, which is narrower close to anchor and wider at the end or electrode area for a cantilever. Compare to uniform beam, this beam have lower spring constant which reduce the pull down voltage. A comprehensive model for spring constant and pull down voltage of the nonuniform cantilever is developed through basic force deflection mechanism of the suspended beam

The microwave dielectric properties of dual-layer PZT/ZrO2 thin films deposited by chemical solution deposition

The dielectric properties of dual-layer PZT/ZrO2 thin films were measured at microwave frequencies in both a metal?insulator?metal (MIM) capacitor and a coplanar waveguide (CPW) up to 50?GHz. Both PZT and ZrO2 films were prepared by the chemical solution deposition method. The measured dielectric loss of the PZT/ZrO2 film was approximately 0.08 at 30?GHz, much lower than that of typical PZT thin films. The dielectric constants obtained using the MIM capacitor with 360?nm PZT/65?nm ZrO2 and using the CPW with 420?nm PZT/280?nm ZrO2 were 47 and 130, respectively, at 50?GHz. Capacitance tunability was ~30% at +25?V and up to 50?GHz. The measured values obtained indicate that PZT/ZrO2 thin films may be suitable for the use of dielectric layers in tunable RF devices and RF MEMS capacitive switches operating at millimetre wave frequencies.

TUNABLE BAND-PASS FILTER USING RF MEMS CAPACITANCE AND TRANSMISSION LINE

In this paper we present the design and fabrication of an RF MEMS tunable band-pass fllter. The band-pass fllter design uses both distributed transmission lines and RF MEMS capacitances together to replace the lumped elements. The use of RF MEMS variable capacitances gives the ∞exibility of tuning both the centre frequency and the band-width of the band-pass fllter. A prototype of the tunable band-pass fllter is realized using parallel plate capacitances. The variable shunt and series capacitances are formed by a combination of parallel plate RF MEMS shunt bridges and series cantilevers. The fllter operates at C-X band. The measurement results agree well with the simulation results.

Modeling, design and simulation of tunable band pass filter using RF MEMS capacitance and transmission line

In this paper we have shown design of a RF MEMS band pass filter. A high capacitance ratio and low actuation voltage RF MEMS shunt switch was designed and modeled the switch as a variable capacitance. The capacitance can be varied as a function of the actuation voltage. The capacitance is modeled as a lumped component, as used in a conventional LC filter. The design uses a novel approach to implement both distributed transmission line and RF MEMS capacitance together to replace the lumped elements. The use of RF MEMS variable capacitance gives the flexibility of tuning the cut-off and center frequency of bandpass filter. In this paper we show a design of 5.8 GHz center frequency band pass filter using the theory of stepped impedance transmission line and MEMS capacitance filter.

Si 3 N 4 /SiO 2 dielectric stacks for high reliable capacitive RF MEMS switch

SiO2/Si3N4 double-layer dielectric stacks, instead of single dielectric layer, have been investigated to mitigate charge accumulation in the dielectric for the purpose of high reliable capacitive microelectromechanical switch. Two kinds of double-dielectric-layers with different thickness ratios are structured, and SiO2 single-layer dielectric structure is also fabricated for comparison. The charge injection kinetics in the dielectric layer has been investigated by performing C-V measurements on metal-insulator-semiconductor (MIS) capacitor structure instead of an actual switch. The experiment results generally show that low charge accumulation has been achieved by using double-layer dielectric stacks. More in detail, the experiment results further show that the charge accumulation behaviors varied greatly with the different thickness ratio of Si3N4 to SiO2. With same positive dc bias voltage for charge injection, we found that net negative charge accumulated in the thin-oxide MNOS structure and net positive charge accumulated in the thick-oxide MNOS structure as the electron injection is suppressed by the thick oxide. It can be anticipated that the charge accumulation in the switch dielectric can be minimized by optimizing the thickness ratio of double-layer dielectric.

Tunable Lowpass Filter with RF MEMS Capacitance and Transmission Line

We have presented an RF MEMS tuneable lowpass filter. Both distributed transmission lines and RF MEMS capacitances were used to replace the lumped elements. The use of RF MEMS capacitances gives the flexibility of tuning the cutoff frequency of the lowpass filter. We have designed a low-pass filter at 9–12 GHz cutoff frequency using the theory of stepped impedance transmission lines. A prototype of the filter has been fabricated using parallel plate capacitances. The variable shunt capacitances are formed by a combination of a number of parallel plate RF MEMS capacitances. The cutoff frequency is tuned from C to X band by actuating different combinations of parallel capacitive bridges. The measurement results agree well with the simulation result.

Investigation of charge accumulation in the dielectric for robust RF MEMS switches

For higher-power-handling RF MEMS switches, the design of the switch is based on fixed-fixed beam capacitive structure with electrostatic actuation. Such RF MEMS switches are perceived to be unreliable because of the stiction and screening of the beam caused by charge accumulation in the dielectric layer. The research effort for a robust RF MEMS solution has been made for more than a decade. In this paper the models for stiction and screening caused by charge accumulation have been reviewed. As the first part of this paper, the possible charging mechanisms will be described, such as, 1) the dielectric charging arises from charges distributed throughout the dielectric material, 2) the presence of charges at the dielectric interface. In order to avoid the charge accumulation, trapped charges in the dielectric layer have to quickly vanish. Relaxing mechanisms of short time must be created inside of the dielectric for quick charge recombination. The second part of this paper will report the recent effort to create relaxing mechanisms of short time by using, such as doping dielectric, nano-composite dielectrics, or multi-layer stack of dielectric. Actuation wave form dependence of the charge accumulation will be also presented.

A Counter-Flow Refinery Concentration Technique for Monitoring Waterborne Protozoa in Large Volumes of Environmental Water

The authors presented the counter-flow refinery (CFR) system, which is a novel approach of continuous pathogen enrichment device for large-volume raw water. The device is comprised by two refining levels, in each of which the counter-flow microconcentrator units are arranged in series. The designed CFR module is able to concentrate 100-L water samples by a concentrating factor >500. By spiking Cryptosporidium Parvum oocysts in surface water, the system achieved the recovery efficiency as high as 89.2% without clogging for a processing time of <1.5h.