P. D. van der Wal

Extremely stable Nafion based carbon monoxide sensor

Abstract Carbon monoxide sensors using Nafion solid polymer electrolyte are described. Dry Nafion sensors showed stability problems; on the other hand sensors equipped with a water reservoir (wet Nafion sensors) were extremely stable. The proposed manufacturing technology, compatible with hybrid technology is suitable for cheap mass fabrication.

Enzyme-based choline and l-glutamate biosensor electrodes on silicon microprobe arrays

Brain-implantable microprobe arrays, 6.5 mm shaft-length, incorporating several recessed Pt microelectrodes (50 μm×150 μm) and an integrated Ag/AgCl reference electrode fabricated by silicon micromachining dry etching techniques (DRIE) are described. The microelectrodes are coated by an enzyme membrane and a semi-permeable m-phenylenediamine layer for the selective detection of the neurotransmitters choline and L-glutamate at physiologically relevant concentrations. The functionalisation is based on electrochemically aided adsorption (EAA) combined with chemical co-cross-linking using glutaraldehyde and electrochemical polymerisation, respectively. These deposition methods are fully compatible with the fabricated microprobe arrays for the simultaneous detection of several analytes in different brain target areas. They are spatially controlled and allow fabricating biosensors on several microelectrodes in parallel or providing a cross-talk-free coating of closely spaced microelectrodes with different enzyme membranes. A sensitivity of 132±20 μA mM(-1) cm(-2) for choline and 95±20 μA mM(-1) cm(-2) for L-glutamate with limits of detections below 0.5 μM was obtained. The results of in vitro and in vivo experiments confirm the functional viability of the choline and l-glutamate biosensors.

Universal approach for the fabrication of Ca2+-, K+- and NO3−-sensitive membrane ISFETs

Abstract A new method to functionalize silanol-terminated polysiloxanes is presented. The method can be used for the realization of tailor-made ion-selective membranes. A siloxane copolymer containing polar cyano groups combined with a condensation-type cross linking overcomes the earlier encountered problem of high membrane resistance. After modification of this material with methacrylate groups, a photocurable polysiloxane was obtained. Potassium- and calcium-selective ISFETs with excellent sensitivities and selectivities (log KK,i

Biosensor microprobes with integrated microfluidic channels for bi-directional neurochemical interaction

This paper reports on silicon-based microprobes, 8 mm long and 250 µm × 250 µm cross-section, comprising four recessed biosensor microelectrodes (50 µm × 150 µm) per probe shank coated with an enzymatic layer for the selective detection of choline at multiple sites in brain tissue. Integrated in the same probe shank are up to two microfluidic channels for controlled local liquid delivery at a defined distance from the biosensor microelectrodes. State-of-the-art silicon micromachining processing was applied for reproducible fabrication of these experiment-tailored multi-functional probe arrays. Reliable electric and fluidic interconnections to the microprobes are guaranteed by a custom-made holder. The reversible packaging method implemented in this holder significantly reduces cost and assembly time and simplifies storage of the biosensor probes between consecutive experiments. The functionalization of the electrodes is carried out using electrochemically aided adsorption. This spatially controlled deposition technique enables a parallel deposition of membranes and is especially useful when working with microelectrode arrays. The achieved biosensors show adequate characteristics to detect choline in physiologically relevant concentrations at sufficient temporal and spatial resolution for brain research. Sensitivity to choline better than 10 pA µm(-1), detection limit below 1 µM and response time of 2 s were obtained. The proposed combination of biosensors and microfluidic injectors on the same microprobe allows simultaneous chemical stimulation and recording as demonstrated in an agarose gel-based brain phantom.

Multi-ion sensing device for horticultural application based upon chemical modification and special packaging of ISFETs

A multi-ion sensing device, based on ISFETs, is described for horticultural applications. The advantages of a new packaging technique based on back-side contacted ISFETs are outlined. The basic pH-sensitive ISFETs can be modified to, e.g., potassium-sensitive devices by using neutral carrier-based membranes and an intermediate hydrogel. Both membrane and hydrogel are chemically anchored to the ISFET surface and the ionophore is chemically bonded to the membrane. It is shown that these chemical modifications of the membrane system lead to an increased lifetime for the sensor.

Flexible polysiloxane Interconnection Between Two Substrates For Microsystem Assembly

Polysiloxane layers with a thickness of several hundred micrometers are used as flexible interconnection between two substrates. Subsequent bonding to the substrates is obtained by using two independent curing schemes. The layer is bonded and structured onto the first substrate by UV photolithography. The bond to the second substrate is obtained by condensation crosslinking.

High-k dielectrics for use as ISFET gate oxides

Two binary oxides, Ta/sub 2/O/sub 5/ and HfO/sub 2/, were investigated for use as the pH-sensitive gate oxide of ion-sensitive field-effect transistors (ISFETs). Both materials have been extensively studied as high-k materials for advanced CMOS technologies. They are both deposited by CVD methods, which enable batch processing of several wafers at the same time. After deposition, these materials are thermally annealed, during which step the oxide properties are optimized for use as ISFET gate oxide. The performance of the ISFETs is evaluated by characterization of several parameters including the pH-sensitivity, drift and light sensitivity.

Ion-selective microelectrode array for intracellular detection on chip

The design and fabrication of an Ion-Selective Electrode (ISE) array platform for in-vitro intracellular recording are presented. The platform is composed of two parts: 1) a glass chip with microchannels whose bottom part is patterned with a silver layer and 2) a silicon chip in with an array of 30 /spl mu/m long silicon nitride micropipettes with an inner diameter of 1.7 /spl mu/m long silicon nitride micropipettes with an inner diameter of 1.7 /spl mu/m are structured. The Ca/sup 2+/ selective membrane is based on the neutral carrier ionophore ETH 129. To be compatible with hepatocyte cell cultures the 24 ISEs are arranged in a 2/spl times/8 array with 150 /spl mu/m spacing and four additional electrodes located on both sides of the array at 300 /spl mu/m.

P1.9.5 UV-Curable Adhesive as the Low-Cost Material of Choice for Microfluidic Forensic Applications

There is a push towards disposable, polymer-based microfluidic devices for medical and forensic applications to reduce cost and cross contamination between different samples. Therefore, more and more polymer-based systems are developed and they replace the common systems made of silicon or glass. But one of the main challenges of systems made of polymers is the adsorption/absorption of molecules. For microfluidic-based chemical sensors, it is essential that the analyte is not adsorbed on the walls of the microfluidic channels before detection. Here we present a study of the adsorption of cocaine molecules by low-cost polymer microfluidic devices. We manufactured the systems by a simple and low-cost rapid-prototyping method using a UV-curable adhesive. Remarkable low adsorption values (up to 100% recovery rate) were found by liquid chromatography – mass spectroscopy (LC-MS) measurements for this potential polymer for forensic applications.

Integration of a microfluidic flow cell on a CMOS biosensor for DNA detection

This paper describes the fabrication technique for the realization a microfluidic flow cell to be integrated on a CMOS biosensor for DNA hybridization detection. The main element of the microfluidic system is made in polydimethylsiloxane (PDMS) elastomer and takes up an area of 5 mm2. PDMS is cast against a silicon master patterned by deep reactive ion etching (DRIE) and then bonded on the chip by means of oxygen plasma activation. The micro channels patterned in the flow cell are connected with capillary tubes that can be easily interconnected to a common syringe.