Toshihide Kuriyama

A lift-off method for patterning enzyme-immobilized membranes in multi-biosensors

Abstract A new method for preparing enzyme-immobilized membranes of multi- biosensors has been developed and demonstrated by fabricating a multi- biosensor for glucose and urea, based on the pH-selective ion-sensitive field effect transitor. The enzyme solution, containing glutaraldehyde, is spin coated onto a water covered with a patterned photoresist. The resulting enzyme-immobilized membrane is lifted off by ultrasonic vibration in acetone, except for the membrane on the transitor gates. The deposited membrane is precisely patterned and difficult to peel off. The method is compatible with IC processes and applicable to multi-biosensor mass production

An immobilized enzyme membrane fabrication method using an ink jet nozzle

Abstract A novel enzyme immobilization method, which realized the efficient use of enzymes for biosensors, was developed. An ink jet nozzle, originally developed for printing equipment, was used as a tool for precise enzyme deposition onto an ISFET device. Two sorts of immobilization method were attempted: one is liquid phase immobilization, in which an enzyme solution was emitted at first onto an ISFET sensor region. After drying it under room temperature, glutaraldehyde solution was emitted into the enzyme membrane for immobilization. In this method, the membrane became very thin (e.g. less than 0.1 μm) in a region around the center. In addition, membrane thickness control was rather difficult because the enzyme solution redissolved into the glutaraldehyde solution, and membrane localization at the peripheral region occurred. Next, the method was improved so as to maintain the shape of the original enzyme drops: gas phase immobilization. At first, enzyme solution drops were emitted onto an ISFET device whose position was precisely determined using an X-Y stage controlled by a personal computer. Enzyme immobilization was realized by keeping the device in a chamber filled with glutaraldehyde vapor. In this case, the resulting membrane shape maintains the original enzyme shape. These methods will have great merit in very expensive enzyme immobilization and in the fabrication of a multi-biosensor, which has various kinds of immobilized enzyme membranes on a sensor chip.

An integrated SOS/FET multi-biosensor☆

A monolithically integrated SOS/FET multi-biosensor has been realized. The multi-biosensor has four ISFETs, and can detect urea, glucose and potassium simultaneously. Four MOSFET pairs constitute source follower circuits, where an individual MOSFET works as a simple quasi-constant current synthesizing circuit, and needs only two constant voltage power supplies. The gate potential of an ISFET can be measured as an ISFET source potential, so differential measurements can easily be realized. By using a gold layer deposited on the sapphire back surface as a pseudo-reference electrode, and substrate concentration, of urea for example, is measured as a differential output between an ISFET modified by urease, for example, and a normal ISFET. Two of the four ISFET surfaces were modified by glucose oxidase and urease, respectively. One of the remaining ISFETs is modified by a liquid membrane that contains valinomycin as a potassium-sensitive ionophore. The last ISFET has an albumin crosslinking membrane on the surface. Minute amounts of enzyme or ionophore were used as sensitive elements. The differential output from the ISFETs shows a good relationship with glucose concentration from 1 to 50 mg/dl and with urea from 1 to 100 mg/dl, and shows a linear relationship with potassium from 10−3 to 2 × 10−2 Eq/l.

A Micro Planar Ampehometric Glucose Sensor Using an Isfet as a Reference Electrode

Abstract A very small glucose sensor has been realized, which consists of a gold working electrode with a glucose oxidase immobilized membrane on it, and a gold counter electrode, all made on a sapphire substrate. By using the pH sensitive ISFET as a reference electrode, the potential for a solution, whose pH is constant, can be measured and irreversible metal electrodes, such as gold or platinum, can be used as working electrode and counter electrode. The sensor is very suitable for miniaturizing and mass production, because the Integrated Circuit (IC) fabrication process can be applied. The glucose oxidase immobilized membrane was also deposited by a lift off method, one of the IC processes. A glucose concentration, from 1 to 100 mg/dl, was measured with good linear current output.

An integrated multibiosensor for simultaneous amperometric and potentiometric measurement

Abstract A multibiosensor, in which a glucose sensor based on amperometry and a urea sensor based on potentiometry are integrated, has been realized by complementary use of ISFETs and micro-patterned planar gold electrodes. This multibiosensor is composed of two ISFETs and three micro-planar gold electrodes on a silicon on sapphire (SOS) device. On the back surface gold layer, one of the electrodes works both as a counter electrode for the amperometric measurement, and as a pseudo reference electrode for the potentiometric measurement. Glucose oxidase (GOD)-immobilized membrane, urease-immobilized membrane, and bovine serum albumin (BSA) crosslinking membranes were deposited in appropriate positions by a lift-off method, one of the integrated circuit (IC) fabrication processes. Consequently the multibiosensor is very suitable for miniaturization and mass production. A glucose concentration in the range 1 to 100 mg/dl and a urea concentration in the range 5 to 100 mg/dl were measured with a good relationship. In the multibiosensor, amperometry and potentiometry exist on a complementary basis and each process provides what the other needs. The multibiosensor can thus be called a ‘complementary multibiosensor (COMBIS)’.

Miniaturized thin-film magnetic field probe with high spatial resolution for LSI chip measurement

It is important to obtain the absolute value of current flowing through each power line on a large-scale integrated (LSI) circuit by measurement because this current on an LSI chip is regarded as conductive noise. We have developed a thin-film magnetic field probe that has spatial resolution high enough to obtain the absolute value of high-frequency power current on an LSI chip. Spatial resolution was enhanced by miniaturizing the shielded loop coil, the detection part of the probe. The outer size of the new coil is 50/spl times/22 /spl mu/m. In taking measurements with the new probe over a 60 /spl mu/m wide microstrip line used as a device under test (DUT), we obtained a 6 dB decrease point of 40 /spl mu/m, which indicates the spatial resolution of the probe. This value is comparable to the typical width of power lines on an LSI chip, around 50 /spl mu/m and is less than half that of our conventional probes, around 90 /spl mu/m. In measurements with the new probe over an LSI chip, we obtained such a fine magnetic near-field distribution that the magnetic fields generated from the lines on the chip were separated. On-chip decoupling was also confirmed by using the new probe. The new probe enables direct verification of a circuit design for suppressing electromagnetic interference (EMI), while conventional coarse mapping of the magnetic near-field cannot be used to evaluate such conductive noise.

Evaluation of an albumin-based, spin-coated, enzyme-immobilized membrane for an ISFET glucose sensor by computer simulation

Abstract An ISFET biosensor response was analyzed and evaluated using computer simulation, based on a ping-pong mechanism model [1], one of the two commonly used substrate models. Diffusion coefficients and Km values for glucose and oxygen were determined by comparing calculated responses with glucose sensor responses measured with an albumin-based membrane formed by the lift-off method. Diffusion coefficients for glucose and oxygen were estimated to be 2.5 x 10-9 cm2 sec and 7.5 x 10-9 cm2/sec, respectively. These low diffusion coefficients values mean that the membrane has a relatively dense structure. Km values for glucose and oxygen were estimated to be 8 mM and 0.05 raM, respectively. These values suggest that the enzyme activity in the membrane is influenced by the membrane electric charge or mechanical condition. Responses for a biosensor with a membrane less than 1 μm thick were well described by the model.

High frequency magnetic near field measurement on LSI chip using planar multi-layer shielded loop coil

Magnetic near-field measurements of circuitry are gathering increasing interest as an effective technique for detecting noise emission current sources. Against this background, we developed planar thick-film multi-layer shielded loop coils with loop apertures of 20 /spl mu/m x 1000 /spl mu/m and 600 /spl mu/m x 600 /spl mu/m. The shielded-loop structures main feature is the cancellation of voltage induced by the electric field. A 60-/spl mu/m wide microstrip line was used as the device under test (DUT). In a spatial resolution test conducted at 1GHz, we obtained optimum spatial resolution of 90 /spl mu/m at the 6 dB degrading point for a rectangular coil with a 20/spl mu/m x 1000 /spl mu/m aperture. This resolution level is 2.8 times better than that we obtained with our previous product comprising a low temperature co-fired ceramic (LTCC) board, because with the new coils we were able to successfully reduce the mean distance between the loop and the DUT. In measuring nonuniform magnetic field distribution near the 1.58 mm-wide microstrip line and the internal chip of a large-scale integrated (LSI) circuit, we found the new model could measure a finer distribution than our previous probe.

A novel blood glucose monitoring system based on an ISFET biosensor and its application to a human 75 g oral glucose tolerance test

Abstract A novel blood glucose monitoring system was developed by applying an SOS/ISFET (silicon on sapphire/ion-sensitive field-effect transistor) biosensor to an SEF (suction effusion fluid). The effusion rate of the SEF was 11.9 ± 3.7 μlh −1 cm −2 and the measurement was made every 7.5 min. Glucose concentrations measured using SEF showed a good correlation with those measured by using serum with a slight delay of about 10 min. The blood glucose monitoring system was successfully applied to a non-invasive transcutaneous blood glucose monitoring on human 75 g oral glucose tolerance test. This result shows it will enable realization of a portable blood glucose monitoring device and the system will become very useful in medical treatment.

A Rapid And Selective Anodic Bonding Method

A new anodic bonding technique suitable for dynamical microstructure fabrication has been developed, which shortens production time, enhances bonding reliability and yield rate, as well as improves temperature characteristics of devices. This method comprises the following two techniques. (1) A built-in mesh bias electrode on the glass layer to enhance the electric field for faster anodic bonding. (2) A built-in ground electrode on the glass layer, which controls capacitive electrode potential to prevent a movable electrode in the Si layer from sticking.