- Email: [email protected]
Non-contact magnetic temperature sensor for biochemical applications
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) e1761–e1762
Non-contact magnetic temperature sensor for biochemical applications H. Osada*, S. Chiba, H. Oka, H. Hatafuku, N. Tayama, K. Seki Department of Electrical and Electronic Engineering, Faculty of Engineering, Iwate University, 4-3-5, Ueda Morioka 020-8551, Japan
Abstract A non-contact magnetic temperature sensor is an electromagnetic device utilizing magnetic properties of a temperature-sensitive ferrimagnetic film. The sensor can detect temperature changes as low as 0.01 C, since magnetic properties of the film has marked temperature dependence. In the meantime, the thermal effect which this sensor gives to the samples is very small, because only the film without self-heating contact the samples. Therefore, the sensor is suitable for biochemical applications. r 2004 Elsevier B.V. All rights reserved. PACS: 07.20.D; 75.50.G; 85.70.K; 87.80 Keywords: Enzyme sensor; Ferrites; Magnetic film; Biosensors
1. Introduction The conventional enzyme sensor is an electronic device using the semiconductor properties of a thermistor [1]. On the other hand, the magnetic temperature sensor is an electromagnetic device utilizing magnetic properties of the temperature-sensitive ferrimagnetic film. In previous magnetic temperature sensor, the magnetic film and a magnetic– electric signal converter must have contacted each other in the sample cell [2]. The proposing sensor has succeeded in doing them non-contacting by the improvement in the performance of the film and the converter. In the sensor, the self-heating observed in the thermistor is not generated. Therefore, the sensor can measure the small temperature change at the high accuracy. In this study, the magnetic temperature sensor was examined as enzyme sensor. 2. Fabrication Fig. 1 shows the schematic drawing of the magnetic temperature sensor. The sensor is composed of an exclusive sample cell (volume: 10 ml) and a magnetic
temperature sensing unit. The temperature-sensitive ferrimagnetic film and a magnetic–electric signal converter and a magnet construct the sensing unit. The magnet supplies the unit with a bias magnetic flux. The MI element (AICHI STEEL Co.) was used as the signal converter [3]. The MI element has magnetic field sensitivity over 1000 times of the MR element that used in previous sensor. The magnetic film ½Mn0:14 Zn0:18 Fe0:68 O4 ; 5.0 mm square with a thickness of 1.5 mm is prepared by a special annealing treatment of a sputtered temperature-sensitive MnZn ferrite. Fig. 2 shows temperature dependence on the saturation magnetization of the film. The film has marked temperature dependence in the room temperature range. The sensor is covered by water jackets in order to keep to the constant temperature of 30 C. In the cell, the magnetization of the magnetic film changes, when the temperature of the sample changes by chemical reaction. This magnetization variation causes the magnetic flux to change. The MI element detects the minute magnetic flux change, and converts it into an output voltage using an amplifier and a filter circuit. 3. Experimental results
*Corresponding author. Tel.:/fax: +81-19-621-6381. E-mail address: [email protected] (H. Osada).
We measured an enzyme reaction heat using this sensor. Generally the enthalpy change of an enzyme
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.989
ARTICLE IN PRESS H. Osada et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1761–e1762
e1762
Output voltage [mV]
20 Sample: D-glucose Enzyme: glucose-oxidase 10
0 Time [50 s/div]
Fig. 1. Schematic drawing of the magnetic temperature sensor.
250
Output peak voltage [mV]
3
Magnetization [emu/cm ]
Fig. 3. Transient response of the magnetic temperature sensor for an oxidase enzyme to a D-glucose solution.
200 150 100 50 0 10
20
30 40o 50 Temperature [ C]
150
100
60
50
0
1
2
3 4 distance [mm]
5
6
Fig. 2. Temperature dependence on the saturation magnetization of the magnetic film.
Fig. 4. Output peak voltage vs. distance between the magnetic film and the magnetic–electric signal converter.
reaction heat is very small. Fig. 3 shows the transient response of the sensor for an oxidase enzyme solution (volume: 1 ml, concentration: 0.001 mol/l) and a Dglucose solution (volume: 10 ml, concentration: 0.001 mol/l). The output signal increased with the progress of the enzyme reaction, and it decreased with the end of the reaction. It was proven that the output peak changed by enzymatic type and concentration of the sample, when various samples were measured by this sensor. In the measurement of Fig. 3, the distance between the film and the magnetic–electric signal converter was 4 mm. The output signal decrease with increases the distance. In the magnetic temperature sensor, it was possible to read the output signal to the distance of about 5 mm (Fig. 4). However, in order to keep a reasonable S/N ratio, the sensor should be placed at a distance of at most 4 mm from the magnetic film.
4. Conclusions We have investigated a non-contact magnetic temperature sensor. The maximum distance between the temperature-sensitive magnetic film and the magnetic– electric signal converter was 4 mm. The thermal effect which this sensor gives to samples is very small, since the film which contacts the sample does not generate a heat.
References [1] G. Decristoforo, B. Danielsson, Anal. Chem. 56 (1984) 263. [2] Y. Yachi, S. Chiba, H. Osada, et al., IEEE Trans. Magn. 36 (2000) 3730. [3] K. Mohri, K. Kawashima, T. Kohzawa, H. Yoshida, IEEE Trans. Magn. 28 (1992) 3150.
Journal of Magnetism and Magnetic Materials 272–276 (2004) e1761–e1762
Non-contact magnetic temperature sensor for biochemical applications H. Osada*, S. Chiba, H. Oka, H. Hatafuku, N. Tayama, K. Seki Department of Electrical and Electronic Engineering, Faculty of Engineering, Iwate University, 4-3-5, Ueda Morioka 020-8551, Japan
Abstract A non-contact magnetic temperature sensor is an electromagnetic device utilizing magnetic properties of a temperature-sensitive ferrimagnetic film. The sensor can detect temperature changes as low as 0.01 C, since magnetic properties of the film has marked temperature dependence. In the meantime, the thermal effect which this sensor gives to the samples is very small, because only the film without self-heating contact the samples. Therefore, the sensor is suitable for biochemical applications. r 2004 Elsevier B.V. All rights reserved. PACS: 07.20.D; 75.50.G; 85.70.K; 87.80 Keywords: Enzyme sensor; Ferrites; Magnetic film; Biosensors
1. Introduction The conventional enzyme sensor is an electronic device using the semiconductor properties of a thermistor [1]. On the other hand, the magnetic temperature sensor is an electromagnetic device utilizing magnetic properties of the temperature-sensitive ferrimagnetic film. In previous magnetic temperature sensor, the magnetic film and a magnetic– electric signal converter must have contacted each other in the sample cell [2]. The proposing sensor has succeeded in doing them non-contacting by the improvement in the performance of the film and the converter. In the sensor, the self-heating observed in the thermistor is not generated. Therefore, the sensor can measure the small temperature change at the high accuracy. In this study, the magnetic temperature sensor was examined as enzyme sensor. 2. Fabrication Fig. 1 shows the schematic drawing of the magnetic temperature sensor. The sensor is composed of an exclusive sample cell (volume: 10 ml) and a magnetic
temperature sensing unit. The temperature-sensitive ferrimagnetic film and a magnetic–electric signal converter and a magnet construct the sensing unit. The magnet supplies the unit with a bias magnetic flux. The MI element (AICHI STEEL Co.) was used as the signal converter [3]. The MI element has magnetic field sensitivity over 1000 times of the MR element that used in previous sensor. The magnetic film ½Mn0:14 Zn0:18 Fe0:68 O4 ; 5.0 mm square with a thickness of 1.5 mm is prepared by a special annealing treatment of a sputtered temperature-sensitive MnZn ferrite. Fig. 2 shows temperature dependence on the saturation magnetization of the film. The film has marked temperature dependence in the room temperature range. The sensor is covered by water jackets in order to keep to the constant temperature of 30 C. In the cell, the magnetization of the magnetic film changes, when the temperature of the sample changes by chemical reaction. This magnetization variation causes the magnetic flux to change. The MI element detects the minute magnetic flux change, and converts it into an output voltage using an amplifier and a filter circuit. 3. Experimental results
*Corresponding author. Tel.:/fax: +81-19-621-6381. E-mail address: [email protected] (H. Osada).
We measured an enzyme reaction heat using this sensor. Generally the enthalpy change of an enzyme
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.989
ARTICLE IN PRESS H. Osada et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1761–e1762
e1762
Output voltage [mV]
20 Sample: D-glucose Enzyme: glucose-oxidase 10
0 Time [50 s/div]
Fig. 1. Schematic drawing of the magnetic temperature sensor.
250
Output peak voltage [mV]
3
Magnetization [emu/cm ]
Fig. 3. Transient response of the magnetic temperature sensor for an oxidase enzyme to a D-glucose solution.
200 150 100 50 0 10
20
30 40o 50 Temperature [ C]
150
100
60
50
0
1
2
3 4 distance [mm]
5
6
Fig. 2. Temperature dependence on the saturation magnetization of the magnetic film.
Fig. 4. Output peak voltage vs. distance between the magnetic film and the magnetic–electric signal converter.
reaction heat is very small. Fig. 3 shows the transient response of the sensor for an oxidase enzyme solution (volume: 1 ml, concentration: 0.001 mol/l) and a Dglucose solution (volume: 10 ml, concentration: 0.001 mol/l). The output signal increased with the progress of the enzyme reaction, and it decreased with the end of the reaction. It was proven that the output peak changed by enzymatic type and concentration of the sample, when various samples were measured by this sensor. In the measurement of Fig. 3, the distance between the film and the magnetic–electric signal converter was 4 mm. The output signal decrease with increases the distance. In the magnetic temperature sensor, it was possible to read the output signal to the distance of about 5 mm (Fig. 4). However, in order to keep a reasonable S/N ratio, the sensor should be placed at a distance of at most 4 mm from the magnetic film.
4. Conclusions We have investigated a non-contact magnetic temperature sensor. The maximum distance between the temperature-sensitive magnetic film and the magnetic– electric signal converter was 4 mm. The thermal effect which this sensor gives to samples is very small, since the film which contacts the sample does not generate a heat.
References [1] G. Decristoforo, B. Danielsson, Anal. Chem. 56 (1984) 263. [2] Y. Yachi, S. Chiba, H. Osada, et al., IEEE Trans. Magn. 36 (2000) 3730. [3] K. Mohri, K. Kawashima, T. Kohzawa, H. Yoshida, IEEE Trans. Magn. 28 (1992) 3150.