Investigation of ZnO nanorod/ZnO-based ion-sensitive field-effect-transistor biosensors

• Main Authors: Ying-ShuoChiu, 邱英碩
• Other Authors: Ching-Ting Lee
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/57393222093124236838

博士 === 國立成功大學 === 微電子工程研究所 === 103 === In this dissertation, the ZnO nanorod/ZnO-based ion-sensitive field-effect-transistor biosensor was successful fabricated using the vapor cooling condensation system and aqueous solution growth method. To effectively minimize the dimension of the extended-gate field-effect-transistor (EGFET)-based biosensors and shorten the path of sensing signal between the sensing head and the field-effect-transistor, the ZnO sensing membrane was integrated with the ZnO-based field-effect-transistor as the ion-sensitive field-effect-transistor (ISFET)-based biosensors. To increase the sensing surface area, the aqueous chemical solution method was applied to grow the ZnO nanorod arrays on the sensing region of the ZnO-based ISFET biosensors. Furthermore, to suppress the influence of the Fermi level pinning effect induced by the dangling bonds and surface states resided on the ZnO nanorod arrays, the photoelectrochemical method was applied. The X-ray diffraction spectrum of the grown ZnO nanorod arrays revealed the obvious peak at 2θ of 34.5° originating from (002) plane which indicated that the ZnO nanorod arrays possessed the favorable crystal orientation characteristic. The SEM images of ZnO nanorod arrays and top view of the fabricated ZnO nanorod/ZnO-based ion-sensitive field-effect-transistor biosensor demonstrate that the vertical and uniform ZnO nanorod arrays were successfully grown on the sensing region. The measured XPS spectrum showed that the PEC-passivated ZnO film revealed the obvious chemical bond structure of Zn-OH bonds located at the binding energy of 532.2 eV comparing to the unpassivated one. To investigate pH sensing performances of the ZnO nanorod/ZnO-based ISFET pH sensors with PEC passivation, the ZnO-based ISFET pH sensors and the ZnO nanorod/ZnO-based ISFET pH sensors without PEC passivation were fabricated to compare. Among the three ISFET pH sensors, the passivated ZnO nanorod/ZnO-based ISFET biosensors showed the pH sensitivity of 56.35 mV/pH comparing other pH sensors. In addition, the site-binding model which described the sensing behavior of the pH sensors was also introduced to calculate the sensitivity parameter β for further verifying the experimental results. The linear response and sensitivity parameter β of 2.05 were obtained for the passivated ZnO nanorod/ZnO-based ISFET pH sensors ISFETs. The favorable calculating and fitting results could be concluded that the experimental results properly fitted the sensing behaviors described by the site-binding mode. The glucose sensing performance of the passivated ZnO nanorod/ZnO-based ISFET glucose biosensors showed that the glucose sensing sensitivity was 32.43 uA/mM which was much better than other glucose biosensors. Moreover, the passivated ZnO nanorod/ZnO-based ISFET glucose biosensors also exhibited the broader linear sensing range and faster response time less than 9 seconds. The superior pH and glucose sensing performance were owing to the increase of sensing surface provided by the ZnO nanorods and the suppression of Fermi level pinning induced by the dangling bonds and surface states via the PEC passivation function. Finally, the apparent Michaelis–Menten constant, a reflection index of the enzymatic affinity, was introduced to calculate using the Lineweaver–Burk equation. The low K value of 2.05 mM showed that the passivated ZnO nanorod/ZnO-based ISFET glucose biosensors could effectively retain its bioactivity and possess the high affinity between the glucose oxidase and the glucose.