Impedance Analysis of Chitin Nanofibers Integrated Bulk Acoustic Wave Humidity Sensor with Asymmetric Electrode Configuration.

This paper fabricated a high-performance chitin nanofibers (ChNFs)-integrated bulk acoustic wave (BAW) humidity sensor with an asymmetric electrode configuration. The ChNFs were successfully prepared from crab shells and used as moisture-sensitive materials to compare the performance of quartz crystal microbalance (QCM) humidity sensors with symmetric and asymmetric electrode structures. The QCM humidity sensor with a smaller electrode area exhibited high sensitivity of 58.84 Hz/%RH, competitive response/recovery time of 30/3.5 s, and low humidity hysteresis of 2.5% RH. However, it is necessary to choose a suitable electrode diameter to balance the stability and sensitivity because the impedance analysis result showed that the reduction of the electrode diameter leads to a sharp decrease in the Q value (stability). Next, the possible humidity-sensitive mechanism of the ChNFs-integrated asymmetric n-m electrode QCM humidity sensor was discussed in detail. Finally, the reasons for the highest sensitivity of the asymmetric n-m electrode QCM humidity sensors having a smaller electrode diameter were analyzed in detail in terms of both mass sensitivity and fringing field effect. This work not only demonstrates that the chitin nanofiber is an excellent potential material for moisture detection, but also provides a new perspective for designing high-performance QCM humidity sensors.

Humidity-Sensing Properties of a BiOCl-Coated Quartz Crystal Microbalance.

The performance of a bismuth oxychloride (BiOCl)-based quartz crystal microbalance (QCM) humidity sensor was studied using an oscillating circuit method. The BiOCl powder was prepared by a hydrolysis method. Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy were used to characterize the BiOCl sample. Its humidity-sensing property was analyzed by combining it with a QCM at room temperature (25 °C). Experimental results indicated that the BiOCl-based QCM sensor showed good humidity characteristics from 11.3 to 97.3%, such as good logarithmic frequency response to humidity levels (R 2 = 0.994), fast response time (5.2 s)/recovery time (4.5 s), good reversibility, stability, repeatability, and low humidity hysteresis. In addition, the response to human nose breaths showed excellent practicability. Finally, the humidity sensing mechanism of the BiOCl-based QCM humidity sensor was discussed in detail. This work demonstrates that BiOCl is a promising candidate material for humidity detection.

The Exploration and Confirmation of the Maximum Mass Sensitivity of Quartz Crystal Microbalance.

After the advent of the quartz crystal microbalance (QCM) technology, various QCM-based sensing systems have got certain applications in many science and technology fields and resulted in dramatic progress in these fields. The core advantage of QCM is its high mass sensitivity which leads to high accuracy and low detection limit. For a QCM, the mass sensitivity is determined by the diameter and thickness of the electrode to a certain extent when the frequency of the quartz wafer is already determined. Theoretical approximate calculation reveals that there is an optimum electrode diameter corresponding to the maximum sensitivity. This is different from the traditional opinion that the smaller the electrode, the higher the mass sensitivity. A plating experiment was carried out using 28 QCMs with different electrode diameters, and the experimental results verified the existence of the optimum diameter. This study is helpful to obtain higher mass sensitivity by optimizing electrode parameters.

The p16INK4a Antibody Immobilization Method for Immonosensor Application.

BACKGROUND: The p16INK4a is a protein that expressed in Liquid-based cervical cytology specimens and has been proved link to cervical cancer. The p16INK4a could be detection by piezoelectric immunosensor and the immobilization of the p16INK4a antibody influence the sensitivity of the piezoelectric immunosensor. MATERIALS AND METHODS: 5µL mouse polyclonal antibody against p16INK4a was bound onto the surface of immonosensor through two methods. (directly immobilized method; protein A method). Absorb of the p16INK4a antibody on the surface of immonosensor caused a shift in the resonant frequency of the immunosensor and The frequency changes recorded showed a better reproducibility. The activity of the immobilization antibody with the directly method and protein A method was tested with p16INK4a antigen. RESULTS: The resonant frequency for different antibody immobilization methods were different, and the sensitivity for p16INK4a detection also different. CONCLUSIONS: The protein A method was found to be much more better than the directly method for the immobilization of the p16INK4A antibody on the gold electrode of the quartz crystal for cervical lesion detection. The Protein A method created more reproducible and stable immobilization antibody layers with p16INK4A antigen.

Rapid detection of ovarian cancer from immunized serum using a quartz crystal microbalance immunosensor.

BACKGROUND: The objective of this study was to measure the antibody content of NuTu-19 ovarian cancer cells in serum samples using a quartz crystal microbalance (QCM) immunosensor. MATERIALS AND METHODS: NuTu-19 cells were first cultured onto the electrode surfaces of crystals in Dulbecco's modified Eagle medium, and then specified amounts of immunized serum samples of immunized rabbit were also added. The change in mass caused by specific adsorbtion of antibodies of NuTu-19 to the surfaces of the crystals was detected. RESULTS: The change in resonance frequency of crystals caused by immobilization of NuTu-19 cells was from 83 to 429 Hz. The antibody content of NuTu-19 detected was 341 ng/ul. The frequency shifts were linearly dependent on the amount of antibody mass in the range of 69 to 340 ng. The positive detection rate and the negative detection rate were 80% and 100%, respectively. CONCLUSION: This immunoassay provides a viable alternative to other early ovarian cancer detection methods and is particularly suited for health screening of the general population.