A piezoelectric flexural plate wave (FPW) Bio-MEMS sensor with improved molecular mass detection for point-of-care diagnostics

The Respiratory Syncytial Virus (RSV) is responsible or a high rate of post-neonatal deaths. A fast and early diagnosis with accurate detection is vital for an effective treatment. Common diagnostics for the identification of unknown pathogens require large sample volumes and are time consuming. In this work, a piezoelectric flexural plate wave (FPW) Bio-MEMS sensor has been developed. The detection is based on the frequency shift of a FPW membrane due to binding of an additional mass depending on the applied functionalisation treatment. There are many acoustic sensors for molecular mass detection. However, the operating frequencies of sensors, such as shear horizontal surface acoustic wave (SH-SAW), surface transverse wave (STW) are usually larger than 100 MHz, which substantially complicates the readout electronics and increases the overall device costs. Only flexural plate wave (FPW) sensors have lower operating frequencies, allow for high mass sensitivity, and their phase velocity is less than the sound velocity in liquid, thus resulting only in minor energy dissipation into a testing liquid. A piezoelectric FPW-sensor with multiplexing capability has been developed for a point of care device in this work. The FPW-sensor consists of an electrode configuration termed as an interdigital transducer (IDT) placed on a membrane. An input IDT excites and an output IDT detects the propagating acoustic waves through a PZT layer. Design optimizations and fabrication improvements of the FPW sensor led to significantly reduced attenuation of the wave signal and the damping of the propagating waves between the IDTs. While a frequency shift of about 350 Hz was detected for design A, about 7 kHz can be measured with the improved sensor design B. Thus the resolution was significantly improved from 0.7 Hz/nM to 14 Hz/nM chemokine in complex solution.