Locally resonant porous phononic crystal sensor for heavy metals detection: A new approach of highly sensitive liquid sensors

In this research, a novel and highly sensitive phononic crystal (PnC) sensor is presented for the detection
of CdBr2 concentrations at a low scale (ppm) which is considered a highly toxic heavy metal ion in freshwater.
The proposed sensor is composed of two thin layers of rubber covering both the top and bottom
surfaces of a one-dimensional ternary porous silicon (PSi) PnC. As a result, the whole designed structure is
arranged as {rubber/[PSi1/PSi2/PSi3]N/rubber}. The appearance of local resonant modes is due to the presence
of two thin rubber layers as a cap layer of the PnC design. In particular, the spectral position of the
modes is significantly tuned when filling the PSi layers with CdBr2 ions. It is worth mentioning that the
novelty of this work is mainly focused on three axes. The first one is the use of locally resonant PnCs (not
conventional defective ones) as highly sensitive biosensors. The second one, the liquid of interest here is
considered a dangerous aqueous solution with a very low scale (ppm). The last promising point, we proposed
the pores inside Si layers are filled with a liquid material in contrast to most of the micromechanics
methods of composite materials that supposed the pores are empty (just voids are inside). To realize the
best performance of this sensor, an optimization strategy of some related parameters such as the rubber
layer thickness, the geometry of the PnC, and the unit cell number was conducted. In this regard, the proposed
sensor provides promising values of sensitivity, quality factor, detection limit, and damping rate of
47.25 Hz/ppm, 2756.2, 82 ppm, and 0.00018, respectively. Therefore, the present design could be of serious
contribution to liquid sensors and bio-sensing applications due to its simplicity, novelty, and high
performance.