Flexible SAW Microfluidic Devices as Wearable pH Sensors Based on ZnO Nanoparticles

Abstract

In this work, a new flexible and biocompatible microfluidic pH sensor based on surface acoustic waves (SAWs) is presented. The device consists of polyethylene naphthalate (PEN) as a flexible substrate on which aluminum nitride (AlN) has been deposited as a piezoelectric material. The fabrication of suitable interdigitated transducers (IDTs) generates Lamb waves (L-SAW) with a center frequency ≈500 MHz traveling in the active region. A SU-8 microfluidics employing ZnO nanoparticles (NPs) functionalization as a pH-sensitive layer is fabricated between the IDTs, causing a shift in the L-SAW resonance frequency as a function of the change in pH values. The obtained sensitivity of ≈30 kHz/pH from pH 7 to pH 2 demonstrates the high potential of flexible SAW devices to be used in the measurement of pH in fluids and biosensing.

Emerging Wearable Chemical Sensors Enabling Advanced Integrated Systems toward Personalized and Preventive Medicine

“…In addition to humidity, VOCs, and blood glucose, sweat is another indicator correlated with human pathological conditions or diseases. − Sweat pH contains a lot of information related to human pathological conditions, including but not limited to metabolic alkalosis, skin diseases, and cystic fibrosis, making the monitoring of sweat pH very meaningful. Figure f presents a flexible gravimetric pH sensor designed by Scarpa et al., and the flexibility of the sensor was realized by fabricating the piezoelectric thin AlN membrane on a polyimide substrate .…”

Functionality of Flexible Pressure Sensors in Cardiovascular Health Monitoring: A Review

“…The purpose of a flexible substrate is to safeguard flexible, conformal contact connecting human bodies to the electronics and should be capable of long-term reliability. The most commonly used substrate materials are elastomers, self-healing materials, hydrogels, and UV cross-linkable materials. , Flexible polymeric materials such as polydimethylsiloxane (PDMS), polyesters (polyethylene terephthalate (PET) and polyethylene napthalate (PEN)), polyurethane (PU), polyether sulfone (PES), poly­(ether ether ketone) (PEEK) and polyimide (PI), silicones (Ecoflex rubber), rubbers, and some natural materials (Cellulose) are favorable candidates to be used as substrates in flexible devices. PDMS has been used as the most common flexible substrate material in wearable electronic devices due to its inherent transparency and impressive stretchability.…”

Multifunctional and Wearable Patches Based on Flexible Piezoelectric Acoustics for Integrated Sensing, Localization, and Underwater Communication

“…Flexible and wireless sensors have attracted profound interest owing to their widespread applications in healthcare, [1][2][3] wearable Extensive studies have been done for flexible acoustic wave devices used in various fields such as sensing (temperature, [21] humidity, [22] UV, [23] biosensing, [20,24] strain, [25][26][27][28] and pH), [29] acoustofluidics, [30] and flexible RF filter/oscillator. [17] Depending on the structural designs, piezoelectric devices with different vibration modes have been fabricated, e.g., surface acoustic wave (SAW) devices, [31] Lamb wave devices, [32] and film bulk acoustic resonators (FBAR).…”

“…There are huge interest recently in the development of flexible acoustic wave devices, mainly because of their promising properties (such as mechanical bendability, lightweight, cost‐effectiveness, biocompatibility, and disposability). [ 17–20 ] Extensive studies have been done for flexible acoustic wave devices used in various fields such as sensing (temperature, [ 21 ] humidity, [ 22 ] UV, [ 23 ] biosensing, [ 20,24 ] strain, [ 25–28 ] and pH), [ 29 ] acoustofluidics, [ 30 ] and flexible RF filter/oscillator. [ 17 ] Depending on the structural designs, piezoelectric devices with different vibration modes have been fabricated, e.g., surface acoustic wave (SAW) devices, [ 31 ] Lamb wave devices, [ 32 ] and film bulk acoustic resonators (FBAR).…”