Surface Acoustic Wave (SAW) for Chemical Sensing Applications of Recognition Layers

Abstract

Surface acoustic wave (SAW) resonators represent some of the most prominent acoustic devices for chemical sensing applications. As their frequency ranges from several hundred MHz to GHz, therefore they can record remarkably diminutive frequency shifts resulting from exceptionally small mass loadings. Their miniaturized design, high thermal stability and possibility of wireless integration make these devices highly competitive. Owing to these special characteristics, they are widely accepted as smart transducers that can be combined with a variety of recognition layers based on host-guest interactions, metal oxide coatings, carbon nanotubes, graphene sheets, functional polymers and biological receptors. As a result of this, there is a broad spectrum of SAW sensors, i.e., having sensing applications ranging from small gas molecules to large bio-analytes or even whole cell structures. This review shall cover from the fundamentals to modern design developments in SAW devices with respect to interfacial receptor coatings for exemplary sensor applications. The related problems and their possible solutions shall also be covered, with a focus on emerging trends and future opportunities for making SAW as established sensing technology.

Gas Sensors Based on Conducting Polymers

“…Surface acoustic wave resonators represent one of the most prominent acoustic devices for their exceptionally high frequency from several hundred MHz to GHz, which can record remarkably diminutive frequency shifts resulting from exceptionally small mass loadings making them potentially suitable in mass sensing applications [183]. Clearly, SAW resonator is a sensitive layer coated on the gap between a transmitter (an input) and a receptor (an output) interdigital transducers (IDTs) coating on the top of the piezoelectric crystal to design a SAW gas sensor [184].…”

Comparison of AlN vs. SIO2/LiNbO3 Membranes as Sensitive Elements for the SAW-Based Acceleration Measurement: Overcoming the Anisotropy Effects

“…Recent developments based on monolithic solid-state constructionsare characterized by relatively high stability of parameters, low energy consumption (0.5-1 W) [1]. Although SAW-based micromechanical accelerometers (MMA) are currently still under development, commercially available SAW sensors are widely used in other applications ranging from medicine and life safety to unmanned devices exemplified by vapor and gas analyzers [2][3][4], temperature control systems [5,6] as well as pressure detection systems [7].…”

Guided acoustic wave sensors for liquid environments

“…The affinity of the membrane towards a specific target analyte is a fundamental prerequisite as it can drive the sensor selectivity towards a specific application. In gas sensing applications, the sensing membrane can be a thin Pd film [2,3], a thin lead phthalocyanine (PbPc) film [4] a graphene-like nano-sheet [5], a calixarene layer [6] or a polyethynyl-fluorenol layer [7], to cite just few examples, to detect H 2 , NO 2 , carbon monoxide, organic vapors or simply the relative humidity of the surrounding environment. In liquid phase sensing applications, the membrane can be poly(isobutylene) (PIB), poly(epichlorohydrin) (PECH), or poly(ethyl acrylate) (PEA) to test toluene, xylenes, and ethyl benzene solutions [8], or polysiloxane film containing acidic functional groups for detection of organic amines in aqueous phase [9], or macrocyclic calixarenes for the detection of organic pollutants in drinking water [10].…”

“…6 shows the derivative of the ℎ and of the first five LMs in ST 90°-x quartz/SiO 2 with respect to the layer normalized thickness. As it can be seen, the magnitude of the gravimetric sensitivity…”