Bulk and Surface Acoustic Wave Biosensors for Milk Analysis

Abstract

Milk and dairy products are common foods and, therefore, are subject to regular controls. Such controls cover both the identification and quantification of specific components and the determination of physical parameters. Components include the usual milk ingredients, mainly carbohydrates, proteins, and fat, and any impurities that may be present. The latter range from small molecules, such as drug residues, to large molecules, e.g., protein-based toxins, to pathogenic microorganisms. Physical parameters of interest include viscosity as an indicator of milk gelation. Bulk and surface acoustic wave sensors, such as quartz crystal microbalance (QCM) and surface acoustic wave (SAW) devices, can principally be used for both types of analysis, with the actual application mainly depending on the device coating and the test format. This review summarizes the achievements of acoustic sensor devices used for milk analysis applications, including the determination of physical liquid parameters and the detection of low- and high-molecular-weight analytes and microorganisms. It is shown how the various requirements resulting from the respective analytes and the complex sample matrix are addressed, and to what extent the analytical demands, e.g., with regard to legal limits, are met.

Keywords: EMPAS; bulk acoustic wave; drug residues; lab-on-a-chip; milk; pathogens; proteins; quartz crystal microbalance; surface acoustic wave; toxins.

Figure 1

Schematics of bulk acoustic wave devices: (a) quartz crystal microbalance (QCM); (b) electromagnetic piezoelectric sensor (EMPAS); (c) film bulk acoustic resonator (FBAR).

Figure 2

Schematics of surface acoustic wave devices: (a) delay line configuration; (b) two-port resonator; (c) one-port resonator.

Figure 3

Label-free biosensor test formats used for analyte detection in milk with acoustic biosensors (see Section 3): (a) direct detection; (b) sandwich assay; (c) displacement assay; (d) competitive assay; (e) binding inhibition assay.