3.1. Quartz crystal microbalance (QCM) aptasensor for detection of Brucella melitensis
QCM sensors are composed of a thin piezoelectric plate with two metal electrodes on either side (Singh et al., 2013). These sensors are coated with immobilized bioreceptors such as aptamer (short synthetic oligonucleotide sequences of single stranded DNA or RNA with unique 3D structures; aptamer-based biosensors are called aptasensors) or antibody molecules for the target bacterium on their surface. Hence, QCM is a sensitive method which is performed based on the measurement of mass changes on quartz crystal surface (Bayramoglu, Ozalp, Oztekin, & Arica, 2019; Urmann, Modrejewski, Scheper, & Walter, 2016).
As shown in figure 4, Bayramoglu et al. designed a novel quartz crystal microbalance (QCM) aptasensor for the detection of Brucella melitensis (Bayramoglu et al., 2019). In this method, the surface of the magnetic nanoparticles was modified by 3-aminopropyltriethoxysilane (APTES) and then grafted with a hydrophilic macromonomer poly(ethyleneglycol)-methacrylate (PEG-MA) and glycidylmethacrylate (GMA). The specific aptamer sequence was also immobilized on the QCM chip and utilized for the identification of B. melitensis (Bayramoglu et al., 2019).