Detection of Lactose in Milk Samples Using a Wireless Multi-Enzyme Biosensor

A wireless biosensor for analysis of lactose in milk samples has been developed by co-immobilizing -galactosidase (GLA), glucose oxidase (GOD), and catalase onto a magnetoelastic ribbon-like sensor which was pre-coated with a layer of pH-sensitive polymer. The GLA-catalyzed hydrolyzation of lactose produces -d-glucose, which was oxidized to gluconic acid under the catalysis of GOD, resulting in the pH-responsive polymer shrinking, and consequently the resonance frequency (f_r) of the sensor increasing. The shifts in frequency were linearly proportional to the concentration of lactose from 2 mM to 16 mM with a detection limit of 0.72 mM. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was applied to calibrate and confirm sensor measurements. The proposed wireless sensor can be extended for assays of lactose in sealed opaque containers.