Towards a field deployable pathogen detection system by quartz-crystal microbalance

Abstract

Quartz crystal microbalance (QCM) sensors have been applied to detect foodborne pathogens such as Salmonella Typhimurium, E.coli O157:H7, and Campylobacter jejuni. As pathogens are placed on vibrating quartz surface, the change in mass of the pathogens affects the characteristic of a QCM. The presence of pathogens that antibody captures can be correlated to the shift in resonance frequency. Thus, theoretical description is necessary to understand the relationship between the change in frequency and mass. In this work, the relationship between theoretical and experimental results is examined by comparing the frequency shift caused by different type of liquids. In general, a QCM can be represented by a Butterworth-Van-Dyke (BVD) circuit made up of resistance R, inductance L, and capacitance C. With physical properties of quartz, viscosity-density product of the liquid has an effect on inductance as well as resistance. As a preliminary experiment, measurements of mixtures of water and glycerol were conducted to evaluate results from the different levels of viscosity and density. The results of the experiments showed that higher viscosity and density resulted in lower resonant frequencies. With regard to theoretical calculation, increase of R and L resulted in a proportional increase in the square root of the viscosity-density product. Increased lumped parameters explains the decreased resonant frequency. Therefore, the shift of the resonant frequency of the load and unloaded QCM could be calculated based on the admittance from circuit components. Blank (air) sample, water, glycerol and water mixture have shown proportional shift in the resonant frequencies. The experiments and theoretical model were matched within reasonable range. The average difference between the theory and the experiments (Matlab/FEM model) was 7.04 %.