Utilizing a high fundamental frequency quartz crystal resonator as a biosensor in a digital microfluidic platform

Abstract

We demonstrate the operation of a digital microfluidic lab-on-a-chip system utilizing Electro Wetting on Dielectrics (EWOD) as the actuation principle and a High Fundamental Frequency (HFF; 50 MHz) quartz crystal microbalance (QCM) resonator as a mass-sensitive sensor. In a first experiment we have tested the reversible formation of a phosphor-lipid monolayer of phospholipid vesicles out of an aqueous buffer suspension onto a bio-functionalized integrated QCM sensor. A binding of bio-molecules results in an altered mass load of the resonant sensor and a shift of the resonance frequency can be measured. In the second part of the experiment, the formation of a protein multilayer composed of the biomolecule streptavidin and biotinylated immunoglobulin G was monitored. Additionally, the macroscopic contact angle was optically measured in order to verify the bio-specific binding and to test the implications onto the balance of the surface tensions. Using these sample applications, we were able to demonstrate and to verify the feasibility of integrating a mass-sensitive QCM sensor into a digital microfluidic chip.

Advances in Microfluidic Materials, Functions, Integration, and Applications

“…219 An open droplet microfluidic system integrated with QCM resonator was used to detect binding of lipids and proteins from a single droplet on a functionalized sensor surface. 220 Various electrochemical biosensors have also been studied. Amperometric principles were employed in the mass transport study of glucose and lactate in a microspike sensor.…”

Relaxor-PT Single Crystal Piezoelectric Sensors

“…In addition, piezoelectric materials with high mechanical quality factor are usually used for acoustic bio-sensors. For example, the quartz crystal microbalance (QCM) has been used to measure very small mass changes in the order of pictograms (Figure 8) [5,112]. To detect the presence of pathogens in aqueous samples, QCM with immobilized antibody to pathogens have been successfully utilized [113].…”

Adjustment and Measurement of Contact Angle with Electrowetting on a Quartz-Crystal Microbalance

“…On combining EWOD and a QCM, droplet spreading can be generated and controlled with EWOD and simultaneously detected with a QCM. Integrating EWOD and a QCM on a single microfluidic device has been shown previously, but the QCM worked primarily as a separate sensor to detect the formation of a protein multilayer [26]. Our work provides the first report to demonstrate EWOD on a QCM chip for the dynamic measurement of contact angle; with this setup, we are able to monitor the potential-dependent change of contact angle of a water droplet in oil.…”

“…in which ∆f is the shift of the resonance frequency, f 0 is the initial resonance frequency, ∆m is the change of the surface mass, A is the area of the QCM electrode, ρ q is the density of quartz (2648 kg/m 3 [16,19,26]), µ q is the shear modulus equal to ρ q ν q 2 with ν q as the shear-wave velocity of quartz (3340 m/s [16,19,27]), and S is the sensitivity of unit mass defined with…”