Studying resonant frequency and dissipation shifts in a mechanical resonator using a fixed-frequency drive

• Main Author: Guha, Arnab
• Format: Dissertation
• Language: English
• Published: Loughborough University 2018
• Subjects: Biomolecules; Dissipation; Fixed-frequency drive; Mechanical Engineering not elsewhere classified; Mechanical resonator; Quartz crystal resonator; Resonant frequency shift; Time resolution

Measurement of biomolecular interactions are widely used in various sectors including life sciences, pharmaceutical, clinical diagnostics, and industrial, food and environmental monitoring. The shifts in resonant frequency and dissipation of mechanical resonators have been extensively used for biomolecular measurements. Conventional resonant frequency and dissipation measurement techniques are largely limited in terms of simplicity, time resolution and potentials for on-chip integration and multiplexability. This PhD research focused on the development of a simple method for quantification of resonant frequency and dissipation shifts of a mechanical resonator, which could potentially allow system-integrable and multiplexable biomolecular measurements with high time resolution. A quartz crystal resonator was chosen as a model mechanical resonator due to its wide applicability. Analytical expressions obtained utilising Butterworth Van Dyke model allowed real-time measurements of resonant frequency and dissipation from each acquired impedance data point at a fixed frequency and amplitude. The method is suited over a broad resonance bandwidth. Quantitative validations were performed against frequency sweep method for inertial and viscous loading experiments using a 14.3 MHz quartz crystal resonator. Resonant frequency shifts related to temporal steps of quick needle touches on a selfassembled-monolayer-functionalised 14.3 MHz quartz crystal resonator surface were estimated with a time resolution of 112 s, which is nearly hundred times smaller than the reported time resolution in the quartz crystal microbalance literature. The fixed frequency drive method has been utilised for demonstration of label-free detection of a gram negative bacterial infection biomarker namely N-hexanoyl-L-Homoserine lactone (~199.2 Da), using molecular imprinted polymer nanoparticles as the receptor. The feasibility of the method has also been tested for direct detection of a large immunoprotein such as immunoglobulin E (~190 kDa), using an aptamer as the receptor. This fixed frequency based method for determination of resonant frequency and dissipation of a mechanical resonator, with no need for averaging, fitting or measurement dead time, potentially allows a simple and low-cost method suitable for integration into online or miniaturised system with significantly improved time resolution and multiplexability.