Utilizing photothermally induced oscillation damping parameters for the determination of bacterial load suspended in microfluidic resonators

Abstract

Microchannel resonators containing a miniaturized volume of a solution can have various applications in different fields. In this study, a microchannel cantilever was loaded with a solution containing a very small number of Pseudomonas fluorescens bacteria suspended in M9 growth medium. The liquid-filled microchannel cantilever was irradiated with a 532-nm laser. The shift in the frequency of the cantilever due to varying bacterial loads is less reliable; therefore, it could not be used for monitoring the bacterial concentration. The energy loss of the cantilever extracted from the quality factor exhibited reliable results and a very strong correlation with the bacterial concentration. The results showed a linear relation between the damping factor of the cantilever and the bacterial concentration. Accordingly, these findings were expected because the bacteria inside the solution can be considered as particles acting against the cantilever motion due to the solution’s viscosity. Thus, more bacteria caused more damping, in agreement with the experimental observations. A semiquantitative experiment was conducted with a heat source (i.e., laser beam) that focused at the cantilever tip to demonstrate the redistribution of the bacterial load within the solution due to the thermal gradient.

Keywords

• Microfluidic resonators
• Oscillation
• Damping parameters
• Bacteria
• Thermal gradient