Monolithic glass suspended microchannel resonators for enhanced mass sensing of liquids

Suspended microchannel resonators (SMRs) have been recently developed as highly sensitive platforms to study bacteria, cell populations, antibiotic resistance and other micron-sized analytes. Unfortunately, the time-consuming and challenging fabrication process represents the main drawback for the implementation of these platforms as new point-of-care devices. In this work, we show that femtosecond laser direct writing can be successfully implemented as a rapid and cost-effective 3D fabrication process able to define the suspended resonant structure and the embedded microfluidic channel in one-step, only. Furthermore, the use of a fused silica substrate guarantees a totally transparent resonator, a useful property in view of adding optical analyses to the mechanical one. The resonance properties of the fabricated SMRs were accurately characterized in terms of frequency, quality factor and Allan deviation, in different working conditions. The monolithic glass SMR is able to analyze with high precision liquids with different mass density, thanks to a density resolution (1.04·10-3 kg/m3) that is the highest among SMRs and microcapillaries used for this purpose. Finally, the effective biosensing capability is demonstrated by evaluating the microbial load of aqueous solutions containing different concentrations of P. fluorescens.