(Invited) Hyper-Multimodal Sensing with Heater-Integrated Fluidic Resonators
Authors: Lee Jungchul , Ko Juhee 
Published: December 2024

Mechanical resonators with embedded fluidic channels (hereafter referred to as fluidic resonators), known as suspended micro/nanochannel resonators (SMRs or SNRs) [1, 2], allow precise and sensitive measurements of single micro/nanoparticles or single cells in transit, adsorbed biomolecules and liquid analytes. To date, the majority of studies using fluidic resonators have been performed at a fixed steady-state temperature close to room temperature, since temperature modulation inevitably changes the resonance frequency of the fluidic resonators, one of the key measurement variables.
To maintain physiologically relevant conditions or to perform measurements at different temperatures, fluidic resonators have been heated. Initially, slow heating methods such as heating bath circulation or hot plate were used, followed by fast photothermal heating to raise the temperature of the fluidic resonators and the sample together. Of note, the major drawbacks of fast photothermal heating are the need for a complicated optical system and tedious alignment, and less precise and less quantitative temperature modulation. Integration of heating electrodes into fluidic resonators during device fabrication is considered to be the best option, although fabrication complexity and cost are expected to increase or device yield may be compromised. However, if heating electrodes are successfully integrated into fluidic resonators, new measurement modalities such as microcalorimetry and thermogravimetry would be enabled and a variety of coupled phenomena between dynamics, fluid mechanics and heat transfer could be effectively studied.
Recently, we have developed heater-integrated fluidic resonators (HFRs), which allow fast, quantitative, alignment-free and wide-range temperature modulation [3]. Because the integrated heater can also act as a resistive thermometer, HFRs can track temperature and resonant frequency as they are heated by resistive thermometry and resonant densitometry. With and without a dispensing nozzle, HFRs are used for atomised spray dispensing, thermophysical property measurements and microchannel boiling studies. These are the first demonstrations of transient operation of fluidic resonators over a significantly extended temperature range. The performance of HFRs has been further enhanced by reducing mechanical and thermal losses in vacuum [4].
Our current focus is on hyper-multimodal measurements with HFRs, providing primary properties (mass density, dynamic viscosity, thermal conductivity and specific heat) and secondary properties (thermal diffusivity, kinematic viscosity and Prandtl number) of various liquid samples at elevated temperatures. Once cooperatively combined with machine learning, such hyper-multimodal measurements appear to be exclusively useful for the identification and analysis of liquid mixtures. Measured spectra of mechanical and thermophysical properties of mixtures can be separated into corresponding spectra of individual components. We envisage that these will become the basis of mechanical and thermophysical spectroscopy, enabling separation-free analysis of liquid mixtures.

References

[1] T. Burg, M. Godin, S. Knudsen, W. Shen, G. Carlson, J. Foster, K. Babcock, and S. Manalis, “Weighing of biomolecules, single cells and single nanoparticles in fluid”, Nature 446, 1066-1069 (2007)
[2] J. Lee, W. Shen, K. Payer, T. Burg, and S. Manalis, “Toward attogram mass measurements in solution with suspended nanochannel resonators”, Nano Lett. 10(7), 2537-2542 (2010)
[3] J. Ko, F. Khan, Y. Nam, B. Lee, and J. Lee, “Nanomechanical sensing using heater-integrated fluidic resonators”, Nano Lett. 22(19), 7768-7775 (2022)
[4] J. Ko, B. Lee, and J. Lee, “Advanced operation of heated fluidic resonators via mechanical and thermal loss reduction in vacuum”, Microsyst. Nanoeng. 9:127 (2023)

Figure 1