Nanomechanical Sensing Using Heater-Integrated Fluidic Resonators

Abstract

Micro/nanochannel resonators have been used to measure cells, suspended nanoparticles, or liquids, primarily at or near room temperature while their high temperature operation can offer promising applications such as calorimetric measurements and thermogravimetric analysis. To date, global electrothermal or local photothermal heating mechanisms have been attempted for channel resonators, but both approaches are intrinsically limited by a narrow temperature modulation range, slow heating/cooling, less quantitative heating, or time-consuming optical alignment. Here, we introduce heater-integrated fluidic resonators (HFRs) that enable fast, quantitative, alignment-free, and wide-range temperature modulation and simultaneously offer resistive thermometry and resonant densitometry. HFRs with or without a dispensing nozzle are fabricated, thoroughly characterized, and used for high throughput thermophysical properties measurements, microchannel boiling studies, and atomized spray dispensing. The HFR, without a doubt, opens a new avenue for nanoscale thermal analysis and processing and further encourages the integration of additional functions into channel resonators.

Advanced Operation of Heated Fluidic Resonators via Mechanical and Thermal Loss Reduction in Vacuo

“…Steady-state resistance differences between the heating pulse on and off and time constants of resistance at the rising edge are extracted to characterize the temperature response. Considering 30 ms of a pulse heating time previously used 8 and the increased time constant (previously ~1 ms in atmospheric pressure) of HFR in vacuum due to delayed thermal diffusion, pulse heating with 80ms width and 160-ms period (50% duty) is used. 3-mW amplitude and 3-mW DC offset are applied, which corresponds under 3 o C modulation at 27 o C average temperature (in vacuum).…”

“…Figure 3c shows the ΔR with a heating pulse as a function of the thermal conductivity (k) of 6 different liquids filled inside HFR. Measurement points (solid circles) are fitted by ΔR=A/(k-B)+C from dimensional analysis 8 where A, B, and C constants are shown in Figure S5. B must have negative value so that the ΔR does not diverge to infinity at the positive k. Since ΔR is a nonlinear function of k, sensitivity can be defined as the 1 st derivative of fitting function, dΔR/dk as shown in Figure 3d.…”

“…Figures 3c-3d show volumetric heat capacity (𝜌cp) and specific heat capacity (cp) measurements by using a combination of measurement parameters 8 , ΔR, 𝜏, and resonance frequency (f), following the dimensional analysis 8 . Sensitivity can be represented by their slope from linear function fits (𝜏/ΔR=a𝜌cp+b or 𝜏/ΔR/|Δf|=dcp+e) where constants a, b, d, and e are shown in Figure S5.…”

“…Since most microfluidic platforms for thermophysical properties measurement do not equip direct volume or mass measurements, their measurement results tend to be extensive and thus proportional to sample quantity. To integrate thermal sensing with gravimetric sensing metrology 7 , we have recently introduced a simultaneous, fast, and precise thermophysical properties measurement using heated fluidic resonators (HFRs) 8 . With HFRs, three intensive properties-thermal conductivity (k), specific heat capacity (cp), and density (ρ)-are simultaneously obtained by resistive heating/thermometry and resonant densitometry.…”

“…The effect of minimizing convection loss is more significant in micro-/nano structures due to the scaling effect of heat transfer 13 where convection coefficients tend to increase with decreasing characteristic dimensions. Since our previous report 8 is based on the atmospheric pressure operation of HFRs, their performance can be improved by decreasing convection loss in vacuum.…”