Heat capacity measurements of sub-nanoliter volumes of liquids using bimaterial microchannel cantilevers

Abstract

Lab-on-a-Chip compatible techniques for thermal characterization of miniaturized volumes of liquid analytes are necessary in applications such as protein blotting, DNA melting, and drug development, where samples are either rare or volume-limited. We developed a closed-chamber calorimeter based on a bimaterial microchannel cantilever (BMC) for sub-nanoliter level thermal analysis. When the liquid-filled BMC is irradiated with infrared (IR) light at a specific wavelength, the IR absorption by the liquid analyte results in localized heat generation and the subsequent deflection of the BMC, due to a thermal expansion mismatch between the constituent materials. The time constant of the deflection, which is dependent upon the heat capacity of the liquid analyte, can be directly measured by recording the time-dependent bending of the BMC. We have used the BMC to quantitatively measure the heat capacity of five volatile organic compounds. With a deflection noise level of ∼10 nm and a signal-to-noise ratio of 68:1, the BMC offers a sensitivity of 30.5 ms/(J g−1 K−1) and a resolution of 23 mJ/(g K) for ∼150 pl liquid for heat capacity measurements. This technique can be used for small-scale thermal characterization of different chemical and biological samples.

Thin Film Analysis by Nanomechanical Infrared Spectroscopy

“…40,41 In particular, photothermal nanomechanical IR sensing (NAM-IR) has been developed for both deflection and resonance frequency detection schemes. 32,33,42−49…”

“…In the last 15 years, nanomechanical sensing has been exploited for biosensing purposes − and material characterization. , In particular, photothermal nanomechanical IR sensing (NAM-IR) has been developed for both deflection and resonance frequency detection schemes. ,,− …”

Nanomechanical Molecular Mass Sensing Using Suspended Microchannel Resonators

“…In this regard, suspended microchannel resonators (SMR) have been demonstrated to be excellent tools for highly sensitive detection of both colloidal particles (measuring its buoyant mass) [ 14 , 15 , 16 , 17 ] and liquid properties (by measuring its mass density, viscosity, etc.) [ 18 , 19 , 20 , 21 , 22 ]. Among other nanomechanical techniques, SMR approach is characterized for placing a liquid inside the resonator while vibrating in vacuum or gaseous atmosphere.…”

Modeling of an Optically Heated MEMS-Based Micromechanical Bimaterial Sensor for Heat Capacitance Measurements of Single Biological Cells

“…In this technique, a BMC undergoes a mechanical deflection in response to the heat produced by the IR radiation. Khan et al demonstrated the use of a BMC as a closed-chamber calorimeter that is optically heated with IR radiation to successfully measure the heat capacity of five volatile organic compounds (VOCs) with varying thermal outputs [37]. The reported system was able to provide online thermal characterization of small volumes of liquids with a resolution of 23 mJ/(gK).…”