The development of ultrasensitive microcalorimeters for bioanalysis and energy balance monitoring

Abstract

Heat generation or consumption is required for all biological processes. Microcalorimetry is an ultrasensitive method to measure heat change for various applications. In this paper, we aimed to review the ultrasensitive microcalorimeter systems and their extensive applications in bioanalysis and energy balance monitoring. We first discussed the basic structure of microcalorimeters, including the closed system and open system, temperature sensing methods, isolation materials, and temperature stabilization. Then, we focused on their applications, such as cell metabolism research, biomolecule interaction measurement, biothermal analysis, and calorimetric detection. Finally, we compared the advantages and disadvantages of commercially available microcalorimeters and their contributions to bioresearch. The development of ultrasensitive microcalorimeters provides the tools for bioanalysis at the single-cell, or even subcellular, level, as well as for precise calorimetric detection.

Keywords: Bioanalysis; Chip calorimeter; Energy balance monitoring; Microfluidics; Thermal analysis.

Fig. 1

Brief history of microcalorimeters. Beginning with the original calorimeter from 1789 ; the first microcalorimeter ; the droplet calorimeter ; the microcalorimeter used to study microbial growth ; a typical parylene-based microfluidic calorimeter ; the first commercialized chip-based DSC system ; the development of a novel thermal sensing method such as resonator vibration and frequency ; a flow-through chip DSC for protein thermal analysis; calorimetric LFA strips combined with photothermal materials for enzyme-linked immunosorbent assay (ELISA) ; a simple fabricated droplet calorimeter for energy balance monitoring ; a microfluidic calorimeter for single-cell study and a capillary-based calorimeter with a commercial thermistor as a temperature sensor , both achieving sub-nW resolution; the use of a calorimeter for fast antimicrobial susceptibility testing ; and a state-of-the-art open system with resolution up to 28 pW .

Fig. 2

Closed calorimeter systems. (a) A microfabricated calorimeter chip with Au/Ni thermopile for sensing and suspended parylene microfluidic structures . (b) A sub-nL calorimeter chip made using BCT with Ti RTD and suspended Si₃N₄ channel . (c) A system consisting of a capillary tube and a commercial SMD thermistor achieving a resolution in the sub-nW level . (d) A flexible closed calorimeter system with Bi/Sb thermopile on PI membrane bonding with PDMS microfluidic structures .

Fig. 3

Open calorimeter systems. (a) Classic structure of open calorimeter system where a droplet is placed on the suspended membrane with embedded thermopile for temperature sensing and covered with glass slide to decrease the evaporation . (b) Combination of microfabricated VO₂ thermistor and PDMS chamber for open system with the sample loaded by pipetting . (c) Open calorimeter system with sample in oil droplet, forming a VRC preventing evaporation fabricated by simplified one-step photolithography and etching to pattern Au RTD on glass substrate . (d) State-of-the-art open calorimeter system achieving a resolution of 28 pW with optimized thermopile and ultra-low noise .

Fig. 4

The use of a calorimeter system for cell metabolism study and molecule detection. (a) An illustration of magnetic cell trapping and single-cell measurement procedure using a closed system . (b) A representative result of the temperature change during the release of the trapped single T. Thermophila . (c) Images of cultured COS7s and the VO₂ thermistor with one cell on it . (d) Temperature change when adding FCCP solution with and without COS7 on the calorimeter . (e) The structures of the closed system for detection of TNF-α . (f) Thermal response during the immunoassay for different sample concentrations . (g) The microfabricated open system and schematic diagram of the sample loading with volume of 1 nL . (h) The calorimetric ELISA results for traztuzumab detection, both on PBS buffer and human serum .

Fig. 5

Combination of calorimeter system with photothermal detection and optic calorimetry. (a) Working principle of the thermal measurement combined with photothermal effect . (b) Visual quantitative detection of PSA spiked in human serum samples . (c) Schematics of the calorimetric LFA based on GNCs with high photothermal conversion efficiency for AFP detection . (d) The results of the AFP detection . (e) The structure of microfluidic optical calorimetry . (f) Thermal measurement from mixing of the EDTA droplets .

Fig. 6

Commercial calorimeter systems. (a) The Flash DSC 1 system with a silicon-based calorimeter chip. (b) The Nano ITC system from TA Instruments, with a specially designed liquid sample reservoir. (c) The Chip DSC-10, with traditional Al crucible for both liquid and solid samples. (d) The calScreener™ system, designed for high-throughput cellular metabolism monitoring.