Nano-watt Microcalorimeter For Monitoring The Energy Balance Of Thermal Reactions

Real-time energy balance monitoring is crucial for characterizing and analyzing the thermodynamics of physical,chemical and biological processes.However,monitoring the energy balance at the micro-and/or nano-scales is challenging,especially with a temperature and power resolution in m K and n W range,respectively.The fluorescent methods based on fluorescent polymeric thermometers,green fluorescent protein or quantum dots are selections for temperature mapping of samples.Nevertheless,they are not capable of measuring the total temperature change,and providing abundant sensitivity and resolution.Microcalorimetry has become a gold standard for characterizing label-free molecular interactions to evaluate their enthalpy,entropy,specific heat and many other parameters.It is capable of processing small volume samples ranging from a fewμL to p L or less,leading to an unprecedented resolution.Therefore,it can measure minute temperature change,dissipated power and consumed energy in real time,which could provide the potential in revealing the mechanism of thermal reactions and cellular thermodynamics.In order to measure the minute temperature change and dissipated power of thermal reactions in small volume,a high-resolution microcalorimeter chip（μC）and a real-time energy balance monitoring system are developed and evaluated.Based on theμC system,the real-time energy balance during the autonomous motions of Pt microrobots and the defensive behavior of Paramecium caudatum（P.caudatum）are monitored.The corresponding temperature change,dissipated power and energy are measured and calculated,resulting in the thermodynamic analysis of self-propelled mechanism of Pt microrobots and defense mechanism of P.caudatum.The main contents are specifically showed as follows:（1）An open chamberμC based on high-performance resistance temperature detector（RTD）is proposed.First,the design considerations ofμCs,including reaction chamber,thermal isolation,fluid handling and temperature sensing,are assessed.Based on the considerations,a high-resolutionμC with an assembled RTD is designed,and its structure and heat transfer efficiency are simulated and evaluated.Then,the detection circuit based on Wheatstone bridge is designed,applying the differential mode to decrease the detection errors.Finally,by using the differential circuit,the thermodynamic parameters ofμC,such as thermal conductance,thermal capacitance and time constant,are measured and calculated to evaluate theμC properties.（2）An ultrasensitive energy balance monitoring method is proposed.Based on the high-performanceμC,a real-time energy balance monitoring platform,consisting of the sample handling system,detection circuit,thermal isolation chamber,data acquisition system and microscopy imaging system,is developed.The properties of theμC system is tested and evaluated,resulting in a detection sensitivity of 27.5 k V·W^-1,and the temperature and power resolution of 49.33μK and 14.00 n W,respectively.TheμC system is then utilized to monitor the mixing of hydrogen peroxide（H₂O₂）with water,and to calculate its temperature change and dissipated power.The results of the mixing experiments demonstrate the capability of the ultrasensitive energy balance monitoring system in the determination of minute temperature change.（3）The self-propelled mechanism of Pt microrobots is studied using the ultrasensitive energy balance monitoring system.First,the chemotactic Pt microrobots are designed and fabricated.The properties are characterized and evaluated by determining their velocity and displacement.Then,the real-time energy balance during the autonomous motions of Pt microrobots in H₂O₂is monitored,and the corresponding temperature change and dissipated power are measured and calculated.Finally,the relationship between H₂O₂ decomposition catalyzed by Pt microrobots and H₂O₂concentration is discussed.The experimental results demonstrate the capability of theμC system in the thermodynamic analysis of self-propelled mechanism of Pt microrobots.（4）The defense mechanism of P.caudatum is studied using the ultrasensitive energy balance monitoring system.First,a single cell capture and extraction method based on the least flow resistance path principle and pressure control is proposed.The microfluidic chip is designed,fabricated and tested,having a single cell capture efficiency of>99%.The experimental results demonstrate that the proposed method can realize the high-efficiency single cell capture and the extraction of captured cell simultaneously.Then,the temperature change and dissipated power are measured and calculated by monitoring the mixing of P.caudatum suspension with water and Triton with water.Finally,the real-time energy balance during the defensive behavior of P.caudatum to Triton is monitored using the ultrasensitiveμC system,and the temperature change,dissipated power and consumed energy are determined.The experimental results demonstrate the capability of theμC system in the thermodynamic analysis of defense mechanism of P.caudatum.In summary,an ultrasensitive energy balance monitoring system with n W resolution based on an open chamberμC is proposed to monitor the real-time energy balance during the autonomous motions of Pt microrobots and the defensive behavior of P.caudatum.The corresponding temperature change,dissipated power and consumed energy are measured and calculated.The thermodynamic analysis of these mechanism demonstrate the capabilities of the proposedμC system and its extensive applications in characterization and analysis of physical,chemical and biological processes.