Review of MEMS differential scanning calorimetry for biomolecular study

Front. Mech. Eng. DOI 10.1007/s11465-017-0451-0 REVIEW ARTICLE Shifeng YU, Shuyu WANG, Ming LU, Lei ZUO Review of MEMS differential scanning calorimetry for biomolecular study © The Author(s) 2017. This article is published with open access at link.springer.com and journal.hep.com.cn Abstract Differential scanning calorimetry (DSC) is one of the few techniques that allow direct determination of enthalpy values for binding reactions and conformational transitions in biomolecules. It provides the thermodynamics information of the biomolecules which consists of Gibbs free energy, enthalpy and entropy in a straightforward manner that enables deep understanding of the structure function relationship in biomolecules such as the folding/unfolding of protein and DNA, and ligand bindings. This review provides an up to date overview of the applications of DSC in biomolecular study such as the bovine serum albumin denaturation study, the relationship between the melting point of lysozyme and the scanning rate. We also introduce the recent advances of the development of micro-electro-mechanic-system (MEMS) based DSCs. Keywords differential scanning calorimetry, biomolecule, MEMS, thermodynamic 1 Introduction Differential scanning calorimetry (DSC) as a thermoanalytical technique was developed by Watson and O’Neill in 1966 [1]. Since then, a lot of research has been focused on developing high throughput, high sensitivity DSC and Received November 6, 2016; accepted March 9, 2017 ✉ Shifeng YU, Lei ZUO ( ) Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24061, USA E-mail: Shuyu WANG Department of Mechanical Engineering, Stony Brook University, Stony Brook, NY 11794, USA Ming LU Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA applying it into different research areas such as polymer study, biomolecular study, and drug design. A differential scanning calorimeter consists of twin cells (sample and reference) in which temperature sensor and heating module are integrated and operate in differential mode. During a differential temperature scanning process, the difference in temperature (power consumption) between the sample and reference material is measured as a function of linear temperature cycle. The difference directly reveals the heat release or absorption of the sample over temperature which further indicates the heat capacity change. There are mainly two types of DSCs based on the working principle: Power compensated DSC and heat flux DSC. For the power compensated DSC, the temperature of the sample and reference material are always kept the same by varying the heat flow to the sample and reference during the linear temperature scanning process. While in a heat flux DSC, the temperature difference is directly recorded during the same procedure. Together with the thermal resistance, the temperature difference can be converted to the heat flow difference [2]. Recently, another type of DSC was developed which is called temperature modulated differential scanning calorimetry (TMDSC) or alternative current differential scanning calorimetry (AC DSC) [3– 5]. The basic idea of the TMDSC is to add a controlled temperature modulation to the conventional linear heating. The heating process of TMDSC can be divided into two parts. The first part is to heat the sample at a certain temperature scanning rate just like the conventional DSC. In the second part, the heat capacity component of the heat flow is obtained by applying a controlled oscillating temperature modulation with a zero net temperaturechange. In a TMDSC thermal analysis, the average scanning rate, the period of modulation and the temperature amplitude of modulation are three important variables that are tuned to optimize the experiment. Virtually all biological phenomena depend on molecular interaction. A basic biology problem is to understand the folding and denaturation processes of a protein, i.e., the kinetics and thermodynamics how a protein unfolds and 2 Front. Mech. Eng. folds back into its native state [6]. Both folding/unfolding and denaturation processes are associated with enthalpy changes. The intermolecular interactions such as proteinligand association, protein/DNA interaction [7,8], antigenantibody binding processes are either enthalpically or entropically driven, depending upon the binding modes of the small molecules [9]. The determination of the affinity thermodynamics of binding compounds helps greatly to understand the nature of such molecules [10]. The specificity of binding reactions has fascinated biologists from the very beginning to quantitatively describe the driving forces that govern the formation of biomolecule [11]. This has great significance to the development of vaccines, new drugs and other molecular compounds [12]. There is a rapid growing number of high resolution crystal structures of biomolecules. However, the theoretical concepts which are developed in the tradition of physical-organic chemistry is not enough to understand such driving force of the large complex biomolecular structure straightforwardly. The proteins behave cooperatively and undergo structural rearrangements during the binding reactions. Such binding process has a complicated energy profile involving different energetic expenditures in going from free components to the final complex which can be detected directly by DSC [13]. There are several commercial DSCs for large biomolecular study. One is the MicroCal VP-DSC developed by Malvern. It can directly measure the intramolecular stability of structured macromolecules as well as the intermolecular stability of complexes such as proteins, nucleic acid duplexes and lipid and detergent micellar systems. It consumes 700 µL sample for each test and has a high enthalpy resolution as 0.01 J/oC. The sample concentration typically ranges from 0.1 to 2 mg/mL. As a capillary DSC, it is important to clean the reservoir each time after the test and this limits the concentration of the bio-sample since high concentration protein sample would stick on the wall of the capillary after denaturation and it is hard to be washed away. The maximum scanning rate of the MicroCal VP-DSC is only 1.5 oC/min which leads to relatively low throughput. Another typical commercial DSC is the TA DSC. As the most cost-effective DSC in industry. It has a different sample preparation strategy compared to the MicroCal VP-DSC. Unlike the VP-DSC which use a syringe to inject the liquid sample to the reservoir through a capillary system, the TA DSC utilizes aluminum pan for the sample preparation and sealing. The sample pan and reference pan are then put on the pedestals in the test chamber for temperature scanning. It can measure protein sample with high concentration as 100 mg/mL. It can also be used to conduct thermoanalysis of polymers, solid crystals, etc. One limit of the TA DSC is its relatively low temperature accuracy (0.025 oC for DSC 2500). (...truncated)