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One of the oldest tricks in the book is science is to “heat up a sample.” It’s an old trick, but a good one, and one that is getting better. That’s especially true for differential scanning calorimetry (DSC), which analyzes how heat impacts a sample. With DSC analysis, a sample can be cooled to –180° Celsius and heated up to 2400° Celsius. That provides a wide range for analyzing changes.
In 2013, Christopher Johnson of the U.K.-based Medical Research Council Laboratory of Molecular Biology wrote in the Archives of Biochemistry and Biophysics: “Differential scanning calorimetry measures the heat capacity of states and the excess heat associated with transitions that can be induced by temperature change.” He added, “DSC has found almost universal application in studying biological macromolecules.” There are DSCs that are designed for biopolymers like proteins, lipids, and nucleic acids, and heat up to about 130° Celsius.
In fact, the information collected from DSC can be used in many biology-related ways—often in medical research. In Scientific Reports in 2015, Olga Abian of the University of Zaragoza in Spain and her colleagues wrote: “Recently, [DSC] has been acknowledged as a novel tool for diagnosing and monitoring several diseases.” Then, in 2018, Abian and her colleagues reported in Biochimica et Biophysica Acta (BBA)—General Subjects that thermal liquid biopsies, created with DSC, “could be used in combination with current clinical assessment for the earlier detection of melanoma recurrence and metastasis.”
A new MicroCal
When asked about the latest advance in DSC from Malvern Panalytical (Northhampton, MA), which develops, manufactures, and sells ultrasensitive microcalorimeters used by life science and drug discovery researchers, Verna Frasca—field applications manager, bioscience—says, “Our latest product is the MicroCal PEAQ-DSC, to characterize protein and biopolymer stability by differential scanning calorimetry.”
Malvern Panalytical’s MicroCal PEAQ-DSC can be used to characterize protein and biopolymer stability. (Image courtesy of Malvern Panalytical.)These DSC platforms use matched, fixed-in-place cells: one contains a dilute biopolymer solution in buffer, and the second contains matched buffer. “The DSC instrument heats the sample at a constant rate—up to 240 °C/hour for the PEAQ-DSC—and, as the protein thermally denatures, the DSC measures the change in excess heat capacity of the protein relative to the buffer.”
Along with screening for thermal stability, typically based on the thermal transition or “melting” temperature (Tm), the information collected from DSC thermograms provides a “fingerprint” of protein unfolding. The collected data include: onset temperature, melting temperature, enthalpy of transition, and change in heat capacity. But that’s just the start of the available information. Frasca notes that the DSC platform also provides much more information, including deconvolution of individual transitions fit to an appropriate denaturation model; shape/width of transition peak(s) from DSC thermogram; peak resolution of complex thermograms, such as antibodies; reversibility; concentration dependence; and DSC scan rate dependence. “This information is used during protein engineering and structural biology,” Frasca explains.
That information can be applied in many ways. For instance, Frasca says, “The comparison of DSC fingerprints can be used during biopharmaceutical discovery and development, as well as comparison of biosimilars to innovators, and DSC gives valuable stability information on multi-domain proteins like antibodies.” That information can include higher-order structure characterization.
Scientists use this information to guide protein engineering or compare proteins produced with different expression systems, such as the glycosylation effect on domain stability. In addition, Frasca points out that the results from this platform can be used to “relate changes in functional activity of proteins to stability changes of individual domains.” She adds that this information can be used to evaluate biological membranes, biosimilars, lipids, nucleic acids, and other biopolymers and biomolecular complexes.
With the MicroCal PEAQ-DSC system, scientists can get “an automated format, with an integrated autosampler for DSC cell filling and washing,” Frasca says. With 96-well plates, this automated system can be loaded with up to six plates. That adds up to 288 experiments, using two wells per DSC scan.
Like most any modern analytical platform, the PEAQ-DSC’s performance and capabilities depend, at least in part, on software. “The software tools support the generation of reproducible, reliable, high-quality DSC data, and can generate reports,” Frasca explains. “There is also an optional package for 21 CF Part 11 compliance, when DSC is performed in a regulatory environment.”
More on the market
Differential scanning calorimetry can be used in many applications, including guiding protein engineering—such as in the red, cyan, and green proteins depicted here. (Image courtesy of Peter Allen.)In the DSC market, scientists can consider many platforms. Here are a few more devices on the market.
From Germany, Linseis brings more than 60 years of experience to thermal-analysis equipment. One platform from Linseis is the Chip-DSC10. According to the company, this platform “integrates all essential parts of DSC: furnace, sensor, and electronics in a miniaturized housing. The chip-arrangement comprises the heater and temperature sensor in a chemically inert ceramic arrangement with metallic heater and temperature sensor.” The company also makes the DSC PT 1600, which can expose a sample to a temperature range of –150 to 2400 °C, which is recommended for high-temperature metals and ceramics.
At Mettler-Toledo (Columbus, OH), scientists can choose from various platforms, including the DSC 3, which the company calls “the best choice for manual or automatic operation, from quality assurance and production through to research and development.” Moving up to the DSC 3+ provides what Mettler-Toledo describes as an “innovative DSC sensor with 120 thermocouples which guarantees unbeatable sensitivity and outstanding resolution.”
TA Instruments (New Castle, DE) offers multicell and nano-DSC instruments. For its multicell DSC, the company notes: “Compared with a single-sample DSC, the three removable, reusable sample ampules and one reference ampule in the MC DSC increase sample throughput and ensure high precision and unmatched reproducibility.” The company points out that its “The Nano DSC differential scanning calorimeter is designed to characterize the molecular stability of dilute in-solution biomolecules.” For the Nano DSC, “Solid-state thermoelectric elements are used to precisely control temperature and a built-in precision linear actuator maintains constant or controlled variable pressure in the cell.” Plus, “Automated, unattended continuous operation with increased sample throughput is achieved with the optional Nano DSC Autosampler,” adds TA Instruments.
To review a range of DSC platforms, visit Labcompare’s DSC instrument page. Also, there’s a page of items for DSC sample preparation.
It seems that old is new again when it comes to heating up samples to learn more about them. Actually, heating things up in science labs has never gone out of style, and probably never will. DSC is certainly one area where scientists keep finding new ways to use it.
Mike May is a freelance writer and editor living in Texas. He can be reached at [email protected]