Phase transitions in lipid vesicles detected by a complementary set of methods: heat‐transfer measurements, adiabatic scanning calorimetry, and dissipation‐mode quartz crystal microbalance

Abstract

We report on the use of the heat transfer method, a novel surface‐sensitive technique based on heat transfer through solid–liquid interfaces, to detect phase transitions of model lipid membranes. We selected the lipid DPPC because of its rich phase behavior in an experimentally accessible temperature range. The vesicles were adsorbed on nanocrystalline diamond films, known as a versatile platform material for biosensing with outstanding heat‐conduction properties. Complementary Peltier‐element‐based adiabatic scanning calorimetry (pASC) and quartz crystal microbalance with dissipation monitoring (QCM‐D) measurements were carried out to monitor the phase transitions in multilamellar and small unilamellar vesicles, respectively. The heat‐transfer measurements revealed reversible jumps upon heating and cooling in the thermal resistance in the vicinity of the expected transition temperature and they agree qualitatively with molecular simulations of the thermal conductivity across a lipid bilayer. The results show the capability of the heat transfer method to detect the main phase transition in DPPC, opening new perspectives for the study of more complex lipid systems and different solid platforms. This work confirms QCM‐D as a useful tool for the assessment of the structural changes upon the phase conversion and shows the capability of pASC to provide high‐resolution thermodynamic information on biophysical systems. Temperature profile of the heat transfer resistance Rth during the main phase transition of a DPPC supported vesicle layer adsorbed on a hydrogen‐terminated nanocrystalline diamond substrate. The arrows indicate the sense of the run: heating (red solid line) and cooling (blue solid line).

Improving the sensitivity of the heat‐transfer method (HTM) for cancer cell detection with optimized sensor chips

“…Baseline R th values examining the effect of polishing the aluminum chips, the configuration of the chips in the HTM‐device and the use of silver paste as a thermal coupler between the chip and the copper heat provide. Sample 0 serves as a reference sample as it was used in previous studies . Optimal results were obtained by coupling the polished side of the aluminum directly to the copper heater (sample 3).…”

“…The recently developed heat‐transfer method (HTM) has shown to be a versatile read‐out platform in biosensors . HTM is a fast, label‐free, and sensitive technique that requires a minimum of instrumentation and can be used “on‐the‐bench.” HTM can be used for a wide range of applications including DNA mutation analysis , quantification of DNA sequences of interest , neurotransmitter detection , and phase transition analysis in lipid vesicle layers . Additionally, the platform can be used for the specific detection of human cells in phosphate buffered saline (PBS) solution by combining HTM with SIPs .…”

Real-time analysis of dual-display phage immobilization and autoantibody screening using quartz crystal microbalance with dissipation monitoring

“…Furthermore, the effective thickness before and after phage addition was calculated using the Voigt based model consisting of an elastic element (spring) in parallel with a viscous element (dashpot). 18,20,21 The data of several overtones (third to seventh) were fitted using the software Qtools (Q-Sense AB, Sweden) keeping as fixed parameters the density and the viscosity of the fluid as 1.0 g⋅cm -3 and …”

“…11 To overcome this problem, we designed a dual-display phage system including an autoantigenic target UH-RA. 21 as a biomarker and streptavidin (STV)-binding protein (SBP) as capturing peptide, both being displayed at opposite ends of a filamentous phage. 12 This approach resulted in a higher sensitivity of signal detection assays using STV-coated magnetic beads.…”

“…On the other hand, we monitored the screening of autoantibodies in UH-RA. 21 antibody-positive serum sample using the opposite end functionality, a rheumatoid arthritis biomarker. For assessing the binding ability and stability, we followed the interaction of the dual-display phage onto STV-modified sensors by QCM-D and by complementary surface plasmon resonance (SPR) measurements.…”