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Highlights: [•] Platelet adhesion and subsequent activation is monitored in real-time. [•] QCM-D combined with light microscopy for label-free detection of activation. [•] The interfacial layer affects adhesion and activation of the platelets. [•] The interfacial layer affects coupling to the oscillation, thus the QCM-D signal. [Copyright &y& Elsevier]

Highlights: [•] An example of the application of QCM-D to live cell studies. [•] Detection of human pluripotent stem cell-derived cardiomyocyte cluster beating. [•] Clusters were studied in a thin liquid film and in a large liquid volume. [•] The QCM-D beating profile provides an individual fingerprint of the hPS-CMCs. [ABSTRACT FROM AUTHOR]

Abstract: Organelle transport studies are often performed using melanophores from lower vertebrates due to the ease of inducing movements of pigment granules (melanosomes) and visualizing them by optical microscopy. Here, we present a novel methodology to monitor melanosome translocation (which is a light-sensitive process) in the dark using the quartz crystal microbalance with dissipation monitoring (QCM-D) technique. This acoustic sensing method was used to study dispersion and aggregation of melanosomes in Xenopus laevis melanophores. Reversible sensor responses, correlated to optical reflectance measurements, were obtained by alternating addition and removal of melatonin (leading to melanosome aggregation) and melanocyte-stimulating hormone (MSH) (leading to melanosome dispersion). By confocal microscopy, it was shown that a vertical redistribution of melanosomes occurred during the dispersion/aggregation processes. Furthermore, the transport process was studied in the presence of cytoskeleton-perturbing agents disrupting either actin filaments (latrunculin) or microtubules (nocodazole). Taken together, these experiments suggest that the acoustic responses mainly originate from melanosome transport along actin filaments (located close to the cell membrane), as expected based on the penetration depth of the QCM-D technique. The results clearly indicate the potential of QCM-D for studies of intracellular transport processes in melanophores. [Copyright &y& Elsevier]

Abstract: To improve design processes in the field of nanomedicine, in vitro characterization of nanoparticles with systematically varied properties is of great importance. In this study, surface sensitive analytical techniques were used to evaluate the responsiveness of nano-sized drug-loaded polyelectrolyte complexes when adsorbed to model lipid membranes. Two bioreducible poly(amidoamine)s (PAAs) containing multiple disulfide linkages in the polymer backbone (SS-PAAs) were synthesized and used to form three types of nanocomplexes by self-assembly with human insulin, used as a negatively charged model protein at neutral pH. The resulting nanoparticles collapsed on top of negatively charged model membranes upon adsorption, without disrupting the membrane integrity. These structural rearrangements may occur at a cell surface which would prevent uptake of intact nanoparticles. By the addition of glutathione, the disulfide linkages in the polymer backbone of the SS-PAAs were reduced, resulting in fragmentation of the polymer and dissociation of the adsorbed nanoparticles from the membrane. A decrease in ambient pH also resulted in destabilization of the nanoparticles and desorption from the membrane. These mimics of intracellular environments suggest dissociation of the drug formulation, a process that releases the protein drug load, when the nanocomplexes reaches the interior of a cell. [Copyright &y& Elsevier]

Abstract: The rapid development of surface sensitive biosensor technologies, especially towards nanoscale devices, requires increasing control of surface chemistry to provide reliable and reproducible results, but also to take full advantage of the sensing opportunities. Here, we present a surface modification strategy to allow biotinylated biomolecules to be immobilized to gold coated sensor crystals for quartz crystal microbalance with dissipation monitoring (QCM-D) sensing. The unique feature of QCM-D is its sensitivity to nanomechanical (viscoelastic) properties at the sensing interface. The surface modification was based on mixed monolayers of oligo(ethylene glycol) (OEG) disulfides, with terminal –OH or biotin groups, on gold. Mixtures containing 1% of the biotin disulfide were concluded to be the most appropriate based on the performance when streptavidin was immobilized to biotinylated sensors and the subsequent biotinylated bovine serum albumin (BSA) interaction was studied. The OEG background kept the unspecific protein binding to a minimum, even when subjected to serum solutions with a high protein concentration. Based on characterization by contact angle goniometry, ellipsometry, and infrared spectroscopy, the monolayers were shown to be well-ordered, with the OEG chains predominantly adopting a helical conformation but also partly an amorphous structure. Storage stability was concluded to depend mainly on light exposure while almost all streptavidin binding activity was retained when storing the sensors cold and dark for 8 weeks. The surface modification was also tested for repeated antibody–antigen interactions between BSA and anti-BSA (immobilized to biotinylated protein A) in QCM-D measurements lasting for >10h with intermediate basic regeneration. This proved an excellent stability of the coating and good reproducibility was obtained for 5 interaction cycles. With this kind of generic surface modification QCM-D can be used in a variety of biosensing applications to provide not only mass but also relevant information of the structural properties of adlayers. [Copyright &y& Elsevier]

Abstract: The aim of the present work is to develop a protocol for the specific immobilization of liposomes, via tethers, onto functionalized gold surfaces, and in addition to give one example for such a surface architecture. All surface functionalization steps are charcerized and controlled. First, mixed thiolate self-assembled monolayers (SAMs) prepared from COOH- and OCH3-terminated oligo(ethylene glycol) (OEG) alkane thiols were characterized by polarization modulation reflection absorption infrared spectroscopy (PM-RAIRS) and by X-ray photoemission spectroscopy (XPS). The composition of the mixed SAMs was found to be close to that of the thiol solution. Next, grafting of biotin conjugated with an NH2-terminated OEG spacer (biotin–OEG–NH2) to the COOH groups via conventional amine coupling was optimized with respect to the COOH/OCH3 ratio of the SAM. The grafting of biotin–OEG–NH2 was assessed by monitoring the binding of neutravidin and albumin to the biotinylated surfaces using quartz crystal microbalance with dissipation monitoring (QCM-D), as well as by PM-RAIRS. It was shown that a COOH/OCH3 ratio of around 0.3 was sufficient to saturate the SAMs with neutravidin. Finally, tethering of liposomes onto the neutravidin-terminated SAMs, was achieved. As an application example, of a close packed layer of tethered liposomes was exposed to the membrane-penetrating peptide melittin. As monitored by QCM-D, the liposomes fused when interacting with the peptide and ruptured into an extended, supported lipid bilayer over the whole surface. In summary, the described surface modification has potential for the development of assays requiring tethered intact liposomes, or tethered planar bilayers. Such surface architectures are especially important for the study of transmembrane proteins and peptides. [Copyright &y& Elsevier]