Thrombin aptamer binding strength and stability is dependent on sterical parameters when used for atomic force microscopy sensing applications. Sterical improvements on the linker chemistry were developed for high-affinity binding. For this we applied single molecule force spectroscopy using two enhanced biotinylated thrombin aptamers, BFF and BFA immobilized on the atomic force microscopy tip via streptavidin. BFF is a dimer composed of two single-stranded aptamers (aptabody) connected to each other by a complementary sequence close to the biotinylated end. In contrast, BFA consists of a single DNA strand and a complementary strand in the supporting biotinylated part. By varying the pulling velocity in force-distance cycles the formed thrombin-aptamer complexes were ruptured at different force loadings allowing determination of the energy landscape. As a result, BFA aptamer showed a higher binding force at the investigated loading rates and a significantly lower dissociation rate constant, k(off), compared to BFF. Moreover, the potential of the aptabody BFF to form a bivalent complex could clearly be demonstrated.

Using an acoustic method we showed that the aptamer configuration, especially those comprised of dimers with binding exosites sensitive to heparin and fibrinogen at thrombin, substantially increases the aptasensor sensitivity.

Development of novel polymeric materials capable of efficient CO2 capture and separation under ambient conditions is crucial for cost-effective and practical industrial applications. Here we report the facile synthesis of a new CO2-responsive polymer through postpolymerization modification of poly­(2-vinyl-4,4-dimethyl­azlactone) (PVDMA). The reactive pendant azlactone groups of PVDMA are easily modified with 4-(N-methyl­tetrahydro­pyrimidine)­benzyl alcohol (PBA) without any byproduct formation. FTIR and TGA experiments show the new PBA-functionalized polymer powder can reversibly capture CO2 at room temperature and under atmospheric pressure. CO2 capture was selective, showing a high fixing efficiency even with a mixed gas system (20% CO2, 80% N2) similar to flue gas. CO2 release occurred at room temperature, and release profiles were investigated as a function of temperature. Density functional theory (DFT) calculations coupled with modeling and simulation reveal the presence of two CO2 binding sites in the PBA-functionalized polymer resulting in a two-step CO2 release at room temperature. The ease of material preparation, high fixing efficiency, and robust release characteristics suggest that postpolymerization modification may be a useful route to designing new materials for CO2 capture.

We studied the interaction of the specific DNA aptamer sgc8c immobilized at the AFM tip with its corresponding receptor, the protein tyrosine kinase-7 (PTK7) embedded in the membrane of acute lymphoblastic leukemia (ALL) cells (Jurkat T-cells). Performing single molecule force spectroscopy (SMFS) experiments, we showed that the aptamer sgc8c bound with high probability (38.3 ± 7.48%) and high specificity to PTK7, as demonstrated by receptor blocking experiments and through comparison with the binding behavior of a nonspecific aptamer. The determined kinetic off-rate (koff = 5.16 s−1) indicates low dissociation of the sgc8c–PTK7 complex. In addition to the pulling force experiments, simultaneous topography and recognition imaging (TREC) experiments using AFM tips functionalized with sgc8c aptamers were realized on the outer regions surface of surface-immobilized Jurkat cells for the first time. This allowed determination of the distribution of PTK7 without any labeling and at near physiological conditions. As a result, we could show a homogeneous distribution of PTK7 molecules on the outer regions of ALL cells with a surface density of 325 ± 12 PTK7 receptors (or small receptor clusters) per μm2. Graphical AbstractThe specific interaction of the DNA aptamer sgc8c and protein tyrosine kinase-7 (PTK7) on acute lymphoblastic leukemia (ALL) cells was characterized. AFM based single molecule force spectroscopy (SMFS) yielded a kinetic off-rate of 5.16 s−1 of the complex. Simultaneous topography and recognition imaging (TREC) revealed a PTK7 density of 325 ± 12 molecules or clusters per μm2 in the cell membrane

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