Aptamers are nucleic acid molecules that have been selected in vitro to bind to their molecular targets with high affinity and specificity. Typically, the systematic evolution of ligands by exponential enrichment (SELEX) process is used for the isolation of specific, high-affinity aptamers. SELEX, however, is an iterative process requiring multiple rounds of selection and amplification that demand significant time and labor. Here, we describe an aptamer discovery system that is rapid, highly efficient, automatable, and applicable to a wide range of targets, based on the integration of magnetic bead-based SELEX process with microfluidics technology. Our microfluidic SELEX (M-SELEX) method exploits a number of unique phenomena that occur at the microscale and implements a design that enables it to manipulate small numbers of beads precisely and isolate high-affinity aptamers rapidly. As a model to demonstrate the efficiency of the M-SELEX process, we describe here the isolation of DNA aptamers that tightly bind to the light chain of recombinant Botulinum neurotoxin type A (with low-nanomolar dissociation constant) after a single round of selection.

Significance: Lateral Brownian diffusion of proteins in lipid membranes has been predicted by Saffman and Delbrück to depend only on protein size and on the viscosity of the membrane and of the surrounding medium. Using a single-molecule tracking technique on two transmembrane proteins that bend the membrane differently and are reconstituted in giant unilamellar vesicles, we show that the mobility of a membrane protein is crucially dependent on the local membrane deformation self-generated around the protein, which can be tuned by adjusting membrane tension. The feedback between membrane shaping and mobility is well explained by analytical and numerical models that include the friction of the deformed membrane patch with the surrounding medium and the friction internal to the bilayer.

We introduce a simulation strategy to consistently couple continuum biomembrane dynamics to the motion of discrete biological macromolecules residing within or on the membrane. The methodology is used to study the diffusion of integral membrane proteins that impart a curvature on the bilayer surrounding them. Such proteins exhibit a substantial reduction in diffusion coefficient relative to “flat” proteins; this effect is explained by elementary hydrodynamic considerations.