Inertial manipulation and transfer of microparticles across laminar fluid streams

A general strategy for controlling particle movement across streams would enable new capabilities in single-cell analysis, solid-phase reaction control, and biophysics research. Transferring cells across streams is difficult to achieve in a well-controlled manner, since it requires precise control of fluid flow along with external force fields or precisely manufactured mechanical structures. Herein a strategy is introduced for particle transfer based on passive inertial lift forces and shifts in the distribution of these forces for channels with shifting aspect ratios. Uniquely, use of the dominant wall-effect lift parallel to the particle rotation direction is explored and utilized to achieve controllable cross-stream motion. In this way, particles are positioned to migrate across laminar streams and enter a new solution without significant disturbance of the interface at rates exceeding 1000 particles per second and sub-millisecond transfer times. The capabilities of rapid inertial solution exchange (RInSE) for preparation of hematological samples and other cellular assays are demonstrated. Lastly, improvements to inline flow cytometry after RInSE of excess fluorescent dye and focusing for downstream analysis are characterized. The described approach is simply applied to manipulating cells and particles and quickly exposing them to or removing them from a reacting solution, with broader applications in control and analysis of low affinity interactions on cells or particles.

Effect of residual water and microwave heating on the half-life of the reagents and reactive intermediates in peptide synthesis

Precise microwave heating has changed the way many small molecules are being synthesized and, currently, the field of solid-phase peptide synthesis is undergoing dramatic changes owing to the use of microwave heating. To fully reap the benefits of precise microwave heating for the formation of amide bonds in peptide synthesis, it is important to understand the kinetics of formation and break-down of activated esters and their N-acylation of the nascent peptide chain at elevated temperatures. Herein, we present systematic studies of, first, the rate of formation of activated esters by NMR spectroscopy and, second, their N-acylation during peptide synthesis. A study of the amount of residual water in the solvents revealed a significant effect on electrophilic reagents and intermediates. This observation was expanded into a general study of microwave heating in peptide synthesis.