The sensitivity and speed with which the immune system reacts to host disruption is unrivaled by any detection method for pathogenic biomarkers or infectious signatures. Engagement of cellular immunity in response to infections or cancer is contingent upon activation and subsequent cytotoxic activity by T cells. Thus, monitoring T cell activation can reliably serve as a metric for disease diagnosis as well as therapeutic prognosis. Rapid and direct quantification of T cell activation states, however, has been hindered by challenges associated with antigen target identification, labeling requirements, and assay duration. Here we present an electronic, label-free method for simultaneous separation and evaluation of T cell activation states. Our device utilizes a microfluidic design integrated with nanolayered electrode structures for dielectrophoresis (DEP)-driven discrimination of activated vs naïve T cells at single-cell resolution and demonstrates rapid (<2 min) separation of T cells at high single-pass efficiency as quantified by an on-chip Coulter counter module. Our device represents a microfluidic tool for electronic assessment of immune activation states and, hence, a portable diagnostic for quantitative evaluation of immunity and disease state. Further, its ability to achieve label-free enrichment of activated immune cells promises clinical utility in cell-based immunotherapies.

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We investigate the relationship between temperature and electron wind force in electromigration (EM) of ultrathin gold nanowires by monitoring power and current density at breakdown under a generalized AC bias (AC with a DC offset). Based on model calculations, our driving frequency of 10 MHz is low enough to maintain steady state self-heating behavior of our wires but high enough that the direction of the wind force switches quickly relative to the time-scale of atomic motion through the junction. The maximum and time-average of the squared current density (which dictate the temperature) both exhibit a minimum in DC offset (which dictates the wind force). This is explained by wind force driven annealing of the wire under long-range atomic displacements. Our hypothesis is supported by observations of changing device resistance on the voltage ramp prior to EM onset and by subsequent SEM inspection of electromigrated devices. The frequency dependence of pure AC EM breaking is also presented and interpreted in terms of the effectiveness of damage healing upon current reversal and the degree of wind force driven annealing.

This paper presents several experiments demonstrating the need for a more nuanced picture of electromigration (EM) than that of a fixed critical junction temperature at which EM onset occurs. Our data suggests that even for a fixed cross-sectional geometry the critical junction temperature for EM, T c , varies with environmental temperature, thermal resistance of adjacent regions, and even the direction of the current flow in asymmetric structures. We have performed feedback-controlled EM on nanowires at environmental temperatures between 75 and 260 K and fit the EM onset points with a constant junction power model. We find that average fit critical power is monotonically increasing with decreasing temperature, but is decidedly nonlinear at lower temperatures. We extract and compare the corresponding T c values using several different thermal models which utilize measured values of nanowire thermal conductivity for our devices: these models all agree on a moderately increasing T c with decreasing environmental temperature. This is tentatively explained by enhanced current-driven annealing on the voltage ramp prior to EM onset which decreases structural scattering, thereby increasing the critical temperature at which wind-force-driven hopping events will achieve a critical atomic flux. We also obtain fit critical power for a series of bowtie structures of identical constriction but varying adjacent thermal resistance (R th), and estimate that T c in the constriction varies with R th for higher resistance structures. Critical power measurements on a second series of asymmetric bowties further suggests that T c also depends on the alignment of the electron flow with the temperature gradient at the constriction.

We investigate electron tunneling spectroscopy in the presence of a bound state within a double quantum barrier, single quantum well structure. We demonstrate a new technique to directly measure the intrinsic linewidth of the bound state within the quantum well from the current-voltage signature of the resonant tunneling phenomena and contrast our results with the standing approach in the literature. We then examine the signal behavior for the influence of device temperature and find support for electron-electron interactions within the well. The measured intrinsic bound-state width, Γ E , in the negative differential conductance regime is 1.11±0.01 meV.