Single-cell impedance cytometry is an electrical analysis method, which has been used to count and discriminate cells on the basis of their dielectric properties. The method has several advantages, such as being label free and requiring minimal sample preparation. So far, however, it has been limited to measuring cell properties that are visible at low frequencies, such as size and membrane capacitance. We demonstrate a microfluidic single cell impedance cytometer capable of dielectric characterization of single cells at frequencies up to 500 MHz. This device features a more than ten-fold increased frequency range compared to other devices and enables the study of both low and high frequency dielectric properties in parallel. The increased frequency range potentially allows for characterization of subcellular features in addition to the properties that are visible at lower frequencies. The capabilities of the cytometer are demonstrated by discriminating wild-type yeast from a mutant, which differs in size and distribution of vacuoles in the intracellular fluid. This discrimination is based on the differences in dielectric properties at frequencies around 250 MHz. The results are compared to a 3D finite-element model of the microfluidic channel accommodating either a wild-type or a mutant yeast cell. The model is used to derive quantitative values to characterize the dielectric properties of the cells.
As a complement and alternative to optical methods, wide-band electrical impedance spectroscopy (EIS) enables multi-parameter, label-free and real-time detection of cellular and subcellular features. We report on a microfluidics-based system designed to reliably capture single rod-shaped Schizosaccharomyces pombe cells by applying suction through orifices in a channel wall. The system enables subsequent culturing of immobilized cells in an upright position, while dynamic changes in cell-cycle state and morphology were continuously monitored through EIS over a broad frequency range. Besides measuring cell growth, clear impedance signals for nuclear division have been obtained. The EIS system has been characterized with respect to sensitivity and detection limits. The spatial resolution in measuring cell length was 0.25 μm, which corresponds to approximately a 5-min interval of cell growth under standard conditions. The comprehensive impedance data sets were also used to determine the occurrence of nuclear division and cytokinesis. The obtained results have been validated through concurrent confocal imaging and plausibilized through comparison with finite-element modeling data. The possibility to monitor cellular and intracellular features of single S. pombe cells during the cell cycle at high spatiotemporal resolution renders the presented microfluidics-based EIS system a suitable tool for dynamic single-cell investigations.
We present and demonstrate a general three-step method for extracting the quantum efficiency of dispersive qubit readout in circuit QED. We use active depletion of post-measurement photons and optimal integration weight functions on two quadratures to maximize the signal-to-noise ratio of non-steady-state homodyne measurement. We derive analytically and demonstrate experimentally that the method robustly extracts the quantum efficiency for arbitrary readout conditions in the linear regime. We use the proven method to optimally bias a Josephson traveling-wave parametric amplifier and to quantify the different noise contributions in the readout amplification chain.Many protocols in quantum information processing, like quantum error correction 1,2 , require rapid interleaving of qubit gates and measurements. These measurements are ideally nondemolition, fast, and high fidelity.In circuit QED 3-5 , a leading platform for quantum computing, nondemolition readout is routinely achieved by off-resonantly coupling a qubit to a resonator. The qubit-state-dependent dispersive shift of the resonator frequency is inferred by measuring the resonator response to an interrogating pulse using homodyne detection. A key element setting the speed and fidelity of dispersive readout is the quantum efficiency 6 , which quantifies how the signal-to-noise ratio is degraded with respect to the limit imposed by quantum vacuum fluctuations.In recent years, the use of superconducting parametric amplifiers 7-11 as the front end of the readout amplification chain has boosted the quantum efficiency towards unity, leading to readout infidelity on the order of one percent 12,13 in individual qubits. Most recently, the development of traveling-wave parametric amplifiers 14,15 (TWPAs) has extended the amplification bandwidth from tens of MHz to several GHz and with sufficient dynamic range to readout tens of qubits. For characterization and optimization of the amplification chain, the ability to robustly determine the quantum efficiency is an important benchmark.A common method for quantifying the quantum efficiency η that does not rely on calibrated noise sources compares the information obtained in a weak qubit measurement (expressed by the signal-to-noise-ratio SNR) to the dephasing of the qubit (expressed by the decay of the off-diagonal elements of the qubit density matrix) 16,17 , η = SNR 2 4βm , with e −βm = |ρ01(T )| |ρ01(0)| , where T is the measurement duration. Previous experimental work 14,18-20 has been restricted to fast resonators driven under specific symmetry conditions such that information is contained in only one quadrature of the output field and in steady state. To allow in-situ calibration of η in multi-qubit devices under development 21-25 , a method is desirable that does not rely on either of these conditions.In this Letter, we present and demonstrate a general three-step method for extracting the quantum efficiency of linear dispersive readout in cQED. Our method disposes with previous requirements in both the dynamics an...
This paper reports on a novel impedance-based cytometer, which can detect and characterize sub-micrometer particles and cells passing through a microfluidic channel. The cytometer incorporates a resonator, which is constructed by means of a discrete inductor in series with the measurement electrodes in the microfluidic channel. The use of a resonator increases the sensitivity of the system in comparison to state-of-the-art devices. We demonstrate the functionality and sensitivity of the cytometer by discriminating E. coli and B. subtilis from beads of similar sizes by means of the resonance-enhanced phase shift of the current through the microfluidic channel. The phase shift can be correlated to size and dielectric properties of the measured objects.
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