Classification of chemically modified red blood cells in microflow using machine learning video analysis

We classify native and chemically modified red blood cells with an AI based video classifier. Using TensorFlow video analysis enables us to capture not only the morphology of the cell but also the trajectories of motion of individual red blood cells and their dynamics. We chemically modify cells in three different ways to model different pathological conditions and obtain classification accuracies for all three classification tasks of more than 90% between native and modified cells. Unlike standard cytometers that are based on immunophenotyping our microfluidic cytometer allows to rapidly categorize cells without any fluorescence labels simply by analysing the shape and flow of red blood cells.

Acoustic erythrocytometer for mechanically probing cell viscoelasticity

We demonstrate an acoustic device to mechanically probe a population of red blood cells at the single cell level. The device operates by exciting a surface acoustic wave in a microfluidic channel creating a stationary acoustic wave field of nodes and antinodes. Erythrocytes are attracted to the nodes and are deformed. Using a stepwise increasing and periodically oscillating acoustic field we study the static and dynamic deformation of individual red blood cells one by one. We quantify the deformation by the Taylor deformation index D and relaxation times τ₁ and τ₂ that reveal both the viscous and elastic properties of the cells. The precision of the measurement allows us to distinguish between individual cells in the suspension and provides a quantitative viscoelastic fingerprint of the blood sample at single cell resolution. The method overcomes limitations of other techniques that provide averaged values and has the potential for high-throughput.

Traveling surface acoustic wave (TSAW) microfluidic fluorescence activated cell sorter (μFACS)

We report a microfluidic fluorescence activated cell-sorting (μFACS) device that employs traveling surface acoustic waves (TSAW) to sort cells at rates comparable to conventional jet-in-air FACS machines, with high purity and viability. The device combines inertial flow focusing and sheath flow to align and evenly space cells, improving the sorting accuracy and screening rate. We sort with an interdigital transducer (IDT) whose tapered geometry allows precise positioning of the TSAW for optimal cell sorting. We sort three different cell lines at several kHz, at cell velocities exceeding one meter per second, while maintaining both sorting purity and cell viability at around 90% simultaneously.

Binary Colloidal Nanoparticle Concentration Gradients in a Centrifugal Field at High Concentration

Binary colloidal nanoparticles have been found to form different types of crystalline phases at varied radial positions in a centrifugal field by Chen et al. ( ACS Nano 2015, 9, 6944-50). The variety of binary phase behaviors resulted from the two different nanoparticle concentration gradients, but to date, the gradients can only be empirically controlled. For the first time, we are able to measure, fit, and simulate binary hard-sphere colloidal nanoparticle concentration gradients at high particle concentrations up to 30 vol %, which enables tailor-made gradients in a centrifugal field. By this means, a continuous range of binary particle concentration ratios can be accessed in one single experiment to obtain an extended phase diagram. By dispersing two differently sized silica nanoparticles labeled with two different fluorescence dyes in a refractive index matching solvent, we can use a multi-wavelength analytical ultracentrifuge (MWL-AUC) to measure the individual concentration gradient for each particle size in sedimentation-diffusion equilibrium. The influence of the remaining slight turbidity at high concentration can be corrected using the MWL spectra from the AUC data. We also show that the experimental concentration gradients can be fitted using a noninteracting nonideal sedimentation model. By using these fitted parameters, we are able to simulate nanoparticle concentration gradients, which agreed with the subsequent experiments at a high concentration of 10 vol % and thus allowed for the simulation of binary concentration gradients of hard-sphere nanoparticles in preparative ultracentrifuges (PUCs). Finally we demonstrated that by simulating the concentration gradients in PUCs, a continuous and extended binary nanoparticle phase diagram can be obtained by simply studying the structure evolution along the centrifugal field for one single sample instead of a large number of experiments with discrete compositions as in conventional studies.

Bimorph material/structure designs for high sensitivity flexible surface acoustic wave temperature sensors

A fundamental challenge for surface acoustic wave (SAW) temperature sensors is the detection of small temperature changes on non-planar, often curved, surfaces. In this work, we present a new design methodology for SAW devices based on flexible substrate and bimorph material/structures, which can maximize the temperature coefficient of frequency (TCF). We performed finite element analysis simulations and obtained theoretical TCF values for SAW sensors made of ZnO thin films (~5 μm thick) coated aluminum (Al) foil and Al plate substrates with thicknesses varied from 1 to 1600 μm. Based on the simulation results, SAW devices with selected Al foil or plate thicknesses were fabricated. The experimentally measured TCF values were in excellent agreements with the simulation results. A normalized wavelength parameter (e.g., the ratio between wavelength and sample thickness, λ/h) was applied to successfully describe changes in the TCF values, and the TCF readings of the ZnO/Al SAW devices showed dramatic increases when the normalized wavelength λ/h was larger than 1. Using this design approach, we obtained the highest reported TCF value of −760 ppm/K for a SAW device made of ZnO thin film coated on Al foils (50 μm thick), thereby enabling low cost temperature sensor applications to be realized on flexible substrates.

Enhanced surface acoustic wave cell sorting by 3D microfluidic-chip design

We demonstrate an acoustic wave driven microfluidic cell sorter that combines advantages of multilayer device fabrication with planar surface acoustic wave excitation. We harness the strong vertical component of the refracted acoustic wave to enhance cell actuation by using an asymmetric flow field to increase cell deflection. Precise control of the 3-dimensional flow is realized by topographical structures implemented on the top of the microchannel. We experimentally quantify the effect of the structure dimensions and acoustic parameter. The design attains cell sorting rates and purities approaching those of state of the art fluorescence-activated cell sorters with all the advantages of microfluidic cell sorting.