Tracking B Cell Memory to SARS-CoV-2 Using Rare Cell Analysis System.

Rapid mutations within SARS-CoV-2 are driving immune escape, highlighting the need for in-depth and routine analysis of memory B cells (MBCs) to complement the important but limited information from neutralizing antibody (nAb) studies. In this study, we collected plasma samples and peripheral blood mononuclear cells (PBMCs) from 35 subjects and studied the nAb titers and the number of antigen-specific memory B cells at designated time points before and after vaccination. We developed an assay to use the MiSelect R II System with a single-use microfluidic chip to directly detect the number of spike-receptor-binding domain (RBD)-specific MBCs in PBMCs. Our results show that the number of spike-RBD-specific MBCs detected by the MiSelect R II System is highly correlated with the level of nAbs secreted by stimulated PBMCs, even 6 months after vaccination when nAbs were generally not present in plasma. We also found antigen-specific cells recognizing Omicron spike-RBD were present in PBMCs from booster vaccination of subjects, but with a high variability in the number of B cells. The MiSelect R II System provided a direct, automated, and quantitative method to isolate and analyze subsets of rare cells for tracking cellular immunity in the context of a rapidly mutating virus.

MiSelect R System: the validation of a new detection system of CTCs and their correlation with prognosis in non-metastatic CRC patients.

Circulating tumor cells (CTCs) in blood are accepted as a prognostic marker for patients with metastatic colorectal cancer (CRC). However, there is limited data on the use of CTCs as a prognostic marker for non-metastatic patients. In the current study, we used a rare cell automated analysis platform, the MiSelect R System, to enumerate CTCs from blood in non-metastatic CRC patients, and corelated the number of CTCs with the clinical staging and survival. The presence of CTCs in mesenteric vein blood (MVB) samples from 101 CRC patients was significantly associated with T stage. Patients with 1 or more CTCs per 8 mL of MVB exhibited significantly worse disease-free survival (DFS) and cancer-specific survival (CSS) compared to patient without CTCs. The presence of CTCs before surgery is an independent marker for both DFS and CSS. CTC presence after surgical resection is also a prognostic marker. CTCs are a potentially useful prognostic and predictive biomarker in non-metastatic CRC patients that may further stratify patient's risk status within different stages of disease.

Sequential Ensemble-Decision Aliquot Ranking Isolation and Fluorescence In Situ Hybridization Identification of Rare Cells from Blood by Using Concentrated Peripheral Blood Mononuclear Cells.

Isolation and analysis of circulating rare cells is a promising approach for early detection of cancer and other diseases and for prenatal diagnosis. Isolation of rare cells is usually difficult due to their heterogeneity as well as their low abundance in peripheral blood. We previously reported a two-stage ensemble-decision aliquot ranking platform (S-eDAR) for isolating circulating tumor cells from whole blood with high throughput, high recovery rate (>90%), and good purity (>70%), allowing detection of low surface antigen-expressing cancer cells linked to metastasis. However, due to the scarcity of these cells, large sample volumes and large quantities of antibodies were required to isolate sufficient cells for downstream analysis. Here, we drastically increased the number of nucleated cells analyzed by first concentrating peripheral blood mononuclear cells (PBMCs) from whole blood by density gradient centrifugation. The S-eDAR platform was capable of isolating rare cells from concentrated PBMCs (108/mL, equivalent to processing ∼20 mL of whole blood in the 1 mL sample volume used by our instrument) at a high recovery rate (>85%). We then applied the S-eDAR platform for isolating rare fetal nucleated red blood cells (fNRBCs) from concentrated PBMCs spiked with umbilical cord blood cells and confirmed fNRBC recovery by immunostaining and fluorescence in situ hybridization, demonstrating the potential of the S-eDAR system for isolating rare fetal cells from maternal PBMCs to improve noninvasive prenatal diagnosis.

Isolating Rare Cells and Circulating Tumor Cells with High Purity by Sequential eDAR.

Isolation and analysis of circulating tumor cells (CTCs) from the blood of patients at risk of metastatic cancers is a promising approach to improving cancer treatment. However, CTC isolation is difficult due to low CTC abundance and heterogeneity. Previously, we reported an ensemble-decision aliquot ranking (eDAR) platform for the rare cell and CTC isolation with high throughput, greater than 90% recovery, and high sensitivity, allowing detection of low surface antigen-expressing cells linked to metastasis. Here we demonstrate a sequential eDAR platform capable of isolating rare cells from whole blood with high purity. This improvement in purity is achieved by using a sequential sorting and flow stretching design in which whole blood is sorted and fluid elements are stretched using herringbone features and the parabolic flow profile being sorted a second time. This platform can be used to collect single CTCs in a multiwell plate for downstream analysis.

Simultaneous and selective isolation of multiple subpopulations of rare cells from peripheral blood using ensemble-decision aliquot ranking (eDAR).

Rare cells, such as circulating tumor cells (CTCs), can be heterogeneous. The isolation and identification of rare cells with different phenotypes is desirable, for clinical and biological applications. However, CTCs exist in a complex biological environment, which complicates the isolation and identification of particular subtypes. To address this need, we re-designed our ensemble-decision aliquot ranking (eDAR) system to detect, isolate, and study two subpopulations of rare cells in the same microchip. With this dual-capture eDAR device, we simultaneously and selectively isolated two subsets of CTCs from the same blood sample: One set expressed epithelial markers and the other had mesenchymal characteristics. We could apply other selection schemes with different sorting logics to isolate the two subpopulations on demand. The average recovery rate for each subpopulation was higher than 88% with a nearly 100% selectivity of the targeted cells; the throughput was 50 µL min(-1).

New generation of ensemble-decision aliquot ranking based on simplified microfluidic components for large-capacity trapping of circulating tumor cells.

Ensemble-decision aliquot ranking (eDAR) is a sensitive and high-throughput method to analyze circulating tumor cells (CTCs) from peripheral blood. Here, we report the next generation of eDAR, where we designed and optimized a new hydrodynamic switching scheme for the active sorting step in eDAR, which provided fast cell sorting with an improved reproducibility and stability. The microfluidic chip was also simplified by incorporating a functional area for subsequent purification using microslits fabricated by standard lithography method. Using the reported second generation of eDAR, we were able to analyze 1 mL of whole-blood samples in 12.5 min, with a 95% recovery and a zero false positive rate (n = 15).

An automated high-throughput counting method for screening circulating tumor cells in peripheral blood.

Enumeration of circulating tumor cells (CTCs) has proved valuable for early detection and prognosis in cancer treatment. This paper describes an automated high-throughput counting method for CTCs based on microfluidics and line-confocal microscopy. Peripheral blood was directly labeled with multiple antibodies, each conjugated with a different fluorophore, pneumatically pumped through a microfluidic channel, and interrogated by a line-confocal microscope. On the basis of the fluorescence signals and labeling schemes, the count of CTCs was automatically reported. Due to the high flow rate, 1 mL of whole blood can be analyzed in less than 30 min. We applied this method in analyzing CTCs from 90 stage IV breast cancer patient samples and performed a side-by-side comparison with the results of the CellSearch assay, which is the only method approved by the U.S. Food and Drug Administration at present for enumeration of CTCs. This method has a recovery rate for cultured breast cancer cells of 94% (n = 9), with an average of 1.2 counts/mL of background level of detected CTCs from healthy donors. It detected CTCs from breast cancer patients ranging from 15 to 3375 counts/7.5 mL. Using this method, we also demonstrate the ability to enumerate CTCs from breast cancer patients that were positive for Her2 or CD44(+)/CD24(-), which is a putative cancer stem cell marker. This automated method can enumerate CTCs from peripheral blood with high throughput and sensitivity. It could potentially benefit the clinical diagnosis and prognosis of cancer.

High-throughput fluorescence-activated nanoscale subcellular sorter with single-molecule sensitivity.

Recent single-cell and single-molecule studies have shown that a variety of subpopulations exist within biological systems, such as synaptic vesicles, that have previously been overlooked in common bulk studies. By isolating and enriching these various subpopulations, detailed analysis with a variety of analytical techniques can be done to further understand the role that various subpopulations play in cellular dynamics and how alterations to these subpopulations affect the overall function of the biological system. Previous sorters lack the sensitivity, sorting speed, and efficiency to isolate synaptic vesicles and other nanoscale systems. This paper describes the development of a fluorescence-activated nanoscale subcellular sorter that can sort nearly 10 million objects per hour with single-molecule sensitivity. Utilizing a near-nanoscale channel system, we were able to achieve upward of 91% recovery of desired objects with a 99.7% purity.

Determining the number of specific proteins in cellular compartments by quantitative microscopy.

This protocol describes a method for determining both the average number and variance of proteins, in the few to tens of copies, in isolated cellular compartments such as organelles and protein complexes. Other currently available protein quantification techniques either provide an average number, but lack information on the variance, or they are not suitable for reliably counting proteins present in the few to tens of copies. This protocol entails labeling of the cellular compartment with fluorescent primary-secondary antibody complexes, total internal reflection fluorescence microscopic imaging of the cellular compartment, digital image analysis and deconvolution of the fluorescence intensity data. A minimum of 2.5 d is required to complete the labeling, imaging and analysis of a set of samples. As an illustrative example, we describe in detail the procedure used to determine the copy number of proteins in synaptic vesicles. The same procedure can be applied to other organelles or signaling complexes.

Protein quantification at the single vesicle level reveals that a subset of synaptic vesicle proteins are trafficked with high precision.

Protein sorting represents a potential point of regulation in neurotransmission because it dictates the protein composition of synaptic vesicles, the organelle that mediates transmitter release. Although the average number of most vesicle proteins has been estimated using bulk biochemical approaches (Takamori et al., 2006), no information exists on the intervesicle variability of protein number, and thus on the precision with which proteins are sorted to vesicles. To address this, we adapted a single molecule quantification approach (Mutch et al., 2007) and used it to quantify both the average number and variance of seven integral membrane proteins in brain synaptic vesicles. We report that four vesicle proteins, SV2, the proton ATPase, Vglut1, and synaptotagmin 1, showed little intervesicle variation in number, indicating they are sorted to vesicles with high precision. In contrast, the apparent number of VAMP2/synaptobrevin 2, synaptophysin, and synaptogyrin demonstrated significant intervesicle variability. These findings place constraints on models of protein function at the synapse and raise the possibility that changes in vesicle protein expression affect vesicle composition and functioning.

Bioconjugation of ultrabright semiconducting polymer dots for specific cellular targeting.

Semiconducting polymer dots (Pdots) represent a new class of ultrabright fluorescent probes for biological imaging. They exhibit several important characteristics for experimentally demanding in vitro and in vivo fluorescence studies, such as their high brightness, fast emission rate, excellent photostability, nonblinking, and nontoxic feature. However, controlling the surface chemistry and bioconjugation of Pdots has been a challenging problem that prevented their widespread applications in biological studies. Here, we report a facile yet powerful conjugation method that overcomes this challenge. Our strategy for Pdot functionalization is based on entrapping heterogeneous polymer chains into a single dot, driven by hydrophobic interactions during nanoparticle formation. A small amount of amphiphilic polymer bearing functional groups is co-condensed with the majority of semiconducting polymers to modify and functionalize the nanoparticle surface for subsequent covalent conjugation to biomolecules, such as streptavidin and immunoglobulin G (IgG). The Pdot bioconjugates can effectively and specifically label cellular targets, such as cell surface marker in human breast cancer cells, without any detectable nonspecific binding. Single-particle imaging, cellular imaging, and flow cytometry experiments indicate a much higher fluorescence brightness of Pdots compared to those of Alexa dye and quantum dot probes. The successful bioconjugation of these ultrabright nanoparticles presents a novel opportunity to apply versatile semiconducting polymers to various fluorescence measurements in modern biology and biomedicine.

Deformability considerations in filtration of biological cells.

Biological cells are highly sensitive to variation in local pressure because cellular membranes are not rigid. Unlike microbeads, cells deform under pressure or even lyse. In isolating or enriching cells by mechanical filtration, pressure-induced lysis is exacerbated when high local fluidic velocity is present or when a filter reaches its intended capacity. Microfabrication offers new possibilities to design fluidic environments to reduce cellular stress during the filtration process. We describe the underlying biophysics of cellular stress and general solutions to scale up filtration processes for biological cells.

A new USP Class VI-compliant substrate for manufacturing disposable microfluidic devices.

As microfluidic systems transition from research tools to disposable clinical-diagnostic devices, new substrate materials are needed to meet both the regulatory requirement as well as the economics of disposable devices. This paper introduces a UV-curable polyurethane-methacrylate (PUMA) substrate that has been qualified for medical use and meets all of the challenges of manufacturing microfluidic devices. PUMA is optically transparent, biocompatible, and exhibits high electroosmotic mobility without surface modification. We report two production processes that are compatible with the existing methods of rapid prototyping and present characterizations of the resultant PUMA microfluidic devices.

Method for the accurate preparation of cell-spiking standards.

Preparation of calibration standards for cell enumeration is critical in characterizing the performance of any method or apparatus intended for recovering rare cells. Diluting a cell suspension serially is prone to statistical sampling errors as the cell suspension becomes more dilute, whereas transferring and injecting cells individually into a diluent with a micromanipulator is time-consuming. We developed a simple and robust method using a surface-modified glass capillary to siphon and eject cells. One-dimensional confinement of cells offered by the capillary made cell enumeration by visual counting simple and rapid, and cell ejection from the capillary was near 100% when the appropriate surface coating and cell solution was used. The residence time of cells in the capillary, however, could affect the percentage of cells that was ejected from the capillary. To characterize the performance of this method, we enumerated the ejected cell using both visual counting under a microscope and automated detection using a chip-based flow cytometer.

Fabrication improvements for thermoset polyester (TPE) microfluidic devices.

Thermoset polyester (TPE) microfluidic devices were previously developed as an alternative to poly(dimethylsiloxane) (PDMS) devices, fabricated similarly by replica molding, yet offering stable surface properties and good chemical compatibility with some organics that are incompatible with PDMS. This paper describes a number of improvements in the fabrication of TPE chips. Specifically, we describe methods to form TPE devices with a thin bottom layer for use with high numerical aperture (NA) objectives for sensitive fluorescence detection and optical manipulation. We also describe plasma-bonding of TPE to glass to create hybrid TPE-glass devices. We further present a simple master-pretreatment method to replace our original technique that required the use of specialized equipment.

Continuous-flow single-molecule CE with high detection efficiency.

This paper describes the use of two-beam line-confocal detection geometry for measuring the total mobility of individual molecules undergoing continuous-flow CE separation. High-sensitivity single-molecule confocal detection is usually performed with a diffraction limited focal spot (approximately 500 nm in diameter), which necessitates the use of nanometer-sized channels to ensure all molecules flow through the detection volume. To allow for the use of larger channels that are a few micrometers in width, we employed cylindrical optics to define a rectangular illumination area that is diffraction-limited (approximately 500 nm) in width, but a few micrometers in length to match the width of the microchannel. We present detailed studies that compare the performance of this line-confocal detection geometry with the more widely used point-confocal geometry. Overall, we found line-confocal detection to provide the highest combination of signal-to-background ratio and spatial detection efficiency when used with micrometer-sized channels. For example, in a 2 microm wide channel we achieved a 94% overall detection efficiency for single Alexa488 dye molecules when a 2 microm x 0.5 microm illumination area was used, but only 34% detection efficiency with a 0.5 microm-diameter detection spot. To carry out continuous-flow CE, we used two-beam fluorescent cross-correlation spectroscopy where the transit time of each molecule is determined by cross-correlating the fluorescence registered by two spatially offset line-confocal detectors. We successfully separated single molecules of FITC, FITC-tagged glutamate, and FITC-tagged glycine.

Optical gradient flow focusing.

This paper describes a new method for carrying out flow cytometry, which employs optical gradient forces to guide and focus particles in the fluid flow. An elliptically shaped Gaussian beam was focused at the center of a microchannel to exert radiation pressure on suspended nanoparticles that are passing through the channel, such that these particles are guided to the center of the channel for efficient detection and sorting. To verify the efficiency of this optical-gradient-flow-focusing method, we present numerical simulations of the trajectories of the nanoparticles in both electroosmotic flow (EOF) and pressure-driven flow (PDF).

Accurate sizing of nanoparticles using confocal correlation spectroscopy.

The ability to accurately size low concentrations of nanoscale particles in small volumes is useful for a broad range of disciplines. Here, we characterize confocal correlation spectroscopy (CCS), which is capable of measuring the sizes of both fluorescent and nonfluorescent particles, such as quantum dots, gold colloids, latex spheres, and fluorescent beads. We accurately measured particles ranging in diameter from 11 to 300 nm, a size range that had been difficult to probe, owing to a phenomenon coined biased diffusion that causes diffusion times, or particle size, to deviate as a function of laser power. At low powers, artifacts mimicking biased diffusion are caused by saturation of the detector, which is especially problematic when probing highly fluorescent or highly scattering nanoparticles. However, at higher powers (>1 mW), autocorrelation curves in both resonant and nonresonant conditions show a structure indicative of an increased contribution from longer correlation times coupled with a decrease in shorter correlation times. We propose that this change in the autocorrelation curve is due to the partial trapping of the particles as they transit the probe volume. Furthermore, we found only a slight difference in the effect of biased diffusion when comparing resonant and nonresonant conditions. Simulations suggest the depth of trapping potential necessary for biased diffusion is > 1 k(B)T. Overcoming artifacts from detector saturation and biased diffusion, CCS is particularly advantageous due to its ability to size particles in the small volumes characteristic of microfluidic channels and aqueous microdroplets. We believe the method will find increasing use in a wide range of applications in measuring nanoparticles and macromolecular systems.

Cavity-enhanced emission from a dye-coated microsphere.

We have observed whispering gallery modes in the inelastic emission from a 9.8 microm polystyrene bead coated with a monolayer of AlexaFluor 488 dye. Using a separate near-IR trapping laser and an Ar+ excitation laser enables us to isolate and study a single dye-coated bead in a colloidal suspension without causing any bead damage.