Cellular separations: A review of new challenges in analytical chemistry

The effects of flow type on aptamer capture in differential mobility cytometry cell separations

In this work, differential mobility cytometry (DMC) was used to monitor cell separation based on aptamer recognition for target cells. In this device, open-tubular capillaries coated with Sgc8 aptamers were used as affinity chromatography columns for separation. After cells were injected into the columns, oscillating flow was generated to allow for long-term cell adhesion studies. This process was monitored by optical microscopy, and differential imaging was used to analyze the cells as they adhered to the affinity surface. We investigated the capture time, capture efficiency, purity of target and control cells, as well as the reusability of the affinity columns. Capture time for both CCRF-CEM cells and Jurkat T cells was 0.4+/-0.2 s, which demonstrated the high separation affinity between aptamers and target cells. The capture efficiency for CCRF-CEM cells was 95% and purity was 99% in a cell mixture. With the advantage of both high cell capture efficiency and purity, DMC combined with aptamer-based separation emerges as a powerful tool for rare cell enrichment. In addition, aptamer-based DMC channels were found to be more robust than antibody based channels with respect to reuse of the separation device.

Microsystems for the capture of low-abundance cells

Efficient selection and enumeration of low-abundance biological cells are highly important in a variety of applications. For example, the clinical utility of circulating tumor cells (CTCs) in peripheral blood is recognized as a viable biomarker for the management of various cancers, in which the clinically relevant number of CTCs per 7.5 ml of blood is two to five. Although there are several methods for isolating rare cells from a variety of heterogeneous samples, such as immunomagnetic-assisted cell sorting and fluorescence-activated cell sorting, they are fraught with challenges. Microsystem-based technologies are providing new opportunities for selecting and isolating rare cells from complex, heterogeneous samples. Such approaches involve reductions in target-cell loss, process automation, and minimization of contamination issues. In this review, we introduce different application areas requiring rare cell analysis, conventional techniques for their selection, and finally microsystem approaches for low-abundance-cell isolation and enumeration.

"Print-n-Shrink" technology for the rapid production of microfluidic chips and protein microarrays

An innovative method for the production of microfluidic chips integrating protein spots is described. The technology, called "Print-n-Shrink", is based on the screen-printing of a microfluidic design (using a dielectric ink) onto Polyshrink polystyrene sheets. The initial print which has a minimum size of 15 microm (height) x 230 microm (width) is thermally treated (30 seconds, 163 degrees C) to shrink and generate features of 85 microm (height) x 100 microm (width). Concomitantly, proteins such as monoclonal antibodies or cellular adhesion proteins are spotted onto the Polyshrink sheets and shrunk together with the microfluidic design, creating a complete biochip integrating both complex microfluidic designs and protein spots for bioanalytical applications.

Tipping the balance of deterministic lateral displacement devices using dielectrophoresis

We report the use of dielectrophoresis (DEP) to achieve tunability, improve dynamic range and open up for the separation of particles with regard to parameters other than hydrodynamic size in deterministic lateral displacement (DLD) devices. DLD devices have been shown capable of rapidly and continuously separating micrometer sized plastic spheres by size with a resolution of 20 nm in diameter and of being able to handle the separation of biological samples as wide ranging as bacterial artificial chromosomes and blood cells. DEP, while not exhibiting the same resolution in size separation as DLD, has the benefit of being easy to tune and can, by choosing the frequency, be used to probe a variety of particle properties. By combining DLD and DEP we open up for the advantages, while avoiding the drawbacks, of the two techniques. We present a proof of principle in which the critical size for separation of polystyrene beads is tuned in the range 2-6 microm in a single device by the application of moderate (100 V cm(-1)), low frequency (100 Hz) AC electric fields. The behaviour of the device was further investigated by performing simulations of particle trajectories, the results of which were in good qualitative agreement with experiments, indicating the potential of the method for tunable, high-resolution separations with respect to both size and polarisability.

Relation of structure to performance characteristics of monolithic and perfusive stationary phases

Commercially available polymer-based monolithic and perfusive stationary phases were evaluated for their applicability in chromatography of biologics. Information on bed geometry, including that from electron microscopy (EM), was used to interpret and predict accessible volumes, binding capacities, and pressure drops. For preparative purification of biologics up to at least 7 nm in diameter, monoliths and perfusive resins are inferior to conventional stationary phases due to their low binding capacities (20-30 g/L for BSA). For larger biologics, up to several hundred nanometers in diameter, calculations from EM images predict a potential increase in binding capacity to nearly 100 g/L. The accessible volume for adenovirus calculated from the EM images matched the experimental value. While the pores of perfusive resins are essentially inaccessible to adenovirus under binding conditions, under non-adsorbing conditions the accessible intrabead porosity is almost as large as the interbead porosity. Modeling of breakthrough curves showed that the experimentally observed slow approach to full saturation can be explained by the distribution of pore sizes.

Separation of particles by pulsed dielectrophoresis

In this paper, we introduce a dielectrophoresis (DEP)-based separation method that allows for tunable multiplex separation of particles. In traditional DEP separations where the field is applied continuously, size-based separation of particles uses the cubic dependence of the DEP force on particle radius, causing large particles to be retained while small particles are released. Here we show that by pulsing the DEP force in time, we are able to reverse the order of separation (eluting the large particles while retaining the small ones), and even extract mid-size particles from a heterogeneous population in one step. The operation is reminiscent of prior dielectrophoretic ratchets which made use of DEP and Brownian motion, but we have applied the asymmetric forces in time rather than in a spatial arrangement of electrodes, thus simplifying the system. We present an analytical model to study the dynamic behavior of particles under pulsed DEP and to understand the different modes of separation. Results from the model and the experimental observations are shown to be in agreement.

Organelle proteomics

The proteome of the cell is at the frontier of being too complex for proteomic analysis. Organelles provide a step up. Organelles compartmentalize the cell enabling a proteome, physiology and metabolism analysis in time and in space. Protein complexes separated by electrophoresis have been identified as the next natural level to characterize the organelles' compartmentalized membrane and soluble proteomes by mass spectrometry. Work on mitochondria and chloroplasts has shown where we are in the characterization of complex proteomes to understand the network of endogenous and extrinsic factors which regulate growth and development, adaptation and evolution.

Magnetic enrichment of bronchial epithelial cells from sputum for lung cancer diagnosis

BACKGROUND

Sputum is an easily accessible diagnostic material for lung cancer early detection by cytologic and molecular genetic analysis of exfoliated airway epithelial cells. However, the use of sputum is limited by its cellular heterogeneity, which includes >95% macrophages and neutrophils and only about 1% bronchial epithelial cells. We propose to obtain concentrated and purified bronchial epithelial cells to improve early detection of lung cancer in sputum samples.

METHODS

Sputum was collected from patients with stage I nonsmall-cell lung cancer, cancer-free smokers, and healthy nonsmokers. Magnetic-assisted cell sorting (MACS) with anti-CD14 and anti-CD16 antibody beads were used to enrich bronchial epithelial cells by depleting macrophages and neutrophils from sputum. Fluorescence in situ hybridization (FISH) analysis for detection of FHIT deletion and cytology were evaluated in the enriched specimens.

RESULTS

The bronchial epithelial cells were concentrated to 40% purity from 1.1% of the starting population, yielding an average of 36-fold enrichment and at least 2.3 x 10(5) cells per sample. Detecting FHIT deletions for lung cancer diagnosis produced 58% sensitivity in the enriched sputum, whereas there was 42% sensitivity in the unenriched samples (P = .02). Cytologic examination of the enriched sputum resulted in 53% sensitivity, as compared with 39% sensitivity in unenriched sputum (P = .03). Furthermore, only 2 cytocentrifuge slides of the unenriched sputum were needed for the analyses, as compared with up to 10 cytocentrifuge slides required from the unprocessed specimens.

CONCLUSIONS

The enrichment of bronchial epithelial cells could improve the diagnostic value of sputum and the efficiency of genetic and cytologic analysis of lung cancer.

Laser-guidance based detection of cells with single-gene modification

An optical method with single-gene sensitivity for cell detection based on laser guidance was explored. Guided by the optical force from a weakly focused laser beam, a cell will move along the laser axis. Cells with different properties experience different optical forces and thus guidance speeds. The guidance speeds of the TC-1 cell and its genetically modified counterpart with only one gene change, L-10 cell, were studied under the same conditions. The results demonstrated that this laser guidance-based speed-measurement method can precisely distinguish cells that differ by only one gene.

Open-tubular capillary cell affinity chromatography: single and tandem blood cell separation

In this paper, an open-tubular capillary cell affinity chromatography (OT-CAC) method to enrich and separate target cells is described. Open tubular capillaries coated with anti-CD4, anti-CD14, or anti-CD19 antibodies were used as affinity chromatography columns to separate target blood cells. Cells were eluted using either shear force or bubbles. Bubbles were used to elute the captured cells without diluting the captured cells appreciably, while maintaining viability (the viability of the recovered cells was 85.83 +/- 7.34%; the viability of the cells was 90.41 +/- 3.49% before separation). Several aspects of the OT-CAC method were studied, such as the affinity of one antibody between two different cell lines, the effect of shear force, and the recovery of captured cells. Single- and multicell type separations were demonstrated by isolating CD4+ cells with antiCD4 coated capillary and isolating CD4+ and CD19+ cells with two capillaries in tandem from blood samples. In the one cell type isolation test, an average of 87.7% of the recovered cells from antiCD4 capillary were lymphocytes and an average of 97.7% of those lymphocytes were CD4+ cells. In the original blood sample, only 14.2% of the leukocytes were CD4+ cells. Two capillary columns were also run in tandem, separating two blood cell types from a single sample with high purity. The use of different elution shear forces was demonstrated to selectively elute one cell type. This method is an inexpensive, rapid, and effective method to separate target cells from blood samples.