Isolation and counting of multiple cell types using an affinity separation device

Affinity chromatography: A review of trends and developments over the past 50 years

The field of affinity chromatography, which employs a biologically-related agent as the stationary phase, has seen significant growth since the modern era of this method began in 1968. This review examines the major developments and trends that have occurred in this technique over the past five decades. The basic principles and history of this area are first discussed. This is followed by an overview of the various supports, immobilization strategies, and types of binding agents that have been used in this field. The general types of applications and fields of use that have appeared for affinity chromatography are also considered. A survey of the literature is used to identify major trends in these topics and important areas of use for affinity chromatography in the separation, analysis, or characterization of chemicals and biochemicals.

Synthesis of a red fluorescent dye-conjugated Ag@SiO2 nanocomposite for cell immunofluorescence

In this work we describe a one-step approach for incorporating a red fluorophore (2SBPO) into core-shell nanoparticles for metal-enhanced fluorescence immunolabels. The 2SBPO-MEF nanoparticles are particularly attractive as cell labels because their ∼ 670 nm emission has minimal overlap with cell autofluorescence and from overlap with many conventional probes. 2SBPO was incorporated through physical entrapment during the Stöber process. Antibody-based cell labels were then synthesized using covalent linkage. The nanoparticle fluorescence was 7.5-fold higher than control nanoparticles lacking a metal core. We demonstrated labeling of CD4 + HuT 78 T lymphocytes using anti-CD4-conjugated nanoparticle labels. Cells labeled with anti-CD4 nanoparticles showed a 35-fold fluorescence signal compared to anti-CD4 coreless controls. This simple synthesis protocol can be applied to a variety of hydrophilic fluorophore types and has broad potential in bioanalytical and biosensing applications.

Cell affinity separations on microfluidic devices

Separating cells from a heterogeneous sample on microfluidic devices is a very important unit operation in biological and medical research. Microfluidic affinity cell chromatography is a label-free separation technique, providing ease of operation, low cost, and rapid analysis. In this chapter, protocols for cell affinity separation in polydimethylsiloxane (PDMS)-glass microdevices and glass capillaries are described.

Facile Functionalization of Ag@SiO2 Core-Shell Metal Enhanced Fluorescence Nanoparticles for Cell Labeling

We describe a versatile approach for functionalizing core-shell Ag@SiO2 nanoparticles for live-cell imaging. The approach uses physical adsorption and does not need covalent linkage to synthesize antibody-based labels. The surface orientation is not controlled in this approach, but the signal enhancement is strong and consistent. Antibodies were then attached using a non-covalent process that takes advantage of biotin-avidin affinity. Metal-enhanced nanoparticles doped with rhodamine B were used as the luminescent reporter. The enhancement of rhodamine B was between 2.7-6.8 times. We demonstrated labeling of CD19+ Ramos B lymphocytes and CD4+ HuT 78 T lymphocytes using anti-CD19 and anti-CD4 nanocomposite labels, respectively. This physical adsorption process can accommodate a variety of fluorophore types, and has broad potential in bioanalytical and biosensing applications.

Manipulating biological agents and cells in micro-scale volumes for applications in medicine

Recent technological advances provide new tools to manipulate cells and biological agents in micro/nano-liter volumes. With precise control over small volumes, the cell microenvironment and other biological agents can be bioengineered; interactions between cells and external stimuli can be monitored; and the fundamental mechanisms such as cancer metastasis and stem cell differentiation can be elucidated. Technological advances based on the principles of electrical, magnetic, chemical, optical, acoustic, and mechanical forces lead to novel applications in point-of-care diagnostics, regenerative medicine, in vitro drug testing, cryopreservation, and cell isolation/purification. In this review, we first focus on the underlying mechanisms of emerging examples for cell manipulation in small volumes targeting applications such as tissue engineering. Then, we illustrate how these mechanisms impact the aforementioned biomedical applications, discuss the associated challenges, and provide perspectives for further development.

Recent advances in microfluidic cell separations

The isolation and sorting of cells has become an increasingly important step in chemical and biological analyses. As a unit operation in more complex analyses, isolating a phenotypically pure cell population from a heterogeneous sample presents unique challenges. Microfluidic systems are ideal platforms for performing cell separations, enabling integration with other techniques and enhancing traditional separation modalities. In recent years there have been several techniques that use surface antigen affinity, physical interactions, or a combination of the two to achieve high separation purity and efficiency. This review discusses methods including magnetophoretic, acoustophoretic, sedimentation, electric, and hydrodynamic methods for physical separations. We also discuss affinity methods, including magnetic sorting, flow sorting, and affinity capture.

Selective individual primary cell capture using locally bio-functionalized micropores

Background

Solid-state micropores have been widely employed for 6 decades to recognize and size flowing unlabeled cells. However, the resistive-pulse technique presents limitations when the cells to be differentiated have overlapping dimension ranges such as B and T lymphocytes. An alternative approach would be to specifically capture cells by solid-state micropores. Here, the inner wall of 15-µm pores made in 10 µm-thick silicon membranes was covered with antibodies specific to cell surface proteins of B or T lymphocytes. The selective trapping of individual unlabeled cells in a bio-functionalized micropore makes them recognizable just using optical microscopy.

Methodology/Principal Findings

We locally deposited oligodeoxynucleotide (ODN) and ODN-conjugated antibody probes on the inner wall of the micropores by forming thin films of polypyrrole-ODN copolymers using contactless electro-functionalization. The trapping capabilities of the bio-functionalized micropores were validated using optical microscopy and the resistive-pulse technique by selectively capturing polystyrene microbeads coated with complementary ODN. B or T lymphocytes from a mouse splenocyte suspension were specifically immobilized on micropore walls functionalized with complementary ODN-conjugated antibodies targeting cell surface proteins.

Conclusions/Significance

The results showed that locally bio-functionalized micropores can isolate target cells from a suspension during their translocation throughout the pore, including among cells of similar dimensions in complex mixtures.

A quartz nanopillar hemocytometer for high-yield separation and counting of CD4(+) T lymphocytes

We report the development of a novel quartz nanopillar (QNP) array cell separation system capable of selectively capturing and isolating a single cell population including primary CD4(+) T lymphocytes from the whole pool of splenocytes. Integrated with a photolithographically patterned hemocytometer structure, the streptavidin (STR)-functionalized-QNP (STR-QNP) arrays allow for direct quantitation of captured cells using high content imaging. This technology exhibits an excellent separation yield (efficiency) of ~95.3 ± 1.1% for the CD4(+) T lymphocytes from the mouse splenocyte suspensions and good linear response for quantitating captured CD4(+) T-lymphoblasts, which is comparable to flow cytometry and outperforms any non-nanostructured surface capture techniques, i.e. cell panning. This nanopillar hemocytometer represents a simple, yet efficient cell capture and counting technology and may find immediate applications for diagnosis and immune monitoring in the point-of-care setting.

Controlled viable release of selectively captured label-free cells in microchannels

Selective capture of cells from bodily fluids in microchannels has broadly transformed medicine enabling circulating tumor cell isolation, rapid CD4(+) cell counting for HIV monitoring, and diagnosis of infectious diseases. Although cell capture methods have been demonstrated in microfluidic systems, the release of captured cells remains a significant challenge. Viable retrieval of captured label-free cells in microchannels will enable a new era in biological sciences by allowing cultivation and post-processing. The significant challenge in release comes from the fact that the cells adhere strongly to the microchannel surface, especially when immuno-based immobilization methods are used. Even though fluid shear and enzymes have been used to detach captured cells in microchannels, these methods are known to harm cells and affect cellular characteristics. This paper describes a new technology to release the selectively captured label-free cells in microchannels without the use of fluid shear or enzymes. We have successfully released the captured CD4(+) cells (3.6% of the mononuclear blood cells) from blood in microfluidic channels with high specificity (89% ± 8%), viability (94% ± 4%), and release efficiency (59% ± 4%). We have further validated our system by specifically capturing and controllably releasing the CD34(+) stem cells from whole blood, which were quantified to be 19 cells per million blood cells in the blood samples used in this study. Our results also indicated that both CD4(+) and CD34(+) cells released from the microchannels were healthy and amenable for in vitro culture. Manual flow based microfluidic method utilizes inexpensive, easy to fabricate microchannels allowing selective label-free cell capture and release in less than 10 minutes, which can also be used at the point-of-care. The presented technology can be used to isolate and purify a broad spectrum of cells from mixed populations offering widespread applications in applied biological sciences, such as tissue engineering, regenerative medicine, rare cell and stem cell isolation, proteomic/genomic research, and clonal/population analyses.

Comparison of inlet geometry in microfluidic cell affinity chromatography

Cell separation based on microfluidic affinity chromatography is a widely used methodology in cell analysis research when rapid separations with high purity are needed. Several successful examples have been reported with high separation efficiency and purity; however, cell capture at the inlet area and inlet design have not been extensively described or studied. The most common inlets-used to connect the microfluidic chip to pumps, tubing, etc.-are vertical (top-loading) inlets and parallel (in-line) inlets. In this work, we investigated the cell capture behavior near the affinity chip inlet area and compared the different performances of vertical inlet devices and parallel inlet devices. Vertical inlet devices showed significant cell capture capability near the inlet area, which led to the formation of cell blockages as the separation progressed. Cell density near the inlet area was much higher than that in the remaining channel, whereas for parallel inlet chips cell density at the inlet area was similar to that in the rest of the channel. In this paper, we discuss the effects of inlet type on chip fabrication, nonspecific binding, cell capture efficiency, and separation purity. We also discuss the possibility of using vertical inlets in negative-selection separations. Our findings show that inlet design is critical and must be considered when fabricating cell affinity microfluidic devices.

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.

Cellular separations: A review of new challenges in analytical chemistry

The ability to generate a sample of cells of a given phenotype is a prerequisite for many cellular assays. In response to this growing need, numerous methods for cell separation have been developed in recent years. This Review covers recent progress in the field of cell separations and cell chromatography. Cell separation principles-such as size and affinity capture-are discussed, as well as conventional methods such as fluorescence-activated cell sorting and magnetic sorting. Planar flow cell arrays, dielectrophoresis, field-flow methods, and column separation devices are reviewed, as well as applications of these methods to medicine and biotechnology. Cell attachment and adhesion strategies and a comparison of techniques are also presented.