An automated programmable platform enabling multiplex dynamic stimuli delivery and cellular response monitoring for high-throughput suspension single-cell signaling studies

A microfluidic array enabling generation of identical biochemical stimulating signals to trapped biological cells for single-cell dynamics

Microfluidic-based analyses of single-cell dynamics in response to dynamic biochemical signals are emerging as pivotal approaches for investigating the effects of extracellular microenvironmental biochemical factors on cellular structure, function, and behavior. However, current devices often fail to consistently apply identical dynamic biochemical signals to trapped cells. In this study, we introduce a novel radially distributed single-cell trapping microfluidic array, designed to quantitatively and consistently apply identical biochemical stimulating signals to each trapped cell. Numerical simulations were employed to optimize microchannel geometry, enhancing trapping efficiency while minimizing signal distortion. Experimental validation demonstrated the trapping success rate and the single-cell trapping efficiency exceeding 99% and 85%, respectively. The microarray's capability to deliver identical dynamic biochemical stimulating signals, with various waveforms, to each unit was confirmed through fluorescein transport tests. Furthermore, we examined the intracellular calcium dynamics of U-2 OS human osteosarcoma cells in response to dynamic ATP signals, observing both single-peak calcium responses and calcium oscillations, which were modelled by a second-order system with a natural frequency of 1.6 mHz. Overall, our proposed microfluidic array offers a robust and valuable framework for advancing the understanding of single-cell dynamics.

L-2L ladder digital-to-analogue converter for dynamics generation of chemical concentrations

Cellular response to dynamic chemical stimulation encodes rich information about the underlying reaction pathways and their kinetics. Microfluidic chemical stimulators play a key role in generating dynamic concentration waveforms by mixing several aqueous solutions. In this article, we propose a multi-layer microfluidic chemical stimulator capable of modulating chemical concentrations by a simple binary logic based on the electronic-hydraulic analogy of electronic R-2R ladder circuits. The proposed device, which we call L-2L ladder digital-to-analogue converter (DAC), allows us to systematically modulate 2 ⁿ levels of concentrations from single sources of solution and solvent by a single operation of 2n membrane valves, which contrasts with existing devices that require complex channel geometry with multiple input sources and valve operations. We fabricated the L-2L ladder DAC with n = 3 bit resolution and verified the concept by comparing the generated waveforms with computational simulations. The response time of the proposed DAC was within the order of seconds because of its simple operation logic of membrane valves. Furthermore, detailed analysis of the waveforms revealed that the transient concentration can be systematically predicted by a simple addition of the transient waveforms of 2n = 6 base patterns, enabling facile optimization of the channel geometry to fine-tune the output waveforms.

Live imaging of apoptotic signaling flow using tunable combinatorial FRET-based bioprobes for cell population analysis of caspase cascades

Understanding cellular signaling flow is required to comprehend living organisms. Various live cell imaging tools have been developed but challenges remain due to complex cross-talk between pathways and response heterogeneities among cells. We have focused on multiplex live cell imaging for statistical analysis to address the difficulties and developed simple multiple fluorescence imaging system to quantify cell signaling at single-cell resolution using Förster Resonance Energy Transfer (FRET)-based chimeric molecular sensors comprised of fluorescent proteins and dyes. The dye-fluorescent protein conjugate is robust for a wide selection of combinations, facilitating rearrangement for coordinating emission profile of molecular sensors to adjust for visualization conditions, target phenomena, and simultaneous use. As the molecular sensor could exhibit highly sensitive in detection for protease activity, we customized molecular sensor of caspase-9 and combine the established sensor for caspase-3 to validate the system by observation of caspase-9 and -3 dynamics simultaneously, key signaling flow of apoptosis. We found cumulative caspase-9 activity rather than reaction rate inversely regulated caspase-3 execution times for apoptotic cell death. Imaging-derived statistics were thus applied to discern the dominating aspects of apoptotic signaling unavailable by common live cell imaging and proteomics protein analysis. Adopted to various visualization targets, the technique can discriminate between rivalling explanations and should help unravel other protease involved signaling pathways.

A Microfluidic Array Device for Single Cell Capture and Intracellular Ca2+ Response Analysis Induced by Dynamic Biochemical Stimulus

A microfluidic array was constructed for trapping single cell and loading identical dynamic biochemical stimulation for gain a better understanding of Ca2+ signalling in single cells by applying extracellular dynamic biochemical stimulus. This microfluidic array consists of multiple radially aligned flow channels with equal intersection angles, which was designed by a combination of stagnation point flow and physical barrier. Numerical simulation results and trajectory analysis shown the effectiveness of this single cell trapping device. Fluorescent experiment results demonstrated the effects of flow rate and frequency of dynamic stimulus on the profiles of biochemical concentration which exposed on captured cells. In this array chip, the captured single cells in each trapping channels were able to receive identical extracellular dynamic biochemical stimuli which being transmitted from the entrance at the middle of the microfluidic array. Besides, after loading dynamic Adenosine Triphosphate (ATP) stimulation on captured cells by this device, consistent average intracellular Ca2+ dynamics phase and cellular heterogeneity were observed in captured single K562 cells. Furthermore, this device is able to be used for investigating cellular respond in single cells to temporally varying environments by modulating the stimulation signal in terms of concentration, pattern, and duration of exposure.

Time-resolved microwell cell-pairing array reveals multiple T cell activation profiles

The differences in behaviour between individual cells in a large population are often important, yet are masked in bulk analyses where only average parameters are measured. One unresolved question in the field of immunology is the extent to which important immunological phenomena such as immunodominance to cancer antigens correlates with the average activity of a population of antigen-specific T lymphocytes, or with the activity of individual "outlier" cells. Despite progress in single cell technologies, few platforms are available that can deliver time-resolved, functional analysis at single cell resolution, for these investigations. We have developed an accessible high-throughput platform to measure single T cell signalling in real time following time-controlled stimulation by live antigen presenting cells. The cell-trap array consists of thousands of individual microwells cast in an agarose block, which is biocompatible and permeable to nutrients. Single T cells are isolated in wells via passive sedimentation and size exclusion, achieving up to 90% occupancy. The device enables simultaneous activation of thousands of single CD8⁺ cells. Stimulation with soluble reagents (ionomycin, anti-CD3 antibodies) or antigen presenting cells leads to changes in intracellular calcium concentrations which were measured using calcium-chelating fluorophore dyes. The platform was used to demonstrate a range of activation profiles among individual cells of a cloned, antigen specific CD8⁺ T cell hybridoma in response to both nonspecific stimuli and specific, physiologically relevant antigen stimulation. The presence of two different activation profiles was demonstrated, together with rare outlier behaviour among cells that are essentially clonal.

A review on microfluidics manipulation of the extracellular chemical microenvironment and its emerging application to cell analysis

Spatiotemporal manipulation of extracellular chemical environments with simultaneous monitoring of cellular responses plays an essential role in exploring fundamental biological processes and expands our understanding of underlying mechanisms. Despite the rapid progress and promising successes in manipulation strategies, many challenges remain due to the small size of cells and the rapid diffusion of chemical molecules. Fortunately, emerging microfluidic technology has become a powerful approach for precisely controlling the extracellular chemical microenvironment, which benefits from its integration capacity, automation, and high-throughput capability, as well as its high resolution down to submicron. Here, we summarize recent advances in microfluidics manipulation of the extracellular chemical microenvironment, including the following aspects: i) Spatial manipulation of chemical microenvironments realized by convection flow-, diffusion-, and droplet-based microfluidics, and surface chemical modification; ii) Temporal manipulation of chemical microenvironments enabled by flow switching/shifting, moving/flowing cells across laminar flows, integrated microvalves/pumps, and droplet manipulation; iii) Spatiotemporal manipulation of chemical microenvironments implemented by a coupling strategy and open-space microfluidics; and iv) High-throughput manipulation of chemical microenvironments. Finally, we briefly present typical applications of the above-mentioned technical advances in cell-based analyses including cell migration, cell signaling, cell differentiation, multicellular analysis, and drug screening. We further discuss the future improvement of microfluidics manipulation of extracellular chemical microenvironments to fulfill the needs of biological and biomedical research and applications.

Dynamic Environmental Control in Microfluidic Single-Cell Cultivations: From Concepts to Applications

Microfluidic single-cell cultivation (MSCC) is an emerging field within fundamental as well as applied biology. During the last years, most MSCCs were performed at constant environmental conditions. Recently, MSCC at oscillating and dynamic environmental conditions has started to gain significant interest in the research community for the investigation of cellular behavior. Herein, an overview of this topic is given and microfluidic concepts that enable oscillating and dynamic control of environmental conditions with a focus on medium conditions are discussed, and their application in single-cell research for the cultivation of both mammalian and microbial cell systems is demonstrated. Furthermore, perspectives for performing MSCC at complex dynamic environmental profiles of single parameters and multiparameters (e.g., pH and O₂ ) in amplitude and time are discussed. The technical progress in this field provides completely new experimental approaches and lays the foundation for systematic analysis of cellular metabolism at fluctuating environments.

Modeling immune cell behavior across scales in cancer

Detailed, mechanistic models of immune cell behavior across multiple scales in the context of cancer provide clinically relevant insights needed to understand existing immunotherapies and develop more optimal treatment strategies. We highlight mechanistic models of immune cells and their ability to become activated and promote tumor cell killing. These models capture various aspects of immune cells: (a) single‐cell behavior by predicting the dynamics of intracellular signaling networks in individual immune cells, (b) multicellular interactions between tumor and immune cells, and (c) multiscale dynamics across space and different levels of biological organization. Computational modeling is shown to provide detailed quantitative insight into immune cell behavior and immunotherapeutic strategies. However, there are gaps in the literature, and we suggest areas where additional modeling efforts should be focused to more prominently impact our understanding of the complexities of the immune system in the context of cancer.

This article is categorized under:

Biological Mechanisms > Cell Signaling

Models of Systems Properties and Processes > Mechanistic Models

Models of Systems Properties and Processes > Cellular Models

A System for Analog Control of Cell Culture Dynamics to Reveal Capabilities of Signaling Networks

Cellular microenvironments are dynamic. When exposed to extracellular cues, such as changing concentrations of inflammatory cytokines, cells activate signaling networks that mediate fate decisions. Exploring responses broadly to time-varying microenvironments is essential to understand the information transmission capabilities of signaling networks and how dynamic milieus influence cell fate decisions. Here, we present a gravity-driven cell culture and demonstrate that the system accurately produces user-defined concentration profiles for one or more dynamic stimuli. As proof of principle, we monitor nuclear factor-κB activation in single cells exposed to dynamic cytokine stimulation and reveal context-dependent sensitivity and uncharacterized single-cell response classes distinct from persistent stimulation. Using computational modeling, we find that cell-to-cell variability in feedback rates within the signaling network contributes to different response classes. Models are validated using inhibitors to predictably modulate response classes in live cells exposed to dynamic stimuli. These hidden capabilities, uncovered through dynamic stimulation, provide opportunities to discover and manipulate signaling mechanisms.

Single-cell Analysis with Microfluidic Devices

A microfluidic device as a pivotal research tool in chemistry and life science is now widely recognized. Indeed, microfluidic techniques have made significant advancements in fundamental research, such as the inherent heterogeneity of single-cells studies in cell populations, which would be helpful in understanding cellular molecular mechanisms and clinical diagnosis of major diseases. Single-cell analyses on microdevices have shown great potential for precise fluid control, cell manipulation, and signal output with rapid and high throughput. Moreover, miniaturized devices also have open functions such as integrating with traditional detection methods, for example, optical, electrochemical or mass spectrometry for single-cell analysis. In this review, we summarized recent advances of single-cell analysis based on various microfluidic approaches from different dimensions, such as in vitro, ex vivo, and in vivo analysis of single cells.

Transport of dynamic biochemical signals in a microfluidic single cell trapping channel with varying cross-sections

Dynamic biochemical signal control in vitro is important in the study of cellular responses to dynamic biochemical stimuli in microenvironment in vivo. To this end, we designed a microfluidic single cell trapping channel with varying cross-sections. In this work, we analyzed the transport of dynamic biochemical signals in steady and non-reversing pulsatile flows in such a microchannel. By numerically solving the 2D time-dependent Taylor-Aris dispersion equation, we studied the transport mechanism of different signals with varying parameters. The amplitude spectrum in steady flow shows that the trapping microchannel acts as a low-pass filter due to the longitudinal dispersion. The input signal can be modulated nonlinearly by the pulsatile flow. In addition, the nonlinear modulation effects are affected by the pulsatile flow frequency, the pulsatile flow amplitude and the average flow rate. When the flow frequency is much smaller or larger than that of the biochemical signal, the signal can be transmitted more efficiently. Besides, smaller pulsatile flow amplitude and larger average flow rate can decrease the nonlinear modulation and promote the signal transmission. These results demonstrate that in order to accurately load a desired dynamic biochemical signal to the trapped cell to probe the cellular dynamic response to the dynamic biochemical stimulus, the transport mechanism of the signals in the microchannel should be carefully considered.

A microfluidic platform with pneumatically switchable single-cell traps for selective intracellular signals probing

To investigate rapid suspension cell signaling, a microfluidic platform was urgently needed for flexibly manipulation of single cells and simultaneous generation of controllable chemical signals to stimulate single cells. In this paper, a microfluidic biosensor was developed to monitor intracellular calcium signal, integrated with single-cell trapping, chemical stimulation and releasing. Selective entrapment and discharge of individual cell were achieved by controlling the deformable membrane with pneumatic traps. The activation of intracellular calcium signal was qualitatively and quantitatively investigated by high-controllable chemical single-cell stimulation based on flexible hydrodynamic gating. And performing chemical stimulation and control assay in the same channel would improve the experimental robustness and effectiveness. Further investigation of the cellular responses to ATP pulses of varying concentrations and durations indicated that 20 μM ATP pulses with duration as short as 200 ms resulted in the same level of Ca²⁺ response induced by sustained stimulations. Washing with buffer for 30 s was sufficient for single cell to recover from receptor desensitization caused by ATP stimulation. In addition, the responses of cells to ATP stimulation were heterogeneous. The developed microfluidic method opens up a new avenue for intracellular signaling studies and drug screening.

A Microfluidic Fluorescent Flow Cytometry Capable of Quantifying Cell Sizes and Numbers of Specific Cytosolic Proteins

This study presents a microfluidics based cytometry capable of characterizing cell sizes and counting numbers of specific cytosolic proteins where cells were first bound by antibodies labelled with fluorescence and then aspirated into a constriction microchannel in which fluorescent levels were measured. These raw fluorescent pulses were further divided into a rising domain, a stable domain and a declining domain. In addition, antibody solutions with labelled fluorescence were aspirated through the constriction microchannel, yielding curves to translate raw fluorescent levels to protein concentrations. By using key parameters of three domains as well as the calibration curves, cell diameters and the absolute number of β-actins at the single-cell level were quantified as 14.2 ± 1.7 μm and 9.62 ± 4.29 × 10⁵ (A549, n_cell = 14 242), 13.0 ± 2.0 μm and 6.46 ± 3.34 × 10⁵ (Hep G2, n_cell = 35 932), 13.8 ± 1.9 μm and 1.58 ± 0.90 × 10⁶ (MCF 10 A, n_cell = 16 650), and 12.7 ± 1.5 μm and 1.09 ± 0.49 × 10⁶ (HeLa, n_cell = 26 246). This platform could be further adopted to measure numbers of various cytosolic proteins, providing key insights in proteomics at the single-cell level.

A programmable platform for sub-second multichemical dynamic stimulation and neuronal functional imaging in C. elegans

Caenorhabditis elegans (C. elegans) is a prominent model organism in neuroscience, as its small stereotyped nervous system offers unique advantages for studying neuronal circuits at the cellular level. Characterizing temporal dynamics of neuronal circuits is essential to fully understand neuronal processing. Characterization of the temporal dynamics of chemosensory circuits requires a precise and fast method to deliver multiple stimuli and monitor the animal's neuronal activity. Microfluidic platforms have been developed that offer an improved control of chemical delivery compared to manual methods. However, stimulating an animal with multiple chemicals at high speed is still difficult. In this work, we have developed a platform that can deliver any sequence of multiple chemical reagents, at sub-second resolution and without cross-contamination. We designed a network of chemical selectors wherein the chemical selected for stimulation is determined by the set of pressures applied to the chemical reservoirs. Modulation of inlet pressures has been automated to create robust, programmable sequences of subsecond chemical pulses. We showed that stimulation with sequences of different chemicals at the second to sub-second range can generate different neuronal activity patterns in chemosensory neurons; we observed previously unseen neuronal responses to a controlled chemical stimulation. Because of the speed and versatility of stimulus generated, this platform opens new possibilities to investigate neuronal circuits.

A microfluidic flow cytometer enabling absolute quantification of single-cell intracellular proteins

Quantification of single-cell proteomics provides key insights into cellular heterogeneity while conventional flow cytometry cannot provide absolute quantification of intracellular proteins of single cells due to the lack of calibration approaches. This paper presents a constriction channel (with a cross sectional area smaller than cells) based microfluidic flow cytometer, capable of collecting copy numbers of specific intracellular proteins. In this platform, single cells stained with fluorescence labelled antibodies were forced to squeeze through the constriction channel with the fluorescence intensities quantified and since cells fully filled the constriction channel during the squeezing process, solutions with fluorescence labelled antibodies were flushed into the constriction channel to obtain calibration curves. By combining raw fluorescence data and calibration curves, absolute quantification of intracellular proteins was realized. As a demonstration, copy numbers of beta-actin of single tumour cells were quantified to be 0.90 ± 0.30 μM (A549, n_cell = 14 228), 2.34 ± 0.70 μM (MCF 10A, n_cell = 2455), and 0.98 ± 0.65 μM (Hep G2, n_cell = 6945). The travelling time for individual cells was quantified to be roughly 10 ms and thus a throughput of 100 cells per s can be achieved. This microfluidic system can be used to quantify the copy numbers of intracellular proteins in a high-throughput manner, which may function as an enabling technique in the field of single-cell proteomics.

Microfluidics in systems biology-hype or truly useful?

Systems biology often relies on large-scale measurements and model-building to understand how complex biological systems function. Microfluidic technology has been touted as a tool for high-throughput experiments and has been a valuable tool to some systems biology research. This review focuses on applications where microfluidics can enhance experimental sensitivity and throughput, particularly in recent development in single-cell analyses and analyses on multi-cellular or complex biological entities. We conclude that microfluidics is not necessarily always useful for systems biology, but when used appropriately can greatly enhance experimentalists' ability to measure and control, and thereby enhance the understanding of and expand the utility of biological systems.

Lab-on-a-chip mRNA purification and reverse transcription via a solid-phase gene extraction technique

Extraction and purification of high quality RNA is a crucial initial step required for a variety of genomic assays. We report a solid phase gene extraction (SPGE) method for automated extraction, purification and reverse transcription of mRNA in a microfluidic device. This is performed using a 130 μm diameter stainless steel needle that is amino-linked to dT(15) oligonucleotides for selective hybridization of mRNA. By inserting this probe into the biological sample for only 30 seconds, mRNA is captured with high selectivity and a yield greater than 10 pg per mm of probe length. The probe is then inserted into a lab-on-a-chip device, where the bound poly-adenylated RNA is thermally released and immediately reverse transcribed for subsequent PCR amplification. The insertion of the probe into the microfluidic device is straightforward: the microchannel is formed with an elastomer (PDMS) that, when punctured, will seal around the probe. The specificity and RNA loading capacity of the probes were evaluated using conventional qPCR. This procedure was successfully used to extract, purify, and transcribe mRNA from rat glioblastoma cell spheroids in less than seven minutes. Analysis of the product confirmed that the SPGE technique selectively captures and inherently purifies high-quality mRNA directly from biological material with no need for additional pre-processing steps. Integrating this elegant sample preparation method into a complete lab-on-a-chip system will substantially enhance the speed and automation of mRNA assays for research and clinical diagnostics.

Single-cell resolution of intracellular T cell Ca2+ dynamics in response to frequency-based H2O2 stimulation

Adaptive immune cells, such as T cells, integrate information from their extracellular environment through complex signaling networks with exquisite sensitivity in order to direct decisions on proliferation, apoptosis, and cytokine production. These signaling networks are reliant on the interplay between finely tuned secondary messengers, such as Ca2+ and H2O2. Frequency response analysis, originally developed in control engineering, is a tool used for discerning complex networks. This analytical technique has been shown to be useful for understanding biological systems and facilitates identification of the dominant behaviour of the system. We probed intracellular Ca2+ dynamics in the frequency domain to investigate the complex relationship between two second messenger signaling molecules, H2O2 and Ca2+, during T cell activation with single cell resolution. Single-cell analysis provides a unique platform for interrogating and monitoring cellular processes of interest. We utilized a previously developed microfluidic device to monitor individual T cells through time while applying a dynamic input to reveal a natural frequency of the system at approximately 2.78 mHz stimulation. Although our network was much larger with more unknown connections than previous applications, we are able to derive features from our data, observe forced oscillations associated with specific amplitudes and frequencies of stimuli, and arrive at conclusions about potential transfer function fits as well as the underlying population dynamics.

New insights into mammalian signaling pathways using microfluidic pulsatile inputs and mathematical modeling

Temporally modulated input mimics physiology. This chemical communication strategy filters the biochemical noise through entrainment and phase-locking. Under laboratory conditions, it also expands the observability space for downstream responses. A combined approach involving microfluidic pulsatile stimulation and mathematical modeling has led to deciphering of hidden/unknown temporal motifs in several mammalian signaling pathways and has provided mechanistic insights, including how these motifs combine to form distinct band-pass filters and govern fate regulation under dynamic microenvironment. This approach can be utilized to understand signaling circuit architectures and to gain mechanistic insights for several other signaling systems. Potential applications include synthetic biology and biotechnology, in developing pharmaceutical interventions, and in developing lab-on-chip models.

Three-dimensional models for studying development and disease: moving on from organisms to organs-on-a-chip and organoids

Human development and disease are challenging to study because of lack of experimental accessibility to in vivo systems and the complex nature of biological processes. For these reasons researchers turn to the use of model systems, ranging in complexity and scale from single cells to model organisms. While the use of model organisms is valuable for studying physiology and pathophysiology in an in vivo context and for aiding pre-clinical development of therapeutics, animal models are costly, difficult to interrogate, and not always equivalent to human biology. For these reasons, three-dimensional (3D) cell cultures have emerged as an attractive model system that contains key aspects of in vivo tissue and organ complexity while being more experimentally tractable than model organisms. In particular, organ-on-a-chip and organoid models represent orthogonal approaches that have been able to recapitulate characteristics of physiology and disease. Here, we review advances in these two categories of 3D cultures and applications in studying development and disease. Additionally, we discuss development of key technologies that facilitate the generation of 3D cultures, including microfluidics, biomaterials, genome editing, and imaging technologies.

Microfluidic techniques for high throughput single cell analysis

The microfabrication of microfluidic control systems and the development of increasingly sensitive molecular amplification tools have enabled the miniaturization of single cells analytical platforms. Only recently has the throughput of these platforms increased to a level at which populations can be screened at the single cell level. Techniques based upon both active and passive manipulation are now capable of discriminating between single cell phenotypes for sorting, diagnostic or prognostic applications in a variety of clinical scenarios. The introduction of multiphase microfluidics enables the segmentation of single cells into biochemically discrete picoliter environments. The combination of these techniques are enabling a class of single cell analytical platforms within great potential for data driven biomedicine, genomics and transcriptomics.

Innovative Tools and Technology for Analysis of Single Cells and Cell-Cell Interaction

Heterogeneity in single-cell responses and intercellular interactions results from complex regulation of cell-intrinsic and environmental factors. Single-cell analysis allows not only detection of individual cellular characteristics but also correlation of genetic content with phenotypic traits in the same cell. Technological advances in micro- and nanofabrication have benefited single-cell analysis by allowing precise control of the localized microenvironment, cell manipulation, and sensitive detection capabilities. Additionally, microscale techniques permit rapid, high-throughput, multiparametric screening that has become essential for -omics research. This review highlights innovative applications of microscale platforms in genetic, proteomic, and metabolic detection in single cells; cell sorting strategies; and heterotypic cell-cell interaction. We discuss key design aspects of single-cell localization and isolation in microfluidic systems, dynamic and endpoint analyses, and approaches that integrate highly multiplexed detection of various intracellular species.

Secondary anchor targeted cell release

Personalized medicine offers the promise of tailoring therapy to patients, based on their cellular biomarkers. To achieve this goal, cellular profiling systems are needed that can quickly and efficiently isolate specific cell types without disrupting cellular biomarkers. Here we describe the development of a unique platform that facilitates gentle cell capture via a secondary, surface-anchoring moiety, and cell release. The cellular capture system consists of a glass surface functionalized with APTES, d-desthiobiotin, and streptavidin. Biotinylated mCD11b and hIgG antibodies are used to capture mouse macrophages (RAW 264.7) and human breast cancer (MCF7-GFP) cell lines, respectively. The surface functionalization is optimized by altering assay components, such as streptavidin, d-desthiobiotin, and APTES, to achieve cell capture on 80% of the functionalized surface and cell release upon biotin treatment. We also demonstrate an ability to capture 50% of target cells within a dual-cell mixture. This engineering advancement is a critical step towards achieving cell isolation platforms for personalized medicine.

Capture and enumeration of mRNA transcripts from single cells using a microfluidic device

Accurate measurement of RNA transcripts from single cells will enable the precise classification of cell types and characterization of the heterogeneity in cell populations that play key roles in normal cellular physiology and diseases. As a step towards this end, we have developed a microfluidic device and methods for automatic hydrodynamic capture of single mammalian cells and subsequent immobilization and digital counting of polyadenylated mRNA molecules released from the individual cells. Using single-molecule fluorescence imaging, we have demonstrated that polyadenylated mRNA molecules from single HeLa cells can be captured within minutes by hybridization to polydeoxyribothymidine oligonucleotides covalently attached on the glass surface in the device. The total mRNA molecule counts in the individual HeLa cells are found to vary significantly from one another. Our technology opens up the possibility of direct digital enumeration of RNA transcripts from single cells with single-molecule sensitivity using a single integrated microfluidic device.