Real-Time Monitoring and Detection of Single-Cell Level Cytokine Secretion Using LSPR Technology

Label-free optical detection of calcium ion influx in cell-derived nanovesicles using a conical Au/PDMS biosensor

Ion channels, which are key to physiological regulation and drug discovery, control ion flux across membranes, and their dysregulation leads to various diseases. Ca2+ monitoring is crucial for cellular signaling when performing Ca-based assays in ion channel research; these assays are widely utilized in both academic and pharmaceutical contexts for drug screening and pharmacological profiling. However, existing detection methods are limited by slow detection speeds, low throughput, complex processes, and low analyte viability. In this study, we developed a label-free optical biosensing method using a conical Au/polydimethylsiloxane platform tailored to detect Ca2+ influx in A549-originated nanovesicles facilitated by the transient receptor potential ankyrin 1 (TRPA1) channel. Nanovesicles expressing cellular signaling components mimic TRPA1 signal transduction in cell membranes and improve analyte viability. The conical Au/polydimethylsiloxane sensor converted Ca2+ influx events induced by specific agonist exposure into noticeable changes in relative transmittance under visible light. The optical transmittance change accompanying Ca2+ influx resulted in an enhanced sensing response, high accuracy and reliability, and rapid detection (∼5 s) without immobilization or ligand treatments. In the underlying sensing mechanism, morphological variations in nanovesicles, which depend on Ca2+ influx, induce a considerable light scattering change at an interface between the nanovesicle and Au, revealed by optical simulation. This study provides a foundation for developing biosensors based on light-matter interactions. These sensors are simple and cost-effective with superior performance and diverse functionality.

Ex vivo T cell differentiation in adoptive immunotherapy manufacturing: Critical process parameters and analytical technologies

Adoptive immunotherapy shows great promise as a treatment for cancer and other diseases. Recent evidence suggests that the therapeutic efficacy of these cell-based therapies can be enhanced by the enrichment of less-differentiated T cell subpopulations in the therapeutic product, giving rise to a need for advanced manufacturing technologies capable of enriching these subpopulations through regulation of T cell differentiation. Studies have shown that modifying certain critical process control parameters, such as cytokines, metabolites, amino acids, and culture environment, can effectively manipulate T cell differentiation in ex vivo cultures. Advanced process analytical technologies (PATs) are crucial for monitoring these parameters and the assessment of T cell differentiation during culture. In this review, we examine such critical process parameters and PATs, with an emphasis on their impact on enriching less-differentiated T cell population. We also discuss the limitations of current technologies and advocate for further efforts from the community to establish more stringent critical process parameters (CPPs) and develop more at-line/online PATs that are specific to T cell differentiation. These advancements will be essential to enable the manufacturing of more efficacious adoptive immunotherapy products.

Integration of secreted signaling molecule sensing on cell monitoring platforms: a critical review

Monitoring cell secretion in complex microenvironments is crucial for understanding cellular behavior and advancing physiological and pathological research. While traditional cell culture methods, including organoids and spheroids, provide valuable models, real-time monitoring of cell secretion of signaling molecules remains challenging. Integrating advanced monitoring technologies into these systems often disrupts the delicate balance of the microenvironment, making it difficult to achieve sensitivity and specificity. This review explored recent strategies for integrating the monitoring of cell secretion of signaling molecules, crucial for understanding and replicating cell microenvironments, within cell culture platforms, addressing challenges such as non-adherent cell models and the focus on single-cell methodologies. We highlight advancements in biosensors, microfluidics, and three-dimensional culture methods, and discuss their potential to enhance real-time, multiplexed cell monitoring. By examining the advantages, limitations, and future prospects of these technologies, we aim to contribute to the development of integrated systems that facilitate comprehensive cell monitoring, ultimately advancing biological research and pharmaceutical development.

Recent Progresses in Optical Biosensors for Interleukin 6 Detection

Interleukin 6 (IL-6) is pleiotropic cytokine with pathological pro-inflammatory effects in various acute, chronic and infectious diseases. It is involved in a variety of biological processes including immune regulation, hematopoiesis, tissue repair, inflammation, oncogenesis, metabolic control, and sleep. Due to its important role as a biomarker of many types of diseases, its detection in small amounts and with high selectivity is of particular importance in medical and biological fields. Laboratory methods including enzyme-linked immunoassays (ELISAs) and chemiluminescent immunoassays (CLIAs) are the most common conventional methods for IL-6 detection. However, these techniques suffer from the complexity of the method, the expensiveness, and the time-consuming process of obtaining the results. In recent years, too many attempts have been conducted to provide simple, rapid, economical, and user-friendly analytical approaches to monitor IL-6. In this regard, biosensors are considered desirable tools for IL-6 detection because of their special features such as high sensitivity, rapid detection time, ease of use, and ease of miniaturization. In this review, current progresses in different types of optical biosensors as the most favorable types of biosensors for the detection of IL-6 are discussed, evaluated, and compared.

Development of Nano-Micro Fused LSPR Chip for In Situ Single-Cell Secretion Analysis

Single-cell analysis has become increasingly important in uncovering cell heterogeneity, which has great implications in medicine and biology for a deep understanding of cell characteristics. Owing to its significance, it is vital to create novel devices that can reveal special or unique cells. In this work, we developed a single-cell secretion detection chip consisting of microwells that can trap single cells. Each well is surrounded by Au nanopillars capable of localized surface plasmon resonance (LSPR) measurement. Using microfabrication and nanofabrication techniques, Au nanopillar and microwell structures were fabricated on a COP film. The Au nanopillar was modified with IL-6 antibodies for the direct detection of single-cell secreted IL-6 via LSPR absorbance peak shift. Specific IL-6 detection was successfully demonstrated using a null and IL-6 oversecreting Jurkat cell. A high single-cell trapping efficiency of over 80% was also achieved. Overall, the development of this single-cell secretion detection chip with a simple LSPR measurement setup represents a significant development in the field of cell biology and immunology, providing researchers with a powerful tool for studying individual cells and their secreted cytokines, and is useful for point-of-care testing (POCT) diagnostics.

Spatiotemporal dissection of tumor microenvironment via in situ sensing and monitoring in tumor-on-a-chip

Real-time monitoring in the tumor microenvironment provides critical insights of cancer progression and mechanistic understanding of responses to cancer treatments. However, clinical challenges and significant questions remain regarding assessment of limited clinical tissue samples, establishment of validated, controllable pre-clinical cancer models, monitoring of static versus dynamic markers, and the translation of insights gained from in vitro tumor microenvironments to systematic investigation and understanding in clinical practice. State-of-art tumor-on-a-chip strategies will be reviewed herein, and emerging real-time sensing and monitoring platforms for on-chip analysis of tumor microenvironment will also be examined. The integration of the sensors with tumor-on-a-chip platforms to provide spatiotemporal information of the tumor microenvironment and the associated challenges will be further evaluated. Though optimal integrated systems for in situ monitoring are still in evolution, great promises lie ahead that will open new paradigm for rapid, comprehensive analysis of cancer development and assist clinicians with powerful tools to guide the diagnosis, prognosis and treatment course in cancer.

Optical Sensing Strategies for Probing Single-Cell Secretion

Measuring cell secretion events is crucial to understand the fundamental cell biology that underlies cell-cell communication, migration, proliferation, and differentiation. Although strategies targeting cell populations have provided significant information about live cell secretion, they yield ensemble profiles that obscure intrinsic cell-to-cell variations. Innovation in single-cell analysis has made breakthroughs allowing accurate sensing of a wide variety of secretions and their release dynamics with high spatiotemporal resolution. This perspective focuses on the power of single-cell protocols to revolutionize cell-secretion analysis by allowing real-time and real-space measurements on single live cell resolution. We begin by discussing recent progress on single-cell bioanalytical techniques, specifically optical sensing strategies such as fluorescence-, surface plasmon resonance-, and surface-enhanced Raman scattering-based strategies, capable of in situ real-time monitoring of single-cell released ions, metabolites, proteins, and vesicles. Single-cell sensing platforms which allow for high-throughput high-resolution analysis with enough accuracy are highlighted. Furthermore, we discuss remaining challenges that should be addressed to get a more comprehensive understanding of secretion biology. Finally, future opportunities and potential breakthroughs in secretome analysis that will arise as a result of further development of single-cell sensing approaches are discussed.

Recent Advances in Aptasensor for Cytokine Detection: A Review

Cytokines are proteins secreted by immune cells. They promote cell signal transduction and are involved in cell replication, death, and recovery. Cytokines are immune modulators, but their excessive secretion causes uncontrolled inflammation that attacks normal cells. Considering the properties of cytokines, monitoring the secretion of cytokines in vivo is of great value for medical and biological research. In this review, we offer a report on recent studies for cytokine detection, especially studies on aptasensors using aptamers. Aptamers are single strand nucleic acids that form a stable three-dimensional structure and have been receiving attention due to various characteristics such as simple production methods, low molecular weight, and ease of modification while performing a physiological role similar to antibodies.

Cytokines: From Clinical Significance to Quantification

Cytokines are critical mediators that oversee and regulate immune and inflammatory responses via complex networks and serve as biomarkers for many diseases. Quantification of cytokines has significant value in both clinical medicine and biology as the levels provide insights into physiological and pathological processes and can be used to aid diagnosis and treatment. Cytokines and their clinical significance are introduced from the perspective of their pro- and anti-inflammatory effects. Factors affecting cytokines quantification in biological fluids, native levels in different body fluids, sample processing and storage conditions, sensitivity to freeze-thaw, and soluble cytokine receptors are discussed. In addition, recent advances in in vitro and in vivo assays, biosensors based on different signal outputs and intracellular to extracellular protein expression are summarized. Various quantification platforms for high-sensitivity and reliable measurement of cytokines in different scenarios are discussed, and commercially available cytokine assays are compared. A discussion of challenges in the development and advancement of technologies for cytokine quantification that aim to achieve real-time multiplex cytokine analysis for point-of-care situations applicable for both biomedical research and clinical practice are discussed.

Measuring single-cell protein secretion in immunology: Technologies, advances, and applications

The dynamics, nature, strength, and ultimately protective capabilities of an active immune response are determined by the extracellular constitution and concentration of various soluble factors. Generated effector cells secrete such mediators, including antibodies, chemo‐ and cytokines to achieve functionality. These secreted factors organize the individual immune cells into functional tissues, initiate, orchestrate, and regulate the immune response. Therefore, a single‐cell resolved analysis of protein secretion is a valuable tool for studying the heterogeneity and functionality of immune cells. This review aims to provide a comparative overview of various methods to characterize immune reactions by measuring single‐cell protein secretion. Spot‐based and cytometry‐based assays, such as ELISpot and flow cytometry, respectively, are well‐established methods applied in basic research and clinical settings. Emerging novel technologies, such as microfluidic platforms, offer new ways to measure and exploit protein secretion in immune reactions. Further technological advances will allow the deciphering of protein secretion in immunological responses with unprecedented detail, linking secretion to functionality. Here, we summarize the development and recent advances of tools that allow the analysis of protein secretion at the single‐cell level, and discuss and contrast their applications within immunology.

Digital Microfluidics for Single Bacteria Capture and Selective Retrieval Using Optical Tweezers

When screening microbial populations or consortia for interesting cells, their selective retrieval for further study can be of great interest. To this end, traditional fluorescence activated cell sorting (FACS) and optical tweezers (OT) enabled methods have typically been used. However, the former, although allowing cell sorting, fails to track dynamic cell behavior, while the latter has been limited to complex channel-based microfluidic platforms. In this study, digital microfluidics (DMF) was integrated with OT for selective trapping, relocation, and further proliferation of single bacterial cells, while offering continuous imaging of cells to evaluate dynamic cell behavior. To enable this, magnetic beads coated with Salmonella Typhimurium-targeting antibodies were seeded in the microwell array of the DMF platform, and used to capture single cells of a fluorescent S. Typhimurium population. Next, OT were used to select a bead with a bacterium of interest, based on its fluorescent expression, and to relocate this bead to a different microwell on the same or different array. Using an agar patch affixed on top, the relocated bacterium was subsequently allowed to proliferate. Our OT-integrated DMF platform thus successfully enabled selective trapping, retrieval, relocation, and proliferation of bacteria of interest at single-cell level, thereby enabling their downstream analysis.