Although many advanced biosensing techniques have been purposed for cytokine profiling, there are no clinically available methods that integrate high-resolution immune cell monitoring and in situ multiplexed cytokine detection together in a biomimetic tissue microenvironment. The primary challenge arises due to the lack of suitable label-free sensing techniques and difficulty for sensor integration. In this work, we demonstrated a novel integration of a localized-surface plasmon resonance (LSPR)-based biosensor with a biomimetic microfluidic ‘adipose-tissue-on-chip’ platform for an in-situ label-free, high-throughput and multiplexed cytokine secretion analysis of obese adipose tissue. Using our established adipose-tissue-on-chip platform, we were able to monitor the adipose tissue initiation, differentiation, maturation and simulate the hallmark formation of crown-like structures (CLS) during pro-inflammatory stimulation. With integrated antibody-conjugated LSPR barcode sensor arrays, our platform enables simultaneous multiplexed measurements of pro-inflammatory (IL-6, and TNF-α) and anti-inflammatory (IL-10, and IL-4) cytokines secreted by the adipocytes and macrophages. As a result, our adipose-tissue-on-chip platform is capable of identifying stage-specific cytokine secretion profiles from a complex milieu during obesity progression, highlighting its potential as a high-throughput preclinical readout for personalized obesity treatment strategies.

In this work, we fabricate microfluidic probes (MFPs) in a single step by stereolithographic 3D printing and benchmark their performance with standard MFPs fabricated via glass or silicon micromachining. Two research teams join forces to introduce two independent designs and fabrication protocols, using different equipment. Both strategies adopted are inexpensive and simple (they only require a stereolithography printer) and are highly customizable. Flow characterization is performed by reproducing previously published microfluidic dipolar and microfluidic quadrupolar reagent delivery profiles which are compared to the expected results from numerical simulations and scaling laws. Results show that, for most MFP applications, printer resolution artifacts have negligible impact on probe operation, reagent pattern formation, and cell staining results. Thus, any research group with a moderate resolution (≤100 µm) stereolithography printer will be able to fabricate the MFPs and use them for processing cells, or generating microfluidic concentration gradients. MFP fabrication involved glass and/or silicon micromachining, or polymer micromolding, in every previously published article on the topic. We therefore believe that 3D printed MFPs is poised to democratize this technology. We contribute to initiate this trend by making our CAD files available for the readers to test our “print & probe” approach using their own stereolithographic 3D printers.

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Isolated microfluidic stagnation points – formed within microfluidic interfaces – have come a long way as a tool for characterizing materials, manipulating micro particles, and generating confined flows and localized chemistries.

Single‐cell analyses of secretory proteins are essential to fully understand cellular functional heterogeneity and unravel the underlying mechanisms of intercellular signaling and interactions. Retrieving dynamic information of protein secretion at single‐cell resolution reflects the precise, real‐time functional states of individual cells in physiological processes. Such measurements remain very challenging in single‐cell analysis, which requires highly integrated systems capable of performing on‐chip single‐cell isolation and subsequent real‐time protein detection. Here, recent advances in microfluidics‐based single‐cell manipulation and emerging approaches for label‐free single‐cell biosensing are reviewed. The advantages and limitations of these technologies are summarized and challenges to establish the integrated microfluidic biosensing systems for real‐time single‐cell secretomics are discussed. Recent efforts on integrated platforms for on‐chip single‐cell protein assays are highlighted and some perspectives on future directions in this field are provided.

In this work, for first time, circulating tumor cells (CTCs) are captured on an open biofunctionalized substrate with multiplexing capability. This is achieved by developing a new microfluidic probe (MFP) integrated with radially staggered herringbone (HB) elements for microvortex generation. The new tool, named as herringbone microfluidic probe (HB‐MFP), is a channel‐less microfluidic system with physically separated bottom capture substrate and top fluidics delivery system. The concept allows for functionalizing the capture substrate with multiple biorecognition ligands (in this work, stripes of different capture antibodies) and scanning the fluidics delivery system across the substrate in a 2D printing‐like movement. Using the HB‐MFP, CTCs are efficiently captured from prostate cancer blood samples through their specific EpCAM, PSMA, and PSA antigens in a single run, with counts ranging from as low as 6 CTCs mL‐1 (localized cancer patients) to as high as 280 CTCs mL‐1 (metastatic cancer patients). In the process, CTC clusters with sizes of as high as 40–50 cells are also successfully captured. The results indicate that multiplex profiles of CTCs could reveal certain cellular phenotypes based on PSMA and PSA expression levels. The developed HB‐MFP is simple and robust to use, allows for high throughput sample processing, and provides seamless access to captured CTCs for further downstream characterization.

Cell separation and patterning are of great interest to numerous biomedical applications. This work presents the microelectrofluidic probe, which separates cells within an open microfluidic system, and patterns cells in a 2D printing approach.

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