Pathologies in adipose (fat) tissue function are linked with human diseases such as diabetes, obesity, metabolic syndrome, and cancer. Dynamic, rapid release of metabolites has been observed in adipocyte cells and tissue, yet higher temporal resolution is needed to adequately study this process. In this work, a microfluidic device with precise and regular valve-automated droplet sampling, termed a microfluidic analog-to-digital converter (μADC), was used to sample secretions from ∼0.75 mm diameter adipose explants from mice, and on-chip salt water electrodes were used to merge sampled droplets with reagent droplets from two different fluorometric coupled enzyme assays. By integrating sampling and assays on-chip, either glycerol or non-esterified fatty acids (NEFA), or both, were quantified optically within merged 12 nanoliter droplets using a fluorescence microscope with as high as 20 second temporal resolution. Limits of detection were 6 μM for glycerol (70 fmol) and 0.9 μM for NEFA (10 fmol). Multiple ex vivo adipose tissue explants were analyzed with this system, all showing clear increases in lipolytic function after switching from feeding to fasting conditions. Enabled by high temporal resolution, lipolytic oscillations of both glycerol and NEFA were observed for the first time in the range of 0.2 to 1.6 min⁻¹. Continuous wavelet transform (CWT) spectrograms and burst analyses (0.1 to 4.0 pmol bursts) revealed complex dynamics, with multiplexed assays (duplex for glycerol and NEFA) from the same explants showing mostly discordant bursts. These data support separate mechanisms of NEFA and glycerol release, although the connection to intracellular metabolic oscillations remains unknown. Overall, this device allowed automated and highly precise temporal sampling of tissue explants at high resolution and programmable downstream merging with multiple assay reagents, revealing unique biological information. Such device features should be applicable to various other tissue or spheroid types and to other assay formats.

中文翻译：

---

使用基于液滴的微流体对离体脂肪组织进行动态采样支持甘油和脂肪酸分泌的不同机制


脂肪（脂肪）组织功能的病理与糖尿病、肥胖、代谢综合征和癌症等人类疾病有关。已在脂肪细胞和组织中观察到代谢物的动态、快速释放，但需要更高的时间分辨率来充分研究这一过程。在这项工作中，一种具有精确和常规的阀门自动液滴采样的微流体装置，称为微流体模数转换器 （μADC），用于对小鼠直径为 ∼0.75 mm 的脂肪外植体的分泌物进行采样，并使用片上盐水电极将采样液滴与来自两种不同荧光偶联酶测定的试剂液滴合并。通过在芯片上集成采样和检测，使用荧光显微镜以高达 20 秒的时间分辨率对合并的 12 纳升液滴中的甘油或非酯化脂肪酸 （NEFA） 或两者进行光学定量。甘油 （70 fmol） 的检测限为 6 μM，NEFA （10 fmol） 的检测限为 0.9 μM。使用该系统分析了多个离体脂肪组织外植体，均显示从进食条件切换到禁食条件后脂肪分解功能明显增加。在高时间分辨率的支持下，首次在 0.2 至 1.6 ^min-1 范围内观察到甘油和 NEFA 的脂解振荡。连续小波变换 （CWT） 频谱图和脉冲群分析（0.1 至 4.0 pmol 脉冲）揭示了复杂的动力学，来自同一外植体的多重分析（甘油和 NEFA 的双重）显示大多数不一致的脉冲。这些数据支持 NEFA 和甘油释放的不同机制，尽管与细胞内代谢振荡的联系仍然未知。 总体而言，该设备允许以高分辨率对组织外植体进行自动化和高精度的时间采样，并与多种分析试剂进行可编程的下游合并，揭示独特的生物学信息。此类设备功能应适用于各种其他组织或球体类型以及其他检测形式。