微压花：在纳米纤维素纸基微流控上制造微通道的便捷工艺
1School of Advanced Technology,Xi’an Jiaotong – Liverpool University, 2Department of Electrical Engineering and Electronics,University of Liverpool, 3State Key Laboratory for Manufacturing Systems Engineering,Xi’an Jiaotong University, 4School of Intelligent Manufacturing and Smart Transportation,Suzhou City University
Summary
该协议描述了一种简单的过程，该过程利用方便的塑料微模具进行简单的微压花操作，以在纳米纤维化纤维素纸上制造微通道，实现最小宽度为200μm。
Abstract
纳米纸源自纳米纤维化纤维素，作为一种有前途的微流体应用材料，已经引起了人们的极大兴趣。它的吸引力在于一系列卓越的品质，包括异常光滑的表面、出色的光学透明度、具有纳米级孔隙率的均匀纳米纤维基质以及可定制的化学特性。尽管基于纳米纸的微流控技术发展迅速，但目前用于在纳米纸上创建微通道的技术，如3D打印、喷涂或手动切割和组装，对实际应用至关重要，但仍具有一定的局限性，特别是对污染的敏感性。此外，这些方法仅限于毫米级通道的生产。本研究介绍了一种简单的工艺，利用方便的塑料微模具进行简单的微压花操作，在纳米纸上制造微通道，实现最小宽度 200 μm。所开发的微通道优于现有方法，实现了四倍的改进，并且可以在 45 分钟内完成。此外，还优化了制造参数，并为应用程序开发人员提供了方便的快速参考表。演示了层流混合器、液滴发生器和基于纳米纸的功能性分析设备 （NanoPAD） 的概念验证，这些设备设计用于使用表面增强拉曼光谱进行罗丹明 B 传感。值得注意的是，NanoPAD表现出卓越的性能和改进的检测限。这些出色的结果可归因于纳米纸的卓越光学性能和最近开发的精确微压花方法，使NanoPAD的集成和微调成为可能。
Introduction
最近，纳米纤维化纤维素 （NFC） 纸（纳米纸）已成为一种非常有前途的基板材料，可用于柔性电子、能源器件和生物医学等各种应用 1,2,3,4。纳米纸来源于天然植物，具有成本效益、生物相容性和可生物降解性，使其成为传统纤维素纸的有吸引力的替代品5,6。其特殊性能包括表面粗糙度小于 25 nm 的超光滑表面和致密的纤维素基质结构，允许创建高度结构化的纳米结构7。纳米纸中丰富的羟基有助于其紧凑和紧密堆积的纳米纤维素结构8.纳米纸具有出色的光学透明度和最小的光学雾度，非常适合光学传感器。此外，其固有的亲水性使无泵流动，即使其结构较厚，也能提供自主流体运动9,10。纳米纤维素在生物传感器、导电电子设备、细胞培养平台、超级电容器、电池等方面具有多种应用，展示了其多功能性和潜力11,12。特别是，纳米纤维素在纸基分析微流控装置（μPAD）中很有前途，与传统的色谱纸相比具有独特的优势。
在过去十年中，μPAD因其经济实惠、生物相容性、无泵操作和易于生产而受到广泛关注13,14。这些设备已成为有效的即时诊断工具，特别是在资源有限的环境中15,16,17。该领域的一项重大进步是由George Whitesides18和Bingcheng Lin小组19率先开发的蜡印刷，通过在色谱纸上加入微通道来创建功能性μPAD。随后，μPADs迅速发展，各种生物传感技术，包括电化学方法20、化学发光21和酶联免疫吸附测定（ELISA）22、23、24，成功用于检测各种生物标志物，如蛋白质25,26、DNA、27,28、RNAs29,30和蛋白质25,26、DNA、27,28、RNAs29,30和外泌体31.尽管取得了这些成就，μPAD仍然面临挑战，包括流速慢和溶剂蒸发。
已经提出了几种在纳米纸32,33,34上创建微通道的方法。一种方法涉及将牺牲成分 3D 打印到材料中，但它需要疏水涂层来限制无泵操作33。另一种技术涉及使用胶水在纳米纸之间手动堆叠通道层，这是劳动密集型的32。或者，将纳米纤维素纤维喷涂到预图案化的模具上可以产生微通道，但它涉及耗时且昂贵的模具制备34。值得注意的是，这些方法仅限于毫米级微通道，损害了微流控设备在试剂体积消耗和集成度方面的优势。开发具有微米级分辨率的简单纳米纸微通道图案化工艺仍然是一个挑战。
本研究提出了一种基于实际微压花的独特纳米纸微通道图案化方法。与现有方法相比，该方法具有多项优势，因为它不需要昂贵或专门的设备，简单、经济高效且高度准确。凸微通道模具是通过激光切割聚四氟乙烯 （PTFE） 薄膜制成的，聚四氟乙烯 （PTFE） 薄膜以其化学惰性和不粘特性而闻名。然后使用该模具将微通道压印到纳米纸凝胶膜上。在顶部涂上第二层纳米纸凝胶以形成封闭的空心通道。使用这种图案化技术，开发了纳米纸上的基本微流控设备，包括层流混合器和液滴发生器。此外，还演示了表面增强拉曼显微镜（SERS）NanoPAD的制备。通过在通道中引入两种化学试剂（AgNO3 和 NaBH4），实现了基于银纳米颗粒的 SERS 底物的原位制备，从而在低检测限 （LOD） 下获得了卓越的性能。
Protocol
1. 纳米纸微通道图案的微压花工艺 模具准备注：有关模具制备的详细信息，请参阅 Yuan 等人 12 。按照 材料表中的指示准备PTFE薄膜。 激光切割准备好的PTFE薄膜以制作凸微通道模具（图1A-I）。注意：PTFE模具的尺寸决定了线性一阶函数关系中的微通道尺寸（图2E，F<strong…
Representative Results
通过方便的微压花技术，利用实用的塑料微模具，设计了一种在纳米纸上创建微通道图案的独特方法。值得注意的是，该方法在小至200μm的尺度上实现了微通道图案化，与现有方法相比，这代表了四倍的改进32,33,34。在对图案参数进行微调后，所提供的指南在制造过程中表现出出色的可重复性，其特点是标准偏差最小。观察到?…
Discussion
本研究的主要重点是开发一种在纳米纸上制造微通道的简单方法。设计了一种使用 PTFE 作为模具的高效压花技术来应对这一挑战12.通过优化温度和压花压力，进行了一系列实验，建立了可靠的NanoPAD制造工艺。此外，还演示了使用快速参考表来调整NanoPADs在不同领域的应用。虽然这种方法高效稳定，但也遇到了一些挑战。最初，金属因其光滑性而被用作模具，但在将它们从粘合剂?…
Divulgations
The authors have nothing to disclose.
Acknowledgements
作者感谢江苏省高等学校自然科学基金（22KJB460033）和江苏省科技计划-青年学者（BK20200251）项目的资助。这项工作还得到了西交利物浦大学人工智能大学研究中心、西交利物浦大学江苏省数据科学与认知计算工程研究中心和SIP AI创新平台（YZCXPT2022103）的部分支持。还感谢制造系统工程国家重点实验室通过开放项目（SKLMS2023019）和仿生工程教育部重点实验室的支持。
Materials
| AgNO3 | Hushi (Shanghai, China) | 7761-88-8 | >99% |
| Ethanol | Hushi (Shanghai, China) | 64-17-5 | >99% |
| Hexadecane | Macklin (Shanghai, China) | 544-76-3 | >99% |
| LabSpec software | Horiba (Japan) | LabSpec5 | |
| Melamine | Macklin (Shanghai, China) | 108-78-1 | >99% |
| NaBH4 | Aladdin (Shanghai, China) | 16940-66-2 | >99% |
| Origin lab software | OriginLab (USA) | ||
| Polyethylene terephthalate (PET) | Myers Industries (Akron, USA) | ||
| Polytetrafluoroethylene films | Shenzhen Huashenglong plastic material Co., Ltd. (Shenzhen, China) | Teflon film | |
| PVDF filter membrane | EMD Millipore Corporation (USA) | VVLP04700 | pore size: 0.1 μm |
| Raman spectrometer | Horiba (Japan) | Xplo RA | |
| Rhodamine B | Macklin (Shanghai, China) | 81-88-9 | >95% |
| Scanning electron microscopy (SEM) | FEI(USA) | Scios 2 HiVac | |
| Silicon wafer | Horiba (Japan) | diameter: 5 mm | |
| TEMPO-oxidized NFC slurry | Tianjin University of Science and Technology | 1.0 wt% solid, carboxylate level 2.0 mmol/g solid, average nanofiber diameter: 10 nm |
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