Microembossing: A Convenient Process for Fabricating Microchannels on Nanocellulose Paper-Based Microfluidics

Summary

This protocol describes a straightforward process that utilizes convenient plastic micro-molds for simple microembossing operations to fabricate microchannels on nanofibrillated cellulose paper, achieving a minimum width of 200 µm.

Abstract

Nanopaper, derived from nanofibrillated cellulose, has generated considerable interest as a promising material for microfluidic applications. Its appeal lies in a range of excellent qualities, including an exceptionally smooth surface, outstanding optical transparency, a uniform nanofiber matrix with nanoscale porosity, and customizable chemical properties. Despite the rapid growth of nanopaper-based microfluidics, the current techniques used to create microchannels on nanopaper, such as 3D printing, spray coating, or manual cutting and assembly, which are crucial for practical applications, still possess certain limitations, notably susceptibility to contamination. Furthermore, these methods are restricted to the production of millimeter-sized channels. This study introduces a straightforward process that utilizes convenient plastic micro-molds for simple microembossing operations to fabricate microchannels on nanopaper, achieving a minimum width of 200 µm. The developed microchannel outperforms existing approaches, achieving a fourfold improvement, and can be fabricated within 45 min. Furthermore, fabrication parameters have been optimized, and a convenient quick-reference table is provided for application developers. The proof-of-concept for a laminar mixer, droplet generator, and functional nanopaper-based analytical devices (NanoPADs) designed for Rhodamine B sensing using surface-enhanced Raman spectroscopy was demonstrated. Notably, the NanoPADs exhibited exceptional performance with improved limits of detection. These outstanding results can be attributed to the superior optical properties of nanopaper and the recently developed accurate microembossing method, enabling the integration and fine-tuning of the NanoPADs.

Introduction

Recently, nanofibrillated cellulose (NFC) paper (nanopaper) has emerged as a highly promising substrate material for various applications such as flexible electronics, energy devices, and biomedicals^1,2,3,4. Derived from natural plants, nanopaper is cost-effective, biocompatible, and biodegradable, making it an appealing alternative to traditional cellulose paper^5,6. Its exceptional properties include an ultra-smooth surface with a surface roughness of less than 25 nm and a dense cel....

Protocol

1. Microembossing process for microchannel patterning on nanopaper

1. Mold preparation
   NOTE: Refer to Yuan et al.¹² for details on mold preparation.
   1. Prepare a PTFE film as indicated in the Table of Materials.
   2. Laser-cut the prepared PTFE film to make a convex microchannel mold (Figure 1A-I).
      NOTE: The dimensions of the PTFE mold determine the microchannel dimensions (Figure 2E,F) in a linear first-order function relationship.
2. Nanopaper preparation
   ....

Results

A unique method for creating microchannel patterns on nanopaper has been devised utilizing the practical plastic micro-molds through the convenient microembossing technique. Notably, this method accomplishes microchannel patterning at a scale as small as 200 µm, which represents a fourfold improvement compared to existing methods^32,33,34. After fine-tuning the patterning parameters, the provided guidelines exhibit excellent repe.......

Discussion

The primary focus of this study is to develop a simple method for fabricating microchannels on nanopaper. An efficient embossing technique was devised using PTFE as the mold to address this challenge¹². By optimizing the temperature and embossing pressure, a series of experiments were conducted to establish a reliable fabrication process for NanoPADs. Additionally, the use of a quick-reference table to adjust the applications of NanoPADs in different fields was demonstrated. Although this method i.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
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