纸基微流控芯片 | Encyclopedia MDPI

纸基微流控芯片: History

Please note this is an old version of this entry, which may differ significantly from the current revision.

Contributor: Yuhang Jin , Aziz ur Rehman Aziz ,

Bin Wu

Ying Lv

, Hangyu Zhang , Na Li , Bo Liu , Zhengyao Zhang

Traditional detectors mostly consist of complex structures that are difficult to use. However, paper-based microfluidic chips combine the advantages of small size, high efficiency, easy processing and environmental protection. Paper-based microfluidic chips for biomedical applications focus on efficiency, accuracy, integration and innovation. As a result, continuous progress has been observed in the transition from single-channel to multi-channel detection and from qualitative to quantitative detection. These developments have improved the efficiency and accuracy of single cells and biochemical markers detection. Paper-based microfluidic chips can provide insights into multiple fields, including biomedicine and other related fields.

paper-based microfluidics chips
biomedicine
biomarker
clinical detection

1. Introduction

The perfect integration of medicine and engineering has led to the development of many biotechnologies, such as marker detection, gene amplification, cell culture, etc.In professional laboratories, however, professional instruments are used, which raises costs, makes relevant experiments more difficult, and restricts discipline development. So, biomedical research has slowly moved toward making new devices that are economical, easy to use, environmentally friendly, and yield great results.

In 1990, microfluidics was first proposed for microfluidic control in microelectrome chanical systems (MEMS) [ 1 ]. Microfluidic chips were initially applied for chemical analysis [ 2 ]. Among different types of microfluidic chips, paper-based microfluidic chips have recently gained attention in the biomedical field because of their potential for developing into ideal biomedical devices [ 3 , 4 ].

2. Overview of Paper-Based Microfluidic Chips

2.1. Characteristics of Paper-Based Microfluidic Chips

Microfluidic chips are small and lightweight devices with highly integrated detection.It integrates sample preparation, reaction, separation, detection, and other components at the micron scale level with fine processing technology. As a result, it can carry out complex physical and chemical processes as well as complete the whole experimental analysis, from adding samples to reading results. Therefore, itisalsocalled“labonchip” [ 5、6、7 ]. Whitesides’research group at Harvard University in the United States proposed the concept of paper-based microfluidic analytical devices ( µ PADs) in 2007 [ 8 ]. For “lab on papers”, filter paper is used as a substrate for microfluidic chips instead of inorganic or polymeric materials.There are several advantages to using paper-based microfluidic chips: the paper itself has a capillary effect, which can guide reagent flow without requiring additional power sources. Paper is relatively inexpensive, easy to obtain and process, so chip preparation cost is reduced. Similarly, the size is small and the volume is light, making it easy to transport and store. As it degrades more easily than other synthetic materials, it reduces the environmental restrictions on chips’ use and is more environmentally friendly. Thus, µ PADs are more economical, safer, and easier to use and transport than other microfluidic chips [ 9、10、11 ].

2.2. Materials of Paper-Based Microfluidic Chips

The design and preparation of a paper-based material plays a decisive role in determining how well the µ PADs will perform. There are currently three paper-based materials widely used for the production of paper chips: filter paper [ 12 ], nitrocellulose paper [ 13 ] , and glass fiber paper [ 14 ]. All of them have their own characteristics and applications (described in Table 1), and can also be used alone or combined with each other to achieve the overall function. Furthermore, parameters such as the thickness of the paper and the porosity of the paper also affect fluid velocity. These parameters should be taken into consideration when performing more detailed fluid control calculations [ 15 ].

Table 1. Materials of paper-based microfluidic chips [ 12 , 13 , 14 ].

Material	Characteristics	Applications
Filter paper	Suitable water absorption, easy to obtain, low cost, poor strength	Suitable for all kinds of paper chips, the most widely used paper-based materials
Nitrocellulose paper	It can bind and fix protein, and high cost	Detection based on Western blot reaction, colloidal gold test paper reaction zone
Glass fiber paper	Stable properties, not easy to break, high temperature resistance, corrosion resistance	Detection based on chemical reactions

3. Preparation Method of Paper-Based Microfluidic Chip

3.1. Two-Dimensional Paper Chip Preparation

Paper-based chips differ from glass, plastic, or other materials-based chips. For example, the hydrophilic channels flanked by hydrophobic barriers in paper-based microfluidic devices guide liquid flow and the reaction is etched on the substrate. As technology develops, paper chip preparation methods become more sophisticated. Paper in a broad sense includes various analytical devices prepared by simple splicing or stacking of paper-derived materials. Fluid control is undoubtedly a top priority in paper chip design [ 16 ]. This section focuses on common methods for making channels on paper for fluid flow (as described in Table 2) [ 17,18,19 ].

Table 2. Preparation method of paper-based microfluidic chips.

Methods	Advantages	Disadvantages
Photolithography	The earliest method for making paper chips, precise channel structure [ 20 ]	The process is complicated The resulting paper chips are not suitable for bending [ 8 ]
Plasma treatment technology	More suitable for mass production and have low cost [ 21 ]	Depends on templates, reducing flexibility [ 22 ]
Wax printing	Simple processing, environmentally friendly materials [ 23 , 24 ]	Rely on wax spray printers, heating-induced horizontal diffusion reduces structure accuracy [ 25 ]
Inkjet method	Simple processing can be drawn with ink pen, no heating diffusion, more precise structure [ 26 , 27 ]	Hydrophobic inks can be toxic, ink pens are inaccurate for hand drawing, still rely on inkjet printers [ 28 ]
Screen printing	Ideal for mass production, simple process, and low cost [ 29 , 30 ]	Rely on templates, greatly reducing flexibility during research [ 31 ]
Laser processing technology	Very precise structures can be prepared [ 32 ]	Rely on expensive laser equipment and difficult to popularize[ 33 ]
3D origami method	3D structure has more functions, direct registration of each layer [ 34、35 ]	Means of fixing are required between layers, only single material can be used [ 36 ]
3D lamination method	3D structure has more functions, can use a variety of materials [ 37 ]	Fixed means are required between layers, registration methods are required [ 38 ]
Other 3D methods	Highly innovative and has huge development potential [ 39 ]	Special uses, difficult to promote [ 40 ]

3.2. Three-Dimensional Paper Chips Preparation

In fact, three-dimensional paper chips are just a superposition of two-dimensional paper chips, but they achieve the goal of “1 + 1 > 2”. By providing a multilayer structure and vertical flow channels, the flux of the paper chip is increased and the layers of the paper chip are enriched, allowing for a more controlled detection reaction in time and space, one of the new directions for paper chip development [44、45]. In comparison to 2D paper chips, 3D paper chips are more difficult to fabricate at a higher cost, but they are more convenient, accurate, and sensitive [46].

4. Analysis Method of Paper-Based Microfluidic Chip

The paper-based microfluidic chip focuses on the results being presented in a visual way. Using colorimetry, electrochemistry, and fluorescence, the paper chip can find out both qualitative and quantitative information about different substances based on their physical, biological, and chemical properties [ 48、49、50 ] (described in Table 3).

Table 3. Analysis Method of paper-based microfluidic chips.

Methods	Advantages	Disadvantages
Colorimetric method	Intuitive results, easy to read with the naked eye, low cost [ 51 , 52 ]	Unable to achieve accurate quantitative detection [ 53 ]
Electrochemical method	Quantitatively accurate, fast reading [ 54 , 55 ]	Rely on electrochemical workstation, increase cost and reduce flexibility [ 56 ]
Fluorescence method	Low detection limit, very sensitive [ 57 , 58 ]	Relying on fluorescence detection equipment, easily affected by the signal of paper fluorescent agent [ 59 ]
United electronics	Combining the aforementioned methods enables non-professionals to obtain accurate results [ 60 , 61 ]	Need to install a mobile APP or even larger devices, reducing flexibility [ 4 ]

This entry is adapted from the peer-reviewed paper 10.3390/mi13111835

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1. Introduction

2. Overview of Paper-Based Microfluidic Chips

2.1. Characteristics of Paper-Based Microfluidic Chips

2.2. Materials of Paper-Based Microfluidic Chips

Material

Characteristics

Applications

Filter paper

Suitable water absorption, easy to obtain, low cost, poor strength

Suitable for all kinds of paper chips, the most widely used paper-based materials

Nitrocellulose paper

It can bind and fix protein, and high cost

Detection based on Western blot reaction, colloidal gold test paper reaction zone

Glass fiber paper

Stable properties, not easy to break, high temperature resistance, corrosion resistance

Detection based on chemical reactions

3. Preparation Method of Paper-Based Microfluidic Chip

3.1. Two-Dimensional Paper Chip Preparation

Methods

Advantages

Disadvantages

Photolithography

The earliest method for making paper chips, precise channel structure [ 20 ]

The process is complicated

The resulting paper chips are not suitable for bending

[ 8 ]

Plasma treatment technology

More suitable for mass production and have low cost [ 21 ]

Depends on templates, reducing flexibility [ 22 ]

Wax printing

Simple processing, environmentally friendly materials [ 23 , 24 ]

Rely on wax spray printers, heating-induced horizontal diffusion reduces structure accuracy [ 25 ]

Inkjet method

Simple processing can be drawn with ink pen, no heating diffusion, more precise structure [ 26 , 27 ]

Hydrophobic inks can be toxic, ink pens are inaccurate for hand drawing, still rely on inkjet printers [ 28 ]

Screen printing

Ideal for mass production, simple process, and low cost [ 29 , 30 ]

Rely on templates, greatly reducing flexibility during research [ 31 ]

Laser processing technology

Very precise structures can be prepared [ 32 ]

Rely on expensive laser equipment and difficult to popularize[ 33 ]

3D origami method

3D structure has more functions, direct registration of each layer [ 34、35 ]

Means of fixing are required between layers, only single material can be used [ 36 ]

3D lamination method

3D structure has more functions, can use a variety of materials [ 37 ]

Fixed means are required between layers, registration methods are required [ 38 ]

Other 3D methods

Highly innovative and has huge development potential [ 39 ]

Special uses, difficult to promote [ 40 ]

3.2. Three-Dimensional Paper Chips Preparation

4. Analysis Method of Paper-Based Microfluidic Chip

Methods

Advantages

Disadvantages

Colorimetric method

Intuitive results, easy to read with the naked eye, low cost [ 51 , 52 ]

Unable to achieve accurate quantitative detection [ 53 ]

Electrochemical method

Quantitatively accurate, fast reading [ 54 , 55 ]

Rely on electrochemical workstation, increase cost and reduce flexibility [ 56 ]

Fluorescence method

Low detection limit, very sensitive

[ 57 , 58 ]

Relying on fluorescence detection equipment, easily affected by the signal of paper fluorescent agent [ 59 ]

United electronics

Combining the aforementioned methods enables non-professionals to obtain accurate results [ 60 , 61 ]

Need to install a mobile APP or even larger devices, reducing flexibility [ 4 ]