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.
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 |
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].
| 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] |
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 [41][42]. 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 [43].
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 [44][45][46] (described in Table 3).
| Methods | Advantages | Disadvantages |
|---|---|---|
| Colorimetric method | Intuitive results, easy to read with the naked eye, low cost [47][48] | Unable to achieve accurate quantitative detection [49] |
| Electrochemical method | Quantitatively accurate, fast reading [50][51] | Rely on electrochemical workstation, increase cost and reduce flexibility [52] |
| Fluorescence method | Low detection limit, very sensitive [53][54] | Relying on fluorescence detection equipment, easily affected by the signal of paper fluorescent agent [55] |
| United electronics | Combining the aforementioned methods enables non-professionals to obtain accurate results [56][57] | Need to install a mobile APP or even larger devices, reducing flexibility [4] |