Applications of microfluidic paper-based chips in environmental analysis and detection

Microfluidic paper-based chips have many advantages such as ease of integration, miniaturization, and automation; high throughput; low production cost; easy portability; easy storage and transportation, environmental friendliness, and feasibility of instantaneous detection. These chips are widely used in clinical diagnosis, food quality control, and immunoassays. With the continuous development of microfluidic paper microarrays in recent years, they have also received great attention for environmental contaminant analysis and detection, and research in this field has been intensive, showing excellent prospects for application. This review summarizes the latest research progress in environmental analysis from the perspective of the application of microfluidic paper-based chips, as well as future development trends and challenges. More than 150 papers from the Science Citation Index (SCI) and Chinese core journals are cited in this paper. This review includes the advantages of microfluidic paper-based chips for environmental analysis and detection; the introduction of paper chip fabrication methods, including wax printing, photolithography, dicing, plasma, laser, and inkjet etching; and the introduction of advanced analytical methods based on paper chips, such as electrochemical analysis, fluorescence analysis, colorimetric analysis, surface-enhanced Raman analysis, and integrated sensing methods. The future development trends and prospects of environmental analysis based on microfluidic paper-based chips are also reviewed. Through a rich and comprehensive review of recent related research, it is shown that although microfluidic paper-based chip technology has only been developed for little more than a decade since its introduction, this technology has seen rapid development in environmental analysis-related research and has yielded rich results. The hydrophilic and porous nature of cellulose in paper as a chip substrate allows the passive transport of liquids without an external power source. The diversity of available microfluidic paper-based chip fabrication and analysis methods allows flexible selection and matching according to different environmental conditions and detection requirements, so that the best detection results can be obtained. Moreover, microfluidic paper chips as detection platforms show good biocompatibility in the analysis and detection of environmental pollutants, enabling the analysis of more types of pollutants. The used paper is biodegradable and can be directly disposed of as ordinary garbage after appropriate degradation treatment; thus it is environmentally friendly and does not impact the health of the operators. In addition, the low production cost and simple operation of the paper chip design study make it possible to fabricate low-cost, portable, and practical analytical equipment, which is important for rapid testing of the conventional environment. However, there are some inherent disadvantages: the mechanical strength of the paper is not sufficiently high to resist deformation; degree of fluid control is difficult to achieve the desired effect, and the sample flow may be lost due to leakage; multiple contaminants may interfere with one another when analyzed in parallel; there are difficulties in commercial mass production. However, these problems also point to the direction for the research and development of microfluidic paper-based chips in the field of environmental testing. With continuous advances in manufacturing and analysis technologies, microfluidic paperbased chips are expected to play a more prominent role in future environmental analysis.