The Design And Fluorescence Detection Of Paper-Based Microfluidic Device Based On Carbon Dots

In medical,environmental,food and other related fields,it is necessary to analyze and detect related substances quickly and easily.As a portable device,the paper-based microfluidic device（μPAD）can concentrate multiple steps of analysis and detection on a tiny piece of filter paper,and rapid detection of multiple components can be achieved.Carbon dots（CDs）,as a fluorescent nanomaterial,can be well loaded on the paper,so that they can be combined with smartphones to achieve quantitative detection.In this paper,μPAD was designed and fabricated,and CDs were combined with it for fluorescence analysis and detection.The specific research contents are as follows:（1）On-site analytical detection of multiple enzymes is critical for disease diagnosis,treatment,and prognosis.To date,portable,low-cost,and efficient detection of multiple enzymes remains a formidable challenge.We therefore developed a simultaneous point-of-care（POCT）platform for the detection of alkaline phosphatase（ALP）and butyrylcholinesterase（BChE）,combining ratiometric fluorescence detection with 3D origamiμPAD based on CDs.The 3D origamiμPAD was fabricated by one-step drawing using a black oil-based marker and a custom-made metal mold.It consists of two parallel channels and four layers of foldable paper sheets,which could initiate cascade catalytic reactions in turn through simple folding:the substrate of ALP（pyrophosphate,PPi）and the product of BChE（thiocholine,TCh）can be strongly complexed with Cu²⁺,and Cu²⁺can oxidize o-phenylenediamine（OPD）to 2,3-diaminophenazine（oxOPD,emission wavelength 565 nm）,which can quench fluorescence of the CDs（maximum emission peak at 445 nm）via inner filter effect.Finally,a smartphone was used to take a fluorescent picture of the detection area,and the RGB value of the picture was read through the software to achieve quantitatively analyze ALP and BChE,where the linear range and LOD for detecting ALP are 5.0–350.0 U L^-1 and 3.6 U L^-1,respectively;the linear range and LOD for the detection of BChE were 1.0–25.0 U m L^-1 and 0.4U m L^-1,respectively.Based on the proposed detection platform,the activities of ALP and BChE in human serum samples were successfully detected with recoveries of 97.6%–104.0%and RSD less than 5.2%,behaving good precision and high accuracy,and it can open up broad prospects for detection of multiple biomarkers.（2）Pesticide is currently widely used in modern agriculture,but pesticide residues may cause food and environmental pollution and endanger human health.Rapid and accurate detection of pesticide residues in agricultural products is of great significance to protect public health and the environment.To this end,we fabricated a paper chip using a custom-made oily stamp in one step,which was combined with hydrophilic dual-emission wavelength CDs for ratiometric fluorescence detection of thiophanate-methyl（TM）:CDs have two emission wavelengths at 450 nm and 660 nm,respectively.Hg²⁺can quench the fluorescence of CDs at 660nm.Since TM can complex with Hg²⁺,when TM is added,the fluorescence at 660 nm will gradually recover.Therefore,as the concentration of TM increases,the fluorescence image of detection area gradually changes from blue to purple.Finally,TM can be quantitatively detected by smartphone photography and analysis.The linear range of detection is 1.0–30.0μM,and the LOD is 0.80μM.The paper chip has been successfully used in the high-throughput detection of TM in many practical samples due to its simple and rapid fabrication method.The recoveries are 95.8%–105.6%,and the RSD is less than 8.3%,indicating that the method has good detection accuracy.It will be widely used in various fields of analysis and detection in the future.