Fabrication And Analytical Application Of Colorimetric Microfluidic Paper-based Devices

Microfluidic paper-based analytical devices（μPADs）,known as paper-based microfluidic devices,are a promising microfluidic analytical platform.μPADs combine a series of experimental operations such as injection,reaction and detection together on a single paper chip,which have great advantages including low-cost,fast,portable,small sample requirement,good biocompatibility,low detection background,no pollution and so on.Further more,multiple analysis can be easily achieved by the rational designing of microfluidic channels.ColorimetricμPAD can be fabricated by combining colorimetric analysis methods withμPAD based detection technology.ColorimetricμPAD can realize simple,rapid and visual quantitative analysis by reading color changing on the paper chip.Because of its unique advantages,colorimetricμPAD have great application potentials for on-site analysis,food quality detection,biochemical analysis,environmental monitoring,and clinical diagnosis and so on.This paper focuses on the preparation and analytical application of colorimetricμPADs,and carried out the following research experiments:A double-layer 3DμPAD with L-shaped circuitous microfluidic channel design was fabricated for the simultaneous determination of six metal ions,including Fe（Ⅲ）,Ni（Ⅱ）,Cr（Ⅵ）,Cu（Ⅱ）,Al（Ⅲ）and Zn（Ⅱ）.The 3DμPAD is consists of two paper layers,including the top pretreatment layer and the bottom colorimetric detection layer.The sample solution added to the central sample cell of the 3DμPAD can be automatically divided into eight flow paths,and automatically flow through the pretreatment zones located in the microfluidic channel for pretreatment,and then reach the detection zone to carry out the colorimetric reactions automaticly.The pretreatment and colorimetric detection of samples through the double-layer 3DμPAD with L-shaped circuitous microfluidic channel design can effectively prevent the random diffusion of the sample solution and significantly improve the color uniformity and repeatability.Improved colorimetric performance,expanded detection range and improved sensitivity could be further achieved by using LED light as upward lighting sources and a smartphone as portable detector.Finally,the double-layer 3DμPAD was applied to multiplexed determination of six metal ions in mixtures and environmental samples,with satisfactory results.For Fe（Ⅲ）,Ni（Ⅱ）,Cr（Ⅵ）,Cu（Ⅱ）,Al（Ⅲ）,and Zn（Ⅱ）,the detection limits are 0.2,0.3,0.1,0.03,0.08,and 0.04 mg/L,respectively.The obtained detection limits are about an order of magnitude lower than previously reportedμPAD for the related metal ions detection.The fabricated 3DμPAD with L-type circuitous microfluidic channel design has advantages of simplicity,rapidity,good selectivity,high sensitivity and humanization,and has great application potential for multiplex analysis and real-time on-site analysis.A novel cyclodextrin modified gold-palladium（β-CD-Pd@Au）nanocatalytic material was synthesized,and its morphology,composition and catalytic performance were studied.The synthesizedβ-CD-Pd@Au could efficiently catalyze the oxidation of various substrates,such as 3,3′,5,5′-tetramethylbenzidine（TMB）,mixture of 4-amino antipyrine（4-AAP）and 3,5-dichloro-2-hydroxy acid sodium（DHBS）（4-A-D）,and mixture of 4-AAP and N-Ethyl-N-（3-sulfopropyl）-3-methyl-aniline sodium salt（TOPS）（4-A-T）,by H₂O₂ to generate visual blue,purple and pink color,respectively.The catalytic activity ofβ-CD-Pd@Au was enhanced by 4-times than that of Pd@Au.By using TMB as model chromogenic substrate andβ-CD-Pd@Au as nanocatalyst,simple colorimetric assays were fabricated for the determination of H₂O₂ and glucose.Further,a colorimetric paper chip for glucose detection was further prepared with detection limit as low as 9.27μM/L.The developedβ-CD-Pd@Au based colorimetric assay and colorimetric paper chip were successfully applied to the detection of glucose in human blood sample with ideal results.