Preparation And Preliminary Application Of Low "coffee Ring" Effect Fluorescent Paper

Up to date,a series of analysis methods have been explored with high detection sensitivity for probing heavy metal ions in the environmental media,which may,however,mostly encounter with some disadvantages of expensive equipment,complex operation,time-consuming measurement,and on-site monitoring inability.Alternatively,the paper-based test strips have been widely employed as the analysis tool that is simple,rapid,and field-appliable for the in-site analysis.However,common test strips have been being trapped by the undesirable distribution of the sensitive materials or probes immoblized on test strips,which might be caused by the formidable "Coffee Ring" effect.As a result,they may allow for the qualitative or half-quantitative analysis because of the poor detection reproducibility,sensitivity,and accuracy.Therefore,suppressing the "Coffee Ring" effect of the probe materials dispersed on the test strips is of crucial importance to improve the analytical performances of the test strips-based analysis methods.In the present thesis,two kinds of preparation technologies have been developed for effectively suppressing the "Coffee Ring" effect of the probes on test strips,one by constructing a hydrophobic surface with a "lotus effect" and other by introducing the temperature-sensitive gelatin,both of which could combine with the vacuum-aided rapid drying route.Furthermore,two types of fluorescent test strips were developed accordingly for sensing mercury ions by using gold and silver nanoclusters（Au-AgNCs）and silver nanoclusters（AgNCs）as the examples of sensitive probes.The main contents include:（1）The fluorimetric test strips have been developed based on the “lotus effect” with the vacuum-aided fast drying for the rapid detection of Hg²⁺ ions.Firstly,the glass slides were treated with hexadecyltrimethoxysilane to create the hydrophobic surfaces for drying test strips with the probes.Next,the test strips were immersed into the solutions of Au-AgNCs probes and further placed onto the hydrophobic surfaces for the rapid drying in vacuum.Lastly,the test strips immobilized with probes were coated with a hydrophilic aminosilane for the hydrophilization treatment.The results indicate thatthe hydrophobic constraining forces from the hydrophobic patterns could,on one hand,effectively supress the transportation of Au-AgNCs materials on test strips.On the other hand,the vacuum-aided fast reagent evaporation would control the exterior transportation and then boost the interior Marangoni flow of dispersed probe materials involved to effectly suppress the "Coffee Ring" effect of the Au-AgNCs probe on the surface of the test strips,so that the probes could be evenly distributed onto the test strips.Moreover,the further hydrophilic treatment of test strips with the amine-derivatized silicane could facilitate the probes anchored with the high environmental stability,firmness,and especially enhanced fluorescence intensities.The developed test strips could allow for the detection of Hg²⁺ ions in the concentrations linearly ranging from 0.20 to 5000 nM,with a limit of detection of 0.10 nM.Additionally,the test strips were applied for quantifying Hg²⁺ ions in wastewater,showing no significant difference in the analysis results between the developed test strip-based fluorimetric method and the classic ICP-MS method.Such a simple and effective fabrication method for suppressing the "Coffee Ring" effect on test strips may expand the analysis applications of test strips in the biological and environmental fields.（2）The fluorimetric test strips were fabricated for the rapid detection of Hg²⁺ ions with the low "Coffee Ring" effect by using thermosensitive gelatin.The test strips were immersed into the mixture of AgNCs of fluorescent probes and gelatin solution and further cryopreserved at low temperature,followed by the fast drying in vacuum at low temperature（-20℃）.Studies have shown that gelatin with a gel-gel transition（35℃）performance could not only effectively protect and stabilize AgNCs probes,but also prevent the outward capillary flow of the probe suspensions on test strips during the drying.The resulting test strips could achieve the effectively suppressed "Coffee Ring" effect of fluorescent probes on test strips with the uniform distribution.The as-prepared test strips could faciliated the analysis of Hg²⁺ ions with the concentrations linearly ranging from 0.10 to 625 nM,with a limit of detection of 0.050 nM.In addition,the test strips were applied for quantifying Hg²⁺ ions in blood.It was found that there was no significant difference in the analysis results between the developed test strip-based fluorimetric method and the classic ICP-MS method.