Surface-enhanced Raman Properties Of Superhydrophilic And Hydrophobic Alumina Nanoprotrusions And Nanopore Composite Arrays

The surface-enhanced Raman technology based on the enhancement effect of the local electromagnetic field strength of the nanostructured surface to achieve the amplification of the Raman characteristic signal of the surface-adsorbed molecules is extremely promising as a practical method for rapid and quantitative analysis of the object to be detected.This requires that the surface of the structure first satisfy two aspects:1.The highly ordered array structure ensures the high sensitivity of the signal while ensuring the uniformity of the signal;2.The surface can achieve uniform and rapid adsorption of the test object at the same time.Superhydrophobic-superhydrophilic hybrid surface with highly ordered tip-capped nanopore arrays can well meet the above two conditions.On the one hand,highly ordered tip-capped nanopore arrays provides the "hot spots" required for local electromagnetic field enhancement.These areas can ensure that the structure itself has a good Raman signal enhancement effect.On the other hand:the hydrophilic-hydrophobic composite surface can fix the droplets of the analyte in the hydrophilic area,and evaporating the droplets in the air can make the molecules of the analyte enriched and concentrated in the hydrophilic area,thereby increasing the unit detection.Based on this,we successfully achieved the preparation of superhydrophobic-superhydrophilic hybrid surface with highly ordered tip-capped nanopore arrays by combining the programmed multi-step mild oxidative,pore expansion technology and selective chemical modification.The results show that the surface can be used as an intelligent and fast platform to achieve the goal of detecting different concentrations and different analyte solutions at the same time by surface enhanced Raman spectroscopy(SERS).Details as follows:1.Fabrication and detection of SERS performance of highly ordered tip-capped nanopore arrays(HOTCN).We have achieved the preparation of HOTCN through a programmed multi-step mild oxidation and pore widen process.This programmed preparation scheme can be summarized as a two-step oxidation(900 s and 1600 s)and two-step widen(40 min and 100 min).The traditional 8-hour immersion modification method was used for Raman detection of the array structure from the aspects of Raman sensitivity and signal stability.This structure can detect all characteristic peaks with a concentration of 10-10 M rhodamine 6G(R6G),and can also resolve some characteristic peaks at 10-11 M.At the same time,we found that by randomly collecting 50 groups of 10-6 M R6G Raman signals on three independent samples,the relative standard deviation of the characteristic peak height at the position of 1358 cm-1 is about 3.61%.2.Detection of SERS performance of superhydrophobic-superhydrophilic hybrid surface with highly ordered tip-capped nanopore arrays.We have modified the surface of HOTCN to a surface with superhydrophilic and superhydrophobic composite properties by means of selective chemical modification.The modified superhydrophilic and superhydrophobic surface can fix the droplets of the analyte in the superhydrophilic area.After it is naturally evaporated to dryness,the molecules of the analyte will be uniformly concentrated in the superhydrophilic area.The concentration effect achieved by such a surface can greatly enhance the number of molecules of the analyte in a unit area,shorten the modification time and improve the detection effect.In this study,we constructed superhydrophobic and superhydrophilic regions on the surface of the array by chemical modification and Au ion sputtering,respectively.Their static contact angles(CA)were approximately 161° and 8°.We also carried out Raman research on the superhydrophilic and superhydrophobic surfaces in terms of detection sensitivity and stability,and the detection results are also excellent.We concentrated R6G solutions on the hydrophilic and hydrophobic surfaces with a volume of 50-?L,10-7 M,10-8 M,10-9 M,10-10 M,10-11 M,and 10-12M.After dripping and natural evaporation to dryness,the results show that R6G Raman characteristic peaks with a concentration of 10-11 M can be resolved.In the stability comparison,we compared the Raman signals of R6G droplets randomly collected in different independent hydrophilic regions with a concentration of 10-7 M and a volume of 10-?L.The results show that the standard deviation of the loudness of the Raman characteristic peak at 1358 cm-1 is about 12.5%.In order to verify its practicality,we concentrated 50-?L thiram(a common insecticide)droplets on the surface and evaporated to dryness.The results show that Fumeishuang double-droplets with a concentration of 10-8 M can be distinguished.The Raman characteristic peaks can be fully resolved,and the intensity is linear with concentration.Due to the compatibility of manufacturing technology with industry,this smart surface has the potential to develop into a universal platform for the development of various advanced chemical and biological sensors.