Microfluidic chips hold great potential for the application in the area of biological and chemical research, by integrating all the basic operations (chemical reaction, selection, separation, and detection) in a stamp size chip. It was evaluated to be the century technique by Nature. Till now the application of microfluidic chips has covered the fields of analytical chemistry, medical science, pharmaceutical, biology, environmental analysis, chemical engineering, material science etc. However there are many challenges to realize the catalytic reaction in a microfluidic system, e.g. it is hard to fix the catalysts position, the contact area between the catalysts and the reactants is relatively small, and the reaction efficiency is low. In order to solve these problems, it is crucial to improve the efficiency by integrating multifunctional elements in the non-planar microfluidic channel.
Periodically conical microstructures were fabricated by femtosecond laser direct writing (FsLDW) in a "Y" shape channel based on silicon wafer substrate by a China-Japan joint research group. After hydrogenated by HF solution, Silver nanoparticles (AgNPs) could be in-situ grown on the BS surface and form Ag-BS micro/nano hierarchical structures. The Ag-BS hierarchical structure has large specific surface area and roughness, which helps improving the catalytic reaction efficiency (checked by pNP to pAP reaction). In the same time, this structure could also serve as a SERS substrate, for it would generate localized surface plasmon polaritons (LSPPs) to enhance the electromagnetic field. When used for SERS detection, the Ag-BS structure realized in-situ detection of the catalytic reaction. The sensitivity was tested to be as low as 10-8 mol/L using Rhodamine 6G. The results are reported in Chinese Optics Letters, Vol. 13, No. 10, 2015 (Z. X. Yan et al., Silver Hierarchical Structures Grown on Microstructured Silicon in Chip for Microfluidic Integrated Catalyst and SERS Detector).
It was the first time to the best of the authors' knowledge that a chemical growth method was applied to grow silver nanoparticles (AgNPs) on BS on a microfluidic chip as catalytic reactor and SERS substrate. The obtained Ag-BS composite structures might create new opportunities for various applications in highly integrated chemical synthesis and analysis, and biomedical sensing and diagnosis. "The idea of integrating multifunctional Ag-BS micro/nano structures in microfluidic chip is very impressive. It provides a strong technical support for microfluidic technique toward practical application." says Dr. Jihong Zhao from Jilin University, who is a member of this joint group.
The following works will be focused on fabrication of other metal-BS hierarchical structures, such as Au-BS, Pt-BS, and Pd-BS, and comparison of the relationship between the reaction efficiency and metal materials by in-situ SERS detection. The final goal is to achieve the optimized microfluidic system with high catalytic efficiency and good SERS performance.
中国和日本的一个联合研究小组利用飞秒激光直写技术，在硅基“Y”型通道内部加工出周期性尖峰微结构（这种微结构硅表面被称为黑硅）。该黑硅表面在经过氢氟酸氢化处理后，可实现银纳米粒子在尖峰微结构表面的原位化学生长，进而利用银－黑硅（Ag-BS）复合结构的大比表面积及粗糙度，提高了对硝基苯酚还原成对氨基苯酚催化反应的效率及反应活性。同时Ag-BS复合结构有助于表面等离子共振基元的形成，可用作表面增强拉曼散射（SERS）检测。利用SERS检测技术实现了对催化反应的状态的原位监测。以罗丹明6G分子作为探针材料，证实了该衬底的检测浓度极限为10-8 mol/L。相关研究成果发表在Chinese Optics Letters 2015年第10期上 （Z. X. Yan et al., Silver Hierarchical Structures Grown on Microstructured Silicon in Chip for Microfluidic Integrated Catalyst and SERS Detector）。
后续工作将尝试多种金属-黑硅微纳复合结构的制备，如Au-BS, Pt-BS, Pd-BS等微纳复合结构器件；比较分析不同金属-黑硅微纳复合结构对催化反应效率的影响，并通过SERS原位监测催化反应的进程；最终在微流控芯片内实现更加高效的催化反应及SERS检测功能。