Fiber SERS probes, made by fabricating metal nanostructures onto the surface of fibers, have the advantages of flexibility, compactness, reliability, high repeatability and the capability of in-situ remote sensing, which are potentially applicable in the rapid, field, and trace detection of pesticide residues, polychlorinated biphenyls (PCBs) and so on. Nowadays, many chemical methods (such as chemical immobilization, liquid phase synthesis, photochemical deposition methods) and physical methods (such as physical vapor deposition methods, nanosphere lithography, and transferred electron beam lithography) have been developed to fabricate fiber SERS probes. However, as for these methods, it is difficult to simultaneously realize simple, low-cost, high-throughput fabrications as well as high sensitivity, desirable repeatability of probes.

A collaborative research performed by Prof. MAO Qinghe in Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Sciences (AIOFM) and Prof. MENG Guowen in Institute of Solid State Physics, Hefei Institutes of Physical Sciences (ISSP) recently develops a simple and low-cost method of laser-induced self-assembly in a specific meniscus to fabricate fiber SERS probes with high sensitivity and excellent repeatability.

In their work, the collaborative research team demonstrates a simple, low-cost laser-induced self-assembly method for the rapid fabrication of highly sensitive fiber SERS probes. By lifting the fiber facet above a pre-synthesized nanoparticle colloid, a meniscus can be formed with the help of the surface tension of the liquid.

Using irradiation from an induced laser guided by the fiber, the localized thermal effects on the nanoparticles in the meniscus control the growth of the fiber probes and the electromagnetic interactions among the closely spaced nanoparticles assist the arrangement of nanoparticle clusters on the fiber facet.

In addition to showing a very high SERS sensitivity of 10^-10 M for p-aminothiophenol through a portable commercial Raman spectrometer with a short integration time of 2 s, the prepared fiber probes also present excellent repeatability with relative standard deviations <2.8% in the SERS peak intensities for different detections with the same probe and 7.8% for different fiber probes fabricated under the same conditions.

This technique could be importantly applicable in the detection of pollutants in the field, in remote in-situ monitors for chemical reactions, for in-vivo measurements in biomedicine and in some types of quantitative analysis.

Supported by the National Key Basic Research Program of China and the Natural Science Foundation of China, this research was published as a cover article in the journal of Nanoscale entitled Highly sensitive fiber surface-enhanced Raman scattering probes fabricated using laser-induced self-assembly in a meniscus. 

 (a) TEM image of the pre-synthesized Ag nanocubes; (b) SEM images from the center of the fiber SERS probe fabricated by the laser-induced self-assembly method; (c) SERS spectra for different concentrations of p-ATP by the optimized fiber SERS probe; (d) Repeatability of SERS detections using five fiber SERS probes prepared under the same conditions. (Image by LIU Ye)