Hybrid femtosecond laser processing, which consists of femtosecond laser assisted wet etching, selective metallization, and laser induced periodic surface structure (LIPSS) formation, has enabled fabricating three-dimensional microfluidic surface enhanced Raman scattering (SERS) chips for highly sensitive sensing. To investigate the dependence of laser wavelength on the period of LIPSS which strongly affects the sensitivity of SERS substrate, two different wavelengths (515 nm and 1030 nm) of femtosecond laser beams have been employed. We observed the morphology of nanoripple on the metal layers under different laser parameters to optimize laser parameters, resulting in fabrication of homogenous LIPSS. The nanoripple with narrower groove (~40 nm) fabricated by 515 nm femtosecond laser induced stronger Raman scattering to achieve the SERS analytical enhancement factor exceeding 1 × 108. Furthermore, we introduced a novel method termed liquid-interface assisted SERS (LI-SERS) to realize extremely sensitive sensing, which achieved the detection limit of aM with analytical enhancement factor exceeding 1 × 1014 for R6G detection. We found the LI-SERS was able to locally aggregate the analyte molecules by Raman excitation laser irradiation at the interface of air and analyte solution containing the analytes in a microchannel. The aggregation forced the analyte molecules to enter into the “hot-spots” by Marangoni effect, which extraordinarily increased the SERS intensity. Furthermore, we employed LI-SERS to detect DNA bases which realized the DNA discrimination in the microfluidic channel by LI-SERS.
The purpose of this paper is to review laser trimming and precision control of alloy strip resistors, which is extensively applied for electronic vehicles and other power electronics. This mini review especially introduces the laser trimming of background, methodology, mechanism, influencing factor and main problem in details. The existing problems and the future development trend of laser trimming are also discussed.
Heavy metal pollution in developing countries urgently becomes a serious environmental issue due to rapid industrial development. Therefore, to detect the trace of heavy metal ions in water and food is very critical for environmental governance and human health. Surface-enhanced Raman scattering (SERS) based on electromagnetic field extraordinary enhanced in the proximity of metal nanostructures can generate strong Raman scatting, which is an effective method for trace detection. Most of SERS devices have been fabricated on the solid substrate surfaces, while detection of toxic substances in the close environment is much more preferable. In this paper, we propose the novel technique that can create 2D periodic metal (Cu-Ag) nanostructure inside 3D glass microfluidic channel by all-femtosecond-laser-processing. Specifically, after fabrication of 3D glass microfluidic channel by femtosecond laser assisted wet etching, Cu-Ag thin films are formed inside the microfluidic channel by femtosecond laser selective metallization. The thin films are then 2D nanostructured by femtosecond laser induced periodic surface structure (fs-LIPSS) formation. The dimension of nanostructured Cu-Ag film is quarter of laser wavelength. By testing with rhodamine 6G, we demonstrate the fabricated microchips can be used as a sensitive SERS device with an enhancement factor larger than 107 and 8.8% relative standard deviation. Consequently, the Real-time SERS detection in microfluidic chips was successfully demonstrated, which verified capability of the fabricated microchips as an excellent microfluidic SERS platform with ultrasensitive and uniform enhancement.