Ran Zhang

A SERS-active microfluidic device with tunable surface plasmon resonances†

A surface‐enhanced Raman scattering (SERS)‐active microfluidic device with tunable surface plasmon resonances is presented here. It is constructed by silver grating substrates prepared by two‐beam laser interference of photoresists and subsequent metal evaporation coating, as well as PDMS microchannel derived from soft lithography. By varying the period of gratings from 200 to 550u2009nm, surface plasmon resonances (SPRs) from the metal gratings could be tuned in a certain range. When the SPRs match with the Raman excitation line, the highest enhancement factor of 2×107 is achieved in the SERS detection. The SERS‐active microchannel with tunable SPRs exhibits both high enhancement factor and reproducibility of SERS signals, and thus holds great promise for applications of on‐chip SERS detection.

Whispering-gallery-mode microdisk lasers produced by femtosecond laser direct writing.

We report in this Letter fabrication of whispering-gallery-mode microdisk lasers by femtosecond laser direct writing of dye-doped resins. Not only is well-defined disk shape upheld on an inverted cone-shaped supporter, but the disk also exhibits significant lasing actions characteristic of an abrupt increase of light output and the significant narrowing of the spectral lines when the threshold is approached. This work shows that the laser micronanofabrication technology is not only applicable to passive micro-optical components, but also it may play an important role in fabrication of active optoelectronic devices and their integrated photonic circuits.

Maskless laser tailoring of conical pillar arrays for antireflective biomimetic surfaces

Herein, we report a facile approach for rapid and maskless production of subwavelength structured antireflective surfaces with high and broadband transmittance-direct laser interference ablation. The interfered laser beams were introduced into the surface of a bare optical substrate, where structured surfaces consisting of a micropillar array were produced by two-step laser irradiation in the time frame of seconds. A multiple exposure of the two-beam interference approach was proposed instead of multiple-beam interference to simply realize planar patterns of a high aspect ratio. Tall sinusoidal pillars were created and shaped by pulse shot number control. As an example of the application, zinc sulfide substrates were processed with the technology, from which high transmission at an infrared wavelength, over 92%, at normal incidence was experimentally achieved.

Programmable assembly of CdTe quantum dots into microstructures by femtosecond laser direct writing

Reported here is the programmable assembly of CdTe quantum dots (QDs) into various pre-designed microstructures by using a femtosecond laser direct writing (FsLDW) technique. As nanobuilding blocks, CdTe QDs could be driven by a focused femtosecond laser beam to construct arbitrarily-shaped micropatterns with high resolution (∼170 nm). The optical properties of pristine CdTe QDs were well inherited after the FsLDW induced programmable assembly, which has been confirmed by the luminescence spectrum and the high resolution transmission electron microscope (HR-TEM) image of the assemblies. By using this technique, the CdTe QDs microstructures were integrated within microfluidic devices, which showed the capability of qualitative on-chip detection of heavy metal ions. The FsLDW induced assembly of QDs may open up a new way for the designable assembly of QDs towards the flexible fabrication and integration of QDs-based microdevices.

Fabrication of photopolymer hierarchical micronanostructures by coupling electrospinning and photolithography for SERS substrates

AbstractReported here is the fabrication of photopolymer hierarchical micronanostructures through a combinative process of electrospinning and subsequent photolithography. Electrospun SU-8 (epoxy-based negative photoresist) nanofiber films have been patterned into gratings with periods of 100, 200, 300, and 400 μm, respectively. Deposition of a silver nanolayer on these interlaced nanofiber films would lead to the formation of various plasmonic nanostructures, and therefore, giving rise to abundant surface-enhanced Raman scattering (SERS) “hot spots”. In the detection of Rhodamine 6G (R6G), probing molecule, the resultant SERS substrates show both high sensitivity and good reproducibility. The SERS enhancement factor could reach as high as ∼108, indicating high efficiency. The fabrication of patterned, highly efficient SERS substrates may hold a great promise for the integration of SERS substrates in various microdevices such as microfluidic chips.n