Yuyang Wang

A highly sensitive microfluidics system for multiplexed surface-enhanced Raman scattering (SERS) detection based on Ag nanodot arrays

We report a method for fabricating a highly sensitive, microfluidic surface-enhanced Raman scattering (SERS) chip with highly ordered Ag nanodot arrays as the enhancement substrate for the detection of multiplexed low-concentration analytes. The microfluidic SERS chip features a highly-ordered Ag nanodot array on quartz slides fabricated by depositing Ag with an ultrathin anodic aluminium oxide (AAO) film as template and a channel-patterned polydimethylsiloxane (PDMS) cover on top, allowing a tremendous enhancement of electromagnetic field in the proximity of the chip surface because of the localized surface plasmon resonance (LSPR) of the Ag nanodots. Via the utilization of a self-built SERS microspectrometer with an inverted configuration, the multiplexed SERS signals of low concentration adenine and thiram can be readily detected with a detection limit down to 5.0 × 10−7 M. This detection system that we developed is flexible and has potential for real commercialization.

Propagating and localized surface plasmons in hierarchical metallic structures for surface-enhanced Raman scattering.

PSPs spread along the metal fi lm, which are most commonly employed using prisms to couple light into the metal in Kretschmann/Otto confi gurations, [ 6 , 7 ] also can be coupled using periodic gratings or waveguide confi gurations. [ 4 , 8 ] The characteristics of PSPs are that they can effectively transform the energy of incident light into surface wave, and the excitation and emission are dependent on the incident angle. However, the electromagnetic enhancement from the multiples of PSPs is trivial. [ 9 ] In contrast, LSPs, excited from rough metal surfaces and localized on metal nanostructures, can enhance the electromagnetic fi eld around the metal nanostructures. [ 10 ]

Preparation of hierarchically structured anodic aluminum oxide by a hexagonal embedded nanosphere array

This study explored a built-in nanosphere template for anodic aluminum oxide (AAO) preparation and a hierarchically structured AAO with multilayered channels was achieved. A “defect anodization” mechanism based on a new voltage/interpore distance relationship was proposed and would be a reference for the AAO preparation based on pre-patterning methods.

Hierarchical ultrathin alumina membrane for the fabrication of unique nanodot arrays.

Ultrathin alumina membranes (UTAMs) as evaporation masks have been a powerful tool for the fabrication of high-density nanodot arrays and have received much attention in magnetic memory devices, photovoltaics, and nanoplasmonics. In this paper, we report the fabrication of a hierarchical ultrathin alumina membrane (HUTAM) with highly ordered submicro/nanoscale channels and its application as an evaporation mask for the realization of unique non-hexagonal nanodot arrays dependent on the geometrical features of the HUTAM. This is the first report of a UTAM with a hierarchical geometry, breaking the stereotype that only limited sets of nanopatterns can be realized using the UTAM method (with typical inter-pore distance of 100 nm). The fabrication of a HUTAM is discussed in detail. An improved, longer wet etching time than previously reported is found to effectively remove the barrier layer and widen the pores of a HUTAM. A growth sustainability issue brought about by pre-patterning is discussed. Spectral comparison was made to distinguish the UTAM nanodots and HUTAM nanodots. Our results can be an inspiration for more sophisticated applications of pre-patterned anodized aluminum oxide in photocatalysis, photovoltaics, and nanoplasmonics.

A facile method of removing several common surface-enhanced Raman scattering probe molecules adsorbed on Ag with sodium borohydride solution

Ag nanoparticles and nanostructured surfaces have been widely used as surface-enhanced Raman scattering (SERS) substrates, which can enhance the Raman signals when molecules are adsorbed on the surface of Ag by the effect of Ag-thiol bonds. In this paper, we propose an efficient method to remove the molecules adsorbed on Ag with sodium borohydride solution, providing a protocol to realize a reproducible and practicable Ag SERS substrate. A theoretical density function theory approach has been used to explain the mechanism of desorption.

A stable aggregate system of silyl ether substituted quinacridone and its aggregation-state changes induced by fluoride-ions: inspiration for a dual guaranteed strategy for probe design

A sterically hindered silyl ether substituted quinacridone was successfully synthesized and its aggregation behaviors in different solvents were studied. It was demonstrated that the aggregate system of t-butyldiphenylsilyl ether substituted quinacridone in tetrahydrofuran was very stable and its aggregation-state could be tunable by fluoride-ion induced intermolecular force (e.g. hydrogen bonding and π–π stacking interactions) destructions and a chemical bond cleavage. The two aggregation-state changes of the system could be applied for a new dual guaranteed strategy for real-time naked-eye detection of fluoride-ions, which could provide assurance for both rapid responsive time and extraordinary selectivity.

Modulation of hot regions in waveguide-based evanescent-field-coupled localized surface plasmons for plasmon-enhanced spectroscopy

Coupling efficiency between the localized surface plasmons (LSPs) of metal nanoparticles (NPs) and incident light dominates the sensitivities of plasmon-based sensing spectroscopies and imaging techniques, e.g., surface-enhanced Raman scattering (SERS) spectroscopy. Many endogenous features of metal NPs (e.g., size, shape, aggregation form, etc.) that have strong impacts on their LSPs have been discussed in detail in previous studies. Here, the polarization-tuned electromagnetic (EM) field that facilitates the LSP coupling is fully discussed. Numerical analyses on waveguide-based evanescent fields (WEFs) coupled with the LSPs of dispersed silver nanospheres and silver nano-hemispheres are presented and the applicability of the WEF-LSPs to plasmon-enhanced spectroscopy is discussed. Compared with LSPs under direct light excitation that only provide 3–4 times enhancement of the incidence field, the WEF-LSPs can amplify the electric field intensity about 30–90 times (equaling the enhancement factor of 106–108 in SERS intensity), which is comparable to the EM amplification of the SERS “hot spot” effect. Importantly, the strongest region of EM enhancement around silver nanospheres can be modulated from the gap region to the side surface simply by switching the incident polarization from TM to TE, which widely extends its sensing applications in surface analysis of monolayer of molecule and macromolecule detections. This technique provides us a unique way to achieve remarkable signal gains in many plasmon-enhanced spectroscopic systems in which LSPs are involved.