Femtosecond laser-induced nanoparticle implantation into flexible substrate for sensitive and reusable microfluidics SERS detection

Surface-enhanced Raman spectroscopy(SERS)microfluidic system,which enables rapid detection of chemical and biological analytes,offers an effective platform to monitor various food contaminants and disease diagnoses.The efficacy of SERS microfluidic systems is greatly dependent on the sensitivity and reusability of SERS detection substrates to ensure repeated use for prolonged periods.This study proposed a novel process of femtosecond laser nanoparticle array(NPA)implantation to achieve homogeneous forward transfer of gold NPA on a flexible polymer film and accurately integrated it within microfluidic chips for SERS detection.The implanted Au-NPA strips show a remarkable electromagnetic field enhancement with the factor of 9×108 during SERS detection of malachite green(MG)solution,achieving a detection limit lower than 10 ppt,far better than most laser-prepared SERS substrates.Furthermore,Au-NPA strips show excellent reusability after several physical and chemical cleaning,because of the robust embedment of laser-implanted NPA in flexible substrates.To demonstrate the performance of Au-NPA,a SERS microfluidic system is built to monitor the online oxidation reaction between MG/NaClO reactants,which helps infer the reaction path.The proposed method of nanoparticle implantation is more effective than the direct laser structuring technique.It provides better performance for SERS detection,robustness of detection,and substrate flexibility and has a wider range of applications for microfluidic systems without any negative impact.

Surface-enhanced Raman Scattering Effect of Ordered Gold Nanoparticle Array for Rhodamine B with Different Morphologies

In this study, well-ordered gold nanoparticle array on silicon substrate was adopted as an active surface-enhanced Raman scattering substrate for detecting rhodamine B （RB）, and the influence of RB morphologies on surface-enhanced Raman scattering （SERS） properties was discussed. The Au nanoparticle array was prepared by using patterned P4VP nanodomains of poly（styrene-b-4-vinylpyridine） （PS-b-P4VP） diblock copolymer thin films as nanoreactors which is a simple and economical approach. The results show that Raman spectra of RB on the Au nanopaticle array have much stronger intensity than those on the bare silicon substrate by detecting same RB solution. It indicates that the prepared Au nanoparticle array on silicon substrate has a significant Raman enhancement for RB. Interestingly, the Raman intensity of RB from its ethanol solution is much stronger than that from its aqueous solution due to the special morphologies of RB formed in their ethanol solutions. This work provides an effective approach to prepare highly sensitive and stable surface-enhanced Raman scattering substrate.

Grazing-incidence small-angle X-ray scattering property of double-layered gold nanoparticle arrays

Gold nanoparticle arrays fabricated via layerby-layer technique were investigated using grazing-incidence small-angle X-ray scattering(GISAXS) method.Samples containing two gold nanoparticle layers that were separated by 5,11,15 and 21 poly electrolyte(PE) interlayers were studied.By using different X-ray incident angles,correlations of gold nanoparticles(GNPs) in the same layer and in two different layers were investigated.It is found that both sideway correlations between GNPs in the same layer and vertical correlation between two gold nanoparticle layers depend on the thickness of PE interlayers.According to sideway correlation,the size of GNPs is determined to be(13.0±0.5) nm in all of the four samples,which was also proved by scanning electron microscopy(SEM) and theoretical calculation of form factor of spherical particles.From vertical correlation,distance between two gold nanoparticle layers was determined for sample with 11,15 and 21 PE layers.These distances can be reasonably explained with the number of PE layers and the thickness of single PE layer.These results indicate that by repeated depositing of oppositely charged PE layers,a true three-dimensional(3 D) nanostructure can eventually be designed.

Interplay between out-of-plane magnetic plasmon and lattice resonance for modified resonance lineshape and near-field enhancement in double nanoparticles array

Two-dimensional double nanoparticle （DNP） arrays are demonstrated theoretically, supporting the interaction between out-of-plane magnetic plasmons and in-plane lattice resonances, which can be achieved by tuning the nanoparticle height or the array period due to the height-dependent magnetic resonance and the periodicity-dependent lattice resonance. The interplay between the two plasmon modes can lead to a remarkable change in resonance lineshape and an improvement on magnetic field enhancement. Simultaneous electric field and magnetic field enhancement can be obtained in the gap region between neighboring particles at two resonance frequencies as the interplay occurs, which presents “open” cavities as electromagnetic field hot spots for potential applications on detection and sensing. The results not only offer an attractive way to tune the optical responses of plasmonic nanostructure, but also provide further insight into the plasmon interactions in periodic nanostructure or metamaterials comprising multiple elements.

Survey of plasmonic gaps tuned at sub-nanometer scale in self-assembled arrays

Creating nanoscale and sub-nanometer gaps between noble metal nanoparticles is critical for the applications of plasmonics and nanophotonics. To realize simultaneous attainments of both the op- tical spectrum and the gap size, the ability to tune these nanoscale gaps at the sub-nanometer scale is particularly desirable. Many nanofabrication methodologies, including electron beam lithography, self-assembly, and focused ion beams, have been tested for creating nanoscale gaps that can de- liver significant field enhancement. Here, we survey recent progress in both the reliable creation of nanoscale gaps in nanoparticle arrays using self-assemblies and in the in-situ tuning techniques at the sub-nanometer scale. Precisely tunable gaps, as we expect, will be good candidates for future investigations of surface-enhanced Raman scattering, non-linear optics, and quantum plasmonics.

Patterning of Triblock Copolymer Film and Its Application for Surface-enhanced Raman Scattering

In this paper, microphase behavior of an ABC triblock copolymer, polystyrene-block-poly（2-vinylpyridine）-block- poly（ethylene oxide）, namely PS-b-P2VP-b-PEO, was systematically studied during spin-coating and solvent vapor annealing based on various parameters, including the types of the solvent, spin speed and thickness. The morphological features and the microdomain location of the different blocks were characterized by atomic force microscope （AFM） and high resolution transmission electron microscopy （HRTEM）. With increasing thickness, the order-order transition from nanopores array to the pattern of nanostripes was observed due to microdomain coarsening. These processes of pattern transformation were based on the selectivity of toluene for different blocks and on the contact time between solvent molecules and the three blocks. This work provides different templates for preparation of gold nanoparticle array on silicon wafer, which can be adopted as an active surface-enhanced Raman scattering （SERS） substrate for poly（3-hexylthiophene） （P3HT）.

Design and applications of lattice plasmon resonances

With their unique optical properties associated with the excitation of surface plasmons, metal nanoparticles （NPs） have been used in optical sensors and devices. The organization of these NPs into arrays can induce coupling effects to engineer new optical responses. In particular, lattice plasmon resonances （LPRs）, which arise from coherent interactions and coupling among NPs in periodic arrays, have shown great promise for realizing narrow linewidths, angle-dependent dispersions, and high wavelength tunability of optical spectra. By engineering the materials, shapes, sizes, and spatial arrangements of NPs within arrays, one can tune the LPR-based spectral responses and electromagnetic field distributions to deliver a multitude of improvements, including a high figure-of-merit, superior light-matter interaction, and multiband operation. In this review, we discuss recent progress in designing and applying new metal nanostructures for LPR-based applications. We conclude this review with our perspective on the future opportunities and challenges of LPR-based devices.