Surface‑Enhanced Raman Scattering Fiber Probe Based on Silver Nanocubes

Surface-enhanced Raman scattering(SERS)provides a novel method for low concentration molecular detection.The performances were highly dependent on the sizes,geometries and distributions of metal nanostructures.Here,highly sensitive SERS fber probe based on silver nanocubes(Ag NCs)was fabricated,by assembled nanostructures on planar and tapered fber tips.Ag NCs were synthesized by polyol method,and controlled by reductant content,reaction temperatures and crystal growth durations.Tapered fbers with diferent cone angles were prepared by chemical etching.The electromagnetic distribution simulation indicated that nanocubes had stronger electric feld between two cubes and vertex corners than nanosphere,under 532 nm laser excitation.The intensity could reach 53.52 V/m,for cubes with 70 nm edge length.The SERS performance of probes was characterized using crystal violet analyte.The detectable lowest concentration could reach 10^(-9) and 10^(-10) M for planar and tapered fber probes,respectively.The corresponding enhancement factor could be 9.02×10^(7) and 6.22×10^(8).The relationship between SERS peak intensities and analyte concentrations showed well linear,which indicated both fber probes could be applied for both qualitative and quantitative analysis.Furthermore,optimal cone angle of tapered fber SERS probe was 8.3°.The tapered fber SERS probes have highly sensitive activity and great potential in substance detection.

Silver nanocubes monolayers as a SERS substrate for quantitative analysis

Surface-enhanced Raman scattering(SERS)is a powerful spectroscopic tool in quantitative analysis of molecules,where the substrate plays a critical role in determining the detection performance.Herein,a silver nanocubes/polyelectrolyte/gold film sandwich structure was prepared as a reproducible,highperformance SERS substrate by the wate r/oil inte rfacial assembly method.In addition to the hot spots on the nanocubes surface,the edge-to-edge interspace of the Ag nanocubes led to marked enhancement of the SERS intensity,with a limit of detection of 10~(11)mol/L and limit of quantitation of 10~(10)mol/L for crystal violet.When rhodamine 6 G and crystal violet were co-adsorbed on the Ag nanocube surfaces,the characteristic SERS peaks of the two molecules remained well resolved and separated,and the peak intensities varied with the respective concentration,which could be exploited for concurrent detection of dual molecules.Results from this work indicate that organized ensembles of Ag nanocubes can serve as effective SERS substrate can for sensitive analysis for complex molecular systems.

Size and crystallinity effect on the ultrafast optical response of chemically synthesized silver nanoparticles

The excited localized surface plasmon(LSP)in metallic nanoparticles is known to relax through several processes such as electron-electron scattering,electron-phonon coupling,and phonon-phonon scat-tering.In the current research,the ultrafast electron-phonon(e-ph)coupling relaxation processes for different average sizes and crystallinity of chemically synthesized silver nanoparticles were evaluated utilizing transient absorption spectroscopy.The nanoparticle size and crystallinity of similar linear dimension polycrystalline spherical and monocrystalline cubic nanoparticles ranging from ca.30-60 nm was related to their electron relaxation time constants and revealed very different dependencies.For the monocrystalline nanocubes,the electron-phonon coupling was not dependent on the cube edge length,while for the polycrystalline nanospheres,it was linearly decreasing with diameter.We demonstrate that the e-ph coupling time constant could be used to evaluate crystallinity and crystallite size in plasmonic metal nanoparticles when the size(surface area)of the nanoparticle is known.