Silver nanoparticles self assembly as SERS substrates with near single molecule detection limit

Abstract

Highly sensitive SERS substrates with a limit of detection in the zeptomole (for Nile blue A and oxazine 720) range were fabricated through a bottom-up strategy. Ag nanoparticles (Ag NPs) were self-assembled onto glass slides by using 3-mercaptopropyltrimethoxysilane (MPTMS) sol-gel as linker. The substrates were characterized by UV-Vis and AFM after each deposition of Ag NPs. It was found that the glass slide presented just a few Ag NPs aggregates scattered throughout the surface after just one deposition. The glass surface was gradually covered by a homogeneous distribution of Ag NPs aggregates as the deposition number increased. Surface-enhanced Raman scattering (SERS) of the substrates was examined at different numbers of Ag NPs deposition using nile blue A and oxazine 720 as probe molecules and two laser excitations (632.8 nm and 785 nm). Optimum SERS was observed after six depositions of Ag NPs. SERS mapping indicated that at lower deposition numbers (less than 3 Ag NPs depositions) the substrates presented a few SERS "hot-spots" randomly distributed at the surface. After 7 Ag NPs depositions, spatial distribution of the SERS signal followed a Gaussian statistics, with a percent relative standard deviation (RSD%) of approximately 19%. In addition, the sample-to-sample reproducibility of the SERS intensities under both laser excitations was lower than 20%. It was also found that these substrates can provide giant Raman signal enhancement. At optimum conditions and with a 632.8 nm laser, the signal from an estimated of only approximately 44 probe molecules (100x objective) can still be detected.

Effects of solid substrate on the SERS‐based immunoassay: a comparative study

“…This substrate was fabricated by soaking the silver substrate in an APTMS sol-gel, which was prepared following the method reported by Fan [20] and Jena. [21] Briefly, 168 µl of APTMS and 140 µl of 0.1 M HCl were added into 14 ml of deionized water.…”

Produção de substratos sers eficientes através da deposição de ouro sobre um molde de microesferas de poliestireno

“…O desvio padrão médio das intensidades SERS da 4-pyS medido nestes substratos vidro-Au foi da ordem de 20%, que é comparável à reprodutibilidade obtida para alguns substratos apresentados na literatura. 14,23,24 A flutuação nas profundidades e diâmetros das estruturas de Au, observada nas Figuras 3S e 4S (material suplementar), respectivamente, também contribui para uma diminuição na reprodutibilidade do sinal SERS. Esta heterogeneidade leva a uma distribuição de condições de ressonância plasmônica, de tal forma que se tem uma distribuição de intensificações ao longo de toda a superfície, o que leva aos desvios observados de intensidade absoluta das bandas SERS da 4-pyS.…”

Surface-Enhanced Raman Scattering: Metal Nanostructures Coated With Langmuir-Blodgett Films

“…The reproducible fabrication of nanostructures with maximum enhancement factor, as required for SMD, remains a challenge though. Different strategies have been developed to produce average enhancement factor (up to 10 7 ), or higher, in SERS-active substrates, which involve traditional methods such as colloids 29 , large aggregated nanoparticles 30,31 , thermally evaporated thin films 32 , oblique angle vapor deposition 33 and electrodeposition 34 , self-assembly of AuNPs with different diameters in an array 35 , dendrimer/Ag nanowire layer-by-layer (LbL) films 36 , AgNP film formed by in-situ reaction 37 or cast in a bottom-up strategy onto treated glass slides 38 , AuNPs distributed along nanocanals 39 , polymer-encapsulated AuNPs by self-assembly 40 and gap-tailorable Au-Ag core-shell nanodumbbells 41 . Recently, we reported on LbL films containing AgNPs trapped within a phospholipid matrix 42 to achieve SERS and SERRS, which can be used in investigating interactions between guest molecules and phospholipids in membrane mimetic systems.…”