Surface Enhanced Visible Absorption of Dye Molecules in the Near-Field of Gold Nanoparticles

Abstract

Surface enhanced absorption is a plasmonic effect parenting to surface enhanced fluorescence and Raman scattering, and it was clearly reported to occur in the infrared region of the spectrum of light. In this paper, we unambiguously show that it also occurs in the visible region of the spectrum by using a dye; i.e. an azo-dye, which exhibits a good light absorption in that region, and gold nanoparticles, which act as plasmonic nanoantennas that capture and re-radiate light, when the azo-dyes and the nanoparticles are incorporated in the bulk of solid films of polymer. In such a configuration, it is possible to use a dye concentration much larger than that of the nanoparticles and absorption path lengths much larger than those of the molecularly thin layers used in surface enhanced effects studies. In addition, the dye undergoes shape and orientation change; i.e. isomerization and reorientation, upon polarized light absorption; and the observation of surface enhanced visible absorption is done by two separate experiments; i.e. UV-visible absorption spectroscopy and photo-induced birefringence, since the signals detected from both experiments are directly proportional to the extinction coefficient of the dye. Both the dye's absorption and photoorientation are enhanced by the presence of the nanoparticles.electrical current when integrated in photovoltaic cells 27 . Gold NPs (Au-NPs) have been used for enhancing photovoltaic properties of dye-sensitized solar cells 28,29 and perovskite solar cells 30 , as well as in photocatalysis and environmental remediation [13][14][15]31,32 , and plasmonic photothermal therapy of cancer 33 as well as applications in imaging, sensing, biology and medicine 20 . Thin films containing photoresponsive units act as transducers that can convert incident light into molecular motion, resulting in numerous applications such as holography and data storage, as well as photomechanics and mass motion and micro-nano machines [34][35][36][37][38][39] , and so on 40,41 . For optically thin films, increasing the absorption results in improved transduction. In this paper, we report on the plasmonic enhancement of absorption and photo-orientation of azo-dye molecules in the presence of Au-NPs embedded in solid polymer films. The azo-dyes absorb visible light efficiently and undergo molecular shape change; i.e. trans ↔cis photoisomerization, and reorientation upon light absorption; i.e. photoorientation 42,43 .Azo-dye containing materials have been studied extensively in the past decades owing to interest in both fundamental and applications aspects [44][45][46][47][48][49] , and recent reviews provide a comprehensive view about the progress of research in this field 40,41 , and few studies reported the use of metal and semi-conductor NPs to enhance optical storage in azo-polymers 50,51 . The study reported in this paper is along the series of the studies, carried out by our group, which combine photo-reactivity in layered dielectric organic materials and plasmonic materials, including metals and ...

Effect of conjugation with organic molecules on the surface plasmon resonance of gold nanoparticles and application in optical biosensing

“…S. Elhani1 et al provided a colloid of Au NPs in chloroform by removing the particles from water and transferring them into chloroform as a colloidal solution. 54 It was done by using surfactants that cover the surface of Au-NPs and separate them from water. 54,55 In brief, the surfactants used for the transfer are amphiphilic molecules with a hydrophobic head that binds to Au NPs, and a hydrophilic tail, which like water.…”

“…54 It was done by using surfactants that cover the surface of Au-NPs and separate them from water. 54,55 In brief, the surfactants used for the transfer are amphiphilic molecules with a hydrophobic head that binds to Au NPs, and a hydrophilic tail, which like water. By adding Au nanocolloid to the desired solvent containing appropriate surfactants, the transfer process would have happened.…”

“…The transfer mechanism is a very important mechanism that enables us to obtain colloids from Au NPs with a wide variety of solvents and consequently different colors. 54,55 The reason for these color changes is understandable with this The model was used for this case. Fig.…”

Optical Characterization of Ultra-Thin Films of Azo-Dye-Doped Polymers Using Ellipsometry and Surface Plasmon Resonance Spectroscopy

“…SPs and localized surface plasmons (LSPs) were reported long ago [6,7], and their use is of the utmost importance in, for example, the field of bio-sensing [8][9][10], enhanced spectroscopies [11], dye-sensitized solar cells [12], and photocatalysis [13]. Important reviews summarize the developments in the field [9,[14][15][16][17][18][19].…”

“…The research discussed in this paper is part of a series of works published by our group in the field of plasmonics, combining metals and dielectric organic materials. This includes work on surface-enhanced visible absorption of dye molecules by LSPs at gold nanoparticles [11], optical characterization of nano-thin layers of dielectric and metals [1,2,[20][21][22], sensing of photoreactions in molecularly thin layers, plasmons coupling at metal-insulator-metal (MIM) structures, glucose sensing using such structures [23][24][25], plasmons and waveguides (WGs), WG-WG coupling generating Fano resonances (FR), external control of FR by light action, and so on (for examples, see [26,27]).…”