Smart Modulators Based on Electric Field-Triggering of Surface Plasmon-Polariton for Active Plasmonics.

Design and properties of a plasmonic modulator in situ tunable by electric field are presented. Our design comprises the creation of periodic surface pattern on the surface of an elastic polymer supported by a piezo-substrate by excimer laser irradiation and subsequent selective coverage by silver by tilted angle vacuum evaporation. The structure creation was confirmed by AFM and FIB-SEM techniques. An external electric field is used for fine control of the polymer pattern amplitude, which tends to decrease with increasing voltage. As a result, surface plasmon-polariton excitation is quenched, leading to the less pronounced structure of plasmon response. This quenching was checked using UV-Vis spectroscopy and SERS measurements, and confirmed by numerical simulation. All methods prove the proposed functionality of the structures enabling the creation smart plasmonic materials for a very broad range of advanced optical applications.

Detection of trace amounts of insoluble pharmaceuticals in water by extraction and SERS measurements in a microfluidic flow regime.

Detection of trace amounts of poorly water-soluble pharmaceuticals or related (bio)solutions represents a key challenge in environment protection and clinical diagnostics. However, this task is complicated by low concentrations of pharmaceuticals, complex sample matrices, and sophisticated sample preparative routes. In this work, we present an alternative approach on the basis of an on-line flow extraction procedure and SERS measurements performed in a microfluidic regime. The advantages of our approach were demonstrated using ibuprofen (Ibu), which is considered as a common pharmaceutical contaminant in wastewater and should be monitored in various bioliquids. The extraction of Ibu from water to the dichloromethane phase was performed with an optimized microfluidic mixer architecture. As SERS tags, lipophilic functionalized gold multibranched nanoparticles (AuMs) were added to the organic phase. After microfluidic extraction, Ibu was captured by the functionalized AuM surface and recognized by on-line SERS measurements with up to 10-8 M detection limit. The main advantages of the proposed approach can be regarded as its simplicity, lack of need for preliminary sample preparation, high reliability, the absence of sample pretreatment, and low detection limits.

Plasmon-assisted grafting of anisotropic nanoparticles - spatially selective surface modification and the creation of amphiphilic SERS nanoprobes.

Amphiphilic nanoparticles (NPs) with a spatially selective distribution of grafted functional groups have great potential in the field of sensing, advanced imaging, and therapy due to their unique surface properties. The main techniques for the spatially selective functionalization of NPs utilize the surface-assisted approaches, which significantly restrict their production throughput. In this work, we propose an alternative plasmon-based route for the spatially selective grafting of anisotropic gold nanorods (AuNRs) using iodonium and diazonium salts. Utilization of longer laser wavelengths leads to the excitation of longitudinal plasmon resonances on AuNR tips, plasmon-assisted homolysis of the C-I bond in iodonium salts and the formation of aryl radicals, which are further grafted to the tips of AuNRs. The sides of AuNRs were subsequently decorated through spontaneous diazonium surface grafting. As a result, the AuNRs with spatially separated functional groups were prepared in a versatile way, primarily in solution and without the need for a sophisticated technique of NP immobilization or surface screening. The versatility of the proposed approach was proved on three kinds of AuNRs with different architectures and wavelength positions of plasmon absorption bands. Moreover, the applicability of the prepared amphiphilic AuNRs was shown by efficient trapping and SERS sensing of amphiphilic biomolecules.

Flexible Conductive Polymer Film Grafted with Azo-Moieties and Patterned by Light Illumination with Anisotropic Conductivity.

In this work, we present the method for the creation of an anisotropic electric pattern on thin poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) films through PSS grafting by azo-containing moieties followed by light-induced polymers redistribution. Thin PEDOT:PSS films were deposited on the flexible and biodegradable polylactic acid (PLLA) substrates. The light-sensitive azo-groups were grafted to PSS using the diazonium chemistry followed by annealing in methanol. Local illumination of azo-grafted PEDOT:PSS films through the lithographic mask led to the conversion of azo-moieties in Z-configuration and further creation of the lateral gradient of azo-isomers along the film surface. The concentration gradient led to the migration of PSS away from the illuminated area, increasing the PEDOT chains' concentration and the corresponding increase of local electrical conductivity in the illuminated place. Utilization of mask with linear pattern results in the appearance of conductive PEDOT-rich and non-conductive PSS-rich lines on the film surface, and final, lateral anisotropy of electric properties. Our work gives an optical lithography-based alternative to common methods for the creation of anisotropic electric properties, based on the spatial confinement of conductive polymer structures or their mechanical strains.

Rapid SERS-based recognition of cell secretome on the folic acid-functionalized gold gratings.

Nowadays, functionalization of the plasmon-supported nanostructured surface is considered as a powerful tool for tumour cell recognition. In this study, the SERS on a surface plasmon polariton-supported gold grating functionalized with folic acid was used to demonstrate an unpretentious recognition of melanoma-associated fibroblasts. Using cultivation media conditioned by different cells, we were able to detect reproducible differences in the secretome of melanoma-associated and normal control fibroblasts. The homogeneous distribution of plasmon energy along the grating surface was proved to provide excellent SERS signal reproducibility, while, to increase the affinity of (bio)molecules to SERS substrate, folic acid molecules were covalently grafted to the gold gratings. As proof of concept, fibroblasts were cultured in vitro, and culture media from the normal and tumour-associated lines were collected and analysed with our proposed SERS substrates. Identifying individual peaks of the Raman spectra as well as comparing their relative intensities, we showed that the proposed functional SERS platform can recognise the melanoma-associated cells without the need for further statistical spectral evaluation directly. We also demonstrated that the SERS chip created provided a stable SERS signal over a period of 90 days without loss of sensitivity. Graphical abstract.

Helicene-SPP-Based Chiral Plasmonic Hybrid Structure: Toward Direct Enantiomers SERS Discrimination.

Achieving chiral plasmon response based on the combination of achiral plasmonic nanostructures with highly chiral surrounding medium represents an attractive way for creation of hybrid optically active plasmonic materials. In this work, we present an attractive design and fabrication of chiral plasmon substrates based on a surface plasmon-polariton-supported structure coupled with extremely optically active helicene enantiomers. Such approach allows us to excite chiral plasmon waves and to design optically active surface-enhanced Raman spectroscopy substrates. Its further combination with standard Raman spectroscopy makes possible enantioselective detection/recognition of optical enantiomers with detection limits below those of standard spectral techniques. The chiral optical response of new plasmonic system was observed and controlled by the optical rotation of helicenes. Without necessity of previous chiral separation or implementation of sophisticated experimental equipment, we were able to estimate the concentration of enantiomers in their mixture by using left- or right-handed chiral plasmon substrates.

Ultrasensitive and reproducible SERS platform of coupled Ag grating with multibranched Au nanoparticles.

Surface-enhanced Raman scattering (SERS) spectroscopy is an extremely sensitive analytical technique that is capable of identifying the vibration signatures of target molecules up to single-molecule sensitivity. In this work, the ultrahigh sensitivity of SERS has been achieved through the immobilization of sharp-edges specific nanoparticles - so-called gold multibranched NPs (AuMs) on the silver grating surface through the biphenyl dithiol. This approach allows combining the extremely high SERS enhancement factor (better than that in the case of AuMs immobilized on the flat Ag film) with perfect reproducibility of Raman signals. The grating was created on the polymer substrate using the excimer laser modification and further metal deposition and has an "active" area 5 × 10 mm2, enabling the macroscale SERS substrate preparation. The wet-chemistry synthesized AuMs were then immobilized on the grating surface and the produced structure allows SERS measurements with a portable Raman spectrophotometer. The prepared structures were checked using the AFM, UV-Vis, and Raman spectroscopy techniques.

Synthesis, Characterization, and Antimicrobial Activity of Near-IR Photoactive Functionalized Gold Multibranched Nanoparticles.

Surface-modified gold multibranched nanoparticles (AuMs) were prepared by simple chemical reduction of gold chloride aqueous solution followed by in situ modification by using water-soluble arenediazonium tosylates with different functional organic groups. Chemical and morphological structures of the prepared nanoparticles were examined by using transmission electron and scanning electron microscopies. The covalent grafting of organic compounds was confirmed by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and Raman spectroscopy techniques. Covalent functionalization of nanoparticles significantly expands the range of their potential uses under physiological conditions, compared with traditional non-covalent or thiol-based approaches. The antibacterial effect of the surface-modified AuMs was evaluated by using Escherichia coli and Staphylococcus epidermidis bacteria under IR light illumination and without external triggering. Strong plasmon resonance on the AuMs cups leads to significant reduction of the light power needed kill bacteria under the mild conditions of continuous illumination. The effect of the surface-modified AuMs on the light-induced antibacterial activities was founded to be dependent on the grafted organic functional groups.

Preparation of periodic surface structures on doped poly(methyl metacrylate) films by irradiation with KrF excimer laser.

In this work, we describe laser modification of poly(methyl methacrylate) films doped with Fast Red ITR, followed by dopant exclusion from the bulk polymer. By this procedure, the polymer can be modified under extremely mild conditions. Creation of surface ordered structure was observed already after application of 15 pulses and 12 mJ cm(-2) fluence. Formation of grating begins in the hottest places and tends to form concentric semi-circles around them. The mechanism of surface ordered structure formation is attributed to polymer ablation, which is more pronounced in the place of higher light intensity. The smoothness of the underlying substrate plays a key role in the quality of surface ordered structure. Most regular grating structures were obtained on polymer films deposited on atomically 'flat' Si substrates. After laser patterning, the dopant was removed from the polymer by soaking the film in methanol.

Surface morphology and optical properties of porphyrin/Au and Au/porphyrin/Au systems.

Porphyrin/Au and Au/porphyrin/Au systems were prepared by vacuum evaporation and vacuum sputtering onto glass substrate. The surface morphology of as-prepared systems and those subjected to annealing at 160°C was studied by optical microscopy, atomic force microscopy, and scanning electron microscopy techniques. Absorption and luminescence spectra of as-prepared and annealed samples were measured. Annealing leads to disintegration of the initially continuous gold layer and formation of gold nanoclusters. An amplification of Soret band magnitude was observed on the Au/meso-tetraphenyl porphyrin (TPP) system in comparison with mere TPP. Additional enhancement of luminescence was observed after the sample annealing. In the case of sandwich Au/porphyrin/Au structure, suppression of one of the two porphyrins' luminescence maxima and sufficient enhancement of the second one were observed.