1,720,983 research outputs found
A Raman and SERS study on the interactions of aza[5]helicene and aza[6]helicene with a nanostructured gold surface
No full textWe studied the interaction of 5-aza[5]helicene and 5-aza[6]helicene with gold nanostructured substrates by SERS spectroscopy and DFT calculations. By comparing Raman and SERS experiments we observe significant changes for the normal modes involving nitrogen. This behavior, together with further evidence coming from SERS experiments carried out on the quaternary salts of the same azahelicenes, clearly highlight the direct interaction of nitrogen with the gold surface. DFT calculations on azahelicene models interacting with Au20 gold clusters reveal the charge transfer between azahelicene and gold. The information obtained from this study is useful in the field of sensor applications, where knowledge of the molecular mechanisms of interaction is fundamental for an appropriate design of the device
Laser tailored nanoparticle arrays to detect molecules at dilute concentration
No full textBy nanosecond pulsed laser ablation in an ambient gas gold nanoparticles (NPs) were produced that self-assemble on a substrate resulting in increasingly elaborated architectures of growing thickness, from isolated NP arrays up to percolated films. NPs nucleate and grow in the plasma plume propagating through the gas. Process parameters including laser wavelength, laser energy density, target to substrate distance, nature and pressure of the gas affect plasma expansion, thus asymptotic NP size and kinetic energy. NP size, energy and mobility at landing determine film growth and morphology that affect the physico-chemical properties of the film. Keeping fixed the other process parameters, we discuss the sensitive dependence of film surface nanostructure on Ar pressure and on laser pulse number. The initial plume velocity and average ablated mass per pulse allow predicting the asymptotic NP size. The control of growth parameters favors fine-tuning of NP aggregation, relevant to plasmonics to get optimized substrates for surface enhanced Raman spectroscopy (SERS). Their behavior is discussed for testing conditions of interest for clinical application. Both in aqueous and in biological solutions we obtained good sensitivity and reproducibility of the SERS signals for the anti-Parkinson drug apomorphine, and for the anti-epilepsy drug carbamazepine
SERS Detection of the Anti-Epileptic Drug Perampanel in Human Saliva
Get PDFSurface-Enhanced Raman Scattering (SERS) can obtain the spectroscopic response of specific analytes. In controlled conditions, it is a powerful quantitative technique. However, often the sample and its SERS spectrum are complex. Pharmaceutical compounds in human biofluids with strong interfering signals from proteins and other biomolecules are a typical example. Among the techniques for drug dosage, SERS was reported to detect low drug concentrations, with analytical capability comparable to that of the assessed High-Performance Liquid Chromatography. Here, for the first time, we report the use of SERS for Therapeutic Drug Monitoring of the Anti-Epileptic Drug Perampanel (PER) in human saliva. We used inert substrates decorated with gold NPs deposited via Pulsed Laser Deposition as SERS sensors. We show that it is possible to detect PER in saliva via SERS after an optimized treatment of the saliva sample. Using a phase separation process, it is possible to extract all the diluted PER in saliva from the saliva phase to a chloroform phase. This allows us to detect PER in the saliva at initial concentrations of the order of 10(-7) M, thus approaching those of clinical interest
Protein-Metal Interactions Probed by SERS: Lysozyme on Nanostructured Gold Surface
No full textSurface-enhanced Raman scattering is a well-established technique for molecular detection at low concentration, which is becoming increasingly popular in the field of biotechnology and health sciences. Since the process is understood in depth, the technique is becoming reliable. In this contribution, we consider another aspect of SERS besides molecular detection, focusing on the binding mechanisms of a complex system such as a protein to the noble metal substrates required by the technique itself. We also show that using a solid nanostructured substrate produced by controlled pulsed laser deposition SERS enables label-free detection of a protein. This is checked on lysozyme as a well-known prototype. Use of solid substrates with controlled morphology proves advantageous over colloidal systems for SERS applications. Moreover, such substrates are superior in terms of shelf life, packaging and ease of shipment
Deposizione a laser pulsato e caratterizzazione di film di nanoparticelle di rodio SERS-attive
No full textLAUREA MAGISTRALELe proprietà fisico-chimiche delle NP sono molto attraenti, ma possono essere ottimizzate solo avendo il controllo sulla dimensione e sulla morfologia delle NP. Una tecnica di produzione che ha dimostrato di poter raggiungere questo obiettivo è la Deposizione a Laser Pulsato (PLD). Una particolare proprietà delle NP metalliche riguarda i plasmoni di superficie, oscillazioni collettive degli elettroni di conduzione, che rendono possibili un elevato assorbimento di
radiazione elettromagnetica e l'amplificazione del campo elettrico della stessa in prossimità della superficie. Queste proprietà plasmoniche sono alla base della Surface Enhanced Raman Spectroscopy (SERS), tecnica spettroscopica che amplifica di alcuni ordini di grandezza la sensibilità della spettroscopia Raman. In questa tesi l'attenzione è rivolta allo studio di NP di rodio autoassemblate con proprietà plasmoniche che rendano possibile l'amplificazione SERS. La scelta del rodio è motivata dalla possibilità di ottenere UV-SERS, dalla possibile migliore biocompatibilità rispetto all'oro (SERS-attivo) e dall'opportunità di studiare meccanismi catalitici propri del rodio tramite spettroscopia Raman. Presso l'Istituto dei Processi Chimico-Fisici del CNR sez. di Messina sono stati depositati i film tramite PLD ed è stata svolta l'analisi dell'espansione del plasma di ablazione, tramite iCCD Fast Photo, al fine di ricavare dati da inserire in modelli di espansione del plasma e di generazione di NP nel plasma stesso. La caratterizzazione dei film ha compreso microscopia elettronica a scansione (SEM) e a trasmissione (TEM) per indagare la morfologia dei substrati, spettroscopia di assorbimento UV-Vis per esplorarne le proprietà plasmoniche e spettroscopia Raman per verificare la presenza dell'intensificazione del segnale Raman dell'analita di riferimento studiato, Rodamina 6G. Questo studio si pone a valle di
una campagna sperimentale su film di NP di oro e argento create con la stessa tecnica.The physico-chemical properties of nanoparticles (NPs) are attractive, but they can be optimized
only once their size and morphology are carefully controlled. One technique that
can achieve this goal is Pulsed Laser Deposition (PLD). Surface plasmons are a peculiar
property of metallic NPs and consist of collective oscillations of conduction electrons. They
make possible a high absorption of electromagnetic radiation and an amplification of the
associated electric field at the NP surface. Such plasmonic properties make possible the Surface
Enhanced Raman Spectroscopy (SERS), a technique that can enhance by several orders
of magnitude the typical Raman signal. In this thesis work, the efforts are focused on the production by PLD and the study of rhodium NPs whose plasmonic properties favour significant SERS enhancement. The choice of rhodium is dictated by the possibility to achieve UV-SERS, by the possible better biocompatibility of Rh respect to SERS-active Au and by the opportunity to study the catalytic properties of rhodium by means of Raman Spectroscopy.
At IPCF-CNR (Messina), films were deposited by PLD and the analysis of the plasma
expansion was carried out (with sequential ICCD Fast Photo) to get data to be included
in the plasma expansion and NP generation model. This allows for a better understanding
of the relationship between the obtained nanostructure and the ablation parameters. Film characterization includes: scanning electron microscopy (SEM) (Energy Dept. PoliMi) and transmission electron microscopy (TEM) (CIMA Università degli Studi di Milano) to investigate substrate morphology; UV-Vis absorption spectroscopy to characterize the plasmonic properties and Raman spectroscopy to verify the presence of SERS enhancement of Rhodamine 6G signal (CMIC Dept. PoliMi). This study follows previous investigation on Ag and Au NPs films produced by the same technique
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Functionalization of nanostructured gold substrates with chiral chromophores for SERS applications: The case of 5-Aza[5]helicene
No full textNanostructured gold thin films can be fabricated by controlled pulsed laser deposition to get efficient sensors, with uniform morphology and optimized plasmon resonance, to be employed as plasmonic substrates in surface enhanced Raman scattering spectroscopy. By attaching 5‐aza[5]helicen‐6‐yl‐6‐hexanethiol to such gold nanostructures, used in a previous work for label‐free drug sensing with biomedical purposes, we successfully prepared functionalized substrates with remarkable surface enhanced Raman scattering activity. The long‐term motivation is to develop probes for drug detection at low concentrations, where sensitivity to specific chiral targets is required
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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