Name: Single-Nanoparticle Electrochemical SERS Microscopy and Spectroscopy Measurements
Uploaded: 2023-05-12T15:00:00
Description: Watch this Scientific Journal Video about Single-Nanoparticle Electrochemical SERS Microscopy and Spectroscopy Measurements at JoVE.com

single-nanoparticle electrochemical sers microscopy and spectroscopy measurements

Analysere den heterogene ytelsen til enkeltnanopartikler med elektrokjemiske metoder

Electrochemistry is an important measurement science for studying charge transfer, charge storage, mass transport, etc., with applications in diverse disciplines, including biology, chemistry, physics, and engineering1,2,3,4,5,6,7. Conventionally, electrochemistry involves measurements over an ensemble &#8212;&#160;a&#160;large collection of single entities such as molecules, crystalline domains, nanoparticles, and surface sites. However, understanding how such single entities contribute to ensemble-averaged responses is key for bringing forth new fundamental and mechanistic understandings in chemistry and related fields because of the heterogeneity of electrode surfaces in complex electrochemical environments8,9. For example, ensemble reduction has revealed site-specific reduction/oxidation potentials10, the formation of intermediates and minor catalysis&#160;products11, site-specific reaction kinetics12,13, and charge carrier dynamics14,15. Reducing ensemble averaging is particularly important in improving our understanding beyond model systems to applied systems, such as biological cells, electrocatalysis, and batteries, in which extensive heterogeneity is often found16,17,18,19,20,21,22.
In the past decade or so, there has been an emergence of techniques to study single-entity electrochemistry1,2,9,10,11,12. These electrochemical measurements have provided the capabilities to measure small electrical and ionic currents in several systems and revealed new fundamental chemical and physical characteristics23,24,25,26,27,28. However, electrochemical measurements do not provide information about the identity or structure of molecules or intermediates at the electrode surface29,30,31,32. Chemical information at the electrode-electrolyte interface is central to understanding electrochemical reactions. Interfacial chemical knowledge is typically obtained by coupling electrochemistry with spectroscopy31,32. Vibrational spectroscopy, such as Raman scattering, is well-suited to provide&#160;complementary chemical information on charge transfer and related events in electrochemical systems that predominately utilize, but are not limited to, aqueous solvents30. Coupled with microscopy, Raman scattering spectroscopy provides spatial resolution down to the diffraction limit of light33,34. Diffraction presents a limitation, however, because nanoparticles and active surface sites are smaller in length than optical diffraction limits, which, thus, precludes the study of individual entities35.
Surface-enhanced Raman scattering (SERS) has been demonstrated to be a powerful tool in studying interfacial chemistry in electrochemical reactions20,30,36,37,38. In addition to providing the vibrational modes of reactant molecules, solvent molecules, additives and the surface chemistries of electrodes, SERS provides a signal that is localized to the surface of materials that support collective surface electron oscillations, known as localized surface plasmon resonances. The excitation of plasmon resonances leads to the concentration of electromagnetic radiation at the surface of the metal, thus increasing both the flux of light to and the Raman scattering from surface adsorbates. Nanostructured noble metals such as Ag and Au are commonly used plasmonic materials because they support visible light plasmon resonances, which are desirable for detecting emission with highly sensitive and efficient charge-coupled devices. Although the largest enhancements in SERS come from aggregates of nanoparticles39,40, a new SERS substrate has been developed that allows SERS measurements from individual nanoparticles: gap-mode SERS substrate&#160;(Figure 1)41,42. In gap-mode SERS substrates, a metallic mirror is fabricated and coated with an analyte. Next, nanoparticles are dispersed over the substrate. When irradiated with circularly polarized laser light, a dipolar plasmon resonance formed by the coupling of the nanoparticle and substrate is excited, which enables SERS measurements on single nanoparticles. SERS emission is coupled to the dipolar plasmon resonance43,44,45, which is oriented along the optical axis. With the parallel alignment of the radiating electric dipole and collection optics, only high-angle emission is collected, thus forming distinct donut-shaped emission patterns46,47,48,49 and allowing the identification of single nanoparticles. Aggregates of nanoparticles on the substrate contain radiating dipoles that are not parallel to the optical axis50. In this latter case, low-angle and high-angle emissions are collected and form solid emission patterns46.
Here, we describe a protocol for fabricating gap-mode SERS substrates and a procedure to employ them as working electrodes to monitor electrochemical redox events on single Ag nanoparticles using SERS. Importantly, the protocol using gap-mode SERS substrates allows for the unambiguous identification of single nanoparticles by SERS imaging, which is a key challenge for current methodologies in single nanoparticle electrochemistry. As a model system, we demonstrate the use of SERS to provide a readout of the electrochemical reduction and oxidation of Nile Blue A (NB) on a single Ag nanoparticle driven by a scanning or stepped potential (i.e., cyclic voltammetry, chronoamperometry). NB undergoes a multi-proton, multi-electron reduction/oxidation reaction in which its electronic structure is modulated out of/in resonance with the excitation source, which provides a contrast in the corresponding SERS spectra10,51,52. The protocol described here is also applicable to non-resonant redox-active molecules and electrochemical techniques, which may be pertinent to applications such as electrocatalysis.

Forfatter Spotlight: Sporing av elektrokjemi på enkeltnanopartikler med overflateforbedret Raman-spredningsspektroskopi og mikroskopi  

Sporing av elektrokjemi på enkle nanopartikler med overflateforbedret Raman-spredningsspektroskopi og mikroskopi

A common theme in our research is using light matter interactions and electrical energy to measure, drive, and control interfacial chemical transformations at the nanoscale. In particular, we seek to understand how local environments and reaction intermediates affect selectivity in electric catalysis. Catalytic transformations are traditionally evaluated with ensemble average measurements of the products and the catalyst attributes.The frontier challenges to produce chemical products selectively include reducing this measurement averaging while maintaining the measurement sensitivity, so that we can better understand the actions of individual molecules in the reactive sites of the catalyst. Electrochemical techniques alone do not provide any chemical information on species that form and transform at the electrode surface. Our protocol enables electrochemical measurements at a single nanoparticle using vibrational spectroscopy as a readout, enabling correlations between electrochemical processes and molecular changes.Moving forward, our laboratory will continue to push the boundaries of measurement resolution and space and time to understand chemical and material processes at the single-molecule level and at the timescale of chemical reactions.

Watch this Scientific Journal Video about Single-Nanoparticle Electrochemical SERS Microscopy and Spectroscopy Measurements at JoVE.com

Single-Nanoparticle Electrochemical SERS Microscopy and Spectroscopy Measurements  

Elektrokjemiske SERS-mikroskopi- og spektroskopimålinger med enkeltnanopartikler

Plasser den elektrokjemiske cellen fremstilt med gap-modus SERS-substratet på scenen av et omvendt optisk mikroskop. Fest substratet til mikroskoptrinnet ved å tape kantene for å forhindre bevegelse under spectro elektrokjemiske målinger på grunn av spenningen på ledningene som forbinder cellen med potensiostaten. Plasser referanseelektroden sølv-sølvklorid i det hjemmebygde stativet og fest posisjonen ved å stramme skruen på elektrodeholderstativet.Fest referanseelektroden til potensiostatens referanseelektrodealligatorklemme. Fest deretter platinatrådtellerelektroden til potensiostatens motelektrodealligatorklips. Til slutt klipper du kobbertråden festet til sølvfilmen til potensiostatens arbeidselektrodealligatorklips.Sett platinatråden og alligatorklemmen inn i elektrodeholderen og stram skruen for å sikre posisjonen. Plasser elektrodeholderen over den elektrokjemiske cellen for å sette inn elektrodene. Slå deretter på 642-nanometer laseren og juster effekten til 500 mikrowatt.Deretter legger du til en dråpe nedsenkningsolje til objektivlinsen. Beveg deretter fokusknappen for å heve målet til oljen kommer i kontakt med bunnen av underlaget. Fokuser laseren på overflaten av SERS-underlaget for gapmodus.Etter å ha fjernet et av øyestykkene fra mikroskopet, sett adapteren på plass. Endre modus til video på kameraapplikasjonen og zoom inn så mye som mulig. Skann SERS-substratet i gapmodus ved å flytte mikroskoptrinnet for å søke etter et isolert smultringformet SERS-utslippsmønster.Når det smultringformede utslippsmønsteret er lokalisert, flytter du lysavlederspaken på mikroskopet for å lede det tillatte lyset til spektrometeret. Sett graderingsposisjonen til 1000 bølgetall for å oppdage Stokes forskjøvet ramenspredning fra 400 til 1600 bølgetallregion. Hold laserlyset fokusert på det smultringformede utslippsmønsteret, tilsett 3 ml av en 0, 1 molar fosfatbuffer av pH 5 i den elektrokjemiske cellen.I potensiostatens programvare utarbeide et syklisk voltammogrameksperiment med minst tre sykluser fra 0 til minus 0,6 volt mot sølv-sølvklorid og en skannehastighet på 50 millivolt per sekund. Kjør deretter de samtidige sykliske voltammetri- og SERS-eksperimentene. Til slutt, flytt lysavlederspaken, slik at lyset rettes mot telefonkameraet og begynn å ta opp en video mens du kjører det sykliske voltammetrieksperimentet.Individuelle sølvnanopartikler på den sølvtynne filmen kan entydig identifiseres ved et smultringformet utslippsmønster i motsetning til et fast utslippsmønster produsert av nanopartikkeldimerer, trimere eller multimerer. SERS sykliske voltammogrammer ble målt for enkle nanopartikler, og Nilens blå molekyler i og rundt gapet mellom sølvnanopartikkelen og sølvfilmen ble elektrokjemisk redusert. Spektroelektrokjemiske målinger ble gjort med samme anvendte potensialområde.Elektrokjemisk modulering av Nilens blå SERS-spektrum ved å gå potensialet fører til at toppintensiteten i 592-bølgenummerområdet reduseres med tiden på grunn av reduksjonen av Nilblå molekyler. Størrelsen på den elektriske skjevheten endret reduksjonskinetikken, noe som gjenspeiles av forfallet av området under 592-bølgetallsregionens topp.

Research

JoVE Journal

Chemistry

Single-Nanoparticle Electrochemical SERS Microscopy and Spectroscopy Measurements

Tracking Electrochemistry on Single Nanoparticles with Surface-Enhanced Raman Scattering Spectroscopy and Microscopy

Studying electrochemical reactions on single nanoparticles is important to understand the heterogeneous performance of individual nanoparticles. This ...