CV-DasG.pdf

Photonic Sensors, 2019

We suggested a plasmonic platform based on a cubic pattern of gold spheres for surface enhanced Raman spectroscopy (SERS). In the case of linear polarization along the symmetry axes, the SERS enhancement per area is identical to hexagonally patterned surfaces. The validity of this model was tested using the simulation package of COMSOL Multiphysics® Modeling Software. We found an improved sensitivity in the near infrared and visible region of the electromagnetic spectrum. This method considered tolerance towards stacking faults and suggested a plasmonic platform for ultra-sensing applications. The design can be extended towards the molecular detection if the proposed plasmonic platform is used with SERS.

Nano convergence, 2016

Plasmonic nanostructures strongly localize electric fields on their surfaces via the collective oscillations of conducting electrons under stimulation by incident light at a certain wavelength. Molecules adsorbed onto the surfaces of plasmonic structures experience a strongly enhanced electric field due to the localized surface plasmon resonance (LSPR), which amplifies the Raman scattering signal obtained from these adsorbed molecules. This phenomenon is referred to as surface-enhanced Raman scattering (SERS). Because Raman spectra serve as molecular fingerprints, SERS has been intensively studied for its ability to facilely detect molecules and provide a chemical analysis of a solution. Further enhancements in the Raman intensity and therefore higher sensitivity in SERS-based molecular analysis have been achieved by designing plasmonic nanostructures with a controlled size, shape, composition, and arrangement. This review paper focuses on the current state of the art in the fabrica...

Plasmonics: Metallic Nanostructures and Their Optical Properties VII, 2009

In this work we perform correlated structural and optical studies of single nanoparticles as well as explore the generality of SMSERS. First, wide-field plasmon resonance microscopy is used to simultaneously determine the LSPR spectra of multiple Ag nanoprisms, whose structure is determined using TEM. Next, the structure-property relationships for welldefined and easily-controlled nanoparticle structures (e.g. monomers, dimers, and trimers) are studied using correlated TEM, LSPR, and SERS measurements of individual SERS nanotags. We present the SER spectrum of reporter molecules on a single nanotag comprised of a Au trimer. It was determined that of 40 individual nanotags, just 19 exhibited SERS. The remaining nanoparticles were established by TEM to be monomers. These results demonstrate that SERS signal is observed from individual nanotags containing a junction or hot spot. Lastly, we explore crystal violet, a triphenyl methane dye that was used in the seminal SMSERS investigations, and reexamine single-molecule sensitivity using the isotopologue approach.

Journal of Materials Science, 2015

Surface Enhanced Raman Scattering is a sensitive and widely used as spectroscopic technique for chemical and biological structure analysis. One of the keys to increase the sensitivity of SERS sensors is to use nanoparticles/nanostructures. Here, we report on the density effect of gold nanodisks on SERS intensity for a highly sensitive detection of chemical molecules. Various densities of gold nanodisks with a height of 30 nm on gold/glass substrate were fabricated by electron beam lithography in order to have a good uniformity and reproducibility. The evolution of the Enhancement Factor with nanodisk density was quantified and compared to numerical calculations. An enhancement factor as high as 2.6×10 7 was measured for the nanodisk with a diameter of 110 nm and a periodicity of 150 nm which corresponds to the biggest density (42.2%).

ACS Nano, 2012

In this work, we report a simple strategy to obtain ultrasensitive SERS nanostructures by selfassembly and bioconjugation of Au nanospheres (NSs). Homodimer aggregates with an interparticle gap of around 8 nm are generated in aqueous dispersions by the highly specific molecular recognition of biotinylated Au NSs to streptavidin (STV), while random Au NS aggregates with a gap of 5 nm are formed in the absence of STV due to hydrogen bonding among biotinylated NSs. Both types of aggregates depict SERS analytical enhancement factors (AEF) of around 10 7 and the capability to detect biotin concentrations lower than 1 Â 10 À12 M. Quite interesting, the AEF for an external analyte, Rhodamine 6G (RH6G), using the dimer aggregates is 1 order of magnitude greater (10 5 ) than using random aggregates (around 10 4 ).

Chemical Society Reviews, 2014

Surface-and tip-enhanced Raman and LSPR spectroscopies have developed over the past 15 years as unique tools for uncovering the properties of single particles and single molecules that are unobservable in ensemble measurements. Measurements of individual events provide insight into the distribution of molecular properties that are averaged over in ensemble experiments. Raman and LSPR spectroscopy can provide detailed information on the identity of molecular species and changes in the local environment, respectively. In this review a detailed discussion is presented on single-molecule and single-particle Raman and LSPR spectroscopy focusing on the major developments in the fields and applications of the techniques.

Nature Nanotechnology, 2012

Current Pharmaceutical Biotechnology, 2010

We examined the photophysical properties of the new near infrared (NIR) fluorescent label SeTau-665 on a plasmonic platform of self-assembled colloidal structures (SACS) of silver prepared on a semitransparent silver film. A SeTau-665 immunoassay was performed on this platform and a control glass slide. The fluorescence properties of this label substantially change due to plasmonic interactions. While the average brightness increase of SeTau 665 in ensemble measurements was about 70-fold, fluorescence enhancements up to four-hundred times were observed on certain "hot spots" for single molecule measurements. The intensity increase is strongly correlated with a simultaneous decrease in fluorescence lifetime in these "hot spots". The large increase in brightness allows the reduction of the excitation power resulting in a reduced background and increased photostability. The remarkable fluorescence enhancements observed for SeTau 665 on our plasmonic platform should allow to substantially improve single molecule detection and to reduce the detection limits in sensing devices.

Journal of Nanophotonics

Single-molecule detection has become a unique and indispensable tool for the study of molecular motions and interactions at the single-molecule level. Unlike ensemble measurement where the information is averaged, single-molecule analysis yields invaluable information on both the individual molecular properties and their microenvironment. Among the various technologies for the detection of single molecules, the detection with optical methods has many advantages in terms of its high sensitivity, electrical passiveness, and robustness. The recent advances in the engineering of either the excitation light or the solution of the molecules have paved the way for enhanced single-molecule detection. We present recent developments and future perspectives for single-molecule detection in the following three regimes: on a dry surface, in solutions at ultralow concentrations, and in solutions at native physiological concentrations.

Nano letters, 2012

We show how the macrocyclic host, cucurbit [8]uril (CB[8]), creates precise subnanometer junctions between gold nanoparticles while its cavity simultaneously traps small molecules; this enables their reproducible surface-enhanced Raman spectroscopy (SERS) detection. Explicit shifts in the SERS frequencies of CB[8] on complexation with guest molecules provides a direct strategy for absolute quantification of a range of molecules down to 10 −11 M levels. This provides a new analytical paradigm for quantitative SERS of small molecules.