Adam D. McFarland

Surface-enhanced: Raman spectroscopy

New substrates and single-molecule detection are just two of the advances that are fueling interest in SERS.

Introductory Lecture : Surface enhanced Raman spectroscopy: new materials, concepts, characterization tools, and applications

Surface-enhanced Raman spectroscopy (SERS) is currently experiencing a renaissance in its development driven by the remarkable discovery of single molecule SERS (SMSERS) and the explosion of interest in nanophotonics and plasmonics. Because excitation of the localized surface plasmon resonance (LSPR) of a nanostructured surface or nanoparticle lies at the heart of SERS, it is important to control all of the factors influencing the LSPR in order to maximize signal strength and ensure reproducibility. These factors include material, size, shape, interparticle spacing, and dielectric environment. All of these factors must be carefully controlled to ensure that the incident laser light maximally excites the LSPR in a reproducible manner. This article describes the use of nanosphere lithography for the fabrication of highly reproducible and robust SERS substrates for both fundamental studies and applications. Atomic layer deposition (ALD) is introduced as a novel fabrication method for dielectric spacers to study the SERS distance dependence and control the nanoscale dielectric environment. Wavelength scanned SER excitation spectroscopy (WS SERES) measurements show that enhancement factors approximately 10(8) are obtainable from NSL-fabricated surfaces and provide new insight into the electromagneticfield enhancement mechanism. Tip-enhanced Raman spectroscopy (TERS) is an extremely promising new development to improve the generality and information content of SERS. A 2D correlation analysis is applied to SMSERS data. Finally, the first in vivo SERS glucose sensing study is presented.

Towards advanced chemical and biological nanosensors - An overview

This paper reviews recent developments in the design and application of two types of optical nanosensor, those based on: (1) localized surface plasmon resonance (LSPR) spectroscopy and (2) surface-enhanced Raman scattering (SERS). The performance of these sensors is discussed in the context of biological and chemical sensing. The first section addresses the LSPR sensors. Arrays of nanotriangles were evaluated and characterized using realistic protein/ligand interactions. Isolated, single nanoparticles were used for chemosensing and performed comparably to the nanoparticle array sensors. In particular, we highlight the effect of nanoparticle morphology on sensing response. The second section details the use of SERS sensors using metal film over nanosphere (MFON) surfaces. The high SERS enhancements and long-term stability of MFONs were exploited in order to develop SERS-based sensors for two important target molecules: a Bacillus anthracis biomarker and glucose in a serum protein mixture.

Nanoparticle optics: Sensing with nanoparticle arrays and single nanoparticles

Recently, nanoparticles have become the platform for many sensing schemes. In particular, the utilization of the optical response of nanoparticles to changes in their nanoenvironment has served as a signal transduction mechanism for these sensing events. For example, silver nanoparticle arrays synthesized using nanosphere lithography have served as an ultrasensitive detection platform for small molecules, proteins, and antibodies with the detection limit of 60,000 and less than 25 molecules/nanoparticle for hexadecanethiol and antibodies, respectively. While this approach is low cost and highly portable, one limitation of the array platform is that the signal arises from approximately 1x106 nanoparticles. A method to improve the overall number of molecules detected would be to decrease the number of nanoparticles probed. Recently, single nanoparticle sensing has been accomplished using dark-field microscopy. A 40 nm shift in the localized surface plasmon resonance induced from less than 60,000 small-molecule adsorbates has been monitored from a single Ag nanoparticle. Additionally, streptavidin sensing has also been demonstrated using a single Ag nanoparticle. Detection platforms based on nanoparticle arrays and single nanoparticles will be discussed and compared.Recently, nanoparticles have become the platform for many sensing schemes. In particular, the utilization of the optical response of nanoparticles to changes in their nanoenvironment has served as a signal transduction mechanism for these sensing events. For example, silver nanoparticle arrays synthesized using nanosphere lithography have served as an ultrasensitive detection platform for small molecules, proteins, and antibodies with the detection limit of 60,000 and less than 25 molecules/nanoparticle for hexadecanethiol and antibodies, respectively. While this approach is low cost and highly portable, one limitation of the array platform is that the signal arises from approximately 1x106 nanoparticles. A method to improve the overall number of molecules detected would be to decrease the number of nanoparticles probed. Recently, single nanoparticle sensing has been accomplished using dark-field microscopy. A 40 nm shift in the localized surface plasmon resonance induced from less than 60,000 small-molecule adsorbates has been monitored from a single Ag nanoparticle. Additionally, streptavidin sensing has also been demonstrated using a single Ag nanoparticle. Detection platforms based on nanoparticle arrays and single nanoparticles will be discussed and compared.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Dynamic Measurement of Altered Chemical Messenger Secretion after Cellular Uptake of Nanoparticles Using Carbon-Fiber Microelectrode Amperometry

In this work, carbon-fiber microelectrode amperometry is used to characterize serotonin exocytosis from murine peritoneal mast cells cocultured with fibroblasts in the presence of Au nanoparticles. In the case of mast cell exposure to 1 nM 28 nm diameter spherical Au nanoparticles, there is a decrease of greater than 30% in the number of successful granule transport and fusion events, greater than 30% increase in the rate of intragranular matrix expansion, and greater than 20% increase in the number of secreted serotonin molecules per granule. These results suggest that nanoparticles interrupt the dense-core biopolymer intragranular matrix and present the potential for systematic studies showing how exocytotic function is influenced by nanoparticle size, shape, and composition.

Refractive-index-sensitive, plasmon-resonant-scattering, and surface-enhanced Raman-scattering nanoparticles and arrays as biological sensing platforms

The intense color of noble metal nanoparticles has inspired artists and fascinated scientists for hundreds of years. These rich hues are due to the interaction of light with the nanostructures localized surface plasmon (LSPR). Here, we describe three optical sensing modalities that are dependant on the effects of the LSPR. Specifically, we will demonstrate the use of LSPR supporting particles as analogues to fluorescent probes and labels for multiplex detection, sensing based on observation of changes in the LSPR spectrum caused by alteration of the local refractive index upon analyte binding, and the spectroscopic labeling of cells and tissues with Surface Enhanced Raman Scatting (SERS) active nanoparticles probes.

Synthesis, crystal structure, and optical properties of CeMn0.5OSe

The new quaternary selenide CeMn0.5OSe has been synthesized by the reaction of Ce, Mn, Se, and SeO2 at 1223 K. This compound crystallizes in space group P4/nmm of the tetragonal system with two formula units in a cell of dimensions at 153 K of a ¼ 4:0260ð7Þ A ˚ , c ¼ 9:107ð2Þ A ˚ . CeMn0.5OSe has the LaAgOS structure type. It is built from [CeO] fluorite-like layers where Ce4O tetrahedra share Ce–Ce edges that alternate with [MnSe] anti-fluorite like layers along [001]. An optical band gap of 2.01 eV has been derived from absorption measurements on the (100) crystal face of a CeMn0.5OSe single crystal. r 2003 Elsevier Inc. All rights reserved.

Nanoparticles with Tunable Localized Surface Plasmon Resonances

This chapter highlights representative research accomplishments in the area of fundamental and applied studies of the tunable LSPR. Specific applications in the Van Duyne laboratory include exploitation of the LSPR as a signal transduction mechanism for sensing applications and optimization of SERS signals. The optical properties of metallic nanostructures will find future application in the areas of dichroic filters, plasmonic waveguides, data storage, biological labels and sensors. Commercialization of nanoparticle devices relies on better understanding of the electromagnetic interaction between nanoparticles as well as the development of techniques that will preserve nanoparticle optical activity in adverse environments.