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Singlet fission (SF) converts a singlet exciton into two triplet excitons in two or more electronically coupled organic chromophores, which may then be used to increase solar cell efficiency. Many known SF chromophores are unsuitable for device applications due to chemical instability or low triplet state energies. The results described here show that efficient SF occurs in derivatives of 9,10-bis(phenylethynyl)anthracene (BPEA), which is a highly robust and tunable chromophore. Fluoro and methoxy substituents at the 4- and 4′-positions of the BPEA phenyl groups control the intermolecular packing in the crystal structure, which alters the interchromophore electronic coupling, while also changing the SF energetics. The lowest excited singlet state (S1) energy of 4,4′-difluoro-BPEA is higher than that of BPEA so that the increased thermodynamic favorability of SF results in a (16 ± 2 ps)−1 SF rate and a 180% ± 16% triplet yield, which is about an order of magnitude faster than BPEA with a comparable triplet yield. By contrast, 4-fluoro-4′-methoxy-BPEA and 4,4′-dimethoxy-BPEA have slower SF rates, (90 ± 20 ps)−1 and (120 ± 10 ps)−1, and lower triplet yields, (110 ± 4)% and (168 ± 7)%, respectively, than 4,4′-difluoro-BPEA. These differences are attributed to changes in the crystal structure controlling interchromophore electronic coupling as well as SF energetics in these polycrystalline solids. [ABSTRACT FROM AUTHOR]

This letter presents the first quantitative, in vivo, transcutaneous glucose measurements using surface enhanced Raman spectroscopy (SERS). Silver film over nanosphere (AgFON) surfaces were functionalized with a mixed self-assembled monolayer (SAM) and implanted subcutaneously in a Sprague-Dawley rat. The glucose concentration was monitored in the interstitial fluid. SER spectra were collected from the sensor chip through the skin using spatially offset Raman spectroscopy (SORS). The combination of SERS and SORS is a powerful new approach to the challenging problem of in vivo metabolite and drug sensing. 10.1021/ac101951j

Despite its high refractive index sensitivity, localized surface plasmon resonance (LSPR) spectroscopy has been generally restricted to large biological analytes. Sensing of smaller molecules is a compelling target for this technique; in particular, LSPR spectroscopy could be utilized to detect hazardous or toxic gases and manage industrial processes involving gaseous chemicals. Here, we report sensing of pure gases over Ag nanoparticles using LSPR spectroscopy, where the detected changes in bulk refractive index are 10.1021/ac102127p

Surface-enhanced Raman spectroscopy (SERS) has been developed as a direct, extractionless, nonhydrolysis tool to detect lake pigments and colorants of various classes used in a variety of artist materials. Presented first is the SERS analysis of the natural colorant turmeric (Curcuma longa L.), main component curcumin, as present in dry lake pigment grains, dyed textile yarns, and reference paint layers containing the lake pigment bound in animal glue painted on glass. This experiment demonstrated that it is possible to detect the chromophore in various matrixes of increasing complexity, allowing its unambiguous identification in a wide range of artists' materials, even at very low concentration and in the presence of binders such as glue. In addition, removal of the colorant from the complex with the inorganic substrate or mordanted yarn was not necessary for identification. This proof-of-concept study was then extended to include analysis of several pastel sticks from a historical pastel box and two samples from a pastel artwork, both attributed to American painter Mary Cassatt (1844-1926). This study represents the first extractionless, nonhydrolysis direct SERS study of multiple artist materials, including identification of natural and synthetic colorants and organic pigments contained in historic artists' pastels spanning a broad range of chemical classes: polyphenols, rhodamines, azo pigments, and anthraquinones. Successful identification is demonstrated on samples as small as a single grain of pigment.

A prototype nanoparticle biosensor based on localized surface plasmon resonance (LSPR) spectroscopy was developed to detect drug binding to human membrane-bound cytochrome P450 3A4 (CYP3A4). CYP3A4 is one of the most important enzymes in drug and xenobiotic metabolism in the human body. Because of the inherent propensity of CYP3A4 to aggregate, it is difficult to study drug binding to this protein in solution and on surfaces. In this paper, we use a soluble nanometer scale membrane bilayer disk (Nanodisk) to functionally stabilize monomeric CYP3A4 on Ag nanoparticle surfaces fabricated by nanosphere lithography. CYP3A4-Nanodiscs have absorption bands in the visible wavelength region, which upon binding certain drugs shift to either shorter (type I) or longer wavelengths (type II). On the basis of the coupling between the LSPR of the Ag nanoparticles and the electronic resonances of the heme chromophore in CYP3A4-Nanodiscs, LSPR spectroscopy is used to detect drug binding with high sensitivity. This paper combines LSPR and Nanodisc techniques to optically sense drug binding to a functionally stable membrane protein, with the goal of integrating this with microfluidics and expanding it into a multiarray format, enabling high-throughput screening.

Tailored ad-hoc methods must be developed for successful identification of minute amounts of natural dyes on works of art using Surface-Enhanced Raman Spectroscopy (SERS). This article details two of these successful approaches using silver film over nanosphere (AgFON) substrates and silica gel coupled with citrate-reduced Ag colloids. The latter substrate functions as the test system for the coupling of thin-layer chromatography and SERS (TLC-SERS), which has been used in the current research to separate and characterize a mixture of several artists' dyes. The poor limit of detection of TLC is overcome by coupling with SERS, and dyes which co-elute to nearly the same spot can be distinguished from each other. In addition, in situ extractionless non-hydrolysis SERS was used to analyze dyed reference fibers, as well as historical textile fibers. Colorants such as alizarin, purpurin, carminic acid, lac dye, crocin, and Cape jasmine were thus successfully identified.

Lactate production under anaerobic conditions is indicative of human performance levels, fatigue, and hydration. Elevated lactate levels result from several medical conditions including congestive heart failure, hypoxia, and diabetic ketoacidosis. Real-time detection of lactate can therefore be useful for monitoring these medical conditions, posttrauma situations, and in evaluating the physical condition of a person engaged in strenuous activity. This paper represents a proof-of-concept demonstration of a lactate sensor based on surface-enhanced Raman spectroscopy (SERS). Furthermore, it points the direction toward a multianalyte sensing platform. A mixed decanethiol/mercaptohexanol partition layer is used herein to demonstrate SERS lactate sensing. The reversibility of the sensor surface is characterized by exposing it alternately to aqueous lactate solutions and buffer without lactate. The partitioning and departitioning time constants were both found to be ~30 s. In addition, physiological lactate levels (i.e., 6-240 mg/dL) were quantified in phosphate-buffered saline medium using multivariate analysis with a root-mean-square error of prediction of 39.6 mg/dL. Finally, reversibility was tested for sequential glucose and lactate exposures. Complete partitioning and departitioning of both analytes was demonstrated.

The exploration of the coupling between the rhodamine 6G (R6G) molecular resonances and the localized surface plasmon resonance (LSPR) of Ag nanoparticles which was systematically explored by monitoring the shift in LSPR wavelength of Ag nanoparticles upon R6G binding is presented.

Localized surface plasmon resonance (LSPR) excitation in silver and gold nanoparticles produces strong extinction and scattering spectra that in recent years have been used for important sensing and spectroscopic applications. […]

This paper presents the first in vivo application of surface-enhanced Raman scattering (SERS). SERS was used to obtain quantitative in vivo glucose measurements from an animal model. Silver film over nanosphere surfaces were functionalized with a two-component self-assembled monolayer, and subcutaneously implanted in a Sprague--Dawley rat such that the glucose concentration of the interstitial fluid could be measured by spectroscopically addressing the sensor through an optical window. The sensor had relatively low error (RMSEC = 7.46 mg/dL (0.41 mM) and RMSEP = 53.42 mg/dL (2.97 mM).

The preparation of black single crystals of the two nonstoichiometric cerium coinage-metal oxysulfide compounds Ce[Cu.sub.x]OS and Ce[Ag.sub.x]OS (x approximately 0.8) by the reactions of [Ce.sub.2][S.sub.3] and CuO or [Ag.sub.2]O at 1223 or 1173 K, respectively is presented. Theoretical calculations with an on-site Coulomb repulsion parameter reveal that the Ce 4f states are fully spin-polarized and are not localized in CeCuOS, Ce[Cu.sub.0.75]OS, or CeAGOS.

The effect of interacting molecular resonances and nanoparticle-localized surface plasmon resonances is investigated. Quantitative assessment based on discrete dipole approximation calculations show that Kramers-Kronig index must be scaled to match the experiment.

We present a coupled wave semiclassical theory to describe plasmonic enhancement effects in surface-enhanced femtosecond stimulated Raman scattering (SE-FSRS). A key result is that the plasmon enhanced fields which drive the vibrational equation of motion for each normal mode results in dispersive lineshapes in the SE-FSRS spectrum. This result, which reproduces experimental lineshapes, demonstrates that plasmon-enhanced stimulated Raman methods provide unique sensitivity to a plasmonic response. Our derived SE-FSRS theory shows a plasmonic enhancement of |gpu|²Im { χR(ω)g² st/Im { χR(ω)}, where |gpu|² is the absolute square of the plasmonic enhancement from the Raman pump, χR(ω) is the Raman susceptibility, and gst is the plasmonic enhancement of the Stokes field in SE-FSRS. We conclude with a discussion on potential future experimental and theoretical directions for the field of plasmonically enhanced coherent Raman scattering. [ABSTRACT FROM AUTHOR]

A new, mixed decanethiol (DT)/mercaptohexanol (MH) partition layer with dramatically improved properties has been developed for glucose sensing by surface-enhanced Raman spectroscopy. This work represents significant progress toward our long-term goal of a minimally invasive, continuous, reusable glucose sensor. The DT/MH-functionalized surface has greater temporal stability, demonstrates rapid, reversible partitioning and departitioning, and is simpler to control compared to the tri(ethylene glycol) monolayer used previously. The data herein show that this DT/MH-functionalized surface is stable for at least 10 days in bovine plasma. Reversibility is demonstrated by exposing the sensor alternately to 0 and 100 mM aqueous glucose solutions (pH ~7). The difference spectra show that complete partitioning and departitioning occur. Furthermore, physiological levels of glucose in two complex media were quantified using multivariate analysis. In the first system, the sensor is exposed to a solution consisting of water with 1 mM lactate and 2.5 mM urea. The root-mean-squared error of prediction (RMSEP) is 92.17 mg/dL (5.12 mM) with 87% of the validation points falling within the A and B range of the Clarke error grid. In the second, more complex system, glucose is measured in the presence of bovine plasma. The RMSEP is 83.16 mg/dL (4.62 mM) with 85% of the validation points falling within the A and B range of the Clarke error grid. Finally, to evaluate the real-time response of the sensor, the 1/e time constant for glucose partitioning and departitioning in the bovine plasma environment was calculated. The time constant is 28 s for partitioning and 25 s for departitioning, indicating the rapid interaction between the SAM and glucose that is essential for continuous sensing.

This research presents the achievement of significant milestones toward the development of a minimally invasive, continuously monitoring, glucose-sensing platform based on the optical quantitation of glucose in interstitial fluid. We expand our initial successes in the measurement of glucose by surface-enhanced Raman scattering (SERS), demonstrating substantial improvements not only in the quality and optical properties of the substrate system itself but also in the robusmess of the measurement methodology and the amenability of the technique to compact, diode laser-based instrumentation. Herein, we compare the long-term stability of gold to silver film over nanosphere (AuFON, AgFON) substrates functionalized with a partitioning self-assembled monolayer (SAM) using both electrochemical and SERS measurements. AuFONs were found to be stable for a period of at least 11 days. The switch to AuFONs not only provides a more stable surface for SAM formation but also yields better chemometric results, with improved calibration and validation over a range of 0.5-44 mM (10-800 mg/dL). Measured values for glucose concentrations in phosphate-buffered saline (pH ~7.4) based on 160 independent SERS measurements on AuFONs have a root-mean-square error of prediction of 2.7 mM (49.5 mg/dL), with 91% of the values falling within an extended A-B range on an expanded Clarke error grid. Furthermore, AuFONs exhibit surface plasmon resonances at longer wavelengths than similar AgFONs, which make them more efficient for SERS at near-infrared wavelengths, enabling the use of low-power diode lasers in future devices.

A detailed wavelength-scanned surface-enhanced Raman excitation spectroscopy (WS SERES) study of benzenethiol adsorbed on Ag nanoparticle arrays, fabricated by nanosphere lithography (NSL), is presented. The WS SERES spectra are correlated, both spatially and spectrally, with the corresponding localized surface plasmon resonance (LSPR) spectra of the nanoparticle arrays.

A comparative analysis of localized and propagating surface plasmon resonance sensors has been presented. The results show the simultaneous binding of Concanavalin A to mannose and galactose-functionalized self-assembled monolayers.

The initial steps toward a miniature, field portable sensor based on surface-enhanced Raman spectroscopy (SERS) are presented. It is demonstrated that a low-cost miniaturized Raman system can be used in place of a larger, higher-cost conventional Raman system. This system was developed by sequentially replacing components of a laboratory scale Raman spectroscopy system with smaller, lower-cost, commercially available components. For example, a green laser pointer was used as the excitation source, a reflectance probe fiber-optic cable was used for laser delivery and collection, and a compact card-based spectrometer was used for dispersion and detection. Spectra, collected with the laser pointer Raman system, are presented of a resonant (Rhodamine 6G) and a non-resonant (trans-1,2-bis(4-pyridyl)ethylene) molecule as well as a self-assembled monolayer (1-decanethiol). Small, low-cost sensors are in demand for a variety of applications, and SERS is positioned to contribute significantly with its remarkable sensitivity and molecular specificity. Key words: Raman, SERS, fiber-optics, sensor.

This work updates the recent progress made toward fabricating a real-time, quantitative, and biocompatible glucose sensor based on surface-enhanced Raman scattering (SERS). The sensor design relies on an alkane-thiolate tri(ethylene glycol) monolayer that acts as a partition layer, preconcentrating glucose near a SERS-active surface. Chemometric analysis of the captured SERS spectra demonstrates that glucose is quantitatively detected in the physiological concentration range (0-450 mg/dL, 0-25 mM). In fact, 94% of the predicted glucose concentrations fall within regions A and B of the Clarke error grid, making acceptable predictions in a clinically relevant range. The data presented herein also demonstrate that the glucose sensor provides stable SERS spectra for at least 3 days, making the SERS substrate a candidate for implantable sensing. Glucose sensor reversibility and reusability is evaluated as the sensor is alternately exposed to glucose and saline solutions; after each cycle, difference spectra reveal that the partitioning process is largely reversible. Finally, the SERS glucose sensor successfully partitions glucose even when challenged with bovine serum albumin, a serum protein mimic.

Nanoparticles, especially those that are triangular and silver in color have a lot of optical properties and the sensitivity of their localized surface plasmon resonance has allowed researchers to build a new class of nanoscale affinity biosensors. The effectiveness of these biosensors was tested and it was found that the instrument might help field-portable environmental diagnostic appliances

Research has been conducted on the quaternary selenides. The synthesis of these compounds carried out via the use of high-temperature solid-state experimental methods is described and their structure, optical and magnetic properties have been investigated and are discussed.