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We report the first demonstration of hydrogen treatment as a simple and effective strategy to fundamentally improve the performance of TiO(2) nanowires for photoelectrochemical (PEC) water splitting. Hydrogen-treated rutile TiO(2) (H:TiO(2)) nanowires were prepared by annealing the pristine TiO(2) nanowires in hydrogen atmosphere at various temperatures in a range of 200-550 °C. In comparison to pristine TiO(2) nanowires, H:TiO(2) samples show substantially enhanced photocurrent in the entire potential window. More importantly, H:TiO(2) samples have exceptionally low photocurrent saturation potentials of -0.6 V vs Ag/AgCl (0.4 V vs RHE), indicating very efficient charge separation and transportation. The optimized H:TiO(2) nanowire sample yields a photocurrent density of ∼1.97 mA/cm(2) at -0.6 V vs Ag/AgCl, in 1 M NaOH solution under the illumination of simulated solar light (100 mW/cm(2) from 150 W xenon lamp coupled with an AM 1.5G filter). This photocurrent density corresponds to a solar-to-hydrogen (STH) efficiency of ∼1.63%. After eliminating the discrepancy between the irradiance of the xenon lamp and solar light, by integrating the incident-photon-to-current-conversion efficiency (IPCE) spectrum of the H:TiO(2) nanowire sample with a standard AM 1.5G solar spectrum, the STH efficiency is calculated to be ∼1.1%, which is the best value for a TiO(2) photoanode. IPCE analyses confirm the photocurrent enhancement is mainly due to the improved photoactivity of TiO(2) in the UV region. Hydrogen treatment increases the donor density of TiO(2) nanowires by 3 orders of magnitudes, via creating a high density of oxygen vacancies that serve as electron donors. Similar enhancements in photocurrent were also observed in anatase H:TiO(2) nanotubes. The capability of making highly photoactive H:TiO(2) nanowires and nanotubes opens up new opportunities in various areas, including PEC water splitting, dye-sensitized solar cells, and photocatalysis.

We report the detection of the proteins lysozyme and cytochrome c as well as the live bacterial cells of Shewanella oneidensis MR-1 in aqueous solutions with sensitivities order(s) of magnitude higher than those previously reported. Two highly sensitive surface-enhanced Raman scattering (SERS)-based biosensors using optical fibers have been employed for such label-free macromolecule detections. The first sensor is based on a tip-coated multimode fiber (TCMMF) with a double-substrate "sandwich" structure, and a detection limit of 0.2 μg/mL is achieved in protein detections. The second sensor is based on a liquid core photonic crystal fiber (LCPCF) with a better confinement of light inside the fiber core, and a detection limit of 10(6) cells/mL is achieved for the bacteria detection. Both SERS biosensors show great potential for highly sensitive and molecule-specific detection and identification of biomolecules.

We report on the synthesis and characterization of Sn-doped hematite nanowires and nanocorals as well as their implementation as photoanodes for photoelectrochemical water splitting. The hematite nanowires were prepared on a fluorine-doped tin oxide (FTO) substrate by a hydrothermal method, followed by high temperature sintering in air to incorporate Sn, diffused from the FTO substrate, as a dopant. Sn-doped hematite nanocorals were prepared by the same method, by adding tin(IV) chloride as the Sn precursor. X-ray photoelectron spectroscopy analysis confirms Sn(4+) substitution at Fe(3+) sites in hematite, and Sn-dopant levels increase with sintering temperature. Sn dopant serves as an electron donor and increases the carrier density of hematite nanostructures. The hematite nanowires sintered at 800 °C yielded a pronounced photocurrent density of 1.24 mA/cm(2) at 1.23 V vs RHE, which is the highest value observed for hematite nanowires. In comparison to nanowires, Sn-doped hematite nanocorals exhibit smaller feature sizes and increased surface areas. Significantly, they showed a remarkable photocurrent density of 1.86 mA/cm(2) at 1.23 V vs RHE, which is approximately 1.5 times higher than that of the nanowires. Ultrafast spectroscopy studies revealed that there is significant electron-hole recombination within the first few picoseconds, while Sn doping and the change of surface morphology have no major effect on the ultrafast dynamics of the charge carriers on the picosecond time scales. The enhanced photoactivity in Sn-doped hematite nanostructures should be due to the improved electrical conductivity and increased surface area.

Facile and reproducible SERS signals from Shewanella oneidensis were obtained utilizing silver nanoparticles (AgNPs) and silver nanowires (AgNWs). Additionally, SERS images identify the distribution of SERS hot-spots. One important observation is the synergistically enhanced SERS signal when AgNPs and AgNWs are used in conjunction, due to constructively enhanced electromagnetic field.

Two portable molecular sensing systems based on surface-enhanced Raman scattering (SERS) have been experimentally demonstrated using either a tip-coated multimode fiber (TCMMF) or a liquid core photonic crystal fiber (LCPCF) as the SERS probe. With Rhodamine 6G as a test molecule, the TCMMF-portable SERS system achieved 2-3 times better sensitivity than direct sampling (focusing the laser light directly into the sample without the fiber probe), and a highly sensitive LCPCF-portable SERS system reached a sensitivity up to 59 times that of direct sampling, comparable to the sensitivity enhancement achieved using fiber probes in the bulky Renishaw system. These fiber SERS probes integrated with a portable Raman spectrometer provide a promising scheme for a compact and flexible molecular sensing system with high sensitivity and portability.

Label-free detections of certain proteins and live bacterial cells in aqueous solutions are demonstrated using surface-enhanced Raman scattering and optical fiber probes, with sensitivities order(s) of magnitude higher than those previously reported.

The vibrational relaxation dynamics following the dissociation of C≡O from M(CO)6 (M=Cr, Mo, W) have been studied with picosecond transient absorption spectroscopy. After dissociation of C≡O, the pentacarbonyl species forms a complex with a solvent molecule. The cooling of these solvated pentacarbonyl complexes was monitored from 1 ps to 1 ns and different rates for vibrational relaxation were found for each of these three compounds. The W(CO)5⋅S (S=cyclohexane) vibrationally relaxes in 35 ps, whereas Mo(CO)5⋅S relaxes twice as quickly, 18 ps. This result is surprising because the higher density of states in W(CO)5⋅S would be expected to lead to faster cooling of the hot solvated complex. The primary cooling of Cr(CO)5⋅S is completed in 18 ps just as in Mo(CO)5⋅S, but a slower cooling of approximately 150 ps is also present. This component is assigned to vibrational relaxation of the C≡O stretching mode. From comparisons with other studies, it appears that the existence of this slower cooling component is present only in first row transition metal carbonyls.

We report the femtosecond transient absorption spectra of the CH2I photoproduct of the methylene iodide (CH2I2) photodissociation. The results indicate a disappearance of this photofragment on a ≈ 350 fs time scale in several different solvents. The implication is that in these simple liquids, methylene iodide is undergoing geminate recombination. Recombination yields, but not rates are shown to be solvent dependent. Comparison to the photodissociation dynamics of other small molecules suggests that the kinetics of geminate recombination are dominated by a single collision with the surrounding solvent cage in a large class of molecules and that the process may be universal.

A study of the photodissociation dynamics of Mn2(CO)10 and the vibrational relaxation of its subsequent photoproducts in solutions has been carried out using picosecond time‐resolved laser techniques. The molecule predissociates in less than 2–3 ps after excitation with a 295 nm photon. Two dissociation channels are open for this excitation wavelength, namely, the Mn–Mn bond breaking and the Mn–CO bond breaking, generating internally hot ⋅Mn(CO)5 and Mn2(CO)9, respectively. These two species have a different absorption spectrum in the visible region and are probed independently by varying the probe laser wavelength. The vibrational relaxation of these nascent photoproducts is observed for the first time. In cyclohexane the vibrationally hot Mn2(CO)9 reaches thermal equilibrium with the solvent through two distinct decay channels with time constants of 15 and 170 ps, respectively. The vibrationally cold Mn2(CO)9 then persists for many nanoseconds. The vibrational relaxation is found to be faster in the 2‐p...

Metal oxides are promising for solar energy conversion applications since they are less expensive and easier to produce than conventional single crystal silicon. In this paper we focused on CdSe and CdS quantum dot (QD) co-sensitized and nitrogen doped TiO 2 (N:TiO 2 ) nanocomposite photoanodes for photoelectrochemical (PEC) water splitting for hydrogen generation. PEC, UV-vis and scanning electron microscopy (SEM) characterizations of the nanostructured films were carried out. The QD co-sensitized and N-doped TiO 2 photoanodes exhibits increased photocurrent compared to co-sensitized TiO 2 without N-doping This is tentativel y attributed to enhanced hole transp ort by oxygen vacancy states that are increased upon nitrogen doping. The enhanced hole transport facilitates overall charge transfer and transport and thereby results in improved photocurrent. Keywords: Hydrogen generation, quantum dot sensitization, nitrogen doping, TiO 2 , photoelectrochemistry, electron-hole recombination, solar energy

The vibrational relaxation dynamics following the dissociation of C≡O from M(CO)6 (M=Cr, Mo, W) have been studied with picosecond transient absorption spectroscopy. After dissociation of C≡O, the pentacarbonyl species forms a complex with a solvent molecule. The cooling of these solvated pentacarbonyl complexes was monitored from 1 ps to 1 ns and different rates for vibrational relaxation were found for each of these three compounds. The W(CO)5⋅S (S=cyclohexane) vibrationally relaxes in 35 ps, whereas Mo(CO)5⋅S relaxes twice as quickly, 18 ps. This result is surprising because the higher density of states in W(CO)5⋅S would be expected to lead to faster cooling of the hot solvated complex. The primary cooling of Cr(CO)5⋅S is completed in 18 ps just as in Mo(CO)5⋅S, but a slower cooling of approximately 150 ps is also present. This component is assigned to vibrational relaxation of the C≡O stretching mode. From comparisons with other studies, it appears that the existence of this slower cooling component is present only in first row transition metal carbonyls.

Quantum dot (QD) fluorescence is effectively quenched at low concentration by nitroxides bearing amine or carboxylic acid ligands. The association constants and fluorescence quenching of CdSe QDs with these derivatized nitroxides have been examined using electron paramagnetic resonance (EPR) and fluorescence spectroscopy. The EPR spectra in the non-protic solvent toluene are extremely sensitive to intermolecular and intramolecular hydrogen bonding of the functionalized nitroxides. Fluorescence measurements show that quenching of QD luminescence is nonlinear, with a strong dependence on the distance between the radical and the QD. The quenched fluorescence is restored when the surface-bound nitroxides are converted to hydroxylamines by mild reducing agents, or trapped by carbon radicals to form alkoxyamines. EPR studies indicate that photoreduction of the nitroxide occurs in toluene solution upon photoexcitation at 365 nm. However, photolysis in benzene solution gives no photoreduction, suggesting that photoreduction in toluene is independent of the quenching mechanism. The fluorescence quenching of QDs by nitroxide binding is a reversible process.

We report the synthesis and photoelectrochemical (PEC) studies of TiO(2) nanoparticles and nanowires simultaneously doped with nitrogen and sensitized with CdSe quantum dots (QDs). These novel nanocomposite structures have been applied successfully as photoanodes for PEC hydrogen generation using Na(2)S and Na(2)SO(3) as sacrificial reagents. We observe significant enhanced photoresponse in these nanocomposites compared to N-doped TiO(2) or CdSe QD sensitized TiO(2). The enhancement is attributed to the synergistic effect of CdSe sensitization and N-doping that facilitate hole transfer/transport from CdSe to TiO(2) through oxygen vacancy states (V(o)) mediated by N-doping. The results demonstrate the importance of designing and manipulating the energy band alignment in composite nanomaterials for fundamentally improving charge separation and transport and thereby PEC properties.

A portable molecular sensing system based on surface-enhanced Raman scattering is experimentally demonstrated using both a tip-coated multimode fiber and a liquid core photonic crystal fiber to achieve the high sensitivity.

The photochromic reaction dynamics of the spiropyran molecule 1',3',3'-trimethyl-6-hydroxyspiro(2H- 1 -benzo- pyran-2,2'-indoline) (HBPS) in solution have been studied with picosecond and femtosecond transient electronic absorption spectroscopy. Following excitation near 300 nm, the C-0 bond of the molecule breaks in less than 100 fs to form a metastable species. A small fraction of this metastable species re-forms the broken C-0 bond on the time scale of 200 fs. The major fraction of the metastable photoproduct vibrationally relaxes in a few picoseconds, and then undergoes isomerization to form a merocyanine product with a decay time constant of about 100 ps, depending on solvent viscosity. This isomerization decay is faster at shorter probe wavelengths and slower at longer wavelengths, indicating that this isomerization gives rise to a red-shifted absorption spectrum. The final merocyanine isomers are stable on the nanosecond time scale. All the results indicate that the initial steps of the photochromic reaction process of HBPS are extremely fast. One of the most important classes of photochromic materials is spiropyran compounds. These compounds have been studied extensively,legO with the nitro derivatives of spirobenzopyran receiving the most attenti~n.'~-~~ Several models have been proposed to explain the properties and photochromic reaction mechanisms of these molecules based on both frequency domain7-'* and time domainIe2* spectroscopic studies. Time-resolved ex- periments have been carried out using techniques such as laser flash photoly~isl~-~~ and time-resolved resonance Raman scat- tering.24.2s These studies found that the reaction dynamics for spiropyrans with a nitro group are significantly different from those for spiropyrans without a nitro group. A triplet state was found to play an important role in the photochemical reaction process of spiropyrans containing a nitro group, as indicated by the sen- sitivity of the dynamics to the presence of O2.IFz2 For molecules containing no nitro group, the photoreaction was dominated by singlet states. These studies have improved the understanding of the reaction mechanisms of photochromic spiropyrans. Previous studies have also found that the photochromic reaction of spiropyran molecules features the dissociation of a C-O bond, producing a distribution of isomer^.'^-^^ However, the rate and mechanism of the initial reaction steps for these molecules are

We report the rational synthesis of nitrogen-doped zinc oxide (ZnO:N) nanowire arrays, and their implementation as photoanodes in photoelectrochemical (PEC) cells for hydrogen generation from water splitting. Dense and vertically aligned ZnO nanowires were first prepared from a hydrothermal method, followed by annealing in ammonia to incorporate N as a dopant. Nanowires with a controlled N concentration (atomic ratio of N to Zn) up to approximately 4% were prepared by varying the annealing time. X-ray photoelectron spectroscopy studies confirm N substitution at O sites in ZnO nanowires up to approximately 4%. Incident-photon-to-current-efficiency measurements carried out on PEC cell with ZnO:N nanowire arrays as photoanodes demonstrate a significant increase of photoresponse in the visible region compared to undoped ZnO nanowires prepared at similar conditions. Mott-Schottky measurements on a representative 3.7% ZnO:N sample give a flat-band potential of -0.58 V, a carrier density of approximately 4.6 x 10(18) cm(-3), and a space-charge layer of approximately 22 nm. Upon illumination at a power density of 100 mW/cm(2) (AM 1.5), water splitting is observed in both ZnO and ZnO:N nanowires. In comparison to ZnO nanowires without N-doping, ZnO:N nanowires show an order of magnitude increase in photocurrent density with photo-to-hydrogen conversion efficiency of 0.15% at an applied potential of +0.5 V (versus Ag/AgCl). These results suggest substantial potential of metal oxide nanowire arrays with controlled doping in PEC water splitting applications.

The exciton binding energy (EBE) in CdSe quantum dots (QDs) has been determined using X-ray spectroscopy. Using X-ray absorption and photoemission spectroscopy, the conduction band (CB) and valence band (VB) edge shifts as a function of particle size have been determined and combined to obtain the true band gap of the QDs (i.e., without an exciton). These values can be compared to the excitonic gap obtained using optical spectroscopy to determine the EBE. The experimental EBE results are compared with theoretical calculations on the EBE and show excellent agreement.

A theoretical model has been developed to study the optical properties of metallic multishell structures on the nanometer scale. The Mie theory was generalized for multiconcentric spherical shell nanostructures and employed to determine the effects and importance of the different parameters of the system such as thickness, size, and other material properties, for instance, the medium index of refraction. A unique hollow gold-silver double-shell structure is used as an example to test the model developed with recent experiments. The surface plasmon resonance (SPR) absorption spectrum of this structure has been calculated as a function of various parameters, including shell thickness and diameter. Using parameters similar to those previously reported experimentally, very good agreement has been found between calculated and experimentally measured SPR spectra, which validates the model. The results provide new insights into the fundamental properties of complex metal nanostructures that give us the ability to control the optical response, which has important implications in the synthesis of new metal nanostructures as well as their application in emerging technologies.

The influence of excitation wavelength and embedding media on fluorescence blinking statistics of 4 nm x 20 nm cadmium selenide (CdSe) nanorods is investigated. Photon antibunching (PAB) experiments confirm nonclassical emission from single CdSe nanorods that exhibit a radiative lifetime of 26 +/- 13 ns. The blinking data show behaviors that can be categorized into two classes: excitation near the energy of the band gap and at energies exceeding 240 meV above the band gap. Excitation at the band gap energy (lambdaor= 560 nm) results in more pronounced "on" time probabilities in the distribution of "on" and "off" events, while those resulting from excitation exceeding the band gap by 240 meV or more (lambdaor= 560 nm) are 200 times less likely to display continuous "on" fluorescence persisting beyond 4 s. The "off" time statistics are also sensitive to the excitation wavelength, showing a similar, but inversely correlated, effect. To understand better the excitation-wavelength dependence, fluorescence measurements are obtained for single nanorods deposited both on a bare microscope coverslip and embedded in 1-ethyl-3-methylimidizolium bis(trifluoromethylsulfonyl)imide room-temperature ionic liquid (RTIL). The embedding RTIL medium has a significant influence on the resultant fluorescence statistics only when the excitation energy exceeds the 240 meV threshold. The results are explained by a threshold to access nonemissive trap states, attributed to self-trapping of hot charge carriers at the higher photon excitation energies.

A hollow core waveguide (HCW) with silver nanoparticles (SNPs) coated on the inner wall has been demonstrated for molecular detection based on surface enhanced Raman scattering (SERS). With rhodamine 6G (R6G) as an analyte molecule and two types of silver nanoparticles (SNPs) as double SERS substrates, the inner wall coated HCW (IWCHCW) exhibits significantly higher sensitivity than previous fiber SERS probes with only one SERS substrate. Two kinds of HCW are used in the experiment, liquid core photonic crystal fiber (LCPCF) and hollow silica waveguide (HSW). SERS signal obtained with either an LCPCF or a HSW IWCHCW is over ten times that obtained in direct detection using a single SERS substrate. The improvement of the SERS sensitivity is attributed to the additional enhancement of the electromagnetic field by the double SERS substrate "sandwich" structure with one substrate coated on the inner wall of the HCW and the other mixed in the sample solution. Furthermore, With an LCPCF IWCHCW, the SERS signal is around 100 times as strong as that in direct detection when measured from the processed fiber tip. This is attributed to the additional R6G/SNPs solution in the fiber pit, increased coupling efficiency due to surface plasmon resonance in the SNPs in the same region, and further increased electromagnetic field in the same region due to nano-structures introduced during the collapse of the cladding holes. The simple architecture and high sensitivity of the inner wall coated HCW make it promising for molecular detection in various analytical and sensing applications.

Purpose: To develop melanoma-targeted hollow gold nanospheres (HAuNS) and evaluate their potential utility for selective photothermal ablation in melanoma. Experimental Design: A new class of photothermal coupling agents based on HAuNS was synthesized. HAuNS were stabilized with polyethylene glycol (PEG) coating and attached with α–melanocyte-stimulating hormone (MSH) analog, [Nle4,D-Phe7]α-MSH (NDP-MSH), which is a potent agonist of melanocortin type-1 receptor overexpressed in melanoma. The intracellular uptake of the NDP-MSH–conjugated PEGylated HAuNS (NDP-MSH-PEG-HAuNS) and the distribution of β-arrestin were examined in murine B16/F10 melanoma cells. The biodistribution of NDP-MSH-PEG-HAuNS was assessed at 4 hours post i.v. injection in tumor-bearing nude mice. Photothermal ablation effect of the nanoparticles was evaluated both histologically using excised tissue and functionally by [18F]fluorodeoxyglucose positron emission tomography. Results: NDP-MSH-PEG-HAuNS consist only of a thin gold wall with hollow interior (outer diameter, 43.5 ± 2.3 nm; shell thickness, 3-4 nm), which displays strong and tunable resonance absorption in near-IR region (peak, 808 nm). The nanoparticles were specifically taken up by melanoma cells, which initiated the recruitment of β-arrestins, the adapters to link the activated G-protein–coupled receptors to clathrin, indicating the involvement of receptor-mediated endocytosis. This resulted in enhanced extravasation of NDP-MSH-PEG-HAuNS from tumor blood vessels and their dispersion into tumor matrix compared with nonspecific PEGylated HAuNS. Successful selective photothermal ablation of B16/F10 melanoma with targeted HAuNS was confirmed by histologic and [18F]fluorodeoxyglucose positron emission tomography evaluation at 24 hours post near IR–region laser irradiation at a low-dose energy of 30 J/cm2. Conclusion: NDP-MSH-PEG-HAuNS have the potentials to mediate targeted photothermal ablation of melanoma.

A molecular sensing system is theoretically analyzed and experimentally demonstrated with a hollow core photonic crystal fiber surface enhanced Raman scattering (SERS) probe to achieve high sensitivity and a portable Raman spectrometer to achieve flexibility.

C→A emission spectra of the water molecule have been observed following two‐photon excitation to various vibrational levels of the C(1B1) electronic state. Photodissociation dynamics on the A(1B1) state potential energy surface were probed through the C→A emission spectra. The different spectra correspond to photodissociation trajectories in the A state starting with a variety of initial conditions. Time‐dependent quantum mechanical simulations of the emission spectra show good agreement with the experimental data and provide further insight into the dissociation dynamics on the A state surface.

A study of the photodissociation dynamics of Mn2(CO)10 and the vibrational relaxation of its subsequent photoproducts in solutions has been carried out using picosecond time‐resolved laser techniques. The molecule predissociates in less than 2–3 ps after excitation with a 295 nm photon. Two dissociation channels are open for this excitation wavelength, namely, the Mn–Mn bond breaking and the Mn–CO bond breaking, generating internally hot ⋅Mn(CO)5 and Mn2(CO)9, respectively. These two species have a different absorption spectrum in the visible region and are probed independently by varying the probe laser wavelength. The vibrational relaxation of these nascent photoproducts is observed for the first time. In cyclohexane the vibrationally hot Mn2(CO)9 reaches thermal equilibrium with the solvent through two distinct decay channels with time constants of 15 and 170 ps, respectively. The vibrationally cold Mn2(CO)9 then persists for many nanoseconds. The vibrational relaxation is found to be faster in the 2‐p...

A simple, classical stochastic model has been developed to study the vibrational energy relaxation of heteronuclear diatomic molecules in simple monatomic liquids. This work is an extension of an earlier study on homonuclear diatomic molecules [D. E. Smith and C. B. Harris, J. Chem. Phys. 92, 1312 (1990)]. The model is based on the generalized Langevin equation for generalized Brownian dynamics. The memory function of each atom in the diatomic is determined directly from classical molecular dynamics simulations in the solvent of interest and then scaled by a screening factor. The memory function is modeled using an autoregressive technique, which provides efficient evaluation of the friction integral. The effect of screening is accounted using a simple model based on the equilibrium structure of the diatomic in the Lennard‐Jones solvent, which is shown to provide very reasonable results. The model developed is applied to simulate the vibrational relaxation of iodine chloride, ICl, in its ground electronic...

Fiber SERS (surface enhanced Raman scattering) sensors have attracted significant interest in molecule sensing. In this paper, we briefly review our previous work on various configurations for fiber SERS probes, including side-polished fibers and various photonic crystal fibers (PCFs). In addition, we will report our recent experiments on a double substrate "sandwich" structure for fiber SERS probe. The approach is to coat one SERS substrate on the tip of a multimode fiber and mix the second substrate in solution with the target analyte molecules. Upon dipping the coated fiber probe into the solution, randomly formed structures of the two substrates will sandwich the analyte molecules in between. Our results show that the "sandwich" configuration exhibits significantly higher sensitivity than direct SERS detection.

A new configuration was designed and tested based on ldquosandwichingrdquo target analyte molecules between two metal nanostructure substrates using surface enhanced Raman scattering (SERS), which exhibits significantly higher SERS enhancement compared to just one substrate.

This work demonstrates the use of a highly sensitive Liquid Core Photonic Crystal Fiber (LCPCF) Surface Enhanced Raman Scattering (SERS) sensor in detecting biological and biochemical molecules. The Photonic Crystal Fiber (PCF) probe was prepared by carefully sealing the cladding holes using a fusion splicer while leaving the central hollow core open, which ensures that the liquid mixture of the analyte and silver nanoparticles only fills in the hollow core of the PCF, therefore preserving the photonic bandgap. The dependence of the SERS signal on the excitation power and sample concentration was fully characterized using Rhodamine 6G (R6G) molecules. The result shows that the LCPCF sensor has significant advantages over flat surface SERS detections at lower concentrations. This is attributed to the lower absorption at lower concentration leading to a longer effective interaction length inside the LCPCF, which in turn, results in a stronger SERS signal. Several biomolecules, such as Prostate Specific Antigen (PSA) and alpha-synuclein, which are indicators of prostate cancer and Parkinson's disease, respectively, and fail to be detected directly, are successfully detected by the LCPCF sensor. Our results demonstrate the potential of the LCPCF SERS sensor for biomedical detection at low concentrations.

Spectra of the lowest 1B2 state of H2O and D2O have been recorded. The state is linear in its equilibrium geometry and has a bond length of 1.02 A. The spectra exhibit vibrational bending progressions and are rotationally resolved. They were recorded from energies of 80 000 to 90 000 cm−1 via two‐photon, laser‐induced flourescence (LIF) and 2+1 multiphoton ionization (MPI).

A temperature dependent Raman scattering study was conducted for the first time on LiAlH 4 and Li 3 AlH 6 in an effort to monitor the reaction kinetics of these hydrides toward its application as a hydrogen storage/delivery system for fuel cell and other applications. LiAlH 4 demonstrated a gradual softening of its Raman modes as the temperature was increased from 25 to 145 °C while Li3AlH6 demonstrated a loss in its Raman signal as the temperature increased from 30 to 90 °C. The more sensitive Raman response of Li 3 AlH 6 is believed to be the result of the weaker attraction between the octahedral AlH 6 3- units in the anionic network of the Li 3 AlH 6 compared to the tetrahedral AlH 4 - units of LiAlH 4 .

In recent years, there has been significant interest in using surface enhanced Raman scattering (SERS) and optical fibers for chemical, biological, and environmental detections. The combination of SERS and optical fibers offers the advantages of the molecular specificity of Raman scattering, huge enhancement factor of SERS, and flexibility of optical fibers. In this paper, we report our work on the development of fiber biosensors based on SERS emphasizing on recent progress in the fabrication of photonic crystal fiber (PCF) SERS sensors for highly sensitive molecular detection. To increase the sensitivity, one needs to increase either the excitation laser power or the amount of analyte molecules in the active region of the sensor. The high excitation intensity is not desirable for biosensors due to the low damage threshold of live tissues or bio-molecules. In our investigation of various fiber configurations, hollow core (HC) PCFs show the greatest advantages over all other types of fiber probes because of the large contact area. The hollow core nature allows the analytes and SERS substrate to fill the inner surface of the air channels. In addition, by sealing the cladding holes of the HCPCF, only the central hole will be open and filled with liquid samples. As both the light and the sample are confined in the fiber core, the sensitivity is significantly improved. The newly developed liquid core PCF sensor was tested in the detection of rhodamine 6G (R6G), human insulin, and tryptophan with good sensitivity due to the enhanced interaction volume.

We previously reported functional regeneration of Caenorhabditis elegans motor neurons after femtosecond laser axotomy. We report here that multiple neuronal types can regrow after laser axotomy using a variety of lasers. The precise pattern of regrowth varies with cell type, stage of animal, and position of axotomy. Mechanosensory axons cut in late larval or adult stages displayed extensive regrowth, yet failed to reach their target area because of guidance errors in the anteroposterior axis. By contrast, mechanosensory axons cut in early larval stages regrew at the same rate but with fewer anteroposterior guidance errors, and were more likely to reach their target area. In adult animals lacking the VAB-1 Eph receptor tyrosine kinase, mechanosensory axon regrowth was more accurate than in the wild type, suggesting that guidance errors of regrowing touch neuron axons are the result of Eph signaling. Kinase-dependent and kinase-independent Eph signaling influenced outgrowth and guidance of regrowing touch neurons, respectively. Mechanosensory neurons regrew when severed proximal to their collateral synaptic branch but did not regrow when severed distal to the branch point. However, the distal axon could regrow if the branch is removed surgically at the same time as distal axotomy, or at a later time. The touch neuron synaptic branch point may act as a sorting area to regulate growth. These findings reveal that multiple influences affect regenerative growth in C. elegans neurons.

Surface enhanced Raman scattering (SERS) sensors incorporating various fiber configurations as probes are reviewed and discussed. These include side-polished and end-polished fibers, photonic crystal fibers (PCFs), and fibers with lens-like tips. All these geometries provide large interaction areas for SERS, with the PCF configuration showing the greatest sensitivity.

In this paper, we report our proof-of-concept demonstration of using a photonic crystal fiber (PCF) as a new surface enhanced Raman scattering (SERS) sensor platform. A liquid core PCF (LCPCF) is fabricated by sealing the cladding holes of a hollow core photonic crystal fiber (HCPCF) while leaving the central core channel open to the outside. In this case, the analyte/SERS solution will only fill the central hole of the HCPCF. Additionally, theoretical simulation ensures that light is well confined in the core of a LCPCF. R6G solutions were used to test the sensor and excitation power dependence was demonstrated.

Experimental studies have been carried out to gain a better understanding of the effects of chromophore orientation and molecular conformation on surface-enhanced Raman scattering (SERS) based on metal nanostructures. A series of alkanoic acids that contain a phenyl ring separated by methylene groups from the carboxylic acid, including phenylacetic acid, 3-phenylpropionic acid, 4-phenylbutyric acid, 5-phenylvaleric acid, and 6-phenylhexanoic acid, was investigated as model molecules with colloidal silver nanoparticles as SERS substrates. As the number of methylene groups increases, the molecules display an interesting zigzag intensity pattern of the phenyl ring bending mode around 1000 cm(-1) as well as a trend of appearance and disappearance of either the degenerate ring breathing mode or C[Double Bond]O vibrational mode near 1585 and 1630 cm(-1), respectively. Molecules containing an odd number of methylene units display a higher ring bending intensity and degenerate ring breathing mode and are suggested to have a trans conformation on the particle surface. Molecules with an even number of methylene units show a C[Double Bond]O vibrational mode and weaker ring bending in their SERS spectra and are suggested to have a gauche conformation on the silver nanoparticle surface. The different conformation is attributed to the varying interactions of the carboxylic group or the phenyl ring pi electrons with the silver surface. The SERS intensity was found to change little as the length between the phenyl ring and the carboxylic group was increased by adding CH(2) spacers. This is possibly because the effective distance between the phenyl ring and the silver surface does not change much with increasing number of CH(2) spacers as a result of changes in molecular conformation and variations in the phenyl ring orientation with CH(2) addition. The insight gained from this study is important for understanding SERS of complex molecules for which chromophore orientation and molecular conformation must be taken into careful consideration.

Nearly monodisperse hollow gold nanospheres (HGNs) with tunable interior and exterior diameters have been synthesized by sacrificial galvanic replacement of cobalt nanoparticles. It is possible to tune the peak of the surface plasmon band absorption between 550 and 820 nm by carefully controlling particle size and wall thickness. Cobalt particle size is tunable by simultaneously changing the concentration of sodium borohydride and sodium citrate, the reducing and capping agent, respectively. The thickness of the gold shell can be varied by carefully controlling the addition of gold salt. With successful demonstration of ensemble as well as single HGN surface-enhanced Raman scattering, these HGNs have shown great potential for chemical and biological sensing applications, especially those requiring nanostructures with near-IR absorption.

Catalytic therapy (CT) is a cancer treatment modality based on the generation of reactive oxygen species (ROS) using a combination of substrate molecules and a catalyst. The most frequently used substrate and catalyst pair is ascorbate/Co phthalocyanine (PcCo). In the present study, porphyrins containing transition metal ions as catalysts in place of PcCo were studied. Porphyrins that are expected to be as efficient as phthalocyanines, but may have fewer side effects, were analyzed. ROS production through the combined use of ascorbate and porphyrins decreased the number of breast cancer tumor cells by 20-40% after a single in vitro treatment, as compared to control cells. Treatment with ascorbate in conjunction with porphyrins stimulated apoptosis and disrupted the cell cycle. These treatments enhanced apoptosis by 20-40% when compared to treatments with ascorbate and porphyrins. In addition, the number of cells accumulating in the sub G0/G1 stage of the cell cycle increased from 3- to 10-fold, potentially reflecting that the treatment was highly effective in inducing DNA damage in the tumor cells, suggesting that porphyrins may be beneficial as a CT catalyst in the treatment of cancer.

We report the development of nanoprobes that exploit the surface-enhanced Raman scattering (SERS) from nonaggregated, hollow, gold nanospheres (HGNSs). The homogeneity of the HGNSs leads to a nearly 10-fold improvement in signal consistency over standard silver SERS substrates, which translates into a significant increase in sensitivity and dynamic range for the model application of pH sensing. Moreover, the small size (30-nm diameter) of these SERS-active nanoparticles represents a major step in advancing sensing technology based on SERS, making this technology more amenable to intracellular sensing.

This paper demonstrates the optical trapping of micron-sized gold nanoparticle aggregates (GNAs) with a ${\mathrm{TEM}}_{00}$ mode laser at $532\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and reports the observation of an unusual light-induced agglomeration phenomenon that occurs besides the trapping of the GNAs. The observed agglomerate has a $60--100\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ donut-shaped metal microstructure with the rate of formation dependent on the laser power used. Citrate capped gold nanoparticles also show light-induced agglomeration, yielding different sized microstructures from those produced with GNAs. While the observed trapping can be explained by a model including the optical radiation and radiometric forces, the light-induced agglomeration cannot be explained by these two forces alone as the size of the agglomerate is much greater than the waist of the Gaussian beam used in the optical trapping. We attribute the additional cause of the light-induced agglomeration to ion detachment from the surface of the nanoparticles (aggregates) due to light illumination or heating. This is supported by the observation of reversible electrical conductivity changes of the solution of the nanoparticles (aggregates) upon laser illumination or direct heating. Light-induced agglomeration can be useful in the design and fabrication of microstructures from nanomaterials for various device applications.

Fiber SERS probes have great potential in chemical and biological sensing. To our knowledge, there has been no demonstration of any single-fiber SERS probes where both the excitation beam and SERS signals are transmitted through the same fiber with a significant length, which is required for a flexible probe. In this paper, we report our proof-of-concept demonstration of a single-fiber SERS probe with a 1 m long fiber. We demonstrate various configurations of the fiber probe, where the SERS substrate is coated on either a side-polished or end-polished fiber surface. While the side-polished fibers provide a large platform for signal generation, the end polished fibers are easy to manipulate and can transmit SERS signals back through the fiber. In our experiments, we have successfully detected SERS signals both at the end where the fiber is polished and coated with the SERS substrate and at the end where the excitation light is coupled into the fiber, using R6G as a testing sample

Yi Zhang and Claire Gu Department of Electrical Engineering, Univer sity of California, Santa Cruz, CA 95064 Phone: (831) 459-4716 Fax: (831) 459-4829 claire@ee.ucsc.edu Adam M. Schwartzberg, Shaowei Chen and Jin Z. Zhang Department of Chemistry, University of California, Santa Cruz, CA 95064 ABSTRACT

Surface-enhanced Raman scattering using silver nanoparticles was applied to detect various forms of lysophosphatidic acid (LPA) to examine its potential application as an alternative to current detection methods of LPA as biomarkers of ovarian cancer. Enhancement of the Raman modes of the molecule, especially those related to the acyl chain within the 800-1300 cm(-1) region, was observed. In particular, the C-C vibration mode of the gauche-bonded chain around 1100 cm(-1) was enhanced to allow the discrimination of two similar LPA molecules. Given the molecular selectivity of this technique, the detection of LPA using SERS may eliminate the need for partial purification of samples prior to analysis in cancer screening.

Energy transfer dynamics in Mn2+-doped ZnSe nanoparticles have been studied by monitoring the photoluminescence using time-integrated and time-resolved spectroscopic techniques. Upon Mn2+ doping, static photoluminescence (PL) spectra show that the bandedge excitonic state is quenched and the characteristic Mn2+ emission appears at 584 nm. Picosecond PL kinetics and femtosecond transient absorption studies have both found that the Mn2+ doping substantially shortens the average lifetimes of the bandedge excitonic state as well as shallow trap states. The energy transfer from ZnSe to Mn2+ likely follows two mechanisms, one mediated through trap states and another without.

The demand for sensors for detecting chemical and biological agents is greater than ever before, including medical, environmental, food safety, military, and security applications. At present, most detection or sensing techniques tend to be either non-molecule specific, bulky, expensive, relatively inaccurate, or unable to provide real time data. Clearly, alternative sensing technologies are urgently needed. In this paper, we present a novel sensor with a nanoparticle surface enhanced Raman scattering (SERS) substrate coated on D-shaped or end-polished fibers for chemical, biological, and environmental detection. The sensor will be highly sensitive, molecular specific, reliable, label-free, non-invasive, inexpensive, easy to produce commercially using existing technologies, compatible with existing lasers and detectors, and applicable to a large number of molecules of interest. This is made possible by the unique sensor architecture based on a combination of optical fiber technology and novel SERS substrates, where SERS provides the high sensitivity (106-1015 enhancement factor), molecular specificity, and applicability to a wide range of compounds, while the novel fiber configurations provide the flexibility, compactness, reliability, low cost, and ease of production.

Electrical and thermal conductivities of metal nanoparticles and their aggregates are important for many device applications involving nanomaterials. In this work, the electrical conductivity of gold nanoparticle aggregates has been measured and found to be a useful probe of the surface chemistry of the nanoparticles. It has been observed that the conductivity of the gold nanoparticle aggregates in solution increases with light illumination or thermal heating and recovers completely to the initial value upon removal of the light or heat. The amount of change in conductivity depends on the amount of heat or light. The conductivity change is tentatively attributed to ion dissociation from the nanoparticle surface due to heating or light illumination. Meanwhile, the thermal conductivity of dried silver nanoparticles (30-60 nm) has been measured and found to be around 2 W/m×K. This is consistent with previous prediction of significantly reduced thermal conductivity of Ag nanoparticles/aggregates. In addition, external DC electrical field enhanced surface-enhanced Raman scattering (SERS) was also observed with the excitation laser light focused in between the electrodes instead of on the electrodes. Various potential were applied and an enhancement factor of 5 has been achieved. Possible explanations for this enhancement are provided.