We report a revised synthetic procedure based on an electrochemical method for preparing an aqueous solution containing suspended Au nanorods. The mean aspect ratios of the Au nanorods can be experimentally adjusted between 1 and 7. The evolution of the longitudinal surface plasmon bands shows an eminently sensitive dependence on the aspect ratios of the nanorods. Their dependence is accordingly described by classical-electrostatic-model predictions. The shape transition of the nanorod particles has been studied by varying some key influencing factors such as the wavelength, the laser fluence, and matrix effects. The nanorods were exposed to laser lines at 532 and 1064 nm, frequencies which correspond closely to the short- and long-axis plasmon resonances, respectively. A photon-induced shape transition process was evidenced, and the corresponding rod-to-sphere conversion contributed by a photoannealing process was observed in both cases. Meanwhile, we observed a new type of “φ-shaped” Au nanostructure in the case of 1064-nm irradiation, which possibly represents the early stage of the shape transition and indicates that the starting location of the atomic-scale restructuring is at the centroid of the Au nanorod. The results of laser fluence-dependence measurements state that an efficient shape transition occurs via a multiphoton process. We also demonstrate the fabrication of the Au nanorod@silica nanostructures for preliminary studies of the matrix effects. As a result of the higher rigidity of the thin-silica-coating layer, the associated shape transition requires higher energy and proceeds less efficiently as compared with the cases for the micelle-stabilized Au nanorods.

A photon-to-thermal energy conversion nanosystem based the near-infrared irradiation of one-dimensional gold nanoparticles (nanorods) is highly efficient and tunable to the incident wavelength. Using ambient photothermal detection, we observed a temperature rise of ca. 30 degrees C upon irradiating an aliquot of an aqueous nanoparticle suspension with a laser for 5 s. The temperature can be elevated even higher by embedding the particles into a poorly thermally conducting solid medium. The illuminated area of a sample containing nanorod particles embedded in a polyurethane matrix can be heated to >100 degrees C upon irradiation for 1 min. This optothermal conversion efficiency can be turned on selectively by tuning the wavelength to match that of the surface plasmon resonance of the particles. This specificity, with respect to the wavelength of the incident light, makes these highly efficient, particle-based, optothermal nanoconvertors suitable for potential use in multicolor detection on biochips and related sensors and as ideal contrasting agents for optoacoustic biomedical imaging applications.

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Iron oxide nanoparticles modified with oleate have been employed for the extraction of peptides and proteins from aqueous solution before matrix-assisted laser desorption/ionization (MALDI) mass spectrometric (MS) analysis. Adsorption of peptides and proteins onto the nanoparticles were mainly through electrostatic attraction and hydrophobic interaction. The analyte-adsorbed iron oxide nanoparticles could be efficiently collected from solution using a magnet. No elution step was needed. With this preconcentration strategy, the lowest detectable concentration of angiotensin I, insulin, and myoglobin in 500 L of aqueous solution were 0.1 nM, 0.1 nM, and 10.0 nM, respectively. In addition, the nanoparticles could extract the analytes from solution with a high content of salt and surfactant, thus eliminating suppression effect during MALDI MS analysis. This method was successfully applied to concentrate the tryptic digest products of cytochrome c. In addition, the tryptic digestion of cytochrome c can be directly conducted on the iron oxide nanoparticles. atrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) has become a routine analytical tool to determine the molecular mass of biomolecules [1][2][3]. However, samples containing excessive amounts of salts, surfactants, or other contaminations suffer from ionization suppression and adduct formation [4,5]. This limits the application of MALDI technique. Therefore, a simple and selective procedure for extraction and concentration of analyte from complex samples before MALDI MS is required.Various methods have been developed to isolate the analyte from complex sample matrix. In surface-enhanced laser desorption/ionization (SELDI), the sample target played an active role in the extraction, purification, or concentration of the analyte of interest [6 -9]. The target surface was derivatized for the selective retention of analyte while removing interferences through on-target washing. Several surface derivatizations have been designed to extract and concentrate the analyte through hydrophobic interaction [10,11], ionic interaction [12,13], or immunoaffinity [14,15]. However, the sensitivity improvement was limited by the number of binding sites on the target. In another approach, the so-called surface-enhanced affinity capture (SEAC), micrometer-sized beads made for chromatography column were used to capture peptides and proteins from sample solution [16]. Various types of beads have been used, which include reverse-phase chromatographic beads [17,18] and immobilized metal ion beads [19 -21]. To speed up the collection of analyteadsorbed beads from sample solution, magnetic particles, which can be simply collected using a magnet, were developed [22][23][24]. After collection, the microbeads were washed and placed on sample target, followed by analyzing with MALDI MS. Unfortunately, the presence of those particles on the sample target was reported to cause decrease in mass accuracy and resolution [25,26].Recently, nanoparticles have become interesting p...

A quantitative technique for flow measurements based on a wash-in analysis is proposed. The technique makes use of the shape dependence of the optical absorption of gold nanorods and the transitions in their shape induced by pulsed laser irradiation. The photon-induced shape transition of gold nanorods involves mainly a rod-to-sphere conversion and a shift in the peak optical absorption wavelength. The application of a series of laser pulses will induce shape changes in gold nanorods as they flow through a region of interest, with quantitative flow information being derived from the photoacoustic signals from the irradiated gold nanorods measured as a function of time. To demonstrate the feasibility of the technique, a Nd:YAG laser operating at 1064 nm was used for irradiation and a 1 MHz ultrasonic transducer was used for acoustic detection. The flow velocity ranged from 0.35 to 2.83 mm/s. Excellent agreement between the measured velocities and the actual velocities was demonstrated, with a linear regression correlation coefficient of 0.93. This study is a pioneer work on wash-in flow estimation in photoacoustic imaging.