Sensing capability of the localized surface plasmon resonance of gold nanorods.

We demonstrate the feasibility of using the longitudinal component of gold nanorod's surface plasmon resonance in biomolecular sensing. The sensitive dependence of the absorption maximum on the dielectric constant of the particle interfacial region makes gold nanorods a promise for constructing a biomolecular sensing scheme. The sensor containing gold nanorods, with a mean aspect ratio of 5.2, exhibits a sensitivity of ca. 366 nm/RIU (refractive index unit), which increases accordingly with the increase of the particle mean aspect ratios. Such a biosensor was further modified to demonstrate its effectiveness in quantitative detection for selective binding events, such as biotin/streptavidin pairs, through a process in which biotin molecules were chemically attached to the gold nanorods' surface prior to detection measurements. Results showed that the spectral lambda(max) shifts linearly to the concentrations of the streptavidin. The results from both experiment and model calculations strongly indicate the efficacy of the longitudinal surface plasmon absorption band in biosensing.

Highly efficient, wavelength-tunable, gold nanoparticle based optothermal nanoconvertors.

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.

Distinct reactivities on segmented selenium nanorods.

We demonstrate a new approach to synthesize several unique nanostructures by tuning the selective reactivities on individual symmetry-breaking segmented selenium nanorods (SBS-SeNRs). The segment-selective reactions from thiolated silane endowed the formation of float-like SBS-SeNR@SiO2 with a silica coating on the t-Se segment. Several other unique nanostructures were further synthesized by applying other selective reactions, such as Se chemical removal and nanogold deposition. Such a segmented nanomaterial of SBS-SeNRs acts as a new chemical template for preparing various segmented nanocomposites.

Silver-coated gold nanoparticles as concentrating probes and matrices for surface-assisted laser desorption/ionization mass spectrometric analysis of aminoglycosides.

A novel method for the determination of aminoglycosides by surface-assisted laser desorption/ionization mass spectrometry (SALDI MS) with the aid of silver-coated gold nanoparticles (Au@AgNPs) has been developed. The Au@AgNPs with surface capped by anionic citrate were used as concentrating probes as well as matrices in SALDI MS. Adsorption of aminoglycosides onto the nanoparticles was mainly through electrostatic attraction. The aminoglycoside-adsorbed nanoparticles were directly characterized by SALDI MS after a simple washing. Using Au@AgNPs to preconcentrate the aminoglycosides from 500 microL buffer solution, the limits of detection (LODs) at signal-to-noise ratio of 3 were 3, 25, 15, 30, and 38 nM for paromomycin, kanamycin A, neomycin, gentamicin, and apramycin, respectively. This method was successfully applied to the determination of aminoglycosides in human plasma samples. The LODs of aminoglycosides in plasma samples were 9, 130, 81, and 180 nM for paromomycin, kanamycin A, neomycin, and gentamicin, respectively. Recoveries of aminoglycosides in plasma samples were about 80%.

Aqueous-organic phase transfer of gold nanoparticles and gold nanorods using an ionic liquid.

The water-immiscible ionic liquid, [C4MIM][PF6], is a solvent medium that allows complete transfer of gold nanoparticles from an aqueous phase into an organic phase. Both spherical and rod-shaped gold nanoparticles are efficiently transferred from an aqueous solution into the organic phase without requiring the use of thiols. The sizes and shapes of the gold nanoparticles were preserved during the phase-transfer process when a surfactant was added to the ionic liquid. This process offers a simple approach for obtaining solutions of differently sized and shaped gold nanoparticles in ionic liquids.