Longitudinal Surface Plasmon Resonance Band Research Articles

Influence the diphenhydramine hydrochloride–sodium carboxymethyl cellulose complex for nanoaggregate formation

This study aimed to create nanoaggregates that improve the synergistic interaction between the opposing charges in drug-polyelectrolyte complexes. In this study, sodium carboxymethyl cellulose (NaCMC) polyelectrolytes and diphenhydramine hydrochloride (DPC) drug molecules were used to form the nanoaggregate. The aggregation behaviour of NaCMC-DPC complexes was determined by using conductivity methods. The critical micelle concentrations (CMC) of NaCMC were reduced from 0.737 to 0.337 g/l in the aqueous and 29.18 mg/l in the DPC. The modified Corrin and Harkins (CH) and Frahm's approaches evaluated the binding efficiency of the NaCMC-DPC interaction. NaCMC-DPC complexes were examined by transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques to conform to the formation of bilayer vesicles. Furthermore, we prepared the silver nanoparticles by using NaCMC-DPC complex mixtures. We demonstrated how NaCMC-DPC mixtures might influence the self-assembly of silver nanochain designs that differed from open "end-to-end" networks. The results indicated that the assembly of silver nanochains was regulated by a variation of electrostatic interactions inside the NaCMC-DPC components, which organized themselves around anisotropic nanochains surfaces. Among the optical properties altered by the linear assembly, the longitudinal surface plasmon resonance band at 624 nm has an enhanced redshift.

The Effects of Single, Janus, and Triple Functionalization of Gold Nanoparticles on Physicochemical Properties and Cellular Uptake

Combining direct targeting, enhanced cellular uptake, photothermal transduction capacity, and biocompatibility in the same system is a challenge to make the application of nanoparticles in biomedicine real. This study involves the functionalization of gold nanoparticles (AuNPs) in a few steps with strategic macromolecules to provide characteristics that are key to theragnostic agents. Polyethylene glycol (PEG) is hydrophilic and can improve nanoparticle stability and circulation lifetime. Polylactic acid (PLA) is a biodegradable hydrophobic polymer important to guarantee the interaction and uptake through the cellular membranes. Folate provides specific targeting because tumors usually overexpress folate receptor proteins. Single, double, and triple functionalization of spherical and rodlike AuNPs with these ligands provided different aggregation, stability, and plasmonic properties. Triple functionalization ensured simultaneous nanoparticle stability in an aqueous medium and enhanced cellular uptake. Infrared irradiation increased the temperature of gold nanorods more than of gold nanospheres due to the longitudinal surface plasmon resonance band. The results suggest that this functionalization strategy can be used to tune the desired properties for applications of gold nanoparticles, such as imaging and photothermal therapy in biomedicine research.

Development of thickness-tunable gold nanorods for anti-oxidant detection

Here, in this study, we strategically utilized low-energy mediated epitaxial deposition of Au0 atoms reduced by gallic acid over preformed gold nanorods (GNRs) seeds. It can be suggested that GNRs seed/Au3+ ratio influences the directional attachment of Au0 atoms to the GNRs. Alteration in the thickness of the GNRs upon deposition of Au0 in presence micromolar levels of antioxidant reduces the aspect ratio of the nanorods. Change in the aspect ratio altogether induces a blue-shift in the longitudinal surface plasmon resonance (LSPR) of the GNRs from the NIR region of the spectrum to the shorter wavelength. TEM imaging, DLS and zeta potential analyses confirms the morphological and surface-charge alterations after interaction with antioxidant. Based on the relation between blue-shift of the LSPR band and the concentration of gallic acid, the sensing platform achieves a linear detectable range of 1.25–35 μM with detection limit as low as 90 nM and the limit of quantification as 300 nM. The method has high selectivity against tested interferents and was found to be reproducible. The potential application of the developed sensor was validated by quantifying gallic acid in commercially available apple juice. High recovery (99.46–100.4%) was obtained, suggesting that the established assay which is reliable and facile can be successfully used for gallic acid detection real food samples. The developed method of tuning the aspect ratio of nanomaterial can be further extended for detection other anti-oxidant molecules.

Label-free gold nanorod-based plasmonic sensing of arsenic(iii) in contaminated water.

In this paper, we report a strategy based on unmodified gold nanorods for sensitive and selective detection of arsenic(iii) in contaminated water for the first time. The strategy relies on the inhibitory effect of arsenic(iii) on iron(iii)-mediated oxidative shortening of gold nanorods (Au-NRs) in acidic pH and at increased temperature. The arsenic(iii)-mediated inhibition of Au-NR oxidation is demonstrated by the red-shift of the longitudinal surface plasmon resonance (LSPR) band of Au-NRs. The novelty of our sensing strategy is the fact that it is label-free as it doesn't include any arsenic(iii) selective functionalization of Au-NRs. Moreover, this strategy can detect the arsenic(iii) content in water down to 10 ppb, which is the maximum permissible limit of the arsenic trace in drinking water according to the World Health Organization (WHO) guidelines. The effect of H2O2 in controlling the selectivity of our sensing strategy is investigated. It is found that in the absence of H2O2, the strategy is selective for arsenic(iii) with a broad dynamic response range (10-500 ppb), except for the interference from copper(ii). However, the interference of copper(ii) is efficiently eliminated by selective removal of copper(ii) from water via magnetic separation using polyethyleneimine-functionalized cobalt ferrite nanoparticles. The morphology of Au-NRs and the shift of the LSPR band during the sensing of arsenic(iii) are established by electron microscopy images and Vis-NIR absorption spectroscopy. This strategy is successfully applied for the estimation of arsenic(iii) in the real water sample and this paves the way for the implementation of our strategy for the real-time estimation of arsenic(iii) contamination levels found across prevalent drinking water sources, which are otherwise difficult to achieve with traditional sensors.

Thermographic Detection and Analysis of the Temporal and Spatial Evolution of Temperature upon Optical Heating of Gold Nanorod Assembly Immobilized in Agar

Photoexcitation of the longitudinal surface plasmon resonance band of gold nanorods (AuNRs) in the near-infrared region has been widely employed in photothermal therapy. Generally, the temperature evolution of the surface of the object of interest reflects the photothermal efficiency. However, the temperature in the object interior may be higher than required and cause unwanted damage to the healthy cells or tissues in the vicinity of the unhealthy areas. In this work, agar served as a biomimicking tissue, and 1 mm3 AuNR agar assembly cubes were placed at different depths with respect to the agar surface and excited with an 808 nm continuous-wave laser or an 850 nm light-emitting diode light. The evolution of the surface temperature was monitored with an infrared thermographic camera and analyzed with a point heat source model. The concentric temperature change suggested that the sample was nonfluidic and that convection and mass flow could be excluded. The depths of the AuNR agar cubes could be determine...

Formation of plasmon quenching dips greatly enhances 1O2 generation in a chlorin e6–gold nanorod coupled system

Photodynamic therapy (PDT), as a noninvasive therapeutic method, has been actively explored recently for cancer treatment. However, owing to the weak absorption in the optically transparent windows of biological tissues, most commercial photosensitizers (PSs) exhibit low singlet oxygen (1O2) quantum yields when excited by light within this window. Finding the best way to boost 1O2 production for clinical applications using light sources within this window is, thus, a great challenge. Herein, we tackle this problem using plasmon resonance energy transfer (PRET) from plasmonic nanoparticles (NPs) to PSs and demonstrate that the formation of plasmon quenching dips is an effective way to enhance 1O2 generation. The combination of the photosensitizer chlorin e6 (Ce6) and gold nanorods (AuNR) was employed as a model system. We observed a clear quenching dip in the longitudinal surface plasmon resonance (LSPR) band of the AuNRs when the LSPR band overlaps with the Q band of Ce6 and the spacing between Ce6 and the rods is within the acting distance of PRET. Upon irradiation with 660 nm continuous-wave laser light, we obtained a seven-fold enhancement in the 1O2 signal intensity compared with that of a non-PRET sample, as determined using the 1O2 electron spin resonance probe 2,2,6,6-tetramethyl-4-piperidine (TEMP). Furthermore, we demonstrated that the PRET effect is more efficient in enhancing 1O2 yield than the often-employed local field enhancement effect. The effectiveness of PRET is further extended to the in vitro level. Considering the flexibility in manipulating the localized SPR properties of plasmonic nanoparticles/nanostructures, our findings suggest that PRET-based strategies may be a general way to overcome the deficiency of most commercial organic PSs in biological optically transparent windows and promote their applications in clinical tumor treatments.

Heat-induced morphological transformation of gold nanodumbbells in ionic surfactant solutions

The thermal stability of gold nanodumbbells (NDs) is studied in aqueous solution of ionic surfactants. It is found in aqueous solution of cetyltrimethylammonium bromide that the blue-shift of longitudinal surface plasmon resonance band of gold NDs occurs at 75 °C and the new gold nanorods (NRs) with shortened aspect ratio are formed at the same time. The aspect ratio of the generated gold NRs gradually decreases and finally approaches ∼1.7 after repeated processing. Similarly, the same results are also obtained in aqueous solution of sodium dodecyl sulfate at room temperature. Mechanism is proposed for the shape transformation of gold NDs.

Spherical gold nanoparticles and gold nanorods for the determination of gentamicin

Gentamicin is an antibiotic indicated to treat mastitis in dairy cattle and for the treatment of bacterial resistance in the context of hospital infections. The effect caused by gentamicin on the optical properties of gold nanoparticles aqueous dispersions were used to develop quantitative methods to determine this antibiotic. Two different aqueous dispersions, one containing spherical Au nanoparticles (AuNPs) and the other containing Au nanorods (AuNRs), had their conditions adjusted to enable a stable and sensitive response towards gentamicin. The use of AuNPs, with measurement at 681nm of the rising coupling plasmon band, enabled a limit of detection (LOD) of 0.4ngmL−1 (0.02ng absolute LOD), ten times lower than the one achieved by measuring the decreasing of the longitudinal surface plasmon resonance band (at 662nm). The linear analytical response of AuNPs measured at 681nm did not require rationing of signal values to correct for linearity. Stability of the analytical response resulted in intermediary precision below 2%. No significant interference was imposed by excipients traditionally present in injectable solutions for veterinary use. Percent recoveries obtained in such formulations were between 94.5 and 98.2% regardless the existence of any difference in the proportion of the compounds known as gentamicin (C1, C1a and C2) in standard and in the samples. The method requires no derivatization with toxic reagents as usually is required in other spectroscopic approaches.

Spinning gold nanoparticles driven by circularly polarized light

This study theoretically examines a spinning gold nanoparticle (GNP) driven by circularly polarized (CP) plane waves. The wavelength-dependent optical torques which were exerted on three different shapes of GNPs (spherical, prolate and oblate spheroids) were analyzed by utilizing Mie theory for the former and the multiple multipole method for the latter two, respectively. Numerical results show that both the absorbed and scattered photons contribute to optical torques in most cases. For the case that the CP wave is incident along the long axis of an oblate spheroid or the short axis of a prolate one, the scattering effect in optical torque is more pronounced than the absorption one. This phenomenon is significant especially when the wavelength of the CP wave is close to the longitudinal surface plasmon resonance band of the GNP. In contrast, when the CP wave is incident along the axes of revolution of these shapes of GNPs, the ratio of optical torque to absorption power is directly proportional to the wavelength. Moreover, this ratio is independent of the size and even the aspect ratio of GNPs. This result suggests that only the absorbed photons contribute to optical torques, but not the scattered ones, due to the conservation of angular momentum for cases of rotational symmetry.

Visual and colorimetric detection of p-aminophenol in environmental water and human urine samples based on anisotropic growth of Ag nanoshells on Au nanorods

A simple, sensitive, selective and high-resolution colorimetric method has been developed for the detection of p-aminophenol in environmental water and human urine samples. In the presence of p-aminophenol, silver ions are reduced to silver atoms and subsequently Ag nanoshells anisotropically grow on the surface of Au nanorods to generate orange slice-like Au@Ag core–shell nanocrystals, thereby resulting in the blue-shift of longitudinal surface plasmon resonance band of Au nanorods accompanying a sharp-contrast multicolor change. Using Au@Ag core–shell nanocrystals as the transducer, sub-micromolar p-aminophenol can be detected by the colorimetric method and 10μmolL−1 p-aminophenol can be visual readout by the naked eyes. Furthermore, a simple, cheap, portable test kit is constructed for the visual assay of urinary p-aminophenol without complicated sample pretreatment and sophisticated instruments. The proposed colorimetric method has the potential for the rapid and on-site analyses of p-aminophenol in environmental water and human urine samples.

Fractionation and Characterization of High Aspect Ratio Gold Nanorods Using Asymmetric-Flow Field Flow Fractionation and Single Particle Inductively Coupled Plasma Mass Spectrometry

Gold nanorods (GNRs) are of particular interest for biomedical applications due to their unique size-dependent longitudinal surface plasmon resonance band in the visible to near-infrared. Purified GNRs are essential for the advancement of technologies based on these materials. Used in concert, asymmetric-flow field flow fractionation (A4F) and single particle inductively coupled mass spectrometry (spICP-MS) provide unique advantages for fractionating and analyzing the typically complex mixtures produced by common synthetic procedures. A4F fractions collected at specific elution times were analyzed off-line by spICP-MS. The individual particle masses were obtained by conversion of the ICP-MS pulse intensity for each detected particle event, using a defined calibration procedure. Size distributions were then derived by transforming particle mass to length assuming a fixed diameter. The resulting particle lengths correlated closely with ex situ transmission electron microscopy. In contrast to our previously reported observations on the fractionation of low-aspect ratio (AR) GNRs (AR < 4), under optimal A4F separation conditions the results for high-AR GNRs of fixed diameter (≈20 nm) suggest normal, rather than steric, mode elution (i.e., shorter rods with lower AR generally elute first). The relatively narrow populations in late eluting fractions suggest the method can be used to collect and analyze specific length fractions; it is feasible that A4F could be appropriately modified for industrial scale purification of GNRs.

Plasmon induced self-assembly of gold nanorods in polymer films.

Photoactivated orientation of gold nanorods (AuNRs) incorporated into polymethylmethacrylate and SU-8 photoresist films occurs under red light activation. Excitation of the longitudinal surface plasmon resonance band leads to selective orientation of the nanostructures, revealed by a change in the absorption spectra.

Synthesis of anisotropic gold nanoparticles and their catalytic activities of breaking azo bond in sudan-1

Here, we report the high yield synthesis of different shaped gold nano particles (AuNPs) through seed mediated growth process in aqueous medium. Shape dependent surface plasmon resonance (SPR) and the gradual shift of longitudinal SPR band are observed with increasing anisotropy of AuNPs. Structural changes during the growth processes are observed by transmission electronic microscopy (TEM). Here, spherical nano seeds are transformed into rice and dendrimer shaped nanoparticles in the subsequent four stage growth processes. Gold nanoparticles have been demonstrated to be very efficient catalysts for the cleavage of NN of sudan-1 and it is investigated by monitoring the reduction of sudan-1 in the presence of excess NaBH4. It has been observed that the reaction is first order with respect to the concentration of sudan-1 and the catalytic efficiency of dendrimer shaped AuNPs is higher than the other as synthesized AuNPs.

A green chemical approach for synthesis of shape anisotropic gold nanoparticles

A complete green chemical reaction between aurochloric acid and tea polyphenols resulted in the reduction of Au 3? ? Au 0 . The reaction was carried out in a Teflon-coated bomb digestion vessel at 200 C. It was observed that with increasing the reaction time from 1 to 5 h, the shape of the nanoparticles changed from spherical- to rod-like structures. The reaction was followed with the help of UV-vis spectrometer, which showed a single absorption peak at 548 nm for 1-h reaction product and two peaks for a 5-h reaction product at 533 and 745 nm cor- responding to the transverse and longitudinal surface plasmon resonance bands. Microstructures obtained from transmission electron microscope revealed that the samples obtained after 1-h reaction are predominantly spherical in shape with an average size of 15 nm. Whereas samples obtained after 5 h of reaction exhibited rod-like structures with an average size of 45 nm.

Post-synthesis reshaping of gold nanorods using a femtosecond laser

This work describes the interaction between femtosecond laser pulses (~130 fs, 800 nm) and gold nanorods (NRs) leading to reshaping of the NRs. We focus on the investigation of structural changes of the NRs and the parameters influencing the reshaping, like surface modification using sodium sulphide, laser power and the position of the longitudinal surface plasmon resonance band (l-SPR) with respect to the laser wavelength. A thermogravimetric analysis experiment is performed to examine changes in the composition of NRs upon heating. A new type of banana-shaped NPs is described and the conditions of their appearance are discussed.

Au@Pt nanostructures: a novel photothermal conversion agent for cancer therapy

Due to aspect ratio dependent localized surface plasmon resonance (SPR), gold nanorods (Au NRs) can be tuned to have a strong absorption in the near infrared region (NIR) and convert light to heat energy, which shows promises in cancer photothermal therapy. In this study, we introduced another more efficient NIR photothermal agent, Au nanorods coated with a shell of Pt nanodots (Au@Pt nanostructures). After surface modification with Pt dots, the Au@Pt nanostructure became a more efficient photothermal therapy agent as verified both in vitro and in vivo. To clarify the mechanism, we assessed the interaction between the MDA-MB-231 cells with Au@Pt or Au NRs. Results showed that the slightly higher uptake and the reduced sensitivity of the longitudinal SPR band on the intracellular aggregate state may contribute to the better photothermal efficiency for Au@Pt NRs. The theoretical studies further confirmed that the Au@Pt nanostructure itself exhibited better photothermal efficiency compared to Au NRs. These advantages make the Au@Pt nanostructure a more attractive and effective agent for cancer photothermal therapy than general Au NRs.

Morphological Control in Aggregates of Amphiphilic Cylindrical Metal–Polymer “Brushes”

Controlled self-assembly of gold nanorods (AuNRs) into nanostructures of various morphologies has attracted considerable interest because it provides a high degree of freedom in tailoring the properties of the nanostructures by the coupling of the optical and electronic properties of the individual AuNRs. This paper presents a new strategy for making AuNR aggregates of tunable morphologies. In this approach, the surface of AuNRs is chemically coated with an amphiphilic diblock copolymer. The coating gives the AuNRs a cylindrical brush structure. By varying the nature of the common solvent or the interparticle electrostatic repulsion, the self-assembly of the amphiphilic cylindrical AuNR–polymer “brushes” can produce water-soluble aggregates of controllable morphologies, including single-rod ellipsoidal micelles, curved circular lamellae, and nanospheres. The AuNRs in the various aggregates generate different surface plasmon resonance (SPR) absorption patterns, with the longitudinal SPR band in the near-in...

Morphology dependent photosensitization and formation of singlet oxygen (1Δg) by gold and silver nanoparticles and its application in cancer treatment.

Singlet oxygen is a very important reactive oxygen species (ROS) involved in peroxidation of olefins and polymers, as well as in clinical photodynamic therapy treatments of tumors. Previously, it was reported that singlet oxygen can be formed via sensitization by spherical metal nanoparticles upon photo-excitation of the surface plasmon resonance (SPR) bands. In this paper, we report that sensitization and formation of singlet O2 is strongly dependent on the morphologies of gold and silver nanostructures. For example, singlet O2 can be generated via photo-irradiation and sensitization of silver decahedrons and silver triangular nanoplates, but not by silver nanocubes and gold decahedrons. The sensitization patterns of silver and gold nanoparticles are the reverse of each other. In the case of gold nanorods, singlet O2 can be generated via photo-excitation at the longitudinal SPR band, but not by excitation at the transverse SPR band. The controlling factors for such a morphology dependent singlet O2 sensitization will be discussed. Furthermore, we also demonstrate in vitro morphology dependent sensitization behaviour of silver nanoparticles in the photodynamic cancer treatment. Our results indicate that metal nanoparticles with certain morphologies are potentially very promising dual functional nanomaterials with capabilities of simultaneously serving as near infrared (NIR) activatable photodynamic therapy and photothermal therapy reagents for cancer treatments.

The Effect of Aspect Ratio of Gold Nanorods on Cell Imaging with Two-Photon Excitation

To make the gold nanorod (AuNR) a better photoluminescence (PL) probe for cell imaging under two-photon excitation (TPE), the effect of the aspect ratio of AuNRs was studied. The AuNRs with the aspect ratios of 2.7, 3.2, 4.1, and 4.5 and correlated longitudinal surface plasmon resonance (LSPR) bands of 710, 760, 820, and 870 nm were compared. The approach of two-photon excited PL was used to measure the two-photon absorption cross section (TPACS) of these AuNRs in aqueous solutions. Under TPE of an 800-nm femtosecond laser, the TPACS of AuNRs with an aspect ratio of 3.2 was found to be the highest (about 3 × 109 GM), and that of AuNRs (aspect ratio of 2.7) was only 1.5 × 109 GM. The probe function of these two AuNRs was further compared in cell imaging studies using the human liver cancer cell (QGY) as the cell model. Both TPE PL image and confocal reflectance image of AuNR-loaded cells were acquired comparatively in measurements. The brightness and contrast of confocal reflectance images for these two AuNRs in cells are similar. In contrast, the PL images of cellular AuNRs (2.7) under TPE of 800 nm are weak but that of cellular AuNRs (3.2) is much better. These results show that when the LSPR band of AuNRs is coincided with the excitation wavelength, the TPACS of these AuNRs will be enhanced ensuring a good quality of cell imaging under TPE. The LSPR band is correlated to the aspect ratio of AuNRs. Therefore, in cell imaging studies with TPE, the aspect ratio effect of AuNRs should be taken into consideration.

Probing the behaviors of gold nanorods in metastatic breast cancer cells based on UV-vis-NIR absorption spectroscopy.

In this work, behaviors of positively-charged AuNRs in a highly metastatic tumor cell line MDA-MB-231 are examined based on UV-vis-NIR absorption spectroscopy in combination with inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy (TEM) and dark-field microscopic observation. It is found that characteristic surface plasmon resonance (SPR) peaks of AuNRs can be detected using spectroscopic method within living cells that have taken up AuNRs. The peak area of transverse SPR band is shown to be proportionally related to the amount of AuNRs in the cells determined with ICP-MS, which suggests a facile and real time quantification method for AuNRs in living cells. The shape of longitudinal SPR band in UV-vis-NIR spectrum reflects the aggregation state of AuNRs in the cells during the incubation period, which is proved by TEM and microscopic observations. Experimental results reveal that AuNRs are internalized by the cells rapidly; the accumulation, distribution and aggregation of AuNRs in the cells compartments are time and dose dependent. The established spectroscopic analysis method can not only monitor the behaviors of AuNRs in living cells but may also be helpful in choosing the optimum laser stimulation wavelength for anti-tumor thermotherapy.