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An anisotropic structure, gold (Au) nanoplates was synthesized using a two-step wet chemical seed mediated growth method (SMGM) directly on the substrate surface. Prior to the synthesis process, poly-l-lysine (PLL) as a cation polymer was used to enhance the yield of grown Au nanoplates. The electrostatic interaction of positive charged by PLL with negative charges from citrate-capped gold nanoseeds contributes to the yield increment. The percentage of PLL was varied from 0% to 10% to study the morphology of Au nanoplates in term of shape, size and surface density. 5% PLL with single layer treatment produce a variety of plate shapes such as hexagonal, flat rod and triangular obtained over the whole substrate surface with the estimated maximum yield up to ca. 48%. The high yield of Au nanoplates exhibit dual plasmonic peaks response that are associated with transverse and longitudinal localized surface plasmon resonance (TSPR and LSPR). Then, the PLL treatment process was repeated twice resulting the increment of Au nanoplates products to ca. 60%. The thin film Au nanoplates was further used as sensing materials in plasmonic sensor for detection of boric acid. The anisotropic Au nanoplates have four sensing parameters being monitored when the medium changes, which are peak position (wavelength shift), intensity of TSPR and LSPR, and the changes on sensing responses. The sensor responses are based on the interaction of light with dielectric properties from surrounding medium. The resonance effect produces by a collection of electron vibration on the Au nanoparticles surface after hit by light are captured as the responses. As a conclusion, it was found that the PLL treatment is capable to promote high yield of Au nanoplates. Moreover, the high yield of the Au nanoplates is an indication as excellent candidate for sensing material in plasmonic sensor., Competing Interests: The authors have declared that no competing interests exist.

In this study, copper (Cu) is introduced as a foreign metal ion replacing platinum by modifying the recipe of GNBPs and the final structure obtained is gold bone nanorods (GBNRs). The aspect ratio and surface density of GBNRs were investigated by varying the growth time during the growth process from 30 minutes to 5 hours. It was found that the growth solution has been changed from colourless to light blue and violet colour with increasing growth time, indicating the formation of GBNRs. The UV-Vis analysis shows two resonance plasmon peaks for t-SPR and l-SPR at 583 nm and 766 nm with the intensity of 1.433 a.u and 2.236 a.u at the optimum 5 hours growth time. For morphological analysis, it was found that the sample with lower growth time produced gold nanosphere shapes and with increasing time, more GBNRs with large aspect ratios were produced. HR-TEM characterization reveals that bone nanorods are formed due to the influence of Cu foreign metal ions, which cause selective deposition of Au atoms onto {111} facet of gold nanorods, while simultaneously reducing the overgrowth rate of the {110} facet for the edge regions and the {100} facet for the tip regions of the nanorods. In addition, the influence of Cu foreign metal ions on the growth mechanism of Au nanoseeds into nanorods and the shape transformation of nanorods into bone nanorods are also discussed in this work. In conclusion, the GBNRs have been successfully synthesized using SMGM by induced Cu as foreign metal ions. [ABSTRACT FROM AUTHOR]

A simple technique of seed-mediated growth has been successfully performed to grow anisotropy gold nanoparticles on solid substrates. The growth of the gold nanoparticles has been carried out in the presence of a binary surfactant mixture of hexadecyltrimethylammonium bromide with two different molecular weights of a capping agent, namely polyvinylpyrrolidone: 40,000 and 55,000. In this study, the effect of process parameters, growth time and molecular weight of capping agent was investigated. The growth time shows a significant impact on the shape and size of nanoparticles. The shorter growth time produced small spherical to square-like shape particles, whereas bigger particles including nanorods, nanosquares and nanotriangles were formed with longer growth time. The shape controlling agent, polyvinylpyrrolidone, was used to synthesis gold nanoparticles. It was found that monodisperse gold nanoparticles with uniform shape and size are hardly obtained when polyvinylpyrrolidone 40,000 was used as capping agent. Polyvinylpyrrolidone 55,000 produced more uniform shape and size of gold nanoparticles. Thus, these process parameters were found affected to the size, shape, surface density and uniformity of gold nanoparticles. This sample was further applied as a sensing material in the detection of toxic fungicide, namely chlorothalonil. The sensitivity of the sensor system was determined by the changes in peak positions and intensities of the transverse and longitudinal surface plasmon resonance peaks on different medium, that is, air, deionized water and chlorothalonil solution. The sensor response of gold nanoparticles thin film in 30 mM chlorothalonil showed two resonance peaks in comparison to the control experiment without gold nanoparticle thin film. The gold nanoparticles thin film sensor was successfully synthesized and potentially useful as a sensing material for fungicide detection. [ABSTRACT FROM AUTHOR]

The gold nanobipyramids (GNBPs) have attracted wide attention in field of sensing, biomedicine, catalysis and optoelectronics due to strong local electric field enhancement and surface plasmon resonance originated from their sharp tips. In GNBPs synthesis process, CTAB is usually used as a surfactant which plays a role as capping and stabilizing agents. However, CTAB surfactant is known as a toxic and thus hindering the GNBPs application in a biomedical related research. In this paper, for the first time we reported the simplest approach for surface modification of CTAB surfactant capped GNBPs using an amine functionalization or known as amine functionalized GNBPs. The optical properties and functionalization mechanism were investigated in this paper. In addition, the detailed understanding of the GNBPs-amine bond and its physical arrangement also were explained in this work. The amine functionalized GNBPs systems have exciting potential applications in the field of biosensing and in targeted drug delivery platforms. [ABSTRACT FROM AUTHOR]

We demonstrate the structural reorganization of gold nanorods (GNRs) that could fine-tune localized surface plasmon resonance (LSPR) by using modified wet chemical synthesis on the solid substrate. Controlling the growth solution ageing time using the modifiable GNRs is an approach to overcome the limitations of rods formation due to inhomogeneous and uncontrollable size and aspect ratio. In this study, the suitable ageing time of GNRs was determined to produce optimum GNRs in terms of surface density and aspect ratio. As the ageing time was increased from 30 min to 24 h, the colour of the growth solution was changed from light to dark purple. The change is associated with the density of the nanorods formation. The optical spectral peaks of GNRs occur in a range between 500 nm and 800 nm in the visible and near-infrared region spectrum for transverse surface resonance (t-SPR) and longitudinal surface resonance (l-SPR), respectively. From the morphological analysis, it was found that 20 h ageing time resulting in high density and homogeneous GNRs with 74.81% surface density with 4.23 ± 0.04 aspect ratio. Hence, the growth ageing time of GNRs can be manipulated to control their shape evolution and dimension in terms of size and aspect ratio. The controllable aspect ratio and size GNRs can be potentially used as sensing material in plasmonic applications. [ABSTRACT FROM AUTHOR]

The structure of gold nanobipyramids (GNBPs) is very promising for specific Localized Surface Plasmon Resonance (LSPR) properties, and thus potentially to be used in various applications, especially in sensing. This work reported growth time dependency on the formation of GNBPs for application in LSPR sensors for chlorpyrifos detection. The study on the growth time found that GNBPs formation at the initial stage is dominated by elongation direction and its optimum growth time is 2 h. The optimum GNBPs with 106.32 ± 2.50 in length, 42.17 ± 0.82 in width and an aspect ratio of 2.55 ± 0.08 were implemented as a sensing material for direct and rapid localized surface plasmon resonance (LSPR) sensors to detect chlorpyrifos. The mechanism is based on the change in spectrum intensity and wavelength shift between GNBPs when tested in deionized water and chlorpyrifos solution. The change arises from molecular interaction between the targeted analyte and the sensing material and effectively changes the dielectric features of the medium. The presence of chlorpyrifos in the 1 – 100 mg/mL concentration range has been successfully detected. The proposed sensor offers better sensitivity as high as 1.22 times for transverse LSPR mode and 2.04 for longitudinal LSPR mode than the LSPR sensor based on gold nanosphericals. Moreover, the sensor stability and repeatability response showed a reliable performance for determining chlorpyrifos. Furthermore, this sensor also shows high selectivity towards chlorpyrifos compared to other organophosphate and organochlorine pesticides such as malathion, chlorothalonil, and triclopyr-butotyl. [ABSTRACT FROM AUTHOR]

The presence of sharp tips and edges of gold nanobipyramids (GNBPs) lead to strong local electromagnetic field enhancement. Herein for the first time we present a study on efficacy of additive acid on the formation of GNBPs. The effect of additive acid type and its concentration in growth solution were investigated to obtain various yield and aspect ratio of GNBPs. Morphological characterization shows the nanoseeds that were grown in growth solution prepared using HCl, H 2 SO 4 , and HF at concentration from 0 to 1 mL produced GNBPs with yield ranges from 5.21 ± 0.44 to 91.46 ± 3.32% and aspect ratio from 2.00 ± 0.02 to 2.76 ± 0.05. The optical response of GNBPs exhibit dual plasmon band at wavelength around 550 nm–570 nm, corresponding to transverse surface plasmon resonance (t-SPR) and at wavelength around 700 nm–800 nm, corresponding to longitudinal surface plasmon resonance (l-SPR). The presented approach may be used to produce tunable morphological GNBPs nanostructures which potentially used in sensors, SERS, catalysis, and photonics. (A) Schematic representation of the effect of additive acid types on the morphology of GNBPs and (B) TEM image of GNBPs. Image 1 • Effects of additive acids on the morphological properties of GNBPs were investigated. • The surface density of GNBPs can be adjusted from 5.21 ± 0.44 to 91.46 ± 3.32%. • The aspect ratios of GNBPs from 2.00 ± 0.02 to 2.76 ± 0.05 were obtained. • The presented approach may be used to produce tunable morphological GNBPs. [ABSTRACT FROM AUTHOR]