Micrometer-sized gold nanoplates: starch-mediated photochemical reduction synthesis and possibility of application to tip-enhanced Raman scattering (TERS)

Abstract

In this report, we propose a novel starch-mediated photochemical reduction method for synthesizing micrometer-sized gold nanoplates and the possibility of using them as a tip-enhanced Raman scattering (TERS) substrate. To reduce gold ions, a starch chain firstly forms a complex with AuCl(4)(-), and the gold ion is subsequently reduced by receiving an electron from a chloride ion and generating a chloride radical when the [AuCl(4)(-)-starch] complex is irradiated by sunlight. Due to the slow reaction rate and the capability of starch as a template, gold structure can thermodynamically grow along the (111) facet which is the lowest energy facet of the gold face-centered cubic (fcc) crystal. This method can provide various shapes of gold plates such as triangle, truncated triangle, hexagon, polygon, etc. The plate size can be controlled in the range from a few micrometers to more than one hundred micrometers by increasing the acidity of solution while the plate thickness is less than 100 nm. Potential application of the gold plates as TERS substrates is demonstrated by collecting Raman signals while approaching a silver-coated tungsten tip to the surface of the micrometer-sized gold nanoplate covered by crystal violet (CV) molecules. The results show that less than one hundred CV molecules can be detected in our study.

Facile interfacial synthesis of large sized 3D gold spherical architectures with strong individual particle SERS response and high reproducibility

“…The OEA molecules used not only lower the surface energy of the as-generated Au but also act as a capping agent. 53 As the pH value of the aqueous phase was adjusted to 4.0, the thorned spheres with a diameter of about 2 mm were obtained, but some irregular large particles were also generated concomitantly ( Fig. This is in favor of anisotropic growth and the formation of specific morphology, such as flexible nanoflake-constructed AuSAs in this case.…”

Photobiological synthesis of noble metal nanoparticles using Hydrocotyle asiatica and application as catalyst for the photodegradation of cationic dyes

“…The sunlight irradiation technique has been formerly reported for the synthesis of nanoparticles using few plant materials such as Allium sativum [29], Andrachnea chordifolia [30], Piper betle [31], Bacillus amyloliquefaciens [32] and Achyranthus aspera [33]. Apart from plant materials, dendrimers and starch are also used as reducing/stabilizing agents in the sunlight-induced synthesis of nanoparticles [34,35]. The nanoparticles produced by bio route have good stability due to the presence of capping agents like alkaloids, flavonoids and polyphenols, which are the major constituents present in the natural sources.…”

Tip enhanced Raman scattering: plasmonic enhancements for nanoscale chemical analysis

“…Similarly, dyes attached to other materials, for example TiO 2 , can be detected in TERS [112]. An interesting observation reported from experiments on crystal violet is only Raman bands associated with carbon double bonds are observed [113].…”