This study describes an inexpensive, simple and green method to form silver nanoparticles from different leaf extracts of Achyranthes aspera and Scoparia dulcis plants. The silver nitrate is reduced by Achyranthes aspera and Scoparia dulcis leaf extracts respectively to generate two silver nanoparticle types symbolized as AA.AgNPs and SD.AgNPs. The optical absorption, size and morphology of silver nanoparticles are significantly impacted by extract types. The ultraviolet visible spectrum of AA.AgNPs shows a 433-nm peak being more broadened than that of SD.AgNPs. The Fourier infrared transform spectra of two of these silver nanoparticles revealed that their surface is modified by organic constituents from extracts, and thus they are stabilized in solution without any additional reaction. Images from transmission electron microscopy and scanning electron microscope indicate that AA.AgNPs are in clusters with the size of 8–52 nm almost possessing oval shape, while SD.AgNPs are smaller size of 5-45 nm separated well in diversified shapes (spherical, triangle, quadrilateral and hexagonal). Moreover, both AA.AgNPs and SD.AgNPs exhibit the highly antifungal effect against Aspergillus niger, Aspergillus flavus and the most strong impact on Fusarium oxysporum. For these obtained results, two new silver nanoparticles are promising fungicides for various applications of medical and agricultural fields.

It is essential to develop a simple and sensitive method to rapidly detect residual fungicides in agricultural products to protect human health. So far, little studies have been reported on potential application of gold nanospheres (AuNSps) as a surface plasmon resonance based sensor for in-situ detection of residual fungicides. Therefore, in this study, we investigated the potential application of AuNSps as a surface plasmon resonance based sensor for in-situ detection of fungicides. AuNSps were successfully synthesized via a seed-mediated method with some modifications. Firstly, gold nanoseeds were made during the reduction of chloroauric acid by trisodium citrate dihydrate (TSC). Then, AuNSps were grown from the seeds by using HAuCl 4 , TSC and EDTA. AuNSps were subsequently dropped on a glass substrate before covered by thiophanate methyl, a broad-spectrum systemic fungicide. The AuNSps coated glass substrate was subsequently dried in the air for further surface-enhanced Raman spectroscopy (SERS) measurements. Optical properties, shape and size of AuNSps were confirmed by UV-vis spectroscopy, XRD, SEM-EDX and TEM. The results showed that AuNSps were successfully synthesized with the size of 53 nm, and their resonance peak was located at 560 nm. The Raman signal intensity of thiophanate methyl covered on AuNSps is higher than that without AuNSps, indicating SERS effects of AuNSps deposited glass substrate.

The use of gold nanorods (AuNRs) as surface-enhanced Raman scattering (SERS) substrates has gained much attraction due to their remarkably aspect-ratio-dependent plasmonic properties. In this report, we described the development of AuNRs with a high aspect ratio and longitudinal surface plasmon resonance (LSPR) >850 nm through a hydroquinone-based fabrication with minor modifications. The synthesis started with the reduction of chloroauric acid (HAuCl4) by sodium borohydride (NaBH4) to make gold nanoseeds from which AuNRs were grown with the aid of silver nitrate (AgNO3), HAuCl4, cetyltrimethylammonium bromide (CTAB), and hydroquinone (HQ). Scanning electron microscopy coupled with energy-dispersive X-ray (SEM-EDX), Transmission electron microscope (TEM), X-ray diffraction (XRD) and Ultra-violet-Visible spectroscopy (UV-Vis) were performed to study the shape, size, and structural and optical properties of AuNRs, respectively. The results showed that AuNRs with high aspect ratios (AR > 3) were single crystals with a heterogenous size distribution, and that the growth of Au nanoseeds into AuNRs took place along the [001] direction. AuNRs exhibited two plasmon resonance peaks at 520 nm and 903 nm, while gold nanoseeds had only a plasmon resonance peak at 521 nm. The as-synthesized AuNRs also showed SERS effects for thiophanate methyl, a broad-spectrum fungicide, with the limit of detection down to 5 mg/L of the fungicide. AuNR-coated glass can serve as a SERS-based sensing platform for rapid detection of thiophanate methyl with high sensitivity and reproducibility.