الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Food additives, which play a crucial role in enhancing food quality, have raised concerns regarding their carcinogenicity, particularly in the case of malachite green (MG) and β-myrcene. These additives were removed from the United States Food and Drug Administration (US FDA) approved list due to identified cancer risks. This study delves into the intricate realm of trace detection using surface-enhanced Raman spectroscopy (SERS) by harnessing the local plasmon of silver nanoparticle substrates. Different chemical methods have been employed to synthesize various silver nanostructures, such as nanospheres, nanorods, nanotriangles, and nanostars. A comprehensive characterization of these diverse shapes of the prepared nanoparticles has been executed, using transmission electron microscope (TEM) analysis to determine the shapes of nanoparticles and UV/visible (UV/Vis) spectrophotometry to reveal distinct plasmon resonance peaks, influenced by the morphology, aggregation, and the surrounding medium. In addition, dynamic light scattering (DLS) and zeta potential (ZP) to determine different sizes and charges, respectively.
Three different plasmonic substrates; (one liquid (L) and two solids (S1, S2)) were investigated using silver nanostars (AgNSs) as SERS substrates. We provide a comprehensive comparison between solid and liquid SERS substrates, utilizing diverse morphologies of the AgNSs for the sensitive detection of malachite green and β-myrcene. Although SERS in the colloidal method provides good reproducibility with a 3.4% relative standard deviation, it suffers from instability over time.
In the case of solid substrates, the importance of the functionalization process of solid substrates to enhance reproducibility has been discussed. The Raman mapping technique is applied to explore the uniformity of the Raman signal on the solid substrate, especially after the functionalization process. Finite difference time domain (FDTD) simulations underscore the influence of core size and arm number on local electric fields. The simulation shows the robust hot spots along the edges and the influence of the surrounding medium on the electric field intensity. SERS examinations reveal that liquid substrates outperform their solid counterparts, achieving a remarkable limit of detection (LOD) of 0.037 fM for MG, a minimum detected value compared to other reported values that reach 2.5 nM. These findings are comprehensively discussed in the context of the FDTD simulation results.
We also argue observed disparities in enhancement factors between the two solid substrates, S1 and S2, which were prepared using distinct deposition strategies. The S1 was prepared by centrifuging the analyte molecules with AgNSs before deposition on the glass substrate, while S2 was prepared through the deposition DROP of the analyte molecules on the dry plasmonic substrate of AgNSs.
Although there is limited published work available on the Raman spectra of β-myrcene, we have achieved the minimum LOD of β-myrcene of 70 pM with S2 substrate. This result for β-myrcene is due to the incompatibility of β-myrcene with the liquid substrate.