Dielectric Nanoparticles Coated upon Silver Hollow Nanosphere as an Integrated Design to Reinforce SERS Detection of Trace Ampicillin in Milk Solution

Abstract

Surface-enhanced Raman scattering (SERS) technique is competent to trace detection of target species, down to the single molecule level. The detection sensitivity is presumably degraded by the presence of non-specific binding molecules that occupy a SERS-active site (or hot spot) on the substrate surface. In this study, a silver hollow nano-sphere (Ag HNS) with cavity has been particularly designed, followed by depositing dielectric nanoparticles (Di NPs) upon Ag HNS. In the integrated nanostructures, Di NPs/Ag HNS were furthermore confirmed by cutting through the cross sections using the Focused Ion Beam (FIB) technique, which provides the Scanning Electron Microscope (SEM) with Energy-dispersive Spectroscope (EDS) mode for identifying the distribution of Di NPs upon Ag HNS. The results have indicated that Di NPs/Ag HNS exhibits small diameter of cavity, and among Di NPs in this study, Al 2 O 3 with lower dielectric constant provides a much higher SERS enhancement factor (e.g.,~6.2 × 10 7 ). In this study, to detect trace amounts (e.g., 0.01 ppm) of Ampicillin in water or milk solution, Al 2 O 3 NPs/Ag HNS was found to be more efficient and less influenced by non-specific binding molecules in milk. A substrate with integrated plasmonic and dielectric components was designed to increase the adsorption of target species and to repulse non-specific binding molecules from SERS-active sites.Coatings 2020, 10, 390 2 of 15 techniques to provide rapid, food quality preserved, and bio-safety evaluation or analysis for related laboratories or industries [9][10][11].Surface-enhanced Raman scattering (SERS) technique delivers fingerprint information about a given substance using nearly roughened metal surfaces, metal nanoparticles (NPs), or metal nanostructures owing to their strong effect on the Raman-active peak(s) of target molecule. The enhancement of Raman-active modes is mainly due to the contribution of two effects through chemical mechanism (CM) and electromagnetic mechanism (EM) [12][13][14][15]. The CM depends on the adsorption of target molecules upon the "hot spots", which are generated at SERS-active sites; charge transfer occurs between the target molecule and the substrate, which may be enhanced by the polarizability of the molecule [16]. On the other hand, the EM relies on the physical attributes of the substrate as it is highly dependent on the composition, shape, and size of the metal substrate, which affect localized surface plasmon resonance (LSPR) in the metallic nanostructures. Therefore, available hot spots are formed in between the plasmonic nanostructures [15]. Aside from the mentioned factors, the intensity of SERS signals is also affected by the induced Raman laser wavelength, and thereafter, the interactions of target molecules toward the substrate [17,18].It has been widely accepted that the formation of Raman-active sites generates a highly enhanced EM field that leads to high enhancement factor (EF). The "hot spots" can be observed or even predicted using computer simulation and modeling to de...

A label-free and selective SERS-based sensor for determination of ampicillin contamination in water using a fabric gold–silver alloy substrate with a handheld Raman spectrometer

“…The performance of other representative SERS sensors toward ampicillin determination in DI water is summarized in Table 1. 42–47 The LOD of our SERS fabric substrate for ampicillin (1.3 μM) detection using a handheld Raman spectrometer was higher than those of the previously reported SERS substrates using a Raman microscope. It is because a Raman microscope coupled with an objective lens with higher magnification (100× or 50×) offers great SERS signal amplification than a portable one with lower magnification objective lenses (<5×).…”

“…It is because a Raman microscope coupled with an objective lens with higher magnification (100× or 50×) offers great SERS signal amplification than a portable one with lower magnification objective lenses (<5×). 13,48–50 However, our SERS substrate with a handheld Raman spectrometer can possibly be used for fast-screening and onsite detection.…”

Microwave Split Ring Resonator Sensor for Determination of the Fluids Permittivity With Measurement of Human Milk Samples

“…The sensors are able to determine the dielectric properties of food by resonance frequency (Amar et al., 2020). This method has led to the amount of rare particles present in food such as ampicillin (Lee et al., 2020). The results also determined that among nutrients, protein has the greatest effect on the dielectric properties of milk (Zhu et al., 2014), but these results do not have the same answer at all frequencies because in (Abdullah et al., 2019) has been showed that at different frequency bands these results may change and many factors are involved in this issue.…”

Challenges of SERS technology as a non-nucleic acid or -antigen detection method for SARS-CoV-2 virus and its variants

“…Aside from the advantages and limitations of SERS technology in comparison to other diagnostic methods, it is also important to emphasize that since a SERS-active substrate, the main component, is comprised of a plasmonic metal or a dielectric material ( Lee et al, 2020 ; Sitjar et al, 2019 ); it needs not be used urgently as it is stable and thus could be stored for a long time, given that a proper storage condition and environment are followed. Processes involved in the fabrication of substrates are thus crucial in coming up with an effective SERS-active substrate.…”