SERS Hotspot Engineering by Aerosol Self‐Assembly of Plasmonic Ag Nanoaggregates with Tunable Interparticle Distance

Abstract

Surface‐enhanced Raman scattering (SERS) is a powerful sensing technique. However, the employment of SERS sensors in practical applications is hindered by high fabrication costs from processes with limited scalability, poor batch‐to‐batch reproducibility, substrate stability, and uniformity. Here, highly scalable and reproducible flame aerosol technology is employed to rapidly self‐assemble uniform SERS sensing films. Plasmonic Ag nanoparticles are deposited on substrates as nanoaggregates with fine control of their interparticle distance. The interparticle distance is tuned by adding a dielectric spacer during nanoparticle synthesis that separates the individual Ag nanoparticles within each nanoaggregate. The dielectric spacer thickness dictates the plasmonic coupling extinction of the deposited nanoaggregates and finely tunes the Raman hotspots. By systematically studying the optical and morphological properties of the developed SERS surfaces, structure–performance relationships are established and the optimal hot‐spots occur for interparticle distance of 1 to 1.5 nm among the individual Ag nanoparticles, as also validated by computational modeling, are identified for the highest signal enhancement of a molecular Raman reporter. Finally, the superior stability and batch‐to‐batch reproducibility of the developed SERS sensors are demonstrated and their potential with a proof‐of‐concept practical application in food‐safety diagnostics for pesticide detection on fruit surfaces is explored.

Nanosensor Applications in Plant Science

“…In plants, most peaks of the SERS spectra are attributed to adenine-containing materials, flavins, chlorophyll, and lipids [ 84 ]. SERS has been used extensively for the detection and determination of a wide range of biological molecules in plants [ 85 ], such as for plant hormones [ 86 , 87 ], and have practical applications in food-safety diagnostics such as for pesticide detection [ 88 , 89 ] ( Table 3 ).…”

“…SERS utilising gold nanoparticles has been used in the real-time monitoring of pesticide translocation in tomato plant tissues, including in the leaves and flowers [ 226 ]. In addition, flame aerosol technology has been used to rapidly self-assemble uniform SERS sensing films to detect pesticides [ 89 ]. This technology combines particle synthesis and facile film fabrication in a cost-effective and single process step.…”

“…Pesticide residues collected from the surface of an apple and dissolved in an ethanol solution were applied to the SERS substrate for SERS measurements to be taken. The presence of the pesticide parathion-ethyl was verified, demonstrating an application in food-safety diagnostics for pesticide detection on fruit surfaces [ 89 ].…”

Qualitative and quantitative detection and identification of two benzodiazepines based on SERS and convolutional neural network technology

“…Nanomaterials for providing hot spots and enhancing Raman signals play a crucial role in SERS technology. 34,35 At the same time, the training of CNN models requires large amounts of data and high-quality datasets; therefore, a base with good uniformity and repeatability is also essential. Based on the above two points, the properties of Ag NPs and the paper-based Ag NP substrate were characterized as shown in Fig.…”

Highly Efficient Near‐IR Photothermal Microneedles with Flame‐Made Plasmonic Nanoaggregates for Reduced Intradermal Nanoparticle Deposition

“…[36,38] It has been previously shown that tuning the dielectric SiO 2 spacer content in flame-made plasmonic nanoaggregates controls the interparticle distance of individual nanospheres which directly affects their optical extinction by plasmonic coupling. [36,[38][39][40] First, we studied the properties of Au nanocoatings as a function of SiO 2 content to fine-tune the photothermal effect in the NIR region. The UV/vis spectra in Figure 2a Second, to investigate whether the tuning of the plasmonic coupling can be attributed to varying dielectric spacer content in the Au/SiO 2 nanocoatings produced here, we analyzed the nanoscale morphology of Au/SiO 2 NPs via scanning transmission electron microscopy (STEM) images combined with energy-dispersive X-ray spectroscopy (EDX) and energy-loss spectroscopy (EELS).…”