Stabile SERS Encoded Silver Silica Nanocomposites for Industrial Labeling – The Case of COVID-19 Diagnosis

Biosensors, especially those with a SERS readout, are required for an early and precise healthcare diagnosis. Unreproducible SERS platforms hamper clinical SERS. Here we report a synthetic procedure to obtain stabile, reproducible and robust highly-SERS performing nanocomposites for labelling. We control the NPs agglomeration and codification which results in an increased number of hot spots, thus exhibiting reproducible and superior Raman enhancement. We studied fundamental aspects affecting the plasmonic thiol bond resulting in pH exhibiting a determining role. We validated their biosensing performance by designing a SERS-based ELISA SARS-CoV-2 detections assay which exhibits limits of detection below 0.01 ng/μL.

Spray-Drying-Based Surface-Enhanced Raman Spectroscopy: Effect of the Silver Nanoparticle Aggregate Size on the Enhancement of Raman Scattering

We report a spray-drying method to fabricate silver nanoparticle (AgNP) aggregates for application in surface-enhanced Raman spectroscopy (SERS). A custom-built system was used to fabricate AgNP aggregates of three sizes, 48, 86, and 218 nm, from drying droplets containing AgNPs atomized from an AgNP suspension. Sample solutions of Rhodamine B (RhB) at 10–6, 10–8, and 10–10 M concentrations were dropped onto the AgNP aggregates as probe molecules to examine the enhancement of the Raman signals of the RhB. The ordering of the analytical enhancement factors (AEFs) by aggregate size at a given RhB concentration was 86 nm > 218 nm > 48 nm. The AEFs of the 86 nm AgNP aggregates were higher than those of the 218-nm aggregates, although the 218-nm aggregates had more hot spots where Raman enhancement occurred. This finding was attributable to the deformation and damping of the electron cloud in the highly aggregated AgNPs, reducing the sensitivity for Raman enhancement. When RhB was premixed with the AgNP suspension prior to atomization, the AEFs at 10–8 M RhB rose ~100-fold compared to those in the earlier experiments (the post-dropping route). This significant enhancement was probably caused by the increased opportunity for the trapping of the probe molecules in the hot spots.

Silver Flowerlike Structures for Surface-Enhanced Raman Spectroscopy

Micro- and nanoflowers are a class of materials composed of particles with high surface-to-volume ratio. They have been extensively studied in the last decade due to simple preparation protocols and promising applications in biosensing, as drug delivery agents, for water purification, and so on. Flowerlike objects, due to their highly irregular surface, may act also as plasmonic materials, providing resonant coupling between optical waves and surface plasmon excitations. This fact allows us to infer the possibility to use micro- and nanoflowers as effective surface-enhanced Raman scattering (SERS) substrate materials. Here, we report on the design and Raman enhancement properties of silver flowerlike structures, deposited on aluminum surface. A simple and cost-effective fabrication method is described, which leads to SERS substrates of high developed surface area. The morphology of the silver flowers on a nanoscale is characterized by self-organized quasiperiodic stacks of nanosheets, which act as plasmonic cavity resonators. The substrates were tested against rhodamine-6G (R6G) water solutions of concentration varying between 10−3 M and 10−7 M. Optimal SERS enhancement factors of up to 105 were established at R6G concentrations in the 10−6–10−7 M range.

Silver Flowerlike Structures for Surface-Enhanced Raman Spectroscopy

Micro- and nanoflowers are a class of materials composed of particles with high surface-to-volume ratio. They are being extensively studied in the last decade due to simple preparation protocols and promising applications in biosensing, as drug delivery agents, for water purification and so on. Flowerlike objects, due to their highly irregular surface, may act also as plasmonic materials, providing resonant coupling between optical waves and surface plasmon excitations. This fact infers for the possibility to use micro- and nanoflowers as effective surface-enhanced Raman scattering (SERS) substrate materials. Here, we report on the design and Raman enhancement properties of silver flowerlike structures, deposited on aluminum surface. A simple and cost-effective fabrication method is described, which leads to SERS substrates of high developed surface area. The morphology of the silver flowers on a nanoscale is characterized by self-organized quasiperiodic stacks of nanosheets, which act as plasmonic cavity-resonators. The substrates were tested against rhodamine-6G (R6G) water solutions of concentration varying between 10–3 M and 10–7 M. Optimal SERS enhancement factors of up to 105 were established at R6G concentrations in the range 10–6 – 10–7 M.

Cyclodextrin-assisted surface-enhanced Raman spectroscopy: a critical review

Numerous approaches have been proposed to overcome the intrinsically low selectivity of surface-enhanced Raman spectroscopy (SERS), and the modification of SERS substrates with diverse recognition molecules is one of such approaches. In contrast to the use of antibodies, aptamers, and molecularly imprinted polymers, application of cyclodextrins (CDs) is still developing with less than 100 papers since 1993. Therefore, the main goal of this review is the critical analysis of all available papers on the use of CDs in SERS analysis, including physicochemical studies of CD complexation and the effect of CD presence on the Raman enhancement. The results of the review reveal that there is controversial information about CD efficiency and further experimental investigations have to be done in order to estimate the real potential of CDs in SERS-based analysis. Graphical abstract

Stabile SERS Encoded Silver Silica Nanocomposites for Industrial Labeling – the Case of COVID-19 Diagnosis

Biosensors, especially those with a SERS readout, are required for an early and precise healthcare diagnosis. Unreproducible SERS platforms hampers the clinical translation of SERS. Here we report a synthetic procedure to obtain stabile, reproducible and robust highly-SERS performing nanocomposites for labelling. We control the NPs agglomeration and codification which results in an increased number of hot spots, thus exhibiting reproducible and superior Raman enhancement. We studied fundamental aspects affecting the plasmonic thiol bond resulting in pH exhibiting a determining role. We validated their biosensing performance by designing a SERS-based sandwich immunoassay against COVID-19. The limits of detection for the recombinant SARS-CoV-2 protein is below 0.01 ng/μL. We offered herein one nanostructure with robust and homogeneous SERS signal which can be potentially applied for biodiagnosis.