Flexible and Transparent Substrates Based on Gold Nanoparticles and TiO2 for in Situ Bioanalysis by Surface-Enhanced Raman Spectroscopy

Abstract

Flexible and transparent substrates are emerging as low cost and easy-to-operate support for surface-enhanced Raman spectroscopy (SERS). In particular, in situ SERS detection approach for surface characterization in transmission modality can be efficiently employed for non-invasive analysis of non-planar surfaces. Here we propose a new methodology to fabricate a homogenous, transparent, and flexible SERS membrane by the assistance of a thin TiO2 porous layer deposited on the PDMS surface, which supports the uniform loading of gold nanoparticles over large area. The substrate was first characterized for homogeneity, sensitivity and repeatability using a model molecule for SERS, i.e., 7-mercapto-4-methylcoumarin. Satisfactory intra-substrate uniformity and inter-substrates repeatability was achieved, showing an RSD of 10%, and an analytical sensitivity down to 10 nM was determined with an EF of 3.4 × 105 ± 0.4 × 105. Furthermore, SERS detection of pyrimethanil (PMT), a commonly employed pesticide in crops for human consumption, was performed in situ, exploiting the optical transparency of the device, using both model surfaces and non-flat bio-samples. PMT contamination at the phytochemical concentration levels corresponding to commonly used infield doses was successfully detected on the surface of the yellow Ficus benjiamina leaves, supporting the use of this substrate for food safety in-field application.

Insight on Mercapto-Coumarins: Synthesis and Reactivity

“…It is also indicated as a suitable matrix for the analysis of small molecular compounds [ 40 ]. The other described incorporation of this highly valuable scaffold is as a reporter molecule [ 41 ], reporters for thiol interactions at the nanoparticle surface [ 42 ], fluorescent probe [ 43 , 44 , 45 ], sugar acceptor [ 46 ], Raman reporter [ 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 ], an excellent substrate for fluorescence spectroscopy [ 57 ], photodimerizable and healable reactant [ 58 ], fluorescent dye [ 59 , 60 ], and probe molecule on gold-coated silicon nanowires [ 61 ].…”

Influence of Plasma Treatment Parameters on the Structural-Phase Composition, Hardness, Moisture-Resistance, and Raman-Enhancement Properties of Nitrogen-Containing Titanium Dioxide

“…One should also keep in mind the possibility of the formation of a TiO 2 dielectric–TiN semiconductor composite structure during the action of nitrogen plasma in an open atmosphere on the titanium surface. Composite and heterostructures based on TiO 2 are used as surface-enhanced Raman spectroscopy (SERS) substrates [ 18 , 19 ]. It should be noted that the influence of the crystal structure of TiO 2 on its Raman-active properties has not been studied.…”

DNA-Induced Assembly of Silver Nanoparticle Decorated Cellulose Nanofiber: A Flexible Surface-Enhanced Raman Spectroscopy Substrate for the Selective Charge Molecular Detection and Wipe Test of Pesticide Residues in Fruits

“…The mentioned general methods for conventional rigid or colloids SERS substrates should complexly purify the target analytes and follow tedious preparation processes before analysis, so they are not suitable for practical application . Thus, the existing research focus gradually shifts to flexible SERS substrates exhibiting characteristic superiorities over conventional rigid substrates. − Thus far, plentiful materials have acted as the backbone to construct flexible SERS substrates (e.g., polymers, filter papers, and graphene). The properties of the mentioned matrix materials determined the application directions of the SERS substrates.…”