Design and Synthesis of Novel Raman Reporters for Bioorthogonal SERS Nanoprobes Engineering

Abstract

Surface-enhanced Raman spectroscopy (SERS) exploiting Raman reporter-labeled nanoparticles (RR@NPs) represents a powerful tool for the improvement of optical bio-assays due to RRs’ narrow peaks, SERS high sensitivity, and potential for multiplexing. In the present work, starting from low-cost and highly available raw materials such as cysteamine and substituted benzoic acids, novel bioorthogonal RRs, characterized by strong signal (103 counts with FWHM < 15 cm−1) in the biological Raman-silent region (>2000 cm−1), RRs are synthesized by implementing a versatile, modular, and straightforward method with high yields and requiring three steps lasting 18 h, thus overcoming the limitations of current reported procedures. The resulting RRs’ chemical structure has SH-pendant groups exploited for covalent conjugation to high anisotropic gold-NPs. RR@NPs constructs work as SERS nanoprobes demonstrating high colloidal stability while retaining NPs’ physical and vibrational properties, with a limit of detection down to 60 pM. RR@NPs constructs expose carboxylic moieties for further self-assembling of biomolecules (such as antibodies), conferring tagging capabilities to the SERS nanoprobes even in heterogeneous samples, as demonstrated with in vitro experiments by transmembrane proteins tagging in cell cultures. Finally, thanks to their non-overlapping spectra, we envision and preliminary prove the possibility of exploiting RR@NPs constructs simultaneously, aiming at improving current SERS-based multiplexing bioassays.

Multilayered Bioorthogonal SERS Nanoprobes Selectively Aggregating in Human Fluids: A Smart Optical Assay for β-Amyloid Peptide Quantification

“…Multilayered Au@RR@AuNPs were realized starting with the synthesis of 50 ± 1 nm diameter gold nanospheres, which serve as cores, followed by immediate exchange of the stabilizing agent (sodium citrate) with a Raman reporter, recently synthesized and characterized by our group . Then, an additional gold shell of desired thickness was grown by adding gold salt (HAuCl 4 ) with citrate ions serving as both capping and mild reducing agents.…”

“…Multilayered Au@RR@AuNPs were realized starting with the synthesis of 50 ± 1 nm diameter gold nanospheres, which serve as cores, followed by immediate exchange of the stabilizing agent (sodium citrate) with a Raman reporter, recently synthesized and characterized by our group. 16 Then, an additional gold shell of desired thickness was grown by adding gold salt (HAuCl 4 ) with citrate ions serving as both capping and mild reducing agents. The volume and the concentration of the RR solution in the ligand exchange step were critical parameters to be adjusted to avoid particle–particle aggregation as well as to achieve full gold surface covering, resulting in a higher Raman signal ( Figure S1 , Supporting Information).…”

Portable SERS-Based POCT Kit for Ultrafast and Sensitive Determining Paraquat in Human Gastric Juice and Urine

“…26 Introducing salt into the colloidal solution is a common practice to overcome this limitation, aiming to foster nanoparticle aggregation and induce localized electromagnetic (EM) field enhancement. 27 The addition of KI expels the anionic citrate molecules from the NP surface, allowing the analyte molecules to attach to the gold surface, where I − and positively charged PQ interact electrostatically. The most pronounced EM interactions materialize when the nanogap between particles diminishes to less than 1 nm.…”

Emerging integrated SERS-microfluidic devices for analysis of cancer-derived small extracellular vesicles

“…119,120 Typically, aromatic compounds such as 5,5′-dithiobis (2-nitrobenzoic acid) (DTNB), 4-mercaptobenzoic acid (4-MBA), 4-mercaptopyridine (4-MPY) are used as Raman reporters because of their ability to form covalent bonds with the metallic core via –SH and –NH 2 groups and distinct Raman spectra. 121,122…”

“…119,120 Typically, aromatic compounds such as 5,5′dithiobis (2-nitrobenzoic acid) (DTNB), 4-mercaptobenzoic acid (4-MBA), 4-mercaptopyridine (4-MPY) are used as Raman reporters because of their ability to form covalent bonds with the metallic core via -SH and -NH 2 groups and distinct Raman spectra. 121,122 To prevent unspecific binding to the surface of nanotag the protective layer around it is necessary to minimise interference during the detection process. Typically, silica, polymers, metal-organic frameworks, polyethylene glycol (PEG) and bovine serum albumin (BSA) are commonly used as the protective shell due to their biocompatibility, high uniformity, and stability.…”