Elucidation of the bonding of a near infrared dye to hollow gold nanospheres – a chalcogen tripod

Abstract

Determining how Raman labels orientate on the surface of HGNs to aid in future advancements of designing NIR nanosensors.

Design and evaluation of Raman reporters for the Raman-silent region

“…Dye 9 was synthesized by emulating the work performed by VanAllan and coworkers [20], in which cyano-containing pyrylium dyes could be synthesized by allowing cyanoacetic acid to react with pyranones. The chalcogen tripod [25] was adapted in order to engender reporter molecules with higher affinity for typical SERS substrates such as gold or silver nanoparticles. 2,6-di(thiophen-2-yl)-4H-thiopyran-4one (10a) was treated with dimethyl sulfate, thus yielding 4-methoxy-2,6-di(thiophen-2-yl)thiopyrylium hexafluorophosphate (17) in 52% yield [26].…”

In memory of Michael R. Detty, PhD

“…Using these novel dyes as resonant Raman reporters in Moritz Kircher's Lab at Memorial Sloan Kettering Cancer Center, we produced SERRS nanoparticles with attomolar sensitivity [2]. Together with researchers at the University of Strathclyde, Mike demonstrated how the contact angle of the Raman reporter on the gold nanoparticle surface dictated its Raman signature opening up a whole new realm of Raman-based sensing applications [4].…”

Sensitive SERS nanotags for use with a hand-held 1064 nm Raman spectrometer

“…Dyes 1–17 incorporate sulfur and selenium atoms in the chalcogenopyrylium core and, as previously mentioned, the 2-thienyl and 2-selenophenyl substituents on select members of this library provide unique attachment points for adsorbing onto the gold surface of the HGNs [ 28 ]. It has previously been reported that dye 14 binds to the HGN surface with a chalcogen tripod arrangement, essentially with two selenium atoms and one sulfur atom directly facing the gold surface [ 17 ]. SERS, SERRS, theoretical calculations and sum-frequency generation vibrational spectroscopy were all used to define the orientation and manner of attachment.…”

“…Nonetheless, the poor signal response can be overcome by attaching or trapping molecules close to the surface of metallic nanoparticles, thus giving rise to the phenomenon known as surface-enhanced Raman scattering (SERS) [1,16]. The intensity of scattering from SERS is dependent on coupling with the plasmon from the enhancing surface and can give intense signals well into the infrared [17,18]. Enhancements of 10 6 have been reported, thus are several orders of magnitude greater than those reported for conventional Raman scattering [19][20][21].…”

“…It should be noted that the nanotags were compared based on their intensities. Therefore, when comparing the most intense peak at approximately 1600 cm −1 which arises due to heterocyclic aromatic ring stretching within the molecule [17,28,36,37]; the pentamethine dyes (16 and 17) produced the strongest SERS response with the hand-held spectrometer, followed by the trimethine substituents, then the monomethine substituents and finally the commercial reporters produced the weakest SERS response. Generally, these results abide by the selection rules of SERRS; with The SERRS effect alone, however, could not be used to determine which nanotag would produce the best Raman signals as we have shown previously that the number of sp 2 carbons present in the chalcogenopyrylium backbone and functional groups used for binding to the HGN surface all have an effect on the signal [28,29].…”