Spontaneous formation of branched nanochains from room temperature molten amides: visible and near-IR active, SERS substrates for non-fluorescent and fluorescent analytes

Abstract

Highly stable, branched gold nanoworms are formed spontaneously in an acetamide-based room temperature molten solvent without any additional external stabilizing or aggregating agent. The nanoworms can be anchored onto solid substrates such as indium tin oxide (ITO) without any change in morphology. The anchored nanoworms are explored as substrates for surface enhanced Raman scattering (SERS) studies using non-fluorescent 4-mercaptobenzoic acid (4-MBA) and fluorescent rhodamine 6G (R6G) as probe molecules. The anchored nanostructured particles respond to near IR (1064 nm) as well as visible (785, 632.8 and 514 nm) excitation lasers and yield good surface enhancement in Raman signals. Enhancement factors of the order 10 6 -10 7 are determined for the analytes using a 1064 nm excitation source. Minimum detection limits based on adsorption from ethanolic solutions of 10 28 M 4-MBA and aqueous solutions of 10 27 M R6G are achieved. Experimental Raman frequencies and frequencies estimated by DFT calculations are in fairly good agreement. SERS imaging of the nanostructures suggests that the substrates comprising of three dimensional, highly interlinked particles are more suited than particles fused in one dimension. The high SERS activity of the branched nanoworms may be attributed to both electromagnetic and charge transfer effects.

SERS and DFT investigation of the adsorption behavior of 4-mercaptobenzoic acid on silver colloids

“…The observed bands are similar to those found in previous works [10,14,16,33]. 4-MBA shows two strong SERS bands at 1587 (ring C-C stretch, asymmetric C-H in-plane bending) and 1080 cm −1 (aromatic ring breathing, symmetric C-H in-plane bending, C-S stretching) [32,33]. The band observed around 1417 cm −1 was assigned to v s (COO − ), symmetric stretching vibration of the carboxylate group.…”

“…The band observed around 1417 cm −1 was assigned to v s (COO − ), symmetric stretching vibration of the carboxylate group. At pH 2, the broad feature rises at 1296 and 1318 cm −1 belongs to the ring inplane C-H bending mode and C-O stretching mode, respectively [32]. It indicates that the carboxylate group is protonated.…”

“…It indicates that the carboxylate group is protonated. At neutral and alkaline conditions, the 846 and 719 cm −1 bands were assigned to ı(COO − ), bending vibration and (CCC), out-of-plane ring vibration, respectively [10,32]. At acidic conditions, the above two bands shift to 801 and 696 cm −1 .…”

Controllable preparation of graphene oxide/metal nanoparticle hybrids as surface-enhanced Raman scattering substrates for 6-mercaptopurine detection

“…According to previous studies, the predominant bands were located at 1084, 1188, and 1590 cm À1 , which were assigned to a 1 modes of vCS, dCH, and vCC. 21,22 In the SERS spectrum, the vCS band at 1084 cm À1 shied to 1079 cm À1 , due to Ag-S bond formation. The band dCH at 1188 cm À1 shied to 1180 cm À1 , and the vCC shied from 1590 cm À1 to 1587 cm À1 aer pMBA adsorption on the silver surface.…”

Spontaneous assembly of iridium nanochain-like structures: surface enhanced Raman scattering activity using visible light

“…It was also demonstrated both theoretically and experimentally that strong electromagnetic field enhancements would arise at the interparticle junctions in nanoparticle aggregates upon interaction with visible radiation. 31,32 Concentration dependent studies were carried out by dipping the Ir modified glass substrate into 2 mL of different concentrations of the analyte (1 mM to 0.1 mM) for 30 minutes and subsequently drying the substrate before Raman spectral measurements were carried out. The detection limit for 4-MPy in the present study is observed to be 0.1 mM.…”