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•Glucosamine binds to gold nanoparticles obtained from laser ablation in liquid.•Aggregation of glucosamine at 10 mM concentration causes new UV–VIS band at 625 nm.•SERS spectra of ...glucosamine in clean gold colloid were obtained for 0.1 mM and 1 mM glucosamine concentrations.•Strongest SERS bands are at 1563, 1586 and 1652 cm−1 (fron C-NH3+ bending modes), at 1165 cm−1 (C-N stretching coupled with C-C stretching motion) and at 1075 cm−1 (C-O stretching coupled with ring C-C stretching mode)
The binding of glucosamine to gold in water solutions of glucosamine hydrochloride mixed with clean colloidal gold nanoparticles obtained by laser ablation in liquid was studied using surface-enhanced Raman scattering (SERS), dynamic light scattering (DLS) and UV–VIS spectroscopy. The purpose of this study was to establish whether the binding of charged aminogroup to gold nanoparticles (AuNPs) is taking place, and if it does, how can it be identified by means of SERS.
The average size of dried gold nanoparticles was (20 ± 4) nm determined by averaging the sizes observed in transmission electron microscopy micrographs, which is smaller than the average size of gold nanoparticles in water solution as determined by DLS: (52 ± 2) nm. Upon adding the glucosamine solutions to gold colloid, average hydrodynamic diameter of ions was slightly larger for 0.1 mM glucosamine solution (55 ± 2 nm), while it increased to (105 ± 22) nm in the case of 1 mM solution, and was (398 ± 54) nm when 10 mM glucosamine solution was added.
Most prominent Raman bands observed both for 0.1 mM and 1 mM glucosamine solutions were located at 1165 cm−1, 1532 and 1586 cm−1 and assigned to C-N coupled with C-C stretching, and C-NH3+ deformation angles bending. In SERS spectrum of 1 mM GlcN+ solution, two strong bands at 999 and 1075 cm−1 were found and attributed to C-Oring stretching coupled with C-NH3+ bending (999 cm−1) and to dominantly C-O stretching vibration. The differences in SERS spectra are attributed to different number of glucosamine molecules that attach to gold nanoparticles and their orientation with respect to the metal particle surface, partly due to presence of beta anomers protonated at anomeric oxygen position. The assignment of glucosamine bands was further corroborated by comparison with vibrational spectra of alpha and beta glucose and of polycrystalline powder of glucosamine hydrochloride. For all three substances comprehensive calculation of vibrational density of states was conducted using density functional theory. Benchmark bands for polycrystalline glucose anomers distinction are 846 and 915 cm−1 for alpha glucose, and 902 cm−1 for beta glucose. However, the bands observed in SERS spectra of 0.1 mM glucosamine solution at 831, 899, and 946 cm−1 or in 1 mM solution at 934 cm−1 cannot be easily identified as belonging either to alpha or beta glucosamine anomer, due to complexity of atomic motions involved. The identification of vibrational bands associated with –CNH3+ group will aid SERS studies on amino acids, especially in cases when several atomic groups could possibly bind to AuNPs.
Modern diagnostic tools ever aim to reduce the amount of analyte and the time needed for obtaining the result. Surface-enhanced Raman spectroscopy is a method that could satisfy both of these ...requirements, provided that for each analyte an adequate substrate is found. Here we demonstrate the ability of gold-sputtered silicon nanowires (SiNW) to bind p-mercaptobenzoic acid in 10−3, 10−4 and 10−5M and adenine in 30 and 100μM concentrations. Based on the normal mode analysis, presented here for the first time, the binding of p-mercaptobenzoic acid is deduced. The intensity enhancement of the 1106cm−1 band is explained by involvement of the CS stretching deformation, and the appearance of the broad 300cm−1 band attributed to SAu stretching mode. Adenine SERS spectra demonstrate the existence of the 7H tautomer since the strongest band observed is at 736cm−1. The adenine binding is likely to occur in several ways, because the number of observed bands in the 1200–1600cm−1 interval exceeds the number of observed bands in the normal Raman spectrum of the free molecule.
Not annealed (left) Au sputtered Si nanowires are better SERS substrates. Display omitted
•Gold-sputtered not annealed silicon nanowire hybrid substrates were prepared by electroless chemical etching.•Not annealed substrates have better surface density of hot spots.•Normal modes of 4-mercaptobenzoic acid were calculated and assigned.
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