Greener One-Pot Synthesis of Gold Nanoparticle Glycoconjugates Using Functionalized Sugars

Abstract

Carbohydrates have been used to decorate metallic nanoparticles to form nanoglycoconjugates. However, the synthetic conditions typically require the utilization of increased temperatures and other reagents that negatively impact the stability of the conjugates. For the first time, this study is reporting the synthesis of gold–nanoparticle glycoconjugates (AuNP-GCs) in aqueous media at ambient temperatures. A series of sugars and small molecules acting as reducing, capping, and stabilizing agents were reacted with gold(III) chloride salt to produce the AuNP-GCs. Specifically, β-d-lactose, d-mannose, and d-galactose were utilized to synthesize (N-lactosyl)-5-aminosalicylic acid gold nanoparticles (L5AS-AuNPs), (N-galactosyl)-5-aminosalicylic acid gold nanoparticles (G5AS-AuNPs), and (N,N′-dilactosyl)diaminodiphenylethylene gold nanoparticles (LAEA-AuNPs), respectively. The formation of AuNP-GCs was monitored via ultraviolet–visible spectrophotometry, and the results confirmed the presence of the characteristic surface plasmon resonance peaks. Additional characterization data using transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction (XRD) confirmed the formation of AuNP-GCs. Of the AuNP-GCs produced, the XRD data confirmed that L5AS-AuNPs (∼20 nm), G5AS-AuNPs (∼5 nm), and LAEA-AuNPs (∼50 nm) were crystalline with predominant 111 orientations. All of the AuNP-GCs exhibited unique fluorescence and Raman activities except 4,4′-diaminodiphenylsulfone (PSA). The analytical enhancement factor, an important characterization parameter for assessing the surface-enhanced Raman scattering effect, was determined. LAEA-AuNPs resulted in enhancement factors of 11 × 104 and 6 × 104. LPSA-AuNPs resulted in enhancement factors of 8 × 104 and 6 × 104. The resulting AuNP-GCs retained stability for up to a year. 1H and 13C nuclear magnetic resonance spectra of the sugar ligand and the corresponding AuNP-GCs revealed that both hydroxyl groups on sugar moieties and aromatic protons enhanced the stability of AuNP-GCs. The findings showed that the chemistry and concentration of sugar ligands played a critical role in obtaining the desired size, shape, and optical properties.