Application of silver nanoparticles decorated with β-cyclodextrin in determination of 6-mercaptopurine by surface-enhanced Raman spectroscopy

Abstract

Although classical silver nanospheres were widely used as probes in surface-enhanced Raman spectroscopy (SERS), they lacked long-term stability. In the present work, silver nanoparticles decorated with β-cyclodextrin (β-CD–AgNPs) were used as probes and the stability was improved. The adsorption characteristics of 6-mercaptopurine (6-MP) on classical silver nanospheres and β-CD–AgNPs were studied cautiously using SERS, and chemical information about the molecular structure was obtained. The binding of the 6-MP molecule to the surface of AgNPs is based on the stable Ag–S covalent bond. The electrostatic adsorption between the protonated N⁷ atom or N¹ atom and the silver surface results in a notable Raman enhancement. The intensity of the Raman band of 6-MP at 866 cm⁻¹ was used to determine 6-MP. Experimental conditions, such as the volume of CD–AgNP solution, incubation time, pH value and concentration of sodium chloride, were examined and optimized. Compared with classical silver nanospheres, when β-CD–Ag nanoparticles were used, the sensitivity was higher, the analytical time was shorter, and the linear range was wider. A good linearity (r = 0.996) in the range of (0.040–2.0) × 10⁻⁷ mol L⁻¹ was obtained for determining 6-MP. The limit of detection was 0.024 × 10⁻⁷ mol L⁻¹ and the limit of quantification was 0.080 × 10⁻⁷ mol L⁻¹. This method was successfully applied to the determination of 6-MP in real samples and the results were satisfactory.