Rapid Surface Enhanced Raman Scattering (SERS) Detection of Sibutramine Hydrochloride in Pharmaceutical Capsules with a β-Cyclodextrin- Ag/Polyvivnyl Alcohol Hydrogel Substrate

Abstract

Sibutramine hydrochloride (SH) is a banned weight-loss drug, but its illegal addition to health products is still rampant. This suggests a very urgent need for a fast and precise detection method for SH. Surface Enhanced Raman Scattering (SERS) is a promising candidate for this purpose, but the weak affinity between SH and bare metal limits its direct SERS detection. In the present work, β-cyclodextrin was capped in situ onto the surface of Ag nanoparticles to function as a scaffold to capture SH. The obtained Ag nanoparticles were encapsulated into polyvinyl alcohol (PVA) to fabricate a SERS active hydrogel with excellent reproducibility. A facile SERS strategy based on such substrate was proposed for trace SH quantification with a linear range of 7.0-150.0 µg·mL^-1, and a detection limit low to 3.0 µg·mL^-1. It was applied to analyze seven types of commercial slimming capsules with satisfactory results, showing good prospect for real applications.

Keywords: Surface Enhanced Raman Scattering; polyvinyl alcohol; sibutramine hydrochloride; β-cyclodextrin.

Figure 1

Characterization of the β-CD-Ag/PVA substrate. (a) Photograph of the β-CD-Ag/PVA sol before hydrogel formation; (b) Photograph of the β-CD-Ag/PVA hydrogel; (c,d) SEM images of the β-CD-Ag/PVA hydrogel at different magnification.

Figure 2

(a) Comparison of the SERS performance for SH detection with different substrates; (b) Adsorption kinetics of SH on PVA, Ag/PVA and β-CD-Ag/PVA (298 K).

Figure 3

(a) UV-Vis spectra of Ag NP suspensions prepared with different synthesis pH values ranging from 9.5 to 13.35; (b) SERS spectra of SH on β-CD/Ag NPs synthesized at different pH values; (c) UV-Vis spectra of Ag NPs obtained at different ratio of AgNO₃ and β-CD: 0.2:1, 0.5:1, 1:1, 3:1, 6:1, and 12:1; (d) TEM micrograph of β-CD/Ag obtained with AgNO₃ and β-CD at a ratio of 1:1 ratio.

Figure 4

SERS intensity change of SH at 1594 cm⁻¹ using β-CD-Ag/PVA with different densities of β-CD-Ag NPs (from 1 to 9 mmol·L⁻¹).

Figure 5

Raman responses of the substrate β-CD-Ag/PVA after being soaked in water at different pH values.

Figure 6

(a) SERS spectra of different concentrations of SH; (b) A correlation between the Raman intensity at 1594 cm⁻¹ and the concentration of SH. The inset in (b) showed the linear range within 7–150 µg·mL⁻¹ between the intensity at 1594 cm⁻¹ and the concentration of SH.

Figure 7

(a) Results of confirming the selectivity for SH detection; (b) SERS intensity (at the 1594 cm⁻¹ peak) of 100 μg mL⁻¹ SH on eight batches of β-CD-Ag/PVA substrates, five spots were randomly chosen for each batch of substrate.