Detection of staphylococcal enterotoxin A (SEA) at picogram level by a capacitive immunosensor

Abstract

This work presents the use of a flow injection capacitive immunosensor to detect staphylococcal enterotoxin A (SEA). The study was based on the direct detection of a capacitance change due to the binding between SEA and anti-SEA immobilized on a gold electrode. The optimal regeneration solution, flow rate, sample volume and buffer conditions were studied. Under the optimum conditions, this label-free biosensor provided linearity between 1 × 10⁻¹² g L⁻¹ and 1 × 10⁻⁸ g L⁻¹ of SEA and the limit of detection was 1 × 10⁻¹² g L⁻¹ which was much lower than the infectious dose (0.5 × 10⁻⁶ – 1 × 10⁻⁶ g L⁻¹). Using the regeneration solution of, 15.0 mM glycine-HCl pH 2.20, to break the binding between SEA and the immobilized anti-SEA enabled the electrode to be reused up to 39 times. This technique was applied to analyze SEA in liquid and solid food samples. Any matrix effect can be eliminated by simple dilution. SEA contamination was found in three samples, iced tea with milk (28 ± 1 ng L⁻¹), orange juice (113 ± 6 ng L⁻¹) and fried chicken (1.1 ± 0.2 ng g⁻¹); however, the concentrations were much lower than the infectious dose. The proposed method would be useful for rapid screening of SEA in various matrices.

Keywords:

• Staphylococcal enterotoxin A
• high sensitivity
• capacitive
• immunosensor
• label-free detection

Acknowledgments

This project was supported by The Royal Golden Jubilee Ph.D. Program (RGJ) supported by The Thailand Research Fund; Center for Innovation in Chemistry (PERCH-CIC); the National Research University Project of Thailand, Office of the Higher Education Commission; Trace Analysis and Biosensor Research Center; Graduate School and Faculty of Science, Prince of Songkla University, Hat Yai, Thailand. The authors also thank Dr. Brian Hodgson, Prince of Songkla University, Hat Yai, Songkhla, Thailand for the English assistance with the manuscript.