ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Combining TiO₂ photonic crystals and reagents enhances the sensitivity of endotoxin detection

Ryosuke Nishitsuji, Shotaro Ueda, Kenji Sueyoshi, Hideaki Hisamoto, and Tatsuro Endo

Department of Applied Chemistry, Graduate School of Engineering, Osaka Metropolitan University, Naka, Sakai, Japan

E-mail: t_endo@omu.ac.jp

Received: 21 June 2022  Accepted: 10 September 2022

Abstract:

Endotoxins are lipopolysaccharides, which are components of the cell wall of gram-negative bacteria, and are considerable risk to human health. Additionally, endotoxins are heat-stable and cannot be degenerated under normal sterilization conditions. Therefore, it is important to ensure that pharmaceuticals are not contaminated with endotoxins or that the contamination level is below the standard value. The simple gelation method has been widely used for endotoxin detection using limulus amebocyte lysate (LAL) reagents, but this detection sensitivity is quite low. We improved the sensitivity of endotoxin detection by combining a simple optical system using titanium oxide (TiO₂) photonic crystals (PhCs) and LAL reagents. The response principle was to measure changes in the refractive index during the gelation process of LAL reagents induced by endotoxins. TiO₂ PhC can be fabricated using a liquid phase deposition method. The TiO₂ PhCs exhibited a peak derived from the nanostructure, and the wavelength peak at 630 nm was used for endotoxin detection based on the calculations of finite-difference time-domain simulation. We evaluated the detection method by performing spectral measurement of the gelation process of LAL reagents on PhCs. We confirmed that the peak wavelength shifted with increasing endotoxin concentrations and reaction times. We obtained the limit of detection for endotoxins as 0.0002 endotoxin units/mL and linear range of 0.001–1 EU/mL from the result at a reaction time of 60 min. The limit of detection was the lowest limit reported to date.

Keywords: Photonic crystal; Titanium oxide; Endotoxin; Limulus amebocyte lysate

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-022-02485-6

Chemical Papers 77 (1) 611–615 (2023)