Fiber-optic particle plasmon resonance sensor for detection of interleukin-1β in synovial fluids

Abstract

A facile and label-free biosensing method has been developed for determining an osteoarthritis concerned cytokine, interleukin-1β (IL-1β), in synovial fluids. The biosensing technique, fiber-optic particle plasmon resonance (FOPPR), is based on gold nanoparticles-modified optical fiber where the gold nanoparticle surface has been modified by a mixed self-assembled monolayer for further conjugation of anti-IL-1β antibody and minimization of nonspecific adsorption. Upon binding of IL-1β to anti-IL-1β on the gold nanoparticle surface, the absorbance of the gold nanoparticle layer on the optical fiber changes and the signal change is enhanced through multiple total internal reflections along the optical fiber. Results show that the detection of IL-1β in synovial fluid by this sensor agrees quantitatively with the clinically accepted enzyme-linked immunosorbent assay (ELISA) method but a much shorter analysis time is required (<10 min). The sensor response versus log concentration of IL-1β was linear (r = 0.9947) over the concentration range of 0.050–10 ng/mL and a limit of detection (LOD) of 21 pg/mL (1.2 pM) was achieved. Such a LOD for IL-1β (17 kDa) represents a major advancement in the field of real-time monitoring of low molecular weight proteins in complex biological fluids.

Introduction

In the medical field, there is a great need to investigate real-time expression of biological markers, such as cytokines, to better understand their role in progression of diseases. Hence, development of label-free and real-time biosensors with additional characteristics such as high sensitivity and selectivity, portable for point-of-care, easy to use, and cost-effective is extremely necessary. Recently, particle plasmon resonance (PPR) methods, also known as localized surface plasmon resonance (LSPR) methods, have been widely reported for the measurement of biochemical and chemical species (Kalyuzhny et al., 2001, Nath and Chilkoti, 2002, Endo et al., 2005, Stuart et al., 2005, Chen et al., 2007, Nusz et al., 2008, Cheng et al., 2005, Cheng and Chau, 2003, Chau et al., 2006, Sai et al., 2009). Particle plasmons are charge density oscillation confined to metallic nanoparticles (Willets and Van Duyne, 2007, Stewart et al., 2008). The PPR results when the incident photon frequency is resonant with the collective oscillation of the conduction electron of the nanoparticle and is manifested by a peak in the extinction spectrum of the nanoparticle. The spectral position and magnitude of the PPR depends on the size, shape, composition, and dielectric environment (Willets and Van Duyne, 2007, Stewart et al., 2008, Hutter and Fendler, 2004). The former three properties have been used to tune the PPR spectrum (Stuart et al., 2005, Sun and Xia, 2002, Chen et al., 2007, Chen et al., 2008) while the last property has been exploited for label-free and real-time optical sensing of binding events on those functionalized nanoparticles (Nath and Chilkoti, 2002, Stuart et al., 2005, Chen et al., 2007, Nusz et al., 2008, Cheng et al., 2005, Cheng and Chau, 2003).

Today, many PPR biosensors have been described in the literature (Stewart et al., 2008). Recently, we have developed a fiber-optic particle plasmon resonance (FOPPR) sensing platform for monitoring of bio-recognition events at the nano- to pico-molar level (Cheng and Chau, 2003, Chau et al., 2006). Since light propagates along an optical fiber by virtue of repeated total internal reflections (TIR), the summation of each local evanescent field results in a continuous evanescent field at the waveguide surface immediately adjacent to the region occupied by a propagating mode. Thus, the low absorption of the gold nanoparticle (AuNP) layer can be enhanced by using the fiber-optic evanescent-wave sensing scheme (Cheng and Chau, 2003). With FOPPR, protein binding interactions can be examined in vitro at biologically relevant levels (Lai et al., 2007). Furthermore, the fiber-optic configuration offers several additional advantages: (1) fiber-optic sensors offer complete electrical isolation, thus are safe for in vivo use; (2) the small size of the fiber-optic probe is convenient for quantitative analysis and measurement of binding kinetics in small volume of samples; (3) fiber-optic sensors are inexpensive to fabricate, to the point of being disposable; and (4) the optical setup for FOPPR is simple and cheap, facilitating the development of a portable device.

Most label-free biosensing approaches rely on measurement of adsorbate-induced local refractive index (RI) changes. These measurements are especially challenging for biomolecules of low molecular weights such as cytokines. Cytokines are hormone like polypeptides that are secreted in the course of immunologic and inflammatory responses. Cytokine measurements have become critical indicators of normal and disease states. Interleukin-1β (IL-1β) is a prototypical proinflammatory cytokine and is believed to play an important role in the pathogenesis and progression of osteoarthritis (OA) knee (Shibakawa et al., 2003, Scott et al., 2008, Daheshia and Yao, 2008, Melchiorri et al., 1998). Destructive effects of IL-1β in OA include both elevation of cartilage catabolism and suppression of cartilage anabolism (Daheshia and Yao, 2008). A number of specific biological activities have been identified for the nature form of this protein, which comprises 258–280 amino acid residues and has a molecular mass of 15–18 kDa. The detection of IL-1β is generally performed by use of immunoassay (Fichorova et al., 2008, Westacott et al., 1990), fiber-optic surface plasmon resonance sensor (Battaglia et al., 2005), immunohistochemistry (Towle et al., 1997), and radioimmunoassay (Mannami et al., 1989). These methods in common use are rather tedious and time-consuming, or requiring sophisticated instrumentation. Searching some label-free and real-time detection systems for cytokines (IL-1β) with low cost, high sensitivity and simplicity is of considerable interest for understanding the pathogenesis of OA and, hence, improve patient care. The work described below presents an FOPPR sensor for label-free detection of IL-1β in synovial fluids as a rapid and user-friendly alternative to conventional techniques. Comparison of its performance with enzyme-linked immunosorbent assay (ELISA), the gold standard in immunoassay, will also be discussed.