Talanta 83 (2011) 1436–1441 Contents lists available at ScienceDirect Talanta journal homepage: www.elsevier.com/locate/talanta Fast and accurate peanut allergen detection with nanobead enhanced optical fiber SPR biosensor J. Pollet a , F. Delport a , K.P.F. Janssen a , D.T. Tran a , J. Wouters b , T. Verbiest b , J. Lammertyn a,∗ a BIOSYST-MeBioS, Katholieke Universiteit Leuven, Willem de Croylaan 42, B-3001 Leuven, Belgium b Molecular and Nanomaterials, Katholieke Universiteit Leuven, Celestijnenlaan 200f, B-3001 Leuven, Belgium article info Article history: Received 16 June 2010 Received in revised form 31 October 2010 Accepted 14 November 2010 Available online 19 November 2010 Keywords: Peanut allergy Surface plasmon resonance Fiber optic biosensor Super-paramagnetic nanobeads abstract This paper is the first report of a fiber optic SPR biosensor with nanobead signal enhancement. We evaluated the system with a bioassay for the fast and accurate detection of peanut allergens in complex food matrices. Three approaches of an immunoassay to detect Ara h1 peanut allergens in chocolate candy bars were compared; a label-free assay, a secondary antibody sandwich assay and a nanobead enhanced assay. Although label-free detection is the most convenient, our results illustrate that functionalized nanobeads can offer a refined solution to improve the fiber SPR detection limit. By applying magnetite nanoparticles as a secondary label, the detection limit of the SPR bioassay for Ara h1 was improved by two orders of magnitude from 9 to 0.09 g/mL. The super paramagnetic character of the nanoparticles ensured easy handling. The SPR fibers could be regenerated easily and one fiber could be reused for up to 35 times without loss of sensitivity. The results were benchmarked against a commercially available polyclonal ELISA kit. An excellent correlation was found between the Ara h1 concentrations obtained with the ELISA and the concentrations measured with the SPR fiber assay. In addition, with the SPR fiber we could measure the samples twice as fast as compared to the fastest ELISA protocol. Since the dipstick fiber has no need for microchannels that can become clogged, time consuming rinsing step could be avoided. The linear dynamic range of the presented sensor was between 0.1 and 2 g/mL, which is considerably larger than the ELISA benchmark. © 2010 Elsevier B.V. All rights reserved. 1. Introduction An increasing number of people is confronted with food hyper- sensitivity. At the very top of the food allergen list is the peanut. Although they have an eminent nutritional value, peanuts can be a serious threat towards sensitized individuals [1]. While other food-induced allergies, e.g. allergies triggered by milk or egg pro- teins, mainly affect children and disappear when growing up, peanut hypersensitivity tends to persist into adulthood [2]. Since no medical prophylactic treatment is available so far, the sensi- tive consumer should strictly avoid peanuts. The allergens are heat resistant and are conserved during food production and processing [3]. Hence, accurate and reliable product information is required, especially since the modern food industry frequently processes peanuts or peanut butter in products such as cookies, chocolate, cereal, crackers, and ice cream. Also, some products might contain these nuts inadvertently through contamination of raw materials or equipment used. Even a trace amount of peanut allergens has the potential to be life-threatening by inducing an anaphylactic ∗ Corresponding author. Tel.: +32 16321459; fax: +32 16322955. E-mail address: jeroen.lammertyn@biw.kuleuven.be (J. Lammertyn). shock [4]. Consequently, there is a need for sensitive biosensors that can detect low quantities of peanut allergens in complex food matrices and that can be implemented in food quality and safety laboratories. The current reference method for detecting food allergens is an enzyme-linked immunosorbent assay (ELISA) [5,6]. Although ELISA has proven to be a sensitive and versatile bio-analytical assay, the technique is time-consuming, not reusable, rather expensive, and some steps are difficult to automate [7]. Polymerase chain reac- tion (PCR) techniques have frequently been reported as a promising alternative for ELISA [8]. While the sensitivity of the PCR methods may become superior, there is no fixed correlation between the amount of DNA and the amount of allergens, which may lead to false positive or false negative results. Therefore, immunoassays still remain the method of choice for the quantitative detection of low concentrations of peanut allergens in real food samples [2]. Surface plasmon resonance (SPR) is generally considered as one of the most suited methods to monitor biomolecular interactions and thus can be applied as an accurate allergen immunosensor [9]. Most commercial SPR systems (e.g. Biacore, GE Healthcare, Sweden; Spreeta, Sensata Technologies, Brazil) are fully automated, their sensor chips can be used for many samples and the SPR sen- 0039-9140/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2010.11.032