Biosensors and Bioelectronics 21 (2006) 2263–2269 Luminescent yeast cells entrapped in hydrogels for estrogenic endocrine disrupting chemical biodetection T. Fine a , P. Leskinen b , T. Isobe c , H. Shiraishi c , M. Morita c , R.S. Marks a,∗ , M. Virta d a Department of Biotechnology Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel b Department of Biochemistry, University of Turku, FIN-20014 Turku, Finland c National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba 305-8506, Ibaraki, Japan d Department of Applied Chemistry and Microbiology, University of Helsinki, FIN-00014 Helsinki, Finland Received 14 July 2005; received in revised form 11 October 2005; accepted 8 November 2005 Available online 7 February 2006 Abstract In the construction of luminescent yeast cell based fibre-optic biosensors, we demonstrate a novel approach for estrogenic endocrine disrupting chemical (EDC) biodetection by entrapping genetically modified Saccharomyces cerevisiae cells, containing the estrogen receptor alpha-mediated expression of the luc reporter gene, in hydrogel matrices based on calcium alginate or PVA. In order to insure a significant signal, an optimal immobilization ratio of 1:2 alginate 3% (w/v): 5 × 10 6 [cells/ml], respectively, was used with the highest 17--estradiol (-E2) induction factor after 2.5 h of incubation with 10 [nM] -E2. It was shown that biocompatible alginate beads, 4.27–4.55 × 10 5 [CFU/bead], which were characterized by a detection limit of 0.08 [gl -1 ] and an EC50 of 0.64 [gl -1 ] for -E2, retained their viability for luminescence measurements after 1 month of storage at -80 ◦ C slow freeze condition, and thus repeated cell cultivations were not required. The assay reproducibility for each tested EDC, represented by the coefficients of variation (CV), ranged from 4.35 to 18.47%. An alternative immobilization method, based on a room temperature partial drying of polyvinyl alcohol (PVA) solution (LentiKat ® Liquid) and cell suspension mix, was investigated with only a slightly lower detection limit for -E2 than that reported with alginate beads. Alginate yeast based hydrogels may also be applicable to the analysis of environmental water samples since the trend of detected estrogenic activities with alginate beads roughly correlated with LC–MS–MS analytical results. © 2005 Elsevier B.V. All rights reserved. Keywords: Alginate; -E2; Hydrogel; Luminescence; PVA; Yeast 1. Introduction The organisation for economic co-operation and development (OECD) has defined an endocrine disrupting chemical (EDC) as “an exogenous substance that causes adverse health effects in an intact organism, or its progeny, consequent to changes in endocrine function”. Estrogenic chemicals represent a broad group of EDCs which are potentially detrimental. The expo- sure to these chemicals can cause reproductive abnormalities and feminization of wildlife (Fry and Toone, 1981; Facemire et al., 1995; Jobling et al., 1996) and possible reproductive dis- ∗ Corresponding author at: The National Institute for Biotechnology in the Negev, Ben-Gurion University of the Negev, P.O. Box. 653, Beer-Sheva, 84105 Israel. Tel.: +972 8 6477182; fax: +972 8 6472857. E-mail address: rsmarks@bgu.ac.il (R.S. Marks). orders also in humans (Carlsen et al., 1992; Giwercman et al., 1993; Raloff, 1993). Chemicals that have so far been identi- fied as being capable of producing estrogenic effects in some organisms include industrial or commercial agents (e.g. phta- lates and alkylphenols), pharmaceutical agents (e.g. DES) and pesticides (e.g. kepone and methoxychlor) (Witorsch, 2002). It has been reported that certain sewage treatment processes (Kirk et al., 2002) and pulp mill effluents (Durhan et al., 2002) are responsible for the existence of EDCs in the aquatic ambiance. Since the chemical structures of EDCs vary considerably, the assessment of the risk must be based on biological effect mon- itoring, rather than chemical analysis (Legler, 2002). Reliable short-term screening methods, which rely on biological recog- nition of EDCs, are needed to identify such chemicals and to detect their presence in the environment. Several groups have aimed at answering this need by developing different whole- cell-based bioreporter in vitro assays (Routledge and Sumpter, 0956-5663/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2005.11.004