Biosensors and Bioelectronics 26 (2011) 4842–4847 Contents lists available at ScienceDirect Biosensors and Bioelectronics jou rn al h om epa ge: www.elsevier.com/locate/bios Short communication Bio-Photonic Sensing Cells over transparent substrates for anti-gestrinone antibodies biosensing F.J. Sanza a , M. Holgado a,∗ , F.J. Ortega b , R. Casquel a , D. López-Romero c , M.J. Ba˜ nuls b , M.F. Laguna a , C.A. Barrios c , R. Puchades b , A. Maquieira b a Centro Láser, Universidad Politécnica de Madrid, Campus Sur, 28031 Madrid, Spain b Instituto de Reconocimiento Molecular y Desarrollo Tecnológico, Departamento de Química, Universidad Politécnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain c Instituto de Sistemas Optoelectrónicos y Microtecnología, Universidad Politécnica de Madrid, ETSI de Telecomunicación, Ciudad Universitaria s/n, 28040 Madrid, Spain a r t i c l e i n f o Article history: Received 8 April 2011 Received in revised form 28 May 2011 Accepted 10 June 2011 Available online 17 June 2011 Keywords: Optical biosensing SU-8 nano-pillar Anti-gestrinone detection a b s t r a c t In a previous work we introduced the term Bio-Photonic Sensing Cells (BICELLs), referred to periodic networks of nano-pillar suitable for biosensing when are vertically interrogated. In this article, we demonstrate the biosensing capabilities of a type of micrometric size BICELLs made of SU-8 nano-pillars fabricated over transparent substrates. We verify the biochips functionality comparing the theoreti- cal simulations with the experimental results when are optically interrogated in transmission. We also demonstrate a sensitivity enhancement by reducing the pitch among nano-pillars from 800 to 700 nm. Thus, the Limit of Detection achievable in these types of BICELLs is in the order of 64 pg/mL for 700 nm in pitch among nano-pillars in comparison with 292 pg/mL for 800 nm in pitch when are interrogated by Fourier Transform Visible and Infrared Spectrometry. The experiments exhibited a good reproducibil- ity with a relative standard deviation of 0.29% measured within 8 days for a specific concentration. Finally, BICELLs functionality was tested in real conditions with unpurified rabbit serum for detecting anti-gestrinone antibodies, demonstrating the high performance of this type of BICELLs to detect specific antibodies having immobilized the suitable bioreceptors onto the sensing surface. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Detection and quantification of biomolecules can be of relevant importance for different applications fields: healthcare, environ- ment, pharmaceutical research or drug control, among others. In this sense, immunoassay technology has proven to be highly effi- cient for reliable In vitro diagnostics (IVDs), and advantages such as the capability of offering low detection limits, high selectivity and versatility for detecting target biomolecules are broadly reported in the literature (Luppa et al., 2001). In order to determine whether these target biomolecules are present in a particular analyte, firstly bioreceptors should be immobilized onto specific sensing areas. Once the immobilization process has been performed, the test ana- lytes are introduced into the sensing areas and will react if they have particular contents of the target biomolecules that will be captured by the abovementioned immobilized bioreceptors, in a process called molecular recognition. This recognition process can be monitored by techniques requiring external markers or labeling elements such as fluorescent or radioactive tags for its transduction. By contrast, label-free biosensing do not require external labeling ∗ Corresponding author. Tel.: +34 91 332 42 80; fax: +34 91 336 55 34. E-mail address: m.holgado@upm.es (M. Holgado). elements, as it is the case of the refractometric optical biosensors in which is framed the BICELL-based biosensors subject to this arti- cle. Label-free monitoring are expected to become more impor- tant because offers several well known advantages for IVD (Fang et al., 2008) mainly related to analytical quality, easy operation, cost-effectiveness, screening of analytes which are not easy to tag, and the capability of studying initial “binding” reaction between the analyte and its target, in some cases, on real-time (Cooper, 2003). In a recent work we demonstrated optical label-free biosens- ing capability for BICELLs based fabricated over silicon as substrate (Holgado et al., 2010). This condition involves the use of the reflec- tivity spectra in the characterization of the optical response, being unfeasible the optical interrogation of the sensing micro-sites in transmission. In this article we report the optical biosensing response, under transmission condition, of micrometric size BICELLs over a transparent substrate based on high aspect ratio (HAR) nano- pillars networks. We also study the effect of a pitch reduction among nano-pillars on sensitivity and limit of detection (LOD). We carried out the experiments by an indirect assay format for detecting antibodies against the gestrinone, (17)-13-ethyl-17- hydroxy-18,19-dinorpregna-4,9,11-trien-20-yn-3-one. This syn- 0956-5663/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2011.06.010