Optik 123 (2012) 1400–1403 Contents lists available at SciVerse ScienceDirect Optik j o ur nal homepage: www.elsevier.de/ijleo Polymer thin film structures for ultra-low cost biosensing Manoj M. Varma ∗ Electrical Communication Engineering, Indian Institute of Science, Bangalore 560 012, India a r t i c l e i n f o Article history: Received 1 March 2011 Accepted 25 July 2011 Keywords: Polymer thin film biosensors Thin film stack design a b s t r a c t Reflectance change due to binding of molecules on thin film structures has been exploited for bio- molecular sensing by several groups due to its potential in the development of sensitive, low cost, easy to fabricate, large area sensors with high multiplexing capabilities. However, all of these sensing plat- forms have been developed using traditional semiconductor materials and processing techniques, which are expensive. This article presents a method to fabricate disposable thin film reflectance biosensors using polymers, such as polycarbonate, which are 2–3 orders of magnitude cheaper than conventional semiconductor and dielectric materials and can be processed by alternate low cost methods, leading to significant reduction in consumable costs associated with diagnostic biosensing. © 2011 Elsevier GmbH. All rights reserved. 1. Introduction Highly multiplexed bio-molecular sensors are indispensible for the development of integrative or systems biology where a large number of genomic or proteomic variables must be quantified to infer their interdependences. Such sensing technologies also aid in the diagnosis of diseases through the detection of molecular mark- ers of disease states. Thin film structures whose reflectance changes upon molecular binding on sensor surface had previously been reported [1–4] with noise floors in the range of 1–10 pm matching the performance of surface plasmon resonance (SPR) based sen- sors [5]. The fundamental mechanism of these sensors is based on the reflectance change produced by specific molecular binding on a thin film structure. The sensors described previously [1–4] are single film structures using common semiconductor manufactur- ing materials like SiO 2 on Silicon substrates, perhaps due to the easy availability of these materials and familiarity with associated fabrication processes in academic labs. Single film Si/SiO 2 or Si 3 N 4 based structures reported in the literature have attained good sens- ing performance and these materials and associated fabrication resources such as clean room, and e-beam thin film deposition sys- tems may be easily accessible for a well equipped academic lab. However, these materials and the associated fabrication resources require significant capital investments and running costs result- ing in the sensor chips being unaffordable by a large population in developing countries who ironically are probably in the great- est need for such technology [6,7]. On the other hand polymer thin film materials are significantly cheaper than conventional ∗ Tel.: +91 80 2293 3159; fax: +91 80 2360 0563. E-mail address: mvarma@ece.iisc.ernet.in semiconductor grade materials (cost of silicon, glass slides and polycarobonate (PC) is >$2800/m 2 [8], $185/m 2 [9] and $19/m 2 [10], respectively, calculated from information on vendor web- sites) and can be assembled via several low cost manufacturing processes such as spin coating, electrostatic layer-by-layer self assembly (LbL), and inkjet printing [11], potentially leading to the construction of thin film reflectance biosensors on low cost sub- strates such as polycarbonate (PC), which is the substrate used in the manufacturing of optical compact discs. We advocate the use of polymer based thin film biosensors over conventional semicon- ductor materials based sensors for the following reasons. Firstly, such thin film biosensors could, for instance, be used as ultra-low cost label free microarrays among other applications specifically targeted for developing countries, where there is a great need for such technology. It is true that a polymer thin film biosensor would only lead to a potential cost reduction in the sensing chip while still requiring relatively expensive optics for detection. However, the sensing instrumentation is a one-time capital expenditure whereas the sensor chip, which is disposable, is a continuously running cost. Therefore, as one can imagine, it is the cost of the sensor chip that drives the long-term unit cost of sensing and diagnostics and not the detection instrumentation, unless of course the detection instrumentation is prohibitively expensive, which is certainly not the case with thin reflectance sensing instrumentation described previously requiring a rather simple optical detection setup [1,2]. Secondly, it has been argued that even sensors based on sili- con and similar expensive materials can be made inexpensive if made in large volumes. The author is not aware of any commercial endeavor where this argument has been practically realized. Practi- cal realization of volume scaling cost advantage is difficult to attain because the biosensors market, particularly for label-free biosen- sors, is still in it early development and therefore highly fragmented 0030-4026/$ – see front matter © 2011 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijleo.2011.08.025