IEEE SENSORS JOURNAL, VOL. 12, NO. 9, SEPTEMBER 2012 2791 Detection of Fluorophore-Tagged Recombinant Bovine Somatotropin (rbST) by Using a Silica-on-Silicon (SOS)-PDMS Lab-on-a-Chip Jayan Ozhikandathil, Simona Badilescu, and Muthukumaran Packirisamy Abstract—The presence of potentially harmful substances in milk is a concern for consumers. The discovery of recombinant DNA technology allowed the production of large quantities of recombinant bovine somatotropin (rbST), which is allowed to be used to increase milk and meat production in many countries. The use of rbST is controversial because of its potential effects on animal and human health. Use of the existing large instruments for the detection of rbST suffers disadvantages such as the need of large quantities of reagents, increased time of assays and most importantly, the high cost of equipment, etc. In this paper, a novel optical lab-on-a-chip (LOC) is proposed for the detection of a fluorophore-tagged rbST. The advantages of a silica-on-silicon platform for the optical waveguide and polydimethylsiloxane for microfluidics are exploited for the fabrication of a low-cost LOC. The tagging of rbST with two different types of fluorophores, such as FITC and Alexa-647, is carried out and used for detection in the proposed LOC. Index Terms— Lab-on-a-chip, polydimethylsiloxane (PDMS), recombinant bovine somatotropin (rbST), silica-on-silicon (SOS). I. I NTRODUCTION B OVINE SOMATOTROPIN (bST) is a polypeptide growth hormone naturally produced by the anterior pituitary gland of cows. The primary protein in the pituitary extract, which is responsible for the increase of milk production, is bST. The effect of bST on milk production was discovered in 1937 [1]. Since the 80s, by using the recombinant DNA technologies [2], large quantities of hormones were produced and used to increase the milk production. The use of recombinant bST (rbST) is controversial [3]–[5] because of its potential effects on animal and human health, hence, it is forbidden in many countries. To provide meaningful information to consumers and to identify the rbST-treated animals, highly sensitive analytical methods are required. The concentration of bST was traditionally estimated using, either an enzyme-linked immunosorbent assay (ELISA) [6], Manuscript received April 8, 2012; revised May 21, 2012; accepted May 23, 2012. Date of publication June 1, 2012; date of current version July 24, 2012. This work was supported in part by Développement Économique, Innovation et Exportation Québec and Valeo Gestion, Montreal, QC Canada. The associate editor co-ordinating the review of this paper and approving it for publication was Prof. E. H. Yang. The authors are with the Department of Mechanical and Industrial Engineer- ing, Optical Bio Microsystems Laboratory, Concordia University, Montreal, QC H3G 1M8, Canada (e-mail: j_ozhik@encs.cocordia.ca; badiles@yahoo.fr; pmuthu@alcor.concordia.ca). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2012.2202105 [7], a radioimmunoassay (RIA) [8] or bioassay methods [9]. ELISA assays have a limitation that is the concentration of antibody can only be reported in relative terms such as “titer,” that is, a combination of affinity and concentration. More recently, a sensitive method based on liquid chromatography- mass spectrometry (LC-MS), combined with electrospray ion- ization [10]–[13] has been developed for the discrimination between the recombinant and the endogenous forms of soma- totropin. The principal drawback of this approach is the complexity of the methodology, together with very expensive and large instrumentation, which makes this method difficult to implement for the rapid detection of bST and rbST in milk. Surface Plasmon Resonance (SPR) biosensing method has also been suggested [13] for the detection of rbST, however, the measurements are carried out in an expensive plasmonic instrument such as Biacore 3000. In this context, developing a miniaturized analytical device that allows a rapid and precise detection of growth hormones becomes extremely important. The detection of rbST in milk is very important and still a challenging task, hence, this work proposes an optical lab-on- a-chip platform for the detection of fluorophore-tagged rbST. The advantages of the lab-on-a-chip are principally, a low consumption of reagents, portability, suitability for the Point of Need (PON) application, and low cost, compared to other existing methods. Since 90s, miniaturized total analysis systems (μTAS), alter- natively called Lab-on-a-chips (LOCs) have gained increased attentions as a major breakthrough in analytical chemistry. Though the concept of miniaturization of analytical systems was initially proposed [14] to enhance the analytical perfor- mances, later on, many other benefits such as low consump- tion of carriers, reagents and mobile phase have also been recognized [15], [16]. Moreover, the integration of multiple components in a single chip is also possible, by using the exist- ing and new microfabrication technologies. Well-developed silicon microfabrication technologies were originally adopted for the fabrication of micro total analysis systems, however, for a wide range of applications, new materials and fabrication processes were also reported in literature [17], [18]. Silicon, glass and polymeric materials such as polydimethylsiloxane (PDMS) [19] poly (methyl methacrylate) (PMMA) [20] and SU-8 [21] are widely used material for the fabrication of miniaturized total analysis systems. Even though there are many techniques reported for the bio-detection, fluorescent detection is still a widely used 1530–437X/$31.00 © 2012 IEEE