Biosensors and Bioelectronics 33 (2012) 190–195 Contents lists available at SciVerse ScienceDirect Biosensors and Bioelectronics jou rn al h om epa ge: www.elsevier.com/locate/bios Immobilization of enzyme on long period grating fibers for sensitive glucose detection Akash Deep, Umesh Tiwari ∗ , Parveen Kumar, Vandana Mishra, Subhash C. Jain, Nahar Singh, Pawan Kapur, Lalit M. Bharadwaj Central Scientific Instruments Organisation, Sector (CSIR-CSIO) 30 C, Chandigarh, India a r t i c l e i n f o Article history: Received 15 September 2011 Received in revised form 14 December 2011 Accepted 28 December 2011 Available online 6 January 2012 Keywords: Long period grating Glucose oxidase FTIR spectroscopy Raman spectroscopy Biosensing Glucose a b s t r a c t Glucose oxidase (GOD) immobilized long period grating (LPG) fibers have been proposed for the spe- cific and sensitive detection of glucose. The treatment of LPG fibers with aminopropyl triethoxysilane has induced biding sites for the subsequent GOD immobilization. Field emission scanning electron microscopy, confocal laser scanning microscopy, infrared spectroscopy and Raman spectroscopy have provided detailed evidences about the effectiveness of the adopted biofunctionalization methodology. The enzyme activity is conserved during the immobilization step. Fabricated LPG sensor was tested on different glucose solutions to record the transmission spectra on an optical spectrum analyzer. The wave- length shifts in the transmission spectra are linearly correlated with the glucose concentration in the range of 10–300 mg dL -1 . The fabricated sensor gives fast response and is demonstrated to be of practical utility by determining glucose contents in blood samples. Proposed technique can further be extended to develop LPG fiber based novel, sensitive and label free nanosensors for disease diagnosis and clinical analysis. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Fiber-optic based biosensors have been reported useful for med- ical and environmental applications (Brogan and Walt, 2005; Bosch et al., 2007; Atias et al., 2009; Wolfbeis, 2006). Long period grat- ing (LPG) fibers form a special class of transducers, and have been proposed for some biosensing applications (Kuhlmey et al., 2008; Barnes et al., 2008, 2010). The LPG fiber sensors produce highly sen- sitive resonance wavelength shift signals upon induced changes in the ambient refractive index to offer direct and label free detec- tions. The ability of LPGs to couple light from the fiber core to the fiber cladding helps in direct probing of the surrounding media. Any change in the refractive index of the surrounding media results into spectral shifts, whose demodulation and proper correlations leads to highly sensitive quantitative chemical analyses. Apart from the already cited references, some other important citations on the applications of LPG fibers report the detection of antigen (DeLisa et al., 2000), pH (Goicoechea et al., 2008) and medically relevant parameters (Mishra et al., 2011). Immunosens- ing with LPG requires their surface modification with molecular recognition elements, such as antibodies, enzyme, etc. Main meth- ods for the immobilization of bioreceptors on the LPG surface ∗ Corresponding author. Tel.: +91 172 2659951; fax: +91 172 2659951. E-mail address: uktiwaricsio@yahoo.in (U. Tiwari). include adsorption (Liu et al., 2000), ionic bonding by electrostatic self-assembly technique (Elosúa et al., 2006; Wang et al., 2009), cross-linking by means of multifunctional reagent (Lee and Walt, 2000), covalent bonding (Disley et al., 1998; Stanford et al., 2009), and avidin–biotin interaction (Marks et al., 2002). Covalent binding is considered as the most effective of all the above quoted attach- ment strategies. This approach allows the active sites to remain unobstructed and chemically reactive. Some of the extremely useful inherent properties of the LPG fibers, such as their high sensitivity and smart transduction instru- mentation, have motivated us to exploit them for enzyme based immunosensing of glucose. Presently, only electrochemical meth- ods are more popular for the glucose analysis. Proposed optical based biosensing of glucose with LPG fibers may contribute to the much required developments of alternative detection devices, which can also compete with generally trusted laboratory tests. The work described herein first time demonstrates the feasibility of enzyme coated LPG fibers for the photonics based glucose sens- ing. Since the successful and precise working of the enzyme coated LPG sensor depends entirely upon the quality of the fiber’s cov- erage with the protein molecule, the detailed spectroscopic and microscopic investigations have been undertaken to confirm the effectiveness of the adopted covalent immobilization methodol- ogy. In some published reports, unmodified LPG fibers have been proposed for the non-selective analysis of very highly concentrated glucose solutions, e.g. 300 mg mL -1 (Libish et al., 2011; Kim et al., 0956-5663/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2011.12.051