Reduced graphene oxide modified smart conducting paper for cancer biosensor Saurabh Kumar a , Suveen Kumar a , Saurabh Srivastava a , Birendra K. Yadav b , Seung H. Lee c,n , Jai G. Sharma a , Dinesh C. Doval b , Bansi D. Malhotra a,n a Nanobioelectronics Laboratory, Department of Biotechnology, Delhi Technological University, Shahbad Daulatpur, Delhi 110042, India b Rajiv Gandhi Cancer Institute and Research Centre, Rohini, Delhi 110085, India c Applied Materials Institute for BIN Convergence, Department of BIN FusionTechnology, Chonbuk National University, Jeonju 561-756, Republic of Korea article info Article history: Received 3 March 2015 Received in revised form 16 May 2015 Accepted 17 May 2015 Available online 27 May 2015 Keywords: Conducting paper PEDOT:PSS Biosensor Cancer abstract We report results of the studies relating to the fabrication of a paper based sensor comprising of poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and reduced graphene oxide (RGO) composite. The effect of various solvents like methanol, ethylene glycol and H 2 SO 4 on the electrical conductivity of PEDOT:PSS coated Whatman paper has been investigated. The conductivity of this solution processed conducting paper significantly increases from 1.16  10 4 S cm 1 up to 3.57  10 2 S cm 1 ( 300 times) on treatment with ethylene glycol. The observed significant increase in electrical conductivity is due to conformational rearrangement in the polymer and is due to strong non-covalent cooperative interaction between PEDOT and the cellulose molecules. Further, incorporation of RGO into the conducting paper results in improved electrochemical performance and signal stability. This paper electrode is a promising alternative over the expensive conventional electrodes (ITO, gold and glassy carbon), that are known to have limited application in smart point-of-care (POC) devices. This low cost, flexible and environment friendly conducting paper based biosensor utilized for cancer biomarker (carcinoembryonic antigen, CEA) detection reveals high sensitivity of 25.8 mA ng 1 mL cm 2 in the physiological range, 1–10 ng mL 1 . & 2015 Elsevier B.V. All rights reserved. 1. Introduction Paper based point-of-care (POC) devices are rapidly evolving for desired analytical and clinical applications since these are predicted to be simple, cost-effective, portable, consume low power and are disposable. These devices have potential applica- tions in healthcare, detection of toxicants, explosives and en- vironmental studies. Compared to conventional laboratory assays, these devices are found to be very helpful for making speedy decision for therapeutics. Besides this, the testing can be per- formed near the vicinity of a patient and hence these devices have recently gained considerable attention in health care (Gervais et al., 2011; Kumar et al., 2013a, 2013b; Luppa et al., 2011). Electrochemical sensors are known to play an important role in on-going transition towards the paper based POC diagnostic de- vices. The electrochemical techniques offer high sensitivity, high signal-to-noise ratio, portability and fast response time (Wang, 2006). Therefore, its integration with the paper may be advanta- geous. To ensure the application of paper in an electrochemical sensor, it is essential to make it conducting. In this context, many methods such as screen printing, inkjet printing etc. have been used to incorporate conducting ink on a paper substrate (Jaga- deesan et al., 2012; Tobjörk and Österbacka, 2011). These methods require complex fabrication steps, additional instrumentation, skilled personnel and are time-consuming. Conducting polymers (CPs) have been considered a promising candidate to obtain con- ducting paper due to delocalization of π electrons since they are known to facilitate rapid electron transfer, mechanical flexibility and solution processability. Doping of a conducting polymer has been found to enhance its electronic, optical, physical, chemical and electrochemical properties (Dhand et al., 2011). CPs have been predicted to have enough potential for the development of a low cost and high performance biosensor materials that offer high permeability biocompatibility, and rapid electron transfer (Li et al., 2015; Zhai et al., 2013). Among the various conducting polymers, poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) has been considered to be a interesting candidate for devel- opment of a conducting paper due to its homogeneous entrap- ment in/on a paper using a simple dip coating method with Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/bios Biosensors and Bioelectronics http://dx.doi.org/10.1016/j.bios.2015.05.040 0956-5663/& 2015 Elsevier B.V. All rights reserved. n Corresponding authors. E-mail addresses: lsh1@jbnu.ac.kr (S.H. Lee), bansi.malhotra@gmail.com (B.D. Malhotra). Biosensors and Bioelectronics 73 (2015) 114–122