Sensors and Actuators B 182 (2013) 104–111 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical journal h om epage: www.elsevier.com/ locate/snb A potentiometric immunosensor based on silver nanoparticles decorated ZnO nanotubes, for the selective detection of d-dimer Z.H. Ibupoto a,∗ , N. Jamal a , K. Khun a , X. Liu b , M. Willander a a Physical Electronic and Nanotechnology Division, Department of Science and Technology, Campus Norrköping, Linköping University, SE-60174 Norrköping, Sweden b Department of Physics, Chemistry, and Biology (IFM), Linköping University, 58183 Linköping, Sweden a r t i c l e i n f o Article history: Received 20 December 2012 Received in revised form 18 February 2013 Accepted 19 February 2013 Available online 14 March 2013 Keywords: Silver nanoparticles ZnO nanotubes d-dimer Potentiometric Immunosensor Sensitive Selective a b s t r a c t In this study, a new, simple, fast and highly sensitive potentiometric immunosensor for the selective detection of d-dimer is developed using silver nanoparticles decorated ZnO nanotubes. The d-dimer is a biomarker and found at high levels in the human body when it suffers from deep vein throm- bosis (DVT) disorders. ZnO nanotubes were obtained by the chemical etching of nanorods using a hydrothermal method. The silver nanoparticles were deposited on the ZnO nanotubes using an elec- trodepositing technique. The structure and the composition characterization was measured by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques respectively. The ZnO nanorods are perpendicular to the substrate with uniform distribution. The etching of the nanorods into nanotubes is almost complete and the nanotubes are fully covered with silver nanoparticles. The mouse anti human d-dimer antibody was immobilized on the silver nanoparticles decorated ZnO nanotubes for the selective detection of d-dimer. The potentiometric immunosensor has shown a highly sensitive and linear response for the wide range of 1.00 × 10 -5 –1.00 × 10 0 g/ml d-dimer concentrations prepared in the phosphate buffer solution of pH 7.4. The presented d-dimer biosensor exhibited a detection limit of 1.00 × 10 -6 g/ml. The antibody immobilized immunosensor presents a fast response time of less than 5 s with acceptable selec- tivity, reproducibility and storage stability. The observed performance of the developed immunosensor demonstrates the high usability for the selective detection of the d-dimer from clinical and real samples. © 2013 Elsevier B.V. All rights reserved. 1. Introduction In the United States and Europe, 120–180 people per 100,000 people are facing the chronic disease venous thromboembolism (VTE), comprising deep vein thrombosis (DVT) and pulmonary embolism (PE) [1–3]. The United States is the leading country in the world for life killing incidents by stroke. This chronic dis- ease claims approximately 150,000 lives every year and nearly 300,000 people are living a life of disability [4]. United States cit- izens devote substantial expenses to this life killing disease per annum, between 15 and 30 billion dollars and more than half of these expenses are attributable to disabled people effected by a stroke [5]. The early diagnosis of venous thromboembolism has failed due to a higher variation in the clinical symptoms of this ill- ness. The mortality rate of venous thromboembolism is very high in cases of pulmonary embolism and where the complexity of deep vein thrombosis is found in a higher value [3]. This has probably ∗ Corresponding author. Tel.: +46 11 363 119. E-mail address: zafar.hussain.ibupoto@liu.se (Z.H. Ibupoto). remained undiagnosed even in obscure conditions of patients suf- fering from venous thromboembolism. Enormous efforts have been made for the early and precise diagnosis of venous thromboem- bolism which can be authentically measured by several techniques including ultrasonography or helical computed tomography (CT) [6,7]. However, these techniques are limited by their slowness in response and are not cost effective. In addition to these techniques, the detection of biomarker from plasma is also used. d-dimer is one of the specific fragments that results from the degradation of cross- linked fibrin and it has antigenic characteristics. d-dimer is found on the cross-linked gamma chain ends of the fibrin molecule and it can be found in the patients suffering from deep vein thrombosis [8]. Many d-dimer analysis assays are reported including enzyme linked immunosorbent assays (ELISA), whole blood agglutination and latex agglutination assays. The enzyme linked immunosorbent assays are highly sensitive in the determination of venous throm- boembolism and are therefore known as the gold standard for d-dimer detection [9]. Despite the availability of the (ELISA) assays, there is an increasing need to develop a novel and highly sensitive and selective immunosensor for the early diagnosis of deep vein thrombosis [10]. In the last few decades, the fabrication of affinity 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.02.084