Sensors and Actuators B 174 (2012) 195–201 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical journa l h o mepage: www.elsevier.com/locate/snb Highly selective wide linear-range detecting glucose biosensors based on aspect-ratio controlled ZnO nanorods directly grown on electrodes Rafiq Ahmad a , Nirmalya Tripathy a , Jin Hwan Kim b , Yoon-Bong Hahn a,b,∗ a Department of BIN Fusion Technology, School of Semiconductor and Chemical Engineering, Chonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju 561-756, Republic of Korea b Nanomaterials Processing Research Center, Chonbuk National University, 567 Baekjedaero, Deokjin-gu, Jeonju 561-756, Republic of Korea a r t i c l e i n f o Article history: Received 7 June 2012 Received in revised form 31 July 2012 Accepted 5 August 2012 Available online 13 August 2012 Keywords: Aspect-ratio controlled ZnO nanorods Glucose biosensor Cyclic voltammetry Artificial urine a b s t r a c t Amperometric glucose biosensors have been fabricated using aspect-ratio (AR) controlled zinc oxide nanorods (ZnO NRs) grown directly on Si/Ag electrodes, which showed a high performance in terms of selectivity, response time, linear range and repeatability. Especially, the glucose biosensor with AR = 60 demonstrates the highest sensitivity of 110.76 A/mM cm 2 and a wide linear range of 0.01–23.0 mM with ultrafast response time (<1 s). Such high performance is due to more immobilization on the well-aligned ZnO NRs arrays and direct electron conduction between the NRs and the electrodes. Furthermore the biosensor also showed a promising application for selectively detecting glucose in urine, which is useful for detecting renal glycosuria. © 2012 Elsevier B.V. All rights reserved. 1. Introduction The development of glucose biosensor for frequent testing of physiological glucose levels in diabetes patients is crucial for confirming the treatment effectiveness and to avoid diabetic emer- gency. The so-called “fingerstick” systems (invasive) which take a drop of blood typically from the finger and measure blood glucose level are among the most dominant methodologies. In medicine, it is also known that the presence of detectable levels of glu- cose in the urine is an indicative of diabetes. Hence, an accurate detection of glucose levels in urine using biosensors would facil- itate a reliable, non-invasive approach for proper monitoring of the glycemic state of diabetes patients. It is known that normal concentration of glucose in urine is in the range of 0.0–0.8 mM. However, in case of diabetes, patients normally contain glucose concentration of ∼2.8 mM in urine at highest blood glucose level [1]. Renal glycosuria is also the excretion of glucose into the urine. The appearance of glucose in urine is reflected in the concept of a renal threshold for glucose (RTG) excretion. In some, but not all, textbooks the concept of RTG excretion is propagated with the threshold specified at ∼10 mM [1]. According to this concept, no glucose should be detectable in urine at sub-threshold blood glu- ∗ Corresponding author at: Department of BIN Fusion Technology, School of Semiconductor and Chemical Engineering, Chonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju 561-756, Republic of Korea. Fax: +82 63 270 2360. E-mail address: ybhahn@chonbuk.ac.kr (Y.-B. Hahn). cose levels. If the RTG is so low that even normal blood glucose levels produce the condition, it is referred to as renal glycosuria. At a lower glucose concentration in urine, it is not possible to dis- tinguish between diabetes and renal glycosuria. But at a higher concentration of glucose in urine, the sensor is capable to detect diabetes. Moreover, this biosensor will be useful for patients with known glycemic state, who requires frequent monitoring of blood glucose concentration various times per day in order to manage diet and therapy. Hence such a non-invasive, painless and convenient approach would provide the additional benefits of eliminating the danger of infection resulting from multiple skin punctures. Furthermore, the degree of enzyme immobilization on medi- ators is crucial for the development of high performance glucose sensor, capable to detect glucose concentration with wide linear range, high selectivity and fast sensitivity. Since the glucose level in bloods from diabetic patients easily goes up to 15–20 mM and the linear range of detection is dependent on the amount of immobi- lized enzymes, it becomes necessary to develop biosensors having wide linear range of detection through optimization of enzymes immobilization on zinc oxide (ZnO) nanostructures-mediated elec- trodes. Among various immobilization strategies [2–4], physical adsorption is commonly chosen owing to its simplicity, high selec- tivity and relative low cost [5–7]. In general, the degree of enzyme immobilization is a function of surface area of mediators which is determined by the structural morphology of a nanostructure. How- ever, little work on the glucose biosensor based on aspect ratio (AR) controlled ZnO NRs except our previous work on a choles- terol biosensor [8] has been reported. A higher AR means a greater 0925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2012.08.011