Nanostructured a-Fe 2 O 3 platform for the electrochemical sensing of folic acid† Thandavarayan Maiyalagan,‡ a J. Sundaramurthy,‡ bc P. Suresh Kumar, bc Palanisamy Kannan, * d Marcin Opallo * d and Seeram Ramakrishna * bc a-Fe 2 O 3 nanofibers are synthesized by a simple and efficient electrospinning method and the selective determination of folic acid (FA) is demonstrated in the presence of an important physiological interferent, ascorbic acid (AA), using the a-Fe 2 O 3 nanofiber modified glassy carbon (GC) electrode at physiological pH. Bare GC electrode fails to determine the concentration of FA in the presence of a higher concentration of AA due to the surface fouling caused by the oxidized products of AA and FA. However, modification with a-Fe 2 O 3 nanofibers not only separates the voltammetric signals of AA and FA by 420 mV between AA and FA, but also enhances higher oxidation current. The amperometric current response is linearly dependent on FA concentration in the range of 60–60 000 nM, and the a-Fe 2 O 3 nanofiber modified electrode displayed an excellent sensitivity for FA detection with an experimental detection limit of 60 nM (1.12  10 10 M(S/N ¼ 3)). Furthermore, the a-Fe 2 O 3 nanofiber modified electrode showed an admirable selectivity towards the determination of FA even in the presence of a 1000-fold excess of AA and other common interferents. This modified electrode has been successfully applied for determination of FA in human blood serum samples. 1 Introduction In recent years, the synthesis and fabrication of nanomaterials with tailoring their size, morphology, and porosity have been intensively pursued not only for fundamental scientic interest but also for many technological applications. 1–3 Nanoparticles (zero-dimensional (0-D)) and nanowires/nanorods (one-dimen- sional (1-D)) with controlled size and shape are of key importance because their electrical, optical, and magnetic properties are strongly dependent on their size and shape. 1–3 Currently, one- dimensional (1-D) nanomaterials such as silicon nanowires (SiNWs), carbon nanotubes (CNTs), and conducting polymer nanowires (CP NWs) have opened the possibility to fabricate electrochemical sensors and biosensors. 4–7 Their high sensitivity and new sensing mechanisms are related to intrinsic properties associated with a high surface-to-volume ratio. 4–7 Further, 1-D nanostructures can be used for both efficient transport of elec- trons and optical excitation, and these two factors make them critical to the function and integration of nanoscale devices, and have been the focus of intensive research for many potential applications in electronics, photonics, drug delivery, medical diagnostics, and magnetic materials. 8–11 Hematite (a-Fe 2 O 3 ) is the most stable iron oxide with n-type semiconducting properties (E g ¼ 2.2 eV) under ambient condi- tions. It has been intensively investigated because of its wide applications in catalysts, pigments, magnetic materials, gas sensors, and lithium ion batteries. 4,12–15 Fe 2 O 3 was generally considered to be biologically and electrochemically inert, and its electrocatalytic functionality has been rarely realized directly in the past, 16 whereas Fe 2+ ions (instead of Fe 3+ ) play the dominant role in the oxidation reaction. 17–19 Meanwhile, Fe 2 O 3 was also demonstrated to show both reversible reduction and reversible oxidation of Fe(III) in a basic carbonate buffer solution. 17 Never- theless, in contrast with interests focusing on synthetic and catalytic applications of Fe 3 O 4 , reports on the electrochemical characterization of Fe 2 O 3 nanoparticles are rather rare, and little attention has been paid to the detailed study of their sensing performance. 20–22 In principle, Fe 2 O 3 nanoparticles may effi- ciently mediate the nal heterogeneous chemical oxidation or reduction of the target agent, while the converted iron oxides can be continuously and simultaneously recovered by electro- chemical oxidation or reduction due to their high surface to volume ratio. From this key point, an electrocatalytic study of nanostructured Fe 2 O 3 in biocompatible environments may not a School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore, 637459s b Centre for Nanobers and Nanotechnology, National University of Singapore, Singapore 117576. E-mail: seeram@nus.edu.sg; Fax: +65-6872 5563; Tel: +65-6516 6593 c Department of Mechanical Engineering, National University of Singapore, Singapore 117576 d Institute of Physical Chemistry, Polish Academy of Sciences, 44/52 ul. Kasprzaka, 01- 224 Warszawa, Poland. E-mail: ktpkannan@gmail.com; mopallo@ichf.edu.pl; Tel: +48-223 433 375. Fax: +48-223 433 333 † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3an00070b ‡ Both authors contributed equally to this work. Cite this: Analyst, 2013, 138, 1779 Received 24th November 2012 Accepted 17th January 2013 DOI: 10.1039/c3an00070b www.rsc.org/analyst This journal is ª The Royal Society of Chemistry 2013 Analyst, 2013, 138, 1779–1786 | 1779 Analyst PAPER Downloaded by University of Texas Libraries on 19/04/2013 17:10:23. Published on 31 January 2013 on http://pubs.rsc.org | doi:10.1039/C3AN00070B View Article Online View Journal | View Issue