Published: January 18, 2011 r2011 American Chemical Society 279 dx.doi.org/10.1021/am100923x | ACS Appl. Mater. Interfaces 2011, 3, 279–286 RESEARCH ARTICLE www.acsami.org Fluorescence Sensing of Zinc(II) Using Ordered Mesoporous Silica Material (MCM-41) Functionalized with N-(Quinolin-8-yl)-2-[3-(triethoxysilyl)propylamino]acetamide Parul Pal, †,‡ Shiva K. Rastogi,* ,‡,§ Charlene M. Gibson, § D. Eric Aston, ^ A. Larry Branen, § and Thomas E. Bitterwolf † Department of Chemistry, University of Idaho, Moscow, Idaho 83844-2343, United States § Biosensors and Nanotechnology Applications Laboratory, University of Idaho, Coeur d’Alene, Idaho 83814-2277, United States ^ Department of Chemical and Materials Engineering, University of Idaho, Moscow, Idaho 83844-1021, United States b S Supporting Information ABSTRACT: A novel fluorescent zinc sensor was designed and synthesized on ordered mesoporous silica material, MCM-41, with N-(quinolin-8-yl)-2-[3-(triethoxysilyl)propylamino]acetamide (QTEPA; 3) using a simple one-step molecular self-assembly of the silane. The solution and solid samples were characterized using solid-state nuclear magnetic resonance, transmission elec- tron microscopy, diffuse-reflectance infrared Fourier transform, and thermogravimetric analysis techniques. The QTEPA- modified MCM-41 (4) shows 3-fold fluorescence emission enhancement and about a 55 nm red shift upon addition of 1 μM Zn II ions in a Tris-HCl (pH 7.22) aqueous buffer solution. The UV-vis absorption maximum is at 330 ( 5 nm, and the fluorescence emission maximum wavelength is at 468 nm, with an increase in quantum yield from 0.032 to 0.106 under the same conditions. The presence of other metal ions has no observable effect on the sensitivity and selectivity of 4. This system selectively detects Zn II ions with submicromolar detection to a limit of 0.1 μM. The MCM-41-based systems have the advantage that they can be employed in aqueous solutions without any aggregation. KEYWORDS: MCM-41, quinoline, zinc sensor, Tris-HCl buffer, DRIFT, fluorescence detection 1. INTRODUCTION Fluorescence detection of divalent cations is the most com- mon method employed for biological sensing of metals, espe- cially calcium and magnesium. 1 Designing sensors to be highly selective and sensitive toward a particular analyte is a challenge. In addition, the effects of interfering ions should also be taken into consideration. This becomes even more difficult when the analyte, such as zinc, is present at much lower concentration compared to other common metals in biological systems. Biological sensing of zinc has come into prominence in the past 2 decades. 2-5 Existing primarily as zinc(II) in biological systems, it is the second most abundant transition metal only next to iron. 6,7 In the human body, the concentration of zinc(II) varies in different physiological environments and ranges from 12 μM in intracellular serum to about 0.1-0.5 mM in brain and nerve tissues. 8 Most of the zinc is sequestered by proteins and is responsible for multiple physiological roles such as gene transcription, metalloenzyme regulation, and neural signal transmission. 6,8-11 Severe neurolo- gical diseases such as Alzheimer’s and Parkinson’s are reported to be closely related to disorders in zinc metabolism. 8-11 The 3d 10 4s 0 electronic configuration of zinc(II) renders it spectroscopically silent toward conventional optical methods of detection, making fluorescence the most efficient way of detect- ing zinc in biological systems. 6,8,10 Detecting zinc in low con- centrations in vivo has attracted several researchers to develop fluorescence chemosensors or biosensors, most of which involve signal amplification upon identifying (or binding) the metal in question. Typical designs for such a sensor include a recognition moiety, usually a chelating group, responsible for the selectivity of the analyte. The recognition moiety is connected, via a spacer or not, to one or more photoactive units that generate the fluorescence signal. 12-14 Some of the early sensors for fluorescence detection of zinc(II) were based on derivatives of quinoline such as TSQ, 15 Zinquin, 16-18 and TFLZn. 19 These arylsulfonamides of quino- lines incorporate macrocyclic zinc(II) binding units but were, Received: September 25, 2010 Accepted: December 8, 2010