739 Research Article Received: 7 July 2009 Accepted: 18 August 2009 Published online in Wiley Interscience: 19 October 2009 (www.interscience.wiley.com) DOI 10.1002/jrs.2505 Surface-enhanced Raman spectroscopy coupled with dendritic silver nanosubstrate for detection of restricted antibiotics Lili He, a Mengshi Lin, a* Hao Li b and Nam-Jung Kim b Surface-enhanced Raman spectroscopy (SERS) coupled with dendritic silver nanosubstrates was used in this study for rapid detection and characterization of restricted antibiotics. Dendritic silver nanosubstrates were prepared through a simple replacement reaction and stored in deionized water for months. SERS methods with near-IR excitation at 785 nm using silver nanosubstrates were evaluated for detection of three restricted antibiotics (i.e. enrofloxacin, ciprofloxacin, and chloramphenicol) prepared in standard solutions. SERS was capable of identifying and characterizing three antibiotics quickly and accurately. Silver dendrites exhibit satisfactory and consistent performance with an analytical enhancement factor of ∼10 4 . The limit of detection and limit of quantification for antibiotics could reach the level of 20 ppb. Silver dendrites can be kept in deionized water for up to 6 months with no signs of degradation in SERS performance. These results demonstrate a great potential of using SERS coupled with silver dendrites for rapid detection, classification, and quantification of chemical contaminants. Copyright c  2009 John Wiley & Sons, Ltd. Keywords: SERS; antibiotics; silver dendrites; nanosubstrate Introduction Surface-enhanced Raman spectroscopy (SERS) is a promising analytical method for rapid and accurate detection of chemicals and biochemicals. [1–4] SERS was first observed by Fleishchman et al. [5] in 1974. When sample molecules are de- posited onto metallic nanostructures, their Raman signals can be enhanced tremendously. [6] It is generally accepted that SERS mechanisms involve both electromagnetic enhancement and chemical charge transfer effect, and electromagnetic enhance- ment contributes much more to overall SERS phenomena than the chemical enhancement. [7] The limit of detection (LOD) of SERS could reach the ppb level or even down to a single molecule. [8] A good nanosubstrate is the key to SERS applications. To date, various types of nanostructures have been developed through either ‘bottom–up’ or ‘top–down’ approaches. [1,9,10] However, many of the existing SERS nanosubstrates have the problems of inconsistent performance or involving complex and expensive equipment for substrate fabrication. Therefore, better methods are needed to make nanosubstrates that are reproducible, sta- ble and easy to make, and can provide satisfactory SERS signal enhancement. In this study, we aim to apply SERS coupled with dendritic silver nanosubstrates for rapid detection and char- acterization of restricted antibiotics. In recent years, there has been mounting concern about the residue of illegal or overdose of antibiotics in food products coming into the United States. For instance, in June 2007, the US Food and Drug Administration (FDA) banned importation of five types of farmed seafood products imported from Asia because of contamination with banned antimicrobial drugs. [11] Fluoro- quinolones [e.g. enrofloxacin (ENRO), ciprofloxacin (CIP)] and chloramphenicol (CHL) were implicated in those drug con- tamination incidents. Those broad-spectrum antibiotics are ef- fective in the treatment of various bacterial diseases in an- imal husbandry and aquaculture. However, residues of an- tibiotics in food products are of great concern because of the development of antibacterial resistance to these drugs in humans. [12 – 14] Current analytical methods for detection of antibiotics are mainly chromatography-based methods, including gas chro- matography with mass spectrometry (GC–MS), [15] liquid chro- matography with mass spectrometry (LC–MS), [16 – 18] or fluores- cence detection (LC–fluorescence). [19] Particularly, LC–MS is one of the most popular methods used by the FDA for detection and quantification of antibiotics. The LOD of LC – MS could reach 1 – 10 ppb. [16 – 18,20] However, chromatography-based methods are time consuming and labor intensive, requiring complex procedures of sample treatment and well-trained personnel to perform the test. Therefore, it is of critical importance to develop simpler, quicker, and sensitive analytical methods such as SERS for detection of re- stricted antibiotics. The objective of this study was to develop SERS methods coupled with dendritic silver nanosubstrates for rapid detection, classification, and quantification of three restricted antibiotics. ∗ Correspondence to: Mengshi Lin, Division of Food Systems and Bio- engineering, University of Missouri, Columbia, MO 65211, USA. E-mail: linme@missouri.edu a Division of Food Systems and Bioengineering, University of Missouri, Columbia, MO 65211, USA b Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, MO 65211, USA J. Raman Spectrosc. 2010, 41, 739–744 Copyright c  2009 John Wiley & Sons, Ltd.