Surface-Enhanced Raman Scattering Liquid Sensor for Quantitative Detection of Trace Melamine in Dairy Products

Raman spectroscopy has emerged as a fast, non-invasive, analytical method for the detec‐ tion and quantification of adulterants in many fields (Wong et al., 2007; Weng et al., 2003; Muik et al., 2003; Micklander et al., 2002; Peica et al., 2005; Rubayiza et al., 2005; Ellis et al., 2005; Paradkar et al., 2001; Abalde-Cela et al., 2009; Mulvihill et al., 2008; Zhou et al., 2006). Although signals from conventional Raman spectroscopy are very weak, great progress has been made with the development of surface-enhanced Raman spectroscopy (SERS) as a sensing method. SERS is a powerful spectroscopy technique that can provide ultra-sensitive characterization of adsorbate molecules on roughened metal (e.g., Ag, Au, and Cu) surfaces that produce a large enhancement to the Raman scattering signal (Lin et al., 2008; Lee et al., 1982; Wei et al., 2009; Küstner et al., 2009; Koglin et al., 1996; House et al., 2008; Leopold et al., 2003; Yaffe et al., 2008; Yu et al., 2007; Tiwari et al., 2007; Guingab et al., 2007; Tian et al., 2002; Wang et al., 2005; Chen et al., 2012; Betz et al., 2012). Generally, solid/liquid substrates are necessary to enhance the SERS spectrum to obtain adequate sensitivity.Solid substrates, generally prepared as gold or silver nanoparticles with a silica or alumina shell, have a wide application range. However, only a few examples of liquid substrates have been reported, though they are easily prepared and enhance the analysis some analytes.For example, using a silver colloid, at least a 105-fold enhancement of the Raman signal is achieved for the meas‐ urement of melamine (Zou et al., 2010).