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Nieuwoudt M.K.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Nieuwoudt M.K.,University of Auckland | Holroyd S.E.,Fonterra Research and Development Center | McGoverin C.M.,The Dodd Walls Center for Photonic and Quantum Technologies | And 5 more authors.
Journal of Dairy Science | Year: 2016

Adulteration of milk for commercial gain is acknowledged as a serious issue facing the dairy industry. Several analytical techniques can be used to detect adulteration but they often require time-consuming sample preparation, expensive laboratory equipment, and highly skilled personnel. Here we show that Raman spectroscopy provides a simple, selective, and sensitive method for screening milk, specifically for small nitrogen-rich compounds, such as melamine, urea, ammonium sulfate, dicyandiamide, and for sucrose. Univariate and multivariate statistical methods were used to determine limits of detection and quantitation from Raman spectra of milk spiked with 50 to 1,000 mg/L of the N-rich compounds and 0.25 to 4% sucrose. Partial least squares (PLS) calibration provided limit of detection minimum thresholds <200 mg/L (0.02%) for the 4 N-rich compounds and <0.8% for sucrose, without the need for surface-enhanced Raman spectroscopy. The results show high reproducibility (7% residual standard deviation) and 100% efficiency for screening of milk for these adulterants. © 2016 American Dairy Science Association.

Nieuwoudt M.K.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Nieuwoudt M.K.,University of Auckland | Martin J.W.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Martin J.W.,University of Auckland | And 17 more authors.
Analytical and Bioanalytical Chemistry | Year: 2016

Nanostructured gold substrates provide chemically stable, signal-enhancing substrates for the sensitive detection of a variety of compounds through surface-enhanced Raman spectroscopy (SERS). Recent developments in advanced fabrication methods have enabled the manufacture of SERS substrates with repeatable surface nanostructures that provide reproducible quantitative analysis, historically a weakness of the SERS technique. Here, we describe the novel use of gold-sputtered Blu-ray disc surfaces as SERS substrates. The unique surface features and composition of the Blu-ray disc recording surface lead to the formation of gold nano-islands and nanogaps following simple gold sputtering, without any background peaks from the substrate. The SERS performance of this substrate is strong and reproducible with an enhancement factor (EF) of 103 for melamine. A limit of detection (LOD) for this compound of 70 ppb and average reproducibility of ±12 % were achieved. Gold-sputtered Blu-ray discs thus offer an excellent alternative to more exotic gold SERS substrates prepared by advanced, time-consuming and expensive methods. [Figure not available: see fulltext.] © 2016 Springer-Verlag Berlin Heidelberg

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