Applied Surface Science 420 (2017) 963–969 Contents lists available at ScienceDirect Applied Surface Science jou rn al h om ep age: www.elsevier.com/locate/apsusc Full Length Article Melamine dependent fluorescence of glutathione protected gold nanoclusters and ratiometric quantification of melamine in commercial cow milk and infant formula Gopi Kalaiyarasan a,b , Anusuya K c , James Joseph a,b,∗ a Academy of Scientific and Innovative Research (AcSIR), CSIR-Central Electrochemical Research Institute (CSIR-CECRI) Campus, Karaikudi, 630003, India b Electrodics and Electrocatalysis Division, CSIR-CECRI, Karaikudi, 630003, India c School of Chemistry, Madurai Kamaraj University, Madurai, 625021, India a r t i c l e i n f o Article history: Received 23 March 2017 Received in revised form 3 May 2017 Accepted 23 May 2017 Available online 26 May 2017 Keywords: Melamine Milk adulteration Infant formula Food analysis Optical biosensor Ratiometric fluorescence Gold nanoclusters a b s t r a c t Companies processing the milk for the further production of powdered infant formulation normally check the protein level through a test measuring nitrogen content. The addition of melamine which is a nitrogen-rich organic chemical in milk increases the nitrogen content and therefore enhances its appar- ent protein content. However, the melamine causes kidney failure and death owing to the formation of kidney stone. Thus the determination of melamine in humans and milk products have gained great significance in recent years. The gold nanoclusters (AuNCs) have attracting features due to its unique electronic and optical properties like fluorescence nature. Therefore one can use AuNCs in the field of biosensor, bio-imaging, nanobiotechnology, drug delivery, diagnosis etc. We report, a new ratiometric nanosensor established for the selective and sensitive detection of melamine based optical sensing using glutathione stabilized AuNCs. The AuNCs were characterized by high-resolution transmission electron microscopy (HR-TEM), UV–visible and Photoluminescence (PL) spectroscopic techniques. In the presence of melamine, the PL intensity at 430 nm increases owing to the (turn-on) enhancement in fluorescence, whereas PL intensity at 610 nm decreases due to the melamine-induced aggregation and subsequent aggregation-enhanced emission quenching. The observed changes were ascribed to the hydrogen bond- ing interaction between melamine and AuNCs, which led to the aggregation of the nanoclusters. This was confirmed by dynamic light scattering and HR-TEM measurements. The present probe showed an extreme selectivity towards the determination of 28.2 M melamine in the presence of 100-fold excess of common interfering molecules such as Alanine, Glycine, Glucose, Cystine etc. The proposed method was successfully applied to determine melamine in cow milk. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Melamine (C 3 H 6 N 6 ) is white colored odorless heterocycle compound, which is used in many industries such as melamine- formaldehyde resins, fire-retardant materials and pesticides [1]. Melamine is illegally mixed with milk to increase the protein level due to its high nitrogen content (66.6% by mass) and low cost. David I. Ellis and Royston Goodacre described importance and prob- lems of adulteration/contamination in food such as melamine in ∗ Corresponding author at: Academy of Scientific and Innovative Research (AcSIR), CSIR-Central Electrochemical Research Institute (CSIR-CECRI) Campus, Karaikudi, 630003, India. E-mail addresses: jameskavalam@yahoo.com, jamescecri@cecri.res.in (J. Joseph). milk and infants [2]. High concentration of melamine consumption could induce the formation of insoluble melamine-cyanurate co- crystals in the kidney as a result of renal damage in infants and causes sometimes even death. The concentration of melamine was conventionally quantified by the Kjeldahl method and Dumas test [3]. Several techniques have been used to measure the melamine in milk and its products. For example gas chromatography-mass spectrometry (GC–MS) [4], High Performance Liquid Chromatog- raphy [4], Chemiluminescence [5], near-infrared (NIR) or Raman spectroscopy [6–8], NIR imaging, colorimetric detection [9] and electrochemical methods [10] etc. Still, these methods are relatively high cost, large time consumption, and complicated instrument setup thus not flexible to regular usage. Therefore, it is necessary to develop a simple, low-cost and highly selective reliable detection methods to quantify the trace amount of melamine without sample pre-treatment and long procedure. http://dx.doi.org/10.1016/j.apsusc.2017.05.193 0169-4332/© 2017 Elsevier B.V. All rights reserved.