Simple Chip Electrophoresis Titration of Neutralization Boundary with EDTA Photocatalysis for Distance-Based Sensing of Melamine in Dairy Products

Abstract

Melamine was sometimes adulterated to dairy products for false protein content increase in developing countries. However, a portable sensor has not been developed for on-spot determination of melamine in dairy products yet. Herein, a distance-based sensor was advanced for the quantification of melamine in dairy products based on chip electrophoretic titration (ET) of moving neutralization boundary (NB) and EDTA photocatalysis. In the chip sensor, EDTA, HO, and leucomalachite green (LMG) were added in the anode well. Under UV light, EDTA photocatalyzes HO and colorless LMG as HO and color malachite green (MG) with one positive charge. When applying an electric field, the MG in the anode well migrated into the channel and was neutralized with the base in the channel, resulting in colorless MG-OH and NB. If the melamine-content dairy sample was added into the EDTA-HO-LMG system, HO reacts with melamine, leading to the decrease of MG. Thus, the higher the melamine content in dairy products, the shorter the distance of NB migration under the given time, implying a distance-based sensor of melamine. A series of experiments manifested the validity of ET-NB sensor for detection of melamine. Moreover, the results revealed the numerous merits of ET-NB sensor, such as good selectivity, high sensitivity (LOD down to 0.20 μM for milk and 0.10 μM for infant formula vs the FDA safety limits of 20 μM for milk and 8.0 μM for infant formula), good repeatability and recoveries (87-108% for milk, 90-107% for formula). Particularly, the cell phone-like sensor was portable, simple (no any pretreatment), rapid (within 15 min), as well as low cost, to evaluate the quality of dairy products. The developed sensor has great potential in on-spot detection of melamine in dairy products as well as other analytes, at which we are testing in our lab.

Facile Counting of Ligands Capped on Nanoparticles via a Titration Chip of Moving Reaction Boundary Electrophoresis

“…Herein, we outlined the electrophoresis titration (ET) model of counting ligands capped on NPs by relying on the protein ET, , enzyme catalysis ET, and photocatalysis ET via moving reaction boundary (MRB). Figure and Figure S1 show the NPs-ET model for counting the ligands on the NPs surface.…”

Convenient and sensitive colorimetric detection of melamine in dairy products based on Cu(ii)-H2O2-3,3′,5,5′-tetramethylbenzidine system

“…The result implied the necessity of melamine for the consumption of H 2 O 2 and thus inducing absorbance change and the weak interference of Vit C added as an essential nutrient in both liquid milk and infant formula powder. The weak interference of Vit C might be owing to the following two accounts: the milk proteins in dairy products might induce “disappearance” of Vit C and slowed down the auto-oxidation of Vit C significantly; the excellent reducibility of the three amino groups endows melamine with prior redox of melamine–H 2 O 2 in contrast to Vit C. 49 …”

“…Therefore, when added melamine into the system, melamine can quickly react with H 2 O 2 which possesses good oxidation property to generate a stable addition compound C 3 H 6 N 6 $H 2 O 2 (Reaction 2). 28,49…”

“…The result implied the necessity of melamine for the consumption of H 2 O 2 and thus inducing absorbance change and the weak interference of Vit C added as an essential nutrient in both liquid milk and infant formula powder. The weak interference of Vit C might be owing to the following two accounts: the milk proteins in dairy products might induce "disappearance" of Vit C and slowed down the auto-oxidation of Vit C signicantly; the excellent reducibility of the three amino groups endows melamine with prior redox of melamine-H 2 O 2 in contrast to Vit C. 49 Then, the recovery experiments were carried out by spiking different concentrations of melamine in each sample to evaluate the accuracy of the colorimetric sensing system as no melamine was found in both liquid milk and infant formula powder. As shown in Table 1, the recoveries for melamine are ranging from 96.0% to 104.5%, and the relative standard deviations (RSDs) are all below 4.7%, demonstrating no severe interference in the tested dairy product samples.…”

“…45,46 Considering the fact that melamine can quickly interact with H 2 O 2 producing the addition compound of C 3 H 6 N 6 $H 2 O 2 which is stable even under 100 C according to the thermal analysis results, 48 the determination of melamine based on the consumption of H 2 O 2 in H 2 O 2 related reaction have been reported. 28,49 Inspired by the above reports, herein, we explored a new simple Cu 2+ -H 2 O 2 -TMB system based colorimetric method for the detection of melamine without any modication or preparation of nanomaterials. In this method, Cu 2+ can catalyse the oxidation of TMB to oxidized TMB (oxTMB) with the colour changing from colourless to blue in the presence of H 2 O 2 due to the generation of $OH by the Cu 2+ -based Fenton reaction.…”