Comprehensive experimental design for detecting NO2- in food using gold nanoclusters
[Objective]The concept of nanoclusters has been introduced in the National Standards for the Teaching Quality of Undergraduates in Higher Education Institutions.However,nanocluster-related experiments have not yet been established for undergraduate chemistry students in universities across the country.This paper aims to incorporate the frontier of nanocluster research into comprehensive experimental teaching for undergraduates majoring in chemistry.As an example,we focus on the synthesis and characterization of gold nanoclusters and their application in detecting NO2 in food.[Methods]Herein,gold nanoclusters(AuEH)displaying bright red fluorescence at 640 nm were prepared using egg white and tetrachloro-auric acid(HAuCl4).This was achieved through a one-pot method at pH11 and 90 ℃ for 2 h,after which the reaction medium was adjusted to pH 3 and incubated for 2 h.The resulting AuEH exhibited a large Stokes shift of 260 nm,which is beneficial for the detection of small molecules or ions in biological samples as it can avoid interference from proteins.The AuEH displayed preferential selectivity for NO2-based on NO2-mediated AuEH fluorescence quenching.In addition,EDTA was used to mask the potent interference of Fe3+during actual sample detection.[Results]Compared with the National Food Safety Standards-Determination of nitrite and nitrate in food(GB 5009.33-2016),there was no significant difference between the AuEH method and the National Standard method.Importantly,the AuEH method eliminates the need for degreasing and deproteinization of meat product samples,thereby significantly improving its detection efficiency.In our study,three samples,namely ham sausage,leftover food,and boiled water,were selected for detection.The results showed the following:1)The content of NO2-in ham sausages from five different places of origin meets the National Standard.2)the content of NO2-in leftover food rises with each passing day,suggesting it should not be consumed after being left overnight.3)the content of NO2-in water boiled four times is below the National Standard for drinking water quality(1 mg/L,GB5749-2006),indicating it is safe to drink.Additionally,the NO2-content in the target solution can be determined using a smartphone,according to the color value(R/G/B)of a color card prepared by soaking a filter paper strip in the AuEH solution and air-drying it.Moreover,the AuEH can be used as graffiti and information encryption experiments to increase students'interest in chemical experiments from multiple perspectives.[Conclusions]The preparation process of AuEH involves rich theoretical knowledge,such as protein denaturation,redox reactions,soft and hard acid-base rules,and aggregation-induced luminescence enhancement(AIE).This process provides students with an opportunity to deepen their understanding of chemical knowledge in a practical context,understand the mechanism of AIE,and broaden their knowledge through literature review.Furthermore,by processing samples and determining NO2-content in food,students can master the operation of UV-visible and fluorescence spectrophotometers,thereby experiencing the firsthand impact of cutting-edge technology on experimental teaching reform.Interestingly,the detection of NO2-in several real food samples can help accurately establish healthy eating habits.Moreover,this experiment allows students to explore the frontiers of interdisciplinary subjects through the processing and measurement of actual samples.In short,this experiment is safe,interesting,economical,rich in content,easy to operate,and supports modular teaching.
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