Multicolor Fluorescent Paper Strips For On-site Rapid Visual Quantitative Detection Of Heavy Metal Ions

Lead ions(Pb²⁺)and cadmium ions(Cd²⁺)are two typical heavy metal ions with high toxicity and persistent bioaccumulation.Therefore,it is of great significance for environmental protection to construct a method for rapid quantitative detection of Pb²⁺and Cd²⁺.Multicolor fluorescent probes contain two or more emission,which greatly improves detection accuracy by analyzing emission intensity ratio to provide built-in correction of environmental impact.Fluorescent paper strips are portable,cheap and easy to operate.It can realize the visual detection of analytes without resorting to additional means,but it has difficult in quantitative analysis.Herein,based on the unique fluorescent properties and recognition capabilities of carbon dots?CDs?,gold nanoclusters and luminescent graphene oxides,multicolor fluorescent probes that selectively detect Pb²⁺and Cd²⁺were constructed respectively,and the effect of on-site rapid visual quantitative detection of Pb²⁺and Cd²⁺by multicolor fluorescent paper strips was researched.The main results are as follows.?1?Multicolor fluorescent paper strips for on-site rapid visual quantitativeDesigned and synthesized multicolor fluorescent CDs,and studied the response of CDs to Pb²⁺.CDs that responds to Pb²⁺were used as signal probes,and another CDs that does not respond to Pb²⁺and have different fluorescent color were used as reference probes,and then multicolor fluorescent probes were constructed by optimizing the mixing ratio of CDs.The multicolor fluorescent probes initially showed stable blue fluorescence.In the presence of Pb²⁺,the blue fluorescence was quenched while the red fluorescence remains unchanged.Thus,the obvious color change from blue to red was observed under ultraviolet?UV?lamp.In addition,the Pb²⁺concentration has an excellent linear relationship with the fluorescence intensity ratio(I₄₅₂/I₆₂₀),and the limit of detection?LOD?was as low as 2.89 n M,which is far lower than the minimum allowable content of Pb²⁺in drinking water prescribed by WHO?0.01 mg/L?.The probe has good selectivity and anti-interference ability,and the reaction process can be completed in 5 min.The inkjet printing technology was used to prepare fluorescent paper strips.It was found that the fluorescent color of paper strips changes significantly with the concentration of Pb²⁺,which can realize the visual detection of Pb²⁺.A smartphone was used to identify RGB values of fluorescent color,analyzed the data of Pb²⁺concentration and B/R values obtained a good linear relationship and LOD was45.86 n M.The spiked recovery experiment of actual water samples has obtained high recovery rates of 92.8%?115.2%,which proved that the method of on-site rapid visual quantitative detection of Pb²⁺has practicality.?2?Multicolor fluorescent paper strips for on-site rapid visual quantitative detection of Cd²⁺Designed and synthesized multicolor fluorescent nanomaterials and studied the response to Cd²⁺.It was found that the orange fluorescence of Au NCs can be specifically enhanced by Cd²⁺,and the luminescent graphene oxide modified by ethylenediamine was relatively stable and not affected by Cd²⁺,so they were selected as materials for constructing multicolor fluorescent probes.By introduced copper ions to optimized the visualization effect and selectivity of multicolor fluorescent probe.After added Cd²⁺,the probe can be observed color change from blue to red under UV lamp.It was found that the Cd²⁺concentration versus the fluorescence intensity ratio(I_EDA-GO/I_{Au NCs})has a good linear relationship,the LOD was as low as 33.3 n M,and the probe has high selectivity and high anti-interference ability,the detection process can be completed in about 7 min.The fluorescent paper strips prepared by the inkjet printing technology has obvious fluorescence color changes when detecting Cd²⁺,and can realize rapid visual detection of Cd²⁺.The smartphone was used to identify RGB values of fluorescent color,and it was found that there was a good linear relationship between the Cd²⁺concentration and the R/B values.The LOD calculation result was 0.1?M,which was lower than Cd²⁺maximum allowable limit in rice?0.2 mg/kg?stipulated in the National Food Safety Standard in China?GB 2762-2017?.In addition,the spiked recovery of Cd²⁺in rice samples was 91.4%?99.3%,which proved that the method of on-site rapid visual quantitative detection of Cd²⁺by multicolor fluorescent paper strips was practical.