Nanocluster-based Biosensor For Detection Of Lead Ions In Food

Chemical pollution is an important factor for food safety.The detection of heavy metal ions has drawn an increasing attention.Heavy metal ions can cause not only serious ecological pollution,but also foodborne diseases since they can eventually enter human body through food chain.Known as a major non-degradable environmental pollutant,heavy metal lead ion(Pb2+)is quite harmful to human health and can damage human immune system,cause respiratory diseases,chronic inflammation of kidney and heart,and ultimately affect brain development.Therefore,it is of great significance to develop a reliable,ultra-sensitive and highly specific sensor for Pb2+ detection.In this paper,we successfully synthesized a novel fluorescent silver nanocluster with DNA as a template(DNA-AgNCs).Based on the as-prepared silver nanocluster,a ratiometric fluorescence sensor was constructed for ultrasensitive and specific detection of Pb2+.In our design,single-stranded DNA template silver nanoclusters(G-DNA-AgNCs)exhibit green emission which can exhibit red emission by forming double-stranded DNA silver nanoclusters(ds-DNA-AgNCs)with its complementary DNA strands(R-DNA).The ds-DNA-AgNCs contains rA cleavage site of Pb2+-dependent DNAzyme configuration.In the presence of Pb2+,specific R-DNA fragments are released from the ds-DNA-AgNCs,resulting in discoloration of DNA-AgNCs from red to green.Since Pb2+ can continuously cut the rA site for a certain time,the red-green emission signal transition is amplified,thereby improving the sensitivity for Pb2+ detection.The developed strategy presents advantages as listed in the following.The ratio type fluorescent nanoclusters biosensor has a built-in correction function,is not easily affected by unpredictable factors such as the environment,and can improve the accuracy of detection results.The introduction of a single fluorophore design can eliminate problems such as complication of detection procedures caused by coupling multiple fluorophores.In addition,the biosensor has no obvious response to other metal ions,exhibiting excellent selectivity to Pb2+.Last but not least,the nanocluster-based sensor has realized the Pb2+ detection in real samples including lake water,tap water,sea shellfish food and human serum.A good linear relationship within the concentration range of 0.001 nmol/L to 10 nmol/L is obtained,and the detection limit reaches as low as 1.0 pmol/L.The as-prepared sensor has great potential application in heave metal ion detection in real sample.