A New Strategy And Imaging Application For Enhanced Fluorescence Signal Amplification Based On H-Aggregate

Nanocontainers have high loading capacity and can be loaded with a large number of fluorescent dyes,which were used as carriers to construct signal amplification probes with high sensitivity.However,due to the large amount of loaded-fluorescent dyes,a evident background fluorescence signal was inevitable.To reduce this background signal,fluorescence quencher was introduced to be co-loaded in nanocarrier to obtain high signal-to-background ratio from FRET effect.However,for these nanoprobes,though the addition of fluorescence quenchers causing lower background fluorescence signal,there are still some problems for practical application.For example,the liberative fluorescence quenchers may also affect the signal intensity of probe seriously,and the synthesis of nanoprobe was complicated.To address these issues,a new strategy for construction of quencher-free and low-background nanoprobes needs to be developed.In this paper,based on our previous works,we obtain a novel protein-enhaned fluorophore based on molecular H-aggregation.Furthermore,a low-background signalamplifying nanoprobe was constructed to sense the intracellular enzymes.The specific work is as follows:1.Synthesis of low-background protein-enhancd dyes based on H-aggregation.Our group has reported a fluorescent dye that can bind with cytoplasmic protein to enhance the fluorescence singal intensity.Based on this,the molecular structure of this dye is further improved to increase the hydrophobicity,and it can aggregate in aqueous solution through hydrophobic effect.Besides,a face-to-face stacking effect between moleculars will occur because of the large conjugated and complanate molecular structure,resulting in aggregationinduced quenching(ACQ)phenomenon for dye to quench the fluorescence.But this improved dye still maintains the property of binding with cytoplasmic proteins,and these particular characteristics make it suitable for fluorescent sensing as signal units.Thus,we have synthesized a protein-enhanced dye with low-background fluorescence signal in this section.2.Construction and application of human neutrophil elastase(HNE)sensitive nanoprobe.Utilizing the HNE-responsive polymeric micelles as nanocantainer to load synthetic fluorophore,we constructed a novel nanoprobe to sense HNE.When the probe entered the cell,the nanoprobe maintained a low fluorescence background due to H-aggregation of SQ-D.However,the reaction of HNE with the active polymer can trigger the degradation of micelles to release the dye,and the free dye can further bind to cytoplasmic proteins to greatly enhance the fluorescence.Based on its low background and high signal intensity after target recognition,this signal-amplifying nanoprobe can sense HNE with high signal-to-background ratio,which has potential to diagnose HNE-related diseases in the early stages.