Design,Synthesis And Biological Application Of Near-Infrared Fluorescent Probe With Viscosity Responsive Ability

Cell microenvironments,including viscosity,polarity,temperature,redox,and acidbase state,play a vital role in controlling diffusion,transportation of nutrients and metabolites and intermolecular interaction.Abnormal viscosity can cause the imbalance of the microenvironment in the organism,leading to a variety of diseases.Traditional viscosity measurement tools,such as falling ball viscometers,capillary viscometers and rotational viscometers,have many defects and are not suitable for viscosity measurement in biological microenvironments.Therefore,we need a method that can measure viscosity on the level of cells and even in vivo.Fluorescent probes are now widely used in cell microenvironment detection due to their high sensitivity,high resolution and noninvasiveness.Among them,molecular rotor based fluorescent probes have high sensitivity to viscosity,and the intramolecular rotation can be restricted with a high viscosity medium,and its fluorescence intensity and lifetime will be significantly increased.Therefore,we have developed two types of near-infrared organic small molecule fluorescent probes based on viscosity that can be used in living organisms.The specific work is as follows:1.N,N-diethylamino-substituted coumarin was introduced into the rhodamine fluorophore skeleton to form a D-π-A structure to make its emission wavelength red shift,and the two fluorophores were connected through a rotatable vinyl bond based on the principle of molecular rotor,thereby the near-infrared probe P1 with viscosity responsive ability which targeting the mitochondria was synthesized.The maximum absorption/emission of probe P1 were 621/791 nm,and the fluorescence emission of the probe showed an increase(72-fold)with the viscosity of the water-glycerol mixture gradually increasing.It was found that P1 was insensitive to pH and active substances such as ROS/RSH.This probe has been successfully used for cell and zebrafish imaging,and also exhibited the significant fluorescence increase due to the enhanced viscosity in tumors,bacterial wounds and livers of diabetic mice.2.Based on the main structure of the probe P1 in the previous work,we closed the N,N-diethylamine group at the 7-position of the coumarin ring to block the twisting,leading to the increased photophysical properties and superior sensing performance,thereby the near-infrared probe P2 with viscosity responsive ability was designed and constructed.The maximum absorption/emission of the near-infrared viscosity probe P2 were 654/803 nm,and the fluorescence emission of the probe showed a dramatic increase(113-fold)with the viscosity gradually increasing.Due to the good photothermal and photodynamic properties,probe P2 could not only perform abnormal viscosity imaging on the wound of bacterial infection mice,but also has obvious antibacterial effect on Staphylococcus aureus.Finally,we succeeded in performing photothermal and photodynamic combined therapy on bacterial infected mice through the guidance of fluorescence imaging based on the responses to viscosity.