Bioorthogonal fluorogenic probes are becoming an ideal tool for live-cell fluorescence imaging. With the tetrazine bioorthogonal fluorogenic probe that displays fluorescence enhancement, the tetrazine plays the dual-role of a bioorthogonal reaction unit and the fluorescence quenching unit. The "off" and "on" states of the fluorescence probe are mainly controlled through inverse electron demand Diels-Alder (IEDDA) bioorthogonal reaction. We designed a series of turn-on tetrazine fluorescent probes with Donor-π-Acceptor (D-π-A) structure to achieve a high signal-to-noise ratio and specificity of fluorescence imaging. This series of probes reacted with the dienophile bicyclononyne, and then generated pyridazine structure in-situ that acted as an electron acceptor, resulting in a new D-π-A effect of fluorescent dyes, turning on the intramolecular charge transfer (ICT) effect. By adjusting the electron-donating groups and the degree of conjugation, tunable fluorescence spectra between 400-647 nm with fluorescence turn-on enhanced up to 500-fold have been achieved. This research lays the foundation for the further optimization of tetrazine bioorthogonal fluorescent probes and their applications in molecular imaging and biomedical fields.

Objective:To compare the characteristics of four commonly adopted animal models of hyperuricemia （HUA） for traditional Chinese medicine （TCM） screening， so as to choose the adequate model for screening Chinese herbs and herbal compounds capable of lowering the uric acid. Method:Fifty-four male SD rats were randomly divided into nine groups， namely the normal group， hypoxanthine （HX） + oxonic acid potassium salt （OAPS） model group， yeast extract （YE） + OAPS model group， low-dose adenine （AD） + ethambutol （EMB） model group， high-dose AD + EMB model group， and four positive drug allopurinol （Allo） groups. The modeling lasted for 14 d. The levels of serum uric acid （SUA）， urinary uric acid （UUA）， serum creatinine （SCr）， urea nitrogen （BUN）， kidney injury molecule 1 （KIM-1）， and neutrophil gelatinase-associated lipocalin （NGAL） were detected on the 3rd， 7th， and 14th days. Urine was collected on the 7th and 14th days to investigate changes in urine volume， and the crystals in the residual urine were observed under a polarizing microscope. After the modeling， the kidney was harvested and weighed， followed by pathological examination. Result:The urine volumes in the HX + OAPS model group and high-dose AD + EMB model group were significantly reduced （P<0.05）. The renal indexes of each model group， except for the YE + OAPS model group， were significantly elevated （P<0.05， P<0.01）. The increase in SUA of the HX + OAPS model group and YE + OAPS model group started later （P<0.05）. The KIM-1 and NGAL levels of the HX + OAPS model group rose significantly from the 7th day （P<0.05， P<0.01）， and the BUN increased significantly on the 14th day （P<0.05）. There was no significant difference in the above-mentioned indicators in the YE + OAPS model group. The SUA levels of the low- and high-dose AD + EMB model groups increased significantly on the 3rd day （P<0.05， P<0.01）， with a persistent increase found in the low-dose AD + EMB model group. Besides， the increase in BUN， KIM-1， and NGAL occurred later （P<0.05， P<0.01）. By contrast， the high-dose AD + EMB model group exhibited a transient increase in SUA. Moreover， the SCr， BUN， KIM-1， and NGAL elevation occurred earlier and were more obvious than those in the low-dose AD + EMB model group （P<0.01）. Remarkable histomorphological abnormalities were detected in the kidney of all model groups， except for the YE+OAPS model group， with the most severe injury present in the high-dose AD+EMB model group. Conclusion:The four models commonly used to screen TCM have their own characteristics. In the four models， the SUA elevation in the HX + OAPS model group and YE + OAPS model group started later， with the mild renal injury observed in the HX + OAPS model group instead of the YE + OAPS model group. The SUA of the low-dose AD + EMB model group increased rapidly and lasted for a long time， accompanied by mild renal injury. The SUA of the high-dose AD + EMB model group only showed a transient increase， accompanied by severe renal injury. The investigation on the characteristics and application of different models and the evaluation of these models based on sensitive and objective indicators are helpful for determining the suitable model for the screening of TCM targeting HUA in the future.