DNA self-assembled fluorescent nanoprobes have been developed for bio-imaging owing to their high resistance to enzyme degradation and great cellular uptake capacity. In this work, we designed a new Y-shaped DNA fluorescent nanoprobe (YFNP) with aggregation-induced emission (AIE) characteristic for microRNA imaging in living cells. With the modification of the AIE dye, the constructed YFNP had a relatively low background fluorescence. However, the YFNP could emit a strong fluorescence due to the generation of microRNA-triggered AIE effect in the presence of target microRNA. Based on the proposed target-triggered emission enhancement strategy, microRNA-21 was detected sensitively and specifically with a detection limit of 122.8 pM. The designed YFNP showed higher bio-stability and cell uptake than the single-stranded DNA fluorescent probe, which has been successfully applied for microRNA imaging in living cells. More importantly, the microRNA-triggered dendrimer structure could be formed after the recognition of target microRNA, achieving a reliable microRNA imaging with a high spatiotemporal resolution. We expect that the proposed YFNP will become a promising candidate for bio-sensing and bio-imaging.

Background: The accurate detection of remifentanil and sufentanil in biological samples is challenged by their rapid metabolism and instability, complicating clinical and forensic toxicology analysis. This study aimed to evaluate the stability of remifentanil, sufentanil, and their primary metabolites—remifentanil acid and norsufentanil—in human whole blood and urine. Methods: A high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS/MS) method was developed and validated for simultaneous quantification, demonstrating satisfactory linearity (0.10–200 ng/mL, r² > 0.99), detection limits (0.01–0.20 ng/mL), and recovery rates (85.06–119.42%). Stability was assessed under varying temperatures (4 °C, −20 °C, −80 °C) and anticoagulant conditions (EDTA-K₂, sodium heparin, sodium citrate) over 35 days. Results: Remifentanil exhibited significant instability in whole blood, degrading over 50% within 6 h at 4 °C, whereas stability was markedly improved at −80 °C and in sodium citrate-containing samples. Remifentanil acid remained stable for up to 35 days at −80 °C. Sufentanil was generally more stable, particularly at −80 °C in both blood and urine, while norsufentanil remained stable for 7 days at −20 °C in citrate-anticoagulated blood but degraded rapidly at 4 °C. These findings support specific recommendations for sample preservation, including storage at −80 °C and the use of sodium citrate as an anticoagulant, to enhance detection reliability in toxicological and pharmacokinetic studies.