Depression is a highly prevalent and complex mental disorder with significant therapeutic limitations. This review comprehensively examines how lactic acid bacteria (LAB) and fermented dairy products alleviate depressive symptoms via the microbiota-gut-brain axis (GBA). It further summarizes recent advances in probiotic delivery technologies and outlines future directions for developing effective LAB-based interventions. Acting as psychobiotics, LAB can mitigate depressive-like behaviors in rodent models. Evidence indicates this effect occurs through multiple pathways, including the modulation of tryptophan metabolism, the suppression of neuroinflammation, and the engagement of vagus-nerve-mediated signaling. Specific strains such as Lactiplantibacillus plantarum and Lacticaseibacillus paracasei have demonstrated pronounced antidepressant effects. This is reflected by elevated levels of serotonin (5‑HT) and brain‑derived neurotrophic factor (BDNF). These effects are coupled with reductions in inflammatory markers. The synergistic effects of LAB within fermented‑milk matrices further enhance functionality through the generation of bioactive metabolites such as γ‑aminobutyric acid (GABA), short‑chain fatty acids (SCFAs), and peptides. Translating these findings into practice requires overcoming crucial delivery challenges. Advances in microencapsulation and targeted delivery systems are pivotal for protecting LAB viability and ensuring effective colon release. Future integration of AI for modeling gut-flora homeostasis and personalizing delivery platforms holds great promise. In conclusion, this review consolidates the potential of LAB and fermented dairy products as dietary strategies against depression, synthesizes underlying mechanisms, and highlights delivery technologies. Together, these insights provide a foundation for developing next-generation functional foods and precision-nutrition interventions targeting the GBA.

This study introduced an electrochemical sensor for the rapid, sensitive, and accurate detection of ciprofloxacin (CIP). The sensor utilized a screen-printed carbon electrode (SPCE) modified with Pd@Nb₂C nanocomposites, which were prepared through the in-situ reduction of palladium nitrate on Nb₂C nanosheets, resulting in a uniform distribution of Pd nanoparticles. Subsequently, they were drop-coated onto the SPCE surface, forming a Pd@Nb₂C/SPCE electrochemical sensing platform. The electrochemical analysis demonstrated the excellent electrochemical performance of the sensor. Pd@Nb₂C/SPCE showed a consistent linear correlation between redox peak current (I_P) and CIP concentration (c_CIP) in the range of 10–150 μmol/L, boasting a detection limit of 3 μmol/L. Notably, this technique tracked CIP in both whole and skimmed milk, achieving a high recoveries of 96.36%–105.40% (n = 3). Moreover, the sensor exhibited exceptional selectivity towards CIP, remaining unaffected by various interferences such as sulphonamide, amoxicillin, tetracycline, and chloramphenicol. These findings hold enormous promise for enabling real-time and rapid monitoring of CIP in milk.