Abstract <p>Platinum nanoclusters (<b>PtNC</b>s) with fluorescent properties have been prepared using Acid Red G as a stabilizer, potassium hexachloroplatinate as a precursor, and sodium borohydride as a reducing agent, with a reaction time of about 2 h. The optimal excitation wavelength of the synthesized PtNCs is 333 nm, and the optimal emission wavelength is 431 nm. It has been found that tetracycline (<b>TC</b>) can significantly quench the fluorescence of the synthesized PtNCs. A good linear relationship was observed between the quenching value (F₀–F) of the PtNCs fluorescence intensity and the TC concentration in the range of 5.00–50.00 μM, with a correlation coefficient (<i>r</i>) of 0.9962. Thus, a fluorescence analysis method for measuring TC was established based on the above phenomenon, with a detection limit of 2.04 μM (3σ/<i>k</i>). The standard concentration of TC was added to tap water for spiked recovery experiments, the recovery rate was in the range of 97.37–100.03%, and the relative standard deviation ranged from 1.96 to 4.76%. This indicates that the established method has demonstrated feasibility for detecting TC content in water samples. Meanwhile, PtNCs were used as fluorescent probes to achieve visual quantitative detection of TC concentration using smartphones and colorimetric analysis software.</p>