A novel label-free NIR aptasensor based on triphenylmethane dyes for rapid detection of salicylic acid.

Salicylic acid (SA) is a critical phytohormone involved in plant growth, development, and defense responses, making its precise quantification essential for both agricultural management and environmental monitoring. Here, we report a novel label-free near-infrared aptasensor (NIRApt) for the rapid and sensitive detection of SA, utilizing a rationally selected triphenylmethane (TPM) dye. Through systematic screening, ethyl violet (EV) was identified as the optimal fluorophore, showing pronounced fluorescence enhancement upon binding to a SA-specific aptamer. The sensing mechanism relies on target-induced competitive displacement, in which SA binding triggers the release of EV from the aptamer complex, resulting in a marked quenching of the fluorescence signal. The developed NIRApt exhibits high specificity and sensitivity, with a detection limit of 0.63 μM and a broad linear range of 0-30 μM. Remarkably, it demonstrates an ultrafast response within one minute, highlighting its efficiency for rapid quantitative detection. Its practicality was validated in spiked cherry tomato samples, achieving high detection accuracy. This platform offers key advantages including label-free operation, low background signal, minimal sample preparation and rapid response, demonstrating strong potential for food safety analysis and environmental monitoring of SA.