One of the most common diseases globally which takes numerous lives is lung cancer. The high concentrations of aldehydes found in tobacco smoke and motor vehicle exhaust are among the contributors for lung cancer. There is a lot of interest in developing a nanosensor for identifying long-chain aldehydes. The conventional methods for detecting aldehyde are highly complex, expensive, and time-consuming. To overcome this drawback, alternative detection techniques such as fluorescence techniques are needed for the quick, easy, and affordable identification of aldehydes. Aldehyde molecules and their derivatives are often used as biomarkers to aid in the diagnosis and treatment of lung cancer patients. This property has been exploited to design an effective nanosensor for identification of long-chain aldehydes. In this study, we created a water-soluble fluorescence nanosensor based on dye-encapsulated polymeric nanoparticles consisting of naphthalimide and ethyl cellulose (namely EC@Naph).� According to fluorescence results, the EC@Naph demonstrated excellent performance for recognising long-chain aldehydes. Notably, it offered rapid detection and good sensitivity to octanal and nonanal. This sensing platform showed a limit of detection (LOD) of 41 ?M and a limit of quantification (LOQ) of 275 ?M, towards nonanal sensing in acetate buffer with a pH of 5.0 with a reaction time of 2.0 min. Interestingly, this sensing platform can perform naked-eyed sensing for nonanal. Expectedly, the developed nanosensor possesses a high degree of selectivity and sensitivity for detection of nonanal in aqueous media.