## 2 Results and Discussion
Meanwhile, the photos taken by the laser confocal microscope can be magnified and observed, as shown in Figure 4d, which can easily identify the various morphologies of the PS@TPEE fluorescent microspheres. Due to their excellent luminescent properties, PS@TPEE fluorescent microspheres can be prepared as fluorescent inks. In order to verify the application effect of the fluorescent ink, different patterns including QR codes, school logos, and flowers were printed on the paper. These patterns are invisible under visible light, but display bright blue fluorescence under ultraviolet light, as shown in Figure 4a and Movies S1 and S2. The PS@TPEE fluorescent microspheres' (TPEE content 5%) aqueous dispersion (solid content 10 wt%) can also serve as a filler for water-based anti-counterfeiting inks to write encrypted information on paper. The written content displays clear and bright blue fluorescence under ultraviolet light, and is not visible under sunlight (Figure 5b and Movie S3). Interestingly, the prepared fluorescent ink also exhibits erasability. After prolonged exposure to ultraviolet light, TPEE derivatives undergo cyclization under ultraviolet light to form diphenylphenanthrene (DPP) derivatives with ACQ activity [63; 64], causing the written letters to gradually disappear and the encrypted information to be deleted (Figure 5c). This irreversible erasure prevents encrypted information from being read multiple times, ensuring information security. Although the inks prepared from fluorescent microspheres with different morphologies are identical in the macroscopic view, the morphologies of the microscopic compositions are different when they are enlarged. Inspired by the different microstructures of plant and animal protective colors and fluorescent microsphere inks, we explored their applications in encryption and decryption. Figure 5: **(a)** Photo of screen-printed patterns under daylight (i) and ultraviolet (ii–vi) (PS@TPEE fluorescent microspheres are uniformly dispersed in 4 mass% polyvinyl alcohol in water). **(b)** Photograph of writing on cellulose paper with PS@TPEE fluorescent microspheres as water-based ink. (c) Photograph of letters written in fluorescent ink under ultraviolet light and the process of erasing. Figure 6 showed barcodes printed using fluorescent inks prepared with PS@TPEE microspheres. The barcode consists of several thin lines of different thicknesses, each representing a different piece of information. We used different morphologies of PS@TPEE fluorescent microspheres to produce ink to print a barcode with fluorescence and morphology encryption. In Figure 6, the printed line width of the barcode line composed of spherical PS@TPEE microspheres was defined as \"1\", the printed line width composed of apple-shaped microspheres was defined as \"1.1\", the printed line width composed of hemoglobin-shaped microspheres was defined as \"1.2\", and the printed line width composed of microspheres of different morphologies was the sum of their widths. As shown in the figure, the microsphere morphologies in the fluorescent barcode line were observed by SEM. From left to right, the microsphere morphologies were apple + hemoglobin type, spherical + hemoglobin type, spherical + apple type, and spherical + apple + hemoglobin type. The line widths were 2.3 (1.1 + 1.2), 2.2 (1 + 1.2), 2.1 (1 + 1.1), and 3.3 (1 + 1.1 + 1.2), respectively. By simply changing the PS@TPEE microspheres' morphologies and the corresponding line width, these printed barcode lines can be arranged and combined to obtain anti-counterfeiting patterns in the shape of microspheres that match the barcode. The order of microsphere morphologies in each line of different barcodes corresponds one-to-one with the numbers represented by the barcodes, forming a barcode database.