Precision printing and control of total internal reflection structural colors: Applications in anti-counterfeiting and color blindness detection

Hypothesis The fabrication and optical performance of structural colors are influenced by microstructure geometry and surface interactions. Total internal reflection (TIR)-based structural colors, formed by microspherical crown structures on hydrophobic substrates, are expected to exhibit tunable optical properties such as single-sided visibility and angle dependence. By precisely controlling droplet volume and substrate wettability, it should be possible to achieve customizable anti-counterfeiting features and color blindness detection applications. Experiments Polyacrylic acid (PAA)-based inks were formulated with optimized molecular weight, solid content, and solvent composition to enable stable precision printing. Microspherical crown structures were printed on hydrophobic substrates under varying droplet volumes and contact angles. The printed patterns were characterized using scanning electron microscopy (SEM) and optical spectroscopy to analyze their morphology and color tunability. Environmental stability was tested under UV exposure, high temperatures, and freezing conditions. Findings The printed TIR structural colors displayed single-sided visibility, angle-dependent reflectance, and high color saturation. Controlled variations in microstructure size and contact angle enabled fine-tuning of the optical response. The technique successfully produced transparent anti-counterfeiting labels and a single-sample diagnostic tool for distinguishing different types of color blindness. The structural colors remained stable under environmental stress, demonstrating their potential for practical applications in security features and biomedical diagnostics.