Invisible photonic prints are patterned photonic materials that can reveal hidden patterns under certain stimuli, which are widely used in anti-counterfeiting, identification marking, encoding, and dynamic displays. Traditionally, such photonic prints can be obtained through patterning photonic hydrogels with different responsive polymers. Yet, the visibility of the revealed prints is still not satisfactory due to the limited contrast between the responsive and non-responsive regions. In this study, we report revealable photonic prints with high visibility by patterning photonic hydrogels with two oppositely pH-responsive polymers comprising weak acidic and weak basic groups. The two distinct pH-responsive polymers can be protonated and deprotonated in the same environment, triggering the variation of colors from the initial state to the opposite directions in the different regions of the photonic prints. Therefore, the contrast of the photonic patterns is greatly improved, increasing the naked-eye detection range of colorimetric sensing. This study provides a new opportunity for designing patterned photonic materials for use in improved visual sensors.
High mechanical strength, highly visible, and admirable grafting molecular ability is the key challenge for colloidal photonic crystal (CPC) barcode beads in multiplex analysis fields. To achieve this goal, we proposed self-adhesion particles, polydopamine-coated SiO2 nanoparticles (PDA@SiO2), to construct CPC barcode beads by droplet-based microfluidic approach. Because of the adhesion, broad absorption of light, and “active” functional groups of PDA, the beads are endowed with high robustness, visibility, and excellent biomolecule immobilization. Ultrasonic treatment and compression experiments demonstrated that PDA@SiO2 CPC barcode beads have a high mechanical strength. Color analysis illustrated that PDA@SiO2 CPC beads exhibited a high visibility in color. The verification of fluorescent-tagged biomolecule conjugation together with the antigen detection stated that PDA@SiO2 CPC beads are capable of immobilizing biomolecule by covalent binding. With a sandwich format, the beads were applied to analyze the tumor makers including alpha fetal protein, carcinoembryonic antigen, and prostate specific antigen from practical clinical serum. The proposed suspension arrays using PDA@SiO2 CPC beads as a barcode showed acceptable accuracy and detection reproducibility.
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