Robust, Highly Visible, and Facile Bioconjugation Colloidal Crystal Beads for Bioassay.

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.