Carbon dots (CDs) are a member of fluorescent carbon nanomaterials that are widely applied in bioimaging, photothermal therapy (PTT), and biosensors for its tunable fluorescence, photothermal conversion property, and excellent biocompatibility. Surface passivation and doping especially the doping of N atoms are critical factors to enhance the fluorescent intensity of CDs. Until now, a variety of nitrogen-rich molecules has been applied for the surface passivation of CDs such as L-Dopa, amino acids, and polyethylenimine (PEI). Herein, we report the synthesis of fluorescent polydopamine (PDA)-passivated carbon dots (CD-PDA) via one-pot microwave-assisted pyrolysis within 5 min, dramatically simplifying the reaction process compared with the hydrothermal treatment reported before. DLS, FT-IR, UV-Vis, and fluorescence spectroscopy were used to confirm the components of CD-PDA and to illuminate the mechanism of its tunable photoluminescence (PL). Due to the doping of N atoms by PDA, quantum yield (QY) of the CD-PDA was measured at 5%, which was nearly triple the original CDs without adding PDA. Yield of CD-PDA was about 1.5 times of the CDs on account of the enhancement of nucleation site for the carbon dot formation with the phenolic group provided by PDA. Meanwhile, photothermal conversion efficiency of the CD-PDA was determined to be 35% because of the excellent NIR light-thermal conversion property of PDA. Overall, we provided an extremely efficient approach to fabricate the fluorescent N-doped CD-PDA with stable photothermal conversion efficiency and excellent biocompatibility. More importantly, the passivation of PDA enabled the CD-PDA synthesized in our research compatible for further modification through Michael addition or Schiff base reaction.

Melanin and its analogue polydopamine (PDA) have attracted considerable attention in biomedical science due to their surface-rich metal binding sites, excellent adhesion and good biocompatibility. Bacterial infections at the wound site and uncontrolled bleeding are associated with a high risk of death, and the prevention of wound infections remains a major challenge. On this basis, the four nanoparticles (NPs) of melanin, PDA, copper ion-loaded melanin (Cu(II) loaded melanin) and copper ion-loaded PDA (Cu(II) loaded PDA) were studied in terms of antibacterial and wound healing capabilities. The in vitro experiments showed that Cu(II) loaded PDA NPs had good blood compatibility and low cytotoxicity, showing the best antibacterial effect in comparison with other samples. Not only could the slow release of copper ions from the nanoparticles kill bacteria, but also the phenolic hydroxyl group and amine groups of PDA NPs played a synergistic role in bacterial death. In wound healing experiments, the Cu(II) loaded PDA NPs could easily and tightly bind with biological tissue, demonstrating excellent hemostasis, antibacterial and wound healing capabilities. In summary, the excellent properties of Cu(II) loaded PDA NPs made them a safe and effective drug for preventing wound infection and promoting healing.

A glucose biosensor based on Au nanoparticles (AuNPs), glucose oxidase (GOD) and polynorepinephrine (PNE) was fabricated by a simple and green approach. PNE-functionalized AuNPs (AuNPs@PNE) were synthetized by the polymerization of norepinephrine (NE) onto the surfaces of AuNPs and casted on an Au electrode. After dropping a solution containing NE and GOD on the AuNPs@PNE-modified Au electrode and oxidizing the monomer NE by cyclic voltammetry, a PNE, GOD and AuNP-modified Au electrode (PNE/GOD/AuNPs@PNE/Au) was obtained. The biosensor presented high sensitivity of 35.4 μA mM⁻¹ cm⁻² to glucose in the range from 0.003 mM to 3.43 mM with a response time of less than 3 s, a detection limit of 1.34 μM at a signal/noise ratio of 3, a low Michaelis–Menten constant (6.8 mM) and outstanding selectivity as well as stability. Moreover, the sensitivity and linear detection range of the as-prepared biosensor were further enhanced by the addition of the redox mediator p-benzoquinone.