Simultaneous Passivation and Encapsulation of Black Phosphorus Nanosheets (Phosphorene) by Optically Active Polypeptide Micelles for Biosensors

In a simplistic way, 2D black phosphorus (BP) nanosheets are exfoliated in a polar solvent at room temperature. Afterward, as-obtained BP or phosphorene nanosheets are passivated and encapsulated simultaneously by using an artificial polypeptide polymer having an ability to form micelles. In first step, thin layers of BP nanosheets were obtained by sonication. Next, helical copolymer based on polyethylene glycol and poly(phenyl isocyanidepeptide) blocks is then allowed to blend with the suspension of phosphorene nanosheets for their inclusion in micelles. The size of nanosheets is reduced after their encapsulation inside the polymeric micelle. The copolymer based on polypeptide is also supposed to improve biocompatibility. The microstructures of these 2D nanosheets are investigated by transmission electron microscopy. The transmission electron microscopy results show that the BP nanosheets are included within the helical cavity of the copolymer indicating the hydrophobic nature of the nanosheets. Atomic force microscopy images indicate the formation of smooth and flat nanosheets. Photoluminescence (PL) experiments suggest that the emission from polymer micelles is quenched after nanosheets are embedded within the polymer helical matrix. For polymer micelles, the disappearance of emission proves that electron transfer (ET) occurs between the BP nanosheets and polymer helix. Even after encapsulation, the BP nanosheets are sensitive to light and emits with a sharp signal that shifts slightly toward the blue region. This single step approach for passivation and encapsulation of BP nanosheets provides new solution for protecting the BP nanosheets from oxidation and fabrication without compromising the electronic properties. After fabrication, these 2D active hybrids can be integrated in a device for sensing applications. These 2D nanomaterials can also be introduced in an infected tissue for imaging or delivering a drug particulate.