Partially oxidized black phosphorus nanosheets achieving label-free photoelectrochemical sensing

As a rising-star 2D nanomaterial, black phosphorus (BP) nanosheet could be a potential candidate for photoelectrochemical (PEC) biosensing owing to its tunable bandgap, high carrier mobility, and negligible toxicity. However, the water- and air-instability of BP nanosheet and the accompanying performance degradation greatly limit its applications. Herein, a photoactive composite of BP/carboxylated multiwalled carbon nanotube/polyethylene glycol (BP/MWNTCOOH/PEG) was synthesized by a simple ball-milling method. Instead of fighting the oxidation of BP as a detrimental process, we make use of this phenomenon to our advantage. It is found that the partial oxidation of BP was in favor of increasing the photocurrent of the composite in the atmospheric environment, possibly due to the formation of phosphorus oxides-BP heterojunction. Moreover, a polydopamine (PDA) coating method was utilized to control the oxidation extent of the composite, so as to obtain optimal photoelectric performance. The resulted BP/MWNTCOOH/PEG@PDA nanohybrid provided satisfactory water stability as well as a suitable microenvironment for biomolecules immobilization. Therefore, a label-free PEC sensor constructed based on the novel hybrid achieved sensitive detection of microRNA-21 with low detection limit (0.23 pM). The present work thus paved the way for the wide application of 2D BP nanosheets in PEC sensing.

Automated summary

This study leveraged the advantages of partially oxidized BP to increase photocurrent and utilized a PDA coating method to control the oxidation extent of the composite for optimal photoelectric performance. The resulting nanohybrid showed good water stability and suitable microenvironment for biomolecule immobilization, enabling sensitive detection of microRNA-21.