Plasmonic Engineering of Black Phosphorus: Constructing Stable, Highly Sensitive Heterojunctions for Noninvasive Glucose Monitoring in Sweat

Although noninvasive glucose monitoring in sweat is a promising, pain-free method for diabetes management, it requires highly sensitive and stable sensors to overcome practical limitations. To overcome this challenge, a photoelectrochemical sensor based on a plasmon-enhanced black phosphorus (BP)/gold (Au) heterojunction was developed in this study. BP nanosheets possess a unique layered structure and intrinsic catalytic activity, but their instability and limited efficiency hinder direct use. Therefore, BP/Au was synthesized using the one-pot method. First-principles calculations revealed that single-layer BP behaved as a quasi-direct bandgap semiconductor. In comparison, the BP/Au heterojunction exhibited metallic characteristics, with anisotropic electron mobility reaching 1.62 cm2·V−1·s−1 along one direction. Charge density analysis confirmed directional charge transfer. Au donated electrons to adjacent P atoms, whereas P atoms forming shorter bonds lost charge. This process was associated with plasmon-assisted photoexcitation at the Au/BP interface, which modulated interfacial charge distribution and enhanced photoelectrochemical activity. By leveraging the Au component’s surface plasmon resonance, the heterojunction considerably augmented light absorption, accelerated interfacial electron transfer, and utilized the wrinkled BP layers to provide abundant active sites. This synergistic effect substantially lowered the oxidation activation energy of glucose. The resulting sensor achieved exceptional performance, with a sensitivity of 266.9 μA·μM−1·cm−2, a low detection limit, and a wide linear range well-suited for detecting glucose in sweat. The findings emphasized the potential of plasmon–semiconductor coupling for advancing noninvasive glucose monitoring and provided valuable design principles for sweat sensors based on metal–semiconductor heterojunctions.