Upcycling e-waste into heterogeneous CuxO nano skeletons for high-performance glucose sensing

As the use of electronic devices continues to rise, the management of electronic waste (e-waste) has become a critical issue. Printed circuit board (PCB) recycling methods are generally classified into physical and chemical approaches. Physical recycling involves mechanical disassembly and separation, while chemical recycling relies on hydrometallurgy or pyrometallurgy. However, these methods are expensive and often cause pollution. Laser technology offers a new, environmentally friendly, and efficient approach for recovering metals from PCBs.

Non-invasive glucose monitoring is crucial for managing diabetes. Sweat contains glucose and other biomarkers, and detecting glucose concentration in sweat using electrochemical sensors has become a research focus. Among these, non-enzymatic glucose sensors are gaining attention due to their low cost and stability. Copper oxide (Cu_xO) is an ideal material for fabricating non-enzymatic glucose sensors because of its biocompatibility and high sensitivity to glucose. Traditional methods for preparing copper oxide electrodes are often complex, time-consuming, and require hazardous chemicals. In contrast, laser-induced processes provide a more eco-friendly, rapid, and scalable approach to fabricating copper-based electrodes.

To tackle the dual challenges of e-waste and diabetes, Guijun Li and colleagues at the Hong Kong University of Science and Technology proposed a laser-induced transfer method that repurposes copper from e-waste to fabricate portable glucose sensor electrodes. They employed a fast, low-cost, environmentally friendly, and scalable laser-induced transfer technique to prepare h-Cu_xO electrodes from discarded PCBs. Before the laser transfer step, the protective coating on the PCB surface was removed using laser ablation. Laser-induced backward transfer (LIBT) was then used to transfer copper from the PCB onto a glass substrate, followed by laser-induced forward transfer (LIFT) to deposit the copper onto a carbon cloth substrate. Using this laser transfer method, the team developed an automated system for continuous electrode production once laser processing parameters were set.

The performance of h-Cu_xO electrodes was compared to commercial Cu₂O and CuO nanoparticles as glucose-sensing electrodes. After electrochemical activation, the h-Cu_xO-EA electrode showed the highest sensitivity among all tested electrodes, achieving 9.893 mA mM^-1 cm^-2 (R²=0.996) with a detection limit of 0.34 μM. The h-Cu_xO-EA electrode also exhibited excellent anti-interference properties. When tested for glucose detection in artificial sweat, the h-CuₓO-EA electrode retained nearly 100% of its current response after eight weeks, indicating outstanding long-term stability.

In addition, Li and colleagues developed a miniature electrochemical workstation capable of wirelessly transmitting real-time data to a smartphone via Bluetooth. The electrochemical curves obtained from the miniature system were consistent with those measured by a PARSTAT electrochemical workstation, confirming the system's reliability. The h-CuₓO-EA electrode's current response to different glucose concentrations, measured with the miniature workstation, showed that higher glucose concentrations produced higher current responses. The fitting curve demonstrated a proportional relationship between current response and glucose concentration, with a sensitivity of 61.67 μA mol^-1. Tests with artificial sweat containing five different glucose concentrations revealed that the calculated values closely matched the actual concentrations. The glucose detection device was miniaturized to enhance portability and scalability, making it more suitable for integration into everyday life.