Red Fluorescent Copper Nanoclusters for Fluorescence, Smartphone, and Electrochemical Sensor Arrays to Detect the Monkeypox A29 Protein

An <i>Orthopox</i> zoonotic viral infection called monkeypox (MPXV) is the leading infectious disease globally. MPXV can easily spread from human to human through direct and indirect sexual contact; therefore, accurate and early detection of MPXV is crucial for reducing mortality. Fluorescence-based materials have received significant attention in recent years for biomedical applications. In this study, we synthesized red-fluorescent copper nanoclusters (CuNCs) with a size of less than 10 nm, which was confirmed by high-resolution transmission electron microscopy (HR-TEM) and atomic force microscopy (Bio-AFM) analysis. The synthesized CuNCs had a high fluorescence nature and were utilized for the detection of the MPXV (A29P) by an antigen-antibody conjugation using fluorescence, smartphone colorimetric, and electrochemical sensing techniques. The antigen (A29P) and antibody (Ab A29) interaction mechanisms were studied by X-ray photoelectron spectroscopic (XPS) analysis. Furthermore, fluorescence and electrochemical sensing were performed in PBS with detection limits of 0.096 and 0.114 nM, respectively. For real-world applications, the prepared immunosensor array can detect A29P in spiked serum samples, and point-of-care (POC) analysis, a smartphone-integrated sensor array, was used to measure the RGB color changes. The results showed that synthesized CuNCs are potential materials for detecting A29P via fluorescence and smartphone colorimetric and electrochemical sensing techniques.