Hybrid point-of-care devices for high-sensitivity visual detection of salivary biomarkers and drugs

Early diagnostics is a crucial part of clinical practice offering a rapid and convenient way to investigate and quantify the presence of key biomarkers related to specific pathologies and increasing the chance of successful treatments. In this regard, point-of-care testing (POCT) shows several advantages, enabling simple and rapid analyses, real-time results, and home-testing [1]. Metallic nanoparticles (NPs), like gold NPs (AuNPs), can be beneficially integrated into POC devices thanks to their tunable plasmonic properties, which provide naked-eye readout [2]. Moreover, the high sensitivity enabled by NPs allows the detection of biomarkers in non-invasive fluids where the concentrations are typically low. These biofluids, like saliva and urine, are functionally equivalent to serum in reflecting the physiological state of the body, whilst they are easier to handle, collect, and store [3]. In this work, we first reported the design and development of a colorimetric strategy based on the morphological change of multibranched plasmonic AuNPs, aimed at detecting glucose in saliva [4]. The sensing approach relied on a target-induced reshaping process, which involves the oxidation of the NP tips and the particle transformation into a spherical shape, characterized by a naked-eye detectable blue-to-pink color change. The platform proved to be beneficial in the early and non-invasive diagnosis of hyperglycemia. The successful technological transfer on a solid substrate paved the way for the realization of a dipstick prototype for home-testing. Then, the strategy was adapted to other biomarkers, leading to the development of a multiplexing test for the simultaneous detection of three salivary analytes (cholesterol, glucose, and lactate) [5]. This multiplexing assay enabled saving reagents, costs, and time, while increasing the overall clinical value of the test. Exploiting the microfluidics applied on a paper sheet, we realized a monolithic and fully integrated POC device, through a low-cost and fast $CO_{2}$ laser cutter. The platform showed excellent selectivity and multiplexing ability, with negligible interferences. The second part of this work was focused on the development of POC devices for the detection of anticancer drug contaminations in water solutions and urine samples. Antiblastic agents have revealed high toxicity for the exposed healthcare workers who prepare and administer these drugs in occupational environments [6]. Hence, continuous monitoring is highly required, and POCT shows tremendous potential in this context. With this aim, we realized a lateral-flow device (LFD) for the assessment of doxorubicin contaminations, using the fluorescent properties of the drug for naked-eye detection [7]. The pharmacological recognition of the dsDNA probe was exploited to overcome the lack of anti-doxorubicin antibodies. The highly sensitive strategy was successfully adapted to a real urine sample, without resorting to complex pretreatment procedures. Then, we developed a competitive LFD device for the detection of methotrexate (MTX). AuNPs were employed as the label molecules and the pharmacological competition of folic acid and MTX for the capture enzyme was used as the recognition mechanism, instead of costly antibodies. Despite the sensitivity requires further improvements, the strategy showed fast and reliable results, demonstrating a high potential for workers’ safety monitoring.