Lab on a Syringe: Strategic Design of 1T SnS<sub>2</sub>/MXene Embedded Single-Stranded Carbon Yarn for Real-Time Stress\nBiomarker Detection

An\nelectrochemical sensor was developed in this study by utilizing\na 1T SnS<sub>2</sub>–Nb<sub>2</sub>CT<sub><i>x</i></sub> heterostructure nanocomposite modified carbon yarn (CY) electrode\nfor detecting serotonin (5-HT) in human biofluids. Utilizing the enhanced\nelectrochemical activity of the 1T phase of SnS<sub>2</sub>, a nanocomposite\nwas made with Nb<sub>2</sub>CT<sub><i>x</i></sub> MXene\nvia a hydrothermal method. The nanohexagon architecture of SnS<sub>2</sub> provides a heterojunction with Nb<sub>2</sub>CT<sub><i>x</i></sub> MXene and enables a conductive electron transfer\nnetwork, leading to improved sensing capabilities with an enhanced\nelectrochemical response. A detailed study was conducted to elucidate\nthe mechanism behind the heterostucture formation with the help of\nultraviolet photoelectron spectroscopy (UPS) analysis. The 1T SnS<sub>2</sub>–Nb<sub>2</sub>CT<sub><i>x</i></sub> nanocomposite\nprovided effective active sites for enhancing its electrochemical\nperformance by the presence of terraces and edges in the hexagonal\nstructured 1T SnS<sub>2</sub> and by the inherent electrochemical\nproperty of Nb<sub>2</sub>CT<sub><i>x</i></sub> MXene. The\nfabricated 1T SnS<sub>2</sub>–Nb<sub>2</sub>CT<sub><i>x</i></sub> nanocomposite based electrochemical sensor demonstrated\na wide linear detection range of 1 to 100 μM for 5-HT, with\na detection limit of 81 nM. In addition, the developed sensor demonstrated\nhigh selectivity, excellent repeatability, reproducibility, as well\nas good stability for 5-HT detection. The sensor was beneficially\nused to determine 5-HT levels in artificial samples of human serum,\ncerebrospinal fluid (CSF), interstitial fluid (ISF), and human sweat,\nconfirming its practicality for real sample analysis. Finally, a “lab\non a syringe” prototype model was developed by placing three\nthread electrodes on a commonly available syringe barrel, and it demonstrated\npromising capabilities for POC applications in next-generation healthcare.