Facile Preparation of WO3−x Dots with Remarkably Low Toxicity and Uncompromised Activity as Co‐reactants for Clinical Diagnosis by Electrochemiluminescence

Abstract The exceptional nature of WO 3− x dots has inspired widespread interest, but it is still a significant challenge to synthesize high‐quality WO 3− x dots without using unstable reactants, expensive equipment, and complex synthetic processes. Herein, the synthesis of ligand‐free WO 3− x dots is reported that are highly dispersible and rich in oxygen vacancies by a simple but straightforward exfoliation of bulk WS 2 and a mild follow‐up chemical conversion. Surprisingly, the WO 3− x dots emerged as co‐reactants for the electrochemiluminescence (ECL) of Ru(bpy) 3 2+ with a comparable ECL efficiency to the well‐known Ru(bpy) 3 2+ /tripropylamine (TPrA) system. Moreover, compared to TPrA, whose toxicity remains a critical issue of concern, the WO 3− x dots were ca. 300‐fold less toxic. The potency of WO 3− x dots was further explored in the detection of circulating tumor cells (CTCs) with the most competitive limit of detection so far.