Al-Doped CuS\nColloidal Nanocrystals as a Highly Efficient\nElectrochemiluminescence Emitter for the Ultrasensitive Detection\nof Circulating Tumor DNA

Herein, CuS colloidal nanocrystals (NCs) with adjustable\nband gap\nand good film forming ability have been synthesized as new ECL materials.\nFurthermore, the band gap and oxygen vacancy (O<sub>V</sub>) content\nof CuS NCs are regulated by Al<sup>3+</sup> doping, which significantly\nimproves the ECL response of CuS NCs. First, the band gap of CuS-Al\nNCs decreases after doping with Al<sup>3+</sup>, which makes it easier\nfor electrons to transition across the band gap. At the same time,\nthe oxygen vacancy of CuS-Al NCs increases, which is conducive to\nimproving the conductivity and promoting charge transfer, thus improving\nthe ECL performance of CuS-Al NCs. Circulating tumor DNA (ctDNA) is\nan important tumor marker, and its sensitive monitoring is of great\nsignificance for tumor diagnosis, treatment, and prognosis detection.\nTherefore, an ECL biosensor for ultrasensitive detection of circulating\ntumor DNA (ctDNA) was prepared by using CuS-Al NCs as luminescent\nmaterial and combining multiple antidromic hybrid chain reaction (anti-HCR)\nstrategy mediated by the target. Compared with the process of target-induced\nHCR generation, this strategy first forms multiple HCR products and\nthen destroys the already formed HCR products by target-induced destruction,\nwhich enhances the sensitivity of target response and improves the\nreaction efficiency. The constructed biosensor has good detection\nperformance, and the detection limit is as low as 2.74 aM. This work\nputs forward the luminescence phenomenon of colloidal nanocrystals\nas new ECL materials, which broadens the application of ECL technology\nin ultrasensitive biochemical detection.