Ternary Z-Scheme Ag-Embedded TiO2–Ag2S Nanojunction as a Novel Photoelectrochemical Converter for CD44 Detection

Abstract

Nanoarrays (NAs) with stable signal output have become the most promising photoelectrochemical (PEC) biosensing substrate. However, a general issue is that interfacial charge-carrier recombination in a single-component semiconductor cannot be easily prevented, resulting in a low photocurrent density. Herein, a biosensor utilizing a Ag-embedded TiO2–Ag2S nanojunction (TiO2–Ag–Ag2S) as a signal converter was developed for the detection of CD44 protein─a transmembrane glycoprotein highly expressed in breast cancer cells. The ternary Z-scheme heterojunction was prepared by a distinctive scheme in which the Ag layer is introduced onto the surface of rutile TiO2 NAs by magnetron sputtering, whereas the Ag2S is rooted in the local sulfuration of Ag. With a sufficient density of oriented nanorods, TiO2–Ag–Ag2S exhibits a smooth photocurrent output and minimal variation among different batches; it is undoubtedly a satisfactory PEC sensing carrier, which enables highly specific identification of target CD44 on the surface of MDA-MB-231 cells due to DNA strand displacement reactions (SDRs) and host–guest recognition between hyaluronic acid (HA) and CD44. The biosensor shows a sensitive PEC response to CD44 over a wide range of 37 to 5.0 × 105 cells/mL. We can conclude that this approach will provide an alternative solution to breast cancer diagnosis.