Ti₃C₂ MXene quantum dot-encapsulated liposomes for photothermal immunoassays using a portable near-infrared imaging camera on a smartphone

Methods based on the photothermal effect (a common phenomenon in nature) have been widely applied in different fields; however, their application in bioanalysis has lagged behind. Herein, we designed a near-infrared (NIR) photothermal immunoassay for the qualitative or quantitative detection of prostate-specific antigen (PSA) using titanium carbide (Ti₃C₂) MXene quantum dot (QD)-encapsulated liposomes with high photothermal efficiency. This system involves a sandwich-type immunoreaction and photothermal measurements. Ti₃C₂ MXene QDs were utilized as innovative photothermal signal beacons and were encapsulated in liposomes for the labeling of the secondary antibody. The assay was carried out by coupling a low-cost microplate with a homemade 3D printed device. Under NIR-laser irradiation, the Ti₃C₂ MXene QDs converted the light energy into heat, and a shift in temperature corresponding with the analyte concentration was obtained on a handheld thermometer. Under optimal conditions, the Ti₃C₂ MXene QD-based photothermal immunoassay exhibited a dynamic linear range from 1.0 ng mL⁻¹ to 50 ng mL⁻¹ with a limit of detection of 0.4 ng mL⁻¹ for PSA detection. Also, we constructed portable equipment using a portable near-infrared imaging camera to collect visual thermal data for the semi-quantitative analysis of the target PSA within 3 min. The specificity, reproducibility and accuracy of the photothermal immunoassay were acceptable. Importantly, our strategy opens new opportunities for protein point-of-care (POC) testing and biosecurity diagnostics.