Dual-mode biosensing platform based on red-emitting carbon dots and CeO₂ nanosheets for sensitive detection of acid...

Acid phosphatase (ACP) functions as a critical biomarker for prostate cancer. However, the prevalent use of single-mode readout in ACP detection makes these methods vulnerable to environmental and instrumental interferences, ultimately compromising both accuracy and reproducibility. Carbon dots (CDs) have emerged as promising nanomaterials for biosensing owing to their favorable biocompatibility, low cytotoxicity, and tunable optical properties. Nevertheless, most reported CDs exhibit blue-green emission, which suffers from significant background interference from endogenous fluorophores that compromises detection reliability. Thus, developing a robust multi-mode sensing platform based on hydrophilic red-emitting CDs capable of providing cross-validated signals holds substantial value for ACP quantification.

In this work, a fluorescence/colorimetric dual-mode sensing platform was constructed for ACP detection by integrating red-emitting neutral red CDs (NR-CDs) with CeO₂ nanosheets exhibiting oxidase-mimicking activity. The detection principle relied on the CeO₂-catalyzed oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) to generate blue-colored oxidized TMB (oxTMB), which showed a characteristic absorption peak at 652 nm and simultaneously quenched the fluorescence of NR-CDs via the inner filter effect (IFE). Upon addition of ACP, sodium ascorbyl phosphate could be hydrolyzed to ascorbic acid (AA), which inhibited the formation of oxTMB, leading to a decrease in absorbance at 652 nm and a concomitant recovery of NR-CDs fluorescence. Based on this signal-switching mechanism, dual-mode quantification of ACP activity was achieved with detection limits of 0.0026 U/L (fluorescence) and 0.0038 U/L (colorimetry). Moreover, by coupling agarose hydrogel with smartphone-based RGB analysis, a portable visual detection system was developed for on-site ACP assessment.

The method was successfully employed for the detection of ACP in human serum with high accuracy and was further extended to the screening of ACP inhibitors using sodium orthovanadate as a model compound. This study presents the initial integration of multi-mode optical and visual sensing platform for ACP activity analysis, demonstrating the practical potential of the proposed platform in point-of-care testing and biomedical research.