Copper (II)-catalyzed polydopamine mediated photothermal sensors for visual quantitative point-of-care testing

Temperature sensing is commonly used in point-of-care (POC) detection technologies, yet the portability and convenience of use are frequently compromised by the complexity of thermosensitive processes and signal transduction. Especially, multi-step target recognition reactions and temperature measurement in the reaction vessel present challenges in terms of stability and integration of detection devices. To further combine photothermal reaction and signal readout in one assay, these two processes enable to be integrated into miniaturized microfluidic chips, thereby facilitating photothermal sensing and achieving a simple visual temperature sensing as POC detection.

A copper ion (Cu²⁺)-catalyzed photothermal sensing system integrated onto a microfluidic distance-based analytical device (μDAD), enabling the visual, portable, and sensitive quantitative detection of multiple targets, including ascorbic acid, glutathione, and alkaline phosphatase (ALP). The polydopamine nanoparticles (PDA NPs) were synthesized by the regulation of free Cu²⁺ through redox or coordination reactions, facilitating the transduction of distinct photothermal response signals and providing the versatile Cu²⁺-responsive sensing systems. Promoted by integration with a photothermal μDAD, the system combines PDA's photothermal responsiveness and thermosensitive gas production of ammonium bicarbonate for improved sensitivity of ALP detection, reaching the detection limit of 9.1 mU/L. The system has successfully achieved on-chip detection of ALP with superior anti-interference capability and recoveries ranging from 96.8 % to 104.7 %, alongside relative standard deviations below 8.0 %.

The μDAD design accommodated both the photothermal reaction of PDA NPs and thermosensitive gas production reaction, achieving the rapid sensing of visual distance signals. The μDAD-based Cu²⁺-catalyzed photothermal sensing system holds substantial potential for applications in biochemical analysis and clinical diagnostics, underscored by the versatile Cu²⁺ regulation mechanism for a broad spectrum of biomarkers.