Multiscale Strategies for Advancing Reader-Free Colourimetric Point-of-Care (POCT) Diagnostics

Colourimetric point-of-care testing (POCT) devices are promising for rapid, cost-effective diagnosis; however, many rely on external devices for quantification, compromising their simplicity, portability, and suitability for low-resource settings. The review underscores the need for next-generation reader-free systems that integrate semi-quantitative measurements with visual interpretability without compromising the operational simplicity of the POCT devices. Simultaneously achieving visual detectability with reliable quantification is a major challenge with existing reader-free colourimetric POCT platforms, as enhanced signal amplification does not always guarantee accurate or reliable interpretation by the naked eye. This study systematically evaluates state-of-the-art colourimetric POCT designs based on lateral flow, dipstick, microfluidic, and hydrogel systems, with a primary focus on improving visual detection thresholds, overcoming subjective interpretation bias, enhancing analytical performance, and moving towards instrument-free quantitative measurement. Thereafter, multiscale signal amplification strategies were discussed, followed by approaches for user-independent semi-quantitative measurement, including colour reference standards, distance-based readouts, and time-dependent visual assays. Overall, this review aims to provide a rationalistic approach towards developing advanced diagnostic platforms that effectively bridge the gap between reliable quantitative analysis and reader-free POCT detection, thereby facilitating deployment in resource-limited settings.