Lateral flow assays (LFAs) are paper-based analytical devices (PADs) widely used in medical diagnostics, food safety, and environmental monitoring. These test strips provide rapid, on-site analysis without the need for specialized equipment, making them both affordable and highly portable. However, traditional LFAs struggle to detect low concentrations of analytes, which are often present during the early stages of diseases. Preconcentration techniques can significantly enhance sensitivity, but current methods that require an external power source compromise the simplicity and portability that make LFAs so valuable. To address this limitation, we propose a novel solution using diffusiophoresis (DP), a solute-driven electrokinetic phenomenon, to concentrate analytes on PADs without the need for external power. By harnessing the spontaneous electric field generated at the interface between electrolytes with different ionic strengths, we aim to achieve online electrokinetic preconcentration while preserving the portability of LFAs. In standard colorimetric LFAs, this approach could dramatically improve detection limits. Mobile coloured nanoparticles conjugated to detection reagents will bind to target analytes, which will then interact with immobilized capture reagents at the test line. Based on DP studies conducted in microchannels, preconcentration factors exceeding 10^4 could be achieved at the test line, potentially leading to over a 10,000-fold improvement in sensitivity without sacrificing the simplicity and ease of use of LFAs.