Matrix-Activated Aptamer Sensors for Human Serum Analysis

Owing to their ease of operation, solution-phase fluorescent sensors hold a crucial position among aptamer-based detection tools. However, their performance is regularly compromised when exposed to increasing levels of blood fluids, such as human serum, which limits their potential in clinical settings. Here, we introduce a sensing platform that behaves advantageously within this biological medium, leveraging the most abundant proteins in the matrix, namely albumin and immunoglobulin G, as endogenous activators of fluorophore-labeled aptamers. In the absence of a target, these serum proteins non-specifically assemble with the aptamer probe in situ. Upon target binding, the aptamer-protein complexes are disrupted, shifting the equilibria toward the probe unbound to biopolymers. The fluorescence anisotropy readout reveals the system's reactivity to small-molecule targets, offering the unique ability to provide both enhanced and consistent responses across a range of high serum levels (25%-90%). As the sensor's performance may be sensitive to inter-sample serum variations, a standard addition calibration approach is used to ensure reliable quantitative analyses. Overall, the proposed strategy addresses substantial serum-induced perturbations and preserves assay functionality under biologically challenging conditions, thereby establishing a practical framework for extending homogeneous aptamer-based sensing to clinically relevant blood matrices.