Ultra-small manganese dioxide nanozyme-packaged aptameric DNA hydrogel for highly sensitive xanthine detection through smartphone-assisted visualization

Herein, a biosensor was constructed based on ultra-small manganese dioxide (MnO₂) nanozyme-encapsulated aptameric DNA hydrogel (MnO₂@DNA hydrogel) for the sensitive and portable detection of xanthine (XA). This DNA hydrogel was fabricated via complementary base pairing-mediated self-assembly. Upon the binding of XA to the aptamer, the aptamer undergoes a conformational change, which reduces cross-linking density of DNA hydrogel and thereby facilitates the release of pre-encapsulated MnO₂ nanozymes. These nanozymes exhibited oxidase-like activity, enabling the oxidation of ABTS into a measurable quantifiable signal. The biosensor demonstrated a linear detection range of 0.01-50 μM for XA, with a low limit of detection of 4.68 × 10^-3 μM. Notably, it showed excellent specificity toward interfering substances. More importantly, the proposed sensor exhibited reliable performance in biological samples, with recoveries ranging from 98.50 % to 105.70 %. and relative standard deviations below 6 %. Smartphone-assisted detection, which quantified signals through extracted RGB/HSV parameters, correlated well with ultraviolet-visible spectroscopy results. Compared to ultraviolet-visible spectroscopy-based detection methodologies, the smartphone-assisted approach, while exhibiting marginally lower sensitivity, enabled rapid on-site testing. This platform thus provides a promising tool for ultra-sensitive detection of XA in clinical diagnostics and resource-constrained settings.