Tyrosine-Capped Pt Nanozyme Functionalized with cDNA: An Innovative Sensor Designed for One-Step Detection of the miRNA-21 Biomarker.

The platinum nanozymes capped with tyrosine (Pt-Tyr NZ) were synthesized which demonstrated peroxidase and oxidase catalytic activities toward 3,3',5,5'-tetramethylbenzidine (TMB). The kinetic analyses revealed that Pt-Tyr NZ exhibited higher catalytic activity and substrate affinity for both HO and TMB compared to horseradish peroxidase (HRP), indicating its superior efficiency in biosensing applications. The synthesized Pt-Tyr NZ was reversibly conjugated with complementary DNA (cDNA), which can selectively hybridize with miRNA-21, a cancer biomarker, and after hybridization with miRNA-21, detaches from the surface of Pt-Tyr NZ. Upon cDNA conjugation, the catalytic activity of Pt-Tyr NZ decreased, but it was restored in the presence of miRNA-21, providing a one-step spectrophotometric biosensing method for miRNA-21 determination. Optimization of parameters affecting the sensitivity of the developed method for miRNA-21 detection was performed, including the tyrosine-to-platinum ratio in Pt-Tyr NZ synthesis, Pt-Tyr NZ concentration, and cDNA concentration for conjugation. The developed method was fully validated and showed promising results in terms of reproducibility (RSD = 1.26%, 95% confidence interval = 0.03, = 6), repeatability (RSD = 0.83%, = 5), and accuracy for spiked miRNA-21 determination in 10% filtered human serum samples (recovery rate = 109.7 ± 4.2%). It showed a linear dynamic range (LDR) from 37.1 to 185 nM, with a limit of detection (LOD) of 11.1 nM and a limit of quantification (LOQ) of 36.9 nM.