Aptasensors Based on Non-Enzymatic Peroxidase Mimics: Current Progress and Challenges

Immunoassays based on antibodies as recognizing elements and enzymes as signal-generating modules are extensively used now in clinical lab diagnostics, food, and environmental analyses. However, the application of natural enzymes and antibodies has some drawbacks, such as relatively high manufacturing costs, thermal instability, and lot-to-lot variations that lower the reproducibility of results. Oligonucleotide aptamers are able to specifically bind their targets with high affinity and selectivity, so they represent a prospective alternative to protein antibodies for analyte recognition. Their main advantages include thermal stability and long shelf life, cost-efficient chemical synthesis, and negligible batch-to-batch variations. At the same time, a wide variety of non-protein peroxidase mimics are now available that show strong potential to replace protein enzymes. Here, we review and analyze non-protein biosensors that represent a nexus of these two concepts: aptamer-based sensors (aptasensors) with optical detection (colorimetric, luminescent, or fluorescent) based on different peroxidase mimics, such as DNAzymes, nanoparticles, or metal-organic frameworks.