Janus nanoparticle-based electrochemical biosensors driven by the protein corona for tumour diagnosis: anisotropy as an analytical asset.

Abstract

A Janus nanoparticle carries two chemically different faces on a single object of 10-500 nm. That broken symmetry lets a sensor do two things that compete for space on an isotropic particle: recognise an analyte on one face and transduce or amplify the recognition event on the other. The advantage is usually presented as geometric. It is not. In plasma, both faces are covered by a protein corona within seconds, and the corona not the engineered surface is what the analyte actually meets. Most of the biosensing literature treats this layer as contamination to be blocked. We argue instead that on an anisotropic particle the corona is a designable part of the interface, and that anisotropy is what makes it designable, because the two faces can be given different wettability, charge and curvature and therefore different coronas. This review examines that proposition in four steps. First, it sets out how Janus architectures are made and assembled on electrodes, and what the two faces contribute analytically. Second, it collects what is known about corona formation on nanoparticles and translates it into the variables a sensor designer can control, separating parameters with direct experimental support from those that are still inferred. Third, it examines how the corona changes charge transfer, mass transport and fouling at a modified electrode, and proposes three operating regimes corona-tolerant, corona-controlled and corona-exploitative with the analytical readout each one supports. Fourth, it compares what has been demonstrated in patient-derived samples with what remains projection. We conclude that the exploitative regime is coherent and testable, that no corona-driven Janus sensor has yet been validated prospectively in a clinical cohort, and that the immediate bottleneck is standardisation of the corona itself rather than ligand chemistry or electrode materials.

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