Quantum Conductance as an In Situ Tool for Accessing Quantum Dots' Electronic States and Biosensing.

We introduce a novel quantum transducer based on cadmium telluride quantum dots for reagentless and label-free biosensing. The device leverages the intrinsic electronic properties of quantum dot assemblies, as quantum conductance measurements directly reflect their quantum-capacitive (electronic) density-of-states according to the quantum-rate theory. This methodology is functionally analogous to scanning tunneling spectroscopy in its ability to map discrete electronic states (dI/dV ∝ dn/dE), but operates in situ in an aqueous medium, making it ideal for electrochemical biosensing applications. By extracting quantum conductance G from admittance measurements (specifically G = ωC″), it provides a sensitive transducer signal, enabling accurate, in situ quantification of C-reactive protein-a key biomarker for cardiovascular and inflammatory disorders. This sensing assay delivers exceptional sensitivity, achieving a detection limit of 10.9 fM and a quantification limit of 36.2 fM in human serum. Our results establish a robust proof-of-concept for ultrasensitive, miniaturized, label-free electrochemical devices that exploit conductance-capacitance coupling in nanomaterials and their association with the electronic structure to diagnose a broad spectrum of infectious and noncommunicable diseases.