sensorgram

A sensorgram is a real-time plot produced by label-free biosensor instruments, most commonly those based on surface plasmon resonance (SPR). It shows the interaction between two molecular species as a function of time. The horizontal axis records time; the vertical axis records the sensor response, usually in response units (RU). The sensor surface carries an immobilized ligand, and an analyte flowing over the surface binds to it, altering the RU.

During the association phase, RU increases as binding occurs; when the analyte is replaced by buffer, RU decreases as the complex dissociates, producing the dissociation phase. The resulting curve provides information about binding kinetics and affinity.

Practically, sensorgrams are used to derive kinetic rate constants (k_on and k_off) and the equilibrium dissociation constant (K_D). They enable comparison of interactions, determination of binding stoichiometry, and evaluation of antibody or receptor specificity. Sensorgrams are fitted to kinetic models, most often the 1:1 Langmuir model, though more complex models are required for heterogeneous or multivalent bindings.

Interpretation must consider factors such as mass transport limitations, non-specific binding, immobilization effects, and instrument drift. Controls and reference channels help address these issues. Sensorgrams are foundational in SPR-based research, including drug discovery, protein interaction studies, and antibody characterization; similar plots are produced by related label-free technologies such as bio-layer interferometry.