nonratiometric

Nonratiometric refers to sensors whose readout is based on a single signal magnitude rather than a ratio of two signals. In practice, nonratiometric sensors produce an output that changes with the quantity of interest as an absolute value, such as fluorescence intensity, absorbance, or electrochemical current. This contrasts with ratiometric sensors, which report a ratio between two signals (colors, wavelengths, or modalities) to compensate for common sources of error like light path length, instrument sensitivity, and probe concentration.

Nonratiometric sensors are common in fluorescence, colorimetric, and electrochemical applications. Examples include single-emission fluorescent probes whose intensity correlates with analyte concentration, pH indicators that shift in brightness or color, and electrochemical sensors that measure current or potential in response to an analyte. They are also used in qualitative assays and some quantitative tests when calibration is well controlled.

Advantages of nonratiometric sensors include simplicity, faster response, and often lower cost and easier implementation in high-throughput or point-of-care settings. Their main drawback is susceptibility to artifacts from variable probe concentration, fluctuations in illumination or detection efficiency, and environmental conditions, which can complicate quantitative interpretation. Proper calibration and consistent assay conditions are essential for reliable results, and results are typically more robust when expressed as an absolute signal tied to a standard curve.

Applications span clinical chemistry, environmental monitoring, and basic research, where straightforward, single-signal readouts are sufficient or preferred. For imaging applications that require robustness to artifacts, ratiometric approaches are generally favored.