Editors' ChoiceBiosensors

A protein sandwich enables real-time in vivo biomarker measurement

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Science Translational Medicine  06 Jan 2021:
Vol. 13, Issue 575, eabg1758
DOI: 10.1126/scitranslmed.abg1758

Abstract

Biosensors allow rapid, accurate, continuous measurement of glucose and insulin in live rats.

Tools that enable continuous measurement of circulating biomarkers in vivo have potential to transform personalized medicine and accurate delivery of therapy with minimal side effects, regardless of inter-patient pharmacokinetic and pharmacodynamic variability. One of the key scientific advances required to realize this goal is the development of continuous biosensors that can measure circulating biomarkers for the purpose of monitoring health status and response to therapeutic interventions.

In a study by Poudineh et al., researchers introduce a sandwich immunoassay: a protein is surrounded by one antibody, custom-tailored to detect a specific biomarker, which then activates a second antibody with a bead that fluoresces. Simultaneously, their assay uses an aptamer-DNA displacement approach to detect a second molecule: fluorescence occurs in the presence of a biomarker when detected by aptamers conjugated to beads, displacing a hybridized DNA competitor strand that maintains a quenched state at baseline. They implemented the assay using whole blood in a custom-built microfluidic chip that uses a high-speed camera to measure bead fluorescence with spatially multiplexed laser illumination. In a key experiment, the researchers demonstrated continuous, simultaneous quantification of insulin and glucose in a living streptozotocin-induced rat model of diabetes, connecting the chip to the rat’s circulation extracorporeally. This real-time, continuous enzyme-linked immunosorbent assay (ELISA) measured both glucose and insulin with picomolar sensitivity and sub-second resolution after an initial incubation time of 30 s. Further, the continuous measurement tool agreed with intermittent conventional ELISA measurements, as demonstrated using cells from four human donors and by blood sampling in three different diabetic rats that displayed varying pharmacokinetics. The real-time ELISA measurements also agreed with glucose meter measurements, and this held true for different formulations of commercially available human insulin.

Practically, there are some technical hurdles to be overcome to translate this tool. First, the addition of non-thrombogenic coating on tubing, implementation of valves to prevent backflow, and miniaturization of the optical equipment will be required. Second, the detection range will need to be expanded to include hypoglycemic concentrations of glucose and basal levels of insulin. Finally, higher levels of multiplexing with optical design would allow detection of an expanded range of analytes—for example, cortisol and lactate—which would inform changes during periods of exercise. Overall, these technical advances are likely surmountable, and the work is important in demonstrating that circulating biomarkers can be accurately and rapidly measured in real time using whole blood from live animals, with broad applications as a research tool and ultimately for disease detection and patient monitoring.

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