Spreadable Biosensing Pregel for Analyte Visualization in Peeled Plant Tissues

Biosensors are typically fabricated in the form of solid-state devices (chips, tapes, or films). Here, we demonstrate a proof-of-concept for an alternative form of biosensor─an amorphous biosensing pregel, which is formed on the interrogated surface of interest after application of a precursor mixture. The reagent cocktail is prepared from dilute agarose and a mixture of assay chemicals, including enzymes and substrates. The readout is either colorimetric or luminometric, and it is facilitated by a digital camera. The main conditions of the biosensing pregel preparation and application have been optimized. The method is particularly suitable for rudimentary macroscopic visualization of metabolites in plant tissues. In one exemplary application, plant leaves are split into two sides using adhesive tape. Following the application of the biosensing cocktail, distributions of target species such as glucose and adenosine triphosphate can be visualized in the peeled tissues. Thus, the approach enables rapid in situ sensing of analytes in the studied flat specimens without fabrication and use of classical solid-state biosensors.