Fig. 2: Hanging-drop-integrated glucose biosensor design.

a Design of the microfluidic channels (PDMS layer in light gray) with rim structures (PDMS layer in dark gray) that confine the medium phase (blue). The flow is driven with a single inlet supplying buffer at ~20 μL min⁻¹ and two outlets withdrawing 10 μL min⁻¹ each. The inlet and outlets can be interchanged to apply two separate conditions in the same chip. The integrated electrodes on the glass substrate (black and red) are in direct contact with the medium phase and provide single-spheroid resolution in each hanging-drop compartment. The connector pins allow direct connection to a potentiostat. b Close-up micrograph of a single hanging-drop compartment within the red box in panel a showing the exposed working electrodes, counter electrode, reference electrode, and rim structures. c Close-up of the microfluidic channels with various dimensions. Cross-section A–A’ shows the electrodes at the glass-medium interface. Cross-section B–B’ shows a large (blue) and small (red) spheroid at the air-liquid interface. Cross-section B–B’ also shows a fillet geometry transition from the hanging-drop compartment (at 500 μm height) to the channel structures (at 250 μm height) to facilitate medium filling.