Fluidic bypass structures for improving the robustness of liquid scanning probes

TL;DR

This paper introduces a microfluidic bypass channel for liquid scanning probes that passively prevents flow obstructions and monitors gap distance, enhancing robustness and broadening application potential.

Contribution

The study presents a novel passive microfluidic bypass design that addresses flow obstructions and gap control in liquid scanning probes, improving operational robustness.

Findings

Bypass channel prevents flow obstruction and leakage.

Capacitive mode monitors gap distance via phase shift.

Significant phase shift observed at 25 μm gap.

Abstract

Objective: We aim to improve operational robustness of liquid scanning probes. Two main failure modes to be addressed are an obstruction of the flow path of the processing liquid and a deviation from the desired gap distance between probe and sample. Methods: We introduce a multi-functional design element, a microfluidic bypass channel, which can be operated in dc and in ac mode, each preventing one of the two main failure modes. Results: In dc mode, the bypass channel is filled with liquid and exhibits resistive behavior, enabling the probe to passively react to an obstruction. In the case of an obstruction of the flow path, the processing liquid is passively diverted through the bypass to prevent its leakage and to limit the build-up of high pressure levels. In ac mode, the bypass is filled with gas and has capacitive characteristics, allowing the gap distance between the probe and the sample to be monitored by observing a phase shift in the motion of two gas-liquid interfaces. For a modulation of the input pressure at 4 Hz, significant changes of the phase shift were observed up to a gap distance of 25 {\mu}m. Conclusion: The presented passive design element counters both failure modes in a simple and highly compatible manner. Significance: Liquid scanning probes enabling targeted interfacing with biological surfaces are compatible with a wide range of workflows and bioanalytical applications. An improved operational robustness would facilitate rapid and widespread adoption of liquid scanning probes in research as well as in diagnostics.