# Color-switching hydrogels as integrated microfluidic pressure sensors

## TL;DR

A new color-changing hydrogel sensor allows non-invasive pressure measurements in microfluidic systems with high precision and ease of use.

## Contribution

A fully integrated, non-invasive microfluidic pressure sensor using color-switching hydrogels is introduced.

## Key findings

- The sensor achieves pressure measurements as low as 20mbar with a resolution of around 10mbar.
- The hydrogel-based sensor is decoupled from the flow path and can be used with various fluid types.
- The system enables 2D pressure or deformation maps with fast response and spatial resolution.

## Abstract

Precisely measuring pressure in microfluidic flows is essential for flow control, fluid characterization, and monitoring, but faces specific challenges such as achieving sufficient resolution, non-invasiveness, or ease of use. Here, we demonstrate a fully integrated multiplexed optofluidic pressure sensor, entirely decoupled from the flow path, that enables local pressure measurements along any microfluidic channel without altering its flow geometry. The sensor itself relies on the compression of a soft mechano-actuated hydrogel, changing color in response to a pressure change. The hydrogel is separated from the fluid circulating in the channel by a thin membrane, allowing for the unrestricted use of different types of fluids. Imaging the gel through the transparent PDMS with a color camera provides a direct, easy, and contact-free determination of the fluid pressure at the sensing location for pressures as small as 20mbar with a resolution of around 10mbar. The sensitivity and accessible pressure range can be tuned via the mechanical properties of the sensing unit. The photonic gel can also be used to acquire 2D pressure or deformation maps, taking advantage of the fast response time and fine spatial resolution.