# Multi-contrast magnetic particle imaging for tomographic pH monitoring using stimuli-responsive hydrogels

## TL;DR

Researchers developed a method to measure pH levels non-invasively using magnetic particle imaging with hydrogels that respond to pH changes.

## Contribution

A novel approach using stimuli-responsive magnetic hydrogels to enable pH monitoring via multi-contrast magnetic particle imaging.

## Key findings

- Magnetic particle spectrometry confirmed that hydrogel swelling modulates magnetic nanoparticle signals based on pH.
- Multi-contrast magnetic particle imaging successfully resolved different pH values in a proof-of-concept demonstration.

## Abstract

Magnetic particle imaging (MPI) is a tomographic imaging technique which determines the spatial distribution of magnetic nanoparticles (MNPs). Multi-contrast MPI provides the ability to detect environmental conditions of MNPs, such as temperature or viscosity. One parameter that has not been investigated but shows high potential for medical diagnosis is the pH value, as it is an indicator of inflamed or tumorous tissue. In this work, we present an approach to resolve the pH value using multi-contrast MPI. Our proof-of-concept is based on a stimuli-responsive, magnetic hydrogel that exhibits reversible swelling in response to a pH change. The pH contrast is generated indirectly via the pH-responsive hydrogel swelling modulating the signal of embedded MNPs. Magnetic particle spectrometry measurements show that the hydrogels’ magnetic response correlates with the pH value, which could provide a new way of contactless pH monitoring. Finally, the feasibility of resolving different pH values in a multi-contrast MPI image is demonstrated.

Bruno Kluwe and colleagues propose using stimuli-responsive, magnetic hydrogels in magnetic particle imaging to resolve pH levels. Non-invasive pH measurement is promising for diagnosing inflamed or tumorous tissues.