# In Situ, Real‐Time Imaging of pH Gradients and Solution Flows through Silica Garden Membranes during Tube Growth

## TL;DR

This paper introduces a method to visualize pH changes and fluid flows in real-time during the growth of silica garden structures.

## Contribution

A novel technique for in situ, real-time ratiometric pH mapping and flow visualization in silica gardens is developed.

## Key findings

- A fluorescent pH probe enables real-time pH mapping in silica gardens at different magnifications.
- The probe's fluorescence changes with pH, allowing for tracking of pH gradients and particle formation.
- Confocal microscopy provides high-resolution pH data through ratiometric analysis.

## Abstract

Silica gardens are self‐organized structures formed by the reaction between high‐alkaline silicate and acidic metal solutions. This reaction generates complex tubular structures driven by osmosis and buoyancy, which are decorated by the precipitation of a diaphragm‐like membrane featuring textural and chemical gradients. It is understood that the initial gradient of pH values and its evolution over time and space are the key parameters controlling textural and chemical patterns and morphogenesis. We have developed a technique that enables simultaneous visualization of membrane formation, fluid and particle flow, and pH evolution at microscopic resolution in real‐time. This is achieved by exploiting the unusual behavior of pH probes in the saturated metal solution, which we have investigated in detail and utilized to perform ratiometric pH mapping in situ and in real‐time, either at low magnification with a color camera or, at high magnification, with a confocal microscope. Using the same probes and setup, confocal fluorescence microscopy allows for mapping pH in the microtubes with higher resolution through ratiometric analysis.

A fluorescent pH probe, added to a saturated metal ion solution, allows for mapping pH during the growth of a silica garden. The probe shows a very intense blue fluorescence at pH around 4 and an intense green fluorescence at pH above 6. The red component of the image allows detection of the formation of particles and tracking solution flows in the silica garden.