Tunable pH indicator dyes

Tunable pH indicator dyes

We offer a comprehensive range of pH indicator dyes that can be covalently immobilised onto a variety of substrates, including cellulose, carboxymethylcellulose, viscose, agarose, polyamide, wool, starch, and paper.

The dyes exhibit pKa values tailored to relevant measurement ranges, making them suitable for applications such as skin monitoring, biological samples, and aqueous environments.

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Broad Application Potential

Our pH indicator dyes enable the integration of visible, colour-changing indicator functions that can be detected directly by the human eye. They are well suited for use in:

• Smart textiles
• Paper-based microfluidics
• Food quality control
• Wound dressings and wound monitoring

The covalent immobilisation of the dyes ensures that no leaching or contamination of the sample occurs.

Safety, Stability, and Sterilisation

• The immobilised dyes are confirmed to be non-toxic (see references).
• The materials can be sterilised using γ-irradiation.
• They offer a shelf life of several years and an operational lifetime of weeks, depending on the application.

These properties make the materials suitable for use in microtechnology, optoelectronics, medical devices, sensors, and photonics.

Availability and Collaboration Models

All pH indicator dyes are available as part of:

• Custom synthesis services
• Research collaborations
• Method development and feasibility projects

Polymerisable Fluorescent pH Indicator

In addition, we offer a polymerisable fluorescent pH indicator that can be copolymerised with monomers of your choice. The indicator has already been successfully immobilised using various methacrylates and has been applied in the fabrication of molecularly imprinted polymers (MIPs).

Our dyes

Discover our covalently immobilisable pH indicator dyes with precisely tuned pKa values for applications in textiles, sensing technologies, medical devices, and research.

Each dye offers a clearly visible colour change, high purity (>95% HPLC-MS), and is available in practical quantities. Detailed product specifications, structural information, and application examples can be found in the respective product view.

Designed for innovative materials with integrated, reliable indicator functionality.

Application examples

pH Indicator Washcloth for Skin-Friendly Body Care Products

Making skin compatibility visible

The protective acid mantle of human skin has a pH value of approximately 5.5 and is therefore slightly acidic. Many skin-friendly detergents, shampoos, and shower gels are adjusted to this pH range. In contrast, soaps and low-cost detergents are often alkaline, with pH values above 8, which may cause skin irritation—particularly in infants and people suffering from dermatitis.

The indicator washcloth provides a simple visual assessment of skin compatibility. A white cotton washcloth is covalently dyed with a pH indicator that changes color depending on the pH value of the washing solution:

• Green: pH below 6 – skin-friendly
• Red: pH 8–9 – potentially skin irritating

The production process is straightforward and scalable, involving spray application of the dye solution followed by rinsing to remove unbound dye. The washcloth is OEKO-TEX® certified and has been washed sixty times at 40 °C and 60 °C with conventional detergents without any loss of color or functionality. The color change is fully reversible.

Wound Dressings for pH Monitoring

Non-invasive monitoring of the wound healing process

Recent research indicates a strong correlation between wound pH and the healing process. A pH value above 8 suggests impaired healing and the need for medical intervention, as optimal wound healing occurs at pH values between 5 and 7.

At JOANNEUM RESEARCH MATERIALS, a functional wound dressing based on indicator dyes has been developed. The bio-nanocellulose wound dressing, designed for burn treatment, exhibits a distinct color change from yellow to red when the pH value becomes too high. The dressing is semi-transparent, allowing visual inspection of the wound without removing the dressing.

In addition, new indicator dyes have been developed that change color from yellow to blue, avoiding interference from the intrinsic coloration of wounds and further improving readability.

Test Strips for the Detection of Food Spoilage

Reliable freshness monitoring for packaged food

Today, most food products are packaged in plastic, making it difficult to detect spoilage by smell. Changes in meat and fish quality are often not visible until advanced stages of degradation.

The test strips developed by JOANNEUM RESEARCH MATERIALS address this challenge by detecting biogenic amines released during the degradation of proteins and amino acids in spoiled meat and fish. The test strips consist of dyed cellulose fibers embedded in water-repellent, food-grade silicone.

The indicator dyes exhibit a clear and intuitive color change from green to red when amines are formed. To ensure food safety, contamination is fully prevented: the dyes are stably bound to the cellulose fibers and additionally encapsulated within silicone.

Extraction tests of the dyed microfibers and sensor layers were conducted in accordance with ISO 10993-5 and ISO 10993-12 , demonstrating no reduction in cell viability.

References

[1] Remazol Brillantblau R (CAS: 2580-78-1), commercially available from Merck as substance R8001, https://www.sigmaaldrich.com/AT/de/product/sigma/r8001.

[2] Indicator washcloth for detecting alkaline washing solutions to prevent dermatitis patients and babies from skin irritation, doi.org/10.1186/s40691-017-0092-2

[3] https://youtu.be/oWDmWVPkNVo

[4] Continuous pH monitoring in wounds using a composite indicator dressing – a feasibility study, doi.org/10.1016/j.burns.2019.02.021

[5] https://www.youtube.com/watch?v=uXN_uv2_PMo

[6] https://www.evomedis.com/evosens.html

[7] Developing a sensor layer for the optical detection of amines during food spoilage, doi.org/10.1016/j.talanta.2017.04.029