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Fluorescent tracer agent-based monitoring systems are built upon two core technology pillars.
Novel fluorescent
tracer agents
are chemically engineered to not interact with the body and to be sufficiently bright to enable detection by transdermal measurement.
Highly engineered
transdermal sensors
are optimized to enable robust detection of fluorescent tracer agents in the body. In addition, advanced mathematical models and software are integrated with the detection instrumentation.
Together these components are designed to enable clinically relevant measurement and monitoring of organ function at the point of care*.
The goal in the development of fluorescent tracer agents for physiological monitoring is to engineer molecules with the following key characteristics.

Biocompatible - Biocompatible fluorescent agents have the quality of not having toxic or injurious effects on biological systems.

Hydrophilic - This is the characteristic of having a tendency to mix with or dissolve in water.

Negligible Protein Binding - The quality of not attaching to proteins within the body is an important characteristic.

Negligible Metabolism - This is measured by quantifying the amount of the agent that is excreted intact.

Negligible Photobleaching - It is important to engineer against any potential photochemical alteration of a fluorophore molecule that would permanently hinder its ability to fluoresce.

Physiologic pH Formulation - The pH of a pharmaceutical solution cannot be too acidic or too basic. The further away one gets from physiological pH (7.4), the greater the irritation. Delivery at physiologic pH is optimal.

Small Dose - The need for only a small amount of fluorescent agent in the body has positive implications for the detection end of transdermal measurement systems. In addition, small dose requirements may enable alternative routes of administration for the fluorescent tracer agents.

Chemical Stability - The tendency of fluorescent tracer agents to resist change or decomposition due to internal reaction, or due to the action of air, heat, light, pressure, etc. helps to ensure the desired engineered properties of a fluorescent agent remain in place so that the product can serve its intended purpose in transdermal measurement systems.

Solubility - Fluorescent tracer agents that are highly soluble tend to be easier to formulate, handle and use.

Photo Stability - To be photostable refers to the tendency of a fluorescent tracer agent to be stable in the presence of light. Highly photo stable compounds are the goal so as to facilitate storage, handling and use in transdermal measurement systems.

Stokes Shift - The Stokes shift is the difference between the emission light wavelength (color of light at which the fluorescent agent glows) and the incident light wavelength (color of light which is shined on the fluorescent agent to make it glow). Fluorescent tracer agents with a large stokes shift are desirable and favor robust and cost-effective transdermal measurement systems.



Highly engineered sensors and advanced mathematical models are required to deliver on the promise of transdermal measurement of physiological function.

The sensor components are designed to automatically adjust for different skin tones and other individual physiological characteristics. In addition, it is important to measure diffusely detected light, which is used to compensate for locally time-varying tissue properties, such as changes in local blood volume. By accurately taking into account these variables and numerous others the transdermal sensors are able to discern the intensity of the fluorescence from the tracer agent that is administered. Changes in the intensity of fluorescence are able to be measured/monitored over time.

Proprietary algorithms that are being continuously improved are designed to enable the translation of the data provided by the transdermal sensors into meaningful and clinically relevant indications of organ function such as Glomerular Filtration Rate (GFR) or a relative level of gastrointestinal permeability.

One of the long-standing challenges in skin imaging is to develop quantitative methods for characterizing anatomy and physiology in different skin structures.
- Journal of Biomedical Optics, In vivo measurements of cutaneous melanin across spatial scales: using multiphoton microscopy and spatial frequency domain spectroscopy, June 2015