Shining a Light on Health: How Photonics are Revolutionizing Medical Diagnostics

Hospitals are increasingly using technology to quickly assess our health. A common example is the pulse oximeter, a clip placed on a finger that instantly reads blood oxygen levels. But how does this simple device, or future technologies, glean so much information without invasive procedures?

The answer lies in the fact that our bodies are more translucent than we realize. Light can pass through our skin, muscles, and blood vessels, carrying valuable information about our internal state. This principle is being harnessed through integrated photonics to create advanced medical diagnostic tools.

The Magic of the Pulse Oximeter

The pulse oximeter uses a simple yet ingenious method to measure blood oxygen levels:

It shines a tiny red LED light through your finger.
Oxygen-free hemoglobin absorbs more red light than its oxygenated counterpart.
A detector on the other side measures the amount of light that passes through.
The ratio of absorbed light reveals the concentration of oxygenated vs. oxygen-free hemoglobin.

However, the size of blood vessels can vary between individuals, leading to inaccurate readings. To address this, a second infrared wavelength LED is used. By comparing the absorbance of red and infrared light, the device can eliminate the blood vessel size effect and provide a more accurate reading.

Integrated Photonics: The Future of Diagnostics

An emerging medical sensor industry is pushing the boundaries of precision chemical fingerprinting using integrated photonics. This technology uses tiny light-manipulating devices, smaller than a tenth of a millimeter, to analyze biological samples.

Integrated photonics uses silicon wires to guide light, similar to water in a pipe. These wires can redirect, reshape, and even temporarily trap light. A key component is the ring resonator, a circular wire that traps specific wavelengths of light, enhancing chemical fingerprinting.

Originally designed for fiber optics communication, this technology is being adapted for miniature chemical fingerprinting labs on chips the size of a penny. These labs-on-a-chip hold the potential to:

Rapidly and non-invasively detect illnesses.
Analyze saliva or sweat samples.
Provide early-warning signals for cancers, infectious diseases, and autoimmune diseases.

How Labs-on-a-Chip Will Work

Labs-on-a-chip will use several methods, including chemical fingerprinting, to analyze trace substances in samples like saliva. The process involves:

Passing light through a saliva sample.
Using fine-tuned rings to siphon off slightly different wavelengths of light.
Sending the light to partner light detectors.
Resolving the cumulative chemical fingerprint of the sample.
Using an on-chip computer with a library of chemical fingerprints to identify molecules and their concentrations.
Diagnosing specific illnesses based on this information.

From communication networks to medical diagnostics, light continues to be a powerful tool for extracting information and driving innovation. The future of medical diagnostics is bright, thanks to the power of integrated photonics.