Wearable skin patches monitor hemoglobin in deep tissues

A team of engineers at the University of California, San Diego, has developed an electronic patch that can monitor biomolecules in deep tissues, including hemoglobin
.
This provides medical professionals with unprecedented critical information that can help detect life-threatening diseases such as malignancy, organ dysfunction, brain or intestinal bleeding, and more
.

"The amount and location of hemoglobin in the body provides critical information
about blood perfusion or build-up at specific locations.
Our device shows great potential in closely monitoring at-risk populations, enabling timely intervention in emergency situations," said
Sheng Xu, a professor of nanoengineering at the University of California, San Diego and corresponding author of the study.

The paper, "Photoacoustic patches for 3D imaging of hemoglobin and core temperature," was published in Nature Communications on December 15
, 2022.

Low blood perfusion in the body can lead to severe organ dysfunction and has been linked to a range of conditions, including heart attacks and vascular disease
in the extremities.
At the same time, abnormal blood accumulation in the brain, abdomen, or cyst may indicate bleeding or malignancy in the brain or internal organs
.
Ongoing surveillance helps diagnose these diseases and helps facilitate timely and potentially life-saving interventions
.

The new sensor overcomes some of the significant limitations
of existing methods for monitoring biomolecules.
Magnetic resonance imaging (MRI) and X-ray computed tomography rely on bulky equipment that is difficult to obtain and often only provides immediate status information about molecules, making them unsuitable for long-term biomolecular monitoring
.

"Continuous monitoring is essential for timely intervention to prevent the rapid progression of life-threatening disease," said
Xiangjun Chen, a nanoengineering doctoral student in Xu's team and co-author of the study.
"Wearable devices based on electrochemical biomolecular detection, not limited to hemoglobin, are good candidates for long-term wearable monitoring applications
.
However, existing technologies only enable skin surface detection
.
”

This new, flexible, low-size wearable patch can be comfortably attached to the skin for non-invasive long-term monitoring
.
It can map hemoglobin in three dimensions at submillimeter spatial resolution in deep tissues down to a few centimeters below the skin, whereas other wearable electrochemical devices can only sense biomolecules
on the surface of the skin.
It can achieve high contrast
with other tissues.
Due to its optical selectivity, it can expand the range of detectable molecules, integrate different laser diodes of different wavelengths, and its potential clinical applications
.

The patch is equipped with a laser diode array and piezoelectric sensor
in its soft silicon polymer matrix.
The laser diode emits pulsed laser light
into the tissue.
Biomolecules in tissues absorb light energy and radiate sound waves
into the surrounding medium.

"Piezoelectric transducers receive sound waves that are processed in electrical systems to reconstruct the spatial mapping of wave-emitting biomolecules," said
Xiaoxiang Gao, a postdoctoral researcher in Xu's lab and co-author of the study.

"It is also much safer than X-ray technology with ionizing radiation due to its low-power laser pulses," said Hongjie Hu, a postdoctoral researcher on Xu's team and co-author of the study
.

Based on the success to date, the team plans to further develop the device, including shrinking the back-end control system to a portable-sized device for laser diode driving and data acquisition, greatly expanding its flexibility and potential clinical applications
.

They also plan to explore the wearable's potential
for core temperature monitoring.
"Because the amplitude of the photoacoustic signal is proportional to temperature, we have demonstrated core temperature monitoring in ex vivo experiments," Xu said
.
"However, verifying core temperature monitoring in humans requires interventional calibration
.
"

They will continue to work with physicians to pursue more potential clinical applications
.