A hemoglobin level in deep tissues can be monitored via a patch that can be worn on the skin

Image by Gerd Altmann from Pixabay

An electronic patch, developed by a team of engineers from the University of California San Diego, is capable of monitoring biomolecules in deep tissues, such as hemoglobin. This provides medical experts with access to vital information previously unavailable to them, which may aid in the early detection of life-threatening illnesses such as cancerous tumors, organ malfunction, hemorrhages in the brain or stomach, and other disorders.

The amount of hemoglobin in the body as well as its location throughout the body give vital information about the circulation of blood or the buildup of blood in particular areas. The device has a significant amount of possibilities in the area of close monitoring of high-risk populations, enabling prompt interventions at crucial times according to Sheng Xu, a professor of nanoengineering at the University of California San Diego and the study’s corresponding author.

The article entitled “A photoacoustic patch for three-dimensional imaging of hemoglobin and core temperature” was published in the edition of Nature Communications that was released on December 15, 2022.

A low blood perfusion rate within the body is linked to a wide variety of illnesses and conditions, including heart attacks and vascular disorders of the extremities. This condition can cause significant disorder in the body’s organs. On the other hand, an abnormal collection of blood in regions such as the brain, abdomen, or cysts may be an indication of cerebral or visceral bleeding or malignant tumors. Continuous monitoring can help with the diagnosis of these illnesses, which in turn can help promote therapies that are swift and might potentially save lives.

The new sensor gets around a number of important restrictions that are present in the technologies that are currently used to monitor biomolecules. Magnetic resonance imaging (MRI) and X-ray computed tomography rely on complicated equipment that can be challenging to obtain. Additionally, these techniques typically only provide data on the direct status of the molecule, which renders them unreliable for long-term monitoring of biomolecules.

Continuous monitoring is important for timely actions to prevent life-threatening conditions from rapidly worsening according to Xiangjun Chen, a nanoengineering Ph.D. student in the Xu group and study co-author. Wearable devices that use electrochemistry for the detection of biomolecules, including but not limited to hemoglobin, are promising candidates for long-term applications of wearable monitoring technology. However, the current technologies are only capable of achieving the capacity to detect the skin surface.

The new wearable patch is flexible, has a low form factor, and can be attached to the skin in a comfortable manner. This makes it possible to do noninvasive long-term monitoring. In contrast to other wearable electrochemical devices, which can only detect biomolecules on the surface of the skin, this one can perform three-dimensional mapping of hemoglobin in deep tissues with a spatial resolution of less than one millimeter, all the way down to just a few centimeters beneath the skin. It is capable of achieving a high contrast in comparison to other tissues. Because of its optical selectivity, it is possible to broaden the spectrum of molecules that may be detected. Additionally, it has the potential to be used in clinical settings and can integrate a variety of laser diodes that operate at varying wavelengths.

The patch’s soft silicone polymer matrix contains arrays of laser diodes as well as piezoelectric transducers for its electronic functionality. Pulsed laser light is emitted by laser diodes, which penetrate the tissues. The optical energy is absorbed by biomolecules in the tissue, which then emit sonic waves into the medium that surrounds the tissue.

According to Xiaoxiang Gao, a postdoctoral researcher in Xu’s lab and co-author of the paper, piezoelectric transducers receive the sonic waves, which are processed in an electrical system to reconstruct the spatial mapping of the wave-emitting biomolecules.

Hongjie Hu, a postdoctoral researcher working in the Xu group and a coauthor on the study, said that with its low-power laser pulses, it is also considerably safer than X-ray procedures that include ionizing radiation. Hongjie Hu is also a collaborator on the paper.

As a result of the progress that has been made thus far, the group intends to continue developing the device. One of their goals is to reduce the size of the backend controlling system so that it can be contained within a portable device. This will significantly increase its adaptability as well as its potential clinical application.

In addition to that, they intend to investigate the capability of the wearable device to monitor core temperature. They  have shown core temperature monitoring on ex-vivo studies. This is due to the fact that the amplitude of the photoacoustic signal is proportional to the temperature.  However, interventional calibration is necessary in order to validate the core temperature tracking on the human body.

They are continuing their collaboration with medical professionals in order to investigate more possible clinical uses.


Xiaoxiang Gao et al. (2022). A photoacoustic patch for three-dimensional imaging of hemoglobin and core temperature, Nature CommunicationsDOI: 10.1038/s41467-022-35455-3