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Wearable electronic patch can 3D map haemoglobin molecules

Researchers have developed an electronic patch that can sense biomolecules in deep tissues. The study, published in Nature Communications, details the development of the new technology, which can be used for three dimensional (3D) mapping of haemoglobin molecules using ultrasonic transducers and lasers. The researchers hope to use the sensor in clinical practise to detect tumours, haemorrhages, and organ dysfunction.

Monitoring blood flow

Red blood cells are packed with haemoglobin molecules, which carry oxygen around the body. Blood must flow to all parts of the body to deliver oxygen for normal functioning. Reduced blood flow and accumulation is seen in various pathologies and clinical settings (heart attacks, vascular disease in extremities, after surgery, during cancer- or trauma- associated inflammation). This makes monitoring blood perfusion an important clinical need. However, existing patch-based wearable sensors are unable to monitor biological molecules in deep tissues and can only achieve skin-surface detection.

Engineers at the University of California San Diego (UCSC) developed a photoacoustic patch which uses ultrasonic transducers (a device used to convert one type of energy into an ultrasonic vibration) and lasers diodes (a semiconductor device which works in an infrared spectrum and produces coherent light beams) to 3D-map haemoglobin molecules.

Sheng Xu, corresponding author and Professor of Nanoengineering at UCSD said, “The amount and location of haemoglobin in the body provide critical information about blood perfusion or accumulation in specific locations. Our device shows great potential in close monitoring of high-risk groups, enabling timely interventions at urgent moments.”

Laser + transducer = photoacoustic patch

The researchers designed a photoacoustic patch (figure 1). The patch was made up of two main components: an array of laser diodes, which was the light source, and an array of piezoelectric transducers, which detected the acoustic waves emitted by the haemoglobin molecules. The laser pulses penetrated more than 2cm into biological tissues. Haemoglobin molecules absorbed the energy and generated acoustic waves when the laser pulses hit them. The transducers received the emitted acoustic waves, which were relayed to a backend system. Using the absorption characteristics of the haemoglobin molecules and the acoustic waves that were emitted, high spatial resolution 3D photoacoustic images were generated.

Figure 1. Schematic of the photoacoustic patch. The patch includes a laser diodes array (as the light source) and a piezoelectric transducer array (to detect the waves). The arrays were connected by copper electrodes.  Source: published in Nature Communications.

Out with the old?

The researchers highlighted the benefits of the new sensor over existing technology. Current sensors and imaging technologies, such as magnetic resonance imaging and X-ray computed tomography, capture a snapshot of what is happening at the time. They are unable to provide continuous long-term monitoring and the equipment is also expensive and bulky.

Hongjie Hu, co-author and Postdoctoral Researcher in the Xu group said, “With its low-power laser pulses, [the photoacoustic patch] is also much safer than X-ray techniques that have ionizing radiation.”

The study opens the door to information that has previously been inaccessible with wearable electronics. The detection of haemoglobin molecules was discussed but the technology can be extended to detect other biological molecules including lipids, glucose and proteins. The researchers are collaborating with medical professionals to develop the technology for clinical use.

Xiangjun Chen, co-author and nanoengineering PhD student in the Xu group said, “Continuous monitoring is critical for timely interventions to prevent life-threatening conditions from worsening quickly. Wearable devices based on electrochemistry for biomolecules detection, not limited to haemoglobin, are good candidates for long-term wearable monitoring applications.”

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