From quantum sensors to sensor pills that you swallow to soft sensors that can be printed on gummy bears: new sensor technologies will improve medical care. Sensors are now an integral part of modern medicine. They are used to monitor bodily functions as well as in diagnostics and treatment. They record bioacoustic signals, such as heart and lung sounds, biothermal signals like body temperature, and biochemical, bioelectrical, biomagnetic, biomechanical, and biooptical signals.
The small sensors are also becoming smarter and more efficient.
Quantum sensors: mobile brain scanners
In the UK, scientists at the University of Nottingham together with the Wellcome Trust Centre for Human Neuroimaging have developed a prototype of a portable brain scanner. The scanner is integrated in a 3D-printed helmet and measures the tiny magnetic fields of electrical currents in the brain.
With classic, stationary devices for magnetoencephalography (MEG), which weigh up to half a ton, the sensors are cooled to -269°C and the patient must not move at all during the procedure. But the 900g helmet scanner works differently: quantum sensors can be used at room temperature and be placed directly on the patient’s head.
The British scientists predict that the sensitivity of magnetic field recognition could increase fourfold for adults and even by a factor of 20 with children and babies. One of the major attractions of this system is that patients can move about freely during the measurement and can drink, for example. The scientists are currently developing a new scanner in a bike helmet design, which can be adjusted to suit different head sizes.
Sensors printed on gummi bears
With micro-electrodes it is possible, for example, to measure electrical signals directly on the heart. This requires soft materials; however, in the past it has been difficult to attach electrodes to material such as these. The Technical University of Munich (TUM) and the Jülich Research Center were able to print microelectrode arrays onto gelatin candy and other soft materials, using a carbon-based liquid. So that the sensors don’t record any unwanted signals, the scientists applied a neutral protective layer over the carbon paths.
They tested the process on silicone PDMS (polydimethylsiloxane) and on gelatin - in the form of melted and re-solidified gummy bears. The 30 micrometer wide microelectrode arrays allow measurements on individual cells, which is difficult to do with conventional printing methods.
“In the future, similar soft structures could be used to monitor nerve or heart functions in the body, for example, or even serve as a pacemaker,” said Bernhard Wolfrum from the TUM. At present, he is working with his team to print more complex three-dimensional microelectrode arrays and sensors that react selectively to chemical substances.
Sensors that can be swallowed to explore the intestine
The Royal Melbourne Institute of Technology (RMIT) in Australia has developed ingestible sensors that monitor the intestine. The capsule contains gas sensors, a temperature sensor, a microcontroller, batteries, and a radio frequency transmitter. When swallowed with some water, the sensor capsule begins its expedition through the gut. During its journey, it collects data about the chemical composition and sends this to a cell phone.
“To investigate microbes in the gut, we have had to rely on fecal samples or operations in the past,” explained Kourosh Kalantar-Zadeh from the RMIT.
However, these measurements would not reflect the actual circumstances. The capsule provides a non-invasive method to measure microbiome activity authentically. With study participants who ate a lot of dietary fibre, the capsules were able to determine the start of fermentation exactly. The monitoring device will help diagnose bowel diseases more accurately and also ensure that diseases don’t occur in the first place.
Approved in the USA: sensor pill will control function
Medical dosage specifications for drugs and the patient’s ingestion behavior often differ considerably. A sensor pill from Japanese pharmaceutical group Otsuka Pharmaceutical should help improve this situation: Abilify MyCite informs the patient via an app when it reaches the stomach.
The active ingredient is an antipsychotic that is prescribed for patients with schizophrenia or bipolar disorders. When the sensor that is integrated in the pill registers that stomach acids are decomposing the pill, it sends an electronic signal to a band-aid on the patient’s skin. This reports ingestion of the pill to a smartphone app via Bluetooth. If the patient agrees, this information can also be provided to physicians, relatives, or carers. After it has completed its mission, the sensor is digested and excreted.
The system was first tested in 2016 in US hospitals and at the end of 2017 was approved by the US Food and Drug Administration (FDA). Abilify MyCite is now being trialed in the US on a small number of people. The sensor pill costs about $1,650 per month.
Infrared sensors: drugs with fewer side effects
Changes to the structure of proteins show whether a drug is effective. With an infrared sensor a team from Ruhr-University Bochum (RUB) was able to investigate quickly and easily which active ingredients affect the structure of proteins and how long the effect lasts. The sensor allows the structural changes on proteins that are triggered by active ingredients to be measured. The new method for active ingredient development could help drugs with few side effects to be developed precisely.
The sensor is based on a crystal that allows infrared light to pass through. The target protein is bonded to its surface. The crystal absorbs the infrared spectra, while solutions with or without the active ingredient are rinsed over the surface. The sensor detects changes in the structure-sensitive spectral range of the protein, the amide region.
If changes occur, it’s clear: the active ingredient has changed the protein form. “In the past, the influence of an active ingredient on the structure of a target protein was investigated with time-consuming methods that provide detailed spatial information - but only after weeks or months,” explained Jörn Güldenhaupt from the RUB. The new method provides information about structural changes within minutes and can also limit the type of structural changes.
Electricity from bacteria: paper batteries for biosensors
Energy supply is a key topic for medical sensors. Scientists at the State University New York in the US developed a paper battery that uses microbes as electron suppliers. In the future, they could supply electricity for simple sensors and medical test kits.
Biosensors work like test strips: when they come into contact with substances, they change colour - a cheap but inaccurate method. A power source could enable the development of more efficient paper-based sensors. But conventional batteries are expensive and cannot be integrated into the paper substrate. The scientists found an alternative: they printed electrodes and traces onto a paper strip and then applied freeze-dried exoelectrogenic bacteria. When they come into contact with water they are re-activated and release electrons that are absorbed by the electrodes.
The scientists were able to operate an LED with the generated energy. However, a 1,000 times higher energy output is required for commercial applications. The team of scientists is now trying to improve the power yield by stacking and interconnecting several paper batteries.
Medical MEMS sensors
In medical technology the components should be as small as possible. MEMS sensors in the micrometer range are increasingly becoming established in diagnostics. The tiny micro-electro-mechanical systems combine several functions of microelectronics and micromechanics on one substrate. In medicine, MEMS are used mainly in pressure sensors, which will be presented at electronica 2018 by Silicon Microstructures (Hall C3, Booth 536), among others.
The most frequent applications are non-invasive blood pressure monitoring. Pressure sensors based on MEMS technology are also used in infusion pumps, respirators and dialysis machines, in eye surgery and to record oxygen, carbon dioxide, glucose, and other blood values. MEMS accelerometers, like the ADXL362 from Analog Devices (electronica exhibitor, Hall C4, Booth 111) are used in areas such as hearing aids and home healthcare devices. The use of MEMS sensors in nerve prostheses is also currently being researched.
Disposable sensors from the 3D printer
With medical sensors the cost factor also plays an important role. There is a trend towards disposable sensors. They can be produced inexpensively with 3D printing which also minimizes the risk of infection. Disinfection is expensive and even after diligent cleaning there is still a residual risk that pathogens could survive. Printed disposable sensors are already used in pulse oximetry - measuring oxygen saturation in arterial blood.