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Engineered pacifier measures glucose in saliva

Wireless sensor could be a convenient way to monitor newborns’ health

by Prachi Patel, special to C&EN
October 16, 2019


Image shows the three component parts of a pacifier biosensor lined up in a row. These include a nipple, a chamber for saliva, and the electronics.
Credit: Anal. Chem.
A pacifier is transformed into a biosensor that can measure glucose in saliva. The nipple (right) has a narrow channel that makes saliva flow away from the mouth to the blue sensing chamber (middle) that contains disposable, enzyme-tipped electrode strips. Electronics embedded in the cap (left) measure and transmit changes in current that correlate to glucose levels in saliva.

Pacifiers can soothe fussy babies and help keep parents sane. Now researchers have turned these baby care must-haves into high-tech sensors that could track levels of glucose and other chemicals in a baby’s saliva (Anal. Chem. 2019, DOI: 10.1021/acs.analchem.9b03379).

Monitoring sick or preterm babies can be difficult. Keeping tab on infants’ vital signs typically requires rigid electrodes stuck to babies’ sensitive skin and connected to monitors via a tangle of wires. Measuring blood levels of chemicals like glucose, lactate, and sodium, meanwhile, means pricking the heel or an intravenous blood draw.

Wireless non-invasive technologies offer a gentler touch. Researchers have recently tested soft, tattoo-like wireless sensors that can measure blood oxygen levels, heart and breathing rate, and temperature. Other technologies already on the market include a smart sock that can monitor heart rate and oxygen levels, and temperature-tracking Bluetooth pacifiers.

But all these devices measure physical parameters, says Joseph Wang, a nanoengineer at the University of California San Diego. “Our pacifier is the first example of a device that measures chemistry markers.”

Image shows a gloved hand holding a pacifier with a small box of electronics attached to the back of the pacifier
Credit: Anal. Chem.
A pacifier biosensor can measure glucose in saliva.

Wang, Alberto Escarpa of the University of Alcalá, and colleagues made the binky biosensor by combining silicone nipples from commercial pacifiers with a custom 3-D printed back end that contains an electrochemical sensor. “The beauty of this pacifier is that everything electronic is outside the mouth so it’s very baby friendly,” Wang says, and the electronics add unnoticeable weight.

They bored a 4 mm wide channel in the silicone nipple and inserted a small PVC tube into it. The tube contains a series of three polystyrene valves shaped like pipette tips that keep saliva from flowing back into the baby’s mouth.

Sucking squeezes the nipple, drawing in saliva and forcing it to the back of the tube. There, behind the mouthpiece, it drops into a small 3-D printed chamber in the pacifier cap where it contacts the tip of a disposable electrode coated with an enzyme that oxidizes glucose. This reaction changes the electric current in proportion to glucose levels.

The back side of the electrode strip connects to electronics in the pacifier cap that measure the current and transmit the data to a smartphone using Bluetooth signals. Putting a different enzyme on the electrode tip could allow the pacifier to measure other chemical biomarkers, Wang says.

The researchers haven’t tested the pacifier on infants yet. With an adult volunteer using the pacifier, it took about five minutes for the saliva to contact the enzyme and the device to generate the glucose signal. The team also tested the device by squeezing saliva samples into the tube manually. They used samples from before and after a meal in four people with type I diabetes. The measurements closely matched those from a glucose sensor using fingertip blood.

The pacifier sensor faces several challenges before it can be used in hospitals. For one, it could be prone to getting dirty. Protective coatings could help keep the saliva-collecting channel and chamber bacteria-free, the researchers say. To make it safe for babies, they also plan to integrate the valves into a single-piece silicone nipple so that there are no small ingestible pieces.

“I think this is a highly innovative approach that could impact the personalized healthcare of babies,” says Wei Gao, a medical engineer at the California Institute of Technology. He says that the technique could be adapted into other types of portable biosensors to analyze saliva in elderly patients with chronic diseases. It could, for instance be turned into a single-use device that adults can spit on for rapid screening of chemicals in saliva, Wang says.


This story was updated on Oct. 23, 2019, to include Alberto Escarpa of the University of Alcalá, one of the study's corresponding authors.


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