Through-skin sensor for human electrolyte

Sandia National Labs has used micromachining to build a painless minimally-invasive sensor for human potassium levels.

Ronen Polsky Sandia skin sensor

Ronen Polsky and Sandia’s potassium sensor

It uses 8um long porous spike-like needles to sample interstitial fluid (fluid between cells) from the skin surface.

“The device is painless because it employs needles so tiny they don’t traumatise nerves when pressed into the skin,” said Sandia.

Potassium passes through pores in needles, through a micro-fluidic chip, and finally to carbon ion-selective sensing electrodes (ISEs).

According to the lab, the electrodes can measure the amount of this electrolyte without being confused by other electrolytes in the fluid. Selectivity can be changed, allowing electrolytes such as sodium or calcium to be measuered by similar carbon electrodes in the same device.

The chip has nine needles, and nine gold disks to on which various ISEs can be formed. (Not the gold contacts just visible at the bottom of the protoype).

The ISEs are 3D structures. Both porous carbon and porous graphene were compared for electrochemical performance, stability, and selectivity; with the carbon version winning out and “measuring potassium across normal physiological concentrations in the presence of interfering ions with greater stability” said Sandia in an Advanced Healthcare Materials paper describing the work.

“We’re proposing a minimally invasive way to move away from centralized laboratory testing,” said said Sandia reearcher Ronen Polsky, pictured holding a prototype.

The paper also describes how the needles were created using a laser.

At the moment, this is a desk-top demonstrator. The intention is to use the same technology in a wearable device, perhaps similar to a watch, to give constant real-time measurements that would now require a lab test.

Work was shared with University of North Carolina and North Carolina State University, and the University of New Mexico will lead human testing of the device.

As well as medical use, the lab sees military and athletic applications where immediate knowledge of electrolytic states could aid improved performance.

“Investors have expressed interest in commercial applications for the technology in healthcare and sports medicine, among other areas,” said Polsky.

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