Optical sensor measures blood glucose through skin
23 January 2015
Swiss research institute Empa and University Hospital Zurich have
developed an optical sensor that measures blood sugar levels through
the skin, without taking any blood.
It was designed to test for hypoglycemia in premature children,
which can cause brain damage if left untreated for over an
hour. Currently, blood samples have to be taken at regular
The Glucolight sensor’s novel measuring technology comprises: a
microdialysis measuring head, developed at the University
Hospital Zurich; a 'smart' membrane, developed at Empa; light
sources; a pump; and a microfluidics chip with a fluorometer, also
developed at University Hospital Zurich.
The membrane contains special dye molecules, known as spiropyrans.
When a UV light is beamed onto these spiropyran molecules they alter
their chemical structure and become charged (polar). When irradiated
with visible light, they revert to their original, neutral
structure. As a result, the membrane 'opens' if irradiated with UV
light and glucose molecules diffuse relatively easily through the
membrane from the skin. If irradiated with visible light,
considerably fewer glucose molecules pass through the membrane.
On left: Glucolight’s measuring head with the smart
membrane. On right: Diagram showing 'open' membrane letting glucose
molecule through. Credit: Empa
The measurement involves placing the measuring head, which is
around three centimeters in size, on the baby’s skin and irradiating
it with visible light. This allows some glucose molecules to diffuse
through the membrane from the skin. On the other side of the
membrane, the glucose is mixed with a fluid and pumped through the
microfluidics chip, while enzymes are added to trigger a reaction.
During the reaction, fluorescence appears, which the fluorometer
measures, and the computer uses the reading to calculate the glucose
concentration. The process is then repeated with UV light. The
computer then uses these two different readings to calculate the
premature baby’s blood sugar level.
Although skin sensors already exist, they have to be calibrated
before use, which means that the skin’s permeability value needs to
be known. In order to establish this, the blood sugar value has to
be determined via a blood sample and the glucose concentration on
the skin measured. Based on these readings, the permeability can
then be calculated and the sensor calibrated.
The researchers filed a patent application for Glucolight in
mid-2014 and the first clinical studies are scheduled at the
University Hospital Zurich for 2015. However, it could be years
before the use of Glucolight becomes standard. Empa and the
University Hospital Zurich are currently in negotiations with
partners for the industrial production of the sensor. For the
future, the researchers also envisage the use of Glucolight in other
fields, such as diabetes.