In earlier times, physicians used to do skin-based diagnosis to reach conclusions to treat a patient. A skin bottle than usual, means fever, a paler, one indicates dehydration, a bluish tinge, on skin implies you need more oxygen; and if it feels wet, ones need to exercise less. However, in today’s pathololgical diagnostics is preferred and medicine prescribed opn the basis of reports..
E-skin
Nowadays, skin specialists follow a procedure in which they attach a thin polymer-based sheet, which contains the desired drug, which is stuck to the skin on your arm or chest and deliver the drug past the sweat fluid directly into the body, using a tiny electric current on the patch. Thus, it is wearable technology, used for personalised medicine—no pills or potions. Now, with the advancement in the field, there also is the option of e-skin based on microelectronics, bio-compatible polymers, and nanoscale wires that can be attached to an external electric power supply, using microscale batteries.
Significance of Sweat in Diagnostics
Sweat is 99 per cent water, containing sodium, potassium, calcium, magnesium and chloride ions, ammonium ions, urea, lactic acid, glucose, and other minor components. The vital role of sweat in our body and the chemicals it contains are increasingly being established and utilised these days.
Notably, sweat does not carry any pathogen; rather, it carries a germ-killer protein, called dermicidin, which can be anti-viral. If it proves to be so, it would be a great relief in these COVID-19 days.
Sweat is secreted out of three types of glands distributed across our skin. It helps keep our body at the optimum temperature of 37 °C (98.4 °F). Our brain has temperature sensitive nerve cells (neurons) which control the sweat glands in releasing the fluid depending on the temperature, physical, and metabolic activity of the body. In this way, sweat regulates the thermal balance of our body.
The sweat based diagnosis is conducted by analysing how the sweat fluid of a patient compares with that of a healthy individual. For e.g., the amount of glucose found in the sweat of a diabetic person is higher than normal. So, the sweat has diagnostic value like any other body fluid. But the shortcoming of this approach is the quantity of sweat available from the skin. It is in such a problem that modern-day technology in the form of microelectronics and e-skin patches come to rescue.
Diagnosis using e-skin
These days scientists have been using e-skin patches for real-time measurements of some chosen component in the sweat using sensors in the patch. But if the patches are loaded with different sensors to measure many components simultaneously, it would be much better. A breakthrough in this direction was made by a group of biologists, material scientists, computer experts, and electrical engineers from California and was published in a report ‘Fully Integrated wearable sensor arrays for multiplexed in situ perspiration analysis’ in science magazine, Nature, dated January 28, 2016. They put six sensor probes—all embedded on an e-skin patch—for Na, K, Cl ions, lactate, glucose, and the temperature of the sweat. Signals coming from each sensor measuring the sweat component as a tiny electrical signal are converted into a digital form, and sent to a micro-controller, and from there to a Bluetooth transceiver and passed on to the interface through SMS or email. The group followed up another experiment and found that the amount of sweat accessible in sedentary people is too low. So, the group resorted to what is called iontophoresis, wherein one can stimulate local secretion of sweat at chosen sites.
In a normal (control) individual, they found 26.7 mM of Na ions and 21.2 mM of Cl ions, whereas in a cystic fibrosis (CF) patient, Na level was 2.3 mM and Cl level was 95.7 mM. The group also found that oral glucose consumption while fasting led to increased glucose levels in sweat and blood. The research was published in a paper in 2017 in proceedings of the National Academy of Science.
Use of Sweat as Power Supply
The sensors and probes need to be powered externally using microbatteries. The question that arises is if these e-skin platforms are to be utilised in robotics and other devices, can we do away with the use of external by using the material in the sweat itself as a biofuel generator of electric power? This was addressed by the group of researchers in their paper in April 2020 in the journal Science Robotics. They added the enzyme Lox on a patch on an individual’s e-skin. The enzyme reacted with the lactate in the sweat and oxidised it to pyruvate in a bioanode, and reduced the oxygen into water in a biocathode, which generated enough electrical (energy to drive the patch with no external energy source.