Using human sweat as diagnostic tool and source of power 

#GS3 #Science&Technology  

A recent breakthrough brings in an e-skin patch with six sensor probes 

  • If the skin feels hotter than usual, you have fever; if it is paler than the usual, you are dehydrated and must drink more water; if it has a bluish tinge, you need to breathe more oxygen; and if it feels wet, you need to exercise less or cut your physical.   
  • Skin-based diagnosis is a gone thing for general practitioners.  
  • These days, skin specialists do an interesting procedure, in which they attach a thin polymer-based sheet which contains the desired drug, stick it 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.   
  • This is thus a wearable technology for personalised medicine — no pills or potions.   
  • And with the advent of microelectronics and bio-compatible polymers, we now have ‘electronic skin’ (e-skin), and nanoscale wires that can be attached and an external electric power supply using micro-scale batteries.  

Role of sweat 

  • Notice in all this, the active body fluid, namely, the sweat, is ignored or treated as an inert carrier of no other value.   
  • The role of sweat fluid in our body and the chemicals it contains are becoming increasingly understood and utilised only recently.   
  • Sweat comes out of three types of glands distributed across all over our skin, secreting water and substances that help keep our body at the optimum temperature of 37 degrees C (or 98.4 degrees F).   
  • Our brain has temperature-sensitive nerve cells (neurons) which control the sweat glands in releasing the fluid depending on the temperature and physical and metabolic activity of the body.   
  • Sweat is thus our body’s thermo-regulator.  
  • Sweat contains 99% water containing sodium, potassium, calcium, magnesium and chloride ions, ammonium ions, urea, lactic acid, glucose and other minor components.   
  • An analysis of the sweat fluid in a patient and how it compares with that of a ‘normal’ individual will thus be of diagnostic value (just as much as other body fluids do).   
  • In the illness called cystic fibrosis, the ratio of the sodium to chloride ions in the sweat is different from that of a normal individual.   
  • Likewise, the amount of glucose in the sweat of a diabetic is higher than normal, but the problem is the amount of sweat available from the skin.  

Diagnosis based on e-skin 

  • Now that microelectronics and e-skin patches are both available, scientists have been using them for real-time measurements of some chosen component in the sweat, using the appropriate probe (sensor) in the patch in order to detect and measure the level of the component.   
  • They put in six sensor probes — for Na, K, Cl ions, lactate, glucose and the temperature of the sweat — all six of them embedded on a e-skin patch, such that a stable sensor-skin contact is maintained.   
  • Signals coming from each sensor measuring the sweat component as a tiny electrical signal are then converted into a digital form, and sent to a micro-controller, and from there to a Bluetooth transceiver, which can be seen on a mobile phone or other screen, and passed on through SMS, email, or uploaded to the Cloud interface.  
  • Since the amount of sweat accessible in sedentary people is too low, the group resorted to what is called iontophoresis, wherein one can stimulate local secretion of sweat at chosen sites, thus getting enough of the fluid, analysing its relevant components in normal (control) individuals, and people with cystic fibrosis and also monitoring glucose levels in the sweat — all this in a similar integrated platform as was used in their Nature paper.   

Sweat as power supply 

  • Note that in all these assays, the probes and sensors need to be powered externally using microbatteries.   
  • On a patch on the individual’s e-skin patch they added the enzyme Lox which would react with the lactate in the sweat and oxidise it to pyruvate in a bioanode, and reduce the oxygen into water in a biocathode, thus generating electrical energy that is sufficient to drive the patch with no external energy source — what a brilliant idea!  
  • Finally, in these COVID-19 days, it is good to know that sweat does not carry any pathogen (bacteria or virus); on the contrary it carries a germ-killer protein called dermcidin.  
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