A novel, simple, low-cost device that quickly diagnoses septicaemia at bedside has been developed by an IIT Delhi researcher working along with a Consultant from Global Medical Education and Research Foundation, Hyderabad.
Septicemia (or, sepsis) is the leading cause for deaths in hospitals worldwide. According to a paper published in October 2015 in the journal Analytical Chemistry, there are about 200,000 cases of sepsis deaths each year in the U.S. alone. Sepsis is caused by the overwhelming response of the immune system to an infection. The main causative agents of sepsis are Gram-negative bacteria due to their predominance in the normal intestinal flora and the environment. Specifically, it is the endotoxin, a major constituent of the Gram-negative bacterial cell wall, that causes sepsis.
In lieu of expensive and time-consuming methods for diagnosis of sepsis, Prof. Shalini Gupta from the Department of Chemical Engineering, IIT Delhi and Dr. Venkataraman Sritharan from Hyderabad have developed a low-cost, disposable, point of care device for bedside use for sepsis diagnosis.
The device is a colorimetric rapid card test to detect endotoxin levels in human serum sample. A commonly used antibiotic colistin is combined with (conjugated) gold nanoparticles to act as a detection probe. “We used the drug to detect endotoxin as we did not want to use the antibody detection method and it also reduces the cost of testing,” said Prof. Gupta.
The drug combined with gold nanoparticles binds to the endotoxin present in serum samples. “The drug has a specific affinity to endotoxin,” she said. Since gold particles are red in colour at the nanoscale, the drug conjugated gold nanoparticles that get bound to endotoxin appear red. Since the amount of endotoxin present varies depending on the severity of sepsis, the amount of drug conjugated gold particles that get bound to endotoxin reveals the degree of infection; the colour of red deepens depending on the severity of sepsis. “More the endotoixin, the more red the colour becomes because more gold nanoparticles get absorbed,” Prof. Gupta said.
To test a sample, a drop of serum is first added to the membrane on the device. Except the endotoxin, the rest of the constituents of the blood get sucked through the membrane. The detection probe consisting of the drug conjugated gold nanoparticles is then added to the membrane. The drug binds to the endotoxin present on the membrane and turns red in colour. “It works on a concentration-dependent manner and so we get to know the degree of infection,” she said.
If the sample is from a person without sepsis, no endotoxin is present on the membrane. And since no binding of the drug to endotoxin takes place no red colour is seen on the membrane. Since the gold nanoparticles are smaller than the pore size of the membrane, the drug conjugated gold particles pass through it in the absence of endotoxin.
The device may eliminate the need for trained scientists and a sophisticated microbiology laboratory. This is an important for India especially in rural areas where access to advanced diagnostic facilities and proper healthcare facilities is poor.
Initial validation on 80 sepsis samples has been carried out and validation using blind samples will soon be undertaken. According to her, the device may be commercially available by the end of this year. The device which took about three years to develop won the Gandhian Young Technology Innovation award in March this year.