A collaboration between American and Indian researchers has produced a nano-biosensor that can detect tuberculosis in early stages. The flexible sensor works coupled to a smartphone and is ideal for point-of-care use. The study, by scientists at Clemson University in South Carolina and Sri Sathya Sai Institute of Higher Learning in Anantapur, has been published online in the journal Physical Chemistry Chemical Physics.
Tuberculosis (TB) is a transmissible bacterial infection that attacks the lungs and other organs. It is caused mostly by Mycobacterium tuberculosis, and it is the most prevalent infectious disease in the world. TB is transmitted by respiratory fluids expulsed by infected people. Latent infections can develop to active disease, and in that stage TB kills 50% of the people if untreated. Around 80% of the population in Africa and South East Asia has contracted TB, mainly due to weaker immune systems affected by HIV-AIDS. Moreover, access to healthcare is rather limited in these areas. Providing points-of-care with a cheap, fast and reliable method of TB detection would help to quickly diagnose new infections that could be treated on time.
Fullerenes and surface plasmons improve stained bacteria fluorescence detection
The researchers based the sensors on a flexible cellulose-acetate substrate. These films were then coated with silver and spherical fullerenes of 60 carbon atoms, the extremely stable molecules also know as buckyballs. Saliva, semen or urine samples are placed in the film, along with a TB positive control. Surface plasmons, the electron oscilations that happen at the interface of any two materials, are used to couple, through the fullerenes, the fluorescent emission of dye-stained bacteria with the silver molecules in the film. The intensity of the emission, observable with the camera of an attached smartphone, is proportional to bacterial density, which allows to infer the stage of the infection.
The key of this technique is the optimization of the capture of fluorescent emission. With common detectors, capture is lower than 1%. The use of fullerenes for surface plasmon coupling increased that percentage to amounts that allow detection of low bacterial densities and thus diagnose TB earlier. Fullerenes work as a spacer of adjustable thickness. This was crucial, given that surface plasmon coupling is affected by the degree of separation between the silver and dye layers.
The new TB detector will mostly be used in remote points-of-care in developing countries and in crime scenes as a forensic tool.