A low-cost, ultra-sensitive device that is capable of detecting the cardiac biomarker troponin T protein has been fabricated by a research team from the Indian Institute of Technology (IIT) Hyderabad. Troponin T is a cardiac protein that is released into the bloodstream after a heart attack.

Unlike the commercially available test that can detect the protein at nanogram per ml concentration, this device can detect the protein at an extremely low concentration of femto gram per ml. This could help pave the way for early diagnosis of a heart attack, increasing a patient’s survival rate. It even has the potential to be able to predict the onset of a heart attack.

Cost-effective fabrication

• Unlike electrodes that are available, it costs very little to fabricate this bioelectrode. This is because a commercially available substrate was used. Further, very little antibody was needed to coat the electrode.
• The electrode was fabricated by depositing perovskite (zinc tin oxide) material electrochemically onto the substrate (indium tin oxide coated polyethylene terephthalate). Glassy carbon electrode coated with the same perovskite material was then used as a control. Perovskite increases the volume-to-surface area of the electrode, thereby increasing its sensitivity.
• The electrodes coated with perovskite were then functionalised to attract proteins. To increase the specificity of the electrode to bind only to the troponin T protein, the electrodes were decorated or coated with the troponin T antibody.

Test findings

• The researchers added various concentrations of the biomarker (ranging from 1 femtogram per ml to 1 microgram per ml) to a buffer solution and measured the impedance (effective resistance in alternating current). Compared with the current limit of detection, the bioelectrode was able to detect troponin T even when it is 10,000 times less in concentration.
• When the troponin antigen binds to the antibody present on the electrode, the impedance increases. As more and more biomarker binds to the antibody, there is increased impedance, which is what we measure. After some time, the electrode is saturated with the troponin protein, so no change in impedance is seen.
• The researchers measured impedance using different concentrations of the protein. They plan to use these impedance values to know the concentration of the protein when testing actual blood samples. And by using a machine learning algorithm, we can measure the concentration of the biomarker in the sample.
• To test the selectivity of the bioelectrode to bind to the biomarker, the researchers tested it on bovine serum albumin (BSA) and human serum albumin (HSA).
• Only a slight change in relative resistance was observed in the case of HSA and BSA as only a small amount of proteins [from HSA and BSA] bind to the bioelectrode. This is unlike troponin where more protein gets bound to the bioelectrode, leading to more impedance.

Focus on miniaturisation

The team is now working on how to miniaturise the readout instrument, will soon be able to capture the signal using a circuit the size of a chip. This will be connected to [a] mobile phone with an app that has a machine learning algorithm for quantification of the troponin biomarker.