Diagnosing Heart Attacks with a Plasmonic Chip

Cardiovascular disease (CVD) is one of the biggest killers in the world where medical ailments are concerned. In normal times, a lot of time and research is dedicated to treating cardiovascular diseases, and while the current coronavirus pandemic is taking up a lot of the medical research and testing efforts, it doesn’t take away from the fact that cardiovascular diseases are responsible for around 31.5% of all deaths globally, i.e. almost a third of all the worlds deaths are due to some kind of cardiovascular disease. There are several tests, monitoring approaches and treatments out there for many cardiovascular diseases, but more are always being developed due to significant mortality rates which come with these diseases.

Myocardial Infarctions aka Heart Attacks

Myocardial infarction is the technical medical term for what many of us know to be a heart attack. Out of all the cardiovascular diseases, heart attacks are the leading cause of cardiovascular-related deaths, in part due to the damage caused and in part because of the sudden nature of them occurring (often without much warning). Overall, heart attacks make up more than 30% of all cardiovascular diseases worldwide, and this translates to over 7.4 million deaths each year around the world. So, while short-term pandemics and other short time-frame diseases can divert resources away at points in time, the high amounts of deaths are why cardiovascular research has been going on for a long time and will continue to progress for many years despite what other medical obstacles are present.

Heart attacks occur when the blood flow to the heart decreases (or stops entirely), causing the areas of tissue where there is no blood flow to become damaged. These damaged areas can become scarred and unable to function normally post heart attack. Most heart attacks occur due to high blood pressure, blocked arteries, poor health choices (e.g. smoking and obesity) and some medical conditions (such as diabetes). One of the worrying factors is that while heart attacks take many lives each year, their occurrence is on the rise due to changes in human behaviour and lifestyle so that the death figures could be much worse in the future. One of the critical areas of research for biomedical scientists is to find new ways of diagnosing heart attacks and predicting the outcome that does not require the usual blood test methods.

Plasmonic Materials in Medical Applications

Plasmonic materials have arisen in many medical applications, particularly in imaging of cancers, but the high sensitivity attributed to plasmonic materials could be translated to heart attack diagnosis. Plasmonic materials utilise noble metals (i.e. very unreactive metals such as gold, silver, platinum) because how light interacts with the free surface electrons in these metals creates surface plasmons, that is, highly oscillating electrons on the surface which can be excited quickly. 

Because surface plasmons can be excited quickly, they tend to enhance the sensitivity of the diagnostic process in many biomedical applications as they illuminate the biomarkers (used in many biomedical tests to identify the presence of a biomolecule of damaged areas) so that they become much clearer. This enables the relevant biomarkers to a biological process (be it the progression of cancer, or damage to tissue) to be identified more clearly, and it also allows the process to be monitored over time by measuring how the biological environment changes over time. So, surface plasmons have become a way of diagnosing and monitoring many diseases, and the focus has now turned to see how surface plasmons can be used to diagnose and monitor the progression of heart attacks in a patient. 

Using a Plasmonic Chip to Diagnose and Monitor Heart Attacks

A research team spanning China, Taiwan and the USA have created a plasmonic chip using gold nano-islands to detect and monitor the progression of heart attacks. The chip provided a microarray analysis using a common biomarker (cardiac troponin I) to detect if a patient had a heart attack by detecting specific antibodies in the sample – by making them bind to specific capture antibodies on the surface of the device.

The approach used was different from other diagnosis and prognosis methods, in that it was approached from both disease diagnosis and application design perspective. The disease diagnosis approach used the plasmonic chip to detect the antibodies using a minimal amount of serum, and the application design perspective provided a tailored monitoring approach by identifying and monitoring the concentration of multiple biomarkers in the sample in rapid analysis times – which in turn could be used to predict the potential outcomes of the patient.

The device itself was created using the gold nanoislands between 80 and 200 nm in diameter, which was spaced apart from each other at distances between 10 and 30 nm. The microarrays containing the capture antibodies used to detect the antibodies in the sample were printed on to the chip, and this enabled the detection of serum antibodies to always occur in a region near the plasmonic surface, enhancing the sensitivity of all detections. 

Out of all the different tests out there, there are not many which can be used to monitor heart attacks at the point of care. Moreover, this device shows a very high sensitivity due to the surface plasmons, which contributed to a 130-fold increase in sensitivity over conventional near-infrared fluorescence methods, including the sensitivity of 100% and a specificity of 95.54%. No-one knows whether new medical devices will make it past the clinical trial stage and be used in front-line testing. However, the results shown by this chip are promising and could offer significant advantages over other tests if they are found to be safe enough to pass clinical trials and are commercially viable enough to manufacture at scale.