Every year, about 735,000 Americans suffer a myocardial infarction, commonly known as a heart attack. Of these, 525,000 are a first heart attack, while 210,000 happen in people who have already had a heart attack.

Diagnosing a heart attack can be difficult for physicians. Many patients have symptoms — such as dizziness or nausea — that may mimic other conditions. Many have normal EKG readings, and a quarter of heart attack patients have no chest pain.

Whether invasive or noninvasive, diagnosing a heart attack requires procedures that can be extensive and expensive, often proving difficult in remote or low-income areas. However, American scientists have now developed a simple, thermometer-like device that can help doctors diagnose heart attacks with minimal materials and cost.

In a recent study, Sangmin Jeon and colleagues noted that one way to tell whether someone has had a heart attack involves measuring the level of the protein troponin in the patient's blood. A troponin test is often the first test that emergency rooms use because the protein appears early, giving physicians a clue to whether a heart attack is occurring. Also, troponin stays in the blood for as long as a week, allowing physicians to identify a heart attack and take action to prevent further damage even if the patient was slow to seek medical care.

However, detecting troponin requires expensive instruments and is often not practical, especially in low-income areas where three-quarters of heart attack deaths occur. So, the researchers used the simplicity of alcohol and mercury thermometers to create a similarly simple method to detect troponin — using a glass vial, specialized nanoparticles, a drop of ink and a skinny tube.

Here's how it works: After researchers sealed a glass vial with a screw cap containing a silicon septum, they inserted a capillary tube containing a drop of ink through the septum. The catalytic dissociation of hydrogen peroxide (H₂O₂) to water and oxygen increased the pressure inside the glass vial and raised the ink level in the capillary tube. The ink level increased with the platinum nanoparticle concentration, which is proportional to the troponin concentration.

According to the research team, the sensitivity of this assay for troponin in human serum after a five-minute dissociation reaction, detected with the naked eye, was 0.1 ng/mL, which was better than the sensitivity of the conventional colorimetric method using the TMB oxidation reaction under the same experimental conditions.

Since early diagnosis of heart attacks could help curb the number of victims, Jeon's team of researchers set out to make a sensitive, more accessible test. Troponin concentration rises when blood is cut off from the heart and the muscle is damaged. When human serum with troponin — even at a minute concentration — was mixed with the nanoparticles and put in the vial, the ink climbed up a protruding tube and could be read with the naked eye, exactly like a thermometer.