Biosensors have come a long way since the first enzyme electrodes were invented in 1962. Today, we have numerous different types of biosensors that allow us to measure dozens of physiological and biochemical parameters.
Here, we’ll look at the different kinds of biosensors used in the medical industry and the many substances they allow us to measure.
What Are Biosensors?
Biosensors are sophisticated analytical devices that combine a biological component with a physicochemical detector to measure the presence or concentration of specific substances.
These devices operate by using a bioreceptor, such as enzymes, antibodies, or nucleic acids, which specifically interacts with the target analyte. This interaction is then converted into a measurable signal by a transducer, and the data is processed and displayed, often via a connected device.
In the MedTech world, these sensors are pivotal tools used to detect and monitor various biological markers, providing real-time data that can inform diagnostics, disease management, and therapeutic interventions.
Types of Biosensors
Several types of biosensors are widely used in the medical field. Each of them employs different mechanisms to achieve their goals.
Electrochemical biosensors are among the most common and include glucose meters for diabetes management, which measure blood glucose levels by detecting the electrical signals generated by enzymatic reactions.
Optical biosensors utilize light to detect changes in the biological element. These types of sensors are often employed in immunoassays and DNA sequencing.
Field-effect transistor (FET) based biosensors use the principles of field-effect transistors to detect biological or chemical substances. These sensors leverage changes in the electrical characteristics of the FET to measure the concentration of specific analytes.
Piezoelectric biosensors measure mechanical changes, such as mass or pressure shifts, and are often used in detecting pathogens and monitoring blood coagulation.
Bioluminescence sensors utilize bioluminescent organisms or enzymes to produce light as a response to specific biochemical reactions. The emitted light serves as the measurable signal, indicating the presence or concentration of a particular analyte. They are often used in applications such as detecting bacterial contamination, monitoring cellular processes, and assessing metabolic activity.
Semiconductor biosensors use semiconductor materials to detect biological or chemical substances through changes in electrical properties.
Antibody biosensors, also known as immunoassay-based sensors, use antibodies as the primary recognition element to detect and quantify specific target molecules, known as antigens. These biosensors leverage the highly specific binding interactions between antibodies and their corresponding antigens to provide sensitive and precise measurements.
Thermal biosensors detect heat changes resulting from biochemical reactions and are typically used in enzyme-based assays.
Nucleic acid-based biosensors utilize nucleic acids, such as DNA or RNA, as the biorecognition element to detect specific genetic material or sequences. These biosensors are particularly valuable in the field of medical diagnostics and biotechnology.
NIR spectroscopy biosensors use near-infrared light to measure the concentration of specific molecules, such as glucose, in biological tissues. By analyzing the absorption and reflection patterns of NIR light, the sensor can determine the concentration of the target molecule.
Ion-selective electrode (ISE) sensors are widely used in the medical industry, particularly for clinical diagnostics. These measure the concentrations of various ions in biological fluids such as blood, urine, and plasma.
Colorimetric biosensors detect color changes that occur when a target analyte interacts with a reagent or sensing element.
Fluorometric biosensors detect and quantify substances based on their ability to emit fluorescence when exposed to specific wavelengths of light.
Flow cytometry-based sensors analyze and quantify various cellular characteristics in a fluid stream. These sensors work by passing a stream of cells or particles through a laser beam one at a time and measuring the scattered light and fluorescence emitted by the cells.
Each type of biosensor offers unique advantages and should be selected for use in sensor devices based on the specific requirements of the medical application.
What We Can Measure
Thanks to the many different types of biosensors available today, we can measure an ever-increasing variety of target substances.
Here is a quick look at the substances that current biosensors are capable of measuring.
Enzymes and Proteins
- Creatinine. Measuring these levels is essential for evaluating kidney function, diagnosing renal disorders, and monitoring the progression of chronic kidney disease. Enzymatic, colorimetric, fluorometric, and electrochemical sensors are all used to measure creatinine.
- Hemoglobin. This measurement is essential for diagnosing and managing anemia, monitoring overall blood health, and evaluating respiratory and cardiovascular function. Many types of biosensors are used to measure hemoglobin, including optical, electrochemical, colorimetric, and fluorometric sensors.
- C-Reactive Protein. CRP measurements are important because they serve as a key biomarker for inflammation, helping to diagnose and monitor inflammatory conditions such as infections, autoimmune diseases, and chronic inflammatory disorders, as well as to assess the effectiveness of treatments. Antibody, electrochemical, colorimetric, and fluorometric sensors are all used to track this marker.
- Bilirubin. Monitoring this substance is crucial for diagnosing and tracking liver function, assessing jaundice in newborns and adults, and evaluating conditions such as liver disease, hemolysis, and bile duct obstruction. Many types of biosensors, including colorimetric, electrochemical, fluorometric, and optical, are used to measure bilirubin.
- Albumin. These measurements are crucial for assessing liver and kidney function, diagnosing and monitoring conditions such as liver disease, nephrotic syndrome, and malnutrition, and evaluating overall protein balance in the body. Biosensors used to measure albumin levels include antibody, colorimetric, fluorometric, and electrochemical sensors.
- Alanine Aminotransferase. ALT measurements are crucial for diagnosing and monitoring liver function, as elevated levels of ALT can indicate liver damage or inflammation due to chronic conditions such as hepatitis, fatty liver disease, or liver cirrhosis. Colorimetric, electrochemical, fluorometric, and antibody sensors are all used to measure ALT.
- Aspartate Aminotransferase. AST measurements are essential for diagnosing and monitoring liver function and muscle disorders, as elevated levels of AST can indicate liver damage, myocardial infarction, or muscle injury. The same types of biosensors used to detect ALT levels can be used to measure AST.
- Gamma-Glutamyl Transferase. Levels of this enzyme are crucial for diagnosing and monitoring liver disease, biliary tract disorders, and alcohol abuse. GGT can be measured with the same types of biosensors used for the other enzymes listed here.
- Creatine Kinase. This measurement is essential for diagnosing and monitoring muscle damage, myocardial infarction, and certain muscle diseases, as elevated levels of CK can indicate injury to heart or skeletal muscles. Colorimetric, electrochemical, fluorometric, and antibody sensors are all used to measure CK levels.
- Fibrinogen. Measuring fibrinogen is crucial for assessing blood clotting function, diagnosing bleeding disorders, and monitoring conditions such as disseminated intravascular coagulation and liver disease. This glycoprotein complex can be measured using the same types of biosensors that work for enzymes.
- Cystatin C. Tracking this marker is important for evaluating kidney function and diagnosing chronic kidney disease, as elevated levels of cystatin C can indicate impaired renal function and provide a more accurate assessment of glomerular filtration rate than creatinine alone. It can be measured using the same kinds of biosensors that work for fibrinogen.
Cardiac and Cardiovascular Markers
- Oxygen Saturation. A common baseline health measurement, oxygen saturation is most commonly measured using optical sensors.
- Heart Rate. Another common baseline measurement, heart rate provides essential insights into cardiovascular health, helps diagnose and monitor heart conditions, and helps assess the body’s response to physical exertion or stress. It’s most often measured using optical sensors, but electrocardiogram and piezoelectric biosensors can also be used.
- Blood Pressure. Tracking this vital sign helps diagnose and manage cardiovascular conditions, such as hypertension and heart disease, monitor the effectiveness of treatments, and assess overall heart health. A number of specialty sensors, including oscillometric, auscultatory, and tonometric sensors, as well as optical sensors. are employed for this use.
- Troponin. This measurement is critical for diagnosing and managing acute myocardial infarction (heart attack) and other cardiac conditions. Various types of biosensors are used to measure troponin, including antibody, colorimetric, fluorometric, and electrochemical sensors.
- Brain Natriuretic Peptide. Measuring BNP levels is crucial for diagnosing and managing heart failure, as elevated levels indicate increased cardiac stress and fluid overload, which are common in conditions such as congestive heart failure. The same types of biosensors used for troponin also work with this marker.
- Prothrombin Time. PT measurements are used to assess blood clotting function, diagnose coagulation disorders, monitor patients on anticoagulant therapy, and manage bleeding and thrombotic risks. Electrochemical, antibody, colorimetric, and fluorometric, sensors are all utilized here.
- Activated Partial Thromboplastin Time. This test is crucial for evaluating the intrinsic and common pathways of the blood clotting cascade, diagnosing and monitoring bleeding disorders, and managing patients on heparin therapy, as abnormal aPTT can indicate issues with clotting factor function or anticoagulant therapy. This test can be completed using the same kinds of biosensors used for PT.
- D-Dimer. This protein fragment is used to diagnose and monitor conditions related to abnormal blood clotting, such as deep vein thrombosis, pulmonary embolism, and disseminated intravascular coagulation. The same types of biosensors used to measure enzymes can also be used to measure levels of this protein.
Blood Components and Metabolites
- Glucose. This is one of the most well-known substances measured using biosensors and is an important indicator in diabetes diagnosis and management. Glucose levels in the blood and subcutaneous fluid can be measured using a number of different biosensor types, including electrochemical, optical, and NIR spectroscopy sensors.
- Lactate. This is an important biomarker for monitoring metabolic activity, especially in sports medicine and clinical diagnostics. It can be measured using several types of biosensors, including electrochemical, optical, NIR spectroscopy, and piezoelectric.
- Cortisol. Monitoring this hormone is vital for diagnosing and monitoring conditions related to stress, adrenal gland function, and disorders such as Cushing’s syndrome and Addison’s disease, and is crucial for assessing the body’s response to stress and overall hormonal balance. To measure cortisol levels, various biosensors are employed, including antibody, electrochemical, fluorescence-based, and optical sensors.
- Uric Acid. Measuring this substance is important for diagnosing and managing conditions such as gout, kidney stones, and metabolic disorders. Many types of biosensors are used to measure uric acid levels, including electrochemical, optical, piezoelectric, and enzyme-based sensors.
- Cholesterol. This important health parameter can be measured using several different sensor types, including electrochemical, colorimetric, fluorescence-based optical, FET-based, and ISE sensors.
- Hemoglobin A1c. Tracking this measurement is crucial for monitoring long-term glucose control in patients with diabetes. The most common biosensors used for A1c are antibody, colorimetric, fluorometric, and electrochemical sensors.
- White Blood Cell Count. This measurement is used to diagnose and monitor a wide range of conditions, including infections, inflammatory diseases, and hematological disorders. Various types of biosensors are used here, including flow cytometry-based, electrochemical, colorimetric, and optical sensors.
- Red Blood Cell Count. Monitoring RBC is important for diagnosing and managing conditions such as anemia, polycythemia, and various hematological disorders. All of the same types of biosensors that work for white blood cell counts will work here as well.
- Platelet Count. These measurements are crucial for diagnosing and managing conditions related to blood clotting and bleeding disorders, such as thrombocytopenia (low platelet count) or thrombocytosis (high platelet count). Biosensor types used to measure blood cell counts can also be used to measure platelet count.
- Neutrophil Count. Monitoring levels of neutrophils is important for diagnosing and tracking a variety of conditions related to the immune system, including infections, inflammatory diseases, and certain cancers, as abnormal neutrophil levels can indicate an underlying infection, immune response disorder, or bone marrow pathology. The same four biosensor types used to count blood cells can be used here, as well.
- Glomerular Filtration Rate. GFR measurements are crucial for assessing kidney function and diagnosing and monitoring chronic kidney disease. Antibody, colorimetric, fluorometric, and electrochemical sensors can be used to measure GFR.
- Insulin. The amount of insulin in the blood can be useful in diagnosing diabetes and other metabolic disorders, as abnormal insulin levels can indicate problems with glucose regulation, such as insulin resistance or insufficient insulin production. The same types of biosensors used to measure GFR can also be used to measure insulin levels.
Lipids, Nutrients, and Ions
- Electrolytes. Tracking electrolytes provides essential information about the body’s fluid and electrolyte balance, which is vital for diagnosing and managing conditions related to hydration, kidney function, and metabolic disorders. Many types of biosensors are used to measure electrolytes, including ISE, conductometric, optical sensors, and FET-based sensors.
- Sodium. Sodium ion concentration is a critical parameter in clinical diagnostics and sports medicine. The concentration of sodium in blood or sweat can be measured using various sensor types, including optical, enzyme-based, FET-based, and ISE sensors.
- Potassium. This is another ion that is important in clinical diagnostics. It can be measured using FET-based, enzyme-based, optical, and ISE sensors.
- Calcium. This is an essential ion involved in many physiological processes, including bone health, muscle function, and cellular signaling. Several types of biosensors are used to measure calcium levels, including ISE, FET-based, optical, and enzyme-based sensors.
- pH. In the medical world, pH measurement is crucial in clinical diagnostics and environmental monitoring. It can be measured using various sensors that employ different mechanisms to detect the hydrogen ion concentration in a solution including electrochemical, optical, and ISE.
- Vitamin D. Measuring the concentration of this vitamin in the body is essential for assessing bone health, diagnosing and managing conditions such as osteoporosis, rickets, and vitamin D deficiency, and evaluating overall metabolic health. Various types of biosensors are used to measure vitamin D, including antibody, fluorometric, colorimetric, and electrochemical sensors.
- Triglycerides. Both cardiovascular issues and some metabolic disorders are associated with elevated triglyceride levels, making this an important lipid to track. Measuring triglycerides can be done with colorimetric, enzymatic, fluorometric, and electrochemical biosensors.
- Vitamin B12. Anemia, neurological disorders, and malabsorption issues can all be influenced by B12 levels. Using antibody, colorimetric, fluorometric, or electrochemical sensors, doctors can monitor these levels to aid in diagnosis and treatment.
- Magnesium. Measuring magnesium concentrations is crucial for diagnosing and managing conditions related to magnesium imbalance, such as cardiovascular diseases, muscle and nerve disorders, and metabolic imbalances. Multiple types of biosensors are used here, including ion-selective electrode, colorimetric, fluorometric, and electrochemical sensors.
- Zinc. Both zinc deficiency and toxicity are concerns, as imbalances can lead to impaired wound healing, growth retardation, and neurological issues. The same kinds of biosensors used to measure magnesium can also be used to test zinc levels.
Hormones and Hormone-Related Markers
- Thyroid-Stimulating Hormone. TSH measurements are critical for diagnosing and managing thyroid disorders, such as hypothyroidism and hyperthyroidism. Various types of biosensors are used to measure TSH, including antibody, colorimetric, fluorometric, and electrochemical biosensors.
- Free Thyroxine. FT4 levels reflect the amount of unbound thyroid hormone available for metabolic activities and help assess thyroid gland function and hormone balance. This measurement can be accomplished with the same kinds of biosensors used for TSH.
- Prostate-Specific Antigen. PSA is used to screen for prostate cancer, benign prostatic hyperplasia, and prostatitis. Antibody, colorimetric, fluorometric, and electrochemical sensors are all used to measure this antigen to aid in the early diagnosis and management of these conditions.
- Estradiol. Levels of this hormone can affect reproductive health, menstrual cycles, and bone density. Accurate measurements, which can be obtained with the same types of biosensors used for PSA, are important for diagnosing conditions related to hormone imbalances.
- Testosterone. Measuring testosterone is crucial for diagnosing and managing conditions related to hormonal imbalances, such as hypogonadism, infertility, and hormone-sensitive cancers, as well as for evaluating sexual development and overall health. Biosensor types used to measure estradiol can also be used to measure testosterone.
- Catecholamines. Accurate measurements of catecholamines, including epinephrine and norepinephrine, help assess the adrenal and sympathetic nervous systems’ activity, guide treatment for disorders like hypertension and panic attacks, and monitor responses to stress. Biosensors, such as antibody, colorimetric, fluorometric, and electrochemical sensors, allow doctors to accurately track these levels.
Other Health Markers
- Alcohol. Biosensors used to measure alcohol levels are critical for applications ranging from medical diagnostics to law enforcement. The most common types of biosensors employed include electrochemical, optical, and semiconductor sensors.
- Body Temperature. Tracking this measurement is crucial to help diagnose and monitor fever, infections, and other conditions affecting thermoregulation, and is essential for assessing overall health and guiding treatment decisions. Various specialty types of biosensors are used to measure body temperature, including thermocouples, thermistors, infrared sensors, and electronic thermometers.
Using Biosensors to Advance Medical Care
Utilizing the diverse measurement capabilities of biosensors has the potential to significantly advance medical care by providing precise, real-time data on various physiological and biochemical parameters. Using these capabilities in conjunction, in the form of multi-sensor wearables and testing platforms, can further enhance their usefulness, leading to more effective and personalized treatment strategies.
Additional innovations in this field have the potential to further transform medical care. Advances in nano-biosensors could offer unprecedented sensitivity and specificity, allowing for early detection of diseases at molecular levels with minimal invasiveness. Wearable biosensors integrated with artificial intelligence could provide continuous, automated health monitoring and predictive analytics, alerting patients and healthcare providers to potential health issues before they become critical.
Lab-on-a-chip technologies could enable complex diagnostic tests to be performed quickly and affordably at the point of care, reducing the need for extensive lab work and expediting treatment decisions. Biosensors combined with telemedicine platforms could facilitate remote patient monitoring and management, making healthcare more accessible and efficient.
Collectively, these advancements promise to enhance diagnostic accuracy, personalize treatments, and improve overall patient outcomes by leveraging the comprehensive measurement capabilities of modern biosensors.