Editorial Feature

A Guide to Understanding Blood Glucose Monitoring Sensors

A glucose monitoring sensor is used to measure the concentration of blood glucose and is a key home glucose monitoring device for diabetes sufferers.

The pathophysiology behind diabetes is based on a lack of insulin abundance which can be due to insufficient release of insulin from beta cells in the pancreas, or inactive insulin receptors that can no longer responds to insulin compounds. Diabetes type II is the most common type of diabetes and is prevalent among people whom are overweight or over middle age. The video below animates the pathophysiology to diabetes.

With approximately 346 million people worldwide living with diabetes, it is no surprise that this disease is costly. An estimated 3.4 million sufferers of diabetes die from poor management of blood glucose. According to the World Health Organization, the number of deaths as a result of diabetes is estimated to double between the periods of 2005 and 2030. Poor diabetes management can be due to a number of factors including the patient’s diet and poor compliance to monitoring blood glucose levels on a regular basis.

Glucose monitors are paramount to helping patients to regularly keep track of blood glucose levels and adjust their diet, medication, and exercise routine. Traditional methods to measure blood glucose involve measuring blood glucose levels in the lab which provides the most accurate representation of a patient’s blood glucose concentration. However, careful measurement techniques and regular extraction of sample blood can be physically demanding for the patient and time-consuming. Blood glucose monitoring techniques advanced by the 1980s, a time during which the healthcare industry stressed the need to better manage type 1 and type 2 diabetes mellitus by using two main types of monitoring techniques: the Lance System and the continuous glucose monitoring system (CGMS) – both second-generation glucose biosensors. The following video describes how a basic glucose monitor works.

Second-generation Monitoring Device

The Lancet System

A lancet device is designed with a needle projecting from one end of the device used to prick the patient’s finger. A basic working overview of this device involves pressing a button on the device which releases the needle to prick the surface of the finger and draws blood. This stage is followed by preparation of a meter strip that needs to be positioned near the sample of blood in order to extract a fraction of the blood sample. When considering this technique in more detail you will understand that there are two techniques adapted to the Lancet testing method: reflectance photometry and the electrochemical technique.

First, let’s consider reflectance photometry: the glucose from the blood sample makes contact with the catalysing enzyme embedded on the test strip. The enzyme oxidizes the glucose into a molecule that can then react with a dye to form a complex that can be measured. By shining an LED light onto this complex, the colour intensity of the dye complex can be determined. A dark dye complex is a clear indication of high glucose concentration. The main limitations to this method include:

  • Large volume of blood sample required (approximately 1–3µL)
  • Time-consuming when consider processing of a blood sample
  • Regular calibration of this technique is required to ensure the test strip delivers the most accurate result
  • Optical interface

The electrochemical method for testing blood glucose concentrations is driven by a current that is directly proportional to the level of blood glucose present in a blood sample (figure 1). The blood is drawn between two electrodes and the testing strip. Alike to the reflectance photometry method, glucose oxidation still occurs transforming the glucose molecule from beta-D-glucose to D-glucagon-1,5-lactone and then hydrolysed to D-gluconic acid. This reaction generates an electrical current that forces electrons to flow between the working electrodes and counter electrodes. With this method, an impregnated enzyme is present so that, when in contact with glucose, a current is generated.

Figure 1. Lancet system – electrochemical technique.

Based on this working principle, the more blood glucose present in a sample, the stronger the voltage generated. The electrical current generated is interpreted by a transducer which records the current in a 30 second timeframe and feeds a reading of blood glucose concentration in mM or mg/dL. Compared to the reflectance photometry technique, this technique is more sensitive as no more than 1µL of blood needs to be drawn as a sample to test for blood glucose concentration. The time taken for a reading to be generated is approximately five seconds for the electrochemical method, making this blood glucose sensor device more efficient.

Continuous Glucose Monitoring System

One of the main disadvantages to the finger-prick test is the inconvenience and heightened chance of contaminating a blood sample. There is the obvious issue of not being able to monitor night-time variation in the patient’s blood glucose levels and so there has been a big demand in the medical industry to introduce techniques that with have better control over blood glucose monitoring without this being a burden on the patient’s lifestyle. Introduction of a continuous glucose monitoring system, though slightly more costly, has allowed for better control of a patient’s blood sugar levels.

This technology is based on an implantable transmitter that detects the blood sugar levels in the body. This transmitter connects with a monitor carried by the patient. An alarm system is encoded into the monitor to regularly alert the patient to when there is fluctuation in blood sugar levels. The most commonly used CGMS devices include the Dexcom STS and the Navigator.

It is a common misconception that this method measures the blood sugar levels; however, what it actually does is estimates the blood glucose level by measuring the glucose concentration of the interstitial fluid between cells in a patient’s body. The sensor is a transmitter connected wirelessly to the portable monitor carried by the patient. Through radiofrequency, the transmitter will send a glucose current every few minutes to a pump that feeds the body with insulin. The sensor current is isolated, amplified, and then has to be interpreted via data acquisition followed by a reading of blood glucose content. The blood glucose reading will determine whether a threshold has been reached, and if so, an alarm is triggered. In the video below, Dr Steven Edelman, MD, discusses the need for continuous monitoring and how this technique will help optimize glucose control.

Advances in Blood Glucose Sensors

Developments in the field of blood glucose monitoring have aimed to try and make testing less invasive for the patient. Researchers from Tokyo University have been involved in the research and development of a blood glucose sensor that interacts with blood glucose and fluoresces. The process involves a hydrogel that measures the intensity of the light emitted as a reflection of glucose concentration in the blood (see video below).

References

  • Lakowicz, J.R., Geddes, C.D. (2006). Glucose Sensing. Topics in Fluorescence Spectroscopy. Volume 11. USA: Springer Science and Business Media, Inc.
  • Gault, V., McClenaghan, N. (2009). Understanding Bioanalytical Chemistry. Principles and Applications. Oxford, UK: John Wiley & Sons, Ltd.
  • McMahon, G. (2007). Analytical Instrumentation: A Guide to Laboratory, Portable and Miniaturized Instruments. West Sussex: John Wiley & Sons Ltd.
  • Zhang, X., Ju, H., Vang, J. (2008). Electrochemical Sensors, Biosensors and Their Biomedical Applications. New York: Elsevier Inc.
  • Munden, J., Foley, M. (2007). Diabetes Mellitus: A Guide to Patient Care. Ambler, Pennsylvania: Lippincott Williams & Wilkins.
  • Porth, C.M. (2011). Essentials of Pathophysiology: Concepts of Altered Health States. China: Wolters Kluwer Health. Lippincott Williams & Wilkins.
  • http://www.who.int/mediacentre/factsheets/fs312/en/index.html
  • Poretsky, L. (2010). Principles of Diabetes Mellitus. 2nd Edition. Springer Science and Business Media, LLC.
  • Baura, G. (2012). Medical Device Technologies: A Systems Based Overview Using Engineering Standards. Oxford, UK: Elsevier Inc.

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