- Biosensors - Biosensors are devices that use specific biochemical reactions (integrated recognition component) to detect chemical compounds using electrical, thermal or optical signals. Biosensors have applications in both clinical (in vivo – long-term implantable or short-term invasive sensors; in vitro – single-shot analysis or multi-analysis) and non-clinical (bioreactive monitoring, forensic science, pharmaceutical drug analysis) environments. In the case of amperometric sensors, current is measured that is produced by the reduction or oxidation of an electroactive species at a constant applied potential. The current is proportional to the concentration of the electroactive product. When we have enzyme-based sensors such as lactate or glucose, the analyte comes into contact with the enzyme and the enzyme catalytically processes the analyte to produce H2O2 as a by product. The response of the sensor results from the oxidation at the transducing element (e.g. Pt-Ir). The electrodes are functionalised with biological receptors also called recognition elements (REs) capable of selectively binding to targeted molecules or cell surface-receptors.
- Wearable sensors – One of the great challenges in health care as well as in sports science today is the need for continuous, non-invasive monitoring of biochemical changes in the human body in order to gain valuable information about the health of the person. There are several major challenges that need to be addressed such as sensor response using small analyte volumes, biofouling, biocompatibility and mechanical stability. Using electrochemical sensors as wearable sensors, tears, saliva, sweat and skin can be monitored. At the Hamlyn Centre we are looking into taking measurements of different components such as lactate and sodium in saliva and into the correlation between the mentioned parameters and the blood. Sweat also contains a lot of information about a person’s health status and that is why it is an excellent biofluid for non-invasive chemo-sensing. Sodium, lactate, ammonium, and calcium levels in sweat are indicators of electrolyte imbalance and cystic fibrosis (CF), physical stress, osteoporosis, and bone mineral loss. We are developing a sweat patch where several different electrochemical sensors are incorporated in one platform. The end goal is the development of small, robust, adaptable/flexible, barely noticeable, disposable/cheap and reliable wireless devices.
- Ion selective electrodes – The transduction process involves generation and subsequent measurement of electrical current (amperometric sensors) or potential (potentiometric sensors). Ion-selective electrodes (ISE) are electrochemical potentiometric sensors. Measurements are taken between an indicator electrode (the ISE) and a reference electrode under zero-current conditions while both are immersed in the analysed sample. ISEs determine the concentration of free ions. Currently, we are developing solid contact ion-selective sensors for the detection of different ion of interest such as pH, sodium and potassium.
- Microfluidics – One of our aims is developing an integrated microfluidic platform for health monitoring and diagnostic applications. Microfluidic systems can be designed to process measurements from small volumes with very high efficiency and speed, which is very important for the development of portable point-of-care (POC) medical diagnostic systems. A lab-on-a-chip (LOC) device integrates several functions (such as microchannels, filters, mixer, etc.) on a single chip of only millimetres to a few square centimetres in size. We have developed and incorporated several different electrochemical electrodes into the micro channel and continuous on body tests are ongoing.
We are working on development of small biosensors which will be used in healthcare. The sensors can monitor different fluids from the body. The information we receive can help us improve or even save lives. One element we detect is pH. So what is pH? Everything around us is made up of elements and atoms and molecules. For example in water (H2O) we have two hydrogen atoms and one oxygen atom bound together. If a water molecule breaks into parts we will have one OH molecule and one H element. If a liquid produces more OH (hydroxide) we call it a base, while if it produces more hydrogen we call it an acid. The pH of a solution can be measured using a scale ranging from 1-14. Acidic solutions have a low pH value between 1 and 7, while basic solution have a high pH in the range 7-14. A solution with a pH of 7 is actually referred to as "neutral", which means that these solutions are neither basic nor acidic. Liquids with pH values of 1 or below or 13 or above are are highly acidic/basic and are very dangerous.
We can also monitor the frequency-dependent electrical resistance (impedance) using sinusoidal current excitations of the tissue and also changes in the concentration of ions such as potassium (K+), sodium (Na+) and pH, which all change depending on local condition of the tissue (e.g. during ischemia). Tissue ischemia induces biochemical and physiological changes. Cells don’t produce energy to “feed” their membrane ion pumps; extracellular water goes into the cell; the cell grows and extracellular space is reduced. This changes low and high frequency tissue impedance and there is a build-up of hydrogen ions and, therefore, tissue pH decreases and the concentrations of potassium (K+), sodium (Na+) and other ions change.
The main challenge in developing wireless integrated biosensors is the development of integrated sensors and circuits on the same chip. For example, the micro-fluidic device we have developed can measure pH, Sodium (Na+) and lactate simultaneously. It responds reliably, sensitively, and rapidly to changes of these biomarkers during physical activity such as cycling. Sweat lactate is a function of the eccrine gland energy metabolism. Increased exercise intensity leads to increased production of sweat lactate. During intense physical activity, the aerobic metabolism is incapable of satisfying the energy demands. In place comes the anaerobic process wherein the stored glycogen is consumed to produce energy and lactate by muscle cells. This process is called “glycolysis” or “lactate acidosis” and involves increased lactate levels in blood. Blood plasma and sweat electrolyte concentrations are related: low plasma water concentration (dehydration) is linked to low sodium concentrations (hyponatremia). Dehydration can be seen as an increase in the sodium concentration in sweat during exercise. Real-time pH measurements in sweat may provide a non-invasive method of detecting the build-up of acid in muscle cells during exercise. In addition to the wearable sensing platform, we have designed implantable multi-modal sensing platforms using the above sensors combined with electrical bio-impedance sensors. These platforms are intended to detect tissue ischemia in the vicinity of surgical sites in the gastrointestinal tract. More regarding this is described in the implant section of the website.
What are we using it for?
We are using biosensors for a range of wearable and implantable applications. In the case of sweat sensing, perspiration can be used for analysis of physical performance in an individual without the need for invasive blood sampling. Sweat lactate is also a sensitive marker for pressure ischemia and tissue viability related to insufficient oxidative metabolism. Measuring ion concentrations directly in bodily fluids such as sweat gives information on both electrolyte volume and concentration in plasma. The information we can obtain with our platform is important not only for the general well-being of a person, but also for sport science applications, as athletes and coaches can use these to optimise their performance and training.