- Wearable biosensors: revolutionising personalised healthcare
- Enzymes and the demand for real-time physiological information
- Features of a model enzyme for biosensor development
- A challenge to consistent reproducibility: overcoming instability
- A challenge to reproducibility: overcoming interference
A paradigm shift towards healthcare that is personalised and autonomous has popularised wearable devices and biosensors as the interest in health, wellbeing, fitness, and disease prevention continues to grow. From self-testing to lab-on-a-chip and wearable devices, biosensors continue to expand the scope of diagnostics as it increasingly moves from the lab to the home. Among them, enzyme-based biosensors have shown immense potential for applications in healthcare. With this, comes unique challenges for the R&D scientist – from enzyme stability and specificity to interference, matrix effects, and biocompatibility – challenges that can be tackled with high-quality biosensor materials for high performance.
Wearable Biosensors: Revolutionising Personalised Healthcare
Wearable biosensors have become widespread in healthcare and biomedical monitoring systems, empowering ongoing, non-invasive measurement of critical biomarkers for continuous monitoring of physiological functions in real-time. Biosensors’ growing popularity owes much to their simplicity, improved sensitivity, ability to perform multiplex analysis, and capability to be integrated with different functions in the same chip.
Yet recently, the most lucrative of their applications has been outside medical care – with broad and far-reaching applications in healthcare monitoring and sports analytics. As obesity remains a significant public health concern, the issue has become a pertinent one in the collective public consciousness. Common societal obsessions, dieting, and exercise, have prompted widespread interest in wearable biosensors – from measuring cholesterol as an indicator of cardiovascular health, through to glucose and ketones for monitoring weight loss and diabetes risk management. Meanwhile, athletes and exercise enthusiasts are increasingly turning to creatinine- and lactate-measuring wearables to determine training zones.
With demand increasing, the market for biosensors has expanded – and with it, the need for raw material components that deliver sensitivity, selectivity and reproducibility. What characteristics should R&D scientists consider when choosing the enzyme that sits at the heart of their biosensor?
Recent advances in ultrasensitive transducer technology, interchangeable biorecognition elements, miniaturisation, integration, and automation of technology have improved biosensor design – but the quality of the biological sensing element, the enzyme immobilised to the electrode surface, is a crucial variable to consider.
In most biosensor studies, glucose oxidase (GOx) or glucose dehydrogenase have been used by diabetics to monitor glucose levels. While the first glucose biosensors were based on GOx, more recently,FAD (flavin adenine dinucleotide)-dependent glucose dehydrogenases have been employed in glucose sensors offering the advantage of oxygen independence. However, a drawback is that the cofactors are relatively expensive. But as the demand for technologies that enable accurate monitoring of several biomarkers to maximise health and performance has grown, enzyme use has expanded.
While the assessment of ketones in dietary adjustment for diabetic patients has long been a core reason for ketone body monitoring, an intense interest in these carbonyl compounds has since been stoked, with growing demand by consumers to gauge their level of ketosis. Understanding the level of ketosis can reveal more than impaired glucose metabolism, supporting performance enhancement for endurance athletes, and aiding weight loss efforts by means of the popularised ketogenic diet. With 3-hydroxybutyrate dehydrogenase, the enzymatic determination of ketone bodies can be successfully achieved within wearable biosensors – providing a greater degree of accuracy relative to urine strips or blood tests.
Cholesterol oxidase and cholesterol esterase have been employed in cholesterol biosensors that can help with the early assessment and monitoring of patients with cardiovascular disease (CVD). In the realm of fitness, monitoring serum lactate is a widely accepted parameter in performance diagnostics. The level of lactate in blood during exercise is used as an indicator for the athlete’s training status and fitness – facilitating the development and delivery of optimal and personal training regimens.
Learn more about Lactate Oxidase for the development of biosensors for fitness-related monitoring and cardiac issues or pulmonary oedema.
Features of a model enzyme for biosensor development
Although becoming increasingly diverse, encompassing hydrogenases to oxidases and more, there are several challenges that enzymes pose in biosensor applications. What are these potential obstacles and what features should R&D scientists be looking for in their search for the appropriate enzyme for biosensor development and beyond?
The selectivity of enzymes is the basis of biosensors; a high specific activity is necessary for biosensor sensitivity and specificity. Aside from this, stability and reproducibility are the foundations of an effective biosensor.
Click here to learn about SEKISUI Diagnostic’s range of biosensor materials – from glucose oxidase and dehydrogenase, to lactate oxidase, 3-hydroxybutyrate dehydrogenase and more.
A Challenge to Consistent Reproducibility: Overcoming Instability
Shelf-life and operational stability are two forms of stability that are relevant in biosensor development. Storage conditions of the enzyme after manufacture but before use can affect the retention of activity (shelf-life), while the maintenance of activity during use underpins operational stability and impacts on the operating lifetime and reproducibility of a biosensor. Stability as reflected by the consistency of enzyme activity must be considered.
Catalytic activity of enzymes is strongly dependent on pH and temperature – and the pH of the test sample is an important consideration. So, when enzymes demonstrate good reactivity under physiological conditions, biosensor responses are optimised and reproducible. By selecting enzymes that display a wide range of pH and temperature stability, consistent high activity is achieved for reproducible biosensor performance. Of course, maintaining the oxidative state of the enzyme needs to be considered for continuous blood glucose monitoring – compatibility with redox cofactors must be considered to allow for amperometric measurement. Crucially, when these factors are accounted for, accuracy can be maintained.
Alongside pH and thermal stability, the enzyme format offers a means to consistency. Freeze dried formats are more stable than solubilised solutions, so selecting freeze-dried formats offers longer shelf life. Aside from the properties of your selected enzyme, a boost to stability can also be achieved during the biosensor development process itself – immobilisation for example improves enzyme stability and allows for continuous use.
A Challenge to Reproducibility: Overcoming Interference
One of the most challenging disadvantages of enzyme-based biosensor detection is signal reduction from interference from macromolecules present in the sample matrix. Contaminants from the enzyme preparation itself can also pose a problem. With high purification, this can be minimised and the selection of highly-purified, additive-free enzymes with low-level contaminants can minimise the risk of interference – as can batch-to-batch consistency that ensures reproducibility and good recovery of enzyme activity.
Enzyme-Powered Wearables: The Next Level in Biosensor Technology
Leaps and bounds made in the field of miniaturisation and materials science – from microfluidic chip integrated electro-sensors for multiple detection, multiplexed sensing platforms, to improved biofluid sampling and advances in flexible materials – have improved the potential for wearable biosensors with real-world applications.
These advances have greatly enhanced the reliability of wearable biosensors, their analyte monitoring capabilities, and wearability. But with the reproducibility, sensitivity, and selectivity of enzymes – the heart of biosensors – the potential to produce innovative wearable biosensing devices has been realised.