Since its origins in the 1960s, the biosensors field has grown to encompass a wide range of sensors, from enzyme-based to immunosensors to thermal biosensors. Along with this, a diverse set of applications have flourished, with biosensors finding roles in food safety, medical diagnostics, and environmental analysis to name just a few.
“Biosensors, as classically defined, incorporate biological or biologically derived sensing elements that harness the exquisite specificity and sensitivity of living systems in conjunction with electronic transducers and processors, to either provide data or to directly actuate an appropriate response,” states Professor Anthony Turner, Head of the Biosensors & Bioelectronics Centre, Linköping University.
A name synonymous with the field, and perhaps most well-known for fuelling the development of home blood glucose monitoring technology, Professor Turner has made several important contributions to the progress of biosensors. Here he tells us about the evolution of biosensors and where they may be headed.
Glucose biosensors lead the way
“The most powerful example [of biosensors] to date, has been the evolution of the artificial or ‘bionic’ pancreas,” he tells us. Since enzyme electrodes were first launched for use by diabetics in their home in 1987, glucose biosensors have seen immense success, becoming wearable devices in 2005, and more recently forming the world’s first closed loop insulin delivery system. Market research suggests that glucose monitoring will hold the largest share of the biosensors market for point-of-care applications by 2022.
“While glucose biosensors have been the highest profile success so far, they are far from the only example and biosensors have been widely commercialised for use in medicine, process monitoring, food quality control, environmental monitoring, defence and law enforcement,” adds Professor Turner.
This versatility looks set to grow, with the emergence of new areas “where biosensors are now recognised to have a potential pivotal role such as in robotic surgery, tissue engineering and the production of biologics.”
Types of Biosensors
Electrochemical biosensors react with an analyte of interest to product an electrical signal proportional to the analyte concentration.
Potentiometric – measures variations in open circuit potential.
Amperometric – measures currents due to the reduction or oxidation of electroactive species.
These biosensors are affinity ligand-based biosensor solid-state devices in which the immunochemical reaction is coupled to a transducer.
Magnetic biosensors measure changes in magnetic properties or magnetically induced effects.
Several biological reactions are associated with the release of heat. Thermometric biosensors measure the temperature change of the solution containing the analyte caused by these enzymatic reactions.
Also referred to as piezoelectric biosensors, these sensors measure the change in the physical properties of an acoustic wave.
The most common type of biosensor, optical biosensors can be label-free or label-based. These biosensors measure the interaction of an optical field with a biorecognition sensing element.
Colorimetric - measures changes in light adsorption
Photometric - measures light intensity
Moving towards personalized health
Despite the potential for the emergence of new biosensing applications, there are likely to be a few hurdles along the way. When considering some of the challenges that wearable sensors have faced, Professor Turner explains that “arguably, the major bottleneck at the current time is the availability of reliable sensors that directly measure key biochemical parameters. Most current devices have ingeniously exploited physical sensors that were readily available and used these to infer relevant secondary information. Chemical sensors and biosensors present greater challenges in sample acquisition, but the direct molecular information that they can deliver is essential to higher level algorithms for personalized management of health.”
Also of importance is the need to reduce the cost, size and reagent demands of sensing systems, to meet the growing need for easy-to-use point-of-care systems. Merging microfluidic technologies with biosensors is a promising option for achieving some of these goals, offering advantages such as increased portability and sensitivity.
Integrating 3D printed microfluidics
Professor Turner has recently been involved in the development of a disposable 3D-printed microfluidic chip for continuous-flow monitoring of adenosine triphosphate (ATP) bioluminescence. Costing just a few dollars, the chip can measure very low levels of ATP concentrations, with good stability and reproducibility. “The combination of SiPM with 3D-printed microfluidic chips resulted in a compact, sensitive and low-cost bioluminescence detection system with wide-ranging applications in chemical or biological analysis and clinical diagnostics,” he tells us.
As well as detection limits comparable to much larger and more expensive commercial systems and almost the same sensitivity across the range of ATP concentrations analysed, the chip offers several advantages. “The system provides quantitative output signals, that do not require post-elaboration of images. It simplifies considerably the signal analysis with respect to traditional systems, which provide as output a number that is the result of a software based image analysis.”
“The ability of the system to perform continuous flow monitoring of bioluminescence reactions was demonstrated, opening the possibility to fabricate compact, sensitive and potentially low-cost bioluminescence detection systems with wide-ranging applications in chemical and biological analysis and clinical diagnostics. One of the most common uses of bioluminescence is for microbial detection and this instrument offers high sensitivity coupled with extremely low cost,” he adds.
A bright future
Despite previous doubts, the biosensors field looks set to see continued growth and success. “A few years ago, one may have been forgiven for considering the area as a mature field with diminishing prospects for innovation,” notes Professor Turner. “However, the recent convergence of thinking around the escalating cost of delivering healthcare, the opportunities offered by mobile heath and the demand for more personalized medicine has reignited enthusiasm for novel interdisciplinary solutions based on biosensors.”
He goes on to say that “with the demand now so clearly in focus, the challenge is to harness the tens of thousands of research reports to hone products that can meet these needs.”
“The future importance of biosensors in clinical diagnostics, health management and research in the life sciences is clear and we need to bring engineers, clinicians and entrepreneurs together to implement effective ways forward.”