A resonant co-planar sensor at microwave frequencies for biomedical applications
Introduction
Human bodily fluids (e.g. blood, spinal fluid and urine) contain a complex combination of compounds including water, glucose, salts, lactate, etc. This represents a challenging combination of materials for analysis and leads to an extensive time lapse between sample acquisition and associated diagnosis.
Accurate real-time measurements of the glucose concentrations in aqueous solutions are essential for both fundamental studies and biomedical applications, in particular for diabetic patients to monitor their condition and to test the efficiency of the drugs [1]. Diabetes is a metabolic disorder, which results from insulin deficiency and hyperglycemia and is reflected by blood glucose concentrations higher or lower than the normal range of 80–120 mg/dl (4.4–6.6 mmol) [2]. Self-monitoring and point-of-care monitoring of blood glucose levels is one of the important technical advances in the management of diabetes in the last few decades. It has given patients and providers remarkable insights into the day-to-day variability of blood glucose concentrations.
Optical techniques [3], [4], [5] are commonly employed for biomedical applications to assist when time is a critical factor. However, these methods can be bulky and expensive to implement and often there is still the requirement for an experienced operator to take time to consider the meaning of results obtained. The current devices on the market all require a sample of blood from the patient and then quantification of glycated haemoglobin (HbA1c). The chemical reaction between glucose and haemoglobin leads to an average blood sugar level and does not show any spikes in blood sugar level. There are also chemical systems, which directly measure the quantity of glucose, but these also require a sample of blood. Furthermore, the majority of methods for detecting glucose levels in the blood rely on in vivo methods utilising complex chemical processes [6], [7] and/or sophisticated equipment, for example, impedance spectroscopy, mid-infrared spectroscopy and optical coherence tomography [8], [9], [10], [11]. Notably, the spectroscopy methods utilise the interaction of the electromagnetic waves at various frequencies with a substance under test and these interactions are of three kinds: the absorption, the emission and the scattering [2]. Glucose biosensors can also be based on electrochemical principle of detection that employ enzymes for molecular recognition, as well as the optical, piezoelectrical, thermal, and mechanical principles [12], [13], [14], [15]. An electromagnetic coupling approach for indirect measurement of glucose concentration in sodium chloride and Ringer–lactate solutions, which have similar to blood properties, was employed at low frequency of 40 kHz [16]. The sensor was able to detect the effect of glucose variations over a wide range of concentrations (∼78–5000 mg/dl), with a sensitivity of ∼0.22 mV/(mg/dl). However, special caution should be taken when exploiting medical devices emitting signals at low frequencies, so as not to interfere with natural biological signals and other hospital diagnostic equipment, such as ECG, EEG, EMG [17].
Obviously, the current methods are inappropriate during a surgical procedure as time is often critical from the perspectives of patient well-being and hospital efficiency. Thus, there is a great desire for tools, which can be used at the point of care to assist medical practitioners in rapidly diagnosing patients. Previous work by the authors [18], [19], [20] with surgeons at local National Health Service (NHS) hospitals has indicated that there is a need for simple but rapid sensing techniques, which can be used during surgical procedures to detect parameters in a variety of patient bodily fluids. In the ideal case, surgeons would like tools, which are either (1) completely non-invasive or (2) minimally invasive. The nature of surgery however often means that invasive procedures are inevitable, so work by the authors has focused on tools, namely electromagnetic sensors, which can be on hand for real-time measurement of bodily fluids as they are extracted during surgical procedures. Future work to develop this sensor technology further will consider the use of the technique for completely non-invasive transcutaneous measurement, which will lead to the technology being used as a more general purpose medical tool.
This paper discusses a novel co-planar resonant structure, which is designed to have an area highly sensitive to changing analyte materials. The device has successfully been patented [21] recently, and improves on previous work, which concentrates on the use of highly sensitive but bulky cavity resonators [18], [19], [20]. While this work presents a proof of concept work, the eventual aim is to encapsulate this in a small hand-held or desktop diagnostic tool for rapid in situ analysis. This paper reports on the design of the sensor and shows laboratory based testing of this sensor's ability to distinguish between the solutions with varying glucose concentration levels. The paper concludes by alluding to future work to be conducted in this area using the proposed device.
Section snippets
Microwave analysis
Microwave sensing is a developing technology, which has shown vast potential in a number of industrial and medical areas [15], [19], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31]. This is a result of the technique being robust, requiring low power and having good depth of penetration in respect of analyte materials. Also, of particular interest in medical applications is the non-ionising nature of microwave radiation; the technique used in this paper has low power output at around 1
Co-planar sensor
The sensor used in this work is based upon a co-planar design. This design was chosen particularly since such devices are known to be resistant to losses and interferences induced from external sources, and thus offer a great deal of control in relation to how the sensor responds to analytes [34]. In particular, the sensor is constructed to ensure that only a small area is sensitive to dielectric change, which enhances significantly its robustness for potential biomedical use. The design of the
Experimental procedure
The sensing system is comprised of a number of components in order to tune the sensing device and minimise the impact of external factors, particularly temperature, on the reliability of the sensing system. The components are (1) the co-planar sensor, (2) tuning capability, (3) analyte temperature measurement, (4) a pump/mixing system and (5) adaptive measurement software. Fig. 4 shows the actual system as configured for experimental purposes.
The sensor was designed for sensing fluid
Results and discussion
The results of the experimental work with the co-planar sensor device are shown in Fig. 5. A significant change in signal amplitude is experienced with changing glucose concentration. As the glucose concentration increases, the amplitude of the S21 signal at approximately 3637 MHz increases. This trend is further highlighted in Fig. 6, and tabulated in Table 1. The response exhibited is assumed to be a direct result of permittivity change related to the changing concentration of glucose in
Conclusion
This paper reports on the implementation of a novel co-planar microwave sensor suitable for application in biomedical situations where the sensor could be placed in-line with tubes used to pump analyte materials of interest, namely bodily fluids for real-time analysis of the patient's condition near bedside in hospital settings. The work presented here shows that the sensor is capable of distinguishing the solutions with various glucose concentrations levels at near to physiological range by
Dr. Alex Mason graduated from the University of Liverpool, UK, with a first class honours degree in Computer and Multimedia Systems, after which he went on to complete a PhD in Wireless Sensor Networks and their Industrial Applications at Liverpool John Moores University, UK. Upon completing his PhD in 2008, he concentrated for 2 years solely on research, working on aspects of non-invasive and non-destructive sensing for the healthcare, automotive and defense sectors. Since 2010, Dr. Mason has
References (37)
- et al.
Ultrasound and transdermal drug delivery
Drug Discovery Today
(2004) - et al.
Fiber grating sensors in medicine: current and emerging applications
Sensors and Actuators A: Physical
(2011) - et al.
Monolithically integrated semiconductor fluorescence sensor for microfluidic applications
Sensors and Actuators B: Chemical
(2005) - et al.
A novel approach to non-invasive glucose measurement by mid-infrared spectroscopy: the combination of quantum cascade lasers (QCL) and photoacoustic detection
Vibrational Spectroscopy
(2005) - et al.
First human experiments with a novel non-invasive, non-optical continuous glucose monitoring system
Biosensors and Bioelectronics
(2003) - et al.
A surface-tension-driven fluidic network for precise enzyme batch-dispensing and glucose detection
Sensors and Actuators A: Physical
(2004) - et al.
Microwave sensors: a new sensing principle. Application to humidity detection
Sensors and Actuators B: Chemical
(2000) - et al.
Microwave dielectric spectroscopy for the determination of pork meat quality
Food Research International
(2010) - et al.
Application of microwaves dielectric spectroscopy for controlling pork meat (Longissimus dorsi) salting process
Journal of Food Engineering
(2010) - et al.
Quality and anti-adulteration control of vegetable oils through microwave dielectric spectroscopy
Measurement: Journal of the International Measurement Confederation
(2010)
Evanescent Microwave Probe Study on Dielectric Properties of Materials
Microwave sensing for an objective evaluation of meat ageing
Journal of Food Engineering
Meat quality assessment using biophysical methods related to meat structure
Meat Science
Resonant microwave sensors for instantaneous determination of moisture in foodstuffs
Food Control
Temperature characterization of dielectric–resonator materials
Journal of the European Ceramic Society
Non-invasive in vitro sensing of d-glucose in pig blood
Medical Engineering and Physics
An implantable triple-function device for local drug delivery, cerebrospinal fluid removal and EEG recording in the cranial subdural/subarachnoid space of primates
Journal of Neuroscience Methods
Glucose monitoring using electromagnetic waves and microsensor with interdigitated electrodes
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Dr. Alex Mason graduated from the University of Liverpool, UK, with a first class honours degree in Computer and Multimedia Systems, after which he went on to complete a PhD in Wireless Sensor Networks and their Industrial Applications at Liverpool John Moores University, UK. Upon completing his PhD in 2008, he concentrated for 2 years solely on research, working on aspects of non-invasive and non-destructive sensing for the healthcare, automotive and defense sectors. Since 2010, Dr. Mason has held a position as a Senior Lecturer within the School of Built Environment and has continued research in many areas, developing an interest in Structural Health Monitoring and Building Performance Analysis, thus utilising his computing and electronics background and applying it to issues relevant to the Built Environment. In addition to teaching Materials, Energy Management and Environmental Studies, he is responsible for a number of PhD students who are working on a wide variety of topical research projects.
Dr. Olga Korostynska has a BEng (1998) and MSc (2000) in Biomedical Engineering from National Technical University of Ukraine (KPI) and PhD (2003) in Electronics and Computer Engineering from the University of Limerick, Ireland. Currently she is EU Research Fellow in Liverpool John Moores University, UK developing microwave sensors for real-time water quality monitoring. Before that she was an engineer in the National Telecommunication Institute in Ukraine; then a Postdoctoral Researcher in the University of Limerick, working on a number of projects, including those funded by IRCSET, EI and EU FP7 and also was a Lecturer in Physics in Dublin Institute of Technology, Ireland. She has published a book, 3 book chapters and over 170 scientific papers in peer-reviewed journals and conference proceedings.
Dr. Montserrat Ortoneda Pedrola has a BSc in Biological Sciences from the University of Girona (Spain), an MSc in Applied Microbiology and a PhD on the topic of in vitro and in vivo antifungal susceptibility of opportunistic fungi, which she completed in 2003 at the University Rovira i Virgili in Reus (Spain). After that she has worked on a number of research projects in Ireland and the UK, including several funded by EU FP6 and EU FP7. These research projects range from the study of fungal genomics to microwave applications for the food industry and for the production of bioethanol and biogas.
Dr. Andy Shaw graduated from Liverpool University with a BEng Hons. in Electrical and Electronic engineering, MSc (Eng) in Materials Science and a PhD titled “the realisation of an industrial free electron laser”, completed in 1995. He worked as a postdoctoral researcher at the university for 8 years working on industrial microwave applications for both material processing and sensor technologies. In 2003 he became a lecturer at Liverpool University within the electrical engineering department whilst researching the use of RF communications for sub-sea communications as part of an MoD funded project and later as an EU funded project. In 2005 he joined Liverpool John Moores University, at first with the General Engineering Research Institute as a Senior Lecturer and then as head of the electrical engineering department within the school of engineering. He is now a Reader in Environmental and sustainable technologies within the BEST research institute as part of the RF and Microwave research group.
Prof. Ahmed Al-Shamma’a is the director of the Built Environment and Sustainable Technologies (BEST) Research Institute at the School of Built Environment at Liverpool John Moores University, UK. He has extensive research interests that cover a wide range of applied industrial sciences, including advance microwave technologies for renewable energies from waste including biodiesel, bioethanol and biobutanol, waste recycling, environmental and sustainable agendas. He has also extensive experience in the design and construction of wireless sensors for the construction, healthcare, automotive and aerospace industries as well as bespoke software solutions to monitor real time energy levels in various industrial applications and near zero carbon initiatives for the energy sectors. Prof. Al-Shamma’a is one of the EU scientific officers on Renewable Energies and has obtained various supported applied research projects funded nationally and internationally by the EU, UK and USA Ministry of Defense, Carbon Trust, Technology Strategy Board and direct funding from industry. He has published over 300 peer reviewed scientific publications, 15 patents and coordinated over 30 research projects.