Biosensors and Invasive Monitoring in Clinical Applications

It is accepted that monitoring ions and metabolites continuously provides further understanding of the physiology and pathology of the human body and improves patients’ diagnosis, treatment and length of hospital stay. Although there have been substantial advances over the past decade in terms of miniaturising clinical devices, monitoring chemicals in medical practice still relies on large pieces of equipment. These are generally located in central laboratories that require specialised technicians and offer delayed diagnosis. Typically blood or other body fluids are sampled from patients at regular intervals, disturbing patient recovery and only providing discrete measurements. These not only have a higher probability of associated human error, but fail to reveal any fluctuating pattern occurring between measurements. At most, the physician obtains information of the patient’s physiology every 2 h, at which transient events that might be relevant for the diagnosis are missed.

The fast progress in medicinal therapies, clinical instrumentation and drugs development have contributed paradoxically to higher demand for patient monitoring in healthcare systems. The higher increase in chronic patients and an aging population has led to the use of intensive and invasive methods in general wards areas, which otherwise were reserved for patients in high level of care environments, such as intensive care units.

Biosensors are defined as analytical devices that combine a biological component (biorecognition) with a physicochemical detector (transducer) capable of converting the analyte into a quantifiable signal. Biosensors for in vivo monitoring have been extensively studied and the literature contains a vast amount of papers describing biosensor’s features, requirements and applications.

Two main approaches have been followed to improve sensors biocompatibility: elimination of biological responses by means of coatings and surface modifications, and substance releasing sensors that increase this biological response further.

Implantable biosensors have been recognised for their ability to continuously monitor with minimal patient intervention compared with common procedure in clinical environments, such as introduction of catheters and surgical drains.

The most commonly used invasive methods in clinical practice today are dialysis and central catheters to deliver medication and continuously monitor patient’s circulatory status.

Microdialysis (MD) is a well-established extracting technique. Its beginnings go back to 1966 when Bito et al. inserted a sterile dialysis sac into a dog’s cortex.

Materials such as cellulose, cuprophane and hospal were extensively used to fabricate MD membranes, since chemical composition was considered to play an important role in the in vitro recovery. Commercially available clinical probes are now being fabricated with supported polycrystalline, polyethylene terephthalate (PET) membranes with specific weight cut-off, typically of 20 kDa and 1 MDa in case of macromolecules studies.

During conventional microdialysis, dialysate samples are periodically analysed offline by lab bench instruments. This approach is inadequate for some applications, especially those that require high temporal resolution and rapid data collection.

Microdialysis advancement from research tool to clinical device occurred during the early 1990s when CMA Microdialysis (Solna, Sweden) marketed the microdialysis catheter and the bedside dialysate analyser. Since then, microdialysis has been recognised as an important technique for point of care and home care monitoring. Microdialysis advantages over other point of care devices are manifested through the continuous sampling and the absence of intensive human intervention.

With the advance in nanotechnology and the use of materials such as silicon and CNT with excellent mechanical, optical and electrochemical properties, the factor that prevents the widespread use of implantable devices for clinical monitoring is their low reliability.

Research in implantable devices is progressing at a fast rate. Glucose implantable devices are at the forefront of this technology due to the high demand for diabetes management. Diabetes research news, blogs and website links present some of the latest commercialised or in process of being commercialised technology.