Sensors in diagnostics and monitoring

The earliest optical sensor in medicine was the naked eye [1], which is still in use by physicians as well as in the home. “You are looking pale” or “This looks red – it might be an inflammation” could be an important part of a diagnosis. It also demonstrates that spectral characteristics of optical sensing give rise to diagnostic observations. Another advantage of light is that it is a non-contact and aseptic measuring method. It is therefore not surprising that optical sensors – although not always recognizable – are often incorporated in many medical devices. The importance of sensors, not only optical ones, is obvious in many respects [2–6]. This year’s COMPAMED Spring Convention focuses on photonics applications for diagnostic and therapeutic methods and biomedical optosensors [7]. In the last year topics were point-of-care sensors and mobile or wearable monitoring. The latter group is currently very “in”, especially in combination with smartphones and apps [8–12]. It forms the most popular aspect of medical diagnostics and monitoring despite being the subject of more critical discussion amongst medical professionals [13].

This special issue on sensors of Photonics & Lasers in Medicine gives an overview of a wide range of new developments in photonic techniques in the fields of diagnostics and monitoring. It starts with plasmonic and Raman methods, which are used in diagnostics of tumors and infectious diseases, and autofluorescence measurements, which are applicable in the control of the cleaning status of medical instruments. Further articles have a special focus on spectroscopic reflectance and transmittance measurements, which are already widely used. Here two applications are presented for skin and blood diagnostics, respectively. For example, measurements made on skin can help to classify the skin color whereas another skin sensor allows the monitoring of chronic heart insufficiency by measuring the water concentration. The spectroscopic properties of blood facilitate the monitoring of the oxygen supply of the patient in an extracorporeal blood circuit and enable a quality check for red blood cell aging in blood bags.

The number of applications in the life sciences using plasmonic techniques is steadily increasing [14]. The review article by Wong et al. [15] gives an overview of in-vitro diagnostics of infectious diseases by surface plasmon resonance (SPR) as a point-of-care technology. The authors also report on their own work in multiplex diagnostics with SPR. As an example of a second plasmonic technique, the possibilities that surface-enhanced Raman spectroscopy (SERS) offers are described for tumor diagnostics in personalized medicine. Raman spectroscopy is used for visualizing biomarkers by so-called “reporter molecules” with specific fingerprint-like Raman spectra. This allows the detection of many biomarkers in parallel (multiplexing) and helps to illustrate the advantage of Raman spectroscopy as compared to fluorescence labeling.

Non-enhanced Raman spectroscopy has also become increasingly more significant as is shown in the review article by Schleusener et al. [16]. This paper evaluates the diagnostic accuracy of the in-vivo discrimination of cancerous and normal skin with data taken from clinical studies. It discusses different ways of overcoming the limitations of low signals and large fluorescence backgrounds. Further possibilities of imaging Raman spectroscopy and its combination with other diagnostic methods are briefly summarized.

The validation of procedures, not only for cleaning medical equipment but also for use in the pharmaceutical/food industry, is the focus of an original article by Cappius et al. [17]. They address the very important unsolved problem of contamination of surfaces with bacteria or organic material after cleaning or sterilization. Ultraviolet light-excited fluorescence detection is used in a handheld device for rapid measurement of contamination. On non-fluorescent substrates, it is possible to identify even minute amounts of residual contaminants. The results are comparable to established methods with the added advantage that here the results are available within seconds.

Safe application of laser radiation or other light-based dermatological procedures is supported by use of a novel skin tone meter. A study was performed by Ash et al. [18] using this sensor on a large group of volunteers. In this preliminary research report, measurements made with the skin tone meter were correlated with the Fitzpatrick scale derived from a color chart. The authors discuss the use of Fitzpatrick skin typing for light-based therapies or aesthetic procedures.

In another preliminary research report, Netz et al. [19] investigated the monitoring of a patient’s oxygen supply during cardiopulmonary bypass using an in-line sensor. A novel aspect of this sensor is the bloodless calibration procedure by optical standards, which simplifies production. Furthermore, when using this sensor no initial adaptation to the individual patient’s blood is required by invasive measurements with a blood gas analyzer.

The same group of Netz et al. [20] presents a short communication about the quality control of red blood cell concentrates. One indicator of blood quality in a blood bag is the increase in the free hemolysis concentration. The authors describe a procedure for the optical measurement of free hemoglobin in the supernatant of blood, measured non-invasively in the tubing connected to the blood bag after a period of gravitational sedimentation.

Schütz et al. [21] demonstrate in a short communication the capability of a near-infrared reflectance sensor for the measurement of water concentration in skin. The need to monitor the status of patients suffering from chronic heart insufficiency when at home, forms the basis for the development of this sensor. The goal is to reduce the risk of decompensation for affected patients by giving an early warning signal when there is a significant increase of water in the skin.

This special issue on sensors shows how diverse the application field is for often quite simple sensors. However, the robustness of sensor readings under individual conditions with individual patients is a crucial point in sensor development and often a limiting factor for the accuracy. The articles presented here show that it is indeed possible to overcome these obstacles.

In this, the 30th year since the founding of Laser- und Medizin-Technologie GmbH, Berlin (LMTB), it is a special honor for us to be the guest editors for this special issue. Sensor development and technology transfer is at the core of our research at the Department of Biomedical Optics at the LMTB. We would be very pleased to welcome you at LASER World of PHOTONICS Congress and Exhibition, which is be held from 22nd to 25th June 2015 at the International Congress Centre Munich, in order to celebrate our anniversary with you while having an interesting discussion about sensors.

Please note that the Deutsche Gesellschaft für Lasermedizin (DGLM) e.V. is organizing an application panel on the topic “Laser-advanced new methods for diagnostics and therapeutics” at the exhibition in Munich [22]. So please also make a note of this date: June 22, 2015! The General Meeting of the DGLM e.V. will also be held on 22nd June 2015. Official invitations will be sent out later in the year, but please do not hesitate to visit the new DGLM’s website (www.dglm.org) for updates and further details.

We are looking forward to your active participation and to interesting discussions.