Günter Gauglitz

Point-of-care applications are gaining increasing interest in clinical diagnostics and emergency applications. Biosensors are used to monitor the biomolecular interaction process between a disease biomarker and a recognition element such as a reagent. Essential are the quality and selectivity of the recognition elements and assay types used to improve sensitivity and to avoid nonspecific interactions. In addition, quality measures are influenced by the detection principle and the evaluation strategies. For these reasons, this review provides a survey and validation of recognition elements, assays, and various types of detection methods for point-of-care testing (POCT) platforms. Common applications of clinical parameters are discussed and considered. In this ever-changing field, a snapshot of current applications is needed. We provide such a snapshot by way of a table including literature citations and also discuss these applications in more detail throughout.

Cadmium is a toxic heavy metal ubiquitously present in the environment and subsequently in the human diet. Cadmium has been proposed to disrupt the endocrine system, targeting in particular the estrogen signaling pathway already at environmentally relevant concentrations. Thus far, the reports on the binding affinity of cadmium towards human estrogen receptor alpha (hERα) have been contradicting, as have been the reports on the in vivo estrogenicity of cadmium. Hence, the mode of interaction between cadmium and the receptor remains unclear. Here, we investigated the interaction between cadmium and hERα on a molecular level by applying a novel, label-free biosensor technique based on reflectometric interference spectroscopy (RIfS). We studied the binding of cadmium to hERα, and the conformation of the receptor following cadmium treatment. Our data reveals that cadmium interacts with the ligand binding domain (LBD) of the ERα and affects the conformation of the receptor. However, the binding event, as well as the induced conformation change, greatly depends on the accessibility of the cysteine tails in the LBD. As the LBD cysteine residues have been reported as targets of post-translational modifications in vivo, we present a hypothesis according to which different cellular pools of ERα respond to cadmium differently. Our proposed theory could help to explain some of the previously contradicting results regarding estrogen-like activity of cadmium.

In biomolecular interaction analysis, direct optical detection is attracting increasing interest in academia and industry. Therefore, a previous review has been updated. Optical principles are given in brief, focussing especially on modern and frequently used techniques. Commercialized methods are listed with some specific applications. In addition, some of the many applications found in the literature are listed; others which have been reviewed elsewhere are cited. Overall, the growing interest in direct optical monitoring of biomolecular interaction is demonstrated and future trends are outlined. Because optical methods is a very wide field, the paper concentrates on the currently most common methods, microrefractometry and microreflectivity.

Patientennahe Diagnostik gewinnt in den letzten Jahren zunehmend Bedeutung in der Notfallmedizin, bei der Intensivmedizin und auch bei der Patientenselbstkontrolle. Neben Anforderungen an für solche Aufgaben geeignete Geräte und Informationen zu den Aufgaben von POCT sind Beipiele für Anwendungen dargestellt. Insbesondere auf optische Methoden wie Totale Interne Fluoreszenzreflexion und Reflektometrische Interferenzspektroskopie wird als Detektionsprinzipien eingegangen. Die Grundlagen von Biosensoren und von Bestimmungsverfahren für die Nachweise von klinisch relevanten Krankheitsmarkern werden gegeben.

A large number of methods using direct detection with label-free systems are known. They compete with the well-introduced fluorescence-based methods. However, recent applications take advantage of label-free detection in protein–protein interactions, high-throughput screening, and high-content screening. These new applications require new strategies for biosensors. It becomes more and more obvious that neither the transduction principle nor the recognition elements for the biomolecular interaction process alone determine the quality of the biosensor. Accordingly, the biosensor system has to be considered as a whole. This chapter focuses on strategies to optimize the detection platform and the biomolecular recognition layer. It concentrates on direct detection methods, with special focus on optical transduction. Since even this restriction still leaves a large number of methods, only microrefractometric and microreflectometric methods using planar transducers have been selected for a detailed description and a listing of applications. However, since many review articles on the physical principles exist, the description is kept short. Other methods are just mentioned in brief and for comparison. The outlook and the applications demonstrate the future perspectives of direct optical detection in bioanalytics.