Biosensors have proven to be indispensable in numerous vital areas. For example, detecting the presence and concentration of specific biomarkers requires sensitive and reliable measurement methods. Rapid developments in the field of nanotechnology lead to nanomaterials with new properties and associated innovative applications. Thus, nanotechnology has a far-reaching impact on biosensors' development, e.g., delivery of biosensing devices with greater sensitivity, shorter response times, and precise but cost-effective sensor platforms. In addition, nanobiosensors hold high potential for integration and miniaturization and can operate directly at the point of care - serving as a bridge between diagnostics and routine tests. This work focuses on applying nanostructured biosensors for the sensitive and label-free detection of analytes. A distinct aim is the continuous monitoring of biomarkers with compact read-out systems to provide direct, valuable feedback in real-time. The first step in achieving this goal is the adequate functionalization of nanostructured sensor surfaces with suitable receptors to detect analytes of interest. Due to their thermal and chemical stability with the possibility for customizable functionalization, DNA-based receptors are selected. Thereupon, universal strategies for confining nanobiosensor platforms are presented using different sensor systems, analytes, and characterization methods. As a first application, a plasmonic biosensor based on vertically aligned gold nanoantennas tracked the immobilization, blocking, and subsequent hybridization of DNA by means of localized surface plasmon resonance (LSPR). At the same time, the LSPR sensor was used to evaluate fundamental hybridization mechanisms on nanostructured and planar surfaces, emphasizing the unique optical properties of metallic nanostructures. In a second application, an electric sensor based on silicon nanowire field-effect transistors (SiNW FET) monitored the level of the stress marker cortisol in human saliva. Based on evaluating the underlying charge distributions within the resulting receptor-analyte complex of molecules, the detection of cortisol within the Debye length is facilitated. Thus, direct, label-free detection of cortisol in human saliva using SiNW FET was successfully applied to the developed platform and compared to cortisol levels obtained using a commercial alternative. In summary, both presented platforms indicate a highly versatile and beneficial performance of nanobiosensors for continuous detection of biomarkers in real-time and preferably point-of-care (POC).