Integrated sampling-and-sensing using microdialysis and biosensing by particle motion for continuous cortisol monitoring

Microdialysis catheters are small probes that allow sampling from biological systems and human subjects with minimal perturbation. Traditionally, microdialysis samples are collected in vials, transported to a laboratory, and analysed with typical turnaround times of hours to days. To realize a continuous sampling-and-sensing methodology with minimal time delay, we studied the integration of microdialysis sampling with a sensor for continuous biomolecular monitoring based on Biosensing by Particle Motion (BPM). A microfluidic flow cell was designed with a volume of 12 μl in order to be compatible with flowrates of microdialysis sampling. The analyte recovery and the time characteristics of the sampling-and-sensing system were studied using a food colorant in buffer and using cortisol in buffer and in blood plasma. Concentration step functions were applied, and the system response was measured using optical absorption and a continuous BPM cortisol sensor. The cortisol recovery was around 80% for a 30 mm microdialysis membrane with a 20 kDa molecular weight cut-off and a flowrate of 2 μl min−1. The concentration-time data could be fitted with a transport delay time and single-exponential relaxation curves. The total delay time of the sampling-and-sensing methodology was about 15 minutes. Continuous sampling-and-sensing was demonstrated over a period of 5 hours. These results represent an important step toward integrated sampling-and-sensing for the continuous monitoring of a wide variety of low-concentration biomolecular substances for applications in biological and biomedical research.</p

Integrated sampling-and-sensing using microdialysis and biosensing by particle motion for continuous cortisol monitoring

Microdialysis catheters are small probes that allow sampling from biological systems and human subjects with minimal perturbation. Traditionally, microdialysis samples are collected in vials, transported to a laboratory, and analysed with typical turnaround times of hours to days. To realize a continuous sampling-and-sensing methodology with minimal time delay, we studied the integration of microdialysis sampling with a sensor for continuous biomolecular monitoring based on Biosensing by Particle Motion (BPM). A microfluidic flow cell was designed with a volume of 12 μl in order to be compatible with flowrates of microdialysis sampling. The analyte recovery and the time characteristics of the sampling-and-sensing system were studied using a food colorant in buffer and using cortisol in buffer and in blood plasma. Concentration step functions were applied, and the system response was measured using optical absorption and a continuous BPM cortisol sensor. The cortisol recovery was around 80% for a 30 mm microdialysis membrane with a 20 kDa molecular weight cut-off and a flowrate of 2 μl min−1. The concentration-time data could be fitted with a transport delay time and single-exponential relaxation curves. The total delay time of the sampling-and-sensing methodology was about 15 minutes. Continuous sampling-and-sensing was demonstrated over a period of 5 hours. These results represent an important step toward integrated sampling-and-sensing for the continuous monitoring of a wide variety of low-concentration biomolecular substances for applications in biological and biomedical research.</p

Don't be misled: 3 misconceptions about external validation of clinical prediction models

Clinical prediction models provide risks of health outcomes that can inform patients and support medical decisions. However, most models never make it to actual implementation in practice. A commonly heard reason for this lack of implementation is that prediction models are often not externally validated. While we generally encourage external validation, we argue that an external validation is often neither sufficient nor required as an essential step before implementation. As such, any available external validation should not be perceived as a license for model implementation. We clarify this argument by discussing 3 common misconceptions about external validation. We argue that there is not one type of recommended validation design, not always a necessity for external validation, and sometimes a need for multiple external validations. The insights from this paper can help readers to consider, design, interpret, and appreciate external validation studies

Common Limitations of Image Processing Metrics:A Picture Story

While the importance of automatic image analysis is continuously increasing, recent meta-research revealed major flaws with respect to algorithm validation. Performance metrics are particularly key for meaningful, objective, and transparent performance assessment and validation of the used automatic algorithms, but relatively little attention has been given to the practical pitfalls when using specific metrics for a given image analysis task. These are typically related to (1) the disregard of inherent metric properties, such as the behaviour in the presence of class imbalance or small target structures, (2) the disregard of inherent data set properties, such as the non-independence of the test cases, and (3) the disregard of the actual biomedical domain interest that the metrics should reflect. This living dynamically document has the purpose to illustrate important limitations of performance metrics commonly applied in the field of image analysis. In this context, it focuses on biomedical image analysis problems that can be phrased as image-level classification, semantic segmentation, instance segmentation, or object detection task. The current version is based on a Delphi process on metrics conducted by an international consortium of image analysis experts from more than 60 institutions worldwide.Comment: This is a dynamic paper on limitations of commonly used metrics. The current version discusses metrics for image-level classification, semantic segmentation, object detection and instance segmentation. For missing use cases, comments or questions, please contact [email protected] or [email protected]. Substantial contributions to this document will be acknowledged with a co-authorshi

Understanding metric-related pitfalls in image analysis validation

Validation metrics are key for the reliable tracking of scientific progress and for bridging the current chasm between artificial intelligence (AI) research and its translation into practice. However, increasing evidence shows that particularly in image analysis, metrics are often chosen inadequately in relation to the underlying research problem. This could be attributed to a lack of accessibility of metric-related knowledge: While taking into account the individual strengths, weaknesses, and limitations of validation metrics is a critical prerequisite to making educated choices, the relevant knowledge is currently scattered and poorly accessible to individual researchers. Based on a multi-stage Delphi process conducted by a multidisciplinary expert consortium as well as extensive community feedback, the present work provides the first reliable and comprehensive common point of access to information on pitfalls related to validation metrics in image analysis. Focusing on biomedical image analysis but with the potential of transfer to other fields, the addressed pitfalls generalize across application domains and are categorized according to a newly created, domain-agnostic taxonomy. To facilitate comprehension, illustrations and specific examples accompany each pitfall. As a structured body of information accessible to researchers of all levels of expertise, this work enhances global comprehension of a key topic in image analysis validation.Comment: Shared first authors: Annika Reinke, Minu D. Tizabi; shared senior authors: Paul F. J\"ager, Lena Maier-Hei

Continuous small-molecule monitoring with a digital single particle switch

The ability to continuously measure concentrations of small molecules is important for biomedical, environmental and industrial monitoring. However, due to their low molecular mass it is difficult to quantify concentrations of such molecules, particularly at low concentrations. Here we describe a small-molecule sensor that is generalizable, sensitive, specific, reversible, and suited for continuous monitoring over long durations. The sensor consists of particles attached to a sensing surface via a double stranded DNA tether. The particles transiently bind to the sensing surface via single molecular affinity interactions and the transient binding is optically detected as digital binding events via the Brownian motion of the particles. The rate of binding events decreases with increasing analyte concentration, because analyte molecules inhibit binding of the tethered particle to the surface. The sensor enables continuous measurements of analyte concentrations due to the reversibility of the inter-molecular bonds and digital read-out of particle motion. We show results for the monitoring of short single-stranded DNA sequences and creatinine, a small-molecule biomarker (113 Da) for kidney function, demonstrating a temporal resolution of a few minutes. The precision of the sensor is determined by the statistics of the digital switching events, which means that the precision is tunable by the number of particles and the measurement time

Continuous Small-Molecule Monitoring with a Digital Single-Particle Switch

The ability to continuously measure concentrations of small molecules is important for biomedical, environmental and industrial monitoring. However, due to their low molecular mass it is difficult to quantify concentrations of such molecules, particularly at low concentrations. Here we describe a small-molecule sensor that is generalizable, sensitive, specific, reversible, and suited for continuous monitoring over long durations. The sensor consists of particles attached to a sensing surface via a double stranded DNA tether. The particles transiently bind to the sensing surface via single molecular affinity interactions and the transient binding is optically detected as digital binding events via the Brownian motion of the particles. The rate of binding events decreases with increasing analyte concentration, because analyte molecules inhibit binding of the tethered particle to the surface. The sensor enables continuous measurements of analyte concentrations due to the reversibility of the inter-molecular bonds and digital read-out of particle motion. We show results for the monitoring of short single-stranded DNA sequences and creatinine, a small-molecule biomarker (113 Da) for kidney function, demonstrating a temporal resolution of a few minutes. The precision of the sensor is determined by the statistics of the digital switching events, which means that the precision is tunable by the number of particles and the measurement time

Reversible Immunosensor for the Continuous Monitoring of Cortisol in Blood Plasma Sampled with Microdialysis

Cortisol is a steroid hormone involved in a wide range of medical conditions. The level of the hormone fluctuates over time, but with traditional laboratory-based assays, such dynamics cannot be monitored in real time. Here, a reversible cortisol sensor is reported that allows continuous monitoring of cortisol in blood plasma using sampling by microdialysis. The sensor is based on measuring single-molecule binding and unbinding events of tethered particles. The particles are functionalized with antibodies and the substrate with cortisol-analogues, causing binding and unbinding events to occur between particles and substrate. The frequency of binding events is reduced when cortisol is present in the solution as it blocks the binding sites of the antibodies. The sensor responds to cortisol in the high nanomolar to low micromolar range and can monitor cortisol concentrations over multiple hours. Results are shown for cortisol monitoring in filtered and in microdialysis-sampled human blood plasma