Colorimetric Determination of Glucose in Sweat Using an Alginate-Based Biosystem.

Glucose is an analyte of great importance, both in the clinical and sports fields. Since blood is the gold standard biofluid used for the analytical determination of glucose, there is high interest in finding alternative non-invasive biofluids, such as sweat, for its determination. In this research, we present an alginate-based bead-like biosystem integrated with an enzymatic assay for the determination of glucose in sweat. The system was calibrated and verified in artificial sweat, and a linear calibration range was obtained for glucose of 10-1000 µM. The colorimetric determination was investigated, and the analysis was carried out both in the black and white and in the Red:Green:Blue color code. A limit of detection and quantification of 3.8 µM and 12.7 µM, respectively, were obtained for glucose determination. The biosystem was also applied with real sweat, using a prototype of a microfluidic device platform as a proof of concept. This research demonstrated the potential of alginate hydrogels as scaffolds for the fabrication of biosystems and their possible integration in microfluidic devices. These results are intended to bring awareness of sweat as a complementary tool for standard analytical diagnosis.

High-Resolution 3D Printing Fabrication of a Microfluidic Platform for Blood Plasma Separation.

Additive manufacturing technology is an emerging method for rapid prototyping, which enables the creation of complex geometries by one-step fabrication processes through a layer-by-layer approach. The simplified fabrication achieved with this methodology opens the way towards a more efficient industrial production, with applications in a great number of fields such as biomedical devices. In biomedicine, blood is the gold-standard biofluid for clinical analysis. However, blood cells generate analytical interferences in many test procedures; hence, it is important to separate plasma from blood cells before analytical testing of blood samples. In this research, a custom-made resin formulation combined with a high-resolution 3D printing methodology were used to achieve a methodology for the fast prototype optimization of an operative plasma separation modular device. Through an iterative process, 17 different prototypes were designed and fabricated with printing times ranging from 5 to 12 min. The final device was evaluated through colorimetric analysis, validating this fabrication approach for the qualitative assessment of plasma separation from whole blood. The 3D printing method used here demonstrates the great contribution that this microfluidic technology will bring to the plasma separation biomedical devices market.

Alginate Bead Biosystem for the Determination of Lactate in Sweat Using Image Analysis.

Lactate is present in sweat at high concentrations, being a metabolite of high interest in sport science and medicine. Therefore, the potential to determine lactate concentrations in physiological fluids, at the point of need with minimal invasiveness, is very valuable. In this work, the synthesis and performance of an alginate bead biosystem was investigated. Artificial sweat with different lactate concentrations was used as a proof of concept. The lactate detection was based on a colorimetric assay and an image analysis method using lactate oxidase, horseradish peroxidase and tetramethyl benzidine as the reaction mix. Lactate in artificial sweat was detected with a R² = 0.9907 in a linear range from 10 mM to 100 mM, with a limit of detection of 6.4 mM and a limit of quantification of 21.2 mM. Real sweat samples were used as a proof of concept to test the performance of the biosystem, obtaining a lactate concentration of 48 ± 3 mM. This novel sensing configuration, using alginate beads, gives a fast and reliable method for lactate sensing, which could be integrated into more complex analytical systems.

TiO2 Nanotubes Alginate Hydrogel Scaffold for Rapid Sensing of Sweat Biomarkers: Lactate and Glucose.

Versatile sensing matrixes are essential for the development of enzyme-immobilized optical biosensors. A novel three-dimensional titanium dioxide nanotubes/alginate hydrogel scaffold is proposed for the detection of sweat biomarkers, lactate, and glucose in artificial sweat. Hydrothermally synthesized titanium dioxide nanotubes were introduced to the alginate polymeric matrix, followed by cross-linking nanocomposite with dicationic calcium ions to fabricate the scaffold platform. Rapid colorimetric detection (blue color optical signal) was carried out for both lactate and glucose biomarkers in artificial sweat at 4 and 6 min, respectively. The superhydrophilicity and the capillarity of the synthesized titanium dioxide nanotubes, when incorporated into the alginate matrix, facilitate the rapid transfer of the artificial sweat components throughout the sensor scaffold, decreasing the detection times. Moreover, the scaffold was integrated on a cellulose paper to demonstrate the adaptability of the material to other matrixes, obtaining fast and homogeneous colorimetric detection of lactate and glucose in the paper substrate when image analysis was performed. The properties of this new composite provide new avenues in the development of paper-based sensor devices. The biocompatibility, the efficient immobilization of biological enzymes/colorimetric assays, and the quick optical signal readout behavior of the titanium dioxide nanotubes/alginate hydrogel scaffolds provide a prospective opportunity for integration into wearable devices.