Ultrastable Lactate Biosensor Linearly Responding in Whole Sweat for Noninvasive Monitoring of Hypoxia.

We report on the lactate biosensor with linear calibration range from 0.5 to 100 mM, which encircles possible levels of this metabolite concentration in both human sweat and blood. The linear calibration range at high analyte concentrations, which exceeds the Michaelis constant of lactate oxidase by several orders of magnitude, is provided by an additional perfluorosulfonated ionomer diffusion membrane. In contrast to the known lactate biosensors, which retain their response within less than a couple of hours, the reported system displays 100% response for dozens of hours even upon high analyte concentrations. The biosensors with an additional diffusion-limiting membrane have been validated for lactate detection both in human blood serum and in undiluted human sweat shortly after its secretion. Both linear response in the entire range of blood and sweat lactate concentrations and ultrahigh operational stability would provide the use of the elaborated biosensor in wearable devices for the monitoring of hypoxia.

Core-Shell Nanozymes "Artificial Peroxidase": Stability with Superior Catalytic Properties.

We report on the nanoparticles composed of the catalytically synthesized Prussian Blue (PB) core stabilized with the nickel hexacyanoferrate (NiHCF) shell. Catalyzing hydrogen peroxide reduction, the resulting nanozymes (ø = 66 nm) display catalytic rate constants, which for pyrogallol or ferrocyanide are, respectively, 25 and 35 times higher than those for peroxidase enzyme. After more than half a year of storage at a room temperature, the core-shell PB-NiHCF nanozymes retain both their size and physicochemical properties; such stability is unreachable for the enzymes. Being immobilized, core-shell PB-NiHCF nanozymes (ø = 45 nm) result in a hydrogen peroxide sensor with a sensitivity similar to that of the sensor based on sole PB nanoparticles. However, whereas the latter response in hard inactivating conditions (25 min in 1 mM H2O2) drops down to 7.5%, the PB-NiHCF nanozymes-based sensor retains >75% of initial sensitivity. Application of the core-shell PB-NiHCF nanozymes "artificial peroxidase" would obviously open new horizons in elaboration of anti-inflammatory drugs and (bio)sensors.

Noninvasive Diabetes Monitoring through Continuous Analysis of Sweat Using Flow-Through Glucose Biosensor.

We propose monitoring of diabetes through continuous analysis of undiluted sweat immediately after its excretion using a flow-through glucose biosensor. The used biosensors are based on Prussian Blue and glucose oxidase immobilized in perfluorosulfonated ionomer or gel of alkoxysilane; the resulting sensitivity with the latter reaches in batch mode 0.23 A M-1 cm-2, and the calibration range is from 1 µM to 1 mM (flow-through mode). On the basis of the glucose tolerance test known to be a clinically relevant procedure to mimic hyperglycemia, a positive correlation between the rates of glucose concentration increase in blood and in noninvasively collected sweat has been observed ( r = 0.75). The observed correlation between sweat and blood considering low-molecular weight metabolites is even better than that observed previously between capillary and vein blood, confirming diagnostic value of sweat for diabetes monitoring. The dynamics of sweat glucose concentration, recorded by means of the proposed biosensor, is in a good accordance with the dynamics of blood glucose content without any time delay, thus offering a prospect for noninvasive monitoring of diabetes.