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Bioresorbable electrochemical sensors remain mostly unexplored despite their ability to provide continuous in situ measurements of critical biomarkers. The primary challenge arises from the direct exposure of the electrodes' thin metal films to biofluids, which poses difficulties in ensuring both proper operational lifetimes and sensing performance. Molybdenum (Mo) presents itself as a promising biometal due to its uniquely gradual dissolution in biofluids, facilitated by the formation of a slower‐dissolving MoOx surface layer. Consequently, carefully engineered MoOx films can endow transient electrochemical sensors with unparalleled stability during extended operational lifetimes. Herein an unprecedented sensor architecture achieved via the unique pairing of sputtered Mo and MoOx thin films, probed as a pH and dissolved oxygen sensor is reported. Compared to a bare Mo electrode, a bilayer Mo+MoOx electrode subjected to post‐deposition annealing (400 °C, 60 min, N2 environment) displayed a largely improved stability (>24 h) in solution and demonstrated predictable functionality during ongoing film dissolution at 37 °C. Collectively, this work establishes a pioneering strategy for the fabrication of reliable and clinically relevant implantable electrochemical sensors. [ABSTRACT FROM AUTHOR]

The optoelectronic properties of semiconductor nanoparticles make them valuable candidates for the long-term monitoring of transmembrane electric fields in excitable cells. In this work, we show that the electric field sensitivity of the fluorescence intensity of type-I and quasi-type-II quantum dots and quantum rods is enhanced under two-photon excitation compared to single-photon excitation. Based on the superior electric field sensitivity of the two-photon excited fluorescence, we demonstrate the ability of quantum dots and rods to track fast switching E-fields. These findings indicate the potential of semiconductor nanoparticles as cellular voltage probes in multiphoton imaging.

Herein, a biomimetic sensor platform that allows sensitive, onsite detection of Escherichia coli (E. coli) with a limit of detection of 30 cells mL−1 in both buffer suspension and rinsing water from an industrial food‐preparation machine is reported. Ultrathin surface‐imprinted polymers are combined with non‐Faradaic impedance spectroscopy to measure the increase in resistance at the solid‐to‐liquid interface due to the binding of target cells by the receptor layer. The detection limit reached with this sensing principle is determined using an established, commercial impedance spectrometer and a low‐cost, home‐built impedance unit. Cross‐selectivity tests, with both an unrelated bacterial species and four species belonging to the same Enterobacteriales order, show that the response is strongest for the target bacterium while only a small cross‐selectivity signal (≈10–25%) is visible for all other types of bacteria. Therefore, this sensor is not only fast and low cost, but also sensitive and selective. Sample preparation is minimal, which is an asset for onsite bacterial detection in a food industry context. [ABSTRACT FROM AUTHOR]

This paper reports a multifunctional platform based on a nanocomposite hydrogel combining poly(ethylene glycol), with rhodamine B‐containing silica nanoparticles (RhB@SiO2), as temperature sensors, and gold nanorods (AuNRs) as plasmonic heaters. This composite material acts as a light‐addressable cellular matrix able to induce 3D temperature gradients locally and dynamically using the localized surface plasmon resonance (LSPR) of AuNRs under near‐infrared (NIR) laser illumination. At the same time, the temperature changes are probed locally by monitoring changes of the RhB@SiO2 NPs fluorescence. As a result of plasmonic heating, and, depending on the preparation protocol, the light‐addressable hydrogel also deforms controllably and reversibly, allowing mechanical and thermal cellular stimulation in a 3D matrix. The hydrogel deformation is quantified by means of inline holographic microscopy. This approach makes it possible to accurately and locally control and simultaneously measure temperature gradients and deformation in soft, 3D deformable materials and will enable novel platforms for studying cellular thermo‐ and mechanobiology. [ABSTRACT FROM AUTHOR]

Shear rheology and atomic force microscopy (AFM) are used to characterize the stiffness of hydrogels in tissue engineering applications, with several studies reporting differences of several orders of magnitude in the elastic moduli determined by these two methods. This work compares the elastic properties of soft fibrin and polyethylene glycol (PEG) hydrogels used for stem cell applications, determined by AFM indentation with different probe sizes (from nano‐ to micrometer) to shear rheometry data. For all hydrogels, AFM nanoscale probing consistently yields higher elastic modulus (E) values and variability than micrometer‐probe indentation, while the shear modulus (G) values determined are the lowest. Colloidal probe AFM results are closer to rheology data for the stiffest samples, where E/G ratios converge to the theoretical Trouton ratio of 3. The results suggest that high polymer concentration hydrogels are better described by the affine elastic network theory, whereas low polymer concentration hydrogels deviate significantly from the Trouton ratio. Thus, for soft hydrogels relevant for stem cell culture, the assumption E = 3G is often invalid and care should be taken when comparing data from studies where different characterization methods are used in order to discern the impact of material properties on cell behavior. [ABSTRACT FROM AUTHOR]