Detection of residual plasmin activity in milk represents a difficult challenge for the dairy industry. Conventional methods are either too expensive or incapable of providing enough data from UHT treated milk. Acoustic wave-based biosensors operated in the thickness shear mode (TSM) showed potential for the detection of proteolysis of β-casein, a milk protein by protease plasmin. An ultra-high frequency device, the electromagnetic piezoelectric acoustic sensor (EMPAS), designed to enhance the sensitivity of TSM, was tested for detection of plasmin at low concentrations. β-casein layers immobilised on the hydrophilic or hydrophobized surfaces of EMPAS quartz discs served as substrate for the enzyme. In contrast with conventional TSM devices, the shearing oscillations in EMPAS are induced contactless, by a magnetic coil located 30 μm below the quartz crystal. This configuration allows the registration of unusually high harmonics (up to the 49 th -53 rd ), thus enhancing the sensitivity of detection. On both surface types, the adsorbed βcasein mass and the stability of the layer was compared, with the result that hydrophobic surfaces provide superior conditions for immobilisation than the hydrophilic case. Consequent proteolysis measurements of these substrate layers were carried out in a broad plasmin concentration range (32 pM -10 nM) in flow mode. Initial reaction rates measured at different enzyme concentrations have been used to construct a calibration curve based on an inverse Michaelis-Menten type equation. The sensitivity of the EMPAS allowed measurements of as low as 32 pM concentration of plasmin, reaching (and often exceeding) levels comparable to state of the art techniques like ELISA. The presented method however, unlike ELISA, is effective on a timescale of minutes.

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Multisensor detectors have merits of low cost, compact size, and capability of supplying accurate and reliable information otherwise hard to obtain by any single sensors. They are therefore highly desired in various applications. Despite the advantages and needs, they face great challenges in technique especially when integrating sensors with different sensing principles. To bridge the gap between the demand and technique, we here demonstrated an integration of electrochemical and colorimetric sensors with a webcam readout for multiple gas detection. Designed with two parallel gas channels but independent sensor cells, the dual-sensor detector could simultaneously detect each gas from their gas mixture by analysis of the group photo of the two sensors. Using Ag electro-dissolution as reporter, the bipolar electrochemical sensor achieved quantitative analysis for the first time thanks to application of pulse voltage. The sacrificed Ag layer used in the bipolar electrochemical (EC) sensor was recycled from CD, which further decreased the sensor cost and supplied a new way of CD recycling. The EC O2 sensor response, edge displacement of Ag layer due to electrochemical dissolution, has a linear relationship with O2 concentration ranging from 0 to 30% and has good selectivity to common oxidative gases. The colorimetric NO2 sensor linearly responded to NO2 concentrations ranging from 0 to 230 ppb with low detection limit of 10 ppb, good selectivity, and humidity tolerance. This integration method could be extended to integrating other gas sensors.

Cell functions rely on signal transduction—the cascades of molecular interactions and biochemical reactions that relay extracellular signals to the cell interior. Dissecting principles governing the signal transduction process is critical for the fundamental understanding of cell physiology and the development of biomedical interventions. The complexity of cell signaling is, however, beyond what is accessible by conventional biochemistry assays. Thanks to their unique physical and chemical properties, nanoparticles (NPs) have been increasingly used for the quantitative measurement and manipulation of cell signaling. Even though research in this area is still in its infancy, it has the potential to yield new, paradigm-shifting knowledge of cell biology and lead to biomedical innovations. To highlight this importance, we summarize in this review studies that pioneered the development and application of NPs for cell signaling, from quantitative measurements of signaling molecules to spatiotemporal manipulation of cell signal transduction.

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