Stabilization of alkaline phosphatase with Au@Ag2O nanoparticles.

Here, we report that a conductive Au@Ag(2)O nanoparticle structure significantly enhances the stability of alkaline phosphatase (AlkP) in the presence of the inhibitors urea and l-phenylalanine (Phe). The enzyme/nanoparticle construct is prepared by associating the enzyme with citrate-capped Au particles, and then adding Ag(+). UV-vis and XPS spectroscopy and transmission electron microscopy confirm the core@shell structure. AlkP activity was quantified in the presence and absence of the two inhibitors using a time-resolved colorimetric assay. The results indicate that 21% of the initial active AlkP is incorporated into the nanoparticle structure. More importantly, however, the Au@Ag(2)O core@shell host reduces the inhibitory effect of urea and Phe by factors ranging from 3 to 12, depending on the inhibitor and its concentration, compared to the wild-type enzyme.

Self-powered sensor for naked-eye detection of serum trypsin.

Here, we report a device for the detection of the proteolytic enzyme trypsin, which is a biomarker for pancreatitis. The sensor is self-powered, easy to use, and signals the presence of trypsin via a light-emitting diode (LED) that is visible to the unaided eye. Assay time is ∼3 h, and the limit of detection is 0.5 µg/mL, which is within the range required for detection of trypsin at levels signaling acute pancreatitis. The sensing mechanism relies on trypsin digestion of a gelled protein layer. Partial digestion of the protein layer permits hydroxide penetration and subsequent etching of an underlying Al membrane. Degradation of both the protein and Al layers exposes an underlying Mg anode and closes an electrochemical circuit that produces ∼2.2 V. This is sufficient voltage to illuminate the LED. A logarithmic relationship is observed between the time required for LED illumination and trypsin concentration. The device is equally effective for trypsin dissolved in buffer or serum media.

A sensing platform based on electrodissolution of a Ag bipolar electrode.

Here we report a new type of sensing platform that is based on electrodissolution of a metallic bipolar electrode (BPE). When the target DNA binds to the capture probe at the cathodic pole of the BPE, it triggers the oxidation and dissolution of Ag metal present at the anodic pole. The loss of Ag is easily detectable with the naked eye or a magnifying glass and provides a permanent record of the electrochemical history of the electrode. More importantly, the decrease in the length of the BPE can be directly correlated to the number of electrons passing through the BPE and hence to the sensing reaction at the cathode.

Detection of an Epstein-Barr genome analog at physiological concentrations via the biometallization of interdigitated array electrodes.

This paper reports a simple DNA sensor having a detection limit of about 24 oligonucleotides and that operates without the need for PCR amplification. The sensor platform is based on an interdigitated array (IDA) of electrodes. The electrodes are modified with DNA capture probes, which are complementary to an analog for the Epstein-Barr genome, and then exposed to an alkaline phosphatase-labeled target. The enzyme catalyzes the formation of L-ascorbic acid, which reduces Ag(+) in solution to yield conductive Ag filaments that span the gap between the electrodes of the IDA. Resistance measurements, made with an inexpensive, hand-held multimeter, signal the presence of the target. The sensor response is insensitive to the presence of a large excess of non-complementary DNA sequences.