Ultrasensitive alkaline phosphatase activity assay based on controllable signal probe production coupled with the cathodic photoelectrochemical analysis

A highly sensitive and selective split-type perovskite-based photoelectrochemical (PEC) platform was developed for measuring alkaline phosphatase (ALP) activity in milk and serum samples. ALP in the test sample hydrolyzed 2-phosphate sesquimagnesium salt hydrate (AAPS) in a 96-microwell plate to produce ascorbic acid (AA), a PEC electron donor. The resulting AA, which could preferentially annihilate the photogenerated holes, indirectly reflects ALP activity. The PEC used a cetyltrimethylammonium bromide (CTAB)-functionalized CH₃NH₃PbI₃ (CTAB@CH₃NH₃PbI₃) film as the cathode to monitor the controlled AA production. Due to the excellent photoelectric characteristics of the CH₃NH₃PbI₃ perovskite and the split-type assay, excellent sensitivity and selectivity for ALP detection were obtained. Under the optimum experimental conditions, ALP activity with a limit of detection (LOD) of 2.6 × 10^-4 U/L in a linear dynamic range of 10^-3 ∼ 10² U/L was obtained. With its sensitive, rapid, and high-throughput detection capabilities, this split-type and label-free PEC platform has great potential for use in food and biomedical analysis.

Deep brain stimulation of terminating axons

BACKGROUND

Deep brain stimulation (DBS) of the subthalamic region is an established treatment for the motor symptoms of Parkinson's disease. Several types of neural elements reside in the subthalamic region, including subthalamic nucleus (STN) neurons, fibers of passage, and terminating afferents. Recent studies suggest that direct activation of a specific population of subthalamic afferents, known as the hyperdirect pathway, may be responsible for some of the therapeutic effects of subthalamic DBS.

OBJECTIVE

The goal of this study was to quantify how axon termination affects neural excitability from DBS. We evaluated how adjusting different stimulation parameters influenced the relative excitability of terminating axons (TAs) compared to fibers of passage (FOPs).

METHODS

We used finite element electric field models of DBS, coupled to multi-compartment cable models of axons, to calculate activation thresholds for populations of TAs and FOPs. These generalized models were used to evaluate the response to anodic vs. cathodic stimulation, with short vs. long stimulus pulses.

RESULTS

Terminating axons generally exhibited lower thresholds than fibers of passage across all tested parameters. Short pulse widths accentuated the relative excitability of TAs over FOPs.

CONCLUSION(S)

Our computational results demonstrate a hyperexcitability of terminating axons to DBS that is robust to variation in the stimulation parameters, as well as the axon model parameters.