Highly Sensitive and Selective Sodium Ion Sensor Based on Silicon Nanowire Dual Gate Field-Effect Transistor

Multi-Modal Multi-Array Electrochemical and Optical Sensor Suite for a Biological CubeSat Payload

CubeSats have emerged as cost-effective platforms for biological research in low Earth orbit (LEO). However, they have traditionally been limited to optical absorbance sensors for studying microbial growth. This work has made improvements to the sensing capabilities of these small satellites by incorporating electrochemical ion-selective pH and pNa sensors with optical absorbance sensors to enrich biological experimentation and greatly expand the capabilities of these payloads. We have designed, built, and tested a multi-modal multi-array electrochemical-optical sensor module and its ancillary systems, including a fluidic card and an on-board payload computer with custom firmware. Laboratory tests showed that the module could endure high flow rates (1 mL/min) without leakage, and the 27-well, 81-electrode sensor card accurately detected pH (71.0 mV/pH), sodium ion concentration (75.2 mV/pNa), and absorbance (0.067 AU), with the sensors demonstrating precise linear responses (R2 ≈ 0.99) in various test solutions. The successful development and integration of this technology conclude that CubeSat bio-payloads are now poised for more complex and detailed investigations of biological phenomena in space, marking a significant enhancement of small-satellite research capabilities.

Designable microfluidic ladder networks from backstepping microflow analysis for mass production of monodisperse microdroplets

Controllable mass production of monodisperse droplets plays a key role in numerous fields ranging from scientific research to industrial application. Microfluidic ladder networks show great potential in mass production of monodisperse droplets, but their design with uniform microflow distribution remains challenging due to the lack of a rational design strategy. Here an effective design strategy based on backstepping microflow analysis (BMA) is proposed for the rational development of microfluidic ladder networks for mass production of controllable monodisperse microdroplets. The performance of our BMA rule for rational microfluidic ladder network design is demonstrated by using an existing analogism-derived rule that is widely used for the design of microfluidic ladder networks as the control group. The microfluidic ladder network designed by the BMA rule shows a more uniform flow distribution in each branch microchannel than that designed by the existing rule, as confirmed by single-phase flow simulation. Meanwhile, the microfluidic ladder network designed by the BMA rule allows mass production of droplets with higher size monodispersity in a wider window of flow rates and mass production of polymeric microspheres from such highly monodisperse droplet templates. The proposed BMA rule provides new insights into the microflow distribution behaviors in microfluidic ladder networks based on backstepping microflow analysis and provides a rational guideline for the efficient development of microfluidic ladder networks with uniform flow distribution for mass production of highly monodisperse droplets. Moreover, the BMA method provides a general analysis strategy for microfluidic networks with parallel multiple microchannels for rational scale-up.

Graphene-Based Ion-Selective Field-Effect Transistor for Sodium Sensing

Field-effect transistors have attracted significant attention in chemical sensing and clinical diagnosis, due to their high sensitivity and label-free operation. Through a scalable photolithographic process in this study, we fabricated graphene-based ion-sensitive field-effect transistor (ISFET) arrays that can continuously monitor sodium ions in real-time. As the sodium ion concentration increased, the current–gate voltage characteristic curves shifted towards the negative direction, showing that sodium ions were captured and could be detected over a wide concentration range, from 10⁻⁸ to 10⁻¹ M, with a sensitivity of 152.4 mV/dec. Time-dependent measurements and interfering experiments were conducted to validate the real-time measurements and the highly specific detection capability of our sensor. Our graphene ISFETs (G-ISFET) not only showed a fast response, but also exhibited remarkable selectivity against interference ions, including Ca²⁺, K⁺, Mg²⁺ and NH₄⁺. The scalability, high sensitivity and selectivity synergistically make our G-ISFET a promising platform for sodium sensing in health monitoring.

Synthesis and solar blind photosensitivity of crystalline boron nanowires

Herein, single crystalline boron nanowires (BNWs) have been synthesized by chemical vapor transport using boron element as boron source, iodine as transport agent, and Au as catalyst. The results demonstrate that BNWs can be all formed at 600 °C-950 °C for 2 h, and possess rhombohedral crystal structure (β-boron). The NWs have diameters from several to hundreds of nanometers, and lengths from several to hundreds of microns. A single nanowire has been fabricated to field effect transistor (FET) which shows excellent solar blind photosensitivity and selectivity. The photo/dark current ratio and photoresponsitity is 1.14 and 97.6 mA W^-1at a bias of 5 V under light illumination of 254 nm with 0.42 mW cm^-2, respectively, and both the rising and decay time of the on-off currents are 4.6 s and 10.3 s, respectively. When the FET is used as a personal breath sensor, the ratio of exsufflating and inhaling currents is 2.7, rising and decay time of the breath currents are 0.4 s and 2.2 s, respectively. So the BNWs are important sense materials.