Wearable Nano-Based Gas Sensors for Environmental Monitoring and Encountered Challenges in Optimization.

With a rising emphasis on public safety and quality of life, there is an urgent need to ensure optimal air quality, both indoors and outdoors. Detecting toxic gaseous compounds plays a pivotal role in shaping our sustainable future. This review aims to elucidate the advancements in smart wearable (nano)sensors for monitoring harmful gaseous pollutants, such as ammonia (NH3), nitric oxide (NO), nitrous oxide (N2O), nitrogen dioxide (NO2), carbon monoxide (CO), carbon dioxide (CO2), hydrogen sulfide (H2S), sulfur dioxide (SO2), ozone (O3), hydrocarbons (CxHy), and hydrogen fluoride (HF). Differentiating this review from its predecessors, we shed light on the challenges faced in enhancing sensor performance and offer a deep dive into the evolution of sensing materials, wearable substrates, electrodes, and types of sensors. Noteworthy materials for robust detection systems encompass 2D nanostructures, carbon nanomaterials, conducting polymers, nanohybrids, and metal oxide semiconductors. A dedicated section dissects the significance of circuit integration, miniaturization, real-time sensing, repeatability, reusability, power efficiency, gas-sensitive material deposition, selectivity, sensitivity, stability, and response/recovery time, pinpointing gaps in the current knowledge and offering avenues for further research. To conclude, we provide insights and suggestions for the prospective trajectory of smart wearable nanosensors in addressing the extant challenges.

Lab-on-a-Contact Lens Platforms Fabricated by Multi-Axis Femtosecond Laser Ablation.

Contact lens sensing platforms have drawn interest in the last decade for the possibility of providing a sterile, fully integrated ocular screening technology. However, designing scalable and rapid contact lens processing methods while keeping a high resolution is still an unsolved challenge. In this article, femtosecond laser writing is employed as a rapid and precise procedure to engrave microfluidic networks into commercial contact lenses. Functional microfluidic components such as flow valves, resistors, multi-inlet geometries, and splitters are produced using a bespoke seven-axis femtosecond laser system, yielding a resolution of 80 µm. The ablation process and the tear flow within microfluidic structures is evaluated both experimentally and computationally using finite element modeling. Flow velocity drops of the 8.3%, 20.8%, and 29% were observed in valves with enlargements of the 100%, 200%, and 300%, respectively. Resistors yielded flow rate drops of 20.8%, 33%, and 50% in the small, medium, and large configurations, respectively. Two applications were introduced, namely a tear volume sensor and a tear uric acid sensor (sensitivity 16 mg L-1 ), which are both painless alternatives to current methods and provide reduced contamination risks of tear samples.

Analog-digital computing let robots go through the motions.

A hybrid analog-digital computing platform using memristors enables faster, more energy-efficient, and adaptive real-time robot control.

Development and Characterization of a PCB-Based Microfluidic YChannel.

Since the introduction of microfluidics in the 1990s, the community has investigated numerous methods for their fabrication. However, there is interest for their inexpensive rapid prototyping. PCB technology as a low-cost, massfabrication approach for the realization of sensors has attracted attention, while its use for microfluidics is also gaining ground. In this paper the development and characterization of a microfluidic Y-channel is presented. The proposed design and assembly process for realizing the device is described in detail and the flow rate and mixing within the microchannel are characterized, demonstrating the feasibility of the proposed novel technology for lab-on-PCB devices.

Scalable Route to Electroactive and Light Active Perylene Diimide Dye Polymer Binder for Lithium-Ion Batteries.

Developing multifunctional polymeric binders is key to the design of energy storage technologies with value-added features. We report that a multigram-scale synthesis of perylene diimide polymer (PPDI), from a single batch via polymer analogous reaction route, yields high molecular weight polymers with suitable thermal stability and minimized solubility in electrolytes, potentially leading to improved binding affinity toward electrode particles. Further, it develops strategies for designing copolymers with virtually any desired composition via a subsequent grafting, leading to purpose-built binders. PPDI dye as both binder and electroactive additive in lithium half-cells using lithium iron phosphate exhibits good electrochemical performance.

Induced neural stem cell differentiation on a drawn fiber scaffold-toward peripheral nerve regeneration.

To achieve regeneration of long sections of damaged nerves, restoration methods such as direct suturing or autologous grafting can be inefficient. Solutions involving biohybrid implants, where neural stem cells are grown in vitro on an active support before implantation, have attracted attention. Using such an approach, combined with recent advancements in microfabrication technology, the chemical and physical environment of cells can be tailored in order to control their behaviors. Herein, a neural stem cell polycarbonate fiber scaffold, fabricated by 3D printing and thermal drawing, is presented. The combined effect of surface microstructure and chemical functionalization using poly-L-ornithine (PLO) and double-walled carbon nanotubes (DWCNTs) on the biocompatibility of the scaffold, induced differentiation of the neural stem cells (NSCs) and channeling of the neural cells was investigated. Upon treatment of the fiber scaffold with a suspension of DWCNTs in PLO (0.039 g l-1) and without recombinants a high degree of differentiation of NSCs into neuronal cells was confirmed by using nestin, galactocerebroside and doublecortin immunoassays. These findings illuminate the potential use of this biohybrid approach for the realization of future nerve regenerative implants.

Feasibility Experiments to Detect Skin Hydration Using a Bio-Impedance Sensor.

We present proof of concept experiment of a sensing method to detect skin hydration using a low-cost bio-impedance sensor. The sensing system is validated by testing its current output over frequencies between 1 kHz and 50 kHz and comparing measured values of impedance. A series of experiments with salt-water mixtures as well as a gelatin-based phantom were carried out to test the sensor's ability to detect small changes in impedance due to changes in water content. We also compared impedance measurements from the phantom to human skin to confirm that the manufactured phantoms can mimic skin properties successfully. Our experimental results show that the sensor can detect small changes in salt concentration and can capture the correlation between the impedance and skin hydration in a reliable manner.

Multi-parametric rigid and flexible, low-cost, disposable sensing platforms for biomedical applications.

The measurement of Na+, K+ and H+ is essential in medicine and plays an important role in the assessment of tissue ischemia. Microfabrication, inkjet- and screen-printing can be used for solid contact ion selective electrodes (ISE) realization; these, however, can be non-standardized, costly and time consuming processes. We present the realization of ISEs on post-processed electrodes fabricated via standardized printed circuit board (PCB) manufacturing techniques. In vitro results are presented from two rigid platforms (32 ISEs) for liquid sample dip-stick measurements and two flexible platforms (6 and 32 ISEs) for post-surgical intestinal tissue monitoring, each with a common reference electrode (RE). These are combined with optimized tetrapolar bioimpedance sensors for tissue ischemia detection. Both electroless and hard gold PCB finishes are examined. Apart from the electroless rigid platform, the rest demonstrated comparable and superior performance, with the pH sensors demonstrating the greatest deviation; the flexible hard gold platform achieved a sensitivity 4.6mV/pH and 49.2mV/pH greater than the electroless flexible and rigid platforms, respectively. The best overall performance was achieved with the hard gold flexible platform with sensitivities as large as 73.4mV/pH, 56.3mV/log [Na+], and 57.4mV/log [K+] vs. custom REs on the same substrate. Simultaneous measurement of target analytes is demonstrated with test solutions and saliva samples. The results demonstrate superior performance to other PCB-based pH sensors and Na+ and K+ PCB-based sensors with comparable performance to potentiometric sensors fabricated with other techniques, paving the way towards mass-produced, low-cost, disposable, multi-parametric chemical sensing diagnostic platforms.

Towards the development of an electrochemical biosensor for hCGbeta detection.

The free beta subunit of human-chorionic-gonadotropin (hCGbeta) is critical for various aspects of human health. Detection and quantification of this protein are essential during pregnancy as it provides clinicians valuable information regarding the progress of a pregnancy and the health of a foetus. Furthermore, it can be used as a biomarker for gestational trophoblastic disease (GTD), germ cell tumours and some non-trophoblastic gynaecological cancers and common epithelial tumours. Monitoring hCGbeta levels is particularly important for patient treatment monitoring and relapse detection especially in GTD. This paper presents an investigation of the characteristics of the first two stages necessary for the development of a bio-impedance hCGbeta sensor, using impedance spectroscopy and commercially available microelectrodes. Additionally, electrical equivalent circuit models based on the experimental results of these stages are presented. The biosensor is based on the formation of stable antibody-antigen complexes on golden microband electrodes covered with a layer of a self-assembled monolayer (SAM) or with both SAM and protein G. The preliminary results and analysis relate the interfacial processes and physical structure of the sensor to its electrical behaviour. Finally, preliminary results obtained from the sensor without protein G, which strongly indicate hCGbeta detection, are also presented.