Self-Assembled Monolayers Coated Porous SnO2 Film Gas Sensor with Reduced Humidity Influence.

Metal-oxide sensors, detect gas through the reaction of surface oxygen molecules with target gases, are promising for the detection of toxic pollutant gases, combustible gases, and organic vapors; however, their sensitivity, selectivity, and long-term stability limit practical applications. Porous structure for increasing surface area, adding catalyst, and altering the operation temperature are proposed for enhancing the sensitivity and selectivity. Although humidity can significantly affect the property and stability of the sensors, studies focusing on the long-term stability of gas sensors are scarce. To reduce the effects of humidity, 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane (PFOTS) was coated on a porous SnO2 film. The interconnected SnO2 nanowires improved the high surface area, and the PFOTS coating provided superhydrophobicity at water contact angle of 159°and perfect water vapor repellency inside E-SEM. The superhydrophobic porous morphology was maintained under relative humidity of 99% and operating temperature of 300 °C. The CO gas sensing of 5, 20, and 50 ppm were obtained with linearity at various humidity. Flame detection was also achieved with practical high humidity conditions. These results suggest the simple way for reliable sensing of nanostructured metal-oxide gas sensors with high sensitivity and long-term stability even in highly humid environments.

A Sensitivity Enhanced MWCNT/PDMS Tactile Sensor Using Micropillars and Low Energy Ar⁺ Ion Beam Treatment.

High sensitive flexible and wearable devices which can detect delicate touches have attracted considerable attentions from researchers for various promising applications. This research was aimed at enhancing the sensitivity of a MWCNT/PDMS piezoresistive tactile sensor through modification of its surface texture in the form of micropillars on MWCNT/PDMS film and subsequent low energy Ar⁺ ion beam treatment of the micropillars. The introduction of straight micropillars on the MWCNT/PDMS surface increased the sensitivity under gentle touch. Low energy ion beam treatment was performed to induce a stiff layer on the exposed surface of the micropillar structured MWCNT/PDMS film. The low energy ion bombardment stabilized the electrical properties of the MWCNT/PDMS surface and tuned the curvature of micropillars according to the treatment conditions. The straight micropillars which were treated by Ar⁺ ion with an incident angle of 0° demonstrated the enhanced sensitivity under normal pressure and the curved micropillars which were treated with Ar⁺ ion with an incident angle of 60° differentiated the direction of an applied shear pressure. The ion beam treatment on micropillar structured MWCNT/PDMS tactile sensors can thus be applied to reliable sensing under gentle touch with directional discrimination.

Controlled self-assembly for high-resolution magnetic printing.

A controlled magnetic field creates patterns of superparamagnetic nanoparticles with a minimum line width of 10 µm on a flexible substrate. This magnetic printing method is also successfully used to print conductive patterns consisting of copper or carbon nanomaterials.

Human-Inspired Tactile Perception System for Real-Time and Multimodal Detection of Tactile Stimuli.

A human can intuitively perceive and comprehend complicated tactile information because the cutaneous receptors distributed in the fingertip skin receive different tactile stimuli simultaneously and the tactile signals are immediately transmitted to the brain. Although many research groups have attempted to mimic the structure and function of human skin, it remains a challenge to implement human-like tactile perception process inside one system. In this study, we developed a real-time and multimodal tactile system that mimics the function of cutaneous receptors and the transduction of tactile stimuli from receptors to the brain, by using multiple sensors, a signal processing and transmission circuit module, and a signal analysis module. The proposed system is capable of simultaneously acquiring four types of decoupled tactile information with a compact system, thereby enabling differentiation between various tactile stimuli, texture characteristics, and consecutive complex motions. This skin-like three-dimensional integrated design provides further opportunities in multimodal tactile sensing systems.

Eco-friendly polycaprolactone-bound diatomite filter for the removal of metal ions and micro/nanoplastics from water.

Over the last few decades, pollution levels in aquatic environments due to heavy metal ions and micro/nanoplastics have increased owing to industrial development, causing adverse effects on microorganisms. Adsorbent-based filtration is a well-developed technique for removing contaminants from aquatic environments. However, this technique should be improved from the perspectives of eco-friendliness and cost-effectiveness, as commercial adsorbents require energy-intensive synthesis and post-processing with chelating agents. In this study, an eco-friendly filtration system was developed. This system employs biodegradable, natural materials, such as diatomite to remove metal ions and micro/nanoplastics and polycaprolactone (PCL) to make the free-form shapes. The filter removes metal ions via adsorption and micro/nanoplastics via physical size filtration and adsorption. This PCL-bound diatomite filter was fabricated from a mixture of acetone, PCL, and diatomite, varying its size, thickness, shape, and stacking number for a particular objective and usage. The adsorption capacity, kinetics, and permeation flux of the membrane were measured, and the stacking number of the membranes were optimized to maximize the removal efficiency of the target contaminants. This filter is completely biodegradable, as indicated by the degradation of the PCL binder within 60 days in water, without any treatment. The degradable, eco-friendly PCL-bound diatomite filter is a low-cost and sustainable component that can be utilized in various applications, especially potable drinking water production from river in developing country and filtering the micro/nanoplastics from the commercially bottled drinking water in daily life.

Parasitic Capacitance-Free Flexible Tactile Sensor with a Real-Contact Trigger.

In this study, a parasitic capacitance-free tactile sensor with a floating electrode that is capable of identifying actual physical contact pressure by distinguishing from parasitic effects and applicable to sensor arrays is presented. Although capacitive pressure sensors are known for their excellent pressure sensing capabilities in wide range with high sensitivity, they tend to suffer from a parasitic capacitance noise and unwanted proximity effects. Electromagnetic interference shielding was conventionally used to prevent this noise; however, it was not entirely successful in multicell array sensors. Parasitic capacitance-free method involves the use of a floating electrode, which functions as a contact trigger by causing sudden changes in capacitance only when the actual physical contact pressure has been applied or removed. The proposed method is robust, consistent, and precise. Experimental results show a wide range of pressure response up to 2.4 MPa with a sensitivity of 0.179 MPa-1 (up to 0.74 MPa) and negligible hysteresis.

Bioinspired nanoscale hierarchical pillars for extreme superhydrophobicity and wide angular transmittance.

Hierarchical structures in nature provide unique functions for living organisms that can inspire technology. Nanoscale hierarchical structured surfaces are essential to realize the dual functions of non-wetting and transparency for applications such as cover glasses and windows; however, these structures are challenging to fabricate. In this study, nano-hierarchical structured glass surfaces were fabricated using multi-step colloidal lithography and etching to obtain tunable morphology. Nanostructured surfaces of mono-pillar structures of diameter 120 and 350 nm and hierarchical-pillar structures of their combinations exhibited superhydrophobicity after perfluoropolyether coating. In particular, the hierarchical nanosurfaces showed excellent non-wetting properties with the apparent, advancing, and receding water contact angles exceeding 177° and contact angle hysteresis below 1°. Water bouncing behaviors - contact time, spreading diameter, and shape of the bouncing motion were also evaluated according to the Weber number to examine the robustness of superhydrophobicity. Hierarchical nanosurfaces showed larger spreading diameters than mono-nanosurfaces with 14 bounces, indicating minimal energy loss from friction, as can be explained by the effective slip length. Furthermore, the nano-hierarchical structures exhibited better transmittance for wide angles of incidence up to 70° than mono-nanostructures owing to their reduced scattering area and multi-periodicity.

Stretchable Printed Circuit Board Based on Leak-Free Liquid Metal Interconnection and Local Strain Control.

In order to realize a transition from conventional to stretchable electronics, it is necessary to make a universal stretchable circuit board in which passive/active components can be robustly integrated. We developed a stretchable printed circuit board (s-PCB) platform that enables easy and reliable integration of various electronic components by utilizing a modulus-gradient polymeric substrate, liquid metal amalgam (LMA) circuit traces, and Ag nanowire (AgNW) contact pads. Due to the LMA-AgNW biphasic structure of interconnection, the LMA is hermetically sealed by a homogeneous interface, realizing complete leak-free characteristics. Furthermore, integration reliability is successfully achieved by local strain control of the stretchable substrate with a selective glass fiber reinforcement (GFR). A strain localization derived by GFR makes almost 50,000% of strain difference within the board, and the amount of deformation applied to the constituent elements can be engineered. We finally demonstrated that the proposed integrated platform can be utilized as a universal s-PCB capable of integrating rigid/conventional electronic components and soft material-based functional elements with negligible signal distortion under various mechanical deformations.

Selective binding and detection of magnetic labels using PHR sensor via photoresist micro-wells.

We have developed a novel platform for selective binding of magnetic labels on planar Hall resistance sensor (PHR) for biosensing applications. The photoresist (PR) micro wells were prepared on the PHR sensor junctions to trap the magnetic bead at specified locations on the sensor surface and thin layer of Au was sputtered in the PR wells immobilize bimolecular. The Au surface is functionalized with single-stranded oligonucleotide and further biotin was used to immobilize streptavidin coated magnetic labels (Dynabeads Myone 1.0 microm, Invitrogen Co.). After removal of the PR wells on the sensor surface the non specific binding magnetic labels were successfully removed and only the chemically bounded magnetic labels were remained on the Au surface for detection of biomolecules using PHR sensor. We controlled the number of magnetic labels on the PHR sensor surface by using different sizes of the PR well on the junctions. The specifically bounded magnetic labels were successfully detected by characterizing the individual PHR sensor junctions. This technique enables the complete control over the magnetic labels for selective binding of biomolecules on the sensor surface for increasing the sensitivity of the PHR sensor as well as removal of the non specific bindings on the sensor surface.

Customizable, Flexible Pressure, and Temperature Step Sensors with Human Skinlike Color.

Durability and multifunctionality are very important factors for human skinlike tactile sensors for measuring physical stimuli if they provide reasonable pressure measurement range and sensitivity. Here, we propose a step tactile sensor with a simple processing unit, showing high repeatability and mechanical stability without drifting caused by thermal and geometrical noise. The proposed sensor, similar to a switch mechanism, detects the applied pressure discretely and has a wide pressure range of 2 kPa to 1.2 MPa according to its geometry. The developed tactile sensor can be designed and fabricated in various morphologies to detect a wide range of tactile stimuli, which help in customizing the sensor as per user demand for practical applications such as a prosthesis arm or hand. It is also easy to extend the sensor size to cover a large area owing to the simple fabrication process by using a 3D printer. Furthermore, with the addition of a flexible exterior layer of leuco dyes and the polydimethylsiloxane mixture, the color of a step tactile sensor not only resembles that of human skin color but also changes its color depending on the temperature changes as human skin does. Thus, the function of a pressure and temperature indicator in a flexible step sensor finds practical applications in various fields, including but not limited to prosthetic applications for the customized and comfortable usage.

Remote tactile sensing system integrated with magnetic synapse.

Mechanoreceptors in a fingertip convert external tactile stimulations into electrical signals, which are transmitted by the nervous system through synaptic transmitters and then perceived by the brain with high accuracy and reliability. Inspired by the human synapse system, this paper reports a robust tactile sensing system consisting of a remote touch tip and a magnetic synapse. External pressure on the remote touch tip is transferred in the form of air pressure to the magnetic synapse, where its variation is converted into electrical signals. The developed system has high sensitivity and a wide dynamic range. The remote sensing system demonstrated tactile capabilities over wide pressure range with a minimum detectable pressure of 6 Pa. In addition, it could measure tactile stimulation up to 1,000 Hz without distortion and hysteresis, owing to the separation of the touching and sensing parts. The excellent performance of the system in terms of surface texture discrimination, heartbeat measurement from the human wrist, and satisfactory detection quality in water indicates that it has considerable potential for various mechanosensory applications in different environments.

An organic substrate based magnetoresistive sensor for rapid bacteria detection.

A point-of-care diagnostic system has been developed to detect pathogenic bacteria rapidly, of which system contains a magnetoresistive (MR) sensor in cooperation with a magnetic bead coated by specific antibody against bacteria. MR sensor with Teflon passivation layer has been fabricated on organic substrate, being flexible and low cost material, and passivated by Teflon layer for maintaining flexibility. The performance of the MR sensor is demonstrated using Magnetospirillum magneticum AMB-1 and its detection limit was found to be 1.3×10(8) cells/ml. Further, Escherichia coli is captured by immobilised anti-E. coli antibodies on the surface of the sensor and detected using magnetic bead labelled with anti-E. coli antibody. The detection limit of E. coli was found to be 1.2×10(3) cells/ml. The technique is simple, rapid, sensitive and does not require pre-treatment of the sample and can detect a variety of microorganisms. The high performance of sensor fabricated on flexible organic substrate may allow its future use for bio-applications in implantable types of devices.

Translocation of bio-functionalized magnetic beads using smart magnetophoresis.

We demonstrate real time on-chip translocation of bio-functionalized superparamagnetic beads on a silicon surface in a solution using a magnetophoresis technique. The superparamagnetic beads act as biomolecule carriers. Fluorescent-labeled Atto-520 biotin was loaded to streptavidin-coated magnetic beads (Dynabead(®) M-280) by means of ligand-receptor interactions. The magnetic pathways were patterned lithographically such that semi-elliptical Ni(80)Fe(20) elements were arranged sequentially for a few hundred micrometers in length. An external rotating magnetic field was used to drive translational forces on the magnetic beads that were proportional to the product of the field strength and its gradient. The translational force at the curving edge of the pathway element of 6 µm diameter was calculated to be ∼1.2 pN for an applied field of 7.9 kA m(-1). However, the force at the flat edge was calculated to be ∼0.16 pN. The translational force was larger than the drag force and thus allowed the magnetic beads to move in a directional way along the curving edge of the pathway. However, the force was not sufficient to move the beads along the flat edge. The top and bottom curving edge semi-elliptical NiFe pathways were obliquely-arranged on the left and right sides of the converging site, respectively. This caused a central translational force that allowed the converging and diverging of the Atto-520 biotin loaded streptavidin magnetic beads at a particular site.