Research on a capacitive particle analysis smoke detector.

Smoke detectors face the challenges of increasing accuracy, sensitivity, and high reliability in complex use environments to ensure the timeliness, accuracy, and reliability of very early fire detection. The improvement and innovation of the principle and algorithm for smoke particle concentration detection provide opportunities for improving the performance of the detector. This study represents a new refinement of the smoke concentration detection principle based on capacitive detection of cell structures, and detection signals are processed by a multiscale smoke particle concentration detection algorithm to calculate smoke concentration. Through experiments, it was found that the detector provides effective detection of smoke particle concentrations ranging from 0 to 10% obs/m; moreover, when the detection accuracy is greater than a certain number of parts per million (PPM), the sensitivity of the detector can reach the PPM level; furthermore, the detector can detect smoke particle concentrations higher than the PPM level accuracy even in an environment with a certain concentration of petroliferous and dust particles of different sizes.

Research on high performance combustible gas concentration sensor based on pyramid beam splitter matrix.

Combustible gas concentration detection faces challenges of increasing accuracy, and sensitivity, as well as high reliability in harsh using environments. The special design of the optical path structure of the sensitive element provides an opportunity to improve combustible gas concentration detection. In this study, the optical path structure of the sensitive element was newly designed based on the Pyramidal beam splitter matrix. The infrared light source was modulated by multi-frequency point signal superimposed modulation technology. At the same time, concentration detection results and confidence levels were calculated using the 4-channel combustible gas concentration detection algorithm based on spectral refinement. Through experiment, it is found that the sensor enables full-range measurement of CH4, at the lower explosive limit (LEL, CH4 LEL of 5%), the reliability level is 0.01 parts-per-million (PPM), and the sensor sensitivity is up to 0.5PPM. The sensor is still capable of achieving PPM-level detections, under extreme conditions in which the sensor's optical window is covered by 2/3, and humidity is 85% or dust concentration is 100mg/m3. Those improve the sensitivity, robustness, reliability, and accuracy of the sensor.

Seaweed-inspired underwater anti-oil-fouling and anti-fogging coating with mechanical durability.

Ecofriendly fabrication of anti-oil-fouling materials is of interest. Surfaces with underwater superoleophobicity have been fabricated which exhibit limited mechanical durability and water resistance. In this study, we report on a bioinspired bilayer design of a transparent anti-oil-fouling coating. Seaweed surfaces show anti-oil-fouling in the sea due to its high surface hydration ability. Mussels can adhere tightly onto a surface with good stability in the sea by virtue of its levodopa-containing secretions. The surface layer was fabricated using a crosslinked combination of carboxymethyl cellulose (CMC) and sodium alginate (AlgS) inspired by seaweed, with the addition of calcium ions. Polydopamine (PDA), a derivative of levodopa, was used as the underlayer to enhance bonding strength and water resistance. Oil that adhered to the coated surface was spontaneously detached upon immersion in water. The mechanism underlying this anti-oil-fouling effect was elucidated using Gibbs free energy theory. The coating exhibited mechanical durability and water resistance. The coating is transparent and preserves the original color of the substrate. The coated glass showed stable anti-fogging and anti-frost performance. These coatings hold promise for a wide range of anti-oil-fouling applications.

A Capacitive Particle-Analyzing Smoke Detector for Very Early Fire Detection.

Smoke detectors face the challenges of increasing accuracy, sensitivity, and high reliability in complex use environments to ensure the timeliness, accuracy, and reliability of very early fire detection. The improvement in and innovation of the principle and algorithm of smoke particle concentration detection provide an opportunity for the performance improvement in the detector. This study is a new refinement of the smoke concentration detection principle based on capacitive detection of cell structures, and detection signals are processed by a multiscale smoke particle concentration detection algorithm to calculate particle concentration. Through experiments, it is found that the detector provides effective detection of smoke particle concentrations ranging from 0 to 10% obs/m; moreover, the detector can detect smoke particles at parts per million (PPM) concentration levels (at 2 and 5 PPM), and the accuracy of the detector can reach at least the 0.5 PPM level. Furthermore, the detector can detect smoke particle concentrations at better than 1 PPM accuracy even in an environment with 6% obs/m oil gas particles, 7% obs/m large dust interference particles, or 8% obs/m small dust interference particles.

Research on High Performance Methane Gas Concentration Sensor Based on Pyramid Beam Splitter Matrix.

Methane gas concentration detection faces the challenges of increasing accuracy and sensitivity, as well as high reliability in harsh environments. The special design of the optical path structure of the sensitive element provides an opportunity to improve methane gas concentration detection. In this study, the optical path structure of the sensitive element was newly designed based on the Pyramidal beam splitter matrix. The infrared light source was modulated by multi-frequency point-signal superimposed modulation technology. At the same time, concentration detection results and confidence levels were calculated using the four-channel methane gas concentration detection algorithm based on spectral refinement. Through the experiment, it was found that the sensor enables the full-range measurement of CH4; at the lower explosive limit (LEL, CH4 LEL of 5%), the reliability level is 0.01 parts-per-million (PPM), and the limit of detection is 0.5 ppm. The sensor is still capable of achieving PPM-level detections under extreme conditions in which the sensor's optical window is covered by two-thirds and humidity is 85% or dust concentration is 100 mg/m3. Those improve the sensitivity, robustness, reliability, and accuracy of the sensor.

Durable Superoleophobic Janus Fabric with Oil Repellence and Anisotropic Water-Transport Integration toward Energetic-Efficient Oil-Water Separation.

Porous materials with opposing superwettability toward oil and water have aroused widespread interest for their selective-wetting advantage in oil-water separation. The separation process, however, requires constant energy input to maintain the driving force. Further reducing the external energy consumption or accelerating the liquid transport during separation is still a challenge. The Janus membrane is an emerging porous material with opposing wettability toward a specific liquid on each side. The asymmetric wettability distribution leads to a surface energy gradient-driven liquid-transport behavior through the thickness, which significantly facilitates liquid transportation. It is conceived that porous materials possessing both Janus features and selective superwettability would reduce energy consumption and strengthen the efficiency in oil-water separation. Herein, a novel durable superoleophobic (SOHB) Janus fabric which possesses oil-repellent and surface energy gradient-driven water-transport properties was developed through one-side superoleophobic/superhydrophilic modification of the superamphiphobic fabric. The SOHB Janus fabric exhibits high mechanical durability and significant superior capacity than the homogeneous superoleophobic/superhydrophilic fabric in separating various oil-water mixtures. Moreover, the SOHB Janus fabric repels oil contaminants and pumps perspiration from the human skin, exhibiting prospects in physical moisture regulation and comfort improvement. Our novel Janus fabric, along with the fabrication principle, provides a feasible solution for energetic-efficient oil-water remediations and would have implications for the fabrication of advanced separation membranes and intelligent functional clothing.

Towards detection of biomarkers in the eye using an aptamer-based graphene affinity nanobiosensor.

We present an approach to enable the sensitive and specific detection of biomarkers in undiluted tears in the eye using an aptamer-based graphene affinity nanosensor. The nanosensor is a graphene field-effect transistor, in which a nucleic acid aptamer and a biomolecule-permeable polyethylene glycol (PEG) nanolayer are immobilized on the graphene surface. The aptamer is capable of specifically recognize the target biomarker and induce a change in the carrier concentration of the graphene, which is measured to determine the biomarker concentration. The PEG nanolayer minimizes nonspecific adsorption of background molecules in the sample that would otherwise interfere with the biomarker detection. Experimental results show that tumor necrosis factor alpha (TNF-alpha), an inflammatory cytokine, can be sensitively and specifically detected in undiluted artificial tears with a limit of detection of 0.34 pM. This ability to detect and measure biomarkers in undiluted physiological fluids allows the nanosensor to be potentially used in applications where sample dilutions are not practical, such as wearable measurements of tear-borne biomarkers in the eye.

Ultrasensitive Graphene-Based Nanobiosensor for Rapid Detection of Hemoglobin in Undiluted Biofluids.

Detection of hemoglobin (Hb), a critical part of the biological system that is responsible for oxygen transportation, is of great significance on clinical diagnosis of various diseases. Particularly, time-efficient Hb detection under nanomole levels has drawn much attention in recent years. Herein, we present a graphene field effect transistor (GFET)-based aptameric nanobiosensor for rapid detection of Hb in undiluted biofluids including serum and urine and for the first time use polyethylenimine (PEI), a kind of comparatively low-cost polymer consisting of numerous amino groups, which can be directly linked with the anchor molecule without any pretreatment as the graphene surface passivation agent. Experimental results indicate the PEI-modified graphene aptameric nanobiosensor can respond to the Hb concentration change in a few minutes (6-8 min) with estimated detection limits of 10.6 fM in 1× PBS, 14.2 fM in undiluted serum, and 11.9 fM in undiluted urine, respectively. Further, considering the potential use of our sensor for implantable and wearable applications, we also examine the sensing performance of the sensor fabricated on an ultrathin flexible polyethylene terephthalate (PET) substrate. The Hb detection results are almost invariable even after 100 cycles of cyclic extension by 120% or 100 cycles of bending with a radius of 1 mm. Hence, our sensor holds great potential for accurate monitoring of nanomole levels of Hb in clinical applications.

Self-Limiting Opto-Electrochemical Thinning of Transition-Metal Dichalcogenides.

Two-dimensional monolayer and few-layer transition-metal dichalcogenides (TMDs) are promising for advanced electronic and photonic applications due to their extraordinary optoelectronic and mechanical properties. However, it has remained challenging to produce high-quality TMD thin films with controlled thickness and desired micropatterns, which are essential for their practical implementation in functional devices. In this work, a self-limiting opto-electrochemical thinning (sOET) technique is developed for on-demand thinning and patterning of TMD flakes at high efficiency. Benefiting from optically enhanced electrochemical reactions, sOET features a low operational optical power density of down to 70 µW µm-2 to avoid photodamage and thermal damage to the thinned TMD flakes. Through selective optical excitation with different laser wavelengths based on the thickness-dependent band gaps of TMD materials, sOET enables precise control over the final thickness of TMD flakes. With the capability of thickness control and site-specific patterning, our sOET offers an effective route to fabricating high-quality TMD materials for a broad range of applications in nanoelectronics, nanomechanics, and nanophotonics.

Hygro-responsive, Photo-decomposed Superoleophobic/Superhydrophilic Coating for On-Demand Oil-Water Separation.

The superoleophobic/superhydrophilic material has attracted considerable interest due to the incomparable property of it for the oil-water separation. However, it is a challenge to make the prepared surface superoleophobic and superhydrophilic at the same time since the oleophobic surface tends to repel water. Herein, a hygro-responsive superoleophobic/superhydrophilic coating was fabricated by liquid-phase deposition of TiO2 with perfluorooctanoic acid. The wettability of the coating could complete the transformation from superoleophobicity/superhydrophilicity to superhydrophobicity/superoleophilicity, both of which exhibit excellent selective superwettability under the air, underwater, salt, alkali, and acid conditions. The hygro-responsive coating can separate different types of oil-water mixtures, and the separation efficiency could be over 99% using different capillary forces acting on the oil and water phases before and after wettability transformation. Last but not least, long-chain perfluoroalkyl substances on the coating could be decomposed by UV irradiation, which could reduce the harm to the environment and human beings. It is anticipated that the developed superoleophobic/superhydrophilic coating provides a feasible solution for the application of oil-water separation.

An Intelligent Graphene-Based Biosensing Device for Cytokine Storm Syndrome Biomarkers Detection in Human Biofluids.

Abnormal elevated levels of cytokines such as interferon (IFN), interleukin (IL), and tumor necrosis factor (TNF), are considered as one of the prognosis biomarkers for indicating the progression to severe or critical COVID-19. Hence, it is of great significance to develop devices for monitoring their levels in COVID-19 patients, and thus enabling detecting COVID-19 patients that are worsening and to treat them before they become critically ill. Here, an intelligent aptameric dual channel graphene-TWEEN 80 field effect transistor (DGTFET) biosensing device for on-site detection of IFN-γ, TNF-α, and IL-6 within 7 min with limits of detection (LODs) of 476 × 10-15 , 608 × 10-15 , or 611 × 10-15 m respectively in biofluids is presented. Using the customized Android App together with this intelligent device, asymptomatic or mild COVID-19 patients can have a preliminary self-detection of cytokines and get a warning reminder while the condition starts to deteriorate. Also, the device can be fabricated on flexible substrates toward wearable applications for moderate or even critical COVID-19 cases for consistently monitoring cytokines under different deformations. Hence, the intelligent aptameric DGTFET biosensing device is promising to be used for point-of-care applications for monitoring conditions of COVID-19 patients who are in different situations.

Superhydrophilic Al2O3 Particle Layer for Efficient Separation of Oil-in-Water (O/W) and Water-in-Oil (W/O) Emulsions.

The separation of oil-water emulsion using superliquiphobic/philic porous coated materials has attracted considerable attention for dealing with environmental pollution and resource recycling issues. The coatings used may lack adequate surface mechanical and chemical durability. This paper proposes a simple method without other modifications for separating the oil-water emulsion. A porous layer was fabricated by superhydrophilic Al2O3 particles, which could separate oil-water emulsions. The particle layer has the property of underwater superoleophobicity after prewetting. For the oil-in-water (O/W) emulsion separation, a 0.3 µm Al2O3 particle layer was used. This layer had a pore size less than about 1 µm to minimize oil flow and to obtain a purity of oil recovery greater than 99 wt %. For the water-in-oil (W/O) emulsion separation, a 40 µm Al2O3 superhydrophilic particle layer was used. Larger particles were used to provide a more porous surface to facilitate oil flow through the layer, resulting in a purity of water recovery purity greater than 99 wt %.

A Wearable and Deformable Graphene-Based Affinity Nanosensor for Monitoring of Cytokines in Biofluids.

A wearable and deformable graphene-based field-effect transistor biosensor is presented that uses aptamer-modified graphene as the conducting channel, which is capable of the sensitive, consistent and time-resolved detection of cytokines in human biofluids. Based on an ultrathin substrate, the biosensor offers a high level of mechanical durability and consistent sensing responses, while conforming to non-planar surfaces such as the human body and withstanding large deformations (e.g., bending and stretching). Moreover, a nonionic surfactant is employed to minimize the nonspecific adsorption of the biosensor, hence enabling cytokine detection (TNF-α and IFN-γ, significant inflammatory cytokines, are used as representatives) in artificial tears (used as a biofluid representative). The experimental results demonstrate that the biosensor very consistently and sensitively detects TNF-α and IFN-γ, with limits of detection down to 2.75 and 2.89 pM, respectively. The biosensor, which undergoes large deformations, can thus potentially provide a consistent and sensitive detection of cytokines in the human body.

Modulating the Linker Immobilization Density on Aptameric Graphene Field Effect Transistors Using an Electric Field.

Aptameric graphene-based field-effect transistors (A-GFETs) always employ linkers, which could immobilize on graphene through π-π stacking between contained pyrenyl groups and graphene, to anchor aptamers. Aptamer density is closely associated with the A-GFET sensitivity and determined by the linker density. Using known linker immobilization methods, the linker density is random, uncontrollable, and limited. In this work, we propose a novel linker immobilization method which can be used to effectively modulate the linker density using an electric field and further bridge the relationship between the linker density and the A-GFET sensitivity. Here, polar molecule 1-pyrenebutanoic acid succinimidyl ester (PASE) is used as a linker representative. In the electric field, PASE is arranged regularly with the electron-rich pyrenyl group forced toward graphene in the solution due to electrostatic repulsion, thereby making it possible to modulate the quantity of PASE molecules that could interact with graphene by tuning the electric field application and then realizing the regulation of the A-GFET sensitivity. Experimental results indicate that the limits of detection (LODs) of A-GFETs for detecting interleukin-6 (IL-6) and insulin can be significantly improved to be 618 and 766 fM, respectively, by applying an electric field at -0.3 V for 3 h during PASE immobilization.

Multifunctional TiO2-Based Superoleophobic/Superhydrophilic Coating for Oil-Water Separation and Oil Purification.

Materials that possess distinguishable superwettability toward oil and water have aroused widespread attention for their application in oil-water separation. Among them, a superoleophobic/superhydrophilic material is considered as the ideal candidate because of its antioil-fouling and water-wetting behavior; however, the fabrication is a challenge and there has been insufficient attention given to multipurpose applications in treating intricate mixtures. Herein, for the first time, a multifunctional superoleophobic/superhydrophilic coating integrated with a photocatalysis property was fabricated by the combination of polarity component-enhanced fluorosurfactant and titanium dioxide (TiO2) nanoparticles. The coating applied on stainless steel mesh preserves the ability to separate immiscible oil-water mixtures, whereas the coated cotton preserves the ability to separate both surfactant-stabilized oil-in-water and water-in-oil emulsions. Notably, benefiting from the photocatalysis property of titanium dioxide, the coating also can be used in liquid purification. Contaminated oil can be separated and purified by a separation-purification process, during which the oil-soluble contamination is degraded under ultraviolet (UV) irradiation. The multipurpose coating provides an alternative solution for oil-water remediations, which has prospects in intricate liquid treatment in industrial and domestic applications.

Pilot study on deformed bullet correlation.

Most studies on bullet identification address test fired bullets that have near pristine striated marks on the land engraved areas (LEAs). However, in case work, bullets found at a crime scene may be severely deformed or fragmented. The resulting missing, expanded, or distorted LEA striations can cause challenges in toolmark comparisons performed by examiners or algorithms. In this paper, an image reconstruction procedure is proposed that, in combination with the Congruent Matching Profile Segments (CMPS) profile comparison method, facilitates the algorithmic correlation of deformed bullets. Initial validation tests were conducted using 57 bullets, with varying degrees of fragmentation or deformation, that were fired from the same 9mm Luger caliber Luger pistol. The bullets spanned 7 different ammunition brands. The CMPS method was applied to correlate the LEA striation profiles extracted from LEA topography images that were corrected for pattern distortion. 15 bullet LEAs, out of 250 bullet LEAs that could be measured, had major distortions. Two sets of comparison tests were conducted, corresponding to a same source and specific source scenario: 1) comparison of the severely distorted LEAs with a near-pristine reference bullet, before and after image reconstruction, and 2) inter comparisons of distorted LEAs, before and after reconstruction. The reconstruction process significantly improved the correlation results when dealing with distorted bullet LEAs. In general, the improvement was larger for samples with relatively large deformation and good striation visibility. Samples with approximately parallel striations tend to have less improvement of CMPS results after profile reconstruction since the CMPS method itself can correct certain scale errors.

Fired bullet signature correlation using the Congruent Matching Profile Segments (CMPS) method.

We introduce the Congruent Matching Profile Segments (CMPS) method for objective comparison of striated tool marks and apply it to bullet signature correlations. The method is derived from the congruent matching cell (CMC) method developed for the comparison of impressed tool marks. The proposed method is designed to increase comparison accuracy by addressing the comparison challenges caused by striae profiles with different lateral scales, varying vertical (height) scales, and sections that are poorly marked or have little to no similarity. Instead of correlating the entire profiles extracted from striated tool marks, the method divides one of the compared profiles into segments. Each segment is then correlated with the other profile. The CMPS method uses the normalized cross-correlation function with multiple correlation peak inspection to determine the number of profile segments that have both significant topography similarity and a congruent registration position. Initial tests were performed on the land engraved areas (LEAs) of 35 bullets fired from 10 consecutively manufactured pistol barrels. The results show clear separation between the CMPS scores of the 549 known non-matching (KNM) LEA profiles and the 46 known matching (KM) LEA profiles. These results are an improvement over those obtained using the correlation coefficient score of whole profiles. The large number of CMPS segment correlations may facilitate a statistical approach to error rate estimations.

Ultraviolet-driven switchable superliquiphobic/superliquiphilic coating for separation of oil-water mixtures and emulsions and water purification.

Materials with switchable wettability by external stimuli are of interest in on-demand oil-water separation. Among these materials, ultraviolet (UV) light-stimuli TiO2-based materials are considered as predominant candidates due to the photoinduced superliquiphilicity of TiO2. Besides the photoinduced superliquiphilic property, the photocatalysis is another important intrinsic property of TiO2 which has applications in liquid purification. Therefore, TiO2-based material with these two properties can achieve both separation of diverse oil-water mixtures and liquid purification. In this study, a substrate-independent, UV-driven switchable superliquiphobic/superliquiphilic coating was developed by a facile one-pot method. The wettability of the coating can be rapidly switched between superhydrophobicity/superoleophilicity and superhydrophilicity/underwater superoleophobicity by UV irradiation and heating process, which can be used for on-demand separation of both immiscible oil-water mixtures and emulsions. Such a coating can also be used for the degradation of soluble contamination in water during UV irradiation due to the photocatalysis property of TiO2. The coating provides an effective solution for both on-demand oil-water separation and water purification, which is of interest in both industrial and domestic applications.

Sensitive detection of lung cancer biomarkers using an aptameric graphene-based nanosensor with enhanced stability.

We present an electrolyte-gated graphene field effect transistor (GFET) nanosensor using aptamer for rapid, highly sensitive and specific detection of a lung cancer biomarker interleukin-6 (IL-6) with enhanced stability. The negatively charged aptamer folds into a compact secondary conformation upon binding with IL-6, thus altering the carrier concentration of graphene and yielding a detectable change in the drain-source current Ids. Aptamer has smaller size than other receptors (e.g. antibodies), making it possible to bring the charged IL-6 more closely to the graphene surface upon affinity binding, thereby enhancing the sensitivity of the detection. Thanks to the higher stability of aptamer over antibodies, which degrade easily with increasing storage time, consistent sensing performance was obtained by our nanosensor over extended-time (>24 h) storage at 25 °C. Additionally, due to the GFET-enabled rapid transduction of the affinity recognition to IL-6, detection of IL-6 can be achieved in several minutes (<10 min). Experimental results indicate that this nanosensor can rapidly and specifically respond to the change in IL-6 levels with high consistency after extended-time storage and a detection limit (DL) down to 139 fM. Therefore, our nanosensor holds great potential for lung cancer diagnosis at its early stage.

Rapid, ultraviolet-induced, reversibly switchable wettability of superhydrophobic/superhydrophilic surfaces.

Controllable wettability is important for a wide range of applications, including intelligent switching, self-cleaning and oil/water separation. In this work, rapid switching and extreme wettability changes upon ultraviolet (UV) illumination were investigated. TiO2 nanoparticles were modified in solutions of trimethoxy(alkyl)silane, and the suspensions were sprayed on glass substrates. For such samples, the water contact angle (WCA) was shown to transition from a superhydrophobic (WCA ≈ 165°) to a superhydrophilic (WCA ≈ 0°) state within 10 min upon UV illumination and subsequent recovery to superhydrophobicity occurred after heat treatment. It was found that the changes in the trimethoxy(alkyl)silane upon UV illumination can explain the rapid decrease of the WCA from more than 165° to almost 0°. To further investigate the wettability transition, trimethoxy(alkyl)silane and Al2O3 nanoparticles (which are not photocatalytic) were mixed and spray-coated onto the glass substrates as the control samples. Then the unrecoverable change of trimethoxy(alkyl)silane under UV illumination can be confirmed. It was found that the presence of trimethoxy(alkyl)silane in the TiO2-trimethoxy(alkyl)silane coating served to speed up the super-wettability transition time from superhydrophobicity to superhydrophilicity, but also limited the number of wettability recycle times. With this understanding, the effect of the trimethoxy(alkyl)silane concentration on the number of recycle cycles was investigated.