Spark Ablation-Generated Nanoparticles on Filter Paper: A 3D SERS Platform for Cost-Effective and Rapid Thiram Sensing

In emergency medicine, the lactate level is commonly used as an indicator of the severity and response to the treatment of hypoperfusion-related diseases. Clinical lactate measurements generally require 3 h for clinical determination. To improve the current gold standard methods, the development of sensor devices that can reduce detection time while maintaining sensitivity and providing portability is gaining great attention. This study aimed to develop a polyaniline (PAni)-based single-sensor platform for sensing lactate in human sweat using a CIELAB color system-based colorimetric device. To establish a lactate sensing platform, PAni nanoparticles were synthesized and adsorbed on the filter paper surface using solvent shift and dip-coating methods, respectively. PAni is characterized by a chemical change accompanied by a color change according to the surrounding environment. To quantify the color change of PAni, a CIELAB color system-based colorimetric device was fabricated. The color change of PAni was measured according to the chemical state using a combination of a PAni-based filter paper sensor platform and a colorimetric device, based on the lactate concentration in deionized water. Finally, human sweat was spiked with lactate to measure the color change of the PAni-based filter paper sensor platform. Under these conditions, the combination of polyaniline-based sensor platforms and colorimetric systems has a limit of detection (LOD) and limit of quantitation (LOQ) of 1 mM, linearity of 0.9684, and stability of 14%. Tbe confirmed that the color of the substrate changes after about 30 s, and through this, the physical fatigue of the individual can be determined. In conclusion, it was confirmed through this study that a combination of the PAni paper sensor platform and colorimeter can detect clinically meaningful lactate concentration.

This paper aims to develop an automatic adjustment method (AAM) that integrates 3D sensor and dynamic balancing platform using 3D computer vision technology and dynamic balance algorithm to improve the efficiency of rotor dynamic balancing. Active rotor dynamic balancing process relies on technicians to mount washers on particular balance columns based on their experience, therefore uncertainty causes productivity decline. The proposed AAM introduce 3D sensors on active rotor dynamic balance machine to get 3D point cloud of rotor and balance columns. First, by 3D depth data, the background noise can be removed to detect the positions of axis center, key phasor and balance columns of rotor automatically. Second, combine with unbalance vector from dynamic balancing machine, the AAM system calculated the optimal balance configuration by the vector analysis algorithm. Experiments in industrial examples showed that, compared to conventional method, the proposed AAM requires fewer rounds to achieve acceptance. In contrast, the industrial rotor balancing method previously used by operators requires more than three rounds in average. That is, the proposed AAM can accurately analyze the dynamic balance and greatly reduce the redundant dynamic balance operations. In conclusion, compared to the conventional approach, the proposed AAM is superior in terms of efficiency, effectiveness and robustness in online optimization of rotor dynamic balance. Notably, the effectiveness of the AAM has also been confirmed by Taiwan manufacturers that use rotor dynamic balance machines.

Urea has attracted attention because of its various potential applications such as hydrogen production, fuel cells, fertilizers, and electrochemical sensors. [1] Their long-term usages can lead to soil acidification and eutrophication, disturbing the ecosystem.[2] As an end-product of human metabolism, urea is a crucial biomarker that can access various human disorders such as kidney and renal function. Thus, the rapid sensing of the urea level in urine can play an important role in diagnostic areas, especially point-of-care testing devices. Most electrochemical biosensors rely on the enzymatic method. However, the utilization of the enzyme for the sensors appears to be limited due to complex processes of enzyme immobilization, high cost, short shelf life from the denaturation of the enzyme. [3] To overcome the limitations from using enzyme, non-enzymatic catalyst, especially nickel oxide, has been attracted with the advantage of good stability re-usability, high sensitivity, simplicity, low cost, and an excellent catalytic activity on detection of urea by the formation of the redox couple of Ni(II) and Ni(III).[4]Despite many efforts to achieve a higher catalytic effect with bimetallic oxides with Co[5], Mo[6], and Mn[7], the improvement of electrochemical response of oxidation of urea is still challenging due to the low exposure of active sites. Therefore, the formation of hollow structured hierarchical catalysts can be considered to improve the sensitivity of urea detection besides exploration of highly performing compositions. Such a hierarchical structure will provide structural stability and facile transport channels for electrolytes by exploiting its inner and outer surface as active sites. For a flexible and disposable sensor platform, the paper has merit due to a porous cellulose matrix. The paper naturally allows a liquid sample to infiltrate the paper matrix by capillary force. Furthermore, the capillary force-driven transport can be utilized in the catalyst loading process to distribute the catalyst and conductive network uniformly within the paper, which made the fabrication process simpler and enhanced performance.In this study, the combination of the hierarchical structure of nickel oxide and the paper matrix has demonstrated an increase in the sensitivity toward electrochemical sensing of urea. A filter paper and CNTs were used for the porous matrix and the conductive network, respectively. The hierarchical nickel cobalt oxide was synthesized with a one-pot hydrothermal method with the variation of Ni:Co atomic ratio, and then applied to the paper substrate. The structure and morphology of paper-based electrodes were characterized by XRD, SEM, and EDS, and the electrochemical response was measured by a potentiostat. A detailed description of the fabrication of paper-based sensors and the effect of hierarchical structure and bimetallic composition will be presented.[1] B. K. Boggs, R. L. King, and G. G. Botte, “Urea electrolysis: direct hydrogen production from urine,” Chem. Commun., no. 32, pp. 4859–4861, Aug. 2009, doi: 10.1039/B905974A.[2] L. Liu, H. Mo, S. Wei, and D. Raftery, “Quantitative analysis of urea in human urine and serum by 1 H nuclear magnetic resonance,” Analyst, vol. 137, no. 3, pp. 595–600, 2012, doi: 10.1039/C2AN15780B.[3] K. Kim et al., “Fabrication of a Urea Biosensor for Real-Time Dynamic Fluid Measurement,” Sensors, vol. 18, no. 8, Art. no. 8, Aug. 2018, doi: 10.3390/s18082607.[4] Nie, Huagui, et al. "Non-enzymatic electrochemical detection of glucose using well-distributed nickel nanoparticles on straight multi-walled carbon nanotubes." Biosensors and Bioelectronics 30.1 (2011): 28-34.[5] Ding, Rui, et al. "Facile synthesis of mesoporous spinel NiCo2O4 nanostructures as highly efficient electrocatalysts for urea electro-oxidation." Nanoscale 6.3 (2014): 1369-1376.[6] Liang, Yanhui, et al. "Enhanced electrooxidation of urea using NiMoO4· xH2O nanosheet arrays on Ni foam as anode." Electrochimica Acta 153 (2015): 456-460.[7] Periyasamy, Sivakumar, et al. "Exceptionally active and stable spinel nickel manganese oxide electrocatalysts for urea oxidation reaction." ACS applied materials & interfaces 8.19 (2016): 12176-12185.

A rapid, precise, low cost, selective and sensitive paper-based electrochemical device for the determination of H2O2 in milk is described here. Commercially available varnish and a simple hand drawing method were used to develop the hydrophobic pattern to generate a hydrophilic detection zone on the filter paper. The electrode system was fabricated on the detection zone in order to detect H2O2 electrochemically. A commercially available graphite pencil and conductive silver ink were used to fabricate the counter electrode and pseudo-reference electrode, respectively. A paste of Prussian blue (PB) modified graphite, unmodified graphite and phenol-formaldehyde polymer were used to fabricate a PB modified graphite working electrode on paper. This modified electrode showed electrocatalytic activity towards the reduction of H2O2 and it was successfully used for the chronoamperometric detection of H2O2 at 0 V vs Ag reference electrode in 0.1 mol l-1 phosphate buffer, buffered at pH 6.0 in 0.1 mol l-1 KCl. Under optimum conditions, the calibration curve for the H2O2 determination was linear from 5 to 50 mmol l-1 with a detection limit (LoD = x ̅ + 3SD) of 4.0 mmol l-1. In addition, the PB modified graphite electrode showed selectivity for H2O2 detection in the presence of ascorbic acid, sucrose and citric acid.

The detection of iodide ions (I−), despite challenges due to low concentrations and potential masking, is crucial for studying physiological processes and diagnosing diseases. A colorimetric sensor was developed to improve I− ion monitoring and facilitate on-site detection based on filter paper, which is a cost-effective platform. The sensor observed color changes in response to the exposure of hydrogen peroxide (H2O2), 3,3′,5,5′-tetramethylbenzidine (TMB), from colorless to yellowish brown. The sensor demonstrated a detection limit of 0.125 × 10−6 M for I− ions in a relatively wide range of 0.01 to 15 × 10−6 M under optimized conditions including gel concentration, temperature, incubation time, TMB and H2O2 concentration, and pH. Furthermore, the proposed sensor was successfully employed in a variety of applications, such as biological (urine and blood serum), food (egg yolk and snacks), and environmental samples (tap water). The study established effective recoveries in complex media for visual on-site I− ion monitoring, indicating the developed assay as a potent, affordable, and practical platform.

Cylindrical conical gears with line contact. (in German) : I. Szekely, Rev. Roumaine Sci. Tech., Ser.Mecan. Appl., 10 (1) (1965) 217–228

Smart phone assisted detection and quantification of cyanide in drinking water by paper based sensing platform