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Polygalacturonase (PG) activity in plants can serve as an important index for plant disease. However, the conventional method to detect PG activity is a complex process and requires a skilled technician and expensive analytical equipment. In this study, a paper-based colorimetric sensor was developed based on the principle of the ruthenium red (RR) dye method for easy and simple measurement of PG activity. The proposed paper-based sensor has a three-layer structure for detection of PG activity in samples. The sensor sensitivity was enhanced by optimizing the pH of the sodium acetate buffer used in polygalacturonic acid (PGA)-RR complex formation and the reaction temperature for PG and the PGA-RR complex. Further, for quantitative analysis of PG activity, Delta RGB analysis was conducted to detect color changes in the sensing window of the sensor. Results presented that the linear measurement range of the paper sensor was 0.02–0.1 unit with the limit of detection of 0.02 unit, which showed a similar detection range, but a lower detection limit, compared to the spectrophotometry. Furthermore, PG activity based on culture condition was measured using samples from Sclerotium cepivorum to verify the potential application of the developed paper-based sensor in the field. The measured activity showed no statistically significant difference from the values obtained from the spectrophotometry at 95% confidence level. Therefore, the paper-based colorimetric sensor can be used to predict plant diseases in Allium crops during the stage of pathogen invasion, potentially contributing to the improvement of crop production. Image 1 • A paper-based colorimetric sensor for detecting PG activity is developed. • The linear measurement range of the paper sensor is 0.02–0.1 unit with the LOD of 0.02 unit. • The measured PG activity of the paper sensor using S. cepivorum samples is similar to that of the spectrophotometry. • The paper sensor has potential for the early detection of plant disease. [ABSTRACT FROM AUTHOR]

Free proline, termed proline, is a biomarker used for diagnosing drought stress in plants. A previously developed proline–ninhydrin reaction-based paper sensor could quickly and easily detect proline, but it was limited by low sensitivity. In this study, we developed an enclosed multilayer paper-based microfluidic sensor with high sensitivity for the quantitative detection of proline in plants. The multilayer paper-based sensor was manufactured using simple wax printing and origami methods, and contained an internal mixing channel to allow good mixing of the proline with ninhydrin, increasing the proline–ninhydrin reactivity and providing accurate and sensitive proline detection. By preloading ninhydrin onto the sample loading area, uniform coloration of the sensing window was achieved, allowing quantitative analysis of various proline concentrations using a constant reaction time. Only the sensing window and sample loading area were exposed to limit sample evaporation and contamination from the external environment. The LOD of the fabricated sensor was 23 μM, which is approximately 29-fold lower than that of the previously proposed paper sensor (657 μM). Samples were extracted from A. thaliana plants subjected to drought stress for proline detection. The proline concentrations measured using the developed paper sensor and a spectrophotometric method were not statistically significant at a confidence level of 95%. Therefore, the developed sensor can be applied to measure proline concentrations precisely in the field with a low detection limit. The developed paper-based sensor can be used to detect the early stages of drought in plants and thus improve crop productivity. Image 1 • An enclosed multilayer paper-based microfluidic sensor for proline quantification is manufactured. • The enclosed multilayer sensor structure avoids sample evaporation and contamination. • The sensor detects proline with a LOD of 23 μM. • The sensor is suitable for the early detection of drought stress in plants. • The measured proline concentration is similar to that measured by spectrometry. [ABSTRACT FROM AUTHOR]

We developed and characterized a paper-based microfluidic sensor for the on-site diagnosis of drought stress in plants. Proline was used as a biomarker for analyzing drought stress, which was extracted by a colorimetric method using the proline-ninhydrin reaction. Paper was used as the main sensor material for the on-site detection of proline as it is easily transportable and cost-effective. The paper-based sensor was fabricated using wax-printing and origami methods, and the sensor was precoated with ninhydrin to allow for easy and convenient on-site use. Furthermore, a sample-to-ninhydrin ratio of 1:2 was found to confer optimal sensitivity to the drought diagnosis sensor. The concentration of proline in a sample was quantified by red-green-blue analysis to determine the change in green color intensity levels in response to distinct proline concentrations, which were detected by the sensor. The limit of detection of proline using the devised sensor was 657 µM, and the green color intensity level decreased with increasing proline concentration. In addition, the sensor was validated in an experimental drought stress model with Arabidopsis and subjected to drought stress for 21 days, and the amount of proline detected was 10 mM. The devised paper-based microfluidic sensor highlights the possibility of the on-site evaluation of drought stress in plants with potential to be utilized in various agricultural areas in the future. [ABSTRACT FROM AUTHOR]

This paper describes a novel micro xy-stage, driven by double-hot arm horizontal thermal micro-actuators integrated with a piezoresistive sensor (PS) for low-voltage operation and precise control. This micro xy-stage structure is linked with chevron beams and optimized to amplify the displacement generated by the micro-actuators that provide a pull force to the movable platform. The PS employed for in situ displacement detection and feedback control is fabricated at the base of a cold arm, which minimizes the influence of temperature change induced by electro-thermal heating. The micro xy-stage structure is defined through the use of a simple micromachining process, released by backside wet etching with a special tool. For an input power of approximately 44 mW, each chevron actuator provides about 16 µm and the total displacement of the platform is close to 32 µm. The sensitivity of the PS is better than 1 mV µm-1, obtained from the amplified voltage output of the Wheatstone bridge circuit. The potential applications of the proposed micro xy-stage lie in micro- or nano-manipulation, as well as the positioning of ultra-small objects in nanotechnology. [ABSTRACT FROM AUTHOR]