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Biocementation consists in using urease enzyme and a solution rich in urea and in calcium to precipitate calcium carbonate (biocement). When applying this treatment in soils, the biocement minerals bond the grains improving overall soil’s hydro-mechanical properties. For the practical use of this technique, it is necessary to be able to predict the properties of the treated soil after following specific protocols, by preference avoiding non-destructive testing such as those performed on samples extracted after the treatment. The amount of biocement precipitated depends on the amount of urease enzyme, urea and calcium. This idea has inspired the development of one magnetoresistive biosensor to detect urease, to be used as a non-destructive monitoring tool during the treatment. A magnetoresistive platform was used to quantify the signal, which is related to the urease concentration through a calibration curve. The sensor was tested to measure the enzyme present in the inflow and outflow fluids used to treat cylindrical soil samples (2.5 cm diameter and 2.0 cm height), prepared with a uniform grading size sand (D50=0.3 mm). Purified urease from Canavalia ensiformis, was used. The improvement of the biocemented sand samples was quantified through measuring the calcium carbonate content of the soil after the treatment and the values were related with the amount of enzyme retained by the soil, determined using the sensor readings. This work found, for the first time, the relationship between the measured concentration of urease retained by soil and the calcium carbonate content precipitated. This relationship is an important tool for monitoring the treatment, without the need to use destructive tests or even stop the treatment.

The potato cyst nematode (PCN), Globodera pallida, has acquired significant importance throughout Europe due to its widespread prevalence and negative effects on potato production. Thus, rapid and reliable diagnosis of PCN is critical during surveillance programs and for the implementation of control measures. The development of innovative technologies to overcome the limitations of current methodologies in achieving early detection is needed. Lab-on-a-chip devices can swiftly and accurately detect the presence of certain nucleotide sequences with high sensitivity and convert the presence of biological components into an understandable electrical signal by combining biosensors with microfluidics-based biochemical analysis. In this study, a specific DNA-probe sequence and PCR primers were designed to be used in a magnetoresistive biosensing platform to amplify the internal transcribed spacer region of the ribosomal DNA of G. pallida. Magnetic nanoparticles were used as the labelling agents of asymmetric PCR product through biotin–streptavidin interaction. Upon target hybridization to sensor immobilized oligo probes, the fringe field created by the magnetic nanoparticles produces a variation in the sensor's electrical resistance. The detection signal corresponds to the concentration of target molecules present in the sample. The results demonstrate the suitability of the magnetic biosensor to detect PCR target product and the specificity of the probe, which consistently distinguishes G. pallida (DV/V > 1%) from other cyst nematodes (DV/V < 1%), even when DNA mixtures were tested at different concentrations. This shows the magnetic biosensor's potential as a bioanalytical device for field applications and border phytosanitary inspections. [ABSTRACT FROM AUTHOR]

The combination of a sensitive and specific magnetoresistive sensing device with an easy DNA extraction method and a rapid isothermal amplification is presented here targeting the on-site detection of Globodera pallida , a potato endoparasitic nematode. FTA-cards were used for DNA extraction, LAMP was the method developed for DNA amplification and a nanoparticle functionalized magnetic-biosensor was used for the detection. The combinatorial effect of these three emerging technologies has the capacity to detect G. pallida with a detection limit of one juvenile, even when mixed with other related species. This combined system is far more interesting than what a single technology can provide. Magnetic biosensors can be combined with any DNA extraction protocol and LAMP forming a new solution to target G. pallida . The probe designed in this study consistently distinguished G. pallida (∆V ac binding /V ac sensor above 1%) from other cyst nematodes (∆V ac binding /V ac sensor below 1%). It was confirmed that DNA either extracted with FTA-cards or Lab extraction Kit was of enough quantity and quality to detect G. pallida whenever present (alone or in mixed samples), ensuring probe specificity and sensitivity. This work provides insights for a new strategy to construct advanced devices for pathogens in-field diagnostics. LAMP runs separately but can be easily integrated into a single device., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Camacho, Albuquerque, Inácio, Martins, Mota, Freitas and de Andrade.)