Patricia Noguera

This work demonstrates an efficient and reproducible method for the covalent biofunctionalization of epoxy solder mask surfaces on printed circuit boards (PCBs) produced using a conventional manufacturing process, enabling the implementation of capacitive biosensors without the need for any additional PCB fabrication steps and thereby supporting low-cost biosensing applications. Surface activation was achieved using 600 mM 3-mercaptopropionic acid (3-MPA) and 600 mM EDC/NHS, followed by immobilization of 600 µM bovine serum albumin (BSA) as a model protein, achieving spatial variability below 10%. This methodology can be directly applied to other proteins by simply substituting the biomolecule of interest. ATR-FTIR analysis confirmed successful chemical modification through the appearance of characteristic carboxyl and amide bands, while BCA assays verified effective protein attachment. The sensing performance of the functionalized surface was evaluated using electrochemical impedance spectroscopy on interdigitated PCB-based electrodes. A clear decrease in the impedance module was observed at 1 MHz after BSA immobilization and subsequent anti-BSA binding with a variation of 2826 ± 235 Ω and 4214 ± 239 Ω respectively (p < 0.001). Remarkably, anti-BSA was detected at concentrations as low as 10 ppb. These results highlight not only the strong biochemical activity and stability of the modified solder mask surface, but also its potential for scalable, robust, and cost-effective PCB-integrated biosensors for clinical biomarker detection and point-of-care diagnostics, as well as other widespread diagnostic and sensing applications.

Current liquid-phase resonant biosensors, such as Quartz Crystal Microbalance, Surface Acoustic Wave, or Surface Plasmon Resonance, typically rely on specialized piezoelectric substrates or complex optical setups. These requirements often necessitate cleanroom fabrication, thereby limiting cost-effective scalability. This study presents a high-integration sensing platform based on standard Printed Circuit Board (PCB) technology, incorporating an embedded inductor within a fluidic system for real-time monitoring. This design leverages industrial manufacturing standards to achieve a compact, low-cost, and scalable architecture. Detection is governed by shifts in the resonance frequency of an LC tank circuit; specifically, increases in bulk ionic strength induce a frequency decrease, whereas biomolecular adsorption at the sensor surface leads to a frequency increase. This phenomenon can be explained by the modulation of the inter-turn capacitance, which is modeled as a combination of capacitive elements accounting for contributions from the bulk electrolyte and the surface-bound dielectric layer. Such divergent responses provide an intrinsic self-discriminating capability, allowing for the analytical differentiation between surface interactions and bulk effects. To the best of our knowledge, this is the first demonstration of an inductor-based resonant sensor fully embedded in a PCB fluidic architecture for continuous liquid-phase analyte monitoring. Validated through a protein-antibody model (Bovine Serum Albumin-anti-Bovine Serum Albumin), the sensor demonstrated a limit of detection of 1.7 ppm (0.026 mM) and a linear dynamic range of 31–211 ppm (0.47–3.2 mM). These performance metrics, combined with a reproducibility of 4 ± 3%, indicate that the platform meets the requirements for robust analytical applications. Its inherent simplicity and potential for miniaturization position this technology as a viable candidate for point-of-care diagnostics in diverse environments.

Purpose: This study explores the preferences for learning methods among the students of seven engineering disciplines in a Spanish technical university. The purpose of this paper is to investigate the students' views and from them contribute to the knowledge of the effectiveness of learning methodologies.Design/methodology/approach: An online anonymous questionnaire survey was adopted to collect students' perceptions. Seven learning methods were compared in seven engineering degrees. The authors sampled 1660 students, and 426 completed responses were analysed. In addition to a descriptive analysis of the results, a multiple correspondence analysis (MCA) was performed using R data processing software.Findings: It was found that project-based learning and problem-based learning were perceived as the more effective ones. MCA identified response patterns between the preference and the efficiency of learning methods showing that students can be classified into two groups according to their preferred level of activeness in learning.Research limitations/implications: The study focusses on a single technical university and not all engineering degrees could be sampled. However, five different engineering fields were studied and no significant differences among them were found.Practical implications: The results add up to the known literature showing that students have different learning needs and consequently they perceive some methods as more effective. Instructors can use this information to strengthen their learning activities. Results also suggest that students can be classified into two groups in relation to their level of activeness in learning. This can also help to enhance general student motivation if two paths with different levels of activeness are planned.Originality/value: No previous studies have compared several learning methods in different engineering fields. Thus, this study contributes to fill this gap and contributes to the body of evidence around learning methodologies from the perspective of students.

Xanthomonas arboricola pv. pruni is a quarantine pathogen and the causal agent of the bacterial spot disease of stone fruits and almond, a major threat to Prunus species. Rapid and specific detection methods are essential to improve disease management, and therefore a prototype of a lateral flow immunoassay (LFIA) was designed for the detection of X. arboricola pv. pruni in symptomatic field samples. It was developed by producing polyclonal antibodies which were then combined with carbon nanoparticles and assembled on nitrocellulose strips. The specificity of the LFIA was tested against 87 X. arboricola pv. pruni strains from different countries worldwide, 47 strains of other Xanthomonas species and 14 strains representing other bacterial genera. All X. arboricola pv. pruni strains were detected and cross-reactions were observed only with four strains of X. arboricola pv. corylina, a hazelnut pathogen that does not share habitat with X. arboricola pv. pruni. The sensitivity of the LFIA was assessed with suspensions from pure cultures of three X. arboricola pv. pruni strains and with spiked leaf extracts prepared from four hosts inoculated with this pathogen (almond, apricot, Japanese plum and peach). The limit of detection observed with both pure cultures and spiked samples was 10⁴ CFU ml^-1. To demonstrate the accuracy of the test, 205 samples naturally infected with X. arboricola pv. pruni and 113 samples collected from healthy plants of several different Prunus species were analyzed with the LFIA. Results were compared with those obtained by plate isolation and real time PCR and a high correlation was found among techniques. Therefore, we propose this LFIA as a screening tool that allows a rapid and reliable diagnosis of X. arboricola pv. pruni in symptomatic plants.

The present study demonstrates that carbon nanoparticles (CNPs) can be used as labels in microarrays. CNPs were used in nucleic acid microarray immunoassays (NAMIAs) for the detection of different Shiga toxin-producing Escherichia coli (STEC) virulence factors: four genes specific for STEC (vt1, vt2, eae, and ehxA) and the gene for E. coli 16S (hui). Optimization was performed using a Box–Behnken design, and the limit of detection for each virulence factor was established. Finally, this NAMIA using CNPs was tested with DNA from 48 field strains originating from cattle feces, and its performance was evaluated by comparing results with those achieved by the reference method q-PCR. All factors tested gave sensitivity and specificity values higher than 0.80 and efficiency values higher than 0.92. Kappa coefficients showed an almost perfect agreement (k > 0.8) between NAMIA and the reference method used for vt1, eae, and ehxA, and a perfect agreement (k = 1) for vt2 and hui. The excellent agreement between the developed NAMIA and q-PCR demonstrates that the proposed analytical procedure is indeed fit for purpose, i.e., it is valuable for fast screening of amplified genetic material such as E. coli virulence factors. This also proves the applicability of CNPs in microarrays.

The use of carbon nanoparticles is shown for the detection and identification of different Shiga toxin-producing Escherichia coli virulence factors (vt1, vt2, eae and ehxA) and a 16S control (specific for E. coli) based on the use of lateral flow strips (nucleic acid lateral flow immunoassay, NALFIA). Prior to the detection with NALFIA, a rapid amplification method with tagged primers was applied. In the evaluation of the optimised NALFIA strips, no cross-reactivity was found for any of the antibodies used. The limit of detection was higher than for quantitative PCR (q-PCR), in most cases between 10⁴ and 10⁵ colony forming units/mL or 0.1–0.9 ng/μL DNA. NALFIA strips were applied to 48 isolates from cattle faeces, and results were compared to those achieved by q-PCR. E. coli virulence factors identified by NALFIA were in very good agreement with those observed in q-PCR, showing in most cases sensitivity and specificity values of 1.0 and an almost perfect agreement between both methods (kappa coefficient larger than 0.9). The results demonstrate that the screening method developed is reliable, cost-effective and user-friendly, and that the procedure is fast as the total time required is <1 h, which includes amplification. Results achieved with multi-analyte NALFIA for E. coli virulence factors. First strip: blank; second to sixth strip: each of the STEC factors; seventh strip: all factors

Selected physical properties of 13 coconut coir dusts from Asia, America, and Africa were compared to physical properties of sphagnum peat. All properties studied differed significantly between and within sources, and from the peat. Coir dusts from India, Sri Lanka, and Thailand were composed mainly of pithy tissue, whereas most of those from Costa Rica, Ivory Coast, and Mexico contained abundant fiber which was reflected by a higher coarseness index (percentage by weight of particles larger than 1 mm in diameter). Coir dust was evaluated as a lightweight material, and its total porosity was above 94% (by volume). It also exhibited a high air content (from 24% to 89% by volume) but a low easily available and total water-holding capacity which ranged from –1 , respectively. Physical properties of coir dust were strongly dependent on particle size distribution. Both easily available and total water-holding capacity declined proportionally with increasing coarseness index, while air content was positively correlated. Relative hydraulic conductivity in the range of 0 to 10 kPa suction dropped as particle size increased. Coir dusts with a particle size distribution similar to peat showed comparatively higher aeration and lower capacity to hold total and easily available water. An air–water balance similar to that in peat became apparent in coir dust at a comparatively lower coarseness index (29% vs. 63% by weight in peat). Stepwise multiple regression analysis showed that particles with diameters in the range of 0.125 to 1 mm had a remarkable and highly significant impact on the physical properties studied, while particles 1 mm had only a slight or nonsignificant effect.

The use of compost with high salt concentration was evaluated, under commercial conditions, as a potential growing media constituent for vegetable transplant production. Two composts were prepared from sweet sorghum bagasse, pine bark, and either urea (compost A) or brewery sludge (compost B) as N source. Three vegetable species — broccoli (Brassica oleracea), tomato (Lycopersicum esculentum), and onion (Allium cepa) with different tolerance to salinity were used. Eleven substrates were formulated and tested: a control consisting of a moss peat-based commercial substrate; compost A; compost B; and, eight mixtures containing 33 or 67% by volume of each compost with either raw peat moss or commercial substrate as diluent. All the substrates prepared had suitable physical, physicochemical and chemical properties for use as growing media, except for the electrical conductivity (ranging from 3.20 to 13.21 dS m⁻¹) which was above the reference levels for soilless cultivation. Broccoli was the least affected by substrate salinity whilst tomato was the most. Onion transplants had an intermediate response to saline conditions. Tomato seed germination was markedly reduced when compost A, with a higher salt concentration, was used at a rate higher than 67%. Media prepared with either of the composts, and mixed with either a commercial substrate or peat in a rate up to 67%, did not cause any detrimental effect on the growth and nutritional status of broccoli, tomato and onion transplants, despite the high initial salinity of the substrates. These composts appear to be acceptable substitutes for Sphagnum peat in seed sowing mixtures.

The microstructure of the mesocarp pithy tissue and short-length fibres of 2 differently processed coconut coir dusts from Mexico and Sri Lanka was studied using scanning electron microscopy and compared with that of a Sphagnum moss peat. Selected physical properties of these materials were also determined for their use in potting media. The 2 coir dusts did not significantly differ in the microstructural parameters studied, whereas they differed remarkably in their particle size and therefore in their physical properties. Pithy tissue was the major constituent of coir dust. Coarse pithy tissue particles (larger than 1 mm) were highly porous, with an internal porosity of 41.0% by volume. These particles exhibited round-shaped external pores which ranged in diameter from 30 to 80 µm, with an average of 44.3 µm, and which accounted for a relative surface porosity of about 40.9%. By contrast, the cells of Sphagnum peat moss leaves showed oval-shaped pores of 20.1 × 11.5 µm, which accounted for a relative surface porosity of only 12.0%. The internal porosity of peat moss leaves was 51.1% by volume. The retting process (soaking in water) applied to the coconut husks in Sri Lanka partially degraded the pithy tissue and coir fibres. Coir dust from Mexico showed lower water-holding capacity and higher aeration than peat, whereas air–water relationships in coir dust from Sri Lanka were similar to those in peat. Although differences observed in microstructure and porosity characteristics could explain the differential physical properties of the three materials studied, the major reason was the different size distribution of their constituent particles.