Printed Circuit Board (PCB) Technology for Electrochemical Sensors and Sensing Platforms

Beyond Flexible: Unveiling the Next Era of Flexible Electronic Systems

Flexible electronics are integral in numerous domains such as wearables, healthcare, physiological monitoring, human-machine interface, and environmental sensing, owing to their inherent flexibility, stretchability, lightweight construction, and low profile. These systems seamlessly conform to curvilinear surfaces, including skin, organs, plants, robots, and marine species, facilitating optimal contact. This capability enables flexible electronic systems to enhance or even supplant the utilization of cumbersome instrumentation across a broad range of monitoring and actuation tasks. Consequently, significant progress has been realized in the development of flexible electronic systems. This study begins by examining the key components of standalone flexible electronic systems-sensors, front-end circuitry, data management, power management and actuators. The next section explores different integration strategies for flexible electronic systems as well as their recent advancements. Flexible hybrid electronics, which is currently the most widely used strategy, is first reviewed to assess their characteristics and applications. Subsequently, transformational electronics, which achieves compact and high-density system integration by leveraging heterogeneous integration of bare-die components, is highlighted as the next era of flexible electronic systems. Finally, the study concludes by suggesting future research directions and outlining critical considerations and challenges for developing and miniaturizing fully integrated standalone flexible electronic systems.

Enhanced Corrosion Protection of Printed Circuit Board Electronics using Cold Atmospheric Plasma-Assisted SiOx Coatings

The miniaturization and widespread deployment of electronic devices across diverse environments have heightened their vulnerability to corrosion, particularly affecting copper traces within printed circuit boards (PCBs). Conventional protective methods, such as conformal coatings, face challenges including the necessity for a critical thickness to ensure effective barrier properties and the requirement for multiple steps of drying and curing to eliminate solvent entrapment within polymer coatings. This study investigates cold atmospheric plasma (CAP) as an innovative technique for directly depositing ultrathin silicon oxide (SiOx) coatings onto copper surfaces to enhance corrosion protection in PCBs. A systematic investigation was undertaken to examine how the scanning speed of the CAP deposition head impacts the film quality and corrosion resistance. The research aims to determine the optimal scanning speed of the CAP deposition head that achieves complete surface coverage while promoting effective cross-linking and minimizing unreacted precursor entrapment, resulting in superior electrical barrier and mechanical properties. The CAP coating process demonstrated the capability of depositing SiOx onto copper surfaces at various thicknesses ranging from 70 to 1110 nm through a single deposition process by simply adjusting the scanning speed of the plasma head (5-75 mm/s). Evaluation of material corrosion barrier characteristics revealed that scanning speeds of 45 mm/s of the plasma deposition head provided an effective coating thickness of 140 nm, exhibiting superior corrosion resistance (30-fold) compared to that of uncoated copper. As a proof of concept, the efficacy of CAP-deposited SiOx coatings was demonstrated by protecting an LED circuit in saltwater and by coating printed circuits for potential agricultural sensor applications. These CAP-deposited coatings offer performance comparable to or superior to traditional conformal polymeric coatings. This research presents CAP-deposited SiOx coatings as a promising approach for effective and scalable corrosion protection in miniaturized electronics.

Performance analysis of capacitive soil moisture, temperature sensors and their applications at farmer's field

This study aims to assess the effectiveness of PCB-based capacitive soil moisture sensors for local field conditions. The electrical scheme of designed sensors has been presented in this study. The PCB-based capacitive soil moisture sensors are calibrated using a linear equation developed between analog values of capacitive sensors and soil moisture content measured from the gravimetric method. The performance of the designed soil moisture sensors was assessed at five different locations at varying depths (i.e., 15 cm, 30 cm, and 45 cm). The calibration results indicated a positive correlation between the soil moisture content and measurement frequency of the sensor for wheat crop, with R2 values of 0.72, 0.83, and 0.83 for 15 cm, 30 cm, and 45 cm depths, respectively. Results reveal that 85% of the sensors accurately detected the patterns in soil moisture fluctuations during the cropping period. The designed capacitive sensors demonstrated a maximum relative error of 5.87% for 45 cm depth. However, the relative error remained below 5% for the 15 cm and 30 cm soil depths. For the sugarcane crop, R2 values vary from 0.66 to 0.82, with the highest relative error of 5.22% at a 15 cm depth. These sensors offer a highly cost-effective solution for farmers, with the entire wireless sensor network system including one sensor node, three soil moisture sensors, and one soil temperature sensor, which is priced at approximately $150, making it a practical and affordable option for widespread adoption.

Design and Analysis of Receiver Coils with Multiple In-Series Windings for Inductive Eddy Current Angle Position Sensors Based on Coupling of Coils on Printed Circuit Boards

We present a method for improving the amplitude and angular error of inductive position sensors, by advancing the design of receiver coil systems with multiple windings on two layers of a printed circuit board. Multiple phase-shifted windings are connected in series, resulting in an increased amplitude of the induced voltage while decreasing the angular error of the sensor. The amplitude increase for a specific number of windings can be predicted in closed form. Windings are placed electrically in series by means of a differential connection structure, without adversely affecting the signal quality while requiring a minimal amount of space in the layout. Further, we introduce a receiver coil centerline function which specifically enables dense, space-constrained designs. It allows for maximization of the number of possible coil windings while minimizing the impact on angular error. This compromise can be fine-tuned freely with a shape parameter. The application to a typical rotary encoder design for motor control applications with five periods is presented as an example and analyzed in detail by 3D finite-element simulation of 18 different variants, varying both the number of windings and the type of centerline functions. The best peak-to-peak angular error achieved in the examples is smaller than 0.1° electrically (0.02° mechanically, periodicity 5) under nominal tolerance conditions, in addition to an amplitude increase of more than 170% compared to a conventional design which exhibits more than twice the angular error. Amplitude gains of more than 270% are achieved at the expense of increased angular error.

Development of a direct PMMA-PCB bonding method for low cost and rapid prototyping of microfluidic-based gas analysers

Rapid prototyping of microfluidic devices requires low cost materials and simple fabrication methods. PMMA and PCB have been used separately for the fabrication of microfluidic devices in a wide range of applications. Although the combined use of PMMA and PCB can have considerable merits, few works have been reported on the direct bonding of these materials. In this work we have investigated the fabrication of microfluidic devices using PMMA and PCB for the analysis of gaseous samples. In order to yield a reliable direct bonding method, four parameters including temperature, pressure, solvent and patterned interface material were experimentally investigated. Results of testing various prototypes showed that a patterned interface of concentric rectangular copper rings exposed to solvent at room temperature and under moderate pressure provided better adhesion strength, sealing and durability. After successful development of the PMMA-PCB direct bonding process, sample prototypes were designed and fabricated to practically assess the combined advantages of two materials. Presented concepts include implementation of heater on a PCB, array of gas sensors coupled with microchannels, serpentine microchannel and fast evaporation of liquid sample using an SMD resistor. It has been shown that advantages of utilizing PMMA such as fabricating the channel easily and with low cost, can be combined with benefits of a PCB including simple sensor installation and the use of copper tracks and electronic components for gas flow modulation. Moreover, it is possible to implement channel, circuit and other electronic components such as microprocessors on a single device.

Designed wrinkles for optical encryption and flexible integrated circuit carrier board

Patterns on polymers usually have different mechanical properties as those of the substrates, causing deformation or distortion and even detachment of the patterns from the polymer substrates. Herein, we present a wrinkling strategy, which utilizes photolithography to define the area of stress distribution by light-induced physical crosslinking of polymers and controls diffusion of residual solvent to redistribute the stress and then offers the same material for patterns as substrate by thermal polymerization, providing uniform wrinkles without worrying about force relaxation. The strategy allows the recording and hiding of up to eight switchable images in one place that can be read by the naked eye without crosstalk, applying the wrinkled polymer for optical anti-counterfeiting. The wrinkled polyimide film was also utilized to act as a substrate for the creation of fine copper circuit by a full-additive process. It generates flexible integrated circuit (IC) carrier board with copper wire density of 400% higher than that of the state-of-the-art in industry while fulfilling the standards for industrialization.

Fully Integrated Multiplexed Wristwatch for Real-Time Monitoring of Electrolyte Ions in Sweat

Considerable progress has already been made in sweat sensors based on electrochemical methods to realize real-time monitoring of biomarkers. However, realizing long-term monitoring of multiple targets at the atomic level remains extremely challenging, in terms of designing stable solid contact (SC) interfaces and fully integrating multiple modules for large-scale applications of sweat sensors. Herein, a fully integrated wristwatch was designed using mass-manufactured sensor arrays based on hierarchical multilayer-pore cross-linked N-doped porous carbon coated by reduced graphene oxide (NPCs@rGO-950) microspheres with high hydrophobicity as core SC, and highly selective monitoring simultaneously for K+, Na+, and Ca2+ ions in human sweat was achieved, exhibiting near-Nernst responses almost without forming an interfacial water layer. Combined with computed tomography, solid-solid interface potential diffusion simulation results reveal extremely low interface diffusion potential and high interface capacitance (598 μF), ensuring the excellent potential stability, reversibility, repeatability, and selectivity of sensor arrays. The developed highly integrated-multiplexed wristwatch with multiple modules, including SC, sensor array, microfluidic chip, signal transduction, signal processing, and data visualization, achieved reliable real-time monitoring for K+, Na+, and Ca2+ ion concentrations in sweat. Ingenious material design, scalable sensor fabrication, and electrical integration of multimodule wearables lay the foundation for developing reliable sweat-sensing systems for health monitoring.

Printed circuit boards: system automation and alternative matrix for biosensing

Circuit integration has revolutionized the diagnostic sector by improving the sensing ability and rapidity of biosensors. Bioelectronics has led to the development of point-of-care (PoC) devices, offering superior performance compared with conventional biosensing systems. These devices have lower production costs, are smaller, and have greater reproducibility, enabling the construction of compact sensing modules. Flexible upgrades to the fabrication pattern of the printed circuit board (PCB) remains the most reliable and consistent means so far, offering portability, wearability, a lower detection limit, and smart output integration to these devices. This review summarizes the advances in PCB technology for biosensing devices for introducing automation and their emerging application as an alternative matrix material for detecting various analytes.

Electrochemical detection of myeloperoxidase (MPO) in blood plasma with surface-modified electroless nickel immersion gold (ENIG) printed circuit board (PCB) electrodes

Printed circuit board (PCB) based biosensors have often utilized hard gold electroplating, that nullifies the cost advantages of this technology as compared to screen printed electrodes. Electroless nickel immersion gold (ENIG) is a popular gold deposition process widely used in PCB manufacturing, but vulnerable to pinhole defects and large surface roughness, which compromises biosensor performance. In this work, we present a method to address these challenges through electrodeposition of methylene blue (MB) to cover surface defects and improve electroactivity of ENIG PCB electrodes. We also demonstrate a process to realize in situ synthesis of gold nanoparticles (AuNPs) using acid-functionalized multi-walled carbon nanotubes (MWCNTs) as scaffold, that are used to immobilize antibody for the target molecule (myeloperoxidase: MPO, early warning biomarker for cardiovascular diseases) through a modified cysteamine/gluteraldehyde based process. The processing steps on the electrode surface are developed in a manner that do not compromise the integrity of the electrode, resulting in repeatable and reliable performance of the sensors. Further, we demonstrate a cost-effective microfluidic packaging process to integrate a capillary pump driven microfluidic channel on the PCB electrode for seamless introduction of samples for testing. We demonstrate the ability of the sensor to distinguish clinically abnormal concentrations of MPO from normal concentrations through extensive characterization using spiked serum and blood plasma samples, with a limit of detection of 15.79 ng/mL.

Flexible-fabricated sensor module with programmable magnetic actuators coupled to L-cysteine functionalized Ag@Fe3O4 complexes for Cu2+ detection in fish tissues

Heavy metal contamination for seafood, particularly fish, is arising great concerns, and consequentially it is necessary to develop a simple and direct detection method. In this work, Ag@Fe₃O₄ is successfully prepared by simple solvothermal method, and we present a flexible-fabricated sensor module with assembled programmable magnetic actuators. The resulting sensor integrates a three-electrode system with two programmable magnetic actuators at the bottom of the device, which regulates the amount of current by adjusting the brake to control the adsorption force and vibration. The L-Cysteine functionalized Ag@Fe₃O₄ is coated on the surface of the electrode, then the Cu²⁺ is dropped into the reaction tank. Its performance is studied by cyclic voltammetry and electrochemical impedance spectroscopy, and the key experimental conditions such as deposition potential, deposition time, and electrolyte pH are gradually optimized. Under optimal conditions, Cu²⁺ can be detected over a wide linear range (0.01 ~ 4 μM) and at a low LOD (0.34 nM). The results show that the proposed method has a good application prospect in the detection of Cu²⁺. This method is successfully applied to Cu²⁺ analysis in fish samples with an acceptable recovery of 93 ~ 102%.

A label-free electrochemical DNA biosensor used a printed circuit board gold electrode (PCBGE) to detect SARS-CoV-2 without amplification

The emergence of coronavirus disease 2019 (COVID-19) motivates continuous efforts to develop robust and accurate diagnostic tests to detect severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Detection of viral nucleic acids provides the highest sensitivity and selectivity for diagnosing early and asymptomatic infection because the human immune system may not be active at this stage. Therefore, this work aims to develop a label-free electrochemical DNA biosensor for SARS-CoV-2 detection using a printed circuit board-based gold substrate (PCBGE). The developed sensor used the nucleocapsid phosphoprotein (N) gene as a biomarker. The DNA sensor-based PCBGE was fabricated by self-assembling a thiolated single-stranded DNA (ssDNA) probe onto an Au surface, which performed as the working electrode (WE). The Au surface was then treated with 6-mercapto-1-hexanol (MCH) before detecting the target N gene to produce a well-oriented arrangement of the immobilized ssDNA chains. The successful fabrication of the biosensor was characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and atomic force microscopy (AFM). The DNA biosensor performances were evaluated using a synthetic SARS-CoV-2 genome and 20 clinical RNA samples from healthy and infected individuals through EIS. The developed DNA biosensor can detect as low as 1 copy per μL of the N gene within 5 minutes with a LOD of 0.50 μM. Interestingly, the proposed DNA sensor could distinguish the expression of SARS-CoV-2 RNA in a patient diagnosed with COVID-19 without any amplification technique. We believe that the proposed DNA sensor platform is a promising point-of-care (POC) device for COVID-19 viral infection since it offers a rapid detection time with a simple design and workflow detection system, as well as an affordable diagnostic assay.

A sprayed graphene transistor platform for rapid and low-cost chemical sensing

We demonstrate a novel and versatile sensing platform, based on electrolyte-gated graphene field-effect transistors, for easy, low-cost and scalable production of chemical sensor test strips. The Lab-on-PCB platform is enabled by low-boiling, low-surface-tension sprayable graphene ink deposited on a substrate manufactured using a commercial printed circuit board process. We demonstrate the versatility of the platform by sensing pH and Na⁺ concentrations in an aqueous solution, achieving a sensitivity of 143 ± 4 μA per pH and 131 ± 5 μA per log₁₀Na⁺, respectively, in line with state-of-the-art graphene chemical sensing performance.

Large-scale nano-biosensing technologies

Nanoscale technologies have brought significant advancements to modern diagnostics, enabling unprecedented bio-chemical sensitivities that are key to disease monitoring. At the same time, miniaturized biosensors and their integration across large areas enabled tessellating these into high-density biosensing panels, a key capability for the development of high throughput monitoring: multiple patients as well as multiple analytes per patient. This review provides a critical overview of various nanoscale biosensing technologies and their ability to unlock high testing throughput without compromising detection resilience. We report on the challenges and opportunities each technology presents along this direction and present a detailed analysis on the prospects of both commercially available and emerging biosensing technologies.

Flexible Film Bulk Acoustic Resonator Based on Low-Porosity β-Phase P(VDF-TrFE) Film for Human Vital Signs Monitoring

P(VDF-TrFE) is a promising material for flexible acoustic devices owing to its good piezoelectric performance and excellent stretchability. However, the high density of internal pores and large surface roughness of the conventional P(VDF-TrFE) results in a high propagation attenuation for acoustic waves, which limits its use in flexible acoustic devices. In this paper, a novel method based on two-step annealing is proposed to effectively remove the pores inside the P(VDF-TrFE) film and reduce its surface roughness. The obtained P(VDF-TrFE) film possesses excellent characteristics, including a high breakdown strength of >300 kV/mm, a high-purity β-phase content of more than 80%, and high piezoelectric coefficients (d₃₃) of 42 pm/V. Based on the low-porosity β-phase P(VDF-TrFE) film, we fabricated flexible film bulk acoustic resonators (FBARs) which exhibit high sharp resonance peaks. The pressure sensor was made by sandwiching the FBARs with two PDMS microneedle patches. Heartbeat and respiration rate monitoring were achieved using the pressure sensor. This work demonstrates the feasibility of high-performance flexible piezoelectric acoustic resonators based on low-porosity P(VDF-TrFE) films, which could see wider applications in the wearable sensors for both physical and chemical sensing.

Comprehensive characterization and environmental implications of spent telecommunication printed circuit boards: Towards a cleaner and sustainable environment

The management and prevention of environmental risks associated with spent telecommunications printed circuit boards (STPCBs) is a concerning issue worldwide. Recycling might be proposed as a proper method to overcome this issue. Despite knowing that, choosing a sustainable method is challenging because of STPCBs complexity. This problem was overcome by analyzing STPCBs using different analytical methods and metal speciation. Understanding these data is essential in selection strategies to maximize selective recycling of metals and to minimize environmental impact. This research focused on characterizing STPCBs based on their structural, morphological, physiochemical, surface, and thermal properties. The accurate measurement of metal contents, indicating 187,900 mg kg^-1 Cu, 22,540 mg kg^-1 Pb, 1320 mg kg^-1 Ag, and 205 mg kg^-1 Au elements, plus other base metals, revealed a remarkable potential value in STPCBs. The results of structural analyses indicated that the powder has a crystalline structure and consists of Cu, Sn and Pb phases as well as different functional groups. In addition, after evaluating the zeta potential of the sample, the isoelectric pH of the sample was observed to be 5.6, which indicates that the powder particles have a negative surface in an environment with a pH higher than this value. Further, the metal speciation via sequential extraction procedure was performed, which showed that a unique harsh recycling strategy is required due to the stable structure of STPCBs. According to the results of this analysis, the global contamination factor (GCF) value was 83.48, which indicates STPCBs have a high degree of contamination. Leaching tests and environmental criteria were also conducted on this waste. The findings suggest that STPCBs needs pretreatments before landfilling to lower the concentration of toxic metals. Also, waste extraction test was the most aggressive procedure to assess mobility. Achieving this information is considered an essential step to choosing the most efficient recycling methods that minimize environmental impact while maximizing selective recycling of metals.

The emerging role of open technologies for community-based improvement of cryopreservation and quality management for repository development in aquatic species

Genetic resources of aquatic species are of tremendous value, but worldwide these are maintained almost exclusively as live populations. This is extremely expensive and insecure, and largely results from a pervasive lack of production capability, quality management, and reproducibility in cryopreservation that are barriers in development of germplasm repositories. Community-based technology approaches are emerging that can stimulate research previously limited by a lack of affordable, customizable equipment. Open-access technologies can provide for custom design and fabrication not available through traditional manufacturing. This can assist repository development with robust sample production methods and strong quality management, and can greatly improve reproducibility and standardization. Open technologies can support establishment of new communities of users, makers, and developers that collectively strive to develop open hardware in a distributed (i.e., non-centralized) fashion that can yield aggregate throughput. This occurs through use of consumer-level tools, supplies, software, and equipment, free exchange of designs and modifications, and a shared sense of mission. For cryopreservation and repository development, we have identified 14 categories of open hardware for a processing pathway, and six categories for a quality management pathway. Open hardware offers economic incentives to develop repositories for aquatic species, something that has not occurred despite 70 years of research largely focused on protocol development rather than practical applications. Advanced development of custom scientific hardware enhancing open technologies will be facilitated by interdisciplinary collaboration across biological and engineering fields. This manuscript is a contribution to the Special Issue in memory of Dr. Duane Garner, a leader in the sperm biology.

Rotating-Coil Measurement System for Small-Bore-Diameter Magnet Characterization

Rotating-coil measurement systems are widely used to measure the multipolar fields of particle accelerator magnets. This paper presents a rotating-coil measurement system that aims at providing a complete data set for the characterization of quadrupole magnets with small bore diameters (26 mm). The PCB magnetometer design represents a challenging goal for this type of transducer. It is characterized by an aspect ratio 30% higher than the state of the art, imposed by the reduced dimension of the external radius of the rotating shaft and the necessity of covering the entire magnet effective length (500 mm or higher). The system design required a novel design for the mechanical asset, also considering the innovation represented by the commercial carbon fiber tube, housing the PCB magnetometer. Moreover, the measurement system is based primarily on standard and commercially available components, with simplified control and post-processing software applications. The system and its components are cross-calibrated using a stretched-wire system and another rotating-coil system. The measurement precision is established in a measurement campaign performed on a quadrupole magnet characterized by an inner bore diameter of 45 mm.

Portable electroanalytical nucleic acid amplification tests using printed circuit boards and open-source electronics

The realization of electrochemical nucleic acid amplification tests (NAATs) at the point of care (POC) is highly desirable, but it remains a challenge given their high cost and lack of true portability/miniaturization. Here we show that mass-produced, industrial standardized, printed circuit boards (PCBs) can be repurposed to act as near-zero cost electrodes for self-assembled monolayer-based DNA biosensing, and further integration with a custom-designed and low-cost portable potentiostat. To show the analytical capability of this system, we developed a NAAT using isothermal recombinase polymerase amplification, bypassing the need of thermal cyclers, followed by an electrochemical readout relying on a sandwich hybridization assay. We used our sensor and device for analytical detection of the toxic microalgae Ostreopsis cf. ovata as a proof of concept. This work shows the potential of PCBs and open-source electronics to be used as powerful POC DNA biosensors at a low-cost.

Chemical activation of commodity plastics for patterned electroless deposition of robust metallic films

A general approach to increase the adhesion of metal films to commodity plastic substrates using a metal-chelating polymer, polyethyleneimine, in conjunction with patterned electroless deposition is described. This general fabrication method is compatible with a diverse array of plastics and metals with properties applicable to flexible electronic circuits and electrochemical cells.

Efficient Point-of-Care Detection of Uric Acid in the Human Blood Sample with an Enhanced Electrocatalytic Response Using Nanocomposites of Cobalt and Mixed-Valent Molybdenum Sulfide

This work efficiently detects uric acid (UA) in a human blood sample using cobalt nanoparticle-immobilized mixed-valent molybdenum sulfide on the copper substrate in a point-of-care (PoC) device. The sensor electrode was fabricated by micromachining of Cu clad boards employing an engraver to generate a three-electrode system consisting of working electrode (WE), reference electrode (RE), and counter electrode (CE). The WE was subjected to physical vapor deposition of mixed-valent MoSx layers by a reaction between Mo(CO)6 and H2S at ∼200 °C using a simple setup following which CoNPs were electrochemically deposited. The RE and CE were covered with Ag/AgCl and Ag paste, respectively. A plasma separation membrane acted as the medium of UA/blood serum delivery to the electrodes. The material and electrochemical characterization confirmed that CoNPs over MoSx provided an enlarged electroactive surface for the direct electron transfer to achieve an enhanced electrocatalytic response. The binary combination of CoNPs and MoSx layers over the Cu electrode reduced the charge-transfer resistance by two times, enhanced the surface adsorption by more than two times, and yielded a high diffusion coefficient of 3.46 × 10-3 cm2/s. These interfacial effects facilitated the UA oxidation, leading to unprecedented mA range current density for UA sensing for the PoC device. The electrochemical detection tests in the PoC device revealed a sensitivity of 64.7 μA/μM cm-2, which is ∼50 times higher compared to the latest reported value (1.23 μA/μM cm-2), a high limit of detection of 5 nM, and shelf life of 6 months, confirming the synergistic effect-mediated high sensitivity under PoC settings. Interference tests confirmed no intervention of similar analytes. Tests on blood samples demonstrated a recovery percentage close to 100% in human serum UA, signifying the suitability of the nanocomposite-based sensor and the PoC device for clinical sensing applications.

Lab-on-PCB: One step away from the accomplishment of μTAS?

The techniques, protocols, and advancements revolving around printed circuit boards (PCBs) have been gaining sustained attention in the realm of micro-total analysis systems (μTAS) as more and more efforts are devoted to searching for standardized, highly reliable, and industry-friendly solutions for point-of-care diagnostics. In this Perspective, we set out to identify the current state in which the field of μTAS finds itself, the challenges encountered by researchers in the implementation of these technologies, and the potential improvements that can be targeted to meet the current demands. We also line up some trending innovations, such as 3D printing and wearable devices, along with the development of lab-on-PCB to increase the possibility of multifunctional biosensing activities propelled by integrated microfluidic networks for a wider range of applications, anticipating to catalyze the full potential of μTAS.

Printed Circuit Boards: The Layers' Functions for Electronic and Biomedical Engineering

This paper describes the fabrication opportunities that Printed Circuit Boards (PCBs) offer for electronic and biomedical engineering. Historically, PCB substrates have been used to support the components of the electronic devices, linking them using copper lines, and providing input and output pads to connect the rest of the system. In addition, this kind of substrate is an emerging material for biomedical engineering thanks to its many interesting characteristics, such as its commercial availability at a low cost with very good tolerance and versatility, due to its multilayer characteristics; that is, the possibility of using several metals and substrate layers. The alternative uses of copper, gold, Flame Retardant 4 (FR4) and silver layers, together with the use of vias, solder masks and a rigid and flexible substrate, are noted. Among other uses, these characteristics have been using to develop many sensors, biosensors and actuators, and PCB-based lab-on chips; for example, deoxyribonucleic acid (DNA) amplification devices for Polymerase Chain Reaction (PCR). In addition, several applications of these devices are going to be noted in this paper, and two tables summarizing the layers' functions are included in the discussion: the first one for metallic layers, and the second one for the vias, solder mask, flexible and rigid substrate functions.

Cost-Sensitive Siamese Network for PCB Defect Classification

After the production of printed circuit boards (PCB), PCB manufacturers need to remove defected boards by conducting rigorous testing, while manual inspection is time-consuming and laborious. Many PCB factories employ automatic optical inspection (AOI), but this pixel-based comparison method has a high false alarm rate, thus requiring intensive human inspection to determine whether alarms raised from it resemble true or pseudo defects. In this paper, we propose a new cost-sensitive deep learning model: cost-sensitive siamese network (CSS-Net) based on siamese network, transfer learning and threshold moving methods to distinguish between true and pseudo PCB defects as a cost-sensitive classification problem. We use optimization algorithms such as NSGA-II to determine the optimal cost-sensitive threshold. Results show that our model improves true defects prediction accuracy to 97.60%, and it maintains relatively high pseudo defect prediction accuracy, 61.24% in real-production scenario. Furthermore, our model also outperforms its state-of-the-art competitor models in other comprehensive cost-sensitive metrics, with an average of 33.32% shorter training time.

Development of a rapid and sensitive quantum dot nanobead-based double-antigen sandwich lateral flow immunoassay and its clinical performance for the detection of SARS-CoV-2 total antibodies

Owing to the over-increasing demands in resisting and managing the coronavirus disease 2019 (COVID-19) pandemic, development of rapid, highly sensitive, accurate, and versatile tools for monitoring total antibody concentrations at the population level has been evolved as an urgent challenge on measuring the fatality rate, tracking the changes in incidence and prevalence, comprehending medical sequelae after recovery, as well as characterizing seroprevalence and vaccine coverage. To this end, herein we prepared highly luminescent quantum dot nanobeads (QBs) by embedding numerous quantum dots into polymer matrix, and then applied it as a signal-amplification label in lateral flow immunoassay (LFIA). After covalently linkage with the expressed recombinant SARS-CoV-2 spike protein (RSSP), the synthesized QBs were used to determine the total antibody levels in sera by virtue of a double-antigen sandwich immunoassay. Under the developed condition, the QB-LFIA can allow the rapid detection of SARS-CoV-2 total antibodies within 15 min with about one order of magnitude improvement in analytical sensitivity compared to conventional gold nanoparticle-based LFIA. In addition, the developed QB-LFIA performed well in clinical study in dynamic monitoring of serum antibody levels in the whole course of SARS-CoV-2 infection. In conclusion, we successfully developed a promising fluorescent immunological sensing tool for characterizing the host immune response to SARS-CoV-2 infection and confirming the acquired immunity to COVID-19 by evaluating the SRAS-CoV-2 total antibody level in the crowd.

Utilising Commercially Fabricated Printed Circuit Boards as an Electrochemical Biosensing Platform

Printed circuit boards (PCBs) offer a promising platform for the development of electronics-assisted biomedical diagnostic sensors and microsystems. The long-standing industrial basis offers distinctive advantages for cost-effective, reproducible, and easily integrated sample-in-answer-out diagnostic microsystems. Nonetheless, the commercial techniques used in the fabrication of PCBs produce various contaminants potentially degrading severely their stability and repeatability in electrochemical sensing applications. Herein, we analyse for the first time such critical technological considerations, allowing the exploitation of commercial PCB platforms as reliable electrochemical sensing platforms. The presented electrochemical and physical characterisation data reveal clear evidence of both organic and inorganic sensing electrode surface contaminants, which can be removed using various pre-cleaning techniques. We demonstrate that, following such pre-treatment rules, PCB-based electrodes can be reliably fabricated for sensitive electrochemical biosensors. Herein, we demonstrate the applicability of the methodology both for labelled protein (procalcitonin) and label-free nucleic acid (E. coli-specific DNA) biomarker quantification, with observed limits of detection (LoD) of 2 pM and 110 pM, respectively. The proposed optimisation of surface pre-treatment is critical in the development of robust and sensitive PCB-based electrochemical sensors for both clinical and environmental diagnostics and monitoring applications.

An Impedimetric Sensing Probe Based on Printed Circuit Board Technology for Monitoring in Cryobiology Applications

Cryopreservation of living cells is an effective tool for protection, maintenance, and distribution of genetic resources, which involves exposure to cryogenic temperatures and requires precise control over various parameters to avoid potential cell damages. Hundreds of protocols have been reported for cryopreservation of aquatic species, but replicating them is challenging without a reliable monitoring technique during a cryopreservation process. In this work, we aim to use electrical impedance as a monitoring parameter to assist standardization of cryopreservation processes and reporting. Specifically, this paper reports an impedance sensing probe compatible with cryogenic temperatures and conventional containers in cryopreservation of aquatic species based on printed circuit board technology its characterization in cryopreservation conditions including different sperm extenders (buffer) compositions and concentrations, presence of cryoprotectant, and multiple cooling rates. The developed probe based on printed circuit board (PCB) technology shows a capability of measuring conditions during cryopreservation differentiating among samples with different buffer contents and cryoprotectants. The probe also demonstrates the capability to distinguish different cooling regimes and detect phase change phenomena. This PCB-based sensing platform provides quantitative impedance measurement data during the cryopreservation process at sample preparation, cooling, and while frozen. Technology such as this offers opportunities for improving the reproducibility of protocols generated by the aquatic species community and can be made widely available as open hardware.

A Radiolucent Electromagnetic Tracking System for Use with Intraoperative X-ray Imaging

In recent times, the use of electromagnetic tracking for navigation in surgery has quickly become a vital tool in minimally invasive surgery. In many procedures, electromagnetic tracking is used in tandem with X-ray technology to track a variety of tools and instruments. Most commercially available EM tracking systems can cause X-ray artifacts and attenuation due to their construction and the metals that form them. In this work, we provide a novel solution to this problem by creating a new radiolucent electromagnetic navigation system that has minimal impact on -ray imaging systems. This is a continuation of our previous work where we showed the development of the Anser open-source electromagnetic tracking system. Typical electromagnetic tracking systems operate by generating low frequency magnetic fields from coils that are located near the patient. These coils are typically made from copper, steel, and other dense radiopaque materials. In this work, we explore the use of low density aluminum to create these coils and we demonstrate that the effect on X-ray images is significantly reduced as a result of these novel changes in the materials used. The resulting field generator is shown to give at least a 60% reduction in the X-ray attenuation in comparison to our earlier designs. We verify that the system accuracy of approximately 1.5 mm RMS error is maintained with this change in design.

Recent Trends in Noble Metal Nanoparticles for Colorimetric Chemical Sensing and Micro-Electronic Packaging Applications

Noble metal NPs are highly attractive candidates because of their unique combination of physical, chemical, mechanical, and structural properties. A lot of developments in this area are still fascinating the materials research community, and are broadly categorized in various sectors such as chemical sensors, biosensors, Förster resonance energy transfer (FRET), and microelectronic applications. The related function and properties of the noble metals in these areas can be further tailored by tuning their chemical, optical, and electronic properties that are influenced by their size, shape, and distribution. The most widely used Au and Ag NPs in dispersed phase below 100 nm exhibit strong color change in the visible range which alters upon aggregation of the NPs. The chemical sensing of the analyte is influenced by these NPs aggregates. In this article, we have summarized the uniqueness of noble metal NPs, their synthesis methods, nucleation and growth process, and their important applications in chemical sensing, microelectronic packaging, and Förster resonance energy transfer.