A novel sensitive cell-based Love Wave biosensor for marine toxin detection

Integrating machine learning and biosensors in microfluidic devices: A review

Microfluidic devices are increasingly widespread in the literature, being applied to numerous exciting applications, from chemical research to Point-of-Care devices, passing through drug development and clinical scenarios. Setting up these microenvironments, however, introduces the necessity of locally controlling the variables involved in the phenomena under investigation. For this reason, the literature has deeply explored the possibility of introducing sensing elements to investigate the physical quantities and the biochemical concentration inside microfluidic devices. Biosensors, particularly, are well known for their high accuracy, selectivity, and responsiveness. However, their signals could be challenging to interpret and must be carefully analysed to carry out the correct information. In addition, proper data analysis has been demonstrated even to increase biosensors' mentioned qualities. To this regard, machine learning algorithms are undoubtedly among the most suitable approaches to undertake this job, automatically learning from data and highlighting biosensor signals' characteristics at best. Interestingly, it was also demonstrated to benefit microfluidic devices themselves, in a new paradigm that the literature is starting to name "intelligent microfluidics", ideally closing this benefic interaction among these disciplines. This review aims to demonstrate the advantages of the triad paradigm microfluidics-biosensors-machine learning, which is still little used but has a great perspective. After briefly describing the single entities, the different sections will demonstrate the benefits of the dual interactions, highlighting the applications where the reviewed triad paradigm was employed.

An electrochemiluminescent dual-signal immunosensor based on a Ru(bpy)32+-doped silica nanoparticle/copper nanocluster composite for okadaic acid detection

In this study, a sensitive dual-signal electrochemiluminescence (ECL) immunosensor was developed for okadaic acid (OA) detection utilizing copper nanoclusters (CuNCs) and Ru(bpy)32+-doped silica nanoparticles (RuSiNPs). Interestingly, the CuNCs could simultaneously enhance both cathodic (-0.95 V) and anodic (+1.15 V) ECL signals of RuSiNPs, forming a dual-signal ECL sensing platform. Further, RuSiNPs@CuNCs were used as immunomarkers by covalently conjugating them with an anti-OA monoclonal antibody (mAb) to form probes. Finally, dual ECL signals of the immunosensor were fabricated and showed good linear relationships with OA concentrations in the range of 0.05-70 ng mL-1, having a median inhibitory concentration (IC50) of 1.972 ng mL-1 and a limit of detection of 0.039 ng mL-1. Moreover, the constant ratio of the cathodic and anodic ECL peaks achieved self-calibration of the detection signal and improved the reliability of the results. Finally, we successfully applied the ECL sensor to detect OA in spiked oyster samples.

FEM Modeling Strategies: Application to Mechanical and Dielectric Sensitivities of Love Wave Devices in Liquid Medium

This paper presents an extended work on the Finite Element Method (FEM) simulation of Love Wave (LW) sensors in a liquid medium. Two models are proposed to simulate the multiphysical response of the sensor. Both are extensively described in terms of principle, composition and behavior, making their applications easily reproducible by the sensor community. The first model is a Representative Volume Element (RVE) simulating the transducer and the second focuses on the sensor's longitudinal (OXZ) cut which simulates the multiphysical responses of the device. Sensitivity of the LW device to variations in the rheological and dielectric properties of liquids is estimated and then compared to a large set of measurements issued from LW sensors presenting different technological characteristics. This integral approach allows for a deeper insight into the multiphysical behavior of the LW sensor. This article also explores the advantages and drawbacks of each model. Both are in good accordance with the measurements and could be used for various applications, for which a non-exhaustive list is proposed in the conclusion.

Advances in Biosensors for the Rapid Detection of Marine Biotoxins: Current Status and Future Perspectives

Marine biotoxins (MBs), harmful metabolites of marine organisms, pose a significant threat to marine ecosystems and human health due to their diverse composition and widespread occurrence. Consequently, rapid and efficient detection technology is crucial for maintaining marine ecosystem and human health. In recent years, rapid detection technology has garnered considerable attention for its pivotal role in identifying MBs, with advancements in sensitivity, specificity, and accuracy. These technologies offer attributes such as speed, high throughput, and automation, thereby meeting detection requirements across various scenarios. This review provides an overview of the classification and risks associated with MBs. It briefly outlines the current research status of marine biotoxin biosensors and introduces the fundamental principles, advantages, and limitations of optical, electrochemical, and piezoelectric biosensors. Additionally, the review explores the current applications in the detection of MBs and presents forward-looking perspectives on their development, which aims to be a comprehensive resource for the design and implementation of tailored biosensors for effective MB detection.

Finite Element Study for Mass Sensitivity of Love Surface Acoustic Wave Sensor with Si3N4-SiO2 Double-Covered Waveguiding Layer

Love surface acoustic wave (L-SAW) sensors are miniaturized, easy to integrate, and suitable for detection in liquid environments. In this paper, an L-SAW sensor with a thin Si3N4-SiO2 double-covered layer was proposed for samples with small mass loads. The output response, phase velocity of the acoustic wave, and the mass sensitivity were analyzed using the finite element method (FEM). The simulation results show that the Si3N4 layer with high wave velocity greatly weakens the limitation of SiO2 on the phase velocity. The phase velocity can reach about 4300 m/s, which can increase the frequency shift when the same mass load is applied. Within a certain range, the mass sensitivity of the sensor is enhanced with the increase in the total thickness of the waveguiding layer and the thickness ratio of Si3N4 in the double-covered layer. When the thickness ratio is 1:2, the peak value of the mass sensitivity of the sensor is approximately 50% higher than that achieved with only the SiO2 waveguiding layer. The surface average stress of the delay line region follows the same trend as the mass sensitivity. The increase in mass sensitivity is the result of the heightened stress on the sensor surface. This L-SAW sensor, featuring a double-covered waveguiding layer, demonstrates high sensitivity and a simple structure. The simulation results lay a foundation for the design and manufacture of SAW sensors.

Okadaic Acid Detection through a Rapid and Sensitive Amplified Luminescent Proximity Homogeneous Assay

Okadaic acid (OA), a marine biotoxin produced by microalgae, poses a significant threat to mariculture, seafood safety, and human health. The establishment of a novel, highly sensitive detection method for OA would have significant practical and scientific implications. Therefore, the purpose of this study was to develop an innovative approach for OA detection. A competitive amplified luminescent proximity homogeneous assay (AlphaLISA) was developed using the principle of specific antigen-antibody binding based on the energy transfer between chemiluminescent microspheres. The method was non-washable, sensitive, and rapid, which could detect 2 × 10-2-200 ng/mL of OA within 15 min, and the detection limit was 4.55 × 10-3 ng/mL. The average intra- and inter-assay coefficients of variation were 2.54% and 6.26%, respectively. Detection of the actual sample results exhibited a good correlation with high-performance liquid chromatography. In conclusion, a simple, rapid, sensitive, and accurate AlphaLISA method was established for detecting OA and is expected to significantly contribute to marine biotoxin research.

Single-stranded DNA binding protein coupled aptasensor with carbon-gold nanoparticle amplification for marine toxins detection assisted by a miniaturized absorbance reader

Okadaic acid (OA), one of the most widely distributed marine toxins worldwide poses a severe threat to human health. Previous sensing methods for OA detection are usually based on antigen-antibody binding mechanism. However, the drawbacks of antibodies especially the enzyme-labeled antibodies, such as the harsh storage condition and high cost, lead to significant challenges to OA detection in biological samples. To overcome these limitations, a single-stranded DNA binding protein (SSB) coupled aptasensor was developed for OA detection. SSB was incubated on the microplate as a substitute for conventional OA-protein conjugations. Carbon-gold nanoparticles were synthesized and labeled with horseradish peroxidase and thiol-modified aptamers to obtain a capture probe (CGNs@HRP-Apt) instead of the enzyme-labeled antibody for signal amplification. OA and SSB competed to bind with limited aptamers on CGNs@HRP-Apt probes followed by colorimetric assay to obtain the optical signals correlated to OA concentration. To achieve on-site detection, a miniaturized and multichannel absorbance reader (Smart-plate reader) was self-designed with full automation for OA detection. Utilizing the SSB coupled aptasensor and the Smart-plate reader, our approach enables cost-effective and on-site OA sensing with a detection range of 2.5-80 ppb and an ultra-low limit of detection of 0.68 ppb. Moreover, novel OA detection kits based on the SSB coupled aptasensor were prepared which can effectively reduce the cost by 15 times lower than that of commercial ELISA kits. Therefore, the developed platform provides a favorable and promising avenue for marine toxin detection in aquaculture and food safety.

Recent advances of surface acoustic wave-based sensors for noninvasive cell analysis

In the past years, the application of surface acoustic waves (SAWs) as sensors for biological applications has reached high relevance in the field of biotechnology. From rapid advances in designs and materials, new opportunities have emerged, especially for sensing of living cells. Additionally, the combination of SAW sensors with microfluidics and optical microscopy has expanded the market of possible applications. Differentiation of infected and healthy red blood cells or aggressive and nonaggressive tumor cells, and monitoring of wound healing, bacteria, or viral antigen concentrations via SAW-based sensors are only a few examples of recent achievements in cell biology. The rapid growth of this field requires frequent reviewing of the recent progress to maintain high research standards and promote future developments.

Love Wave Sensor with High Penetration Depth for Potential Application in Cell Monitoring

Love wave (L-SAW) sensors have been used to probe cell monolayers, but their application to detect changes beyond the focal adhesion points on cell monolayers, as viscosity changes on the cytoskeleton, has not been explored. In this work we present for the first time a Love wave sensor with tuned penetration depth and sensitivity to potentially detect mechanical changes beyond focal adhesion points of cell monolayers. We designed and fabricated a Love wave sensor operating at 30 MHz with sensitivity to detect viscous changes between 0.89 and 3.3 cP. The Love wave sensor was modeled using an acoustic transmission line model, whereas the response of interdigital transducers (IDTs) was modeled with the Campbell’s cross-field circuit model. Our design uses a substrate with a high electromechanical coupling coefficient (LiNbO₃ 36Y-X), and an 8-µm polymeric guiding layer (SU-8). The design aims to overcome the high insertion losses of viscous liquid environments, and the loss of sensitivity due to the low frequency. The fabricated sensor was tested in a fluidic chamber glued directly to the SU-8 guiding layer. Our experiments with liquids of viscosity similar to those expected in cell monolayers showed a measurable sensor response. In addition, experimentation with SaOs-2 cells within a culture medium showed measurable responses. These results can be of interest for the development of novel cell-based biosensors, and novel characterization tools for cell monolayers.

Novel SH-SAW Biosensors for Ultra-Fast Recognition of Growth Factors

In this study, we investigated a label-free time efficient biosensor to recognize growth factors (GF) in real time, which are of gran interesting in the regulation of cell division and tissue proliferation. The sensor is based on a system of shear horizontal surface acoustic wave (SH-SAW) immunosensor combined with a microfluidic chip, which detects GF samples in a dynamic mode. In order to prove this method, to our knowledge not previously used for this type of compounds, two different GFs were tested by two immunoreactions: neurotrophin-3 and fibroblast growth factor-2 using its polyclonal antibodies. GF detection was conducted via an enhanced sequential workflow to improve total test time of the immunoassay, which shows that this type of biosensor is a very promising method for ultra-fast recognition of these biomolecules due to its great advantages: portability, simplicity of use, reusability, low cost, and detection within a relatively short period of time. Finally, the biosensor is able to detect FGF-2 growth factor in a concentration wide range, from 1–25 µg/mL, for a total test time of ~15 min with a LOD of 130 ng/mL.

Acoustic Biosensors and Microfluidic Devices in the Decennium: Principles and Applications

Lab-on-a-chip (LOC) technology has gained primary attention in the past decade, where label-free biosensors and microfluidic actuation platforms are integrated to realize such LOC devices. Among the multitude of technologies that enables the successful integration of these two features, the piezoelectric acoustic wave method is best suited for handling biological samples due to biocompatibility, label-free and non-invasive properties. In this review paper, we present a study on the use of acoustic waves generated by piezoelectric materials in the area of label-free biosensors and microfluidic actuation towards the realization of LOC and POC devices. The categorization of acoustic wave technology into the bulk acoustic wave and surface acoustic wave has been considered with the inclusion of biological sample sensing and manipulation applications. This paper presents an approach with a comprehensive study on the fundamental operating principles of acoustic waves in biosensing and microfluidic actuation, acoustic wave modes suitable for sensing and actuation, piezoelectric materials used for acoustic wave generation, fabrication methods, and challenges in the use of acoustic wave modes in biosensing. Recent developments in the past decade, in various sensing potentialities of acoustic waves in a myriad of applications, including sensing of proteins, disease biomarkers, DNA, pathogenic microorganisms, acoustofluidic manipulation, and the sorting of biological samples such as cells, have been given primary focus. An insight into the future perspectives of real-time, label-free, and portable LOC devices utilizing acoustic waves is also presented. The developments in the field of thin-film piezoelectric materials, with the possibility of integrating sensing and actuation on a single platform utilizing the reversible property of smart piezoelectric materials, provide a step forward in the realization of monolithic integrated LOC and POC devices. Finally, the present paper highlights the key benefits and challenges in terms of commercialization, in the field of acoustic wave-based biosensors and actuation platforms.

Emerging on-chip surface acoustic wave technology for small biomaterials manipulation and characterization

A surface acoustic wave (SAW) is a sound wave travelling on the surface of an elastic material. SAW offers a robust control of the acoustic energy leading to an unparalleled versatility. As an actuator, SAW can exert acoustic forces on particles and fluids thus enabling dexterous micro/nanoscale manipulations. As a sensor, SAW has a unique sensing capability upon changes in the environment. On-chip SAW technology, in which SAW is integrated with modern lab-on-a-chip (LOC), has drawn a lot of attention in recent years and found various exciting applications in micro/nanosystems. In particular, its well-known biocompatibility provides on-chip SAW technology as an exceptional platform for biomaterials research at the small-scale. In this minireview, we highlighted recent advances of on-chip SAW technology for biomaterials manipulation and characterization with a focus on cell-based (e.g. single-cell and multicellular) biomaterials. We also discussed and shared our perspective on future directions for this emerging research field.

Recent advances in acoustic wave biosensors for the detection of disease-related biomarkers: A review

In the past several decades, acoustic wave biosensors, as an emerging kind of biosensors, have been developed and widely used for the detection of mass, viscosity, conductivity and density. Varieties of applications have been explored such as medical diagnosis, drug screening, environmental monitoring, food analysis and biochemical assay. Among them, the detection of disease-related biomarkers based on acoustic sensors has aroused great research interest all over the world. In this review, the classification and characteristics of acoustic wave biosensors are briefly introduced. Then, some classical studies and recent advances in disease-related biomarker detection utilizing these biosensors are summarized and detailed, respectively. Here, the disease-related biomarkers mainly include antigens, small molecular proteins, cancer cells, viruses and VOCs. Finally, challenges and future trends of these typical acoustic wave biosensors are discussed. Compared with other reviews of acoustic wave sensors, this review highlights the great potential of typical acoustic wave biosensors for early disease screening and diagnosis compared with widely-used medical imaging. Moreover, they are integrated with other technologies for the design of multi-analyte, multi-parameter and intelligent devices, collecting more comprehensive information from biomarkers. This review provides a new perspective on the applications and optimization of acoustic wave biosensors to develop more reliable platforms for disease-related biomarker detection and disease diagnosis.

Recent progress in micro/nano biosensors for shellfish toxin detection

Shellfish toxins, as one kind of marine toxin, have attracted worldwide attention due to their severe threat to food safety and human health. Therefore, it is highly essential and urgent to develop a low-cost and convenient method to detect these toxins. With the rapid advance in microfabrication processes, micro/nano biosensors provide novel approaches to address this issue. In addition to their features of low cost, portability, easy operation, high efficiency and high bioactivity, micro/nano biosensors have great potential to realize on-the-spot, rapid detection of shellfish toxins. This review focuses on the most recent advances in the development of micro/nano biosensors for shellfish toxin detection. These biosensors are mainly classified into five categories according to their transducer detection principles, which include optical devices, electrochemical sensors, electrochemiluminescence, field-effect transistors, and acoustic devices. Sensor strategies, toxin analytes, biosensitive elements, coupling methods and field detection performance are highlighted to discuss the applications of shellfish toxin detection. With advances in sensor technology, biomaterials, microfabrication and miniaturized electronics, micro/nano biosensors applied to in-field fast detection of shellfish toxins are expected to play a critical role in food safety, environmental monitoring, and foreign trade in the foreseeable future. Finally, the current challenges and future development trends of micro/nano biosensors for shellfish toxin detection are discussed.

Ensuring seafood safe to spoon: a brief review of biosensors for marine biotoxin monitoring

With harmful algal blooms, marine food poisoning caused by marine biotoxins frequently occurs and is life-threatening if severe. However, the conventional detection methods of marine toxins have a few limitations: low sensitivity and high-cost. Therefore, it is necessary to establish a fast and sensitive on-site detection method for real seafood sample. Biosensors based on aptamers, antibodies, and cells have been applied in marine toxins monitoring. This review presents the classification and toxic effects of marine toxins, and recent biosensor for marine toxin detection. In addition, we have compared the superiority and limitation of these biosensors. Finally, challenges and opportunities of biosensors in food safety detection were discussed. Considering the excellent results achieved by the aptasensor in the field of detection, it seems ready to be put into practical applications.

Shear-horizontal surface acoustic wave sensor for non-invasive monitoring of dynamic cell spreading and attachment in wound healing assays

A Love-wave based biosensor is introduced for analyzing a standardized wound healing assay by observing cell growth and quantifying cell detachment processes. Utilizing the piezoelectric material LiTaO3 36° XY-cut with a thin SiO2-cover layer, shear horizontal surface acoustic waves (SAW) are excited and detected by a set of Interdigital Transducers. Epithelial cells, being cultivated on the substrate and invading the sensors delay line cause a phase shift in the transmitted SAW signal. This phase shift correlates exactly with the surface coverage of the invading cells. After wound healing, emerging fluctuations in the phase shift signal provide information about the cell growth in a confluent cell layer. Additionally, the signal slope allows to quantify the cell detachment process induced by apoptosis, necrosis or cell lysis substances, respectively. Furthermore, culture conditions like temperature or osmolality can be simultaneously monitored by SAW. Based on a theoretical approach and using FEM simulations, we identified the acoustoelectric interaction as the main reason for the phase shift in various frequency- and time-dependent studies. Our model is validated by experimental data and allows predicting the phase change caused by variations in the cell-substrate distance or the volume ratio of the nucleus and the complete cell.

Current research progress of mammalian cell-based biosensors on the detection of foodborne pathogens and toxins

Foodborne diseases caused by pathogens and toxins are a serious threat to food safety and human health; thus, they are major concern to society. Existing conventional foodborne pathogen or toxin detection methods, including microbiological assay, nucleic acid-based assays, immunological assays, and instrumental analytical method, are time-consuming, labor-intensive and expensive. Because of the fast response and high sensitivity, cell-based biosensors are promising novel tools for food safety risk assessment and monitoring. This review focuses on the properties of mammalian cell-based biosensors and applications in the detection of foodborne pathogens (bacteria and viruses) and toxins (bacterial toxins, mycotoxins and marine toxins). We discuss mammalian cell adhesion and how it is involved in the establishment of 3D cell culture models for mammalian cell-based biosensors, as well as evaluate their limitations for commercialization and further development prospects.

Selection and application of aptamers with high-affinity and high-specificity against dinophysistoxin-1

Diarrhetic shellfish toxins (DSTs) are marine toxins distributed widely in the world, which pose a major threat to the health of mankind. Dinophysistoxin-1 (DTX-1) has the most potent toxicity in DSTs. However, the current detection methods have ethical problems and technical defects. Further research is needed, to develop a more suitable alternative to the supervision system. In this work, we successfully obtained an aptamer with high affinity and specificity bound to DTX-1 for the first time. After optimization, a core sequence of the aptamer with a higher K_D of 64 nM was obtained, while the binding mode of the core sequence and DTX-1 was explored. Based on this aptamer, we developed a biolayer interferometry (BLI) biosensor platform for DTX-1 detection. The aptasensor exhibited a broad detection range from 40 to 600 nM DTX-1 (linear range from 80 to 200 nM), and the low detection limit was 614 pM. Morever, the aptasensor showed good reproducibility and stability, which indicated that this novel aptasensor had broad development prospects for the sensitive and rapid detection of DTX-1.

For the first time, the aptamer of dinophysistoxin-1 was successfully obtained with high affinity and specificity by SELEX, and an aptasensor with a detection range from 40 to 600 nM was developed by biolayer interferometry.

Cell-based biosensors: Recent trends, challenges and future perspectives

Existing at the interface of biology and electronics, living cells have been in use as biorecognition elements (bioreceptors) in biosensors since the early 1970s. They are an interesting choice of bioreceptors as they allow flexibility in determining the sensing strategy, are cheaper than purified enzymes and antibodies and make the fabrication relatively simple and cost-effective. And with advances in the field of synthetic biology, microfluidics and lithography, many exciting developments have been made in the design of cell-based biosensors in the last about five years. 3D cell culture systems integrated with electrodes are now providing new insights into disease pathogenesis and physiology, while cardiomyocyte-integrated microelectrode array (MEA) technology is set to be standardized for the assessment of drug-induced cardiac toxicity. From cell microarrays for high-throughput applications to plasmonic devices for anti-microbial susceptibility testing and advent of microbial fuel cell biosensors, cell-based biosensors have evolved from being mere tools for detection of specific analytes to multi-parametric devices for real time monitoring and assessment. However, despite these advancements, challenges such as regeneration and storage life, heterogeneity in cell populations, high interference and high costs due to accessory instrumentation need to be addressed before the full potential of cell-based biosensors can be realized at a larger scale. This review summarizes results of the studies that have been conducted in the last five years toward the fabrication of cell-based biosensors for different applications with a comprehensive discussion on the challenges, future trends, and potential inputs needed for improving them.

A study of Love wave acoustic biosensors monitoring the adhesion process of tendon stem cells (TSCs)

The Love wave biosensor is considered to be one of the most promising probing methods in biomedical research and diagnosis, and has been applied to detect the mechano-biological behaviour of cells attached to the surface of the device. More efforts should be devoted to basic theoretical research and relevant device performance analysis that may contribute to the further developments of Love wave sensors. In this study, a 36º YX-LiTaO₃-based Love wave sensor with a parylene-C wave guiding layer was adopted as a cell-based biosensor to monitor the adhesion process of tendon stem/progenitor cells (TSCs), a newly discovered cell type in tendons. A theoretical model is proposed to describe the Love wave propagation, in which the adherent cells are considered as a uniform viscoelastic layer. The effects of viscoelastic cell layer and wave guiding layer on the propagation velocity υ and propagation loss (PL) are investigated. The numerical results indicate that adherent cell layers of different storage or loss shear modulus in certain ranges can induce pronounced and characteristic variations in υ and PL, revealing the potential of Love wave sensors to provide useful quantitative measures on cellular mechanical properties. The sensor response to the adhesion of TSCs exhibits high consistency with experimental observations, which demonstrates the Love wave biosensor as a very promising sensor platform for investigating cellular activities under multiple physiological conditions.

Study on Fabrication of ZnO Waveguide Layer for Love Wave Humidity Sensor Based on Magnetron Sputtering

The ZnO waveguide layer for the Love wave humidity sensor was fabricated by radio frequency (RF) magnetron sputtering technique using ZnO as the target material. To investigate the effect of RF magnetron sputtering temperature on the ZnO waveguide layer and Love wave device, a series of Love wave devices with ZnO waveguide layer were fabricated at different sputtering temperatures. The crystal orientation and microstructure of ZnO waveguide was characterized and analyzed, and the response characteristics of the Love wave device were analyzed by network analyzer. Furthermore, a humidity measurement system is designed, and the performance of the Love wave humidity sensor was measured and analyzed. The research results illustrate that the performance of the ZnO waveguide layer is improved when the sputtering temperature changes from 25 °C to 150 °C. However, when the sputtering temperature increases from 150 °C to 200 °C, the performance of the ZnO waveguide layer is degraded. Compared with the other sputtering temperatures, the ZnO waveguide layer fabricated at 150 °C has the best c-axis orientation and the largest average grain size (53.36 nm). The Love wave device has the lowest insertion loss at 150 °C. In addition, when the temperature of the measurement chamber is 25 °C and the relative humidity is in the range of 10% to 80%, the fabricated Love wave humidity sensor with ZnO waveguide layer has good reproducibility and long-term stability. Moreover, the Love wave humidity sensor has high sensitivity of 6.43 kHz/RH and the largest hysteresis error of the sensor is 6%.