Microfluidic chip coupled with optical biosensors for simultaneous detection of multiple analytes: A review

Liquid Biopsy on Microfluidics: From Existing Endogenous to Emerging Exogenous Biomarkers Analysis

Liquid biopsy is an appealing approach for early diagnosis and assessment of treatment efficacy in cancer. Typically, liquid biopsy involves the detection of endogenous biomarkers, including circulating tumor cells (CTCs), extracellular vesicles (EVs), circulating tumor DNA (ctDNA), circulating tumor RNA (ctRNA), and proteins. The levels of these endogenous biomarkers are higher in cancer patients compared to those in healthy individuals. However, the clinical application of liquid biopsy using endogenous biomarker analysis faces challenges due to its low abundance and poor stability in circulation. Recently, a promising strategy involving the engineering of exogenous probes has been developed to overcome these limitations. These exogenous probes are activated within the tumor microenvironment, generating distinct exogenous markers that can be easily distinguished from background biological signals. Alternatively, these exogenous probes can be labeled with intrinsic endogenous biomarkers in vivo and detected in vitro after metabolic processes. In this review, we primarily focus on microfluidic-based liquid biopsy techniques that allow for the transition from analyzing existing endogenous biomarkers to emerging exogenous ones. First, we introduce common endogenous biomarkers, as well as synthetic exogenous ones. Next, we discuss recent advancements in microfluidic-based liquid biopsy techniques for analyzing both existing endogenous and emerging exogenous biomarkers. Lastly, we provide insights into future directions for liquid biopsy on microfluidic systems.

Challenges of Using Whole-Cell Bioreporter for Assessment of Heavy Metal Bioavailability in Soil/Sediment

Soil and sediment contamination with heavy metals (HMs) is a critical environmental issue, posing significant risks to both ecosystems and human health. Whole-cell bioreporter (WCB) technology offers a promising alternative to traditional detection techniques due to its ability to rapidly assess the bioavailability of pollutants. Specifically, lights-on WCBs quantify pollutant bioavailability by measuring bioluminescence or fluorescence in response to pollutant exposure, demonstrating comparable accuracy to traditional methods for quantitative pollutant detection. However, when applied to soil and sediment, the signal intensity directly measured by WCBs is often attenuated due to interference from solid particles, leading to the underestimation of bioavailability. Currently, no standardized method exists to correct for this signal attenuation. This review provides a critical analysis of the benefits and limitations of traditional detection methods and WCB technology in assessing HM bioavailability in soil and sediment. Based on the approaches used to address WCB signal attenuation, correction methods are categorized into four types: the assumed negligible method, the non-inducible luminescent control method, the addition of a standard to a reference soil, and a pre-exposure bioreporter. We provide a comprehensive analysis of each method's applicability, benefits, and limitations. Lastly, potential future directions for advancing WCB technology are proposed. This review seeks to establish a theoretical foundation for researchers and environmental professionals utilizing WCB technology for pollutant bioavailability assessment in soil and sediment.

A Review on Optical Biosensors for Monitoring of Uric Acid and Blood Glucose Using Portable POCT Devices: Status, Challenges, and Future Horizons

The growing demand for real-time, non-invasive, and cost-effective health monitoring has driven significant advancements in portable point-of-care testing (POCT) devices. Among these, optical biosensors have emerged as promising tools for the detection of critical biomarkers such as uric acid (UA) and blood glucose. Different optical transduction methods, like fluorescence, surface plasmon resonance (SPR), and colorimetric approaches, are talked about, with a focus on how sensitive, specific, and portable they are. Despite considerable advancements, several challenges persist, including sensor stability, miniaturization, interference effects, and the need for calibration-free operation. This review also explores issues related to cost-effectiveness, data integration, and wireless connectivity for remote monitoring. The review further examines regulatory considerations and commercialization aspects of optical biosensors, addressing the gap between research developments and clinical implementation. Future perspectives emphasize the integration of artificial intelligence (AI) and healthcare for improved diagnostics, alongside the development of wearable and implantable biosensors for continuous monitoring. Innovative optical biosensors have the potential to change the way people manage their health by quickly and accurately measuring uric acid and glucose levels. This is especially true as the need for decentralized healthcare solutions grows. By critically evaluating existing work and exploring the limitations and opportunities in the field, this review will help guide the development of more efficient, accessible, and reliable POCT devices that can improve patient outcomes and quality of life.

A Large-field droplets for high-throughput Escherichia coli identification within one field of view

Droplet microfluidic chips have emerged as an efficient platform for single-cell analysis due to their high sensitivity, efficiency, and throughput, showing significant potential in pathogen detection. However, current droplet microfluidic chips encounter challenges in large-scale droplet quantification and precise imaging, rendering them unsuitable for the high-throughput pathogen detection required for a large number of samples. To address these issues, this study developed a high-precision fluorescence imaging system utilizing a confocal reflective fluorescence approach, which is an advanced microscopy technique that combines confocal microscopy and reflected fluorescence imaging. It can obtain fluorescence signal and reflected light signal in the sample at the same time, so as to provide richer and more comprehensive image information. The system offers a large field of view (17.8 mm × 17.8 mm) and high resolution (20 μm), enabling the rapid imaging of 30,000 droplets within 10 s, thereby significantly enhancing detection efficiency and automation. Additionally, the enzymatic reaction of Escherichia coli (E. coli) was implemented using the droplet microfluidic chip to validate the effectiveness of the optical imaging system, with results demonstrating the system's capability to accurately capture fluorescence changes during the reaction.

Microfluidic biosensors: revolutionizing detection in DNA analysis, cellular analysis, and pathogen detection

Microfluidic chips have emerged as versatile and powerful tools that enable the precise manipulation of fluids and bioparticles at the microscale. Their impact on detection applications is profound, offering advantages such as miniaturization, enhanced sensitivity, multiplexing capability, and integrated functions. These chips can be customized for specific techniques, such as DNA analysis, immunoassays, chemical sensing, and cell-based assays. With a wide range of types available, including Lab-on-a-Chip, droplet-based, paper-based, electrochemical, optical, and magnetic chips, they find applications in diverse fields such as medical diagnostics, DNA analysis, cell analysis, food safety testing, environmental monitoring, and industrial processes. This powerful technology replicates laboratory capabilities on miniature chip-scale devices, resulting in time and cost savings while enabling portability and field-use capability. Its impact spans genetic analysis, proteomic analysis, cell culture, biosensors, pathogen detection, and point-of-care diagnostics, playing a pivotal role in advancing chemical and biological analysis. The overall aim of this review is to provide an overview of the development of microfluidic biochips for biological detection and discuss their various applications.

Synergizing microfluidics and plasmonics: advances, applications, and future directions

In the past decade, interest in nanoplasmonic structures has experienced significant growth, owing to rapid advancements in materials science and the evolution of novel nanofabrication techniques. The activities in the area are not only leading to remarkable progress in specific applications in photonics, but also permeating to and synergizing with other fields. This review delves into the symbiosis between nanoplasmonics and microfluidics, elucidating fundamental principles on nanophotonics centered on surface plasmon-polaritons, and key achievements arising from the intricate interplay between light and fluids at small scales. This review underscores the unparalleled capabilities of subwavelength plasmonic structures to manipulate light beyond the diffraction limit, concurrently serving as fluidic entities or synergistically combining with micro- and nanofluidic structures. Noteworthy phenomena, techniques and applications arising from this synergy are explored, including the manipulation of fluids at nanoscopic dimensions, the trapping of individual nanoscopic entities like molecules or nanoparticles, and the harnessing of light within a fluidic environment. Additionally, it discusses light-driven fabrication methodologies for microfluidic platforms and, contrariwise, the use of microfluidics in the fabrication of plasmonic nanostructures. Pondering future prospects, this review offers insights into potential future developments, particularly focusing on the integration of two-dimensional materials endowed with exceptional optical, structural and electrical properties, such as goldene and borophene, which enable higher carrier densities and higher plasmonic frequencies. Such advancements could catalyze innovations in diverse applications, including energy harvesting, advanced photothermal cancer therapies, and catalytic processes for hydrogen generation and CO2 conversion.

Organoids meet microfluidics: recent advancements, challenges, and future of organoids-on-chip

Organoids are three-dimensional, miniaturized tissue-like structures derived from either stem cells or primary cells, emerging as powerful in vitro models for studying developmental biology, disease pathology, and drug discovery. These organoids more accurately mimic cell-cell interactions and complexities of human tissues compared to traditional cell cultures. However, challenges such as limited nutrient supply and biomechanical cue replication hinder their maturation and viability. Microfluidic technologies, with their ability to control fluid flow and mimic the mechanical environment of tissues, have been integrated with organoids to create organoid-on-chip models that address these limitations. These models not only improve the physiological relevance of organoids but also enable more precise investigation of disease mechanisms and therapeutic responses. By combining microfluidics and organoids, several advanced organoids-on-chip models have been developed to investigate mechanical and biochemical cues involved in disease progression. This review discusses various methods to develop organoids-on-chip and the recently established organoids-on-chip models with their advanced functions. Finally, we highlighted potential strategies to enhance the functionality of organoid models, aiming to overcome current limitations and bridge the gap between current cell culture models and clinical applications, advancing personalized medicine, and improving therapeutic testing.

Recent advances in receptor-based optical biosensors for the detection of multiplex biomarkers

Multiplex biosensors are highly sought-after tools in disease diagnosis. This technique involves the simultaneous sensing of multiple biomarkers, whose levels and ratios can provide a more comprehensive assessment of disease conditions compared to single biomarker detection. In most diseases like cancer due to its complexity, several biomarkers are involved in their occurrence. On the other hand, a single biomarker may be implicated in various diseases. Multiplex sensing employs various techniques, such as optical, electrochemical, and electrochemiluminescence methods. This comprehensive review focuses on optical multiplex sensing techniques, including surface plasmon resonance, localized surface plasmon resonance, fluorescence resonance energy transfer, chemiluminescence, surface-enhanced Raman spectroscopy, and photonic crystal sensors. The review delves into their mechanisms, materials utilized, and strategies for biomarker detection.

Multi-chromatic and multi-component lateral flow immunoassay for simultaneous detection of CP4 EPSPS, Bt-Cry1Ab, Bt-Cry1Ac, and PAT/bar proteins in genetically modified crops

A multi-chromatic and multi-component lateral flow immunoassay (MCMC-LFIA) was developed for simultaneous detection of CP4 EPSPS, Bt-Cry1Ab, Bt-Cry1Ac, and PAT/bar proteins in genetically modified (GM) crops. Captured antibodies specific to these exogenous proteins were separately immobilized on a nitrocellulose membrane as test zones. Multi-colored microspheres, used as visible multi-probes, were conjugated with corresponding antibodies and sprayed on the conjugate pad. The assay results can be visually interpreted within 10 min by observing the appearance of colored bands. The MCMC-LFIA demonstrated high sensitivity, with detection of limits of 7.8 ng/mL for CP4 EPSPS and 2.5 ng/mL for Bt-Cry1Ab, Bt-Cry1Ac, and PAT/bar proteins, significantly improving the performance of previously reported LFIAs. The MCMC-LFIA exhibited excellent specificity and was validated for practical use in field-based applications. The proposed MCMC-LFIA offers a rapid, sensitive, and user-friendly tool for the on-site large-scale screening of GM materials.

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.

Microneedles-Based Theranostic Platform: From the Past to the Future

Fully integrated theranostic devices are highly esteemed in clinical applications, offering immense potential in real-time disease monitoring and personalized care. Microneedles (MNs), as innovative and wearable devices, boast important advantages in biosensing and therapy, thus holding significant promise in the advancement of diagnostic and therapeutic platforms. Encouragingly, advancements in electrochemical sensing technology, micronano fabrication, and biocompatible materials are propelling momentum for MNs-based closed-loop systems, enhancing detection capabilities, biocompatibility, and cost-effectiveness. Moreover, the notable progress in integrating MN chips with other biochips signifies a frontier for growth. Successful clinical trials in target molecule monitoring and drug delivery domains herald excellent clinical translational prospects for the aforementioned theranostic platform. Finally, we delineate both challenges and opportunities in the development of integrated diagnostic and therapeutic MN systems, including continuous monitoring, intelligent control algorithms, safety, and regulatory considerations.

Aptamer Based Nanoprobes for Detection of Foodborne Virus in Food and Environment Samples: Recent Progress and Challenges

Accepting the fact that there is a huge number of virus particles in food that lead to several infectious diseases, eliminating of the foodborne virus from food is tangible. In 2020, the appearance of new SARS-CoV-2 variants had remarked the importance of food safety in our lives. Detection virus is a dynamic domain. Recently, many papers have tried to detect several foodborne viruses by using conventional sensing platforms including ELISA (enzyme-linked immunosorbent assay), PCR (polymerase chain reaction-based methods) and NASBA (nucleic acid sequence-based amplification). However, small sizes, low infective doses and discrete distribution of the foodborne virus have converted these microorganisms into the most challengeable pathogen in the food samples matrix. Foodborne virus detection exploiting aptamer-based biosensors has attracted considerable attention toward the numerous benefits of sourcing from aptamers in which a variety of viruses could be detected by conjugation of aptamer-virus. The development of multiple sensing methodologies and platforms in terms of aptasensor application in real food and environment samples has demonstrated promising results. In this review, we present the latest developments in myriad types of aptasensors (including electrochemical, optical and piezoelectric aptasensor) for the quantification of foodborne viruses. Working strategies, benefits and disadvantages of these platforms are argued.

A SAW-Based Programmable Controlled RNA Detecting Device: Rapid In Situ Cytolysis-RNA Capture-RNA Release-PCR in One Mini Chamber

Viral RNA detection is crucial in preventing and treating early infectious diseases. Traditional methods of RNA detection require a large amount of equipment and technical personnel. In this study, proposed a programmable controlled surface acoustic wave (SAW)-based RNA detecting device has been proposed. The proposed device can perform the entire viral RNA detection process, including cell lysis by cell-microparticle collision through SAW-induced liquid whirling, RNA capture by SAW-suspended magnetic beads, RNA elution through SAW-induced high streaming force, and PCR thermal cycling through SAW-generated heat. The device has completed all RNA detection steps in one mini chamber, requiring only 489 µl reagents for RNA extraction, much smaller than the amount used in manual RNA extraction (2065 µl). The experimental results have shown that PCR results from the device are comparable to those achieved via commercial qPCR instrumental detection. This work has demonstrated the potential of SAW-based lab-on-a-chip devices for point-of-care testing and provided a novel approach for rapidly detecting infectious diseases.

Unpacking the packaged optical fiber bio-sensors: understanding the obstacle for biomedical application

A biosensor is a promising alternative tool for the detection of clinically relevant analytes. Optical fiber as a transducer element in biosensors offers low cost, biocompatibility, and lack of electromagnetic interference. Moreover, due to the miniature size of optical fibers, they have the potential to be used in microfluidic chips and in vivo applications. The number of optical fiber biosensors are extensively growing: they have been developed to detect different analytes ranging from small molecules to whole cells. Yet the widespread applications of optical fiber biosensor have been hindered; one of the reasons is the lack of suitable packaging for their real-life application. In order to translate optical fiber biosensors into clinical practice, a proper embedding of biosensors into medical devices or portable chips is often required. A proper packaging approach is frequently as challenging as the sensor architecture itself. Therefore, this review aims to give an unpack different aspects of the integration of optical fiber biosensors into packaging platforms to bring them closer to actual clinical use. Particularly, the paper discusses how optical fiber sensors are integrated into flow cells, organized into microfluidic chips, inserted into catheters, or otherwise encased in medical devices to meet requirements of the prospective applications.

Advancing Microfluidic Immunity Testing Systems: New Trends for Microbial Pathogen Detection

Pathogenic microorganisms play a crucial role in the global disease burden due to their ability to cause various diseases and spread through multiple transmission routes. Immunity tests identify antigens related to these pathogens, thereby confirming past infections and monitoring the host's immune response. Traditional pathogen detection methods, including enzyme-linked immunosorbent assays (ELISAs) and chemiluminescent immunoassays (CLIAs), are often labor-intensive, slow, and reliant on sophisticated equipment and skilled personnel, which can be limiting in resource-poor settings. In contrast, the development of microfluidic technologies presents a promising alternative, offering automation, miniaturization, and cost efficiency. These advanced methods are poised to replace traditional assays by streamlining processes and enabling rapid, high-throughput immunity testing for pathogens. This review highlights the latest advancements in microfluidic systems designed for rapid and high-throughput immunity testing, incorporating immunosensors, single molecule arrays (Simoas), a lateral flow assay (LFA), and smartphone integration. It focuses on key pathogenic microorganisms such as SARS-CoV-2, influenza, and the ZIKA virus (ZIKV). Additionally, the review discusses the challenges, commercialization prospects, and future directions to advance microfluidic systems for infectious disease detection.

Integrating target-responsive microfluidic-based biosensing chip with smartphone for simultaneous quantification of multiple fluoroquinolones

The presence of fluoroquinolone (FQs) antibiotic residues in the food and environment has become a significant concern for human health and ecosystems. In this study, the background-free properties of upconversion nanoparticles (UCNPs), the high specificity of the target aptamer (Apt), and the high quenching properties of graphene oxide (GO) were integrated into a microfluidic-based fluorescence biosensing chip (MFBC). Interestingly, the microfluidic channels of the MFBC were prepared by laser-printing technology without the need for complex preparation processes and additional specialized equipment. The target-responsive fluorescence biosensing probes loaded on the MFBC were prepared by self-assembly of the UCNPs-Apt complex with GO based on π-π stacking interactions, which can be used for the detection of the two FQs on a large scale without the need for multi-step manipulations and reactions, resulting in excellent multiplexed, automated and simultaneous sensing capabilities with detection limits as low as 1.84 ng/mL (enrofloxacin) and 2.22 ng/mL (ciprofloxacin). In addition, the MFBC was integrated with a smartphone into a portable device to enable the analysis of a wide range of FQs in the field. This research provides a simple-to-prepare biosensing chip with great potential for field applications and large-scale screening of FQs residues in the food and environment.

Microfluidic sensors for the detection of emerging contaminants in water: A review

In recent years, numerous emerging contaminants have been identified in surface water, groundwater, and drinking water. Developing novel sensing methods for detecting diverse emerging pollutants in water is urgently needed, as even at low concentrations, these pollutants can pose a serious threat to human health and environmental safety. Traditional testing methods are based on laboratory equipment, which is highly sensitive but complex to operate, costly, and not suitable for on-site monitoring. Microfluidic sensors offer several benefits, including rapid evaluation, minimal sample usage, accurate liquid manipulation, compact size, automation, and in-situ detection capabilities. They provide promising and efficient analytical tools for high-performance sensing platforms in monitoring emerging contaminants in water. In this paper, recent research advances in microfluidic sensors for the detection of emerging contaminants in water are reviewed. Initially, a concise overview is provided about the various substrate materials, corresponding microfabrication techniques, different driving forces, and commonly used detection techniques for microfluidic devices. Subsequently, a comprehensive analysis is conducted on microfluidic detection methods for endocrine-disrupting chemicals, pharmaceuticals and personal care products, microplastics, and perfluorinated compounds. Finally, the prospects and future challenges of microfluidic sensors in this field are discussed.

Micro- and Nanofluidic pH Sensors Based on Electrodiffusioosmosis

Recently, various kinds of micro- and nanofluidic functional devices have been proposed, where a large surface-to-volume ratio often plays an important role in nanoscale ion transport phenomena. Ionic current analysis methods for ions, molecules, nanoparticles, and biological cells have attracted significant attention. In this study, focusing on ionic current rectification (ICR) caused by the separation of cation and anion transport in nanochannels, we successfully induce electrodiffusioosmosis with concentration differences between protons separated by nanochannels. The proton concentration in sample solutions is quantitatively evaluated in the range from pH 1.68 to 10.01 with a slope of 243 mV/pH at a galvanostatic current of 3 nA. Herein, three types of micro- and nanochannels are proposed to improve the stability and measurement accuracy of the current-voltage characteristics, and the ICR effects on pH analysis are evaluated. It is found that a nanochannel filled with polyethylene glycol exhibits increased impedance and an improved ICR ratio. The present principle is expected to be applicable to various types of ions.

Recent advances in smart wearable sensors for continuous human health monitoring

In recent years, the biochemical and biological research areas have shown great interest in a smart wearable sensor because of its increasing prevalence and high potential to monitor human health in a non-invasive manner by continuous screening of biomarkers dispersed throughout the biological analytes, as well as real-time diagnostic tools and time-sensitive information compared to conventional hospital-centered system. These smart wearable sensors offer an innovative option for evaluating and investigating human health by incorporating a portion of recent advances in technology and engineering that can enhance real-time point-of-care-testing capabilities. Smart wearable sensors have emerged progressively with a mixture of multiplexed biosensing, microfluidic sampling, and data acquisition systems incorporated with flexible substrate and bodily attachments for enhanced wearability, portability, and reliability. There is a good chance that smart wearable sensors will be relevant to the early detection and diagnosis of disease management and control. Therefore, pioneering smart wearable sensors into reality seems extremely promising despite possible challenges in this cutting-edge technology for a better future in the healthcare domain. This review presents critical viewpoints on recent developments in wearable sensors in the upcoming smart digital health monitoring in real-time scenarios. In addition, there have been proactive discussions in recent years on materials selection, design optimization, efficient fabrication tools, and data processing units, as well as their continuous monitoring and tracking strategy with system-level integration such as internet-of-things, cyber-physical systems, and machine learning algorithms.

Mesophilic Argonaute-Based Single Polystyrene Sphere Aptamer Fluorescence Platform for the Multiplexed and Ultrasensitive Detection of Non-Nucleic Acid Targets

The rapid, simultaneous, and accurate identification of multiple non-nucleic acid targets in clinical or food samples at room temperature is essential for public health. Argonautes (Agos) are guided, programmable, target-activated, next-generation nucleic acid endonucleases that could realize one-pot and multiplexed detection using a single enzyme, which cannot be achieved with CRISPR/Cas. However, currently reported thermophilic Ago-based multi-detection sensors are mainly employed in the detection of nucleic acids. Herein, this work proposes a Mesophilic Argonaute Report-based single millimeter Polystyrene Sphere (MARPS) multiplex detection platform for the simultaneous analysis of non-nucleic acid targets. The aptamer is utilized as the recognition element, and a single millimeter-sized polystyrene sphere (PSmm) with a large concentration of guide DNA on the surface served as the microreactor. These are combined with precise Clostridium butyricum Ago (CbAgo) cleavage and exonuclease I (Exo I) signal amplification to achieve the efficient and sensitive recognition of non-nucleic acid targets, such as mycotoxins (<60 pg mL-1) and pathogenic bacteria (<102 cfu mL-1). The novel MARPS platform is the first to use mesophilic Agos for the multiplex detection of non-nucleic acid targets, overcoming the limitations of CRISPR/Cas in this regard and representing a major advancement in non-nucleic acid target detection using a gene-editing-based system.

Automatic Microfluidic Harmonized RAA-CRISPR Diagnostic System for Rapid and Accurate Identification of Bacterial Respiratory Tract Infections

Respiratory tract infections (RTIs) pose a grave threat to human health, with bacterial pathogens being the primary culprits behind severe illness and mortality. In response to the pressing issue, we developed a centrifugal microfluidic chip integrated with a recombinase-aided amplification (RAA)-clustered regularly interspaced short palindromic repeats (CRISPR) system to achieve rapid detection of respiratory pathogens. The limitations of conventional two-step CRISPR-mediated systems were effectively addressed by employing the all-in-one RAA-CRISPR detection method, thereby enhancing the accuracy and sensitivity of bacterial detection. Moreover, the integration of a centrifugal microfluidic chip led to reduced sample consumption and significantly improved the detection throughput, enabling the simultaneous detection of multiple respiratory pathogens. Furthermore, the incorporation of Chelex-100 in the sample pretreatment enabled a sample-to-answer capability. This pivotal addition facilitated the deployment of the system in real clinical sample testing, enabling the accurate detection of 12 common respiratory bacteria within a set of 60 clinical samples. The system offers rapid and reliable results that are crucial for clinical diagnosis, enabling healthcare professionals to administer timely and accurate treatment interventions to patients.

A review of SERS coupled microfluidic platforms: From configurations to applications

Microfluidic systems have attracted considerable attention due to their low reagent consumption, short analysis time, and ease of integration in comparison to conventional methods, but still suffer from shortcomings in sensitivity and selectivity. Surface enhanced Raman scattering (SERS) offers several advantages in the detection of compounds, including label-free detection at the single-molecule level, and the narrow Raman peak width for multiplexing. Combining microfluidics with SERS is a viable way to improve their detection sensitivity. Researchers have recently developed several SERS coupled microfluidic platforms with substantial potential for biomolecular detection, cellular and bacterial analysis, and hazardous substance detection. We review the current development of SERS coupled microfluidic platforms, illustrate their detection principles and construction, and summarize the latest applications in biology, environmental protection and food safety. In addition, we innovatively summarize the current status of SERS coupled multi-mode microfluidic platforms with other detection technologies. Finally, we discuss the challenges and countermeasures during the development of SERS coupled microfluidic platforms, as well as predict the future development trend of SERS coupled microfluidic platforms.

Microsphere-Enabled Micropillar Array for Whispering Gallery Mode Virus Detection

Rapid detection of pathogens and analytes at the point of care offers an opportunity for prompt patient management and public health control. This paper reports an open microfluidic platform coupled with active whispering gallery mode (WGM) microsphere resonators for the rapid detection of influenza viruses. The WGM microsphere resonators, precoated with influenza A polyclonal antibodies, are mechanically trapped in the open micropillar array, where the evaporation-driven flow continuously transports a small volume (∼μL) of sample to the resonators without auxiliaries. Selective chemical modification of the pillar array changes surface wettability and flow pattern, which enhances the detection sensitivity of the WGM resonator-based virus sensor. The optofluidic sensing platform is able to specifically detect influenza A viruses within 15 min using a few microliters of sample and displays a linear response to different virus concentrations.

MscI restriction enzyme cooperating recombinase-aided isothermal amplification for the ultrasensitive and rapid detection of low-abundance EGFR mutations on microfluidic chip

The detection of low-abundance mutation genes of the epidermal growth factor receptor (EGFR) exon 21 (EGFR L858R) plays a crucial role in the diagnosis of non-small cell lung cancer (NSCLC), as it enables early cancer detection and facilitates the development of treatment strategies. A detection platform was developed by combining the MscI restriction enzyme with the recombinase-aided isothermal amplification (RAA) technique (MRE-RAA). During the RAA process, "TGG^CCA" site of the wild-type genes was cleaved by the MscI restriction enzyme, while only the low-abundance mutation genes underwent amplification. Notably, when the RAA product was combined with CRISPR-Cas system, the sensitivity of detecting the EGFR L858R mutation increased by up to 1000-fold for addition of the MscI restriction enzyme. This achievement marked the first instance of attaining an analytical sensitivity of 0.001%. Furthermore, a disk-shaped microfluidic chip was developed to automate pretreatment while concurrently analyzing four blood samples. The microfluidic features of the chip include DNA extraction, MRE-RAA, and CRISPR-based detection. The fluorescence signal is employed for detection in the microfluidic chip, which is visible to the naked eye upon exposure to blue light irradiation. Furthermore, this platform has the capability to facilitate early diagnosis for various types of cancer by enabling high-sensitivity detection of low-abundance mutation genes.

Recent Development of Implantable Chemical Sensors Utilizing Flexible and Biodegradable Materials for Biomedical Applications

Implantable chemical sensors built with flexible and biodegradable materials exhibit immense potential for seamless integration with biological systems by matching the mechanical properties of soft tissues and eliminating device retraction procedures. Compared with conventional hospital-based blood tests, implantable chemical sensors have the capability to achieve real-time monitoring with high accuracy of important biomarkers such as metabolites, neurotransmitters, and proteins, offering valuable insights for clinical applications. These innovative sensors could provide essential information for preventive diagnosis and effective intervention. To date, despite extensive research on flexible and bioresorbable materials for implantable electronics, the development of chemical sensors has faced several challenges related to materials and device design, resulting in only a limited number of successful accomplishments. This review highlights recent advancements in implantable chemical sensors based on flexible and biodegradable materials, encompassing their sensing strategies, materials strategies, and geometric configurations. The following discussions focus on demonstrated detection of various objects including ions, small molecules, and a few examples of macromolecules using flexible and/or bioresorbable implantable chemical sensors. Finally, we will present current challenges and explore potential future directions.

An integrated centrifugal microfluidic strategy for point-of-care complete blood counting

Centrifugal microfluidics holds the potential to revolutionize point-of-care (POC) testing by simplifying laboratory tests through automating fluid and cell manipulation within microfluidic channels. This technology can facilitate blood testing, the most frequent clinical test, at the POC. However, an integrated centrifugal microfluidic device for complete blood counting (CBC) has not yet been fully realized. To address this, we propose an integrated portable system comprising a centrifuge and a hybrid microfluidic disc specifically designed for CBC analysis at the POC. The disc enables the implementation of various spin profiles in different stages of CBC to facilitate in-situ cell separation, solution metering and mixing, and differential cell counting. Furthermore, our system is coupled with a custom script that automates the process and ensures precise quantification of cells using light and fluorescent images captured from the detection chamber of the disc. We demonstrate a close correlation between the proposed method and the hematology analyzer, considered the gold standard, for quantifying hematocrit (R2 = 0.99), white blood cell count (R2 = 0.98), white blood cell differential count (granulocyte/agranulocyte; R2 = 0.89), red blood cell count (R2 = 0.97), and mean corpuscular volume (R2 = 0.94). The integration of our portable system offers significant advantages, enabling more accessible and affordable CBC testing at the POC. Considering the simplicity, affordability (∼$250 capital cost and <$2 operational cost per test), as well as low power consumption (>100 tests using a typical 24 V/10 Ah battery), this system has the potential to enhance healthcare delivery, particularly in resource-limited settings and remote areas where access to traditional laboratory facilities is limited.

Integrated Electrochemical and Optical Biosensing in Organs-on-Chip

Demand for biocompatible, non-invasive, and continuous real-time monitoring of organs-on-chip has driven the development of a variety of novel sensors. However, highest accuracy and sensitivity can arguably be achieved by integrated biosensing, which enables in situ monitoring of the in vitro microenvironment and dynamic responses of tissues and miniature organs recapitulated in organs-on-chip. This paper reviews integrated electrical, electrochemical, and optical sensing methods within organ-on-chip devices and platforms. By affording precise detection of analytes and biochemical reactions, these methods expand and advance the monitoring capabilities and reproducibility of organ-on-chip technology. The integration of these sensing techniques allows a deeper understanding of organ functions, and paves the way for important applications such as drug testing, disease modeling, and personalized medicine. By consolidating recent advancements and highlighting challenges in the field, this review aims to foster further research and innovation in the integration of biosensing in organs-on-chip.

Enhancing particle focusing: a comparative experimental study of modified square wave and square wave microchannels in lift and Dean vortex regimes

Serpentine microchannels are known for their effective particle focusing through Dean flow-induced rotational effects, which are used in compact designs for size-dependent focusing in medical diagnostics. This study explores square serpentine microchannels, a geometry that has recently gained prominence in inertial microfluidics, and presents a modification of square wave microchannels for improved particle separation and focusing. The proposed modification incorporates an additional U-shaped unit to convert the square wave microchannel into a non-axisymmetric structure, which enhances the Dean flow and consequently increases the Dean drag force. Extensive experiments were conducted covering a wide range of Reynolds numbers and particle sizes (2.45 µm to 12 µm). The particle concentration capability and streak position dynamics of the two structures were compared in detail. The results indicate that the modified square-wave microchannel exhibits efficient particle separation in the lower part of the Dean vortex-dominated regime. With increasing Reynolds number, the particles are successively focused into two streaks in the lift force-dominated regime and into a single streak in the Dean vortex-dominated regime, in this modified square wave geometry. These streaks have a low standard deviation around a mean value. In the Dean vortex-dominated regime, the location of the particle stream is highly dependent on the particle size, which allows good particle separation. Particle focusing occurs at lower Reynolds numbers in both the lift-dominated and lift/Dean drag-dominated regions than in the square wave microchannel. The innovative serpentine channel is particularly useful for the Dean drag-dominated regime and introduces a unique asymmetry that affects the particle focusing dynamics. The proposed device offers significant advantages in terms of efficiency, parallelization, footprint, and throughput over existing geometries.

Review on bile dynamics and microfluidic-based component detection: Advancing the understanding of bilestone pathogenesis in the biliary tract

Bilestones are solid masses found in the gallbladder or biliary tract, which block the normal bile flow and eventually result in severe life-threatening complications. Studies have shown that bilestone formation may be related to bile flow dynamics and the concentration level of bile components. The bile flow dynamics in the biliary tract play a critical role in disclosing the mechanism of bile stasis and transportation. The concentration of bile composition is closely associated with processes such as nucleation and crystallization. Recently, microfluidic-based biosensors have been favored for multiple advantages over traditional benchtop detection assays for their less sample consumption, portability, low cost, and high sensitivity for real-time detection. Here, we reviewed the developments in bile dynamics study and microfluidics-based bile component detection methods. These studies may provide valuable insights into the bilestone formation mechanisms and better treatment, alongside our opinions on the future development of in vitro lithotriptic drug screening of bilestones and bile characterization tests.

Step-by-step fabrication of heart-on-chip systems as models for cardiac disease modeling and drug screening

Cardiovascular diseases are caused by hereditary factors, environmental conditions, and medication-related issues. On the other hand, the cardiotoxicity of drugs should be thoroughly examined before entering the market. In this regard, heart-on-chip (HOC) systems have been developed as a more efficient and cost-effective solution than traditional methods, such as 2D cell culture and animal models. HOCs must replicate the biology, physiology, and pathology of human heart tissue to be considered a reliable platform for heart disease modeling and drug testing. Therefore, many efforts have been made to find the best methods to fabricate different parts of HOCs and to improve the bio-mimicry of the systems in the last decade. Beating HOCs with different platforms have been developed and techniques, such as fabricating pumpless HOCs, have been used to make HOCs more user-friendly systems. Recent HOC platforms have the ability to simultaneously induce and record electrophysiological stimuli. Additionally, systems including both heart and cancer tissue have been developed to investigate tissue-tissue interactions' effect on cardiac tissue response to cancer drugs. In this review, all steps needed to be considered to fabricate a HOC were introduced, including the choice of cellular resources, biomaterials, fabrication techniques, biomarkers, and corresponding biosensors. Moreover, the current HOCs used for modeling cardiac diseases and testing the drugs are discussed. We finally introduced some suggestions for fabricating relatively more user-friendly HOCs and facilitating the commercialization process.

Application of microfluidic technology based on surface-enhanced Raman scattering in cancer biomarker detection: A review

With the continuous discovery and research of predictive cancer-related biomarkers, liquid biopsy shows great potential in cancer diagnosis. Surface-enhanced Raman scattering (SERS) and microfluidic technology have received much attention among the various cancer biomarker detection methods. The former has ultrahigh detection sensitivity and can provide a unique fingerprint. In contrast, the latter has the characteristics of miniaturization and integration, which can realize accurate control of the detection samples and high-throughput detection through design. Both have the potential for point-of-care testing (POCT), and their combination (lab-on-a-chip SERS (LoC-SERS)) shows good compatibility. In this paper, the basic situation of circulating proteins, circulating tumor cells, exosomes, circulating tumor DNA (ctDNA), and microRNA (miRNA) in the diagnosis of various cancers is reviewed, and the detection research of these biomarkers by the LoC-SERS platform in recent years is described in detail. At the same time, the challenges and future development of the platform are discussed at the end of the review. Summarizing the current technology is expected to provide a reference for scholars engaged in related work and interested in this field.

A 3D-Printed Micro-Optofluidic Chamber for Fluid Characterization and Microparticle Velocity Detection

This work proposes a multi-objective polydimethylsiloxane (PDMS) micro-optofluidic (MoF) device suitably designed and manufactured through a 3D-printed-based master-slave approach. It exploits optical detection techniques to characterize immiscible fluids or microparticles in suspension inside a compartment specifically designed at the core of the device referred to as the MoF chamber. In addition, we show our novel, fast, and cost-effective methodology, dual-slit particle signal velocimetry (DPSV), for fluids and microparticle velocity detection. Different from the standard state-of-the-art approaches, the methodology focuses on signal processing rather than image processing. This alternative has several advantages, including the ability to circumvent the requirement of complex and extensive setups and cost reduction. Additionally, its rapid processing speed allows for real-time sample manipulations in ongoing image-based analyses. For our specific design, optical signals have been detected from the micro-optics components placed in two slots designed ad hoc in the device. To show the devices' multipurpose capabilities, the device has been tested with fluids of various colors and densities and the inclusion of synthetic microparticles. Additionally, several experiments have been conducted to prove the effectiveness of the DPSV approach in estimating microparticle velocities. A digital particle image velocimetry (DPIV)-based approach has been used as a baseline against which the outcomes of our methods have been evaluated. The combination of the suitability of the micro-optical components for integration, along with the MoF chamber device and the DPSV approach, demonstrates a proof of concept towards the challenge of real-time total-on-chip analysis.

Integration of fluorescence and MALDI imaging for microfluidic chip-based screening of potential thrombin inhibitors from natural products

The microfluidic technology provides an ideal platform for in situ screening of enzyme inhibitors and activators from natural products. This work described a surface-modified ITO glass-PDMS hybrid microfluidic chip for evaluating thrombin interaction with its potential inhibitors by fluorescence imaging and matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI). The fluorescence-labeled substrate was immobilized on a conductive ITO glass slide coated with gold nanoparticles/thiol-β-cyclodextrin modified TiO2 nanowires (Au-β-CD@TiO2 NWs) via Au-S bonds. A PDMS microchannel plate was placed on top of the modified ITO slide. The premixed solutions of thrombin and candidate thrombin inhibitors were infused into the microchannels to form a microreactor environment. The enzymatic reaction was rapidly monitored by fluorescence microscopy, and MALDI MS was used to validate and quantify the enzymatic hydrolysate of thrombin to determine the enzyme kinetic process and inhibitory activities of selected flavonoids. The fluorescence and MALDI MS results showed that luteolin, cynaroside, and baicalin have good thrombin inhibitory activity and their half-maximal inhibitory concentrations (IC50) were below 30 μM. The integration of fluorescence imaging and MALDI MSI for in situ monitoring and quantifying the enzymatic reaction in a microfluidic chip is capable of rapid and accurate screening of thrombin inhibitors from natural products.

Using Biosensors to Study Organoids, Spheroids and Organs-on-a-Chip: A Mechanobiology Perspective

The increasing popularity of 3D cell culture models is being driven by the demand for more in vivo-like conditions with which to study the biochemistry and biomechanics of numerous biological processes in health and disease. Spheroids and organoids are 3D culture platforms that self-assemble and regenerate from stem cells, tissue progenitor cells or cell lines, and that show great potential for studying tissue development and regeneration. Organ-on-a-chip approaches can be used to achieve spatiotemporal control over the biochemical and biomechanical signals that promote tissue growth and differentiation. These 3D model systems can be engineered to serve as disease models and used for drug screens. While culture methods have been developed to support these 3D structures, challenges remain to completely recapitulate the cell-cell and cell-matrix biomechanical interactions occurring in vivo. Understanding how forces influence the functions of cells in these 3D systems will require precise tools to measure such forces, as well as a better understanding of the mechanobiology of cell-cell and cell-matrix interactions. Biosensors will prove powerful for measuring forces in both of these contexts, thereby leading to a better understanding of how mechanical forces influence biological systems at the cellular and tissue levels. Here, we discussed how biosensors and mechanobiological research can be coupled to develop accurate, physiologically relevant 3D tissue models to study tissue development, function, malfunction in disease, and avenues for disease intervention.

Design and Fabrication of a Thin and Micro-Optical Sensor for Rapid Prototyping

Optical sensing offers several advantages owing to its non-invasiveness and high sensitivity. The miniaturization of optical sensors will mitigate spatial and weight constraints, expanding their applications and extending the principal advantages of optical sensing to different fields, such as healthcare, Internet of Things, artificial intelligence, and other aspects of society. In this study, we present the development of a miniature optical sensor for monitoring thrombi in extracorporeal membrane oxygenation (ECMO). The sensor, based on a complementary metal-oxide semiconductor integrated circuit (CMOS-IC), also serves as a photodiode, amplifier, and light-emitting diode (LED)-mounting substrate. It is sized 3.8 × 4.8 × 0.75 mm3 and provides reflectance spectroscopy at three wavelengths. Based on semiconductor and microelectromechanical system (MEMS) processes, the design of the sensor achieves ultra-compact millimeter size, customizability, prototyping, and scalability for mass production, facilitating the development of miniature optical sensors for a variety of applications.

Recent advances in sensor-integrated brain-on-a-chip devices for real-time brain monitoring

Brain science has remained in the global spotlight as an important field of scientific and technological discovery. Numerous in vitro and in vivo animal studies have been performed to understand the pathological processes involved in brain diseases and develop strategies for their diagnosis and treatment. However, owing to species differences between animals and humans, several drugs have shown high rates of treatment failure in clinical settings, hindering the development of diagnostic and treatment modalities for brain diseases. In this scenario, microfluidic brain-on-a-chip (BOC) devices, which allow the direct use of human tissues for experiments, have emerged as novel tools for effectively avoiding species differences and performing screening for new drugs. Although microfluidic BOC technology has achieved significant progress in recent years, monitoring slight changes in neurochemicals, neurotransmitters, and environmental states in the brain has remained challenging owing to the brain's complex environment. Hence, the integration of BOC with new sensors that have high sensitivity and high selectivity is urgently required for the real-time dynamic monitoring of BOC parameters. As sensor-based technologies for BOC have not been summarized, here, we review the principle, fabrication process, and application-based classification of sensor-integrated BOC, and then summarize the opportunities and challenges for their development. Generally, sensor-integrated BOC enables real-time monitoring and dynamic analysis, accurately measuring minute changes in the brain and thus enabling the realization of in vivo brain analysis and drug development.

Recent Advances of Biosensors for Detection of Multiple Antibiotics

The abuse of antibiotics has caused a serious threat to human life and health. It is urgent to develop sensors that can detect multiple antibiotics quickly and efficiently. Biosensors are widely used in the field of antibiotic detection because of their high specificity. Advanced artificial intelligence/machine learning algorithms have allowed for remarkable achievements in image analysis and face recognition, but have not yet been widely used in the field of biosensors. Herein, this paper reviews the biosensors that have been widely used in the simultaneous detection of multiple antibiotics based on different detection mechanisms and biorecognition elements in recent years, and compares and analyzes their characteristics and specific applications. In particular, this review summarizes some AI/ML algorithms with excellent performance in the field of antibiotic detection, and which provide a platform for the intelligence of sensors and terminal apps portability. Furthermore, this review gives a short review of biosensors for the detection of multiple antibiotics.

Spatial Multiplexing of Whispering Gallery Mode Sensors

Whispering gallery mode resonators have proven to be robust and sensitive platforms for the trace detection of chemical and/or biological analytes. Conventional approaches using serially addressed resonators face challenges in simultaneous multi-channel (i.e., multi-species) detection. We present an alternative monitoring scheme that allows for the spatial multiplexing of whispering gallery mode resonators with the simultaneous observation of the resonance spectra from each of them. By imaging arrays of microspheres and monitoring the glare spot intensities through image processing routines, resonance spectra from multiple resonators may be simultaneously recorded without interference or confounding effects of serial excitation/detection. We demonstrate our multiplexed imaging approach with bulk refractive index variations and virus-antibody binding.

A point-of-care biosensor for rapid detection and differentiation of COVID-19 virus (SARS-CoV-2) and influenza virus using subwavelength grating micro-ring resonator

In the context of continued spread of coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 and the emergence of new variants, the demand for rapid, accurate, and frequent detection is increasing. Moreover, the new predominant strain, Omicron variant, manifests more similar clinical features to those of other common respiratory infections. The concurrent detection of multiple potential pathogens helps distinguish SARS-CoV-2 infection from other diseases with overlapping symptoms, which is significant for providing tailored treatment to patients and containing the outbreak. Here, we report a lab-on-a-chip biosensing platform for SARS-CoV-2 detection based on the subwavelength grating micro-ring resonator. The sensing surface is functionalized by specific antibody against SARS-CoV-2 spike protein, which could produce redshifts of resonant peaks by antigen-antibody combination, thus achieving quantitative detection. Additionally, the sensor chip is integrated with a microfluidic chip featuring an anti-backflow Y-shaped structure that enables the concurrent detection of two analytes. In this study, we realized the detection and differentiation of COVID-19 and influenza A H1N1. Experimental results indicate that the limit of detection of our device reaches 100 fg/ml (1.31 fM) within 15 min detecting time, and cross-reactivity tests manifest the specificity of the optical diagnostic assay. Furthermore, the integrated packaging and streamlined workflow facilitate its use for clinical applications. Thus, the biosensing platform presents a promising approach for attaining highly sensitive, selective, multiplexed, and quantitative point-of-care diagnosis and distinction between COVID-19 and influenza.

Microfluidic Gradient Culture Arrays for Cell Pro-oxidation Analysis Using Bipolar Electrochemiluminescence

A microfluidic gradient array is a widely used screening and analysis device, which has characteristics of high efficiency, high automation, and low consumption. Bipolar electrode electrochemiluminescence (BPE-ECL) has special value in microfluidic array chips. The combination of the microfluidic gradient and BPE arrays has potential for high-throughput screening. In this article, a microfluidic BPE array chip for gradient culture and conditional screening of cancer cells was designed. The generation of concentration gradients, continuous culture of cancer cells with high throughput, and drug screening through BPE-ECL of the Ru(bpy)₃²⁺/TPrA system can be performed in one chip. We tested gradient pro-oxidation of MCF-7 by ascorbic acid and the synergistic effect of pro-oxidation on doxorubicin. The method achieves high analysis efficiency through a BPE array while simplifying the tedious procedures required by cell culture methods.

Emerging strategies of engineering retinal organoids and organoid-on-a-chip in modeling intraocular drug delivery: current progress and future perspectives

Retinal diseases are a rising concern as major causes of blindness in an aging society; therapeutic options are limited, and the precise pathogenesis of these diseases remains largely unknown. Intraocular drug delivery and nanomedicines offering targeted, sustained, and controllable delivery are the most challenging and popular topics in ocular drug development and toxicological evaluation. Retinal organoids (ROs) and organoid-on-a-chip (ROoC) are both emerging as promising in-vitro models to faithfully recapitulate human eyes for retinal research in the replacement of experimental animals and primary cells. In this study, we review the generation and application of ROs resembling the human retina in cell subtypes and laminated structures and introduce the emerging engineered ROoC as a technological opportunity to address critical issues. On-chip vascularization, perfusion, and close inter-tissue interactions recreate physiological environments in vitro, whilst integrating with biosensors facilitates real-time analysis and monitoring during organogenesis of the retina representing engineering efforts in ROoC models. We also emphasize that ROs and ROoCs hold the potential for applications in modeling intraocular drug delivery in vitro and developing next-generation retinal drug delivery strategies.

Design of Raman reporter-embedded magnetic/plasmonic hybrid nanostirrers for reliable microfluidic SERS biosensors

Magnetic-based microfluidic SERS biosensors hold great potential in various biological analyses due to their integrated advantages including easy manipulation, miniaturization and ultrasensitivity. However, it remains challenging to collect reliable SERS nanoprobe signals for quantitative analysis due to the irregular aggregation of magnetic carriers in a microfluidic chamber. Here, magnetic/plasmonic hybrid nanostirrers embedded with a Raman reporter are developed as capture carriers to improve the reliability of microfluidic SERS biosensors. Experimental results revealed that SERS signals from magnetic hybrid nanostirrers could serve as microenvironment beacons of their irregular aggregation, and a signal filtering method was proposed through exploring the relationship between the intensity range of beacons and the signal reproducibility of SERS nanoprobes using interleukin 6 as a model target analyte. Using the signal filtering method, reliable SERS nanoprobe signals with high reproducibility could be picked out from similar microenvironments according to their beacon intensity, and then the influence of irregular aggregation of magnetic carriers on the SERS nanoprobe could be eliminated. The filtered SERS nanoprobe signals also exhibited excellent repeatability from independent tests, which lay a solid foundation for a reliable working curve and subsequent accurate bioassay. This study provides a simple but promising route for reliable microfluidic SERS biosensors, which will further promote their practical application in biological analysis.

Biosensor integrated brain-on-a-chip platforms: Progress and prospects in clinical translation

Because of the brain's complexity, developing effective treatments for neurological disorders is a formidable challenge. Research efforts to this end are advancing as in vitro systems have reached the point that they can imitate critical components of the brain's structure and function. Brain-on-a-chip (BoC) was first used for microfluidics-based systems with small synthetic tissues but has expanded recently to include in vitro simulation of the central nervous system (CNS). Defining the system's qualifying parameters may improve the BoC for the next generation of in vitro platforms. These parameters show how well a given platform solves the problems unique to in vitro CNS modeling (like recreating the brain's microenvironment and including essential parts like the blood-brain barrier (BBB)) and how much more value it offers than traditional cell culture systems. This review provides an overview of the practical concerns of creating and deploying BoC systems and elaborates on how these technologies might be used. Not only how advanced biosensing technologies could be integrated with BoC system but also how novel approaches will automate assays and improve point-of-care (PoC) diagnostics and accurate quantitative analyses are discussed. Key challenges providing opportunities for clinical translation of BoC in neurodegenerative disorders are also addressed.

Integrated technologies for continuous monitoring of organs-on-chips: Current challenges and potential solutions

Organs-on-chips (OoCs) are biomimetic in vitro systems based on microfluidic cell cultures that recapitulate the in vivo physicochemical microenvironments and the physiologies and key functional units of specific human organs. These systems are versatile and can be customized to investigate organ-specific physiology, pathology, or pharmacology. They are more physiologically relevant than traditional two-dimensional cultures, can potentially replace the animal models or reduce the use of these models, and represent a unique opportunity for the development of personalized medicine when combined with human induced pluripotent stem cells. Continuous monitoring of important quality parameters of OoCs via a label-free, non-destructive, reliable, high-throughput, and multiplex method is critical for assessing the conditions of these systems and generating relevant analytical data; moreover, elaboration of quality predictive models is required for clinical trials of OoCs. Presently, these analytical data are obtained by manual or automatic sampling and analyzed using single-point, off-chip traditional methods. In this review, we describe recent efforts to integrate biosensing technologies into OoCs for monitoring the physiologies, functions, and physicochemical microenvironments of OoCs. Furthermore, we present potential alternative solutions to current challenges and future directions for the application of artificial intelligence in the development of OoCs and cyber-physical systems. These "smart" OoCs can learn and make autonomous decisions for process optimization, self-regulation, and data analysis.

Lateral flow assays for detection of disease biomarkers

Early diagnosis saves lives in many diseases. In this sense, monitoring of biomarkers is crucial for the diagnosis of diseases. Lateral flow assays (LFAs) have attracted great attention among paper-based point-of-care testing (POCT) due to their low cost, user-friendliness, and time-saving advantages. Developments in the field of health have led to an increase of interest in these rapid tests. LFAs are used in the diagnosis and monitoring of many diseases, thanks to biomarkers that can be observed in body fluids. This review covers the recent advances dealing with the design and strategies for the development of LFA for the detection of biomarkers used in clinical applications in the last 5 years. We focus on various strategies such as choosing the nanoparticle type, single or multiple test approaches, and equipment for signal transducing for the detection of the most common biomarkers in different diseases such as cancer, cardiovascular, infectious, and others including Parkinson's and Alzheimer's diseases. We expect that this study will contribute to the different approaches in LFA and pave the way for other clinical applications.

A Simple Label-Free Aptamer-Based Electrochemical Biosensor for the Sensitive Detection of C-Reactive Proteins

The level of C-reactive protein (CRP) in the human body is closely associated with cardiovascular diseases and inflammation. In this study, a label-free functionalized aptamer sensor was attached to an electrode trimmed with in-gold nanoparticles and carboxylated graphene oxide (AuNPs/GO-COOH) to achieve sensitive measurements relative to CRP. Gold nanoparticles were selected for this study due to super stability, remarkably high electrical conductivity, and biocompatibility. In addition, carboxylated graphene oxide was utilized to promote the anchorage of inducer molecules and to increase detection accuracies. The sensing signal was recorded using differential pulse voltammetry (DPV), and it produced a conspicuous peak current obtained at approximately -0.4 V. Furthermore, the adapted sensor manifested a broad linear span from 0.001 ng/mL to 100 ng/mL. The results also demonstrated that this aptamer sensor had superior stability, specificity, and reproducibility. This aptamer-based electrochemical sensor has enormous potential in complex application situations with interfering substances.

Microfluidic assessment of nutritional biomarkers: Concepts, approaches and advances

Among various approaches to understand the health status of an individual, nutritional biomarkers can provide valuable information, particularly in terms of deficiencies, if any, and their severity. Commonly, the approach revolves around molecular sciences, and the information gained can support prognosis, diagnosis, remediation, and impact assessment of therapies. Microfluidic platforms can offer benefits of low sample and reagent requirements, low cost, high precision, and lower detection limits, with simplicity in handling and the provision for complete automation and integration with information and communication technologies (ICTs). While several advances are being made, this work details the underlying concepts, with emphasis on different point-of-care devices for the analysis of macro and micronutrient biomarkers. In addition, the scope of using different wearable microfluidic sensors for real-time and noninvasive determination of biomarkers is detailed. While several challenges remain, a strong focus is given on recent advances, presenting the state-of-the-art of this field. With more such biomarkers being discovered and commercialization-driven research, trends indicate the wide prospects of this advancing field in supporting clinicians, food technologists, nutritionists, and others.