Construction of a microcavity-based microfluidic chip with simultaneous SERS quantification of dual biomarkers for early diagnosis of Alzheimer's disease

Highly sensitive and reproducible SERS substrate based on ordered multi-tipped Au nanostar arrays for the detection of myocardial infarction biomarker cardiac troponin I

Acute myocardial infarction (AMI) is a severe cardiovascular disease, for which early diagnosis is critical for reducing mortality and improving patient outcomes. Cardiac troponin I (cTnI) is widely recognized as the "gold standard" biomarker for AMI due to its high specificity and sensitivity. The concentration of cTnI correlates directly with different stages of AMI. Therefore, the accurate detection of cTnI concentration is of paramount importance. However, the low concentration of cTnI in biological fluids requires ultrasensitive detection methods. In this study, we developed a sandwiched surface enhanced Raman scattering (SERS)-based biosensor composed of SERS-immune substrate, target antigen, and SERS nanotags and realized sensitive and accurate detection of cTnI. The SERS-immune substrate features an ordered, multi-tipped monolayer of Au nanostars fabricated using a three-phase interfacial self-assembly method and 4-(2-hydroxyerhyl)piperazine-1-erhanesulfonic acid (HEPES) buffer modification. Compared to Au nanosphere SERS substrates, the Au nanostar SERS substrates exhibited about a 3-fold increase in Raman enhancement and demonstrated good uniformity and batch stability. This novel SERS detection platform, leveraging dual plasmonic enhancement from both the SERS-immune substrate and SERS nanotags, achieves detection of cTnI with a limit of detection (LOD) as low as 9.09 pg mL-1 and a relative standard deviation (RSD) as low as 11.24%. Thus, the Au nanostar SERS substrates developed in this study demonstrate significant potential for rapid and accurate detection of cTnI.

Utilizing Nanomaterials in Microfluidic Devices for Disease Detection and Treatment

Microfluidic technology has gained widespread application in the field of biomedical research due to its exceptional sensitivity and high specificity. Particularly when combined with nanomaterials, the synergy between the two has significantly advanced fields such as precision medicine, drug delivery, disease detection, and treatment. This article aims to provide an overview of the latest research achievements of microfluidic nanomaterials in disease detection and treatment. It delves into the applications of microfluidic nanomaterials in detecting blood parameters, cardiovascular disease markers, neurological disease markers, and tumor markers. Special emphasis is placed on their roles in disease treatment, including models such as blood vessels, the blood-brain barrier, lung chips, and tumors. The development of microfluidic nanomaterials in emerging medical technologies, particularly in skin interactive devices and medical imaging, is also introduced. Additionally, the challenges and future prospects of microfluidic nanomaterials in current clinical applications are discussed. In summary, microfluidic nanomaterials play an indispensable role in disease detection and treatment. With the continuous advancement of technology, their applications in the medical field will become even more profound and extensive.

Multiple-Signal Amplification Strategy to Fabricate an Ultrasensitive Electrochemiluminescence Magnetic Immunosensor for Detecting Biomarkers of Alzheimer's Disease via Iridium-Based Self-Enhancing Nanoemitters

Alzheimer's disease (AD) is characterized by progressive memory loss and cognitive decline, significantly impairing the daily life of elderly individuals. The low abundance of blood-based biomarkers in AD necessitates higher analytical technique requirements. Herein, one novel iridium-based ECL self-enhanced nanoemitter (TPrA@Ir-SiO2) was unprecedentedly reported, and it was further used to construct an ultrasensitive ECL magnetic immunosensor by a multiple-signal amplification strategy to unequally sensitively and accurately detect the AD blood-based biomarker (P-tau181) in this work. The initial signal amplification was accomplished via incorporating a new efficient iridium-based luminophore named Ir(mdq)2(acac) and a corresponding coreactant into silica nanoparticles to successfully obtain TPrA@Ir-SiO2. In addition, the specific and high-affinity interactions between streptavidin and biotin were subsequently employed to further facilitate signal amplification. Based on the advantages of the luminophore itself and the high-affinity interactions between biotin and streptavidin, the corresponding ECL immunosensor proposed in this work exhibited remarkable sensitivity, covering a wide linear range from 0.1 pg/mL to 0.1 μg/mL, and achieved an ultralow limit of detection of 68.58 fg/mL (S/N = 3), and it also exhibited outstanding recovery (98-104%) and RSD (1.92-4.86%) in the detection of serum samples by the spiking method. These remarkable results undoubtedly demonstrate the potential of self-enhanced ECL nanoemitters combined with a synergistic signal amplification strategy bearing streptavidin-biotin in detecting AD blood-based biomarkers, providing accurate and reliable solutions for early diagnosis and monitoring of AD, which would open a new avenue to effectively reduce the burden on AD patients' families and society in the future.

Functionalized Optical Microcavities for Sensing Applications

Functionalized optical microcavities constitute an emerging highly sensitive and highly selective sensing technology. By combining optical microcavities with novel materials, microcavity sensors offer exceptional precision, unlocking considerable potential for medical diagnostics, physical and chemical analyses, and environmental monitoring. The high capabilities of functionalized microcavities enable subwavelength light detection and manipulation, facilitating the precise detection of analytes. Furthermore, recent advancements in miniaturization have paved the way for their integration into portable platforms. For leveraging the potential of microcavity sensors, it is crucial to address challenges related to the need for increasing cost-effectiveness, enhancing selectivity and sensitivity, enabling real-time measurements, and improving fabrication techniques. New strategies include the use of advanced materials, the optimization of signal processing, hybrid design approaches, and the employment of artificial intelligence. This review outlines the key strategies toward enhancing the performance of optical microcavities, highlights their broad applicability across various fields, and discusses the challenges that should be overcome to unlock their full potential.

SERS-Based Microfluidic Bioscreening Platform for Selective Detection of β-Amyloid Peptides

This study reports development of a microfluidic device for highly sensitive and selective detection of a β-amyloid peptide (Aβ1-42) in simulated cerebrospinal fluid, using surface-enhanced Raman spectroscopy (SERS). The device ensemble comprises a purine ligand (Pu) and its interaction with silver nanoparticles (AgNPs) to generate SERS hotspots. The low surface energy of the synthesized Pu ligand and high surface energy of AgNPs are utilized for the functionalization and formation of a Pu-AgNP SERS substrate. We have integrated a novel polydimethylsiloxane (PDMS) microfluidic device with Pu-AgNPs using a combination of photo- and soft lithography fabrication, sealed by thermal cross-linking with another layer of PDMS, to produce an effective screening platform for Aβ1-42. The SERS spectrum from the microfluidic device affords almost noise-free measurements, with excellent limit-of-detection values.

Visual and quantitative lateral flow immunoassay based on Au@PS SERS tags for multiplex cardiac biomarkers

Rapid and sensitive detection of multiple biomarkers by lateral flow immunoassay (LFIA) remains challenging for signal amplification for commonly used nanotags. Herein, we report a novel LFIA strip for visual and highly sensitive analysis of two cardiac biomarkers based on functionalized gold nanoparticles @ polystyrene microsphere (Au@PS）microcavity as surface-enhanced Raman scattering (SERS) tags. Antibody-modified Au@PS was designed as a SERS label. The evanescent waves propagating along the surface of the PS microcavity and the localized surface plasmons of the gold nanoparticles were coupled to enhance the light-matter interaction synergistically for Raman signal enhancement. In this strategy, the proposed Au@PS SERS tags-based LFIA was carried out to quantify the content of the heart failure and infarct biomarkers synchronously within 15 min and get the limits of detection of 1 pg/mL and 10 pg/mL for cardiac troponin I (cTnI) and N-terminal natriuretic peptide precursor (NT-proBNP), respectively. The results demonstrated 10-20 folds more sensitivity than that of the standard colloidal gold strip and fluorescent strip for the same biomarkers. This novel quantitative LFIA shows promise as a high-sensitive and visual sensing method for relevant clinical and forensic analysis.

High-Q WGM microcavity-based optofluidic sensor technologies for biological analysis

High-quality-factor (Q) optical microcavities have attracted extensive interest due to their unique ability to confine light for resonant circulation at the micrometer scale. Particular attention has been paid to optical whispering-gallery mode (WGM) microcavities to harness their strong light-matter interactions for biological applications. Remarkably, the combination of high-Q optical WGM microcavities with microfluidic technologies can achieve a synergistic effect in the development of high-sensitivity optofluidic sensors for many emerging biological analysis applications, such as the detection of proteins, nucleic acids, viruses, and exosomes. They can also be utilized to investigate the behavior of living cells in human organisms, which may provide new technical solutions for studies in cell biology and biophysics. In this paper, we briefly review recent progress in high-Q microcavity-based optofluidic sensor technologies and their applications in biological analysis.

On-Chip Photonic Detection Techniques for Non-Invasive In Situ Characterizations at the Microfluidic Scale

Microfluidics has emerged as a robust technology for diverse applications, ranging from bio-medical diagnostics to chemical analysis. Among the different characterization techniques that can be used to analyze samples at the microfluidic scale, the coupling of photonic detection techniques and on-chip configurations is particularly advantageous due to its non-invasive nature, which permits sensitive, real-time, high throughput, and rapid analyses, taking advantage of the microfluidic special environments and reduced sample volumes. Putting a special emphasis on integrated detection schemes, this review article explores the most relevant advances in the on-chip implementation of UV-vis, near-infrared, terahertz, and X-ray-based techniques for different characterizations, ranging from punctual spectroscopic or scattering-based measurements to different types of mapping/imaging. The principles of the techniques and their interest are discussed through their application to different systems.

SERS microfluidic chip integrated with double amplified signal off-on strategy for detection of microRNA in NSCLC

In this work, based on Fe3O4@AuNPs and double amplified signal Off-On strategy, a simple and sensitive SERS microfluidic chip was constructed to detect microRNA associated with non-small cell lung cancer (NSCLC). Fe3O4@AuNPs have two advantages of SERS enhanced and magnetic adsorption, the introduction of microfluidic chip can realize double amplification of SERS signal. First, the binding of complementary ssDNA and hpDNA moved the Raman signaling molecule away from Fe3O4@AuNPs, at which point the signal was turned off. Second, in the presence of the target microRNA, they were captured by complementary ssDNA and bound to them. HpDNA restored the hairpin conformation, the Raman signaling molecule moved closer to Fe3O4@AuNPs. At this time, the signal was turned on and strong Raman signal was generated. And last, through the magnetic component of SERS microfluidic chip, Fe3O4@AuNPs could be enriched to realize the secondary enhancement of SERS signal. In this way, the proposed SERS microfluidic chip can detect microRNA with high sensitivity and specificity. The corresponding detection of limit (LOD) for miR-21 versus miR-125b was 6.38 aM and 7.94 aM, respectively. This SERS microfluidic chip was promising in the field of early detection of NSCLC.

Simultaneous detection method for two cardiac disease protein biomarkers on a single chip modified with mixed aptamers using surface plasmon resonance

A simultaneous detection method for two cardiac disease protein biomarkers present in serum samples on a single planar gold chip using surface plasmon resonance (SPR) is described. The detection of N-terminal pro-brain natriuretic peptide (NT-proBNP) and tumor necrosis factor α (TNF-α), which are known as acute myocardial infarction (AMI) biomarkers, with predetermined clinically relevant concentrations was performed using mixed aptamers specific to each protein tethered on a single gold surface. After the binding of NT-proBNP and/or TNF-α to the mixed aptamers, an antibody specific to each target protein was injected to form a surface sandwich complex to improve selectivity. In order to adjust the dynamic ranges in the known clinically relevant concentration significantly different for NT-proBNP (0.13-0.24 nM) and TNF-α (0.5-3 pM), the surface density ratios of the corresponding pair of aptamer and antibody were first systematically determined, which were the 1:1 mixed aptamer chip with 40 nM anti-NT-proBNP and 100 nM anti-TNF-α. This allowed to establish the distinct dynamic ranges of 0.05-0.5 nM for NT-proBNP and 0.1-5 pM for TNF-α in a buffer, along with detection and quantification limits of 0.03 and 0.19 nM for NT-proBNP and 0.06 and 0.21 pM for TNF-α, respectively. The changes in refractive unit (RU) values observed when exposing both proteins at different concentrations alongside the corresponding fixed concentration of antibodies onto the 1:1 mixed aptamer chip were then correlated to the sum of RU values measured when using the injection of individual protein for evaluating each protein concentration. With a complete characterization of the simultaneous quantification of two protein concentrations in the buffer, the mixed aptamer chip was finally employed for direct measurements of NT-proBNP and TNF-α concentrations in undiluted serum samples from healthy controls and AMI patients. The results of simultaneous SPR measurements for the two proteins in the serum samples were further compared to the individual protein concentration results using an enzyme-linked immunosorbent assay.

Advances in microfluidic chips targeting toxic aggregation proteins for neurodegenerative diseases

Neurodegenerative diseases (NDs) are characterized by nervous system damage, often influenced by genetic and aging factors. Pathological analysis frequently reveals the presence of aggregated toxic proteins. The intricate and poorly understood origins of these diseases have hindered progress in early diagnosis and drug development. The development of novel in-vitro and in-vivo models could enhance our comprehension of ND mechanisms and facilitate clinical treatment advancements. Microfluidic chips are employed to establish three-dimensional culture conditions, replicating the human ecological niche and creating a microenvironment conducive to neuronal cell survival. The incorporation of mechatronic controls unifies the chip, cells, and culture medium optimizing living conditions for the cells. This study provides a comprehensive overview of microfluidic chip applications in drug and biomarker screening for neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, and amyotrophic lateral sclerosis. Our Lab-on-a-Chip system releases toxic proteins to simulate the pathological characteristics of neurodegenerative diseases, encompassing β-amyloid, α-synuclein, huntingtin, TAR DNA-binding protein 43, and Myelin Basic Protein. Investigating molecular and cellular interactions in vitro can enhance our understanding of disease mechanisms while minimizing harmful protein levels and can aid in screening potential therapeutic agents. We anticipate that our research will promote the utilization of microfluidic chips in both fundamental research and clinical applications for neurodegenerative diseases.

A reusable fiber-embedded microfluidic chip for rapid and sensitive on-site detection of kanamycin residues in water environments

The overuse and abuse of antibiotics have led to increased pollution in water environments. Thus, it is crucial to develop a rapid, high-frequency, and cost-effective method for on-site detection of antibiotics. In this regard, a reusable fiber-embedded microfluidic chip was constructed by combining a microfluidic chip with a functionalized fiber bioprobe that served as both a biorecognition element and an optical transducer. The fiber-embedded microfluidic chip enabled the quantitative detection of kanamycin (KANA) by integrating a portable all-fiber evanescent wave fluorescence detection device. Under optimized conditions, quantitative KANA detection was achieved with a detection limit of 0.03 μg L-1 and a linear detection range of 0.21-10.3 μg L-1. The accurate detection of KANA in various water samples can be completed within 25 min without pretreatment. The functionalized fiber-embedded microfluidic chip could be reused more than 200 times without significant performance loss. To demonstrate its suitability for practical applications, the fiber-embedded microfluidic chip was used to investigate KANA residues in surface waters obtained from the Qinghe River in Beijing, China. The results were compared with those of a traditional enzyme-linked immunosorbent assay, which showed a high correlation. Compared to conventional optical microfluidic chips, the proposed fiber-embedded microfluidic chip has several advantages, including its ease of use, miniaturization, cost-effectiveness, reusability, and high flexibility. It is an ideal alternative for rapid, sensitive on-site detection of antibiotics and other trace substances in environmental, food, and medical fields.

SERS-Based Optical Nanobiosensors for the Detection of Alzheimer's Disease

Alzheimer's disease (AD) is a leading cause of dementia, impacting millions worldwide. However, its complex neuropathologic features and heterogeneous pathophysiology present significant challenges for diagnosis and treatment. To address the urgent need for early AD diagnosis, this review focuses on surface-enhanced Raman scattering (SERS)-based biosensors, leveraging the excellent optical properties of nanomaterials to enhance detection performance. These highly sensitive and noninvasive biosensors offer opportunities for biomarker-driven clinical diagnostics and precision medicine. The review highlights various types of SERS-based biosensors targeting AD biomarkers, discussing their potential applications and contributions to AD diagnosis. Specific details about nanomaterials and targeted AD biomarkers are provided. Furthermore, the future research directions and challenges for improving AD marker detection using SERS sensors are outlined.