The application of nanoparticles in point-of-care testing (POCT) immunoassays

Multiplex analysis of ovarian cancer patients using glycan microarray

Investigation of tumor-associated glycan antigens (TAGs) could be helpful for the development of sensitive cancer diagnostics and novel therapies. Glycan microarrays are effective methods for analyzing glycans and anti-glycan antibodies, which are immobilized arrays of oligo- or poly-saccharides on different substrates, making them a promising class of oncological biomarkers. Blood serum samples from patients (n = 203) with ovarian cancer (OvaCan) and healthy volunteers were analyzed using a glycan microarray containing 63 immobilized glycans to determine changes in anti-glycan IgG and IgM antibody profiles in OvaCan. Levels of anti-glycan IgG and IgM antibodies in OvaCan statistically differed from levels in healthy donors: the most prominent statistically significant difference for anti-glycan IgG antibodies was found for 6-O-su-Lec (AUC = 0.657, Se = 48.0 %, and Sp = 73.3 %). The AUC values for certain glycans investigated in diagnosing OvaCan indicated a fingerprint consisting of IgM antibodies to specific glycans, and the most specific anti-glycan IgM antibodies were Ley (AUC = 0.625, Se = 98.0 % and Sp = 45.0 %). The potential of these serological biomarkers to distinguish between OvaCan and other malignancies is still an unresolved issue that requires more large-scale studies to confirm and validate the use of these biomarkers in the diagnosis of different types of cancer.

Plasmonic Geometry-Induced Viscoelastic Biocomplex Formation with Optical Concealment, Liquid Slips, and Soundscapes in Bioassays

Plasmonic nanoparticles (NPs), typically made up of gold or silver, are widely used in point-of-care bio- and chemical sensing due to their role in enhancing detection sensitivity. Key NP properties influencing sensing performance include the material type, NP size, and geometry. While much research has focused on material and size optimization, less attention has been given to understand NP geometry effects and interactions with biomolecules involved in the bioassay. In this context, we investigate the interfacial properties of the biocomplex formed by spherical-shaped gold nanoparticles (AuNPs) and gold nanostars (AuNSts) during a sandwich assay using localized surface plasmon resonance (LSPR) and quartz crystal microbalance with dissipation (QCM-D). The chosen model to study the biocomplex specifically detects interleukin-6 (IL-6). Our results show that AuNSts, with their anisotropic shape and higher surface area, form antibody-antigen complexes more effectively than AuNPs. AuNSts also create a softer, more hydrated layer due to their complex geometry, which leads to larger liquid slips. Lastly, we showed that AuNSts avoid optical concealment at high IL-6 concentrations, unlike AuNPs, making them more reliable for detecting a wider range of concentrations. These findings highlight the importance of optimizing NP geometry for improved bio/chemical sensor performance.

Point-of-care testing: state-of-the art and perspectives

Point-of-care testing (POCT) is becoming an increasingly popular way to perform laboratory tests closer to the patient. This option has several recognized advantages, such as accessibility, portability, speed, convenience, ease of use, ever-growing test panels, lower cumulative healthcare costs when used within appropriate clinical pathways, better patient empowerment and engagement, and reduction of certain pre-analytical errors, especially those related to specimen transportation. On the other hand, POCT also poses some limitations and risks, namely the risk of lower accuracy and reliability compared to traditional laboratory tests, quality control and connectivity issues, high dependence on operators (with varying levels of expertise or training), challenges related to patient data management, higher costs per individual test, regulatory and compliance issues such as the need for appropriate validation prior to clinical use (especially for rapid diagnostic tests; RDTs), as well as additional preanalytical sources of error that may remain undetected in this type of testing, which is usually based on whole blood samples (i.e., presence of interfering substances, clotting, hemolysis, etc.). There is no doubt that POCT is a breakthrough innovation in laboratory medicine, but the discussion on its appropriate use requires further debate and initiatives. This collective opinion paper, composed of abstracts of the lectures presented at the two-day expert meeting "Point-Of-Care-Testing: State of the Art and Perspective" (Venice, April 4-5, 2024), aims to provide a thoughtful overview of the state-of-the-art in POCT, its current applications, advantages and potential limitations, as well as some interesting reflections on the future perspectives of this particular field of laboratory medicine.

Integration of Immunosyringe Sensors with Bar-Chart Chips for Prick-and-Read Testing of Prostate Specific Antigen

Pressure-based signal transduction is of promise in developing microfluidic immunoassays such as volumetric bar-chart chips (V-chips), but new working principles are required to further simplify the methods in point-of-care testing (POCT). Herein, we developed immunosyringe sensors and integrated them with bar-chart chips for simple prick-and-read testing of prostate specific antigen (PSA) as a model target. Disposable syringes served as the host for the construction of the sandwich-type immuno-recognition system. Platinum nanoparticles (Pt NPs) as the peroxidase-mimicking detection probe catalyzed the decomposition of H2O2 to produce O2 in the syringe cylinders, enabling the pressure-driven automatic injection of liquids from the syringes. The immuno-recognition event in the syringes was thereby converted into the quantitative autoinjection behavior of the syringes, namely, immunosyringe sensors. By simply pricking the sensors to bar-chart chips, we visually and quantitatively read the immunoassay signals as the bar-chart injection distance of liquids from the syringes in channels of the chips. The immunoassay showed a limit of detection (LOD) of 0.41 ng/mL in PSA detection with satisfactory accuracy in testing clinical serum samples. Owing to the integration with the immunosyringe sensors, this method, in comparison with conventional V-chips, works in a simpler prick-and-read manner without complex chip configurations and specialized chip operations (e.g., on-chip loading of microvolume reagents and sealing treatments). Therefore, the immunoassay shows great potential in POCT applications.

Proposal of a Rapid Detection System Using Image Analysis for ELISA with an Autonomous Centrifugal Microfluidic System

In this study, with the aim of adapting an enzyme-linked immunosorbent assay (ELISA) system for point-of-care testing (POCT), we propose an image analysis method for ELISAs using a centrifugal microfluidic device that automatically executes the assay. The developed image analysis method can be used to quantify the color development reaction on a TMB (3,3',5,5'-tetramethylbenzidine) substrate. In a conventional ELISA, reaction stopping reagents are required at the end of the TMB reaction. In contrast, the developed image analysis method can analyze color in the color-developing reaction without a reaction stopping reagent. This contributes to a reduction in total assay time. The microfluidic devices used in this study could execute reagent control for ELISAs by steady rotation. In the demonstration of the assay and image analysis, a calibration curve for mouse IgG detection was successfully prepared, and it was confirmed that the image analysis method had the same performance as the conventional analysis method. Moreover, the changes in the amount of color over time confirmed that a calibration curve equal to the endpoint analysis was obtained within 2 min from the start of the TMB reaction. As the assay time before the TMB reaction was approximately 7.5 min, the developed ELISA system could detect TMB in just 10 min. In conventional methods using a plate reader, the assay required a time of 90 min for manual handling using microwell plates, and in the case of using automatic microfluidic devices, 30 min were required. The time of 10 min realized by this proposed method is equal to the time required for detection in an immunochromatographic assay with a lateral flow assay; therefore, it is expected that ELISAs can be performed sufficiently to adapt to POCT.

A review: early detection of oral cancer biomarkers using microfluidic colorimetric point-of-care devices

Oral squamous cell carcinoma (OSCC) is the most common type of head and neck cancers. OSCC constitutes 90% of the head and neck malignancies. The delayed identification of oral cancer is the primary cause of ineffective medical treatment. To address this issue, low-cost, reliable point-of-care devices that can be utilized for large-scale screening, even in low-resource settings, including rural areas and primary healthcare centers, are of great interest. Herein, a comprehensive analysis of numerous salivary biomarkers that exhibit significant variations in concentration between individuals with oral cancer and those without is given. Furthermore, the article explores several point-of-care devices that exhibit potential in the realm of oral cancer detection. The biomarkers are discussed with a focus on their structural characteristics and role in oral cancer progression. The devices based on colorimetry and microfluidics are discussed in detail, considering their compliance with the 'REASSURED' criteria given by the World Health Organization (WHO) and suitability for mass screening in low-resource settings. Finally, the discourse revolves around the fundamental aspects pertaining to the advancement of multiplex, cost-effective point-of-care devices designed for widespread screening purposes.

Nanomaterials in the treatment and diagnosis of rheumatoid arthritis: Advanced approaches

Rheumatoid arthritis (RA), a chronic inflammatory condition that affects persons between the ages of 20 and 40, causes synovium inflammation, cartilage loss, and joint discomfort as some of its symptoms. Diagnostic techniques for RA have traditionally been split into two main categories: imaging and serological tests. However, significant issues are associated with both of these methods. Imaging methods are costly and only helpful in people with obvious symptoms, while serological assays are time-consuming and require specialist knowledge. The drawbacks of these traditional techniques have led to the development of novel diagnostic approaches. The unique properties of nanomaterials make them well-suited as biosensors. Their compact dimensions are frequently cited for their outstanding performance, and their positive impact on the signal-to-noise ratio accounts for their capacity to detect biomarkers at low detection limits, with excellent repeatability and a robust dynamic range. In this review, we discuss the use of nanomaterials in RA theranostics. Scientists have recently synthesized, characterized, and modified nanomaterials and biomarkers commonly used to enhance RA diagnosis and therapy capabilities. We hope to provide scientists with the promising potential that nanomaterials hold for future theranostics and offer suggestions on further improving nanomaterials as biosensors, particularly for detecting autoimmune disorders.

A nanoparticle-assisted signal-enhancement technique for lateral flow immunoassays

Lateral flow immunoassay (LFIA), an affordable and rapid paper-based detection technology, is employed extensively in clinical diagnosis, environmental monitoring, and food safety analysis. The COVID-19 pandemic underscored the validity and adoption of LFIA in performing large-scale clinical and public health testing. The unprecedented demand for prompt diagnostic responses and advances in nanotechnology have fueled the rise of next-generation LFIA technologies. The utilization of nanoparticles to amplify signals represents an innovative approach aimed at augmenting LFIA sensitivity. This review probes the nanoparticle-assisted amplification strategies in LFIA applications to secure low detection limits and expedited response rates. Emphasis is placed on comprehending the correlation between the physicochemical properties of nanoparticles and LFIA performance. Lastly, we shed light on the challenges and opportunities in this prolific field.

Detection of carbofuran in fruits and vegetables by Raman spectroscopy combined with immunochromatography

It has long been desired to develop rapid methods for the rapid identification and quantification of pesticides and their metabolites. Carbofuran, a representative pesticide of the carbamate group, is highly systemic and is used on vegetables, fruits and grains, which has led many countries to test for residues in food and the environment. In this study, gold and silver composite core-shell (Au@Ag) nanoparticles were used to label the carbofuran antibody and Raman molecule 5,5-dithiobis-2-nitrobenzoic acid (DTNB) to synthesize Raman immune probes. The signal value of DTNB was read using a Raman spectrometer, and the quantitative detection technology of carbofuran was established based on lateral flow immunochromatographic assay (ICA) combined with surface-enhanced Raman spectroscopy (SERS). SERS-ICA is a rapid, quantitative and ultrasensitive test for the determination of carbofuran in fruits and vegetables with a sensitivity of 0.1 pg mL-1. Consequently, the results demonstrate that the SERS-based lateral flow immunosensor developed in this study has the advantages of excellent assay sensitivity and remarkable multiplexing capability, and thus it will have great application potential in food safety monitoring.

A novel SERS-lateral flow assay (LFA) tray for monitoring of miR-155-5p during pyroptosis in breast cancer cells

In the study, a novel surface-enhanced Raman scattering (SERS)-lateral flow assay (LFA) tray for the real-time detection of pyroptosis-associated miR-155-5p in breast cancer cells was established and validated. The SERS probe modified with monoclonal antibodies and functionalized HP1@5-FAM was first synthesized. When miR-155-5p was present, HP1@5-FAM on the SERS probe specifically recognized target miRNAs and hybridized with them, resulting in HP2 on the T line only capturing some SERS probes that were not bound to miR-155-5p. The T line appeared as a light orange band or there was no color change, and the corresponding Raman detection result showed a weak or insignificant Raman signal. The SERS probe showed high selectivity, satisfactory stability, and excellent reproducibility, and the limit of detection (LOD) for miR-155-5p was 7.26 aM. Finally, the proposed SERS-LFA tray was applied to detect miR-155-5p in MBA-MD-468 cells that underwent varying degrees of pyroptosis, and the detection results of SERS were consistent with those of the conventional real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay. The study demonstrated that the SERS-LFA tray was a convenient and ultrasensitive method for miR-155-5p real-time detection, which could provide more detailed information for pyroptosis and be of potential value in guiding the treatment of breast cancer.

A new colorimetric aptasensor for paraquat detection based on the designed aptamer with multiple paraquat binding sites in combination with gold nanoparticles

The presence of paraquat in the environment poses a danger to human health, leading to a growing demand for an uncomplicated and highly responsive method to detect paraquat. This work reports a new, simple, and sensitive colorimetric aptasensor based on the designed aptamers containing 1-5 paraquat binding sites (R1-R5) in combination with gold nanoparticles (AuNPs). Although the aptamers with more binding sites exhibited greater paraquat interaction capability, the aptasensor based on the R3 aptamer showed the highest detection sensitivity for paraquat in a linear range of 5-50 nM with a limit of detection of 1.29 nM, meaning that it is 2.14 fold more sensitive than the R1-aptasensor. This R3-aptasensor selectively detected paraquat but not the other tested herbicides, including difenzoquat, 2,4-D, ametryn, atrazine, and glufosinate. Also, it efficiently detected paraquat spiked in water samples within the precision acceptance criterion of recovery rates (96.8-105.0%) and the relative standard deviations (1.50-3.81%). These results demonstrated the development of a new aptasensor for paraquat detection, in which the multiple paraquat binding sites of the aptamers could enhance detection sensitivity.

A portable microfluidic photometric detection method based on enzyme linked immunoscatter enhancement

Currently, the combination of smart phones and microfluidic chips is a commonly used device for point-of-care testing (POCT) detection. Enzyme linked immunosorbent assay (ELISA) is an effective way to detect specific proteins in disease. Because the detection accuracy of smartphone cameras is difficult to directly replace high-precision spectral devices, the combination of smartphones and ELISA has not been widely used. Therefore, this paper proposes a microfluidic photometric detection method based on ELISA scattering enhancement. Firstly, the scattering characteristics of IMB are mined, and the optimal value of absorbance error compensation parameter is obtained. Secondly, the absorbance error compensation model based on scattering enhancement characteristics is established to improve the image acquisition accuracy of smart phones. Finally, the microfluidic photometric detection chip is developed, and the optical path system, optical path adjustment system and POCT detection App of smart phone are designed. The optimal compensation parameters of IMB were obtained based on simulated samples, and the linearity of absorbance and concentration increased by 22.6% after compensation. In the IL-6 sample experiment, the detection results of the platform in this paper had a good linear correlation with IL-6 sample concentration, and the linear correlation coefficient was above 0.95459. At the same time, the detection limit and accuracy meet the detection requirements. Therefore, with the participation of smart phones and microfluidic chips, problems such as difficult carrying and complex operation in traditional ELISA daily detection have been solved, laying a foundation for the future promotion and application of ELISA based POCT platform.

Special Issue "Immunoanalytical and Bioinformatics Methods in Immunology Research"

To effectively control and prevent diseases on a global scale, it is essential to employ precise, sensitive, selective, and rapid immunoanalytical methods [...].

Nanoparticle-Based Bioaffinity Assays: From the Research Laboratory to the Market

Advances in the development of new biorecognition elements, nanoparticle-based labels as well as instrumentation have inspired the design of new bioaffinity assays. This review critically discusses the potential of nanoparticles to replace current enzymatic or molecular labels in immunoassays and other bioaffinity assays. Successful implementations of nanoparticles in commercial assays and the need for rapid tests incorporating nanoparticles in different roles such as capture support, signal generation elements, and signal amplification systems are highlighted. The limited number of nanoparticles applied in current commercial assays can be explained by challenges associated with the analysis of real samples (e.g., blood, urine, or nasal swabs) that are difficult to resolve, particularly if the same performance can be achieved more easily by conventional labels. Lateral flow assays that are based on the visual detection of the red-colored line formed by colloidal gold are a notable exception, exemplified by SARS-CoV-2 rapid antigen tests that have moved from initial laboratory testing to widespread market adaption in less than two years.

Pipette-Free and Fully Integrated Paper Device Employing DNA Extraction, Isothermal Amplification, and Carmoisine-Based Colorimetric Detection for Determining Infectious Pathogens

A pipette-free and fully integrated device that can be used to accurately recognize the presence of infectious pathogens is an important and useful tool in point-of-care testing, particularly when aiming to decrease the unpredictable threats posed by disease outbreak. In this study, a paper device is developed to integrate the three main processes required for detecting infectious pathogens, including DNA extraction, loop-mediated isothermal amplification (LAMP), and detection. All key reagents, including sodium dodecyl sulfate (SDS), NaOH, LAMP reagents, and carmoisine, are placed on the paper device. The paper device is operated simply via sliding and folding without using any bulky equipment, and the results can be directly observed by the naked eye. The optimized concentrations of sodium dodecyl sulfate (SDS), sodium hydroxide (NaOH), and carmoisine were found to be 0.1%, 0.1 M, and 0.5 mg/mL, respectively. The paper device was used to detect Enterococcus faecium at concentrations as low as 102 CFU/mL within 60 min. Also, E. faecium spiked in milk was successfully detected using the paper device, demonstrating the feasible application in real sample analysis.

Extending the Shelf-Life of Immunoassay-Based Microfluidic Chips through Freeze-Drying Sublimation Techniques

Point-of-care testing (POCT) platforms utilizing immunoassay-based microfluidic chips offer a robust and specific method for detecting target antibodies, demonstrating a wide range of applications in various medical and research settings. Despite their versatility and specificity, the adoption of these immunoassay chips in POCT has been limited by their short shelf-life in liquid environments, attributed to the degradation of immobilized antibodies. This technical limitation presents a barrier, particularly for resource-limited settings where long-term storage and functionality are critical. To address this challenge, we introduce a novel freeze-dry sublimation process aimed at extending the shelf-life of these microfluidic chips without compromising their functional integrity. This study elaborates on the mechanisms by which freeze-drying preserves the bioactivity of the immobilized antibodies, thereby maintaining the chip's performance over an extended period. Our findings reveal significant shelf-life extension, making it possible for these POCT platforms to be more widely adopted and practically applied, especially in settings with limited resources. This research paves the way for more accessible, long-lasting, and effective POCT solutions, breaking down previous barriers to adoption and application.

Quantitative injection strip platform using water-soluble paper and magnet based on a lateral flow assay

Quantitative analysis for lateral flow immunoassay (LFA) strips was conducted continuously. Quantitative analysis means measuring concentration, which represents the number of molecules per unit volume. In this study, we designed a quantitative injection (QI) strip by modifying the structure of general LFA strips to inject the same unit volume. To achieve the injection of the same unit volume, we used water-soluble paper and magnet. In addition, the QI strip was fabricated to enable the physical separation of the gold conjugate pad from the nitrocellulose membrane (NC membrane) at the optimized time after sample injection. The optimized time refers to the time from the point at which the sample started flowing on the NC membrane to the point at which the strip was separated. At the samples of same concentration, the LFA strip increases detection signals as the volume of injected sample increases. In contrast to the LFA strip, the QI strip maintained consistent detection signals even with increasing volume of injected sample. Furthermore, the QI strip demonstrated an 11-fold lower deviation compared to the LFA strip. These results are attributed to the separation function of the QI strip. In conclusion, the QI strip is more suitable for quantitative analysis compared to the LFA strip due to the same unit volume without additional equipment such as a pipette. This study is expected to contribute to the development of user-friendly POCT and strip-based quantitative analysis.