Dual sensitivity enhancement in gold nanoparticle‐based lateral flow immunoassay for visual detection of carcinoembryonic antigen

A simplified lateral flow immunosensor for the assay of carcinoembryonic antigen in low-resource settings

Carcinoembryonic antigen (CEA) is a glycoprotein widely used as a tumor marker. In this work, a colorimetric lateral flow immunosensor is developed for rapid and low-cost quantification of CEA in human blood serum. The immunosensor consists of a glass fiber sample/conjugation pad, a nitrocellulose detection pad and a cellulose absorption pad. The detection is based on a sandwich immunoreaction: the sample/conjugation pad is modified with gold nanoparticles (GNPs)-labeled anti-CEA conjugate probes which bind to the CEA target molecules in the sample and the complexes are captured at capture anti-CEA immobilized at the test line. The color intensity of the test line, measured from a scanned image of the strip, is related to the CEA concentration in the sample. The different assay parameters are studied in detail. The linearity holds from 1.25 to 640 ng mL-1 of CEA, the instrumental and visual limits of detection are 0.45 and 0.63 ng mL-1, respectively, and the total assay time is 15 min. The specificity of the immunoassay versus other cancer biomarkers is satisfactory. The recovery in samples of human serum spiked with CEA is in the range of 81-118% and the coefficient of variation of the method is ≤10%. Results obtained with the lateral flow immunosensor correlated well with a reference radioimmunoassay method (R2 = 0.99). This immunosensor can be readily applied to CEA monitoring at the point-of-care (POC) or in resource-limited settings thanks to its low-cost and simplicity.

Gold Nanotapes and Nanopinecones in a Quantitative Lateral Flow Assay for the Cancer Biomarker Carcinoembryonic Antigen

Colorectal cancer is the third most common malignancy and the second leading cause of cancer death globally. Multiple studies have linked levels of carcinoembryonic antigen in patient serum to poor disease prognosis. Hence, the ability to detect low levels of carcinoembryonic antigen has applications in earlier disease diagnosis, assessment, and recurrence monitoring. Existing carcinoembryonic antigen detection methods often require multiple reagents, trained operators, or complex procedures. A method alleviating these issues is the lateral flow assay, a paper-based platform that allows the detection and quantification of target analytes in complex mixtures. The tests are rapid, are point-of-care, possess a long shelf life, and can be stored at ambient conditions, making them ideal for use in a range of settings. Although lateral flow assays typically use spherical gold nanoparticles to generate the classic red signal, recent literature has shown that alternate morphologies to spheres can improve the limit of detection. In this work, we report the application of alternative gold nanoparticle morphologies, gold nanotapes (∼35 nm in length) and gold nanopinecones (∼90 nm in diameter), in a lateral flow assay for carcinoembryonic antigen. In a comparative assay, gold nanopinecones exhibited a ∼2× improvement in the limit of detection compared to commercially available spherical gold nanoparticles for the same antibody loading and total gold content, whereas the number of gold nanopinecones in each test was ∼3.2× less. In the fully optimized test, a limit of detection of 14.4 pg/mL was obtained using the gold nanopinecones, representing a 24-fold improvement over the previously reported gold-nanoparticle-based carcinoembryonic antigen lateral flow assay.

Point-of-care system for rapid real-time detection of SARS-CoV-2 virus based on commercially available Arduino platforms

The COVID-19 pandemic emphasized the importance of rapid, portable, and on-site testing technologies necessary for resource-limited settings for effective testing and screening to reduce spreading of the infection. Realizing this, we developed a fluorescence-based point-of-care (fPOC) detection system with real-time reverse transcriptase loop-mediated isothermal amplification for rapid and quantitative detection of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. The system is built based on the Arduino platform compatible with commercially available open-source hardware-software and off-the-shelf electronic components. The fPOC system comprises of three main components: 1) an instrument with integrated heaters, 2) optical detection components, and 3) an injection-molded polymeric cartridge. The system was tested and experimentally proved to be able to use for fast detection of the SARS-CoV-2 virus in real-time in less than 30 min. Preliminary results of testing the performance of the fPOC revealed that the fPOC could detect the SARS-CoV-2 virus at a limit of detection (LOD50%) at two to three copies/microliter (15.36 copies/reaction), which was comparable to reactions run on a standard commercial thermocycler. The performance of the fPOC was evaluated with 12 SARS-CoV-2 clinical throat swab samples that included seven positive and five negative samples, as confirmed by reverse transcription-polymerase chain reaction. The fPOC showed 100% agreement with the commercial thermocycler. This simple design of the fPOC system demonstrates the potential to greatly enhance the practical applicability to develop a totally integrated point-of-care system for rapid on-site screening of the SARS-CoV-2 virus in the management of the pandemic.

Research Progress and Future Trends of Microfluidic Paper-Based Analytical Devices in In-Vitro Diagnosis

In vitro diagnosis (IVD) has become a hot topic in laboratory research and achievement transformation. However, due to the high cost, and time-consuming and complex operation of traditional technologies, some new technologies are being introduced into IVD, to solve the existing problems. As a result, IVD has begun to develop toward point-of-care testing (POCT), a subdivision field of IVD. The pandemic has made governments and health institutions realize the urgency of accelerating the development of POCT. Microfluidic paper-based analytical devices (μPADs), a low-cost, high-efficiency, and easy-to-operate detection platform, have played a significant role in advancing the development of IVD. μPADs are composed of paper as the core material, certain unique substances as reagents for processing the paper, and sensing devices, as auxiliary equipment. The published reviews on the same topic lack a comprehensive and systematic introduction to μPAD classification and research progress in IVD segmentation. In this paper, we first briefly introduce the origin of μPADs and their role in promoting IVD, in the introduction section. Then, processing and detection methods for μPADs are summarized, and the innovative achievements of μPADs in IVD are reviewed. Finally, we discuss and prospect the upgrade and improvement directions of μPADs, in terms of portability, sensitivity, and automation, to help researchers clarify the progress and overcome the difficulties in subsequent μPAD research.

Monitoring gestational diabetes at the point-of-care via dual glycated albumin lateral flow assays in conjunction with a handheld reader

A dual assay cartridge was developed and used in conjunction with a handheld reader for sensing % glycated albumin to monitor gestational diabetes at home.

On-Site Detection of Carcinoembryonic Antigen in Human Serum

Real-time connectivity and employment of sustainable materials empowers point-of-care diagnostics with the capability to send clinically relevant data to health care providers even in low-resource settings. In this study, we developed an advantageous kit for the on-site detection of carcinoembryonic antigen (CEA) in human serum. CEA sensing was performed using cellulose-based lateral flow strips, and colorimetric signals were read, processed, and measured using a smartphone-based system. The corresponding immunoreaction was reported by polydopamine-modified gold nanoparticles in order to boost the signal intensity and improve the surface blocking and signal-to-noise relationship, thereby enhancing detection sensitivity when compared with bare gold nanoparticles (up to 20-fold in terms of visual limit of detection). Such lateral flow strips showed a linear range from 0.05 to 50 ng/mL, with a visual limit of detection of 0.05 ng/mL and an assay time of 15 min. Twenty-six clinical samples were also tested using the proposed kit and compared with the gold standard of immunoassays (enzyme linked immunosorbent assay), demonstrating an excellent correlation (R = 0.99). This approach can potentially be utilized for the monitoring of cancer treatment, particularly at locations far from centralized laboratory facilities.

Detection of the Chilli Leaf Curl Virus Using an Attenuated Total Reflection-Mediated Localized Surface-Plasmon-Resonance-Based Optical Platform

The development of a nanoparticle-based optical platform has been presented as a biosensor for detecting target-specific plant virus DNA. The binding dynamics of gold nanoparticles has been studied on the amine-functionalized surface by the attenuated total reflection (ATR)-based evanescent wave absorption method monitoring the localized surface plasmon resonance (LSPR). The developed surface was established as a refractive index sensor by monitoring the LSPR absorption peak of gold nanoparticles. This nanoparticle-immobilized surface was explored to establish as a biosensing platform with target-specific immunoglobulin (IgG) antibody-antigen interaction. The IgG concentration-dependent variation of absorbance was correlated with the refractive index change. After successfully establishing this ATR configuration as an LSPR-based biosensor, the single-stranded DNA of the chilli leaf curl virus was detected using its complementary DNA sequence as a receptor. The limit of detection of this sensor was determined to be 1.0 μg/mL for this target viral DNA. This ATR absorption technique has enormous potential as an LSPR based nano-biosensor for the detection of other begomoviruses.

Comparative Study of In Situ Techniques to Enlarge Gold Nanoparticles for Highly Sensitive Lateral Flow Immunoassay of SARS-CoV-2

Three techniques were compared for lowering the limit of detection (LOD) of the lateral flow immunoassay (LFIA) of the receptor-binding domain of severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) based on the post-assay in situ enlargement of Au nanoparticles (Au NPs) on a test strip. Silver enhancement (growth of a silver layer over Au NPs-Au@Ag NPs) and gold enhancement (growth of a gold layer over Au NPs) techniques and the novel technique of galvanic replacement of Ag by Au in Au@Ag NPs causing the formation of Au@Ag-Au NPs were performed. All the enhancements were performed on-site after completion of the conventional LFIA and maintained equipment-free assay. The assays demonstrated lowering of LODs in the following rows: 488 pg/mL (conventional LFIA with Au NPs), 61 pg/mL (silver enhancement), 8 pg/mL (galvanic replacement), and 1 pg/mL (gold enhancement). Using gold enhancement as the optimal technique, the maximal dilution of inactivated SARS-CoV-2-containing samples increased 500 times. The developed LFIA provided highly sensitive and rapid (8 min) point-of-need testing.

(Nano)tag-antibody conjugates in rapid tests

Antibodies (Abs) are naturally derived materials with favorable affinity, selectivity, and fast binding kinetics to the respective antigens, which enables their application as promising recognition elements in the development of various types of biosensors/bioassays, especially in rapid tests. These tests are low-cost and easy-to-use biosensing devices with broad applications including medical or veterinary diagnostics, environmental monitoring and industrial usages such as safety and quality analysis in food, providing on-site quick monitoring of various analytes, making it possible to save analysis costs and time. To reach such features, the conjugation of Abs with various nanomaterials (NMs) as tags is necessary, which range from conventional gold nanoparticles to other nanoparticles recently introduced, where magnetic, plasmonic, photoluminescent, or multi-modal properties play a critical role in the overall performance of the analytical device. In this context, to preserve the Ab affinity and provide a rapid response with long-term storage capability, the use of efficient bio-conjugation techniques is critical. Thanks to their prominent role in rapid tests, many studies have been devoted to the design and development of Abs-NMs conjugates with various chemistries including passive adsorption, covalent coupling, and affinity interactions. In this review, we present the state-of-the-art techniques allowing various Ab-NM conjugates with a special focus on the efficiency of the developed probes to be employed in in vitro rapid tests. Challenges and future perspectives on the development of Ab-conjugated nanotags in rapid diagnostic tests are highlighted along with a survey of the progress in commercially available Ab-NM conjugates.