Optical scattering artifacts observed in the development of multiplexed surface enhanced Raman spectroscopy nanotag immunoassays

Afterglow Nanoprobe-Enabled Quantitative Lateral Flow Immunoassay by a Palm-Size Device for Household Healthcare

Lateral flow immunoassay (LFIA), a classical point-of-care testing (POCT) technique, plays an important role in disease screening and healthcare monitoring. However, traditional LFIA is either designed for qualitative analysis or requires expensive equipment for quantification, limiting its use in household diagnosis. In this study, we proposed a new generation of LFIA for household health monitoring by using ultralong organic phosphorescence (UOP) nanomaterials as afterglow nanoprobes with a self-developed palm-size sensing device. The UOP nanoprobes exhibit a phosphorescence signal with a second-level lifetime, which completely avoids the interference from excitation light and biological background fluorescence. Therefore, an ultraminiaturized and low-cost UOP nanosensor was successfully designed by eliminating the complex optical path and filtering systems. We chose an inflammatory factor, C-reactive protein (CRP), for household POCT validation. The whole analysis was completed within 9 min. A limit of detection (LOD) of 0.54 ng/mL of CRP antigen was achieved with high stability and good specificity, which is comparable to laboratory instruments and fully satisfying the clinical diagnosis requirement.

Biosensors for Detection of Human Placental Pathologies: A Review of Emerging Technologies and Current Trends

Substantial growth in the biosensor research has enabled novel, sensitive and point-of-care diagnosis of human diseases in the last decade. This paper presents an overview of the research in the field of biosensors that can potentially predict and diagnosis of common placental pathologies. A survey of biomarkers in maternal circulation and their characterization methods is presented, including markers of oxidative stress, angiogenic factors, placental debris, and inflammatory biomarkers that are associated with various pathophysiological processes in the context of pregnancy complications. Novel biosensors enabled by microfluidics technology and nanomaterials is then reviewed. Representative designs of plasmonic and electrochemical biosensors for highly sensitive and multiplexed detection of biomarkers, as well as on-chip sample preparation and sensing for automatic biomarker detection are illustrated. New trends in organ-on-a-chip based placental disease models are highlighted to illustrate the capability of these in vitro disease models in better understanding the complex pathophysiological processes, including mass transfer across the placental barrier, oxidative stress, inflammation, and malaria infection. Biosensor technologies that can be potentially embedded in the placental models for real time, label-free monitoring of these processes and events are suggested. Merger of cell culture in microfluidics and biosensing can provide significant potential for new developments in advanced placental models, and tools for diagnosis, drug screening and efficacy testing.

Dual-color magnetic-quantum dot nanobeads as versatile fluorescent probes in test strip for simultaneous point-of-care detection of free and complexed prostate-specific antigen

Simultaneous detection of free and complexed prostate-specific antigen (f-PSA and c-PSA) is critical to the prostate cancer (PCa) diagnostic accuracy for clinical samples with PSA values in the diagnostic gray zone between 4 and 10 ng mL^-1. Herein, red and green magnetic-quantum dot nanobeads (MQBs) with superior magnetic property and high luminescence were fabricated via polyethyleneimine-mediated electrostatic adsorption of numerous quantum dots onto superparamagnetic Fe₃O₄ magnetic cores, and were conjugated with f-PSA antibody and c-PSA antibody, respectively, as versatile fluorescent probes in test strip for immune recognition, magnetic enrichment, and simultaneous detection of f-PSA and c-PSA analytes in complex biological matrix with t-PSA antibody on the test line. A low-cost and portable smartphone readout device with an application was also developed for the imaging of dual-color test strips and data processing. This assay can simultaneously detect f-PSA and c-PSA with the limits of detection of 0.009 ng mL^-1 and 0.087 ng mL^-1, respectively. Clinical serum samples of PCa and benign prostatic hyperplasia patients were evaluated to confirm the clinical feasibility. The results suggest that the proposed dual-color MQBs-based fluorescent lateral flow immunoassay is a promising point-of-care diagnostics technique for the accurate diagnosis of PCa even in resource-limited settings.

Calorimetric lateral flow immunoassay detection platform based on the photothermal effect of gold nanocages with high sensitivity, specificity, and accuracy

BACKGROUND

Lateral flow assays (LFA) play an increasingly important role in the rapid detection of various pathogens, pollutants, and toxins.

PURPOSE

To overcome the drawbacks of low sensitivity and poor quantification in LFA, we developed a new calorimetric LFA (CLFA) using gold nanocages (GNCs) due to their high photothermal conversion efficiency, good stability of photophysical properties, and stronger penetrating ability of NIR light.

METHODS

Thiol-polyethylene glycol-succinyl imide ester (HS-PEG-NHS) was modified onto GNCs, and the complex was conjugated with an antibody. Subsequently, the antibody-conjugated GNCs were analyzed by UV/Vis spectrophotometer, transmission electron microscope, high-resolution transmission electron microscope with energy dispersive spectrometer, dynamic light scattering instrument, and Atom force microscope. The GNC-based CLFA of alpha-fetoprotein (AFP) and zearalenone (ZEN), a food toxin, required nitrocellulose strips, a NIR laser source, and an infrared camera.

RESULTS

The GNC-labeled CLFA platform technique exhibited detection sensitivity, qualitative specificity, and quantitative accuracy. The superior performance of the technique was evident both in sandwich format detection of biomacromolecules (eg, AFP protein) or competitive format detection of small molecules (eg, ZEN). After optimizing various test parameters, GNC-labeled CLFA provided ca. 5-6-fold enhanced sensitivity, higher correlativity (R 2>0.99), and more favorable recovery (82-115%) when compared with visual LFA.

CONCLUSION

GNC-labeled CLFA may be a promising detection platform with high sensitivity, specificity, and precision.

Development of the Troponin Detection System Based on the Nanostructure

During the last 30 years, the World Health Organization (WHO) reported a gradual increase in the number of patients with cardiovascular disease (CVD), not only in developed but also in developing countries. In particular, acute myocardial infarction (AMI) is one of the severe CVDs because of the high death rate, damage to the body, and various complications. During these harmful effects, rapid diagnosis of AMI is key for saving patients with CVD in an emergency. The prompt diagnosis and proper treatment of patients with AMI are important to increase the survival rate of these patients. To treat patients with AMI quickly, detection of a CVD biomarker at an ultra-low concentration is essential. Cardiac troponins (cTNs), cardiac myoglobin (cMB), and creatine kinase MB are typical biomarkers for AMI detection. An increase in the levels of those biomarkers in blood implies damage to cardiomyocytes and thus is related to AMI progression. In particular, cTNs are regarded as a gold standard biomarker for AMI diagnosis. The conventional TN detection system for detection of AMI requires long measurement time and is labor-intensive and tedious. Therefore, the demand for sensitive and selective TN detection techniques is increasing at present. To meet this demand, several approaches and methods have been applied to develop a TN detection system based on a nanostructure. In the present review, the authors reviewed recent advances in TN biosensors with a focus on four detection systems: (1) An electrochemical (EC) TN nanobiosensor, (2) field effect transistor (FET)-based TN nanobiosensor, (3) surface plasmon resonance (SPR)-based TN nanobiosensor and (4) surface enhanced Raman spectroscopy (SERS)-based TN nanobiosensor.

SERS-based lateral flow assay for quantitative detection of C-reactive protein as an early bio-indicator of a radiation-induced inflammatory response in nonhuman primates

In accidental irradiation situations, rapid in-field evaluation of acute radiation syndrome is critical for effective triage and timely medical treatment of irradiated individuals. A surface-enhanced Raman scattering (SERS)-based lateral flow assay was developed for the quantitative detection of C-reactive protein (CRP) as an early bio-indicator of a radiation-induced inflammatory response in nonhuman primates. Raman reporter-embedded gold-core silver-shell nanoparticles with built-in hot spots were synthesized and conjugated with a CRP detection antibody to serve as SERS tags in the lateral flow assay. The proposed SERS-based lateral flow assay can rapidly detect CRP with a limit of detection of 0.01 ng mL-1 and quantitative analysis ability. Furthermore, the assay was applied to evaluate the CRP levels in plasma samples of irradiated nonhuman primates at 0 to 80 h after exposure to sublethal (4 Gy) and lethal (8 Gy) doses of total body irradiation (n = 3 animals per group). The plasma CRP levels increase rapidly within few hours after irradiation. The CRP level peaks are observed at 12 or 24 h after irradiation, with a concentration of 201.30, 386.06 and 475.18 μg mL-1 for the 4 Gy irradiated animals and 197.14, 69.52 and 358.03 μg mL-1 for the 8 Gy irradiated animals. The results indicate the potential application of the proposed SERS-based lateral flow assay to serve as a rapid and accurate point-of-care biodosimetry assay for the quantitative detection of bio-indicators to triage irradiated individuals in the field of a radiation accident.

In Vitro and In Vivo SERS Biosensing for Disease Diagnosis

For many disease states, positive outcomes are directly linked to early diagnosis, where therapeutic intervention would be most effective. Recently, trends in disease diagnosis have focused on the development of label-free sensing techniques that are sensitive to low analyte concentrations found in the physiological environment. Surface-enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy that allows for label-free, highly sensitive, and selective detection of analytes through the amplification of localized electric fields on the surface of a plasmonic material when excited with monochromatic light. This results in enhancement of the Raman scattering signal, which allows for the detection of low concentration analytes, giving rise to the use of SERS as a diagnostic tool for disease. Here, we present a review of recent developments in the field of in vivo and in vitro SERS biosensing for a range of disease states including neurological disease, diabetes, cardiovascular disease, cancer, and viral disease.

Effective Bioactivity Retention of Low-Concentration Antibodies on HFBI-Modified Fluorescence ICTS for Sensitive and Rapid Detection of PSA

Nowadays, increasing analytical sensitivity is still a big challenge in constructing membrane-based fluorescence immunochromatography test strips (FICTS). However, the bioactivity of antibody (Ab) immobilized on the test line (T line) of porous nitrocellulose membrane (PNM), which directly influences the analytical sensitivity, is less studied. In this work, a novel amphiphilic hydrophobin (HFBI) protein was introduced to modify the T line to effectively retain the Abs' bioactivity. The results indicated that HFBI could self-assemble on the PNM and immobilize the Abs in the "stand-up" orientation. Compared with the conventional FICTS, the HFBI-modified FICTS with only 0.2 mg/mL of monoclonal Abs on T line enable more accurate quantitative detection and better sensitivity (0.06 ng/mL for prostate specific antigen), which is more than 2 orders of magnitude lower than that of the conventional FICTS with the same concentration of monoclonal Abs on T line. Furthermore, the accuracy of this HFBI-modified FICTS was investigated by testing 150 clinical serum samples and the detection results were coincident with those by electrochemiluminescence immunoassay. Our results provide a novel and promising strategy of Ab immobilization on FICTS for near-patient and point-of-care application.

Rapid Detection of Listeria by Bacteriophage Amplification and SERS-Lateral Flow Immunochromatography

A rapid Listeria detection method was developed utilizing A511 bacteriophage amplification combined with surface-enhanced Raman spectroscopy (SERS) and lateral flow immunochromatography (LFI). Anti-A511 antibodies were covalently linked to SERS nanoparticles and printed onto nitrocellulose membranes. Antibody-conjugated SERS nanoparticles were used as quantifiable reporters. In the presence of A511, phage-SERS nanoparticle complexes were arrested and concentrated as a visible test line, which was interrogated quantitatively by Raman spectroscopy. An increase in SERS intensity correlated to an increase in captured phage-reporter complexes. SERS limit of detection was 6 × 10(6) pfu·mL(-1), offering detection below that obtainable by the naked eye (LOD 6 × 10(7) pfu·mL(-1)). Phage amplification experiments were carried out at a multiplicity of infection (MOI) of 0.1 with 4 different starting phage concentrations monitored over time using SERS-LFI and validated by spot titer assay. Detection of L. monocytogenes concentrations of 1 × 10(7) colony forming units (cfu)·mL(-1), 5 × 10(6) cfu·mL(-1), 5 × 10(5) cfu·mL(-1) and 5 × 10(4) cfu·mL(-1) was achieved in 2, 2, 6, and 8 h, respectively. Similar experiments were conducted at a constant starting phage concentration (5 × 10(5) pfu·mL(-1)) with MOIs of 1, 2.5, and 5 and were detected in 2, 4, and 5 h, respectively.

SERS immunoassay based on the capture and concentration of antigen-assembled gold nanoparticles

A simple, rapid, and sensitive immunoassay has been developed based on antigen-mediated aggregation of gold nanoparticles (AuNP) and surface-enhanced Raman spectroscopy (SERS). Central to this platform is the extrinsic Raman label (ERL), which consists of a gold nanoparticle modified with a mixed monolayer of a Raman active molecule and an antibody. ERLs are mixed with sample, and antigen induces the aggregation of the ERLs. A membrane filter is then used to isolate and concentrate the ERL aggregates for SERS analysis. Preliminary work to establish proof-of-principle of the platform technology utilized mouse IgG as a model antigen. The effects of membrane pore diameter and AuNP size on the analytical performance of the assay were systematically investigated, and it was determined that a pore diameter of 200 nm and AuNP diameter of 80 nm provide maximum sensitivity while minimizing signal from blank samples. Optimization of the assay provided a detection limit of 1.9 ng/mL, 20-fold better than the detection limit achieved by an ELISA employing the same antibody-antigen system. Furthermore, this assay required only 60 min compared to 24h for the ELISA. To validate this assay, mouse serum was directly analyzed to accurately quantify IgG. Collectively, these results demonstrate the potential advantages of this technology over current diagnostic tests for protein biomarkers with respect to time, simplicity, and detection limits. Thus, this approach provides a framework for prospective development of new and more powerful tools that can be designed for point-of-care diagnostic or point-of-need detection.

Accelerated surface-enhanced Raman spectroscopy (SERS)-based immunoassay on a gold-plated membrane

A rapid and simple SERS-based immunoassay has been developed to overcome diffusion-limited binding kinetics that often impedes rapid analysis in conventional heterogeneous immunoassays. This paper describes the development of an antibody-modified membrane as a flow-through capture substrate for a nanoparticle-enabled SERS immunoassay to enhance antibody-antigen binding kinetics. A thin layer of gold is plated onto polycarbonate track-etched nanoporous membranes via electroless deposition. Capture antibody is immobilized onto the surface of a gold-plated membrane via thiolate coupling chemistry to serve as a capture substrate. A syringe is then used to actively transport the analyte and extrinsic Raman labels to the capture substrate. The fabrication of the gold-plated membrane is thoroughly investigated and established as a viable capture substrate for a SERS-based immunoassay in the absence of sample/SERS label flow. A syringe pump is used to systematically investigate the effect of flow rate on antibody-antigen binding kinetics and demonstrate that active transport to the capture membrane surface expedites antibody-antigen binding. Mouse IgG and goat anti-mouse IgG are selected as a model antigen-antibody system to establish proof of principle. It is demonstrated that the assay for mouse IgG is reduced from 24 h to 10 min and a 10-fold improvement in detection limit is achieved with the flow assay developed herein relative to the passive, i.e., no flow, assay. Moreover, mouse serum is directly analyzed and IgG level is determined using the flow assay.