Au@Ag SERRS tags coupled to a lateral flow immunoassay for the sensitive detection of pneumolysin

Rapid and Ultrasensitive Quantification of Multiplex Respiratory Tract Infection Pathogen via Lateral Flow Microarray based on SERS Nanotags

Respiratory tract infections (RTIs) are severe acute infectious diseases, which require the timely and accurate identification of the pathogens involved so that the individual treatment plan can be selected, including optimized use of antibiotics. However, high throughput and ultrasensitive quantification of multiple nucleic acids is a challenge in a point of care testing (POCT) device.

Methods: Herein, we developed a 2×3 microarray on a lateral flow strip with surface enhanced Raman scattering (SERS) nanotags encoding the nucleic acids of 11 common RTI pathogens. On account of the signal magnification of encoded SERS nanotags in addition to the high surface area to volume ratio of the nitrocellulose (NC) membrane, rapid quantification of the 11 pathogens with a broad linear dynamic range (LDR) and ultra-high sensitivity was achieved on one lateral flow microarray.

Results: The limit of detection (LOD) for influenza A, parainfluenza 1, parainfluenza 3, respiratory syncytial virus, coxiella burnetii, legionella pneumophila, influenza B, parainfluenza 2, adenovirus, chlamydophila pneumoniae, and mycoplasma pneumoniae were calculated to be 0.031 pM, 0.030 pM, 0.038 pM, 0.038 pM, 0.040 pM, 0.039 pM, 0.035 pM, 0.032 pM, 0.040 pM, 0.039 pM, and 0.041 pM, respectively. The LDR of measurement of the target nucleic acids of the eleven RTI pathogens were 1 pM-50 nM, which span 5 orders of magnitude.

Conclusions: We anticipate this novel approach could be widely adopted in the early and precise diagnosis of RTI and other diseases.

Disposable Sensors in Diagnostics, Food, and Environmental Monitoring

Disposable sensors are low-cost and easy-to-use sensing devices intended for short-term or rapid single-point measurements. The growing demand for fast, accessible, and reliable information in a vastly connected world makes disposable sensors increasingly important. The areas of application for such devices are numerous, ranging from pharmaceutical, agricultural, environmental, forensic, and food sciences to wearables and clinical diagnostics, especially in resource-limited settings. The capabilities of disposable sensors can extend beyond measuring traditional physical quantities (for example, temperature or pressure); they can provide critical chemical and biological information (chemo- and biosensors) that can be digitized and made available to users and centralized/decentralized facilities for data storage, remotely. These features could pave the way for new classes of low-cost systems for health, food, and environmental monitoring that can democratize sensing across the globe. Here, a brief insight into the materials and basics of sensors (methods of transduction, molecular recognition, and amplification) is provided followed by a comprehensive and critical overview of the disposable sensors currently used for medical diagnostics, food, and environmental analysis. Finally, views on how the field of disposable sensing devices will continue its evolution are discussed, including the future trends, challenges, and opportunities.

Detection of resistance protein A (MxA) in paper-based immunoassays with surface enhanced Raman spectroscopy with AuAg nanoshells

Myxovirus protein A (MxA) is a biomarker that can be used to distinguish between viral and bacterial infections. While MxA lateral flow assays (LFAs) have been successfully used for viral vs. bacterial differential diagnosis for children, the clinically relevant level of MxA for adults has been reported to be 100 times lower, which is too low for traditional LFAs. We present results applying the use of surface enhanced Raman spectroscopy (SERS) to detect MxA. AuAg nanoshells (AuAg NSs) were used to enhance the Raman signal of mercaptobenzoic acid (4-MBA), enabling readout by SERS. The AuAg NSs were conjugated to antibodies for the biomarker of interest, resulting in a "nanotag", that could be used in a dipstick immunoassay for detection. We first optimized the nanotag parameters using anti-human IgG/human IgG as a model antibody/antigen system, and then demonstrated detection of MxA using anti-MxA antibodies. We show that SERS readout of immunoassays for MxA can quantify MxA levels at clinically relevant levels for adult viral infection.

Magnetic SERS Strip for Sensitive and Simultaneous Detection of Respiratory Viruses

Rapid and early diagnosis of respiratory viruses is key to preventing infections from spreading and guiding treatments. Here, we developed a sensitive and quantitative surface-enhanced Raman scattering-based lateral flow immunoassay (SERS-based LFIA) strip for simultaneous detection of influenza A H1N1 virus and human adenovirus (HAdV) by using Fe₃O₄@Ag nanoparticles as magnetic SERS nanotags. The new type of Fe₃O₄@Ag magnetic tags, which were conjugated with dual-layer Raman dye molecules and target virus-capture antibodies, performs the following functions: specific recognition and magnetic enrichment of target viruses in the solution and SERS detection of the viruses on the strip. Based on this strategy, the magnetic SERS strip can directly be used for real biological samples without any sample pretreatment steps. The limits of detection for H1N1 and HAdV were 50 and 10 pfu/mL, respectively, which were 2000 times more sensitive than those from the standard colloidal gold strip method. Moreover, the proposed strip is easy to operate, rapid, stable, and can achieve high throughput and is thus a potential tool for early detection of virus infection.

Surface-Enhanced Raman Scattering Tags for Three-Dimensional Bioimaging and Biomarker Detection

We have recently witnessed a major improvement in the quality of nanoparticles encoded with Raman-active molecules (SERS tags). Such progress relied mainly on a major improvement of fabrication methods for building-blocks, resulting in widespread application of this powerful tool in various fields, with the potential to replace commonly used techniques, such as those based on fluorescence. We present hereby a brief Perspective on surface enhanced Raman scattering (SERS) tags, regarding their composition, morphology, and structure, and describe our own selection from the current state-of-the-art. We then focus on the main bioimaging applications of SERS tags, showing a gradual evolution from two-dimensional studies to three-dimensional analysis. Recent improvements in sensitivity and multiplexing ability have enabled great advancements toward in vivo applications, e.g., highlighting tumor boundaries to guide surgery. In addition, the high level of biomolecule sensitivity reached by SERS tags promises an expansion toward biomarker detection in cases for which traditional methods offer limited reliability, as a consequence of the frequently low analyte concentrations.

Facile immobilization of glucose oxidase onto gold nanostars with enhanced binding affinity and optimal function

Gold nanoparticles provide a user-friendly and efficient surface for immobilization of enzymes and proteins. In this paper, we present a novel approach for enzyme bioconjugation to gold nanostars (AuNSs). AuNSs were modified with l-cysteine (Cys) and covalently bound to N-hydroxysulfosuccinimide (sulfo-NHS) activated intermediate glucose oxidase (GOx) to fabricate a stable and sensitive AuNSs-Cys-GOx bioconjugate complex. Such a strategy has the potential for increased attachment affinity without protein adsorption onto the AuNSs surface. Good dispersity in buffer suspension was observed, as well as stability in high ionic environments. Using the AuNSs-Cys-GOx bioconjugates showed greater sensitivity in the measuring of low concentrations of glucose based on plasmonic and colorimetric detection. Such a novel approach for enzyme immobilization can lead to AuNSs-Cys-GOx bioconjugate complexes that can be used as catalytic nanodevices in nanobiosensors based on oxidases in biomedical applications.

Inorganic Complexes and Metal-Based Nanomaterials for Infectious Disease Diagnostics

Infectious diseases claim millions of lives each year. Robust and accurate diagnostics are essential tools for identifying those who are at risk and in need of treatment in low-resource settings. Inorganic complexes and metal-based nanomaterials continue to drive the development of diagnostic platforms and strategies that enable infectious disease detection in low-resource settings. In this review, we highlight works from the past 20 years in which inorganic chemistry and nanotechnology were implemented in each of the core components that make up a diagnostic test. First, we present how inorganic biomarkers and their properties are leveraged for infectious disease detection. In the following section, we detail metal-based technologies that have been employed for sample preparation and biomarker isolation from sample matrices. We then describe how inorganic- and nanomaterial-based probes have been utilized in point-of-care diagnostics for signal generation. The following section discusses instrumentation for signal readout in resource-limited settings. Next, we highlight the detection of nucleic acids at the point of care as an emerging application of inorganic chemistry. Lastly, we consider the challenges that remain for translation of the aforementioned diagnostic platforms to low-resource settings.

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.

Rapid, Quantitative, and Ultrasensitive Point-of-Care Testing: A Portable SERS Reader for Lateral Flow Assays in Clinical Chemistry

The design of a portable Raman/SERS-LFA reader with line illumination using a custom-made fiber optic probe for rapid, quantitative, and ultrasensitive point-of-care testing (POCT) is presented. The pregnancy hormone human chorionic gonadotropin (hCG) is detectable in clinical samples within only 2-5 s down to approximately 1.6 mIU mL-1 . This acquisition time is several orders of magnitude shorter than those of existing approaches requiring expensive Raman instrumentation, and the method is 15-times more sensitive than a commercially available lateral flow assay (LFA) as the gold standard. The SERS-LFA technology paves the way for affordable, quantitative, and ultrasensitive POCT with multiplexing potential in real-world applications, ranging from clinical chemistry to food and environmental analysis as well as drug and biowarfare agent testing.

Highly luminescent green-emitting Au nanocluster-based multiplex lateral flow immunoassay for ultrasensitive detection of clenbuterol and ractopamine

A multiplex lateral flow immunoassay sensor based on highly luminescent green-emitting Au nanoclusters (AuNCs-MLFIA sensor) was successfully established for the simultaneous and quantitative determination of clenbuterol (Clen) and ractopamine (RAC) in swine urine. The antigens of Clen and RAC were dispersed on a nitrocellulose membrane as two test lines, and the Au nanoclusters were synthesized from 6-aza-2-thiothymine and l-arginine to obtain highly green luminescence and ultra-small nanoparticles (Arg/ATT/AuNCs). Free carboxyl groups on Arg/ATT/AuNCs enabled conjugation with biomolecules to afford an indicator for the biosensor. The AuNCs-MLFIA sensor is based on the indirect competition assay and could successfully detect samples within 18 min without sample pretreatment, qualitative results can be obtained by visual inspection under a UV lamp. The limits of detection of Clen and RAC by the naked eye were both 0.25 μg L^-1. In addition, the AuNCs-MLFIA sensor allowed quantitative detection combined with a portable fluorescence reader. The half-maximal inhibitory concentrations of Clen and RAC were 0.06 and 0.32 μg L^-1, respectively, with detection limits of 0.003 and 0.023 μg L^-1. Thirty blind-spiked swine urine samples were analyzed by the AuNCs-MLFIA sensor and liquid chromatography-tandem mass spectrometry, and the results of the two methods showed a significant correlation. The newly developed AuNCs-MLFIA sensor overcomes several limitations of conventional LFIA sensors, including their low sensitivity, limitation to quantify analytes, and single-analyte detection.

Label-free identification carbapenem-resistant Escherichia coli based on surface-enhanced resonance Raman scattering

In this study, a surface-enhanced resonance Raman scattering (SERRS) method has been developed for the accurate detection and identification of carbapenem-resistant and carbapenem-sensitive Escherichia coli. A total of 89 human isolates of Enterobacteriaceae, comprising 41 strains of carbapenem-sensitive E. coli (CSEC) and 48 strains of carbapenem-resistant E. coli (CREC), were tested to assess the feasibility of our proposed SERRS method as a clinical tool, and the results showed almost 100% accuracy.

Dual dye-loaded Au@Ag coupled to a lateral flow immunoassay for the accurate and sensitive detection of Mycoplasma pneumoniae infection

We present an attractive model of surface-enhanced Raman scattering-based lateral flow immunoassay (SERS-LFIA) for the sensitive and accurate detection of Mycoplasma pneumoniae (MP) infection in human serum. The SERS-LFIA strip uses Au@Ag nanoparticles (Au@Ag NPs) loaded with two layers of Raman dye 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) as SERS tags. The advantages of the dual dye-loaded SERS tags (Au/DTNB@Ag/DTNB) are the high sensitivity and the bioconjugation flexibility of the detection antibody. As determined from our SERS-LFIA strip, human IgM was quantified by monitoring the SERS signal on the test line. The limit of detection for human IgM was 0.1 ng mL⁻¹, which was 100 times more sensitive than that by using the colorimetric method. Our assay results for 20 MP-specific IgM positive serum specimens showed 100% accuracy and detection rate, whereas the parallel enzyme-linked immunosorbent assay only showed 85% detection rate. The SERS-LFIA strip also exhibited high specificity and potential clinical applications. Therefore, our SERS-based LFIA strip has strong potential for practical applications in the sensitive and rapid detection of MP.

Schematic illustration of quantitative detection of human IgM using SERS-based lateral flow immunoassay.

Facile synthesis of high-performance SiO2@Au core–shell nanoparticles with high SERS activity

This study proposes a facile and general method for fabricating a wide range of high-performance SiO₂@Au core–shell nanoparticles (NPs).

Recent advances in nanoparticle-based lateral flow immunoassay as a point-of-care diagnostic tool for infectious agents and diseases

Recent advances in lateral flow immunoassay-based devices as a point-of-care analytical tool for the detection of infectious diseases are reviewed.

Versatile design and synthesis of nano-barcodes

This review provides a critical discussion on the versatile designing and usage of nano-barcodes for various existing and emerging applications.

Chemical modification of antibodies enables the formation of stable antibody–gold nanoparticle conjugates for biosensing

Antibody-modified gold nanoparticles (AuNPs) are central to many novel and emerging biosensing technologies due to the specificity provided by antibody–antigen interactions and the unique properties of nanoparticles.