Lateral flow immunochromatographic assay for sensitive pesticide detection by using Fe3O4 nanoparticle aggregates as color reagents

Simple and sensitive detection of HBsAg by using a quantum dots nanobeads based dot-blot immunoassay

Simple and sensitive detection of infectious disease at an affordable cost is urgently needed in developing nations. In this regard, the dot blot immunoassay has been used as a common protein detection method for detection of disease markers. However, the traditional signal reporting systems, such as those using enzymes or gold nanoparticles lack sensitivity and thus restrict the application of these methods for disease detection. In this study, we report a simple and sensitive detection method for the detection of infectious disease markers that couples the dot-blot immunoassay with quantum dots nanobeads (QDNBs) as a reporter. First, the QDNBs were prepared by an oil-in-water emulsion-evaporation technique. Because of the encapsulation of several QDs in one particle, the fluorescent signal of reporter can be amplified with QDNBs in a one-step test and be read using a UV lamp obviating the need for complicated instruments. Detection of disease-associated markers in complex mixture is possible, which demonstrates the potential of developing QDNBs into a sensitive diagnostic kit.

Ultrasensitive protein detection: a case for microfluidic magnetic bead-based assays

We review the use of magnetic micro- and nanoparticles ('magnetic beads') in microfluidic systems for ultrasensitive protein detection. During recent years magnetic beads have been used frequently in immunoassays, either as mobile substrates on which the target antigen is captured, as detection labels, or simultaneously as substrates and labels. The major part of the reviewed work has as application the detection of antibodies or disease biomarkers in serum or of biotoxins from food samples. Several of the most sensitive assays allow protein detection down to fg mL(-1) concentrations. We benchmark the performance of these microfluidic magnetic bead-based assays with the most promising earlier work and with alternative solutions.

A PCR based magnetic assembled sensor for ultrasensitive DNA detection

An ultrasensitive method for DNA detection based on magnetic assembly induced by polymerase chain reaction (PCR) was developed. The sensor showed a low limit of detection (LOD) of 4.26 aM with a wide range of target DNA from 0.01 fM to 10,000 fM.

Oligonucleotide-linked gold nanoparticle aggregates for enhanced sensitivity in lateral flow assays

Lateral flow assays (LFAs) as rapid analytical techniques promise to be widely used in point-of-care (POC) diagnostics because of their affordability and simplicity. However, LFAs still suffer from low sensitivity in detection of various biomarkers, e.g., nucleic acids. In this study, we developed a simple and general one-step signal amplification strategy, which employed oligonucleotide-linked gold nanoparticle (AuNP) aggregates to enhance the sensitivity in nucleic acid lateral flow (NALF) assays. Using a nucleic acid sequence of human immunodeficiency virus type 1 (HIV-1) as a model analyte, we observed that the detection limit of the developed NALF assay was 0.1 nM, which was improved by 2.5-fold compared with that of a non-signal amplification approach. The methodology described here could be used to detect a broad range of nucleic acids, and the general signal amplification approach could be potentially adopted in other types of LFAs.

Polyelectrolyte-coated gold magnetic nanoparticles for immunoassay development: toward point of care diagnostics for syphilis screening

Immediate response for disease control relies on simple, inexpensive, and sensitive diagnostic tests, highly sought after for timely and accurate test of various diseases, including infectious diseases. Composite Fe3O4/Au nanoparticles have attracted considerable interest in diagnostic applications due to their unique physical and chemical properties. Here, we developed a simple coating procedure for gold magnetic nanoparticles (GMNs) with poly(acrylic acid) (PAA). PAA-coated GMNs (PGMNs) were stable and monodispersed and characterized by Fourier transform-infrared spectroscopy (FT-IR), transmission electron microscopy, UV-visible scanning spectrophotometry, thermogravimetric analysis, and Zetasizer methodologies. For diagnostic application, we established a novel lateral flow immunoassay (LFIA) strip test system where recombinant Treponema pallidum antigens (r-Tp) were conjugated with PGMNs to construct a particle probe for detection of anti-Tp antibodies. Intriguingly, the particle probes specifically identified Tp antibodies with a detection limitation as low as 1 national clinical unit/mL (NCU/mL). An ample pool of 1020 sera samples from three independent hospitals were obtained to assess our PGMNs-based LFIA strips, which exhibited substantially high values of sensitivity and specificity for all clinical tests (higher than 97%) and, therefore, proved to be a suitable approach for syphilis screening at a point-of-care test manner.

Biosensing approaches for rapid genotoxicity and cytotoxicity assays upon nanomaterial exposure

The increased utilization of nanomaterials could affect human health and the environment due to increased exposure. Several mechanisms regarding the negative effects of nanomaterials have been proposed, one of the most discussed being oxidative stress. Many studies have shown that some metal oxide nanoparticles can enhance reactive oxygen species generation, inducing oxidative stress, DNA damage, and unregulated cell signaling, and eventually leading to changes in cell motility, apoptosis, and even carcinogenesis. 8-Hydroxy-2'-deoxyguanosine (8-OHdG) is one of the predominant forms of oxidative DNA damage, and has therefore been widely used as a biomarker for oxidative stress and carcinogenesis. Ther are two major objectives to this study. Firstly, the development of a novel lateral flow immunoassay (LFIA) is presented to measure the concentration of 8-OHdG in cells and thus reveal the nanotoxicity on the genomic level. The feasibility of this new method is validated by comparison with two other established methods: Alamar Blue assay and a recently developed electrical impedance sensing (EIS) system on the level of cell proliferation/viability. Secondly, the toxicological effects of three metallic nanoparticles (CuO, CdO, and TiO2 ) are investigated and compared using these three methods with completely different mechanisms. The results show that there is a high variation among different nanoparticles concerning their ability to cause toxic effects. CuO nanoparticles are the most potent regarding cytotoxicity and DNA damage. CdO shows a fallen cell viability as well as DNA damage, however, to a lesser extent than CuO nanoparticles. TiO2 particles only cause very limited cytotoxicity, and there is no obvious increase in 8-OHdG levels. In conclusion, LFIA as well as the EIS system are useful methods for quantitative or qualitative nanotoxicity assessments with high sensitivity, specificity, speed of performance, and simplicity.

Self-assembled nanoparticle arrays for multiphase trace analyte detection

Nanoplasmonic structures designed for trace analyte detection using surface-enhanced Raman spectroscopy typically require sophisticated nanofabrication techniques. An alternative to fabricating such substrates is to rely on self-assembly of nanoparticles into close-packed arrays at liquid/liquid or liquid/air interfaces. The density of the arrays can be controlled by modifying the nanoparticle functionality, pH of the solution and salt concentration. Importantly, these arrays are robust, self-healing, reproducible and extremely easy to handle. Here, we report on the use of such platforms formed by Au nanoparticles for the detection of multi-analytes from the aqueous, organic or air phases. The interfacial area of the Au array in our system is ≈25 mm(2) and can be made smaller, making this platform ideal for small-volume samples, low concentrations and trace analytes. Importantly, the ease of assembly and rapid detection make this platform ideal for in-the-field sample testing of toxins, explosives, narcotics or other hazardous chemicals.

The effects of size and synthesis methods of gold nanoparticle-conjugated MαHIgG4 for use in an immunochromatographic strip test to detect brugian filariasis

This study describes the properties of colloidal gold nanoparticles (AuNPs) with sizes of 20, 30 and 40 nm, which were synthesized using citrate reduction or seeding-growth methods. Likewise, the conjugation of these AuNPs to mouse anti-human IgG(4) (MαHIgG(4)) was evaluated for an immunochromatographic (ICG) strip test to detect brugian filariasis. The morphology of the AuNPs was studied based on the degree of ellipticity (G) of the transmission electron microscopy images. The AuNPs produced using the seeding-growth method showed lower ellipticity (G ≤ 1.11) as compared with the AuNPs synthesized using the citrate reduction method (G ≤ 1.18). Zetasizer analysis showed that the AuNPs that were synthesized using the seeding-growth method were almost monodispersed with a lower polydispersity index (PDI; PDI≤0.079), as compared with the AuNPs synthesized using the citrate reduction method (PDI≤0.177). UV-visible spectroscopic analysis showed a red-shift of the absorbance spectra after the reaction with MαHIgG(4), which indicated that the AuNPs were successfully conjugated. The optimum concentration of the BmR1 recombinant antigen that was immobilized on the surface of the ICG strip on the test line was 1.0 mg ml(-1). When used with the ICG test strip assay and brugian filariasis serum samples, the conjugated AuNPs-MαHIgG(4) synthesized using the seeding-growth method had faster detection times, as compared with the AuNPs synthesized using the citrate reduction method. The 30 nm AuNPs-MαHIgG(4), with an optical density of 4 from the seeding-growth method, demonstrated the best performance for labelling ICG strips because it displayed the best sensitivity and the highest specificity when tested with serum samples from brugian filariasis patients and controls.

Immunospot assay based on fluorescent nanoparticles for Dengue fever detection

Dengue fever is one of the most neglected tropical diseases and of highest international public health importance, with 50 million cases worldwide every year. Early detection can decrease mortality rates from more than 20% to less than 1% and the relevant early diagnosis analyte is the viral non-structural glycoprotein, NS1. Currently, enzyme linked immunosorbent assay (ELISA) is the method of choice to detect NS1. However, this is a time consuming method, requiring 3-5h, and it is the bottleneck for routine of clinical analysis laboratory in epidemic periods, when hundreds of samples should be tested. Here we describe an easy method combining principles of fluorophore linked immunosorbent assay (FLISA) and enzyme linked immunospotting (ELISPOT). For detection, we used mouse anti-NS1 IgG labeled with fluorescent nanoparticles. The presented procedure needs only 4 μL of serum samples and requires 45-60 min. The detection limit, 5.2 ng/mL, is comparable to ELISA tests. The comparison of 83 samples with a commercial ELISA revealed a sensitivity of 81% and specificity of 88%. The use of fluorescent nanoparticles provides a higher sensitivity than an assay using usual fluorescent dye molecules, besides avoiding bleaching effects. Based on the results, the proposed method provides fast, specific and sensitive results, and proves to be a suitable method for Dengue NS1 detection in impoverished regions or epidemic areas.

Computational lateral flow biosensor for proteins and small molecules: a new class of strip logic gates

The first example of strip logic gates ("OR" and "AND" functions) for proteins and small molecules has been constructed on the basis of target-induced self-assembly of split aptamer fragments. Using thrombin and ATP as inputs, the corresponding split/integrated aptamers as molecular recognition elements, and gold nanoparticles as a tracer, the output signals can be directly visualized by observing the red bands on the test zones of the strips. The assay is simple, easy to perform, and cost-effective, allowing portable analysis at ambient temperature. The strip logic system is resistant to nonspecific interfering agents and can operate effectively even in human serum samples. Such logic strips hold great promise for application in intelligent point-of-care and in-field diagnostics.