Competitive quenching fluorescence immunoassay for chlorophenols based on laser-induced fluorescence detection in microdroplets

Extra- and Intracellular Monitoring of TGF-β Using Single Immunoplasmonic Nanoprobes

Transforming growth factor-β (TGF-β) is a well-known disease-related biomarker associated with fibrotic diseases, and initiation and progression of cancer in many organs. Therefore, quantitative and sensitive detection of TGF-β and similar biomarkers is crucial for patient treatment in the early stages of diagnosis. In many studies, the detection of TGF-β, an important profibrotic and cancer promoting cytokine, has been generally conducted by fluorescence or absorbance-based immunoassays. However, conventional methods for detecting TGF-β have problems including use of time-consuming sample pretreatment steps and multiple reagents for signal amplification and difficulty in real-time detection from living cells. Herein, we present a plasmon-based immunoassay for TGF-β using antibody-conjugated single gold nanoparticles that act as optically excellent intracellular and extracellular detection probes that do not require additional signal amplification. To detect TGF-β sensitively and selectively, we exploited the localized surface plasmon resonance (LSPR) property of antibody-conjugated plasmonic gold nanoparticles at a single particle level. By measuring the LSPR spectral shifts of the single plasmonic nanoprobes, TGF-β can be detected down to the picomolar level, which is comparable with the conventional methods but without significant interference from other proteins. The optimized plasmonic nanoprobes were applied to quantify and monitor the extracellular TGF-β level secreted from the cells under stress conditions, such as cancer, and exposure to toxic environments. Owing to the ease of cellular internalization of the nanoprobes, we directly image and detect increases in intracellular TGF-β levels in living cells under the given stress conditions without cell lysis. We envision that this strategy of using individual nanoparticles as sensors to monitor protein biomarkers in living cells could be applied for various biological assays and diagnosis.

A novel fluorescence probe based on p-acid-Br and its application in thiourea detection

A novel organic fluorescence system was developed to detect thiourea based on p-acid-Br, which in the range of 0.5–1000 nM and with a detection limit of 0.26 nM. And this method provides a new promising platform for clinical analysis.

Aqueous synthesis of color-tunable CuInS2/ZnS nanocrystals for the detection of human interleukin 6

In this Article, we present a facile microwave-assisted synthesis route for the preparation of water-soluble and high-quality CuInS2/ZnS nanocrystals (NCs) with glutathione as the stabilizer. The as-prepared CuInS2/ZnS NCs exhibited small particle sizes (~3.3 nm), long photoluminescence lifetimes, and color-tunable properties ranging from the visible to the near-infrared by varying the initial ratio of Cu/In in the precursors. The low-toxicity, highly luminescent and biocompatible CuInS2/ZnS NCs were applied to cell imaging, showing that they could be used as promising fluorescent probes. Furthermore, the CuInS2/ZnS NCs were used as the signal labels for a fluoroimmunoassay of the biomarker IL-6, showing their great potential for use as reliable point-of-care diagnostics for biomarkers of cancer and other diseases.

Optical immunosensors for environmental monitoring: How far have we come?

Immunosensing has proved to be a very interesting research area. This review discusses what has actually been achieved in the field of optical immunosensing for environmental screening, and what still needs to be done. The review is presented from a practical point of view. In terms of the basic design of the immunosensor, there is a trend towards decreasing assay time; indeed, this has been reduced from 15-20 minutes to less than 5 minutes. Another goal is to simplify the manifold, and label-free approaches combining indirect assay formats and the detection of antibody binding are popular. Rapid displacement assays have also been investigated thoroughly. In terms of some important features of immunosensing devices, the reusability of the sensing element has been studied in great depth, and working lifetimes of more than five hundred assays can now be found for all assay formats. Multianalyte assays are now being investigated, and current systems are able to monitor 2-3 target compounds, although this number is set to increase greatly (to >30) in the near future. In this sense, an increasing number of publications can be found on microarrays intended for multianalyte determinations. The application of immunosensing to real situations is the main challenge. Immunosensors are barely commercialized and are yet to be established as research or routine tools, due to a lack of validated protocols for a wide range of sample matrices. Regarding compounds considered as analytes, some significant pollutants such as dioxins or pharmaceuticals are rarely chosen as targets, although the current tendency is towards a broader spectrum of analytes. New immunoreagents should be raised for these compounds, for use in immunosensors that can be used as screening tools.

A novel competitive fluorescence immunoassay for the determination of dibutyl phthalate

A novel, sensitive, and specific competitive fluorescence immunoassay has been developed for the quantitative determination of dibutyl phthalate (DBP) using an antibody-coated plate format. Hapten was synthesized in order to produce polyclonal antibodies against dibutyl phthalate. Polyclonal antisera to dibutyl phthalate were generated in rabbits and used to construct the fluorescence immunoassay for measurement of dibutylphthalate. The assay had a detection limit of about 0.02 microg L(-1), a dynamic range of approximately 0.1-300 microg L(-1). Other similar phthalate compounds do not interfere significantly in the analysis using this immunoassay technique, and the cross-reactivity rates were less than 10%. The study demonstrated that the developed antiserum and fluorescence immunoassay procedure can be used to detect dibutyl phthalate in environmental samples such as tap water, river water, drinking water, and leachate from plastic drinking water bottles.

Fluoroimmunoassay for Antigen Based on Fluorescence Quenching Signal of Gold Nanoparticles

A unique, sensitive, and highly specific fluoroimmunoassay system for antigen detection using gold and magnetic nanoparticles has been developed. The assay is based on the fluorescence quenching of fluorescein isothiocyanate caused by gold nanoparticles coated with monoclonal antibody. To demonstrate its analytical capabilities, the magnetic nanoparticles were coated with anti-alpha-fetoprotein polyclonal antibodies, which specifically bound with alpha-fetoprotein. Gold nanoparticles coated with anti-alpha-fetoprotein monoclonal antibodies could sandwich the alpha-fetoprotein captured by the magnetic nanoparticle probes. The sandwich-type immunocomplex was formed on the surface of magnetic nanoparticles and could be separated by a magnetic field. The supernatant liquid, which contained the unbound gold nanoparticle probes, was used to quench the fluorescence, and the fluorescence intensity of fluorescein isothiocyanate at 516 nm was proportional to the alpha-fetoprotein concentration. The result showed that the limit of detection of alpha-fetoprotein was 0.17 nM. This new system can be extended to detect target molecules with matched antibodies and has broad potential applications in immunoassay and disease diagnosis.

Microscopic determination of tetracycline based on aluminum-sensitized fluorescence of a self-ordered ring formed by a sessile droplet on glass slide support

A fluorescent microscopic determination of trace amount of tetracycline is reported based on the aluminum-sensitized fluorescence effect of a self-ordered ring formed by a sessile droplet on glass slide support. Since the evaporative loss of the solvent from the edge wedge of the droplet that is spotted on a hydrophobic-treated glass slide, an outward capillary flow of the interior solvent of the droplet occurs. The resulted outward capillary flow then carries the solute to the perimeter of the droplet spot where the solute accumulates to form a fluorescent self-ordered ring (SOR). Depending on the spotted volume of the aluminum-tetracycline chelate solution, different size of SOR with the outer diameter (o.d.) less than 1.1mm and the ring belt width less than 21.6 microm can be obtained. Data analysis for the imaged SOR by using a digitalized CCD camera showed that the chelate molecule across the fluorescent SOR belt section follows a Gaussian distribution, and the maximum fluorescent intensity (I(max)) was found to be proportional to tetracycline content. When a 0.1 microl droplet was spotted on the solid surface, tetracycline in the range of 7.5-800.0 fmol (or 7.9 x 10(-8) to 800.0 x 10(-8)moll (-1)) can be detected, and the limit of detection can reach 0.8 fmol (or 7.9 x 10(-9) moll (-1)). With present method, the contents of tetracycline in capsule, tablet, urine and fresh milk were satisfactorily detected with the recoveries of 97.0-106.5% and RSD of 1.2-4.2%, correspondingly.