A fluorescent magnetic core-shell nanosensor for detection of copper ions in natural waters.

A nanosensor based on magnetic core-shell nanoparticles functionalized with rhodamine derivative, N-(3-carboxy)acryloyl rhodamine B hydrazide (RhBCARB), using (3-aminopropyl)triethoxysilane (APTES) as a linker, has been synthesized for detection of Cu(II) ions in water. The magnetic nanoparticle and the modified rhodamine were fully characterized, showing a strong orange emission sensitive to Cu(II) ions. The sensor shows a linear response from 10 to 90 µg L-1, detection limit of 3 µg L-1 and no interference of Ni(II), Co(II), Cd(II), Zn(II), Pb(II), Hg(II) and Fe(II) ions. The nanosensor performance is similar to those described in the literature, being a viable option for the determination of Cu(II) ions in natural waters. In addition, the magnetic sensor can be easily removed from the reaction medium with the aid of a magnet and its signal recovered in acidic solution, allowing its reuse in subsequent analysis.

Optimizing and Quantifying Gold Nanospheres Based on LSPR Label-Free Biosensor for Dengue Diagnosis.

The localized surface plasmon resonance (LSPR) due to light-particle interaction and its dependence on the surrounding medium have been widely manipulated for sensing applications. The sensing efficiency is governed by the refractive index-based sensitivity (ηRIS) and the full width half maximum (FWHM) of the LSPR spectra. Thereby, a sensor with high precision must possess both requisites: an effective ηRIS and a narrow FWHM of plasmon spectrum. Moreover, complex nanostructures are used for molecular sensing applications due to their good ηRIS values but without considering the wide-band nature of the LSPR spectrum, which decreases the detection limit of the plasmonic sensor. In this article, a novel, facile and label-free solution-based LSPR immunosensor was elaborated based upon LSPR features such as extinction spectrum and localized field enhancement. We used a 3D full-wave field analysis to evaluate the optical properties and to optimize the appropriate size of spherical-shaped gold nanoparticles (Au NPs). We found a change in Au NPs' radius from 5 nm to 50 nm, and an increase in spectral resonance peak depicted as a red-shift from 520 nm to 552 nm. Using this fact, important parameters that can be attributed to the LSPR sensor performance, namely the molecular sensitivity, FWHM, ηRIS, and figure of merit (FoM), were evaluated. Moreover, computational simulations were used to assess the optimized size (radius = 30 nm) of Au NPs with high FoM (2.3) and sharp FWHM (44 nm). On the evaluation of the platform as a label-free molecular sensor, Campbell's model was performed, indicating an effective peak shift in the adsorption of the dielectric layer around the Au NP surface. For practical realization, we present an LSPR sensor platform for the identification of dengue NS1 antigens. The results present the system's ability to identify dengue NS1 antigen concentrations with the limit of quantification measured to be 0.07 µg/mL (1.50 nM), evidence that the optimization approach used for the solution-based LSPR sensor provides a new paradigm for engineering immunosensor platforms.

Rapid and sensitive detection of ochratoxin A using antibody-conjugated gold nanoparticles based on Localized Surface Plasmon Resonance.

The regulation of tolerable levels of ochratoxin A in food for human and animal consumption has been defined in some countries. To meet these levels, simpler, more efficient, and faster analytical methods are being developed to facilitate the identification of this dangerous contaminant in food. Here, we combined gold nanoparticles (AuNPs) with anti-ochratoxin A (OTA) IgG to detect elementary levels of OTA based on Localized Surface Plasmon Resonance. AuNPs were prepared with trisodium citrate and characterized by UV-visible spectroscopy, X-ray, dynamic light scattering, and transmission electron microscopy. The conjugation of AuNPs to IgG anti-OTA was confirmed by bathochromic shift (UV-vis) and RAMAN spectroscopy. The sensitivity of the nanosensor was investigated by measuring LSPR band λmax shifts. Our results suggest this assay is highly sensitive, with a lower detection limit of about 0.001 pg mL-1. The LSPR nanosensor reduced detection limits by roughly 10 times compared to other methods. We demonstrated that the approach investigated here is a rapid and sensitive method for OTA detection.

CdTe Quantum Dots Modified with Cysteamine: A New Efficient Nanosensor for the Determination of Folic Acid.

In this paper, we report the synthesis, characterization, and application of a new fluorescent nanosensor based on water-soluble CdTe quantum dots (QDs) coated with cysteamine (CA) for the determination of folic acid (FA). CdTe/CA QDs were characterized by high-resolution transmission electron microscopy, the zeta potential, and Fourier-transform infrared (FT-IR), UV-visible, and fluorescence spectroscopy. CdTe QDs coated with mercaptopropionic acid (MPA) and glutathione (GSH) were prepared for comparison purposes. The effect of FA on the photoluminescence intensity of the three thiol-capped QDs at pH 8 was studied. Only CdTe/CA QDs showed a notable fluorescence quenching in the presence of FA. Then, a nanosensor based on the fluorescence quenching of the CdTe QDs at pH 8 was explored. Under optimum conditions, the calibration curve showed a linear fluorescence quenching response in a concentration range of FA from 0.16 to 16.4 µM (R2 = 0.9944), with a detection limit of 0.048 µM. A probable mechanism of fluorescence quenching was proposed. The nanosensor showed good selectivity over other possible interferences. This method has been applied for FA quantification in orange beverage samples with excellent results (recoveries from 98.3 to 103.9%). The good selectivity, sensitivity, low cost, and rapidity make CdTe /CA QDs a suitable nanosensor for FA determination.

Polydiacetylene/triblock copolymer/surfactant nanoblend: A simple and rapid method for the colorimetric screening of enrofloxacin residue.

Colorimetric nanosensors formed of polydiacetylene (PDA), triblock copolymer (L64 or F68), and sodium dodecyl sulfate (SDS), so-called nanoblends, were developed to detect enrofloxacin (ENRO) in aqueous media. The nanosensors show hydrodynamic diameter ranging from 234.2 ±â€¯3.5 to 801.6 ±â€¯17.8 nm for SDS concentrations of 13.0-21.0 mM, respectively. The lowest limit of detection was 0.054 µM, which is five times smaller than the maximum limit allowed by the European Union. The response surfaces showed that both the SDS and ENRO concentrations influenced the colorimetric response (p < 0.05), and kinetic rate of colorimetric transition (RCT). SDS concentration between 11.0 and 14.0 mM in the nanoblend yielded the most sensitive nanosensors for detecting ENRO. When L64 was replaced by F68, the colorimetric response of the nanoblends was similar, but PDA/F68/SDS showed a slower RCT than PDA/L64/SDS. The developed nanosensor is a sensitive and simple device for the fast detection of ENRO.

A label-free and reagentless immunoelectrode for antibodies against hepatitis B core antigen (anti-HBc) detection.

An electrochemical immunosensor devoted the core hepatitis B antibody detection, based on polytyramine (PTy) and carbon nanotubes (CNT) composite was developed. The antibody interactions with immobilized antigens were detected by reduction on the electron transfer from ionic species coming from reactive amine groups of PTy. The synthesis in acid medium of PTy-CNT composite favorite a great amount of NH3+ ionic species, forming a nanocomposite with high catalytic activity on the electrode surface. As proof-of-concept, antibodies against the core hepatitis B virus were label-free and reagentless electrochemically detected by square wave voltammetry (SWV) through decrease on cathodic peaks. It was recently reported that hepatitis B core antigen antibodies (anti-HBc) is a powerful biomarker for hepatitis B virus (HBV) infection, being more specific than HBsAg due to the possibility of detecting the occult HBV infections. The nanostructured film was characterized by atomic force microscopy and electrochemical techniques. This immunosensor showed linear responses from 1.0 to 5.0 ng mL-1 and a limit of detection of 0.89 ng mL-1 anti-HBc. It was also tested in assays with negative and positive blood samples using 0.1 M KCl as electrolyte support on readings showing specific responses. This easy reagentless detection platform, showing a remarkable potential to development of bolder and simpler HBV assay for screening of blood bags, in attempting to circumvent point-of-care testing limitations.

Polydiacetylene/triblock copolymer nanosensor for the detection of native and free bovine serum albumin.

Bovine serum albumin (BSA) has been recognized as a marker of the cow's health, milk quality, an allergenic protein and as a carrier. Its detection is important in the food, pharmaceutical and medical industries. However, traditional techniques used to detect BSA are often time-consuming, expensive, and show limited sensitivity. This paper describes properties of polydiacetylene-triblock copolymer (L64) nanosensors, synthesized to easily detect BSA. Sensor efficiency was studied as a function of nanosensor composition, polydiacetylene chemical structures, BSA conformation and hydrophobic domain availability, using spectroscopic, calorimetric, light scattering, and electrokinetic analyses. Nanosensors were sensitive to detect the average BSA concentration of milk and dairy products and discriminated between native and denatured protein through naked-eye detectable blue-to-red transition. The standard Gibbs free energy (-10.44<ΔG°<-49.52kJM), stoichiometry complex (1<"n"<3), and binding constant (6.7×102

A label-free electrochemical immunosensor for hepatitis B based on hyaluronic acid-carbon nanotube hybrid film.

An electrochemical immunosensor developed for detection of antibodies to hepatitis B core protein (anti-HBc) is described. Anti-HBc is the earliest serological marker from hepatitis B virus (HBV) infection, remaining all life after contact with virus, being considered the most important marker for uses in screening of blood bank. A nanohybrid surface assembled onto a glassy carbon electrode consisting of amino carbon nanotubes recovered by hyaluronic acid was used as sensing platform to detect the anti-HBc. All the steps of electrode surface modification were characterized by Scanning Electronic Microscopy and extensively evaluated by electrochemical techniques. The electrode response was measured by direct anti-HBc antigen interactions by square wave voltammetry, dispensing uses of label or chemical mediators. Under optimal conditions, the anodic peak current which was proportional to the anti-HBs concentration. The immunosensor response was linear toward anti-HBc in concentrations up to 6 ng mL(-1), with a detection limit of 0.03 ng mL(-1). The linear range achieved was according to clinical level, indicating the immunosensor as promising tool for use as a criterion for blood bag disposal. The enhancement of the hyaluronic acid by carbon nanotube promoted an increase of charge electron transfer, besides a stable platform for HBc.

Channel-mediated lactate release by K⁺-stimulated astrocytes.

Excitatory synaptic transmission is accompanied by a local surge in interstitial lactate that occurs despite adequate oxygen availability, a puzzling phenomenon termed aerobic glycolysis. In addition to its role as an energy substrate, recent studies have shown that lactate modulates neuronal excitability acting through various targets, including NMDA receptors and G-protein-coupled receptors specific for lactate, but little is known about the cellular and molecular mechanisms responsible for the increase in interstitial lactate. Using a panel of genetically encoded fluorescence nanosensors for energy metabolites, we show here that mouse astrocytes in culture, in cortical slices, and in vivo maintain a steady-state reservoir of lactate. The reservoir was released to the extracellular space immediately after exposure of astrocytes to a physiological rise in extracellular K(+) or cell depolarization. Cell-attached patch-clamp analysis of cultured astrocytes revealed a 37 pS lactate-permeable ion channel activated by cell depolarization. The channel was modulated by lactate itself, resulting in a positive feedback loop for lactate release. A rapid fall in intracellular lactate levels was also observed in cortical astrocytes of anesthetized mice in response to local field stimulation. The existence of an astrocytic lactate reservoir and its quick mobilization via an ion channel in response to a neuronal cue provides fresh support to lactate roles in neuronal fueling and in gliotransmission.

Proteoliposomes in nanobiotechnology.

Proteoliposomes are systems that mimic lipid membranes (liposomes) to which a protein has been incorporated or inserted. During the last decade, these systems have gained prominence as tools for biophysical studies on lipid-protein interactions as well as for their biotechnological applications. Proteoliposomes have a major advantage when compared with natural membrane systems, since they can be obtained with a smaller number of lipidic (and protein) components, facilitating the design and interpretation of certain experiments. However, they have the disadvantage of requiring methodological standardization for incorporation of each specific protein, and the need to verify that the reconstitution procedure has yielded the correct orientation of the protein in the proteoliposome system with recovery of its functional activity. In this review, we chose two proteins under study in our laboratory to exemplify the steps necessary for the standardization of the reconstitution of membrane proteins in liposome systems: (1) alkaline phosphatase, a protein with a glycosylphosphatidylinositol anchor, and (2) Na,K-ATPase, an integral membrane protein. In these examples, we focus on the production of the specific proteoliposomes, as well as on their biochemical and biophysical characterization, with emphasis on studies of lipid-protein interactions. We conclude the chapter by highlighting current prospects of this technology for biotechnological applications, including the construction of nanosensors and of a multi-protein nanovesicular biomimetic to study the processes of initiation of skeletal mineralization.

High resolution measurement of the glycolytic rate.

The glycolytic rate is sensitive to physiological activity, hormones, stress, aging, and malignant transformation. Standard techniques to measure the glycolytic rate are based on radioactive isotopes, are not able to resolve single cells and have poor temporal resolution, limitations that hamper the study of energy metabolism in the brain and other organs. A new method is described in this article, which makes use of a recently developed FRET glucose nanosensor to measure the rate of glycolysis in single cells with high temporal resolution. Used in cultured astrocytes, the method showed for the first time that glycolysis can be activated within seconds by a combination of glutamate and K(+), supporting a role for astrocytes in neurometabolic and neurovascular coupling in the brain. It was also possible to make a direct comparison of metabolism in neurons and astrocytes lying in close proximity, paving the way to a high-resolution characterization of brain energy metabolism. Single-cell glycolytic rates were also measured in fibroblasts, adipocytes, myoblasts, and tumor cells, showing higher rates for undifferentiated cells and significant metabolic heterogeneity within cell types. This method should facilitate the investigation of tissue metabolism at the single-cell level and is readily adaptable for high-throughput analysis.