Time-dependent complexation of glucose-reduced gold nanoparticles with octadecylamine Langmuir monolayers

Label-free impedimetric immunosensor based on arginine-functionalized gold nanoparticles for detection of DHEAS, a biomarker of pediatric adrenocortical carcinoma

Pediatric adrenocortical carcinoma (pACC) is a rare and aggressive malignancy of high occurrence in Southern Brazil. pACC is characterized by the usual overproduction of dehydroepiandrosterone sulfate (DHEAS), whose detection in serum or plasma can be effective to the early diagnosis of the disease. Therefore, the present paper reports, for the first time, the construction and application of a label-free impedimetric immunosensor to detect DHEAS, which was based on the modification of an oxidized glassy carbon electrode with arginine-functionalized gold nanoparticles (AuNPs-ARG) and anti-DHEA IgM antibodies (ox-GCE/AuNPs-ARG/IgM). AuNPs-ARG was synthesized by a green route, and characterized by UV-VIS spectroscopy, FTIR, TEM, DLS, and XRD. The construction of ox-GCE/AuNPs-ARG/IgM was optimized through factorial design and response surface methodology. Cyclic voltammetry and electrochemical impedance spectroscopy measurements were employed to characterize the optimized immunosensor. The DHEAS detection principle was based on the variation of charge transfer resistance (∆R_ct) relative to the Fe(CN)₆^4-/3- electrochemical probe after immunoassays in the presence of the biomarker. A linear relationship between ∆R_ct and DHEAS concentration was verified in the range from 10.0 to 110.0 µg dL^-1, with a LOD of 7.4 µg dL^-1. Besides the good sensitivity, the immunosensor displayed accuracy, stability, and specificity to detect DHEAS. The promising analytical performance of ox-GCE/AuNPs-ARG/IgM was confirmed by quantifying DHEAS in real patient plasma samples, with results that were comparable to the reference chemiluminescence assay. Our results suggest that the presented immunosensor can find clinical applications in the early diagnosis of pACC and to monitor DHEAS levels in other adrenal pathologies.

Unique supramolecular assembly through Langmuir - Blodgett (LB) technique

The Langmuir-Blodgett (LB) technique is a way of making supra-molecular assembly in ultrathin films with a controlled layered structure and crystal parameter, which have many envisioned technological applications for optical and molecular electronic devices as well as signal processing and transformation. Probably LB technique is the best method to manipulate materials at molecular level and provides a scope to realize the molecular electronics in reality. In this review article, we have discussed about the general introduction of LB technique and recent development on LB and related system including (i) LB methodology, (ii) characterizations of LB films, (iii) LB films and molecular electronics, (iv) historical review of LB films, (v) research and applications including fundamental research and application towards devices.

Colorimetric recognition of pazufloxacin mesilate based on the aggregation of gold nanoparticles

A novel colorimetric nanomaterial-assisted optical sensor for pazufloxacin mesilate was proposed for the first time. Pazufloxacin mesilate could induce the aggregation of glucose-reduced gold nanoparticles (AuNPs) through hydrogen-bonding interaction and electrostatic attraction, leading to the changes in color and absorption spectra of AuNPs. The effect of different factors such as pH, the amount of AuNPs, reaction time and reaction temperature was inspected. Under the optimum condition, UV-vis spectra showed that the absorption ratio (A670/A532) was linear with the concentration of pazufloxacin mesilate in the range from 9×10(-8) mol L(-1) to 7×10(-7) mol L(-1) with a linear coefficient of 0.9951. This method can be applied to detecting pazufloxacin mesilate with an ultralow detection limit of 7.92×10(-9) mol L(-1) without any complicated instruments. Through inspecting other analytes and ions, the anti-interference performance of AuNP detection system for pazufloxacin mesilate was excellent. For its high efficiency, rapid response rate as well as wide linear range, it had been successfully used to the analysis of pazufloxacin mesilate in human urine quantificationally.

Heterogemini surfactant assisted synthesis of monodisperse icosahedral gold nanocrystals and their applications in electrochemical biosensing

Monodisperse icosahedral gold nanoparticles with tunable plasmonic property and high performance electrochemical sensing was synthesized by a heterogemini surfactant.

Synthesis and monolayer behavior of organogermanium clusters

Several organogermanium clusters (Or-GeCs) with different organic capping reagents have been synthesized, and their monolayer behaviors on a water surface studied. GeCl(4) and organic bromides were reacted in a one-pot process using magnesium to synthesize the corresponding Or-GeCs. The structures of the Or-GeCs were characterized by UV-vis, NMR, and FT-IR spectroscopy. GPC measurements were also collected, and the results revealed that the cores of the clusters were composed of a 3-D Ge-Ge network capped with organic reagents. Surface pressure (π)-area (A) isotherms and Brewster angle microscopy (BAM) measurements indicated that the Or-GeCs with alkyl capping regents formed an oil, whereas those with aromatic capping regents formed a solid-like monolayer at the air-water interface. It was concluded that the occurrence of a π-π interaction between the aromatic capping reagents was necessary for the formation of a solid-like film. Phenyl-GeCs, which contained a phenyl group capping reagent, were transferred onto a solid substrate using the Langmuir-Schaeffer method, and atomic force microscopy (AFM) images revealed a uniform film (root mean square roughness of 0.6 nm) of 3-4 nm in thickness. Furthermore, a multilayer phenyl-GeC film was prepared by repeating the deposition process.

Caveolae-mediated endocytosis of biocompatible gold nanoparticles in living Hela cells

Efficient intracellular delivery of gold nanoparticles (AuNPs) and unraveling the mechanism underlying the intracellular delivery are essential for advancing the applications of AuNPs toward in vivo imaging and therapeutic interventions. We employed fluorescence microscopy to investigate the internalization mechanism of small-size AuNPs by living Hela cells. Herein, we found that the caveolae-mediated endocytosis was the dominant pathway for the intracellular delivery of small-size AuNPs. The intracellular delivery was suppressed when we depleted the cholesterol with methyl-β-cyclodextrin (MβCD); in contrast, the sucrose that disrupts the formation of clathrin-mediated endocytosis did not block the endocytosis of AuNPs. Meanwhile, we examined the intracellular localization of AuNPs in endocytic vesicles by fluorescent colocalization. This work would provide a potential technique to study the intracellular delivery of small-size nanoparticles for biomedical applications.

Synthesis and self-assembly of highly monodispersed quasispherical gold nanoparticles

We report the synthesis of cetyltrimethylammonium bromide (CTAB) assisted seed mediated growth of highly pure and monodispersed quasispherical gold nanoparticles (QAuNPs) and their self-assembly on the silica/glass substrates. The seed-mediated growth approach was modified to prepare size-tunable monodispersed QAuNPs with sizes ranging from 20 to 150 nm. The larger, more uniform seeds and lower CTAB concentration resulted in the formation of relatively large QAuNPs with improved monodispersity (relative standard deviation (RSD) of ∼5-8%) and high purity in their shapes. In addition, CATB-capped QAuNPs can be spontaneously assembled into closely packed and highly aligned superstructures with well-defined mutillayers (two to six layers) on silica substrates. Furthermore, CATB-capped QAuNPs can easily construct density-controllable QAuNP chips by electrostatic self-assembly, showing their promising applications for single-nanoparticle plasmonic sensors.

Direct Interaction Between Gold Nanorods and Glucose

In this work, we present the results of the study on the interactions between gold nanorods (GNRs) and glucose. The optical properties of GNRs have higher sensitivity to glucose compared with that of gold nanospheres. The long-wavelength bands of the GNRs obviously decrease as the concentration of glucose increases. At high glucose concentrations, the absorption peak in long-wavelength bands almost disappears, and the absorption intensities corresponding to the transverse plasmon band are also decrease. These results suggest that glucose could seriously affect the optical properties of GNRs. A possible interaction mechanism between gold nanorods (GNRs) and glucose has been proposed. Furthermore, the influence of glucose on different amount GNRs also has been studied.

Noncovalent Interaction between Gold Nanoparticles and Multiwalled Carbon Nanotubes via an Intermediatory

A new and effective method has been developed where self-assembled gold nanoparticles (Au-NPs) of ∼10 nm diameter are successfully attached onto the surface of sidewalls and ends of thiol-terminated multi-walled carbon nanotubes (MWNTs) functionalized with orthomercaptoaniline, acting as a bridging agent. It can bridge the carbon nanotubes (CNTs) and Au-NPs via the bi-functional moiety with benzene unit at one end and thiol group at the other end by self-assembly. Theortho-mercaptoaniline was first grafted onto the surface of the CNTs viaπ-πinteraction between the benzene ring of the mercaptoaniline andπ-conjugated body of MWNTs surface to produce thiol-terminated CNTs. The bare surface of Au-NPs facilitates to attach on the thiol group of the thiol-terminated CNTs. Attenuated total reflectance FTIR, UV-visible, Raman spectroscopy and X-ray powder diffraction studies were used to verify whether the mercapto-benzene moieties have been attached to theπ-conjugated body of functionalized MWNTs. The direct evidence is obtained from transmission electron microscope (TEM) images where self-assembled Au-NPs are attached onto the functionalized MWNTs.

Preparation, characterization and applications of ultrathin cellulose acetate Langmuir-Blodgett films

The preparation and characterization of mono- and multilayers of cellulose acetate (CA) Langmuir-Blodgett films on indium tin oxide and gold surfaces were studied in detail for the first time. These layers were characterized by their thickness, wettability, morphology and structure using various surface techniques. The thickness of a monolayer of CA based on XPS measurement was one nanometre. Multilayers of CA Langmuir films were homogeneously transferred onto solid surfaces. The permeation of different molecules across these films was studied using electrochemistry in various redox solutions. Our findings suggest that a membrane like structure is formed, which is less permeable as the number of layers increases. Finally, potential applications of these ultrathin films as supports for accommodating biomolecules or metal nanoparticles are presented.

Adsorption of carboxylate-modified gold nanoparticles on an octadecylamine monolayer at the air/liquid interface

Gold nanoparticles (Au NPs) were prepared and surface-modified by mercaptosuccinic acid (MSA) to render a surface with carboxylic acid groups (MSA-Au). Octadecylamine (ODA) was used as a template monolayer to adsorb the Au NPs dispersed in the subphase. The effect of MSA concentration on the incorporation of Au NPs on the ODA monolayer and the relevant behavior of the mixed monolayer were studied using the pressure-area (pi-A) isotherm and transmission electron microscopy (TEM) observations. The experimental results showed that the adsorbed density of Au NPs is low without the surface modification by MSA. When MSA was added into the Au NP-containing subphase, the incorporation amount of Au NPs increased with increasing MSA concentration up to approximately 1 x 10-5 M for the particle density of 1.3 x 1011 particles/mL. With a further increase in the MSA concentration, the adsorbed particle density decreases due to competitive adsorption between the free MSA molecules and the MSA-Au NPs. It is inferred that free MSA molecules adsorb more easily than the MSA-Au NPs on the ODA monolayer. Therefore, an excess amount of MSA present in the subphase is detrimental to the incorporation of gold particles. The study on the monolayer behavior also shows that the pi-A isotherm of the ODA monolayer shifts right when small amounts of Au NPs or free MSA molecules are incorporated. However, when larger amounts of particles are adsorbed at the air/liquid interface, a left shift of the pi-A isotherm appears, probably due to the adsorption of ODA molecules onto the particle surface and the transferring of the particles from beneath the ODA monolayer to the air/water interface. According to the present method, it is possible to prepare uniform particulate films of controlled densities by controlling the particle concentration in the subphase, the MSA concentration, and the surface pressure of a mixed monolayer.

Recent developments in bio-molecular electronics techniques for food pathogens

Food borne illnesses contribute to the majority of infections caused by pathogenic microorganisms. Detection of these pathogens originating from different sources has led to increased interest of researchers. New bio-molecular techniques for food pathogen detection are being developed to improve the sensor characteristics such as sensitivity, reusability, simplicity and economic viability. Present article deals with the various methods of food pathogen detection with special emphasis on bio-molecular electronics techniques such as biosensors, microarrays, electronic nose, and nano-materials based methods.