Localized surface plasmon resonance (LSPR) sensors based on plasmonic nanoparticles are sensitive to changes in local refractive index, so that they are used for affinity-based chemical sensing and biosensing. Conventional LSPR sensors are generally based on transmission of light through the sensor and a sample solution, which could be colored or turbid. In this study, we develop backward-scattering-based LSPR sensors that can be applied to colored or turbid sample solutions. Au nanospheres (100 nm diameter) and Au nanoshells (25 nm thick) with SiO2 cores (80 nm diameter) are used as plasmonic nanoparticles and immobilized on a glass substrate. The refractive index sensitivities of the Au nanospheres and nanoshells are 128 and 278 nm RIU−1, respectively, which are in good agreement with simulated values and the values for conventional transmission-based LSPR sensors. The Au nanoshells require a lower amount of Au for the same scattering intensity in comparison with the Au nanospheres. The backward-scattering-based LSPR sensing is possible with the Au nanospheres and nanoshells even in coffee as a colored and turbid sample.
Thermal and chemical stabilities of silver nanoplates (AgPLs), which are triangle plate-shaped silver nanoparticles, were improved by coating with titanium oxide. The titanium oxide layer prepared by a dip-coating method was certainly advantageous for the improvement of thermal stability. Furthermore, the overlayering of titanium oxide by a spray pyrolysis method was quite useful for improving the chemical stability against I− exposure. Such a coating exhibited satisfactory refractive index sensitivities.
Generally, the characterization of a metal layer formed on a planar substrate has been achieved using scanning electron microscopy and transmission electron microscopy. These techniques provide details of the surface and/or the cross-section of a planar structure with high resolution. However, the evaluation of sphere-like structures is troublesome owing to the necessity to observe a sample from various angles and/or to calculate the yield from many values obtained for many samples, since the conventional methods can observe a sample only from one direction. We have developed a simple evaluation method for a thin metal layer on plastic microbeads based on its light-scattering properties using dark-field microscopy coupled with a spectrometer. The light-scattering intensity of gold-nanoparticle-coated microbeads depends significantly on the gold coverage. We believe that our study is significant because it describes the development and evaluation of the surface coverage of a thin metal layer on a sphere-like microstructure.
In this paper, we evaluate randomly adsorbed cap-shaped silver nanoparticles for applications to surface-enhanced Raman spectroscopy, SERS. They were prepared by depositing silver on top of surface-adsorbed monodisperse SiO2 nanospheres, in a manner similar to the method for preparing metal film on nanosphere, MFON, but one major difference lies in the fact that nanospheres are randomly adsorbed rather than as a close-packed MFON. With random MFON, it is possible to incorporate nanospheres with more than one size. Mixing has been found to increase SERS performance. More specifically, by using 50 and 100 nm nanospheres, we found that substrates containing both types outperform substrates prepared from 100% of either 50 or 100 nm nanospheres. As evaluated by spectrophotometry, this increase could not be attributed to an increase in the extinction coefficient of the substrate at the irradiation wavelength of SERS measurements.
A novel strategy for the preparation of protein-decorated gold nanoparticles (Au NPs) was developed inside Escherichia coli cells, where an artificial oxidoreductase, composed of antibody-binding protein (pG), Bacillus stearothermophilus glycerol dehydrogenase (BsGLD) and a peptide tag with gold-binding affinity (H6C), was overexpressed in the cytoplasm. In situ formation of Au NPs was promoted by a natural electron-donating cofactor, nicotinamide adenine dinucleotide (NAD), which was regenerated to the reduced form of NADH by the catalytic activity of the fusion protein (pG-BsGLD-H6C) overexpressed in the cytoplasm of E. coli, with the concomitant addition of exogenous glycerol to the reaction system. The fusion protein was self-immobilized on Au NPs inside the E. coli cells, which was confirmed by SDS-PAGE and western blotting analyses of the resultant Au NPs. Finally, the IgG binding ability of the pG moiety displayed on Au NPs was evaluated by an enzyme-linked immunosorbent assay.
Metal nanoparticles express unique light-scattering characteristics based on the localized surface plasmon resonance, which depends on the metal species, particle size, and aggregation state of the nanoparticles. Therefore, we focused on the light-scattering characteristics of metal nanoparticles, such as silver, gold, and copper oxide, adsorbed on a bacterium. Monodisperse silver nanoparticles expressed the strongest scattered light among them, and showed various colors of scattered light. Although a monodisperse gold nanoparticle produced monochromatic light (green color), the color of the scattered light strongly depended on the aggregation state of the nanoparticles on a bacterium. On the other hand, copper oxide nanoparticles expressed monochromatic light (blue color), regardless of their aggregation states on a bacterium. We examined details concerning the light-scattering characteristics of metal nanoparticles, and discussed the possibility of their applications to bacterial cell imaging.
Dark field microscopy (DFM) was employed to detect amyloid β (Aβ) fibrils-induced gold nanoparticle (AuNP) aggregation at the single-particle level, with a detection limit of 40 pM fibrils. The sensitivity of this method is higher than that of the current fibril-specific detection method using probe dye, such as thioflavin T, for which sub-μM level of fibrils are necessary. This study further proved the potential application of DFM in the analytical methods based on AuNP aggregation.
A spectrofluorimetric method for determination of triazine herbicides was developed. The method involves reaction of ammonical 2-cyanoacetamide with the herbicide. The net fluorescent intensity (FI) of the product was measured at 376 nm using 330 nm as excitation wavelength. A linear relationship between concentration and FI was found in the range of 0.3 – 10 μg mL−1 for atrazine and 0.2 – 10 μg mL−1 for terbutryn. The LOD and LOQ were found to be 0.07 ± 0.023 μg mL−1 and 0.23 ± 0.023 μg mL−1, respectively, with %RSD <12.1% for atrazine and 0.027 ± 0.009 μg mL−1 and 0.091 ± 0.009 μg mL−1, respectively, with %RSD <5% for terbutryn. The %recoveries of the subject triazines from soil and wheat grains were found in the range of 90.0 ± 0.14 to 96.0 ± 0.15% for atrazine and 95.0 ± 0.05 to 98 ± 0.02% for terbutryn.
We describe a new turn off-on chemiluminescence (CL) method for the sensitive and selective determination of cyanide based on the inhibiting effect of gold nanoparticles (AuNPs) on rhodamine B (RohB)-ferricyanide (Fe(CN)63−) reaction. Free RohB can generate strong chemiluminescence emission when oxidized with Fe(CN)63−, but undergoes an intense extinction in the presence of AuNPs. Energy transfer and collisions between RohB molecules and AuNPs are probably the reason for this decreasing effect. Furthermore, it was found that CL intensity gradually recovered in the presence of cyanide due to its interaction with the AuNPs. The relation between the decreased CL intensity and cyanide concentration was exploited to develop a method for the determination of cyanide in the 16.7 – 1333 nmol L−1 concentration range, with a detection limit of 13.6 nmol L−1. In comparison with other nanoparticle-based methods, the presented assay shows good sensitivity and reliability for the determination of cyanide. The method was satisfactorily applied to the determination of cyanide in environmental and biological samples.
In this work, a cost-effective and simple-to-prepare label-free electrochemical immunosensor was, for the first time, fabricated by modifying high-quality graphene oxide (GPO) onto a screen-printed carbon electrode (SPCE). The anti-IgG antibody was then covalently immobilized to the carboxylic group anchoring on the surface of GPO particles. Under the optimized condition, our newly developed immunosensor selectively bound to human immunoglobulin G (IgG), a model biomarker, with high sensitivity at a limit of detection of 1.99 ng mL−1, potentially sensitive enough for IgG detection at the pathophysiological level, and had a linear range of 2.5 to 100 ng mL−1. The proposed immunosensor also exhibited high reproducibility and regenerability, resulting in no significant change in electrochemical signals from different replicates of the electrode, and a robust electrochemical current after being subjected to alkaline base washing with several cycles. To this end, our immunosensor demonstrates ability as a promising diagnostic tool for clinical assessment.
A cost-effective and environmentally friendly approach using a simple sequential injection spectrophotometric system with a non-synthetic reagent from plant extracts was proposed for a green analytical-chemistry methodology. The crude aqueous extracts from heartwood of Ceasalpinia sappan Linn. in acetate buffer pH 5.5 were utilized as an alternative natural reagent for the quantification of aluminium. The extracts contained homoisoflavonoid compounds, brazilin, and brazilein, which reacted with Al3+ to form reddish complexes with the maximum absorption wavelength at 530 nm. The optimum conditions for the sequential injection parameters, such as sequential profile, sample and reagent volumes, and the pH effect, were investigated. Under the optimum conditions, a linear calibration graph in the range of 0.075 – 1.0 mg L−1 Al3+ was obtained with limits of detection and quantification of 0.021 and 0.072 mg L−1 Al3+, respectively. Relative standard deviations of 3.2 and 2.4% for 0.1 and 0.25 mg L−1 Al3+ (n = 11), respectively, and sampling rate of 128 injections h−1 were achieved. The developed system was successfully applied to pharmaceutical preparations, water, and beverage samples. The results agreed well with those obtained from the ICP-AES method. Good recoveries between 87 and 104% were obtained.
Chemiluminescence (CL) with a flow-injection method is reported for the determination of thiabendazole (TBZ) fungicide based on its enhancement effect on diperiodatocuprate(III) (DPC)–sulfuric acid–CL system. The calibration graph was linear in the concentration range of 1 – 2000 μg L−1 (R2 = 0.9999, n = 8) with a limit of detection (S/N = 3) of 0.3 μg L−1. The injection throughput was 160 h−1 with relative standard deviations (RSD, n = 4) of 1.1 – 2.9% in the concentration range studied. The experimental variables e.g., reagents concentrations, flow rates, sample volume, and PMT voltage were optimized, and the potential interferences were investigated individually. The method was successfully applied to the determination of TBZ in water samples showing good agreement and recovery in the range of 92 ± 2.2 – 108 ± 3% (n = 3) using dispersive liquid–liquid micro-extraction (DLLME). The possible CL reaction mechanism for DPC–sulfuric acid–TBZ is also discussed.
Solid-phase extraction (SPE) of divalent metal ions with a lipophilic and potentially divalent hexadentate chelating reagent (H2L), with which octadecylsilyl silica (ODS) was impregnated, was studied to gain more insight into and develop the potential of this methodology. This is the first time to demonstrate that this reagent as well as other common nitrogen-containing reagents were retained both by adsorption due to hydrogen bonding between nitrogen atoms of the reagent and residual silanol groups in the ODS phase and by simple distribution into the hydrophobic space. An appreciably large amount of this reagent could be retained by the adsorption mechanism even with a relatively thin loading solution. The divalent metal ions of Mn2+, Co2+ and Zn2+ were extracted as 1:1 neutral complexes ([ML]), while Ni2+ and Cu2+ as ion-pairs of 1:1 cationic complex ([MHL]+) with anion in SPE with H2L. The extractability and selectivity were substantially the same as that in liquid–liquid extraction.
In this study, we developed an integrated, low-cost microfluidic cell culture system that is easy to use. This system consists of a disposable polystyrene microchip, a polytetrafluoroethylene valve, an air bubble trap, and an indium tin oxide temperature controller. Valve pressure resistance was validated with a manometer to be 3 MPa. The trap protected against bubble contamination. The temperature controller enabled the culture of Macaca mulatta RF/6A 135 vascular endothelial cells, which are difficult to culture in glass microchips, without a CO2 incubator. We determined the optimal coating conditions for these cells and were able to achieve stable, confluent culture within 1 week. This practical system is suitable for low-cost screening and has potential applications as circulatory cell culture systems and research platforms in cell biology.
A detection method of gold nanoparticles in chromatography paper has been developed for a simple, cost-effective and reliable quantitation of immunochromatographic strip test. The time courses of the solution resistance in chromatography paper with the gold nanoparticles solution are electrochemically measured by chrono-impedimetry. The dependence of the solution resistance on the concentration of gold nanoparticles has been successfully observed. The main factor to increase the solution resistance may be obstruction of the ion transport due to the presence of gold nanoparticles. The existence of gold nanoparticles with 1.92 × 109 particles/mL in an indistinctly-colored chromatography paper is also identified by a solution resistance measurement. This indicates that the solution resistance assay has the potential to lower the detection limit of the conventional qualitative assay.
Mercury (Hg) and its derivatives pose a serious threat to the environment and human health. Thus, the development of methods for the selective and sensitive determination of Hg2+ is very important to understand its distribution, and to implement more detailed toxicological studies. Herein, we developed a new method for the detection of Hg2+ based on the tricyanoethylene derivative and mercaptoethanol. This method could selectively detect Hg2+ in a 100% aqueous solution by the naked-eye within the range of 1 – 60 μM. Importantly, this method also could detect Hg2+ quantitatively by ratiometic absorption spectroscopy in the range of 0.1 – 6 μM with a detection limit of 55 nM. We anticipate that this proposed method will be used widely to monitor Hg2+ in the environment.
We previously developed a separation-free ligase detection reaction assay based on fluorescence resonance energy transfer from a donor quantum dot to an acceptor fluorescent dye. This assay could successfully detect one cancer mutation among 10 wild-type templates. In the current study, the mutation-discrimination threshold was improved by one order of magnitude by replacing the original acceptor dye (Alexa Fluor 647) with another fluorescent dye (Cyanine 5) that was spectrally similar but more fluorescent.
We have developed a rapid, automated nucleic acid purification device in a single cartridge containing silica-coated magnetic beads. We succeeded in extracting the matrix protein gene of influenza A virus from pharyngeal swab samples within 3 min. The device will be widely applicable to detect a specific gene from the various samples for clinical diagnosis and genetic research.