Detection of formaldehyde in water: a shape-effect on the plasmonic sensing properties of the gold nanoparticles

Refractive index and formaldehyde sensing with silver nanocubes

We report the synthesis of Ag nanocubes by using a sodium sulfide assisted solvothermal method. Small edge-length nanocubes (32 and 44 nm) were obtained at 145 and 155 °C reaction temperature in the synthesis process. The refractive index sensitivity of synthesized nanocubes was investigated with an aqueous solution of glucose. The refractive index sensitivity of 161 nm per RIU was found in the colloidal dispersion of nanocubes. On the LSPR chip made by immobilization of nanocubes on the (3-aminopropyl)trimethoxysilane modified glass coverslip, the obtained sensitivity was 116 nm per RIU. Detection of formaldehyde in water and milk samples was also performed with nanocubes of edge-length of 44 nm. Formaldehyde detection was performed by utilizing the interaction of the aryl amine of 4-aminothiophenol immobilized on the nanocubes and electrophilic carbon atom of the formaldehyde. In water and in diluted milk, the formaldehyde sensitivity of 0.62 and 0.29 nm μM⁻¹ was obtained, respectively.

A detailed description of refractive index and formaldehyde sensing with Ag nanocubes.

Structurally tunable gear-shaped plasmonic sensor

We present a gear-shaped plasmonic nano-structure with structural tunability and high RI sensitivity. New tunable geometric parameters of the gear-tooth give further flexibility for design. By using FDTD method, the reflection spectrum of the structure is theoretically analyzed with analyte RI in the range of 1.0 to 1.44. The best achieved sensitivity is- 1044 nm/RIU for our proposed structure. The resonance wavelength of the structure is independent of the polarization angle for large number of teeth. The structure can be used to design tunable sensors for biomedical and chemical applications.

Hierarchical Bimetallic AgPt Nanoferns as High-Performance Catalysts for Selective Acetone Hydrogenation to Isopropanol

A combinative effect of two or more individual material properties, such as lattice parameters and chemical properties, has been well-known to generate novel nanomaterials with special crystal growth behavior and physico-chemical performance. This paper reports unusually high catalytic performance of AgPt nanoferns in the hydrogenation reaction of acetone conversion to isopropanol, which is several orders higher compared to the performance shown by pristine Pt nanocatalysts or other metals and metal-metal oxide hybrid catalyst systems. It has been demonstrated that the combinative effect during the bimetallisation of Ag and Pt produced nanostructures with a highly anisotropic morphology, i.e., hierarchical nanofern structures, which provide high-density active sites on the catalyst surface for an efficient catalytic reaction. The extent of the effect of structural growth on the catalytic performance of hierarchical AgPt nanoferns is discussed.

Gold Nanoplates for a Localized Surface Plasmon Resonance-Based Boric Acid Sensor

Localized surface plasmon resonance (LSPR) properties of metallic nanostructures, such as gold, are very sensitive to the dielectric environment of the material, which can simply be adjusted by changing its shape and size through modification of the synthesizing process. Thus, these unique properties are very promising, particularly for the detection of various types of chemicals, for example boric acid which is a non-permitted preservative employed in food preparations. For the sensing material, gold (Au) nanoplates with a variety of shapes, i.e., triangular, hexagonal, truncated pentagon and flat rod, were prepared using a seed-mediated growth method. The yield of Au nanoplates was estimated to be ca. 63% over all areas of the sensing material. The nanoplates produced two absorption bands, i.e., the transverse surface plasmon resonance (t-SPR) and the longitudinal surface plasmon resonance (l-SPR) at 545 nm and 710 nm, respectively. In the sensing study, these two bands were used to examine the response of gold nanoplates to the presence of boric acid in an aqueous environment. In a typical process, when the sample is immersed into an aqueous solution containing boric acid, these two bands may change their intensity and peak centers as a result of the interaction between the boric acid and the gold nanoplates. The changes in the intensities and peak positions of t-SPR and l-SPR linearly correlated with the change in the boric acid concentration in the solution.

Water dispersion of magnetic nanoparticles with selective Biofunctionality for enhanced plasmonic biosensing

Magnetic nanoparticles (MNPs) are widely used in biosensing, bioimaging, and drug delivery. However, high quality superparamagnetic nanoparticles with uniform size were usually synthesized by thermal decomposition using organic solvents. To be suitable for biomedical applications, a facile and efficient water dispersion of iron oxide MNPs from solvent using an innovative agent, sodium oleate (NaOL) was described. The monodispersed MNPs (4 and 15nm respectively) after transfer was biocompatible and stable at a broad temperature range (4-50°C) over months. More importantly, the NaOL coating allows for surface modification with selective functionality, rendering the aqueous MNPs highly customizable for biofunctionalization. Little effect on the superparamagnetism was observed after the water dispersion. To further evaluate its practical application in biosensing, custom MNPs were prepared for specific cardiac troponin I (cTnI) detection for myocardial infarction diagnosis. Specifically, gold nanorod (GNR) biochip was probed by the MNP-captured cTnI target analyte at varying concentrations. The signal transduction of the GNR sensor is based on the localized surface plasmon resonance (LSPR). The application of the MNPs resulted in a significant enhancement of the plasmonic response of the GNRs. As such, the MNP-mediated LSPR biosenisng showed a three times lower sensitivity as compared to the direct cTnI binding without functional MNPs. Computer simulation further elucidated that the enhancement was distance dependent between the MNP and the surface of the nanorod, which corroborated with experimental results.

Gold nanoparticle synthesis coupled to fluorescence turn-on for sensitive detection of formaldehyde using formaldehyde dehydrogenase

Ultrasensitive detection of formaldehyde by coupling enzyme activity with GNP synthesis.

Time-Dependent, Optically Controlled Dielectric Function

We suggest optical modulation of the dielectric function of a molecular monolayer adsorbed on a metal surface as a potential means of controlling plasmon resonance phenomena. The dielectric function is altered using a laser pulse of moderate intensity and linear polarization to align the constituent molecules. After the pulse, the monolayer returns to its initial state. Time-dependent, optically controlled dielectric function is illustrated by molecular dynamics calculations.