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Gold nanoparticle (AuNP) monolayers possess unique optical properties and are widely used in optical devices and biosensors, sometimes necessitating dense but nonclose-packed monolayers. Current self-assembly methods are generally limited to small surfaces and are often plagued by AuNP aggregation. Here, we use a facile method, suitable for substrates of any size or form, to produce dense, unaggregated, randomly packed AuNP monolayers on brushlike films of polystyrene-block-poly-(4-vinylpyridine) (PS-P4VP) obtained by dip-coating flat surfaces from very dilute solutions, where PS forms the brush, and the citrate-stabilized AuNPs interact with the P4VP anchoring layer when the template is incubated in an AuNP colloid. By investigating the effect of molecular weight (Mn), dip-coating solvent, and colloid pH on the characteristics of the adsorbed films and the subsequent deposition of AuNPs, we constructed a morphology map in terms of PS Mn and chain grafting density under favorable pH conditions, showing the region that yields the desired dense well-dispersed AuNP monolayers. Above an upper PS Mn boundary (around 50–60 kg/mol), the PS brushcontinuous or in the form of patchesis too thick and rigid for the AuNPs to access the underlying P4VP and is also subject to kinetic effects, thus causing little or nonuniform, even aggregated, AuNP deposition. These findings have important implications for the future employment of dense, unaggregated AuNP monolayers in miniature sensors and as optical coatings in a wide range of optical devices. [ABSTRACT FROM AUTHOR]

Bovine serum albumin (BSA) containing buffers are the standard blocking buffer in biosensing, yet human serum is the intended application for most clinical sensors. However, the effect of human serum albumin (HSA) on binding assays remains underexplored. A simple and well-studied assay (human IgG/goat anti-human IgG) was investigated with a surface plasmon resonance (SPR) sensor to address this fundamental question in sensing. Calibrations were performed with buffers containing various concentrations of bovine or human serum albumin, as well as full and diluted bovine or IgG-depleted human serum. It was found that HSA or human serum, but not BSA or bovine serum, significantly affected the SPR shift and binding constants of the assay. Interestingly, large differences were also observed depending on whether the animal or human antibody was immobilized on the SPR chip for detection, highlighting that matrix protein/analyte/receptor interactions play a significant role in the response. We find that the interaction of soluble HSA with human IgG interferes with the recognition region, affecting the binding constant, and thus results obtained in BSA are not necessarily applicable to clinical samples or in vivo conditions. We also clearly demonstrate why a minimum dilution of 1 : 10 is often required in SPR assays to remove most background effects. Taken together, these results show that: (1) BSA does not affect the binding constant between antibodies and thus serves its purpose well when only surface blocking is intended, (2) HSA is an adequate surrogate for human serum in assay optimization, and (3) blocking buffers should be prepared with HSA in the optimization steps of assays to be translated to human blood or serum. [ABSTRACT FROM AUTHOR]

A term project was introduced in teaching advanced spectroscopy and notions of nanotechnology to chemistry students at the graduate level (M.Sc. and Ph.D.). This project could also be suited for an honor's thesis at the undergraduate level. Students were assigned a unique combination of nanoparticle synthesis (13 nm Au nanospheres, ~100 nm nanoraspberries or ~50 nm nanostars) and fluorescent/Raman-active ligand (HS-PEG-FITC, rhodamine 6G, 4-mercaptobenzoic acid, 4-nitrobenzenethiol, and phenanthroline). Characterization with transmission electron microscopy allowed the students to confirm the shape and size distribution of nanoparticles. The ligands immobilized on the surface of the nanoparticles were extensively characterized using a suite of optical techniques. UV-vis was used to observe the plasmonic bands of particles of varying shapes, and fluorescent spectroscopy was used to construct fluorescent pathways with the aid of Jablonski diagrams. The vibrational bands of the ligands were identified using IR and Raman spectroscopy. Performing surface-enhanced Raman spectroscopy (SERS) on the nanoparticle at different excitation wavelength (488, 633, and 785 nm) was used to understand the influence of the surface plasmon on SERS and fluorescence spectroscopies. Students were required to write a full scientific paper for the report of the term project.

Plasmonic metal nanostructures have promising applications in biosensing due to their ability to facilitate light–matter interaction. However, the damping of noble metal leads to a wide full width at half maximum (FWHM) spectrum which restricts sensing capabilities. Herein, we present a novel non-full-metal nanostructure sensor, namely indium tin oxide (ITO)–Au nanodisk arrays consisting of periodic arrays of ITO nanodisk arrays and a continuous gold substrate. A narrow-band spectral feature under normal incidence emerges in the visible region, corresponding to the mode-coupling of surface plasmon modes, which are excited by lattice resonance at metal interfaces with magnetic resonance mode. The FWHM of our proposed nanostructure is barely 14 nm, which is one fifth of that of full-metal nanodisk arrays, and effectively improves the sensing performance. Furthermore, the thickness variation of nanodisks hardly affects the sensing performance of this ITO-based nanostructure, ensuring excellent tolerance during preparation. We fabricate the sensor ship using template transfer and vacuum deposition techniques to achieve large-area and low-cost nanostructure preparation. The sensing performance is used to detect immunoglobulin G (IgG) protein molecules, promoting the widespread application of plasmonic nanostructures in label-free biomedical studies and point-of-care diagnostics. The introduction of dielectric materials effectively reduces FWHM, but sacrifices sensitivity. Therefore, utilizing structural configurations or introducing other materials to generate mode-coupling and hybridization is an effective way to provide local field enhancement and effective regulation. [ABSTRACT FROM AUTHOR]

Metallic thin films patterned with micrometer size triangle or hole arrays present plasmonic properties when excited in the Kretschmann configuration, that are improved in comparison to conventional thin film surface plasmon resonance (SPR). These optical properties can be tuned by varying the physical aspects of the microplasmonic structures. Triangles and microhole arrays were prepared with modified nanosphere lithography (NSL) using latex spheres of 0.65, 0.82, 1.0, 1.5, or 3.2 [micro]m in diameter. This allowed the preparation of triangles with edge lengths between 275 to 2000 nm and microhole arrays of various periodicities, diameters, and hole depths. These microstructures were studied to understand the relationship between the physical aspects and the optical properties, such as the sensitivity, working refractive index range, spectral width of the plasmonic peaks, spectral noise, and refractive index resolution. Microhole arrays with a hole diameter equal to half the periodicity were found to combine the advantages of both localized surface plasmon resonance (LSPR) on nanoparticles and SPR on a thin film. These microhole arrays exhibited high sensitivity to refractive index (>3000 nm/RIU), sensitivity to monolayer formation (2-fold improvement compared to thin films), and excellent refractive index resolution ([10.sup.-6] RIU). Finally, a biosensor for the detection of 10 nM of immunoglobulin G (IgG) exhibited a greater response with microplasmonic materials compared to conventional thin Au films. Hence, these novel plasmonic materials exhibit a strong potential as an SPR sensing platform. They can be implemented on existing instrumentation and use detection protocols developed for current SPR sensors. 10.1021/ac100177j