Omar Pandoli

Bacteria-template synthesized silver microspheres with hollow and porous structures as excellent SERS substrate

Template-driven strategy is widely explored for the synthesis of nano/micro materials. Of all the templates studied, naturally occurring biological systems such as proteins, viruses and bacteria have attracted more attention due to the prolific sources and complex structural diversities. Herein, we report a simple bacteria templated synthesis of silver microspheres over a bottom-up controlled route. These as-prepared silver microspheres not only have narrow size distribution but possess hollow and porous structures. Surface enhanced Raman scattering (SERS) experiments using 2-mercaptopyridine (2-Mpy) as probing molecules show that these hollow porous microspheres can act as excellent substrate for ultrasensitive detecting. The detection limit is as low as 10−15 M and the enhancement factor reaches to 1011. Compared with other conventional SERS substrates, the reproducible, high sensitive and cost-effective Ag microspheres could become an ideal substrate choice for practical SERS application.

Chiral guanosine 5′-monophosphate-capped gold nanoflowers: Controllable synthesis, characterization, surface-enhanced Raman scattering activity, cellular imaging and photothermal therapy

AbstractPlasmonics and chirality in metal nanomaterials are intriguing and inspiring phenomena. Nanoscale chirality of metal nanomaterials has emerged as a hot topic in the past several years. Generally, most plasmon-induced circular dichroism (CD) responses of nanomaterials (> 10 nm) have been artificially created by modifying pre-made achiral nanomaterials with chiral agents, because the in situ generation of plasmon-induced CD responses of nanomaterials with larger size (> 10 nm) is not easy. Herein, we report a simple one-pot green synthesis of chiral gold nanoflowers (GNFs) with abundant petal-shaped tips in the chiral reduction environment arising from the presence of chiral guanosine 5′-monophosphate (5′-GMP) and the chiral reducing agent L-ascorbic acid (L-AA). Different reducing agents can impact the shape and chirality of the products. In addition, the size and chirality of the GNFs can be controlled by adjusting the reaction time. The as-synthesized GNFs have good biocompatibility and can be used for surface-enhanced Raman scattering (SERS) enhancement, cellular dark-field imaging and photothermal therapy.

Accurate and simultaneous measurement of thickness and refractive index of thermally evaporated thin organic films by surface plasmon resonance spectroscopy

We demonstrate that Surface Plasmon Resonance spectroscopy can be used for the accurate and simultaneous determination of the thickness and refractive index of transparent thin thermally deposited organic films. The experimental approach is based on a two-metal deposition or a two-thickness method. These methods have been applied to an encapsulated sample containing a thin film of commercial tris(8-hydroxyquinoline) (Alq3). The accuracy of the measurement depends on the control of the film deposition process and suggests the use of SPR spectroscopy as inexpensive and valuable metrology tool for small molecule organic thin films.

A monolithic 5-(pyrrolidin-2-yl)tetrazole flow microreactor for the asymmetric aldol reaction in water–ethanol solvent

An (S)-5-(pyrrolidin-2-yl)-1H-tetrazole organocatalyst has been prepared in the form of a monolithic column through the radical copolymerization of a styryl-functionalized pyrrolidinyl-tetrazole derivative, styrene and divinylbenzene in the presence of porogens (dodecanol and toluene). The activity of the monolithic pyrrolidinyl-tetrazole organocatalyst (triturated polymer) has been initially tested under batch conditions using the asymmetric aldol reaction of cyclohexanone and p-nitrobenzaldehyde as the benchmark. A prerequisite of the study has been the utilization of the eco-friendly water–ethanol mixture as the solvent. After having established the high efficiency and recyclability of the catalyst under these conditions, the effect of the flow regime has been evaluated by fabricating the corresponding monolithic microreactor (pressure-resistant stainless steel column). It has been demonstrated by a brief substrate scope study that the flow regime contributes to preserve the activity of the pyrrolidinyl-tetrazole catalyst over time (5 days on stream) with an almost twofold increase in productivity moving from batch to flow conditions. An added value of the flow procedure has been the optimization of a suitable 2D instrumental setup for simultaneous flow reaction and online flow-injection analysis.

Spherical gold nanoparticles and gold nanorods for the determination of gentamicin.

Gentamicin is an antibiotic indicated to treat mastitis in dairy cattle and for the treatment of bacterial resistance in the context of hospital infections. The effect caused by gentamicin on the optical properties of gold nanoparticles aqueous dispersions were used to develop quantitative methods to determine this antibiotic. Two different aqueous dispersions, one containing spherical Au nanoparticles (AuNPs) and the other containing Au nanorods (AuNRs), had their conditions adjusted to enable a stable and sensitive response towards gentamicin. The use of AuNPs, with measurement at 681nm of the rising coupling plasmon band, enabled a limit of detection (LOD) of 0.4ngmL-1 (0.02ng absolute LOD), ten times lower than the one achieved by measuring the decreasing of the longitudinal surface plasmon resonance band (at 662nm). The linear analytical response of AuNPs measured at 681nm did not require rationing of signal values to correct for linearity. Stability of the analytical response resulted in intermediary precision below 2%. No significant interference was imposed by excipients traditionally present in injectable solutions for veterinary use. Percent recoveries obtained in such formulations were between 94.5 and 98.2% regardless the existence of any difference in the proportion of the compounds known as gentamicin (C1, C1a and C2) in standard and in the samples. The method requires no derivatization with toxic reagents as usually is required in other spectroscopic approaches.

Colloidal silver nanoparticles: an effective nano-filler material to prevent fungal proliferation in bamboo

Silver nanoparticles (Ag-NPs) have attracted attention as a promising nano-filler material for reinforcement and anti-bacterial effect in polymers and composites. In this work bamboo samples, Dendrocalamus Giganteus Munro, were impregnated using a colloidal solution of homemade Ag-NPs with the goal of improving its resistance to attacks by fungi. X-ray microtomography (μCT) was performed to investigate the 3D distribution of Ag-NPs within the biological matrix. 3D image reconstruction showed silver clusters distributed within the parenchymatic tissue. Quantitative information of the Ag-NPs agglomerate population was computed. Ag-NPs were characterized by UV-VIS, SERS, ICP-MS, TSEM, DLS and zeta potential analysis. The antimicrobial activity of homemade and commercial citrate-capped silver nanoparticles was evaluated against the Aspergillus niger fungus. Homemade nanoparticles (NP-01), presenting the smallest diameter (14.3 ± 3.6 nm), and the highest particle concentration (1.25 × 1011 particles per mL) were able to inhibit 53% of Aspergillus niger growth in a concentration of 2.00 mg L−1. Both engineered biocomposite material and untreated specimens were exposed to air and humidity. After five months the treated samples were free of fungal colonies, while colonization by the fungal hyphae was present on untreated bamboo specimens.

Synthesis of oxocarbon-encapsulated gold nanoparticles with blue-shifted localized surface plasmon resonance by pulsed laser ablation in water with CO2 absorbers

Colloidal suspensions of oxocarbon-encapsulated gold nanoparticles have been synthesized in a one-step procedure by pulsed-laser ablation (PLA) at 532 nm of a solid gold target placed in aqueous solution containing CO2 absorbers, but without any stabilizing agent. Multi-wavelength surface enhanced Raman spectroscopy allows the identification of adsorbed amorphous carbon and graphite, Au-carbonyl, Au coordinated CO2-derived bicarbonates/carbonates and hydroxyl groups around the AuNPs core. Scanning electron microscopy, energy dispersive x-ray analysis and high resolution transmission electron microscopy highlight the organic shell structure around the crystalline metal core. The stability of the colloidal solution of nanocomposites (NCs) seems to be driven by solvation forces and is achieved only in neutral or basic pH using monovalent hydroxide counter-ions (NaOH, KOH). The NCs are characterized by a blue shift of the localized surface plasmon resonance (LSPR) band typical of metal-ligand stabilization by terminal π-back bonding, attributed to a core charging effect caused by Au-carbonyls. Total organic carbon measurements detect the final content of organic carbon in the colloidal solution of NCs that is about six times higher than the value of the water solution used to perform PLA. The colloidal dispersions of NCs are stable for months and are applied as analytical probes in amino glycoside antibiotic LSPR based sensing.

Prototyping of meso- and microfluidic devices with embedded TiO2 photocatalyst for photodegradation of an organic dye

AbstractWe present prototyping of meso- and microfluidic photocatalytic devices, functionalized through incorporation of TiO2 nanoparticles in polydimethylsiloxane (PDMS), and comparison of their efficiencies for the degradation of rhodamine B (10−5 mol/L). The prototyping of the photocatalytic devices involves simple and low-cost procedures, which includes microchannels fabrication on PDMS, deposition and impregnation of TiO2 on PDMS, and, finally, plugging on the individual parts. For the microfluidic device with 13 μL internal volume, photocatalytic TiO2—PDMS composite was sealed by another PDMS component activated by O2 plasma (PDMS—TiO2—PDMS). For the mesofluidic device, a homemade polyetheretherketone (PEEK) flow cell with 800 μL internal volume was screwed on a steel support with a glass slide and the photocatalytic composite. The photocatalytic activities of the devices were evaluated using two different pumping flow systems: a peristaltic pump and a syringe pump, both at 0.05 mL/min under the action of 365 nm ultraviolet (UV) light. The characterization of TiO2—PDMS composite was performed by confocal Raman microscopy, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The photocatalytic microreactor was the most efScient, showing high organic dye photodegradation (88.4% at 12.5 mW/cm2).

Analysis of surface plasmon resonance sensor coupled to periodic array of gold nanoparticles

This paper presents a theoretical analysis of a surface plasmon resonance sensor coupled to a periodic array of spherical gold nanoparticles (AuNps). The sensor is in the Kretschmann configuration and composed by five layers: prism, thin gold film, dielectric insulator, array of AuNps and air. The AuNps layer is modeled with an effective permittivity by the Maxwell-Garnett mixing formula, and the wave propagation is analyzed using a generalized reflection coefficient. The results are presented in terms of reflectivity and modal field distributions for different thickness of the layers and geometry of the AuNps array.

PROTOTIPAGEM DE MICRORREATORES FOTOCATALÍTICOS E TESTES DE FOTODEGRADAÇÃO DE CORANTES ORGÂNICOS

A photocatalytic microreactor is defined as a microfluidic device which is integrated with a photocatalytic nanometer coating (ex.: TiO2 nanoparticles) deposited on the inner surface of microchannels. This device is capable of degradation of organic dye solution in water in a continuous flow under the action of ultraviolet (UV) light. The specific goals of this work are the presentation of a rapid and economically viable way for the prototyping of photocatalytic microfluidic devices and the evaluation of their capability for photodegradation of organic dyes dissolved in water by ultraviolet-visible spectrophotometry (UV-VIS).A photocatalytic microreactor is defined as a microfluidic device, which is integrated with a photocatalytic coating of TiO2 deposited on the inner surface of microchannels. This device is capable of degradation of organic dye solution in water in a continuous flow under the action of ultraviolet light. The objectives of this work were to present a rapid and economically viable approach for the prototyping photocatalytic microfluidic devices and to evaluate their photodegradation capability for organic dyes by ultraviolet-visible spectrophotometry. Prototyping of polydimethylsiloxane PDMS/TiO2/glass microreactors includes several procedures such as mold preparation, microchannel confection on PDMS surface, deposition of TiO2 on these microchannels, O2 plasma treatment of PDMS/TiO2 and glass surface for sealing these two parts. The efficiency of the photocatalytic microreactors was evaluated by fluxing two organic dye solutions, rhodamine B and methylene blue, with different flow rates of between 2 and 4 mL h-1. When the flow rate at 2 mL h-1was applied, discoloration of ~ 65% was achieved for both dye solutions, while PDMS/glass microchannels, without TiO2 film, demonstrated much lower discoloration of between 24 and 42% for rhodamine B and methylene blue, respectively. This confirmed that TiO2 was successfully deposited onto PDMS microchannels.