Komal Bagga

Luminescent silicon nanoparticles prepared by ultra short pulsed laser ablation in liquid for imaging applications

Heavy-metal-free semiconductor material like Silicon Nanoparticle (Si-NPs) is attracting scientists because of their diverse applications in biomedical field. In this work, pulsed laser ablation of silicon in aqueous solution is employed to generate Si-NPs in one step avoiding use of chemical precursors. Characterization by absorption, electron and photoluminescence analysis proves the generation of luminescent Si-NPs. The productivity rate of Si-NPs is investigated by Inductively Coupled Plasma Spectrometry. Furthermore, Si-NPs quantum yield and confocal microscopy studies corroborate the potential use of these biocompatible Si-NPs for imaging applications.

Bioconjugated silicon quantum dots from one-step green synthesis†

Biofunctionalized silicon quantum dots were prepared through a one step strategy avoiding the use of chemical precursors. UV-Vis spectroscopy, Raman spectroscopy and HAADF-STEM prove oligonucleotide conjugation to the surface of silicon nanoparticle with an average size of 4 nm. The nanoparticle size results from the size-quenching effect during in situ conjugation. Photoemissive properties, conjugation efficiency and stability of these pure colloids were studied and demonstrate the bio-application potential, e.g. for nucleic acid vector delivery with semiconducting, biocompatible nanoparticles.

Study on the productivity of silicon nanoparticles by picosecond laser ablation in water: towards gram per hour yield

An investigation on the productivity of silicon nanoparticles by picosecond laser ablation in water is presented. A systematic experimental study is performed as function of the laser wavelength, fluence and ablation time. In case of ablation at 1064 nm silicon nanoparticles with a mean diameter of 40 nm are produced. Instead, ablation at 355 nm results in nanoparticles with a mean diameter of 9 nm for short ablation time while the mean diameter decreases to 3 nm at longer ablation time. An original model based on the in-situ ablation/photo-fragmentation physical process is developed, and it very well explains the experimental productivity findings. The reported phenomenological model has a general validity, and it can be applied to analyze pulsed laser ablation in liquid in order to optimize the process parameters for higher productivity. Finally, an outlook is given towards gram per hour yield of ultra-small silicon nanoparticles.

Laser-assisted synthesis of Staphylococcus aureus protein-capped silicon quantum dots as bio-functional nanoprobes

A novel approach for nanofabricating protein-functionalized luminescent silicon nanoparticles based on infrared ultrafast laser ablation of silicon in an aqueous solution of Staphylococcus aureus protein A is reported. It is demonstrated that 8 nm protein A-capped silicon quantum dots with blue-green photoemissive properties are generated. The conjugation efficiency studies reveal a high percentage of protein A attached to the Si nanoparticle surface through physical adsorption phenomena during the in situ laser process. The biological functionality of laser-generated Staphylococcus aureus protein A-capped Si nanoparticles is investigated. Confocal and electron microscopy together with energy dispersive x-ray spectroscopy analysis show that these Si-based bio-nanostructures selectively bind IgG in the cells. Cell viability studies reveal that these protein A-capped Si nanoparticles are suitable for biological applications, demonstrating their potential as universal secondary biomarkers for in vivo applications such as long-term, real-time cell labeling, cell staining and controlled drug delivery.

Influence of organic solvent on optical and structural properties of ultra-small silicon dots synthesized by UV laser ablation in liquid

Ultra small silicon nanoparticles (Si-NPs) with narrow size distribution are prepared in a one step process by UV picosecond laser ablation of silicon bulk in liquid. Characterization by electron microscopy and absorption spectroscopy proves Si-NPs generation with an average size of 2 nm resulting from an in situ photofragmentation effect. In this context, the current work aims to explore the liquid medium (water and toluene) effect on the Si-NPs structure and on the optical properties of the colloidal solution. Si-NPs with high pressure structure (s.g. Fm3m) and diamond-like structure (s.g. Fd3m), in water, and SiC moissanite 3C phase (s.g. F4[combining macron]3m) in toluene are revealed by the means of High-Resolution TEM and HAADF-STEM measurements. Optical investigations show that water-synthesized Si-NPs have blue-green photoluminescence emission characterized by signal modulation at a frequency of 673 cm(-1) related to electron-phonon coupling. The synthesis in toluene leads to generation of Si-NPs embedded in the graphitic carbon-polymer composite which has intrinsic optical properties at the origin of the optical absorption and luminescence of the obtained colloidal solution.

In vitro fibroblast and pre-osteoblastic cellular responses on laser surface modified Ti-6Al-4V.

The success of any implant, dental or orthopaedic, is driven by the interaction of implant material with the surrounding tissue. In this context, the nature of the implant surface plays a direct role in determining the long term stability as physico-chemical properties of the surface affect cellular attachment, expression of proteins, and finally osseointegration. Thus to enhance the degree of integration of the implant into the host tissue, various surface modification techniques are employed. In this work, laser surface melting of titanium alloy Ti-6Al-4V was carried out using a CO2 laser with an argon gas atmosphere. Investigations were carried out to study the influence of laser surface modification on the biocompatibility of Ti-6Al-4V alloy implant material. Surface roughness, microhardness, and phase development were recorded. Initial knowledge of these effects on biocompatibility was gained from examination of the response of fibroblast cell lines, which was followed by examination of the response of osteoblast cell lines which is relevant to the applications of this material in bone repair. Biocompatibility with these cell lines was analysed via Resazurin cell viability assay, DNA cell attachment assay, and alamarBlue metabolic activity assay. Laser treated surfaces were found to preferentially promote cell attachment, higher levels of proliferation, and enhanced bioactivity when compared to untreated control samples. These results demonstrate the tremendous potential of this laser surface melting treatment to significantly improve the biocompatibility of titanium implants in vivo.

Facile laser-assisted synthesis of inorganic nanoparticles covered by a carbon shell with tunable luminescence

We report a one-step strategy at ambient conditions for the production of hybrid inorganic core–carbon shell nanoparticles by means of pulsed laser ablation of inorganic targets (LiNbO3, Au, and Si) in hydrocarbon liquids such as toluene and chloroform. The core of these spherical nanoparticles consists of the target material, whereas the shells are carbon structures (multilayer graphite-type carbon and amorphous carbon), which are formed due to the thermal decomposition of the organic liquid in contact with hot inorganic nanoparticles ejected from the bulk target. These carbon shells emit photoluminescence in the blue-green spectral region and the obtained luminescence, in which the luminescence band maximum position depends on the excitation wavelength, is analogous to the luminescence observed for the so-called “carbon dots”.

Laser assisted synthesis of carbon nanoparticles with controlled viscosities for printing applications

High-quality carbon nanoparticles with controlled viscosity and high aqueous stability were prepared by liquid-phase laser ablation of a graphite target in deionized water. The size distribution was found to vary from 5nm to 50nm with mean size of 18nm, in the absence of any reducing chemical reagents. Efficient generation of short chain polyynes was recorded for high laser repetition rates. Homogeneous and stable nanoparticle suspensions with viscosities ranging from 0.89 to 12mPa.s were obtained by suspending the nanoparticles in different solvent mixtures such as glycerol-water and isopropanol-water. Optical properties were investigated by absorption and photoluminescence spectroscopy. Raman spectroscopy confirmed graphitic-like structure of nanoparticles and the surface chemistry was revealed by Fourier-transform infrared spectroscopy demonstrating sufficient electrostatic stabilization to avoid particle coagulation or flocculation. This paper present an exciting alternative method to engineer carbon nanoparticles and their potential use as a ligand-free nano-ink for ink jet printing (jetting) applications.

Nanoparticle functionalized laser patterned substrate: an innovative route towards low cost biomimetic platforms

Integration of nanotechnology and advanced manufacturing processes presents an attractive route to produce devices for adaptive biomedical device technologies. However, tailoring biological, physical, and chemical properties often leads to complex processing steps and therefore to high manufacturing cost impeding further scalability. Herein, a novel laser-based approach is introduced to manufacture low cost biocompatible polymer substrates functionalized with ultrapure nanoparticles. Laser direct writing was performed to create micron-sized patterns on 188 μm-thick cyclic olefin polymer (COP) substrates using a picosecond pulsed 1064 nm Nd:YAG laser. The Pulsed Laser Ablation in Liquids (PLAL) technique was exploited in this work to prepare colloidal solutions of ultrapure nanoparticles to impart bio-functionality onto laser patterned surfaces. Combining the laser patterns and their modification with PLAL-nanoparticles resulted in a functional and biocompatible substrate for biosensing applications. Our in vitro cell viability studies using a model cell line (human skin keratinocyte, HaCaT) suggest that these nanoparticles immobilized on the surfaces function as a biomimetic platform with the ability to interact with different biological entities (e.g. DNA, antibodies etc.).

Laser micro-engineering of functionalised cyclic olefin polymers for microfluidic applications

Direct-write laser processing has been demonstrated to be capable of both surface patterning of micro- and nanoscale structures on polymer surfaces without significant modification of the surface chemistry or optical transmission of the laser processed area. In this work, the creation of microchannels via direct-write laser processing of 188 μm thickness cyclic olefin polymers is demonstrated, along with a route towards channel functionalization. Cyclic olefin polymers (COP) are an emerging class of polymers noted for their high chemical resistance, biocompatibility and higher optical transparency when compared to other common polymers. These properties make them excellent substrates for the fabrication of microfluidic devices. This paper presents the first investigation into infrared laser processing of COP using a 1064 nm Nd:YAG laser. Scanning electron microscopy and Raman spectroscopy were utilized to investigate the morphology and composition of these laser textured surfaces. A route for functionalization of these substrates for chemical and biological speciation and separation was examined using carbon nanoparticles. The nanoparticles were produced using pulsed laser ablation in liquid (PLAL) which has been reported as a fast and adaptable method for nanoparticle production. The nanoparticles produced were using transmission electron microscopy while the coating of substrates with these CNPs was examined using SEM. These results are discussed in the context of development of a new route for achieving surfaces optimized for microfluidicbased separations and speciation.